Heater-driven preemptive quench schemes for no-insulation superconducting magnets

Abstract

A non-insulated superconducting magnet and related methods and systems are provided herein. In some aspects, the non-insulated superconducting magnet comprises at least one heating element configured to induce a quench of the non-insulated superconducting magnet by asymmetrically heating the non-insulated superconducting magnet. In some aspects, the non-insulated superconducting magnet comprises at least one cable comprising at least one heating element configured to induce quench of the non-insulated superconducting magnet by heating the non-insulated superconducting magnet. In some aspects, the non-insulated superconducting magnet comprises a first plate having at least one groove arranged in a plurality of turns, and a conductor disposed in the at least one groove, wherein a resistivity of the conductor varies along a length of the conductor.

Description

[0001] HEATER-DRIVEN PREEMPTIVE QUENCH SCHEMES FOR NO-INSULATION SUPERCONDUCTING MAGNETS

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit of priority under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 63 / 514,704 filed July 20, 2023 entitled “HEATER-DRIVEN PREEMPTIVE QUENCH SCHEMES FOR NO-INSULATION SUPERCONDUCTING MAGNETS"’, which is hereby incorporated by reference in its entirety.

[0004] FIELD

[0005] This application relates to non-insulated superconducting magnets and, more particularly, to systems and methods for inducing quench in non-insulated superconducting magnets.

[0006] BACKGROUND

[0007] Superconductors are materials that have no electrical resistance to current (are “superconducting”) below some critical temperature. For many superconductors, operation of these materials in a superconducting state below the critical temperature requires significant cooling, such as with liquid helium or supercritical helium.

[0008] Superconductors include low temperature superconductors (LTS), which have critical temperatures typically below 30 K and may be cooled using liquid helium (for example), and high temperature superconductors (HTS), which can have critical temperatures typically greater than 30 K and may be cooled using liquid nitrogen (for example). An HTS magnet is a magnet that includes one or more HTS materials arranged to carry at least a portion of the current of the magnet. Magnets, including HTS magnets can experience quench. Quench is the transition of the superconductor of a magnet from a superconducting state to a non-superconducting state.

[0009] SUMMARY

[0010] According to some embodiments there is provided a non-insulated superconducting magnet, comprising: at least one heating element configured to induce a quench of the non-insulated superconducting magnet by heating the non-insulated superconducting magnet, wherein the at least one heating element is configured to heat the non-insulated superconducting magnet asymmetrically.

[0011] According to some embodiments there is provided a non-insulated superconducting magnet, comprising: at least one cable comprising at least one heating element configured to induce quench of the non-insulated superconducting magnet byheating the non-insulated superconducting magnet.

[0012] According to some embodiments there is provided a system comprising: a plurality of non-insulated superconducting magnets, each of the non-insulated superconducting magnets being configured to produce a toroidal magnetic field and comprising: at least one heating element configured to induce quench of the respective non-insulated superconducting magnet, wherein the at least one heating element is configured to heat the non-insulated superconducting magnet asymmetrically; and circuitry coupled to the plurality of non-insulated superconducting magnets, wherein the circuitry is configured to control the at least one heating element of each of the non-insulated superconducting magnets to induce quench of the respective non-insulated superconducting magnets.

[0013] According to some embodiments there is provided a system comprising: a plurality of non-insulated superconducting magnets, each of the non-insulated superconducting magnets being configured to produce a toroidal magnetic field and comprising: at least one cable comprising at least one heating element configured to induce quench of the respective non-insulated superconducting magnet by heating the respective non-insulated superconducting magnet; and circuitry coupled to the plurality of non-insulated superconducting magnets, wherein the circuitry is configured to control the at least one heating element of each of the non-insulated superconducting magnets to induce quench of the respective non-insulated superconducting magnets.

[0014] According to some embodiments there is provided a method for inducing quench in a non-insulated superconducting magnet comprising a conductor and at least one heating element, the method comprising: controlling the non-insulated superconducting magnet to quench at least in part by heating, with the at least one heating element, the conductor asymmetrically such that at least a portion of a first turn of a plurality of turns of the conductor transitions from a superconducting state to a non-superconducting state before at least a portion of a second turn of the plurality of turns transitions form the superconducting state to the non-superconducting state. According to some embodiments there is provided a method for operating a reactor comprising a non-insulated superconducting magnet configured to generate a toroidal magnetic field and comprising at least one heating element, a second magnet configured to generate a poloidal magnetic field, and a third magnet comprising a solenoid, the method comprising: reducing a current in the second magnet to zero; reducing a current in the third magnet to zero; and inducing a quench of the non-insulated superconducting magnet at least in part by heating the non-insulated superconducting magnet, wherein the at least one heating element is configured to heat the non-insulated superconducting magnet asymmetrically.

[0015] According to some embodiments there is provided a non-insulated superconducting magnet comprising: a first plate having at least one groove arranged in a plurality7of turns; and a conductor disposed in the at least one groove, wherein a resistivity of the conductor varies along a length of the conductor.

[0016] According to some embodiments there is provided a method for inducing a preemptive quench in a non-insulated (NI) superconducting magnet, the method comprising directly heating portions of a superconducting material in the NI superconducting magnet to induce a quench in a portion of the NI superconducting magnet such that remaining portions of the superconducting material are inductively driven to have a non-superconducting resistance characteristic in a manner which results in a substantially uniform distribution of heat energy in the magnet thereby resulting in a desired temperature distribution in the magnet during a quench event.

[0017] According to some embodiments there is provided a non-insulated (NI) superconducting magnet comprising means for inducing a preemptive quench by directly heating portions of a superconducting material in the NI superconducting magnet to induce a quench in a portion of the NI superconducting magnet such that remaining portions of the superconducting material are inductively driven to have a non- superconducting resistance characteristic in a manner which results in a substantially uniform distribution of heat energy in the NI superconducting magnet thereby resulting in a desired temperature distribution in the NI superconducting magnet during a quench event. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 illustrates an example diagram illustrating a process of quenching a magnet via thermal and inductive quenching, according to some embodiments of the technology described herein.

[0019] FIG. 2 illustrates a simulation of quench in a magnet showing formation of hot spots in the magnet, according to some embodiments of the technology described herein.

[0020] FIGs. 3A-3C illustrate example quench simulations illustrating formation of hot spots, according to some embodiments of the technology described herein.

[0021] FIG. 4 illustrates an example diagram showing different phases of a heater-driven preemptive quench technique, according to some embodiments of the technology described herein.

[0022] FIG. 5 illustrates an example method for preemptively inducing quench according to a heater-driven technique, according to some embodiments of the technology described herein.

[0023] FIG. 6 is an example method 900 illustrating further aspects of a quench cascade, according to some embodiments of the technology described herein.

[0024] FIG. 7 illustrates an example method for inducing quench in a non-insulated magnet, according to some embodiments of the technology' described herein.

[0025] FIG. 8 is an example diagram illustrating heating of selected turns of a noninsulated magnet, according to some embodiments of the technology described herein.

[0026] FIG. 9 is an example diagram illustrating inductive quench of adjacent turns of a non-insulated magnet, according to some embodiments of the technology described herein.

[0027] FIG. 10 illustrates an example diagram of a quench cascade in a non-insulated magnet, according to some embodiments of the technology' described herein.

[0028] FIG. 11 illustrates an example diagram of an energy deposition phase of the noninsulated magnet, according to some embodiments of the technology described herein.

[0029] FIG. 12 illustrates the example diagram of FIG. 11, with highlighted areas of temperature variation, according to some embodiments of the technology described herein.

[0030] FIG. 13 illustrates an example arrangement for implementing heating elements in a non-insulated magnet, according to some embodiments of the technology described herein. FIG. 14 illustrates an example heating element which may be implemented with a heater-driven preemptive quench technique, according to some embodiments of the technology described herein.

[0031] FIG. 15 illustrates an example diagram of heating element positioning on a non- insulated magnet, according to some embodiments of the technology described herein.

[0032] FIG. 16 illustrates another example diagram of heating element positioning on a non-insulated magnet, according to some embodiments of the technology described herein.

[0033] FIG. 17 illustrates an example simulation showing variations in critical current density, according to some embodiments of the technology described herein.

[0034] FIG. 18 illustrates another example simulation showing variations in critical current density, according to some embodiments of the technology described herein.

[0035] FIG. 19 illustrates graphs showing variation in critical current under different operating conditions, according to some embodiments of the technology described herein.

[0036] FIG. 20 illustrates an example diagram of a magnet where critical current has been azimuthally flattened, according to some embodiments of the technology described herein.

[0037] FIG. 21 illustrates example graphs illustrating minimum high-temperature superconductor grading needed under different operating conditions, according to some embodiments of the technology described herein.

[0038] FIG. 22 illustrates an example graph showing HTS fill fraction along a conducting according to a grading scheme, according to some embodiments of the technology described herein.

[0039] FIG. 23 illustrates an example of a conductor groove with HTS tape and filler tape disposed therein according to a grading scheme, according to some embodiments of the technology described herein.

[0040] FIG. 24 illustrates a diagram showing aspects of HTS grading on anon-insulated magnet having heating elements, according to some embodiments of the technology' described herein.

[0041] FIG. 25 illustrates temperature variation in a portion of a non-insulated magnet during an energy deposition phase, according to some embodiments of the technology7described herein. FIG. 26 illustrates an example diagram showing temperature variation in a noninsulated magnet having the joint pad optimizations described herein during an energy’ deposition phase, according to some embodiments of the technology described herein.

[0042] FIG. 27 illustrates an example of ajoint pad arrangement that is not optimized for uniformity of magnet energy’ deposition, according to some embodiments of the technology described herein.

[0043] FIG. 28 illustrates an example technique for increasing, and ideally maximizing, uniformity of magnet energy deposition, according to some embodiments of the technology’ described herein.

[0044] FIG. 29 illustrates implementation of example techniques, based on FIGS. 27-28, for increasing, and ideally maximizing, uniformity of magnet energy deposition, according to some embodiments of the technology described herein.

[0045] FIG. 30 illustrates an example diagram showing temperature variation throughout a non-insulated magnet, according to some embodiments of the technology described herein.

[0046] FIG. 31 illustrates an example diagram showing anon-insulated magnet with a conductor of varying material, according to some embodiments of the technology described herein.

[0047] FIG. 32 illustrates an example diagram illustrating a step of selecting a target value of I / Ic for each turn of a magnet, according to some embodiments of the technology described herein.

[0048] FIG. 33 illustrates an example diagram illustrating a step of determining HTS temperature in each turn when that turn reaches a target value of I / Ic, according to some embodiments of the technology described herein.

[0049] FIG. 34 illustrates an example diagram illustrating HTS current when a target value of I / Ic is obtained for that turn, according to some embodiments of the technology’ described herein.

[0050] FIG. 35 illustrates an example of a toroidal field magnet comprising a plurality of plates being configured to implement the heater-driven preemptive quench techniques described herein, according to some embodiments of the technology described herein.

[0051] FIG. 36 is an example system comprising multiple magnets configured to perform a heater-driven preemptive quench technique, according to some embodiments of the technology described herein. FIGS. 37a - 37d are a series of schematic diagrams illustrating switch positions and current flow during (a) normal TF magnet operation; (b) DC power supply shut off: (c) positive TF bus grounding; and (d) activation of heater power to initiate a heater-driven preemptive quench, according to some embodiments of the technology described herein.

[0052] FIGs. 38a - 38d are a series of schematic diagrams illustrating switch positions and current flow during (a) normal TF magnet operation; (b) DC power supply shut off; (c) positive TF bus grounding; and (d) activation of heater power to initiate a heater-driven preemptive quench.

[0053] FIG. 39 illustrates an example method 4300 for implementing a heater-driven preemptive quench.

[0054] DETAILED DESCRIPTION

[0055] Superconductors are materials that have no electrical resistance to current (are “superconducting'’) below' a critical temperature. Superconductors include low' temperature superconductors (LTS). which have critical temperatures typically below 30 K and may be cooled using liquid helium (for example), and high temperature superconductors (HTS), which can have critical temperatures greater than 77 K and may be cooled using liquid nitrogen (for example). Both LTS and HTS materials have found applications in fusion energy, high-efficiency motors, high-efficiency power transmission, magnetic resonance imaging (MRI). nuclear magnetic resonance (NMR). and high-field particle accelerators.

[0056] To remain in a superconducting state, the superconducting material must remain at a temperature below the critical temperature. However, localized energy dissipation (e.g., due to current flow' in the superconductor) can cause localized heating, which, if not controlled or detected, may result in a thermal runaway event that causes the entire superconductor to transition from the superconducting regime to a normal, resistive regime. This is referred to as a quench event (or more simply a “quench”). A quench not only can result in downtime of the superconducting device (e.g., a superconducting magnet) but may result in damage to the superconducting device as well.

[0057] Non-insulated (NI) superconducting magnets have at least partially electrically conductive paths between adjacent turns of a superconducting path (i.e., a path comprising superconducting material). When the superconducting material is in its superconducting state there is zero resistance and all current flows through the superconducting path. Thus, during steady state operation of NI superconducting magnets, there is no voltage difference between turns. The term “NT’ as used herein is intended to cover both magnets traditionally referred to as NI magnets and magnets traditionally referred to as partially insulated (PI) magnets, as the techniques and structures described herein apply to both t pes of magnets.

[0058] An NI magnet may include one or more plates made of steel or another metal, with superconductor material positioned or otherwise disposed in grooves of the plate(s). In some circumstances, however, NI magnets may be become thermally unstable, resulting in quench. A region of superconducting material transitions from a superconducting state to a non-superconducting state when the conditions for maintaining superconductivi ty cease to be met, which occurs, for example, when the temperature of the superconducting material exceeds the critical temperature. The critical temperature may depend upon various parameters. For a high temperature superconductor (HTS), the critical temperature is higher than for low temperature superconductor (LTS).

[0059] In a superconducting magnet, when the coils cease to be superconducting, resistance in the magnet increases. When current flows through areas with increased resistance, heat is generated. The generation of heat in an uncontrolled and undesired manner can lead to damage to the magnet. Damage can occur if magnetic energy becomes focused into small volumes and / or if large currents cause Lorenz loads to exceed allowed values. For an array of coils, structural damage can occur from unbalanced loads if some coils quench earlier than others.

[0060] Described herein are devices, systems and techniques for initiating and controlling a quench in a superconducting magnet. These techniques include grading superconducting material in the superconducting magnet and using heating elements to directly heat only selected portions of the superconducting magnet. The superconducting material (or more simply ' superconductor") may be a high temperature superconductor (HTS).

[0061] The inventors have recognized that a technique for controlling quench would be advantageous. In some instances, a magnet may need to be shut down quickly, requiring it to be quenched on purpose. It is desired to shut off the magnet in a non-damaging manner by intentionally quenching the magnet. It is desired to induce quenching uniformly and quickly, without causing damage to the magnet. Not only is damage to the magnet expensive, potentially requiring replacement parts of the magnet, but damage may lead to undesirable downtime of associated equipment which uses the magnet, such as an MRI machine or a tokamak reactor. Accordingly, systems and techniques are described herein for intentionally and rapidly inducing quench in a non-insulated magnet. The aspects described herein may be used to shut down or ‘'turn off’ the magnet uniformly and rapidly, before damage to the magnet occurs. The aspects described herein may include aspects for preemptively quenching a magnet. Preemptive quench refers to a quench that is intentionally initiated. The inventors have recognized that initiating a quench in an NI superconducting magnet, for example, can be advantageous as preemptive quenching provides the ability to control and direct a quench in a manner that does not cause damage to the superconducting magnet. The magnet and / or the manner in which the magnet is operated may be modified to enhance the speed and uniformity' with which the quench occurs .

[0062] The aspects described herein may be used to perform a heater-driven quench. That is, initiating quench in the non-insulated magnet is facilitated through operation of one or more heating elements that function to heat at least a portion of the non-insulated magnet. Heater-driven quench schemes may involve quenching the non-insulated magnet at least partially through a thermal quench of at least some portions of the non-insulated magnet. Thermal quenching may include directly heating at least some portions of the noninsulated magnet with one or more heating elements until a quench occurs at one or more of the at least some portions of the non-insulated magnet.

[0063] According to some aspects, once a thermal quench is initiated at least some portions of the non-insulated magnet may subsequently undergo an inductively induced quenched. An inductive quench may include indirectly heating at least some portions of the non-insulated magnet as a result of inductive coupling. For example, current in a portion of a non-insulated magnet may increase as a result of a thermal quench. The thermal quench of selected turns (e.g. inner diameter turns) of a superconducting magnet causes over-current in other turns (e.g. adjacent turns) pushing them to I / lc > 1. Such an increase in current may be due to inductive coupling (e.g., due to a decrease in current in a region adjacent to the portion of the non-insulated magnet). The increased current exceeding critical causes the temperature in that portion of the non-insulated magnet to increase until that portion of the non-insulated magnet also quenches. In this way, an inductively driven quench cascade may be initiated. When the quench is initiated in an inner diameter turn of a superconducting magnet, the quench may propagate radially outward to the outer diameter (OD) turns of the superconducting magnet. Some aspects of the concepts described herein provide for quenching at least a portion of the non-insulated magnet using a combination of thermal and inductive quenching. For example, the inventors have recognized that a thermal quench facilitated by operation of one or more heating elements on a selected first portion or turn of a superconducting magnet (e.g., a turn or a portion of a turn, such as an inner diameter turn of a superconducting magnet, or a plurality of turns) may cause coils to quench uniformly azimuthally, resulting in no hot spot formation (and thus, no damage). Subsequent to the thermal quench (induced via heating by one of the one or more heating elements) a second portion of the non-insulated superconducting magnet (e.g., outer diameter turns of the superconducting magnet) may undergo an inductive quench. In some embodiments, the inductive quench can be initiated by the thermal quench. Subsequent portions of the noninsulated magnet may undergo a quenched in response to the inductive quench of the second portion of the non-insulated magnet. In this manner, a “quench cascade” may be initiated by the thermal quenching of the first portion of the non-insulated magnet. Accordingly, the inventors have realized that a heater-driven thermal quench of a portion of a non-insulated magnet may be used to quench other portions of the non-insulated magnet, and in some instances, to quench the entire non-insulated magnet.

[0064] Aspects of the technology described herein may be implemented on various types of non-insulated magnets. In some embodiments, the aspects of the technology are implemented on a non-insulated superconducting magnet. In the illustrated embodiments, the non-insulated superconducting magnet comprises a grooved, stacked-plate noninsulated superconducting magnet, such as the ty pe used to generate a toroidal magnetic field, having a conductor comprising high-temperature superconductor tape. Other configurations are possible, such as tape-on-tape wound coils and hybrid winding schemes.

[0065] Following below are more detailed descriptions of various concepts related to, and embodiments of, techniques for initiating and controlling a quench. It should be appreciated that various aspects described herein may be implemented in any of numerous ways. Examples of specific implementations are provided herein for illustrative purposes only. In addition, the various aspects described in the embodiments below may be used alone or in any combination and are not limited to the combinations explicitly described herein. As described herein, the inventors have recognized that it would be advantageous to control the non-insulated magnet to quench in certain instances. For example, when a magnet quenches in an uncontrolled and / or unintentional manner, the quench may be non- uniform, too slow, and / or too fast. Damage may be caused to the magnet as a result of the uncontrolled quench. Even when the quench is intentional and controlled, simply open circuiting the magnet may result in a slow initiation of quench that may not be fast enough to keep the magnet functioning properly.

[0066] Quench is a process in which a superconducting magnet becomes non- superconducting (e.g., moving from a superconducting state to anon-superconducting state). Quench may occur when there is a rise in temperature in a magnet’s conductor, introducing resistivity in the conductor. As described herein, quench may be induced thermally, by heating the conductor of a magnet to increase the temperature of the magnet’s conductor directly with at least one heating element and / or may be induced inductively by increasing the current in the conductor via inductive coupling. The increase in current above the critical level via inductive coupling causes the magnet conductor to quench.

[0067] The inventors have recognized that, for a non-insulated magnet having a conductor arranged in a plurality of turns, a first turn may be induced to thermally quench while others of the plurality of turns are induced to quench via inductive coupling. FIG. 1 illustrates an example diagram illustrating a process of quenching a magnet via thermal and inductive quenching, according to some embodiments of the technology described herein.

[0068] The diagram shown in FIG. 1 illustrates relative timing of different phases of a preemptive quench process which occurs among the plurality of turns of a non-insulated magnet, specifically first turns which may be the innermost of the plurality of turns, next turns adjacent to the first turns, and the remaining turns of the plurality of turns. FIG. 1 illustrates that when the non-insulated magnet is driven to quench by open circuiting the magnet, the quench proceeds in three phases. A similar response of the magnet can be produced when the magnet is warmed slowly.

[0069] A first phase is an incubation phase. During the incubation phase, the magnet heats up from radial current flow through the magnet. Heating of the magnet in this stage is non- uniform such that some regions of the magnet reach a temperature at which a quench will occur (quench temperature) before other regions of the magnet. For a non-insulated superconducting magnet having the configuration described herein, there may be significant variation in critical current along the plurality of turns of the conductor causing some sections of the magnet to reach critical current well ahead of other sections of the magnet. The incubation phase may have a duration that greater than a duration of other phases. As an example, the incubation phase may last for approximately 100 seconds.

[0070] A second phase is a quench phase. During the quench phase, the turns of the magnet move (or transition or change) from a superconducting state to a non- superconducting state. As shown in FIG. 1, different conductor turns may enter the quench phase at different times. The first turns or sections thereof enter the quench phase first. Subsequently, the adjacent turns enter the quench phase, followed by the remaining turns. The quench phase may have a duration that is relatively short compared to other phases. As an example, if the incubation phase lasts for approximately 100 seconds, the quench phase may last for approximately .2 seconds.

[0071] The first turns or sections thereof quench ‘thermally’ (i.e., temperature increase in the conductor reduces critical current (Ic) causing the ratio of turn cunent to critical current (I / Ic) to exceed quench threshold (I / Ic > 1). The adjacent turns quench both thermally and inductively. Inductive coupling of current from the first turns to the adjacent turns causes current in the adjacent turns to increase. Both effects drive the ratio of turn current to critical current (I / Ic) to exceed the quench threshold (I / Ic > 1). Quench in the remaining turns occurs inductively. Current drop in the adjacent turns due to quench causes current in the remaining turns to rise through inductive coupling. In this manner, a quench cascade through the plurality of turns occurs.

[0072] A third phase is an energy deposition phase, also referred to herein as a copper coil or energy dump phase. After quenching, much of the current continues to flow in the conductor. The conductor effectively turns into a conventional coil (e.g., a copper coil). The stored energy may be turned to heat in this phase. For a non-insulated superconducting magnet having the arrangement described herein, approximately 85% of the stored energy is turned to heat. The energy deposition phase may have a duration that is relatively shorter than the incubation phase and relatively longer than the quench phase. For example, the energy dump phase may last for approximately 2 seconds.

[0073] As described herein, open circuiting the magnet may lead to quench, but the overall process to quench is relatively slow. The natural heat-up rate of the magnet being too slow can lead to damage. Small temperature variations and / or critical current variations in the magnet can cause sections of the magnet to quench too far ahead of others. Sections that quench early can get very hot because magnetic energy is preferentially deposited into those regions.

[0074] FIG. 2 illustrates a simulation of a quench in a magnet showing formation of hot spots in the magnet, according to some embodiments of the technology described herein. FIG. 2 illustrates a section of the magnet (the upper right bend in the magnet labelled as "Quench head start’7in FIG. 2) that quenches earlier than (or before) other sections of the magnet . The quench head start leads to preferential deposition of magnetic energy in this section resulting in this section becoming very hot and burning. That is, sections that quench early can get very hot because magnetic energy is preferentially deposited into those regions.

[0075] In addition, variations in critical current (Ic) can occur along the plurality of turns of the magnet due to variations in magnetic field strength and orientation. For an asymmetrical D-shaped conductor as described herein, which have small bend radii in comers of the magnet, these variations may be even more prevalent. For the non-insulated superconducting magnet shown in the illustrated embodiments, the lowest critical current (Ic) occurred in the tight bend region (shown as the section of the magnet having the quench head start in FIG. 2), coincident with where hot spot damage occurred.

[0076] FIGs. 3A - 3C illustrate the formation of hot spots in a quench simulation. The example simulations shown in FIGs. 3B and 3C illustrate that hot spot formation and hot spot localization to the tight bend region of the magnet is due to strong spatial variations in critical current along the plurality7of turns. The local minimum in critical current shown in Fig. 3C is coincident with the location of the hot spot and bum location seen in the simulations shown in FIG. 3A.

[0077] In view of the desire for a preemptive quench technique, the inventors have developed techniques for intentionally and actively inducing quench in a magnet in a controlled manner. The techniques described herein execute a preemptive quench action via one or more externally driven heating elements to force the magnet to quench fast. The speed at which the magnet is forced to quench helps control the quench and eliminate formation of hotspots. The techniques described herein exploit quench dynamics of a non- insulated superconducting magnet to simplify the heating. As described herein, the inventors have recognized that it is possible to effectively quench the magnet without placing heating elements everywhere along the plurality of turns. Instead, one or more heating elements may be placed at strategic locations throughout the magnet to heat to induce quench asymmetrically.

[0078] FIG. 4 illustrates an example diagram showing different phases of a heater-driven preemptive quench technique, according to some embodiments of the technology described herein. Consider what happens if only the innermost turn of a conductor arranged in a plurality of turns is forced to quench via a system comprising one or more heating elements. The innermost turn will tend to quench without developing a bum because current can navigate around hot spots by flowing into adj acent unquenched turns across the no-insulation pathway of the magnet. When the innermost turn quenches, current in the next turn increases by magnetic induction creating a positive increment in current in the adjacent turn. This positive increment in cunent forms a closed loop that mostly follows the plurality of turns but also closes across it via the no-insulation pathw ay of the non-insulated magnet. If the current in this loop is high enough, it will force the underlying turn to quench uniformly.

[0079] When a turn quenches due to overcurrent, its current drops. The drop in current of the quenched turn induces an overcurrent in the next adjacent turn via magnetic induction. In this way, atum-by-tum quench cascade driven by imbedded heating elements safely quenches the magnet.

[0080] As shown in FIG. 4. the heater-driven preemptive quench technique comprises four phases: (1) heater turn on; (2) thermal quench; (3) inductive quench; and (4) energy dump. The respective phases of the heater-driven preemptive quench technique are further described herein.

[0081] FIG. 4 illustrates the respective phases occurring in the relative turns of the magnet. In particular, the first row illustrates the relative timing of different phases in selected first turns of the magnet. The subsequent rows illustrate the relative timing of the different phases in increasingly adjacent turns of the magnet.

[0082] The first phase of the heater-driven preemptive quench technique is a “heater turnon” phase. During the heater turn on phase, selected turns of the magnet are heated up rapidly. For example, the selected turns of the magnet may be heated to increase the temperature of the selected turns from approximately 8K to greater than 25K. A duration of the heater turn-on phase may be approximately 1 second. The heater tum-on phase may be implemented using one or more heating elements, which are further described herein. As described herein, the heater turn-on phase includes heating selected turns of the magnet. Which of the plurality of turns are the selected turns may vary’. In some embodiments, the selected turns are the innermost turns which are positioned radially closest to a center of the plurality of turns. In some embodiments, the selected turns are the outermost turns which are positioned radially furthest from a center of the plurality of turns. In some embodiments, the selected turns may be one or more turns radially between the innermost and outermost turns.

[0083] As described herein, the inventors have recognized that only a selected portion of turns of the plurality of turns that is fewer than all of the plurality of turns may be driven to quench thermally. Selective placement of the heating elements as described herein may facilitate the heating of the selected turns. Because the heating is directed towards only a portion of the plurality of turns, the heating may be considered to be performed asymmetrically.

[0084] The second phase of the heater-driven preemptive quench technique is the thermal quench phase. Due to high power of the one or more heating elements, and in some instances combined with flattened critical current maps as described herein, the selected turns quench azimuthally uniformly resulting in no hot spot formation and no bum. The quenching of these selected turns is referred to as a thermal quench, because the temperature rise in the selected turns that leads to quenching is due to the heating performed by the one or more heating elements. The thermal quench phase may last approximately .2 seconds. As shown in FIG. 4, the heater turn on in phase one and the thermal quench in phase two occur only in the selected turns of the magnet.

[0085] The third phase of the heater-driven preemptive quench technique is the inductive quench cascade. As described herein, the thermal quench of the selected turns in phase two causes a current drop in the selected turns which leads to an increase in current in adjacent turns via inductive coupling. The increase in current in the adjacent turns leads to overcurrent in the adjacent turns, pushing the I / Ic ratio to greater than the quench threshold (1), thereby inductively inducing quench. The inductive quench cascade phase may last approximately .5 seconds.

[0086] This process of a current drop due to quench, increased current in the adjacent turn due to inductive coupling, and overcurrent pushing the adjacent turn to quench is repeated for the remaining adjacent turns of the magnet. This process is referred to herein as a quench cascade. The quench cascade propagates radially. Where the selected turns comprise the innermost turns of the magnet, the quench cascade propagates radially outward to the last turns of the magnet.

[0087] The fourth phase of the heater-driven preemptive quench technique is the energy deposition phase, also referred to herein as a copper coil phase or an energy dump phase. Subsequent to quenching, the remaining current still flows through the conductor which is now non-superconducting. In this phase, the conductor functions essentially as a copper coil. The remaining magnet stored energy (approximately 85%) subsequent to quench is dissipated, primarily through Joule heating, in the conductor. The energy deposition phase may last approximately 2 seconds.

[0088] As described further herein, the critical current map of the magnet can be optimized to reduce, and ideally minimize, azimuthal asymmetries in energy’ deposition that result in the energy deposition phase. As described further herein, copper coconductor and joint pad geometries may be designed to reduce, and ideally minimize, current focusing and hot spot temperatures during the energy deposition phase.

[0089] The aspects of a preemptive heater-driven quench technique described herein may be embodied in one or more methods. For example, FIG. 5 illustrates an example method for preemptively inducing quench according to a heater-driven technique, according to some embodiments of the technology' described herein.

[0090] The example method 800 illustrated in FIG. 5 may begin at act 802 w here heating of at least one or more portions of selected turns is initiated using one or more heating elements. Act 802 may correspond to the heater on phase described herein.

[0091] The inventors have recognized that it is important that a sufficient number of selected turns are quenched thermally via the one or more heating elements so as to produce a robust induced current response. If an insufficient portion of turns are selected for heating, a quench cascade may not be initiated. In the illustrated embodiments, 3.5 turns out of 14 magnet plate are heated. The number of selected turns in the illustrated embodiments have been found to initiate the desired quench cascade even if some of the one or more heating elements fail.

[0092] The inventors have further recognized that selecting the length of the selected turns to heat with the one or more heating elements is important. In particular, the inventors have recognized that it is important that the selected length include at least a few turns as it is desired to thermally quench an azimuthal ring and cause a radial quench cascade. If the selected length is less than one turn, the resulting quench may be asymmetric. As described herein, the number of the one or more heating elements implemented to perform the heating of the selected turns may be selected based on linear power density’. In an exemplary embodiment, a linear power density of IkW / m or more is used to compensate for residual variations in Ic along the magnet winding that remain after flattening the critical current map, as described herein, due to temperature variation and inaccuracies in the flattening algorithm and / or implementation.

[0093] At act 804, thermal quench of the selected turns occurs. The thermal quench may be driven by (i.e. caused by or a result of) the heating at act 802. Act 804 may correspond to the thermal quench phase described herein.

[0094] At act 806, turns other than the selected turns (e.g. turns adjacent the selected turns) are driven to inductively quench. Act 806 may correspond to the inductive quench phase described herein. As described herein, current drop in the selected turns subsequent to the thermal quench in act 804 causes a positive increment in current in adjacent turns due to inductive coupling. The positive increment in current in the adjacent turns leads to overcurrent in the adjacent turn which leads to inductive quenching. This inductive quenching of the adjacent turn may in turn lead to a quench cascade, whereby adjacent turns iteratively quench and inductively couple current to subsequent turns leading those subsequent turns to inductively quench.

[0095] At act 808, the remaining current in the coil subsequent to the quenching is deposited. Act 808 may correspond to the energy dump phase described herein.

[0096] FIG. 6 is an example method 900 illustrating further aspects of a quench cascade, according to some embodiments of the technology’ described herein. At act 902, heating of at least one or more portions of selected turns is initiated. The heating of the selected turns is performed by operation of one or more heating elements disposed adjacent to the selected turns. At act 904, the selected turns are driven to thermally quench due to the heating performed at act 902. At act 906, current drops in the selected turns due to the thermal quench at act 904. At act 908, overcurrent occurs in turns adjacent to the selected turns. In particular, the current drop in the selected turns at act 906 causes an increase in current in the adjacent turns due to inductive coupling. The increase in current leads to overcurrent in the adjacent turns. At act 910, the adjacent turns are driven to inductively quench due to the overcurrent at act 908. For example, the overcurrent causes the ratio I / Ic to exceed the quench threshold. At act 912, current drops in the adjacent turns due to the inductive quench at act 906. At act 914, overcurrent in subsequent turns adjacent to the adjacent turns occurs. In particular, the current drop in the adjacent turns at act 912 causes an increase in current in the subsequent turns due to inductive coupling. The increase in current leads to overcurrent in the subsequent turns, which leads to quench. In this manner, a quench cascade is achieved whereby the heating of the selected turns performed at act 902 triggers an asymmetrical quench in subsequent turns. That is, the quenching of the turns of the magnet occurs radially asymmetrically, whereby some turns of the plurality of turns quench prior to others of the plurality of turns.

[0097] FIG. 7 illustrates an example method for inducing quench in a non-insulated magnet, according to some embodiments of the technology' described herein. As described herein, the inventors have recognized that it is not necessary to directly heat the entire non-insulated magnet with heating elements in order to induce quench throughout the noninsulated magnet. Rather, the configuration of the non-insulated magnet itself may be leveraged in order to induce quench throughout the magnet using heating elements thermally coupled to only a portion of some turns of the magnet. In embodiments the heating elements may be disposed adjacent or proximate to only a portion of some of the turns of the magnet.

[0098] For example, the example method 1000 of FIG. 7 may begin at act 1002 where a command to induce quench of the non-insulated magnet is received. The command maybe received by a user and / or in response to certain condition(s) being met. For example, the command may comprise a command to shut down the non-insulated magnet.

[0099] At act 1004, one or more heating element are operated to heat the non-insulated magnet asymmetrically. For example, selected turns of the plurality of turns may be preferentially heated. This may be facilitated by the placement of the one or more heating elements closer to the selected turns.

[0100] At least one heating element may be configured to heat the non-insulated superconducting element asymmetrically' by heating the non-insulated superconducting magnet such that at least a portion of a first turn of a plurality' of turns of a conductor of the non-insulated superconducting magnet transitions from a superconducting state to a non-superconducting state before at least a portion of a second turn of the plurality of turns transitions from the superconducting state to the non-superconducting state. The heating may be radially asymmetric such that only certain turns of the plurality of turns are heated by the one or more heating element and only the certain turns are driven to thermally quench due to the heating. At act 1006, quench of the non-insulated magnet is induced. As described herein, the heating of the selected turns drives the selected turns to thermally quench. Adjacent turns may be driven to inductively quench due to inductive coupling. In this way, the heating of the selected turns drive a radially asymmetrical quench of the non-insulated magnet.

[0101] Additional details of the heater-driven preemptive quench techniques are described herein. As described herein, a heater-drive preemptive quench technique may begin by rapidly heating at least some portions of the magnet. FIG. 8 is an example diagram illustrating heating of selected turns of a non-insulated magnet, according to some embodiments of the technology described herein.

[0102] For example, the heating may be targeted at select portions of the magnet, and in some instances, select turns of the magnet. In the illustrate embodiment, the innermost turns (e.g., turns closest to a center of the plurality of turns) are targeted for heating by the one or more heating elements. In other embodiments, others of the plurality of turns may be targeted (e.g., outermost turns furthest from a center of the plurality of turns and / or intermediate turns between the innermost and outermost turns). Any suitable number of turns or portions thereof may be targeted for heating. As described further herein, the selected turns may be targeted for heating using one or more heating elements disposed adjacent to the selected turns. In the illustrated embodiment of FIG. 8, heating elements are disposed adjacent to the innermost turns to rapidly heat the innermost turns. The one or more heating elements are driven by an external power source.

[0103] The heating of the selected turns by the one or more heating elements rapidly increases the temperature of the innermost turns 1102 of the magnet. The temperature increase is uniform in the azimuthal direction. The linear power density (i.e., watts per meter of conductor length) may be chosen to be high enough such that the heaters ‘push’ these turns to quench thermally (driving I / Ic > 1) in an azimuthally uniform manner, despite possible azimuthal nonuniformities in critical current along the turn (e.g., due to high temperature superconductor grading inaccuracies and coil temperature distributions that deviate from ideal). For example, the linear power density may be approximately 1- 2kW along the turns.

[0104] As described herein, the heating of the selected turns drives the selected turns to thermally quench. In particular, the increase in temperature reduces the critical current in the selected turns causing the ratio of turn current to critical current to exceed quench threshold (I / Ic >1).

[0105] FIG. 9 is an example diagram illustrating inductive quench of adjacent turns of a non-insulated magnet, according to some embodiments of the technology described herein. The thermal quench of the selected turns leads to a current drop in the selected turns. Due to inductive coupling, reduction in current of the inner turns causes current to increase in the adjacent turns. The positive increment in current occurs as a closed loop, flowing mostly along the conductor path in the plurality of turns, but also radially through the tum-to-tum no-insulation path. The positive increment in current pushes I / Ic > 1 in the adjacent turns 1104 of the magnet 1100 causing the adjacent turns 1104 to quench inductively in an azimuthally uniform manner.

[0106] FIG. 10 illustrates an example diagram of a quench cascade in a non-insulated magnet, according to some embodiments of the technology described herein. The pattern of quenching, to current drop, to positive current increment due to inductive coupling, to quenching repeats tum-by-tum in a radial pattern, creating an inductive quench cascade until the entire conductor of the magnet is quenched.

[0107] Tum-to-tum inductive coupling combined with an azimuthally flat critical current map facilitates an inductively driven quench cascade. The initiator is an array of embedded heating elements disposed adjacent to the turns selected to thermally quench. For example, as shown in FIG. 10, first the innermost turns 1102 thermally quench. Next, adjacent turns 1104 are driven to inductively quench. Next, first subsequent turns 1106 are driven to inductively quench. Then, second subsequent turns 1108 are driven to inductively quench. This pattern is repeated until all turns have quenched. The cascade moves radially outward because the innermost turns are the first to quench, however, other configurations are possible where others of the plurality of turns are driven to quench first. For example, where the outermost turns are driven to thermally quench first, the cascade moves radially inward. Where turns between the innermost and outermost turns are driven to thermally quench first, the cascade moves radially inward and outward.

[0108] FIG. 11 illustrates an example diagram of an energy deposition phase of the noninsulated magnet, according to some embodiments of the technology described herein. Subsequent to the quenching, the remaining magnetic energy' in the magnet is dissipated throughout the plurality of turns. Subsequent to quenching, the conductor functions as a copper coil. For anon-insulated superconducting magnet having the configuration described herein, approximately 85% of the stored magnetic energy is dissipated in this phase, which may correspond to the energy deposition phase described herein. The primary mechanism by which magnetic energy is dissipated is azimuthal current flow through copper. The peak temperature in the plurality of turns of the conductor may depend on how azimuthally uniform the magnetic energy is deposited in this phase.

[0109] FIG. 11 illustrates the results of a numerical simulation illustrating plate and conductor temperature distribution during the energy deposition phase. As shown in FIG. 11, the temperature of the conductor varies such that certain regions of the conductor have increased or decreased temperature relative to other regions. For example, FIG. 12 illustrates the example diagram of FIG. 11, with highlighted areas of temperature variation, according to some embodiments of the technology described herein. As shown in FIG. 12, certain regions of the magnet exhibit a higher temperature. These areas may be spots where current focuses and forms hot spots. Other areas have low er energy dissipation and lower temperature.

[0110] Azimuthal distribution of energy in the energy deposition phase may be affected by a number of factors. At the azimuthal location of the joint pads, heat dissipation is suppressed due to increased cross-sectional area of copper in the radial plate. Current focusing and hotspots can occur at the transition betw een the joint pad and the conductor on the outer leg 1504 of the magnet 1100. Azimuthal current preferentially flows in the copper joint pads, as it is the path of least resistance. For a toroidal field magnet, peak magnetic field strength along the windings varies along the windings by a factor of approximately 2 azimuthally with a maximum value on the inner leg 1502 of the magnet 1100. Because the critical current of the conductor is most sensitive to temperature at high magnetic field strength, this region tends to quench sooner than other regions, depositing more magnetic energy there. Eddy current heating occurs preferentially on the inner leg 1502 of a toroidal field magnet w here the magnetic field strength is the highest, and thus dB / dt is highest during quench. Spatial variation in temperature of the plurality of turns prior to quench initiation can cause regions of the magnet to enter the energy deposition phase ahead of others, resulting in non-uniform energy deposition. Similarly, non-uniform heat removal by coolant during the heater turn-on phase can cause spatial variation in temperature of the plurality of turns during quench initiation, resulting in a non-uniform energy deposition. As described herein, the preemptive quench techniques developed by the inventors are heater-driven, meaning the quenching is a thermal quench driven by actively heating one or more portions of the magnet with one or more heating elements. Implementation of the one or more heater elements for performing the heater-driven preemptive quench techniques is described herein.

[0111] The one or more heater elements may be positioned adjacent to the selected portions of the conductor which are to be heated to thermal quench. For example, the one or more heating elements may be positioned below; above, or beside the selected portions of the conductor. As described herein, the conductor may be positioned in a groove of the magnet plate. In some embodiments, the one or more heating elements may be positioned in the groove with the conductor (e.g., above, besides, and / or below the conductor).

[0112] FIG. 13 illustrates an example arrangement for implementing heating elements in a non-insulated magnet, according to some embodiments of the technology described herein. FIG. 13 illustrates a stacked plate magnet 1600 of the type described herein. In particular, the stacked plate magnet 1600 comprises a plurality of plates 1602. Each of the plates comprise a groove 1604 into which a conductor 1606 is disposed. The magnet 1600 further comprises heating elements 1608 positioned in the groove.

[0113] In the illustrated embodiment, the heating elements 1608 are positioned adjacent to the conductor 1606 in the groove 1604. Other configurations are possible, however, such as disposing the heating elements 1608 outside of the groove, below, and / or above the conductor 1606 in the groove 1604.

[0114] In the illustrated embodiment of FIG. 13, the groove 1604 of the magnet 1600 is modified to receive a heating element. In particular, as shown in FIG. 13, the heating element 1608 is received in a side portion of the groove 1604 so that the heating element is disposed adjacent to the conductor 1606.

[0115] As shown in FIG. 13, the heating element(s) 1608 are disposed adjacent to selected turns of the plurality of turns of the magnet. In the illustrated embodiment, the selected turns are the innermost turns of the magnet. The selected turns may comprise any number of turns. As described herein, the inventors have recognized that quench cascade techniques may be leveraged such that the selected turns which the heating element(s) is disposed adjacent to need not comprise all turns of the plurality of turns of the magnet. Rather, the selected turns may comprise fewer than all turns of the magnet. In some embodiments, the selected turns comprise fewer than half of the turns of the magnet. In some embodiments, the selected turns comprise fewer than one third of the turns of the magnet. In some embodiments, the plurality of turns of the magnet comprise at least ten turns, and the selected turns comprise five or fewer turns of the magnet. In the illustrated embodiment of FIG. 13, the heating element(s) are disposed adjacent to approximately three and a half turns of the conductor starting from a joint pad of the magnet plate 1602.

[0116] In some embodiments, multiple heating elements may be disposed side-by-side. In such instances, the multiple heating elements provide redundancy as a failsafe in the event one of the heating elements is not functioning.

[0117] The heating element may be inserted into the groove 1606 of the magnet using any suitable technique. For example, a Vacuum Pressure Impregnation (VPI) solder process may be used in some embodiments. In some embodiments, a combined solder reflow-VPI process may be used. When the combined solder reflow-VPI process is used, the groove may be reduced in size and replaced with copper co-wind tapes. Apart from some turns having a heating element disposed therein, the dimensions of the groove are the same for each turn and at all azimuthal locations, which may facilitate azimuthal uniformity’ in quench response.

[0118] FIG. 14 illustrates an example heating element which may be implemented with a heater-driven preemptive quench technique, according to some embodiments of the technology described herein. According to some embodiments, the heating element may be implemented within a cable to form a cable heating element. FIG. 14 illustrates a cable 1700 having a heating element 1702. The cable may be a coaxial cable. The cable may comprise a mineral-insulated cable. The cable with the heating element may be positioned adjacent to the portions of the conductor that are desired to be heated. The heating element may comprise a commercially available heating element such as those manufactured by THERMOCOAX and / or ARi industries.

[0119] FIG. 14 illustrates a cable 1700 having a heating element. The heating element of FIG. 14 comprises a resistive core 1702. The cable 1700 further comprises an insulating sheath 1704. The resistive core may comprise a heated portion 1706 and a cold potion 1708. The cold portion 1708 may be positioned at ends of the resistive core 1702 while the heated portion 1706 is disposed therebetween. In some embodiments, the heated portion 1706 is positioned at one end of the resistive core 1702 and the cold portion 1708 is positioned at an opposing end of the resistive core 1702. The heating elements of the type used herein may operate continuously and may reach temperatures as high as 1273K. For the heater-driven preemptive quench techniques described herein, the heating element(s) are operated for less than five seconds so as to raise the temperature adjacent to the heating element to approximately 35K to initiate quench. The heating elements described herein may also be capable of achieving linear power densities of IkW / m per heater to attain a robust preemptive quench response.

[0120] At fixed linear power density, the overall voltage of a heating element increases linearly with the length of the heating element. To keep heating element voltages less than a target value (e.g., less than IkV), the length of the heated section of the heating element is restricted to a corresponding target value. For the non-insulated superconducting magnets of the type described herein, a maximum heater length of 20 meters may be chosen. For a coaxial cable heating element with a constantan center wire, IkW / m per heater is attained at 38 amps, requiring an overall voltage of 500 V for the heated length of 18.5 meters.

[0121] In view of the restriction on the length of the heating element, the magnet may comprise multiple heating elements positioned end-to-end to achieve the desired heating of the selected turns. As described herein, the heating element may be positioned adjacent to a portion of the turns of the magnet, and in the illustrated embodiments specifically, adjacent to 3.5 turns of the conductor. The 3.5 turns correspond to a length of 37 meters. Therefore, a pair of heating elements are positioned end-to-end adjacent to the selected turns. The heated portions of the heating elements are placed end-to-end while the cold portions exit outside of the magnet.

[0122] FIG. 15 illustrates an example diagram of heating element positioning on a non- insulated magnet, according to some embodiments of the technology described herein. The solid lines shown in FIG. 15 illustrate the heated portion of the heating elements and the dashed lines illustrate cold portions of the heating elements. As described herein and in the illustrated embodiment, the heating element comprises two heating elements with heated portions disposed end-to-end.

[0123] FIG. 15 illustrates arrangement of heating elements on a magnet plate having a conductor that winds in the counterclockwise direction starting from an inner joint pad. FIG. 16 illustrates another example diagram of heating element positioning on a non- insulated magnet, according to some embodiments of the technology described herein. FIG. 16 illustrates arrangement of heating elements on a magnet plate having a conductor that winds in the clockwise direction starting from an inner joint pad.

[0124] As show n in FIGS. 15-16, cold portions of the heating elements pass through the magnet plate. The cold portion 152A of cable 2A passes through at a point 156A where cable 1 A ends. From that point, cable 2A transitions to the heated portion 154A and in the direction of the plurality of turns for approximately 1.7 turns. The cold portion 152B of cable 2B passes through at a point 156B where cable IB ends. From that point, cable 2B transitions to the heated portion 154B and in the direction of the plurality of turns for approximately 1.7 turns. This arrangement enables the cold portions of the heating elements to exit the magnet at the top of the plate for all magnet plates. Similar techniques can be implemented to accommodate additional heating elements with heated portions disposed end-to-end with other heated portions..

[0125] As described herein, critical current density in the high-temperature superconductor material from which the magnet conductor may be formed varies strongly with respect to magnetic field strength and angle. FIGS. 17-18 illustrates example simulations showing variations in critical current density, according to some embodiments of the technology described herein.

[0126] In particular, FIG. 17 illustrates a graph illustrating HTS tape critical current density vs. magnetic field (B-field) and angle at a temperature of 12K. The graph illustrates that the HTS critical current density (Jc) varies strongly with B-field magnitude and angle. FIG. 18 illustrates a simulation showing B-field distribution in a toroidal field magnet. The simulation shows that B-field amplitude on a conductor of a toroidal field magnet varies by a factor of 2 azimuthally.

[0127] FIG. 19 illustrates graphs showing variation in critical current under different operating conditions, according to some embodiments of the technology described herein. The graph on the left of FIG. 19 shows variation in critical current that would occur along each turn in a 14-plate toroidal field magnet where no compensation for variations in critical current are implemented. In this instance, only the toroidal field magnet is operating. The graph on the right of FIG. 19 shows variation in critical current along the 14-plate toroidal field magnet where no compensation for variations in critical current are implemented. In this instance, both the toroidal field magnet and the poloidal field magnet are operating. As described herein, variations in critical current can lead to hot spot formation and conductor bum during quench, as some sections of the magnet with lower critical current tend to quench more quickly than others. The inventors have recognized that the no-insulation magnets described herein may be optimized for quench by minimizing variations in critical current throughout the magnet. This may be referred to as flattening the critical current (Ic) or critical temperature (Tc) profile of the magnet. This flattening is done by a process of tape grading, as described herein. FIG. 20 illustrates an example diagram of a magnet where critical current has been azimuthally flattened, according to some embodiments of the technology described herein.

[0128] A design target for a TF magnet is to operate with I / Ic less than a specified value everywhere at a specified operating temperature. This requirement applies in the presence of the magnetic fields generated by both the TF itself and other coils in the reactor, which include the central solenoid and poloidal field coils. At the time when preemptive quench is initiated, only the toroidal field magnet will be operating, other coils of the reactor will not be operating because in preparation for preemptive quench, currents in the central solenoid and poloidal field coils are reduced to zero.

[0129] A quench-optimized critical current map is shown in FIG. 20, for the situation in which only the toroidal field coil is operating. Using high-temperature superconductor grading, this critical current map is tuned to be azimuthally flat and radially increasing tum-by-tum - while at the same time having the performance needed to satisfy DC performance requirements indicated above when other coils are also operating.

[0130] According to one embodiment, HTS grading may be used to reduce, and ideally minimize, the variations in critical current throughout the magnet. The goal of HTS grading is to flatten the critical current or critical temperature profile azimuthally during operation of only the toroidal field while still retaining enough critical current performance to satisfy minimum critical current with both the toroidal field magnet and poloidal field magnet operating.

[0131] A first step in determining how to implement HTS grading is to consider a grading scheme in which the design value of operating current to critical current (lop / Ic) is substantially equal to (and ideally equal to) the target value everywhere in the magnet under operating conditions of both the toroidal field magnet and the poloidal field magnet. This consideration sets the minimum amount of HTS tape needed in the magnet. FIG. 21 illustrates example graphs illustrating high-temperature superconductor critical current that is attained when only the toroidal field magnet is operating for different HTS tape gradings, according to some embodiments of the technology described herein. The graph on the left of FIG. 21 illustrates critical current along 14 turns in a representative pancake with minimum HTS tape grading, i.e., the minimum amount of HTS needed to satisfy toroidal field magnet and poloidal field magnet operating conditions, as described above. The graph on the right of FIG. 21 illustrates the same, but also shows how the critical current can be made flat on a tum-by-tum basis by adding HTS tape.

[0132] As shown in the graph on the left of FIG. 21, large bumps in critical current occur along the winding because more HTS tape is needed at locations where the local magnetic field strength is enhanced and / or the B-field orientation changes when the poloidal field magnet is turned on. While this critical current map would satisfy minimum critical current requirements under all operating conditions of a reactor, it is desirable to be optimized to perform a safe quench due to the bumps and dips present in the mapping.

[0133] To obtain a quench-optimized critical current map. the map is ‘'flattened7’ by filling in areas of valleys with more HTS tape. The graph on the right of FIG. 21 graphically illustrates this flattening of the critical current map by filling in valleys wi th additional HTS tape. In this case, the critical current value on each turn is flattened at the value corresponding to the peak critical current along that turn for the case of minimum HTS grading.

[0134] FIG. 22 illustrates an example graph showing HTS fill fraction along a conducting according to a grading scheme, according to some embodiments of the technology described herein. In the illustrated graph of FIG. 22, a fill fraction of 1 means that the allotted space in the magnet groove is fully filled with HTS tape. In the illustrated example graph, it is shown that the grading scheme effectively removes HTS tape that is not needed (e.g., the fill fractions are less than 1 in some sections). The resulting bumps and valleys in fill fraction are what is needed to flatten the critical current along the turns of the magnet azimuthally. Bumps in the graph of FIG. 22 correspond to regions of high magnetic field and / or unfavorable B-field angle with respect to the tape, requiring more HTS to compensate.

[0135] FIG. 23 illustrates an example of a conductor groove with HTS tape and filler tape disposed therein according to a grading scheme, according to some embodiments of the technology described herein. As shown in FIG. 23, a conductor unit cell 2700 comprises a fixed-width groove cut into a radial plate 2702 that accepts the filler tape stack 2706, a copper co-conductor ‘cap’ 2704 and optionally accommodates a solder flow channel 2708 for a VPI solder process. This fixed width groove design maintains a fixed cross-sectional area of all constituent components along the conductor. This provides azimuthal uniformity in unit cell heat capacity per unit length of the conductor and electrical resistance per unit length of the conductor, which help to promote azimuthal uniformity of quench evolution.

[0136] The right of FIG. 23 illustrates how HTS fill fraction may be implemented at the tape level. The tape stack comprises a fixed number of tapes that run the fully length of the conductor (e.g., 150 meters in this example). There may be multiple types of tapes, such as HTS tape segments (dashed lines) spliced to non-superconducting filler tape segments (solid lines), HTS tapes that run the full length of the conductor, filler tapes that run the full length of the conductor, and co-wind copper tapes that run the full length of the conductor (dotted lines). In this manner, the number of HTS tapes in the stack vary with distance along the conductor to satisfy the fill fraction profile.

[0137] The fixed number of tapes facilitates a winding process in which HTS and filler tape sections are first spliced together and placed on separate spools. In a typical winding, there could be 100 to 200 tapes, each requiring a separate spool. The tapes are drawn from all the spools together, bundled into a stack and inserted into the groove in the radial plate.

[0138] In some embodiments, the HTS fill fraction profile may be optimized from quench simulations. On turns that have embedded heating elements, the optimum fill fraction profile may be one that makes critical temperature azimuthally flat. This may be because the heating elements increases the temperature of the HTS with azimuthal uniformity, causing the turn to reach critical temperature with azimuthal uniformity. Other turns, which quench inductively, may have an optimum fill fraction profile that makes critical current azimuthally flat.

[0139] FIG. 24 illustrates a diagram showing aspects of HTS grading on a non-insulated magnet having heating elements, according to some embodiments of the technology described herein. HTS grading on turns that are thermally quenched using the one or more heating elements may be optimized towards having azimuthally flat critical temperature (Tc) whereas other turns, which are quenched inductively, may be optimized towards having azimuthally flat critical current (Ic). As described herein, subsequent to quenching, the magnet may enter an energy deposition phase, whereby the remaining current in the magnet is dissipated. The inventors have recognized that it is desirable to increase, and ideally maximize, the uniformity of energy deposition. Increasing, and ideally maximizing, the uniformity of energy deposition may reduce, and ideally minimize, peak conductor temperatures attained in the energy deposition / copper coil phase.

[0140] FIG. 25 illustrates temperature variation in a portion of anon-insulated magnet during an energy deposition phase, according to some embodiments of the technology described herein. As described herein, the magnet may comprise a joint pad. The presence of the highly conductive copper joint pad increases current in the first and last turns of the conductor which couples to the joint pad. Due to reduced overall azimuthal resistance, currents passing through turns that connect to the joint pads decay slower in time than other turns. Combined effects can produce hot spots at the transition between the joint pad and the conductor as shown in FIG. 25.

[0141] The inventors have recognized various solutions to increase, and ideally maximize, uniformity of magnet energy deposition in view of the challenges presented by the joint pads of the magnet. FIG. 26 illustrates an example diagram showing temperature variation in a non -insulated magnet having the joint pad optimizations described herein during an energy deposition phase, according to some embodiments of the technology described herein.

[0142] FIG. 27 illustrates an example of a poor joint pad arrangement, that can result in the hot spots shown in FIG. 25. As shown in FIG. 27, the root cause is from the leading edge 2706 of a joint pad (e.g., an in-wind joint pad 2700 A) being extended relative to a trailing edge 2704 of an opposing joint pad (e.g., an out-wind joint pad 2700B). Doing so can enhance the current focusing effect at the leading-edge extensions. Instead, the joints should be arranged so that the trailing edge of a joint pad is extended relative to leading edge of an opposing joint pad.

[0143] FIG. 28 illustrates additional example techniques for reducing hot spot formation caused by current focusing in the joint pad. according to some embodiments of the technology described herein. As shown in FIG. 28, the joint pad 2800 comprises a plurality' of radial cuts 2802. The inventors have recognized that the impact of the high electrical conductivity of the copper joint pads can be mitigated by adding radial cuts into the joint pads at regular intervals. The inventors have further recognized that adding ‘flares’ (e.g., flare 2804) to the conductor 2806 at the transition between the joint pad and conductor, current density’ in the conductor may be reduced, thereby mitigating hot spot temperature. The flares may comprise sections of the conductor that are outwardly tapered, thereby increasing the cross-sectional area of the conductor at the flare.

[0144] FIG. 29 illustrates implementation of the example techniques of FIGS. 27-28, according to some embodiments of the technology described herein. As shown in FIG. 29, the conductor 2906 comprises flares 2904 at the point where the conductor is coupled to the joint pad. In addition, the joint pad comprises a plurality of radial cuts 2902. Further, the trailing edge 2908 of the in- wind joint pad 2900B is extended relative to the leading edge 2910 of the out-wind joint pad 2900A and the trailing edge 2908 of the out-wind joint pad 2900A is extended relative to the leading edge 2910 of the in-wind joint pad 2900B.

[0145] A further challenge during the energy' deposition phase of the magnet is preferential heating on an inner leg of the magnet. The preferential heating may be due to high-temperature superconductor temperature sensitivity and preferential eddy current heating. FIG. 30 illustrates an example diagram showing temperature variation throughout a non-insulated magnet, according to some embodiments of the technology described herein.

[0146] The temperature sensitivity of the conductor critical current varies with magnetic field strength, being most sensitive on an inner leg 3400 of the magnet. The increased sensitivity of some sections of the magnet can cause some portions of the magnet (e.g., portions of the inner leg) to enter the energy deposition phase ahead of other regions of the magnet. This can lead to more magnetic energy' being deposited in the sections of the magnet that enter the energy deposition phase ahead of others. In some embodiments, preferential eddy current heating in the inner leg 3400 can also lead to the inner leg 3400 entering the energy deposition phase ahead of others.

[0147] The inventors have developed solutions for addressing the preferential heating of certain portions of the magnet. In some embodiments, a resistivity of conductor can be varied radially and / or azimuthally’ along the conductor of the magnet. For example, to compensate for the preferential heating of the inner leg, in some embodiments, the outer leg may be manufactured to have a higher resistivity’. This may be accomplished by varying the material from which the conductor is made. FIG. 31 illustrates an example diagram showing a non-insulated magnet with a conductor of varying material, according to some embodiments of the technology described herein.

[0148] For example, a metal alloy having a higher resistivity may be implemented in regions of the magnet that would otherwise enter the energy deposition phase relatively later than other regions of the magnet. In the illustrated embodiment, for second and third regions 3104, 3106, the conductor may have a higher resistivity and for first region 3102, the conductor may have a lower resistivity. As an example, GlidCop Al- 15 with 92% IACS may be a material having a lower resistivity from which the conductor can be formed (e.g., for the first region) and C18150 with 80% IACS may be a material having a higher resistivity from which the conductor can be formed (e.g., for the second and third regions).

[0149] Additionally or alternatively, the resistivity of different regions of the magnet may be varied by varying the cross-sectional area of the copper cap of the conductor. For example, The cross-sectional area of the copper cap may be lower in regions where higher resistivity is desired (e.g.. second and third regions on the outer leg of the magnet) while the cross-sectional area of the copper cap may be higher in regions where lower resistivity is desired (e.g., the first region on the inner leg of the magnet). The variation in cross- sectional area of the copper cap produces a higher resistance to azimuthal current flow on the outer leg compared to the inner leg, thus causing relatively more energy dissipation in the outer leg.

[0150] A further challenge presented in implementing the quench techniques described herein is non-uniformities in magnet temperature at quench initiation. Non-uniform spatial distribution in magnet temperature (e.g., throughout the plurality of turns of the magnet conductor) prior to quench initiation can lead to non-uniform energy deposition. This may be a result of magnet coolant arrangement. For a magnet with a vertically oriented coil with buoyancy-driven coolant, the top of the coil will be hotter than the bottom. Depending on how severe the temperature difference is, compensation for this effect may be desirable.

[0151] In some instances, non-uniform heat removal by coolant during a heater tum-on phase, as described herein, can cause spatial variation in winding pack temperature during quench initiation. This may lead to non-uniform energy deposition throughout the magnet in the energy' deposition phase. The inventors have recognized that the non-uniform energy deposition caused by non-uniform spatial distribution of magnet temperature may be addressed by fine tuning a critical current map of the magnet for a desired energy deposition phase outcome. In particular, the inventors have recognized that azimuthal distribution of energy deposition can be made to be uniform by arranging for each turn to enter its own “copper phase” or “energy deposition phase” with azimuthal uniformity.

[0152] As described herein, the heater-driven preemptive quench technique provides for a quench cascade where each turn or group of turns quenches in succession. So to can each turn or group of turns be configured to enter the energy' deposition phase with azimuthal uniformity'.

[0153] In some embodiments, this is achieved using a grading scheme. The grading scheme may be determined using numerical quench simulations. A method to obtain the grading scheme with the use of numerical quench simulations is described herein.

[0154] First, a heater-driven preemptive quench response is numerically simulated for a non-insulated magnet. FIG. 32 illustrates an example diagram illustrating a step of selecting a target value of I / Ic for each turn of a magnet, according to some embodiments of the technology described herein. In the illustrated example, an I / Ic value of 1 .3 is chosen.

[0155] Then, values of temperature and current are recorded at the time when a targeted value of turn current divided by critical current (I / Ic) is attained in that turn. FIG. 33 illustrates an example diagram illustrating a step of determining HTS temperature in each turn when that turn reaches a target value of I / Ic, according to some embodiments of the technology described herein. I / Ic may be a good measure of current sharing between the high temperature superconductor and the copper co-conductor. When the targeted value of I / Ic is reached, significant Joule heating in the copper co-conductor has begun in that turn. In the illustrated embodiments, a value of I / Ic ranging from 1.2 to 1.4 is used.

[0156] Subsequently, HTS grading is adjusted so that the targeted values of I / Ic are obtained with azimuthal uniformity for that turn. FIG. 34 illustrates an example diagram illustrating HTS current when a target value of I / Ic is obtained for that turn, according to some embodiments of the technology' described herein.

[0157] Implementation of the heater-driven preemptive quench techniques in a system comprising a toroidal field magnet are discussed further herein. For example, the toroidal field magnet may comprise a plurality of plates, each plate having heating elements described herein and being configured to implement the heater-driven preemptive quench techniques described herein.

[0158] FIG. 35 illustrates an example of a toroidal field magnet comprising a plurality of plates being configured to implement the heater-driven preemptive quench techniques described herein, according to some embodiments of the technology described herein. In the illustrated embodiment of FIG. 35, the magnet comprises 16 pancakes, each comprising four heating elements. As shown in FIG. 35, the plates are mirrored, alternating in orientation between in-wind and out-wind plates. The mirroring of the plates symmetrizes forces and reduces out-of-groove Lorenz loading on the conductor. The radial plate design exploits this symmetry to reduce the number of unique plate types. Half of the plates are radial plates that are ‘ flipped’ with respect to the other half. As shown in FIGS. 15-16, routing techniques for both in-wind and out-wind plates are provided so that the cold portions of the heating elements can exit the magnet regardless of the radial plate orientation.

[0159] At least some of the heating elements of the magnet may connect to a common power source. In the illustrated embodiment of FIG. 35, at the point of exit from the plurality of plates, each heating element connects to a common third rail bus via an in-line fuse. In the event that a heating element develops a low-resistance short circuit, its fuse protects against excessive current draw from the third rail and resultant component damage.

[0160] As described herein, each plate of the magnet may include multiple heating elements that provide redundancy. That is, if one of the heating elements ceases to function, the heater-driven preemptive quench technique may still be implemented by the remaining heating element Accordingly, the heater-driven preemptive quench techniques described herein are tolerant of heating element failure as the techniques do not require that all heating elements function. The in-line fuse described herein allows the individual heating elements to fail “gracefully” without impacting the operation of the remaining heating elements.

[0161] In some embodiments, the system (e.g.. a reactor) comprises multiple of the toroidal field magnets described herein. In one example, the system comprises more than 10, more than 15, and / or up to 20 toroidal field magnets. FIG. 36 is an example system comprising multiple magnets configured to perform a heater-driven preemptive quench technique, according to some embodiments of the technology described herein. In some embodiments, the multiple magnets of the system may share a common power source. As shown in the illustrated embodiment of FIG. 36, all of the magnets couple to the third rail. The multiple magnets may be connected in series.

[0162] The third rail may energize the heating elements of the magnets approximately simultaneously. In some embodiments, the third rail may provide a peak voltage greater than or equal to 500V and / or less than or equal to IkV.

[0163] As described herein, the heating elements may be disposed in a cable having an insulating sheath. In some embodiments, the heating elements may be disposed in a groove of a respective magnet plate and the sheath may be soldered into the groove. In such instances, the magnet plates, high-temperature superconductor and copper coconductor may serve as a ‘ground" for all heating elements. The returning current flows via the terminals in each magnet to the positive (+) and (-) superconducting DC cold buses that links though all of the magnets, as shown in FIG. 36.

[0164] The common connection point of all heating elements to the bus across multiple plates and multiple magnets does not interfere with magnet operation, despite the apparent short circuit that the third rail introduces. This is because with typical heating element resistances of approximately 10 ohms and maximum toroidal field magnet open circuit voltage of approximately 2V, the leakage current through a given heating element is less than approximately ,2A which is negligible compares to the toroidal field magnet operating current of approximately 31.25kA.

[0165] In the illustrated embodiment of FIG. 36, multiple heating elements are implemented in each plate, multiple plates are implemented in each magnet, and multiple magnets are implemented in the reactor. Accordingly, 1152 heating elements are employed, each drawing approximately 38 amps of peak current. Thus, the aggregated third rail current is approximately 44kA at approximately 500V. Peak power of approximately 22MW is delivered to the magnet system for a few seconds.

[0166] FIGS. 37-438 illustrate circuit diagrams during different stages of magnet operation to initiate a heater-driven preemptive quench. FIG. 37 illustrates a circuit diagram in which a DC power supply crowbar switch (S 1) is used to reduce (and ideally, minimize) bypass current dissipation in the magnet. FIG. 38 illustrates a circuitry diagram in which the DC power supply crowbar switch (SI) is not used. In this case, quench is initiated with the toroidal field magnet in an open-circuit condition. Panel (a) of FIG. 37 illustrates a simplified circuit diagram for a power system for one or more active heating elements implemented with a non-insulated magnet. Circuit components L and RBP represent inductances and no-insulation bypass resistances, respectively for sections of the toroidal field magnet that span locations where the heating elements’ sheath ends are grounded to the conductors. There are 575 such sections in the reactor system described herein. The total bypass resistance of the toroidal field magnet (e.g., the summation of all RBP in series) is approximately 72 pOhms.

[0167] A DC power supply delivers operating current (Iop) nominally 31.25 kA to the toroidal field magnet via superconducting cold buses.

[0168] The output terminals of the DC power supply have a ground fault detection circuit, represented in panel (a) of FIG. 37 as shunt resistors (Rs) that span the DC power supply terminals, connecting to a common resistor (RGF) to ground. Current flow through RGF above some cut-off threshold indicates that the toroidal field cold bus and / or winding pack (plurality7of magnet plates) has developed an off-normal ground fault condition - i.e., it has developed a leakage current pathway elsewhere to ground. Typical values of Rs and RGF are on the order of 20 ohms.

[0169] The heater power supply may comprise a stored energy7system (e g., a battery pack and / or a large capacitor), that can deliver heater current (IH) of approximately 44kA at approximately 500V for a duration of a few7seconds.

[0170] RH represents the effective heater element resistance, typically 5 ohms for two heating elements connected in parallel. In-line fuses that are shown in FIG. 35 are omitted in the illustrated circuit diagram.

[0171] Switch SI, with effective resistance RCB, is used to optionally crowbar the power supply terminals in the event that the power supply cannot continue to deliver current (e.g., due to facility power outage, power supply fault).

[0172] The value of RCB is chosen to be low (e.g., approximately 20 pOhm) compared to the overall bypass resistance of the toroidal field magnet (e.g., approximately 72 pOhm) such that when S 1 is closed, most of Iopcontinues to flow around the loop formed by the toroidal field magnet and cold bus, rather than close across the bypass resistances within the windings. This reduces, and ideally minimizes, Joule heating within the windings.

[0173] Switch SI may be a superconducting switch (e.g., a persistent current switch) with RCB = 0, in some embodiments. In this case, essentially all of Iopcontinues to flow7around the toroidal field magnet and cold bus loop with very little dissipation. With a persistent current switch, the toroidal field in the toroidal field magnet could be sustained for many weeks without significant loss in magnetic field strength.

[0174] Switch S2 provides the ability to ground the positive toroidal field cold bus as a precautionary measure during heater operation. Switch S3 connects the positive voltage terminal (approximately 500V) of the heater pow er supply to a third rail, which is common to all heaters. Closure of S2 ensures that the toroidal field cold bus and winding pack is held close to ground potential when the heater power supply is connected to the heaters via closure of S3 despite third rail and / or heater lead wires possibly developing a leakage resistance to ground. Otherwise, the DC pow er supply leads, ground fault detection circuit and instrumentation that is electrically connected to the toroidal field cold bus and winding pack could be biased to a large negative voltage (e.g., approximately - 500V) with respect to ground, which could cause damage of these components.

[0175] As described herein, FIG. 37 illustrates circuit diagrams representing steps taken to initiate a preemptive quench during toroidal field power supply outage for the case when the magnet terminal current is sustained via a power supply crowbar switch. SI. Panel (a) of FIG. 37 illustrates steady state toroidal field magnet operation. At this time, the DC powder supply delivers steady state current (Iop) to the toroidal field magnet via positive and negative superconducting cold buses.

[0176] Panel (b) of FIG. 37 illustrates a power shut-off (e.g., due to facility power outage or fault). Immediately in response to power supply outage, the power supply crowbar switch (SI) is closed. This switch closure allows most of the toroidal field current (lop) to continue to flow' through the toroidal field magnet and external superconducting cold bus loop. The fraction of Iopthat is maintained depends on the value of RCB to RPB.

[0177] Panel (c) of FIG. 37 illustrates closing of the positive toroidal field grounding switch. The negative terminal of the heating element power system is connected to ground through switch S2.

[0178] Panel (d) illustrates closing a heater power source switch (S3). Heater current (In) is delivered to all heating elements simultaneously via the third rail. Heating element return current path is via both the positive and negative legs of the superconducting cold bus.

[0179] Because the negative lead of the heating element pow er source is directly connected to the positive cold bus, most of the heater current (IHI) returns via this bus. The remaining component (IH2) flows via the negative cold bus, through RCB and SI. and then to the negative lead of the heating element power source.

[0180] Im flows in the direction opposite to Iopin the positive cold bus. IH2 flows in the same direction as Iopin the negative cold bus. Thus, the maximum current in any cold bus during the time of heating element turn on will be in the negative leg. However, its magnitude will be no more than Iop+ IH / 2 for the case of a superconducting S 1 (with RCB = 0) and much lower for typical values of RCB that can be obtained via a non- superconducting switch. This means that the superconducting cold bus (and associated cryogenic to room temperature current feeders, not shown in FIG. 37) should preferably be sized to accommodate combined Iopplus heating element currents of roughly 31.25 kA + 22 kA.

[0181] As described herein, FIG. 38 illustrates circuit diagrams representing steps taken to initiate a preemptive quench during toroidal field power supply outage for the case when the magnet terminal current is interrupted (e.g., when the toroidal field magnet is open- circuited). Panel (a) of FIG. 38 illustrates steady state toroidal field magnet operation. At this time, the DC power supply delivers steady state current (Iop) to the toroidal field magnet via positive and negative superconducting cold buses.

[0182] Panel (b) of FIG. 38 illustrates a power shut-off (e.g., due to facility pow er outage or fault). In this case, the power supply crowbar switch (SI) is not closed. The toroidal field magnet is maintained in an open circuit condition. In response, the magnet current (Iop) closes internally in the toroidal field winding pack via the bypass resistance (RBP).

[0183] Current flow in the winding bypass resistance causes the winding pack to heat up fairly uniformly. This situation can be beneficial for raising the winding pack temperature prior to preemptive quench initiation. For example, very cold (e.g., 8K) supercritical helium in the coolant channels can impede the effectiveness of the heating elements to raise the HTS temperature. By allowing the winding pack, and helium in contact with it, to warm up uniformly prior to preemptive quench (e.g., to approximately 15K), the helium density may be reduced significantly. Correspondingly, heat transfer to the helium is reduced significantly during heater turn-on. However, the timing of the heater turn-on needs to be sequenced more carefully in this scenario because if left to quench on its own, as described herein, a high energy NI-HTS magnet will likely become damaged. Panel (c) of FIG. 38 illustrates closing of the positive toroidal field grounding switch. The negative lead of the heating element power system is connected to ground through switch S2.

[0184] Panel (d) illustrates closing a heater power source switch (S3). Heater current (In) is delivered to all heating elements simultaneously via the third rail. Heating element return current path is via the positive leg of the superconducting cold bus. Because the toroidal field magnet is open circuited, Iopdoes not flow in the cold bus. Therefore, the positive cold bus only has IH flowing in it. The negative cold bus has essentially zero current flowing in it. This means that the superconducting cold bus (and associated cry ogenic to room temperature current feeders, not shown in FIG. 38) should preferably be sized to accommodate heater currents of approximately 44kA.

[0185] FIG. 39 illustrates an example method 4300 for implementing a heater-driven preemptive quench technique in a system (e.g., a reactor) comprising one or more toroidal field magnets, according to some embodiments of the technology' described herein. The example method 4300 may begin at act 4302 where currents in magnets of the system are reduced to zero, with the exception of the toroidal field magnet. For example, a poloidal field magnet and / or a central solenoid magnet of the system may be reduced to zero.

[0186] At act 4304, one or more heating elements are operated to heat each of the noninsulated magnet plates of the toroidal field magnets asymmetrically. For example, as described herein, the system may comprise multiple toroidal field magnets, each comprising multiple plates. Act 4304 may comprise operating one or more heating elements corresponding to the respective plates to asymmetrically heat the respective plates according to the techniques described herein. At act 4306, due to the heating performed in act 4306, quench of the toroidal field magnet is induced.

[0187] As used herein, a non-insulated magnet, also referred to herein as a no-insulation magnet, includes a magnet having a conductor arranged in a plurality turns and an electrical resistance between a first turn and second turn of the plurality of turns is no more than 1 megaohm (e.g., greater than 0 and less than 1 megaohm, greater than 0 and less than .75 megaohms, greater than 0 and less than .5 megaohms, greater than 0 and less than .25 megaohms, greater than 0 and less than .1 megaohms). Additionally, while a non- insulated magnet may have little to no electrical resistance between turns of an individual magnet plate, in some cases electrical insulation may be positioned in other locations within a non-insulated magnet. For example, electrical insulation may be placed between respective plates of the magnet, as described above. Accordingly, the language “noninsulated,” “no-insulation,” “NI” and the like in reference to a magnet refers to a low electrical resistance between respective turns, and does not preclude other regions of the magnet from being wholly or partially electrically insulated from one another.

[0188] Various examples of the technology' described herein are provided herein.

[0189] (1) A non-insulated superconducting magnet, comprising: at least one heating element configured to induce a quench of the non-insulated superconducting magnet by heating the non-insulated superconducting magnet, wherein the at least one heating element is configured to heat the non-insulated superconducting magnet asymmetrically.

[0190] (2) The non-insulated superconducting magnet of (10, wherein the at least one heating element is configured to heat the non-insulated superconducting element asymmetrically by heating the non-insulated superconducting magnet such that at least a portion of a first turn of a plurality of turns of a conductor of the non-insulated superconducting magnet transitions from a superconducting state to a non- superconducting state before at least a portion of a second turn of the plurality of turns transitions from the superconducting state to the non-superconducting state.

[0191] (3) The non-insulated superconducting magnet of (2), wherein the at least a portion of the second turn transitions to the non-superconducting state in response to inductive coupling of the second turn with the first turn.

[0192] (4) The non-insulated superconducting magnet of any of (l)-(3), wherein the at least one heating element is configured to heat the non-insulated superconducting magnet radially asymmetrically.

[0193] (5) The non-insulated superconducting magnet of any of (l)-(4), wherein the non-insulated superconducting magnet comprises a conductor arranged in a plurality of turns including a first turn, a second turn, and a third turn, wherein the first turn is inside of the second turn and the second turn is inside of the third turn.

[0194] (6) The non-insulated superconducting magnet of (5), wherein the at least one heating element is disposed radially between the first turn and the third turn.

[0195] (7) The non-insulated superconducting magnet of (5), wherein the at least one heating element is disposed radially between at least some neighboring ones of the plurality7of turns.

[0196] (8) The non-insulated superconducting magnet of (7), wherein the at least some neighboring ones of the plurality of turns comprises fewer than all of the plurality of turns. (9) The non-insulated superconducting magnet of (7), wherein the at least some neighboring ones of the plurality of turns comprises fewer than half of the plurality of turns.

[0197] (10) The non-insulated superconducting magnet of (7), wherein the at least some neighboring ones of the plurality of turns comprises fewer than one third of the plurality of turns.

[0198] (11) The non-insulated superconducting magnet of (7), wherein the plurality of turns comprises at least ten turns and the at least some neighboring ones of the plurality of turns comprises less than five of the plurality of turns.

[0199] (12) The non-insulated superconducting magnet of (7), wherein the at least some neighboring ones of the plurality of turns are disposed closest to a center of the plurality of turns relative to others of the plurality of turns.

[0200] (13) The non-insulated superconducting magnet of any of (1)-(12), wherein the at least one heating element comprises a cable.

[0201] (14) The non-insulated superconducting magnet of (13). wherein the at least one heating element comprises a first coaxial cable and a second coaxial cable disposed end- to-end with the first coaxial cable.

[0202] (15) The non-insulated superconducting magnet of (13), wherein the at least one heating further comprises a third coaxial cable disposed adjacent to the first coaxial cable and a fourth coaxial cable disposed adjacent to the second coaxial cable and end-to-end with the third coaxial cable.

[0203] (16) The non-insulated superconducting magnet of (5), wherein the conductor comprises a high-temperature superconductor (HTS) tape stack.

[0204] (17) The non-insulated superconducting magnet of (5), further comprising a first plate having a first groove in which the conductor is arranged in the plurality of turns.

[0205] (18) The non-insulated superconducting magnet of (17), further comprising a second plate having a second groove in which the conductor is arranged in a second plurality of turns and at least one second heating element configured to heat the noninsulated superconducting magnet asymmetrically.

[0206] (19) The non-insulated superconducting magnet of (5), wherein the plurality of turns are asymmetrical about at least one axis defining a plane of the plurality of turns. (20) The non-insulated superconducting magnet of any of (1)-(19), wherein the at least one heating element comprises a plurality’ of heating elements each having a length of less than 20 meters.

[0207] (21) The non-insulated superconducting magnet of (5), further comprising a first plate on which the conductor is arranged in the plurality of turns and a joint pad for coupling the conductor of the first plate to a second plate.

[0208] (22) The non-insulated superconducting magnet of (21 ). wherein the joint pad comprises a plurality of cuts along the joint pad, wherein the plurality of cuts reduce a conductivity of the joint pad.

[0209] (23) The non-insulated superconducting magnet of (21), wherein the conductor comprises an increased taper at a point where the conductor couples to the joint pad.

[0210] (24) The non-insulated superconducting magnet of (21), wherein the joint pad comprises a first end being coupled to the conductor and a second end distal to the first end, and wherein the second end is extended in length relative to the first end.

[0211] (25) The non-insulated superconducting magnet of (5), wherein the conductor comprises a stack of high-temperature superconductor (HTS) tape and at least one portion of the conductor comprises at least one additional layer of HTS tape to increase a width of the at least one portion of the conductor.

[0212] (26) The non-insulated superconducting magnet of (25), wherein the at least one additional layer of HTS tape has a length that is shorter than a length of the conductor.

[0213] (27) The non-insulated superconducting magnet of (5), wherein a resistivity of the conductor varies along a length of the conductor.

[0214] (28) The non-insulated superconducting magnet of (27), wherein a material of the conductor varies along the length of the conductor.

[0215] (29) The non-insulated superconducting magnet of (28), wherein the material of the conductor varies between first and second types of copper alloys along the length of the conductor.

[0216] (30) The non-insulated superconducting magnet of (27), wherein a cross- sectional area of the conductor varies along the length of the conductor.

[0217] (31) The non-insulated superconducting magnet of (27), wherein the plurality of turns are asymmetrical about a first axis defining a plane of the plurality of turns such that a first side of the plurality of turns is closer to a center of the plurality of turns than a second side of the plurality of turns. (32) The non-insulated superconducting magnet of (31), wherein a resistivity of portions of the conductor running along the first side of the plurality of turns is lower than a resistivity of portions of the conductor running along the second side of the plurality of turns.

[0218] (33) The non-insulated superconducting magnet of (32), wherein a cross- sectional area of the portions of the conductor running along the first side of the plurality of turns is larger than a cross-sectional area of the portions of the conductor running along the second side of the plurality of turns.

[0219] (34) The non-insulated superconducting magnet of (32), wherein a material of the portions of the conductor running along the first side of the plurality of turns has a lower resistivity than a material of the portions of the conductor running along the second side of the plurality of turns.

[0220] (35) A non-insulated superconducting magnet, comprising: at least one cable comprising at least one heating element configured to induce quench of the non-insulated superconducting magnet by heating the non-insulated superconducting magnet.

[0221] (36) The non-insulated superconducting magnet of (35). wherein the at least one cable comprises a coaxial cable.

[0222] (37) The non-insulated superconducting magnet of any of (35)-(36), wherein the at least one cable comprises: a first cable comprising a first heating element; and a second cable disposed comprising a second heating element and positioned end-to-end with the first cable.

[0223] (38) The non-insulated superconducting magnet of (37), wherein the at least one cable further comprises: a third cable comprising a third heating element positioned adjacent to the first cable; and a fourth cable comprising a fourth heating element positioned adjacent to the second cable and positioned end-to-end with the third cable.

[0224] (39) The non-insulated superconducting magnet of any of (35)-(38). further comprising a conductor, wherein the at least one cable is disposed adjacent to at least a portion of the conductor and configured to heat the at least the portion of the conductor.

[0225] (40) The non-insulated superconducting magnet of (39), further comprising a first plate having at least one groove arranged in a plurality of turns, wherein the conductor is disposed in the at least one groove and the at least one cable is disposed in the at least one groove adjacent to the at least the portion of the conductor.

[0226] (41) The non-insulated superconducting magnet of (40), further comprising: a second plate having at least one second groove arranged in a second plurality of turns, wherein the conductor is disposed in the at least one second groove of the second plate; and at least one second cable comprising at least one heating element disposed adjacent to a second portion of the conductor and configured to heat the second portion of the conductor.

[0227] (42) The non-insulated superconducting magnet of (40), wherein the conductor is arranged in a plurality of turns and the at least the portion of the conductor comprises fewer than half of the plurality of turns.

[0228] (43) The non-insulated superconducting magnet of (40), wherein the conductor is arranged in a plurality of turns and the cable is disposed along a portion of the plurality of turns disposed closest to a center of the plurality of turns relative to others of the plurality of turns.

[0229] (44) The non-insulated superconducting magnet of (40), wherein the conductor is arranged in a plurality of turns including a first turn, a second turn, and a third turn, wherein the first turn is inside of the second turn and the second turn is inside of the third turn.

[0230] (45) The non-insulated superconducting magnet of (44). wherein the at least one heating element is disposed radially between the first turn and the third turn.

[0231] (46) The non-insulated superconducting magnet of (39), wherein the conductor comprises a high-temperature superconductor (HTS) tape stack.

[0232] (47) The non-insulated superconducting magnet of (44). wherein the plurality of turns are asymmetrical about at least one axis defining a plane of the plurality of turns.

[0233] (48) The non-insulated superconducting magnet of any of (35)-(48), wherein the at least one cable comprises a plurality of cables each having a length of less than 20 meters.

[0234] (49) The non-insulated superconducting magnet of (39), further comprising: a first plate on which the conductor is arranged in a first plurality of turns; a second plate on which the conductor is arranged in a second plurality of turns; and a joint pad for coupling the conductor from the first plate to the second plate.

[0235] (50) The non-insulated superconducting magnet of (49). wherein the joint pad comprises a plurality of cuts along the joint pad, wherein the plurality of cuts reduce a conductivity of the joint pad.

[0236] (51) The non-insulated superconducting magnet of (49), wherein the conductor comprises an increased taper at a point where the conductor couples to the joint pad. (52) The non-insulated superconducting magnet of (49), wherein the joint pad comprises a first end being coupled to the conductor and a second end distal to the first end, and wherein the second end is extended in length relative to the first end.

[0237] (53) The non-insulated superconducting magnet of (39), wherein the conductor comprises a stack of high-temperature superconductor (HTS) tape and at least one portion of the conductor comprises at least one additional layer of HTS tape to increase a width of the at least one portion of the conductor.

[0238] (54) The non-insulated superconducting magnet of (53), wherein the at least one additional layer of HTS tape has a length that is shorter than a length of the conductor.

[0239] (55) The non-insulated superconducting magnet of (39), wherein a resistivity of the conductor varies along a length of the conductor.

[0240] (56) The non-insulated superconducting magnet of (55), wherein a material of the conductor varies along the length of the conductor.

[0241] (57) The non-insulated superconducting magnet of (56), wherein the material of the conductor varies between first and second types of copper alloys along the length of the conductor.

[0242] (58) The non-insulated superconducting magnet of (55), wherein a cross- sectional area of the conductor varies along the length of the conductor.

[0243] (59) The non-insulated superconducting magnet of (55), wherein the conductor is arranged in a plurality of turns that are asymmetrical about a first axis defining a plane of the plurality of turns such that a first side of the plurality of turns is closer to a center of the plurality of turns than a second side of the plurality' of turns.

[0244] (60) The non-insulated superconducting magnet of (59), wherein a resistivity of portions of the conductor running along the first side of the plurality of turns is lower than a resistivity of portions of the conductor running along the second side of the plurality- of turns.

[0245] (61) The non-insulated superconducting magnet of (60), wherein a cross- sectional area of the portions of the conductor running along the first side of the plurality of turns is larger than a cross-sectional area of the portions of the conductor running along the second side of the plurality of turns.

[0246] (62) The non-insulated superconducting magnet of (60), wherein a material of the portions of the conductor running along the first side of the plurality of turns has a lower resistivity than a material of the portions of the conductor running along the second side of the plurality of turns.

[0247] (63) A system comprising: a plurality of non-insulated superconducting magnets, each of the non-insulated superconducting magnets being configured to produce a toroidal magnetic field and comprising: at least one heating element configured to induce quench of the respective non-insulated superconducting magnet, wherein the at least one heating element is configured to heat the non-insulated superconducting magnet asymmetrically; and circuitry coupled to the plurality of non-insulated superconducting magnets, wherein the circuitry is configured to control the at least one heating element of each of the non-insulated superconducting magnets to induce quench of the respective non-insulated superconducting magnets.

[0248] (64) The system of (63), wherein the circuitry is configured to control the at least one heating element of each of the non-insulated superconducting magnets to initiate heating at a same time.

[0249] (65) The system of any of (63)-(64), further comprising: a second magnet configured to produce a poloidal magnetic field; and a third magnet comprising a solenoid.

[0250] (66) A system comprising: a plurality of non-insulated superconducting magnets, each of the non-insulated superconducting magnets being configured to produce a toroidal magnetic field and comprising: at least one cable comprising at least one heating element configured to induce quench of the respective non-insulated superconducting magnet by heating the respective non-insulated superconducting magnet; and circuitry coupled to the plurality of non-insulated superconducting magnets, wherein the circuitry is configured to control the at least one heating element of each of the non-insulated superconducting magnets to induce quench of the respective non-insulated superconducting magnets.

[0251] (67) The system of (66), wherein the circuitry is configured to control the at least one heating element of each of the non-insulated superconducting magnets to initiate heating at a same time.

[0252] (68) The system of any of (66)-(67), further comprising: a second magnet configured to produce a poloidal magnetic field; and a third magnet comprising a solenoid.

[0253] (69) A method for inducing quench in a non-insulated superconducting magnet comprising a conductor and at least one heating element, the method comprising: controlling the non-insulated superconducting magnet to quench at least in part by heating, with the at least one heating element, the conductor asymmetrically such that at least a portion of a first turn of a plurality of turns of the conductor transitions from a superconducting state to a non-superconducting state before at least a portion of a second turn of the plurality of turns transitions form the superconducting state to the non- superconducting state.

[0254] (70) The method of (69), wherein the first turn of the plurality of turns is closer to a center of the plurality of turns than the second turn of the plurality of turns.

[0255] (71) The method of any of (69)-(70), wherein controlling the non-insulated superconducting magnet to quench further comprises heating, wi th the at least one heating element, the conductor asymmetrically such that the at least the portion of the second turn of the plurality of turns transitions from the superconducting state to the non- superconducting state before at least a portion of a third turn of the plurality of turns transitions from the superconducting state to the non-superconducting state.

[0256] (72) The method of (71), wherein the first turn is closer to a center of the plurality of turns than the second turn, and the second turn is closer to the center of the plurality of turns than the third turn.

[0257] (73) The method of any of (69)-(72), wherein the controlling is performed by control circuitry for the non-insulated superconducting magnet in response to the control circuitry receiving a command to shut down the non-insulated superconducting magnet.

[0258] (74) The method of any of (69)-(73). wherein the conductor of the non-insulated superconducting magnet comprises a high temperature superconductor (HTS) tape stack.

[0259] (75) The method of any of (69)-(74), wherein prior to the controlling the noninsulated superconducting magnet to quench, a resistance between respective turns of the plurality of turns is less than 1 megaohm.

[0260] (76) The method of any of (69)-(75), wherein the at least one heater is disposed along fewer than half of the plurality of turns.

[0261] (77) The method of any of (69)-(76), wherein the at least one heating element is disposed radially between at least some neighboring ones of the plurality of turns.

[0262] (78) The method of (77). wherein the at least some neighboring ones of the plurality of turns comprises fewer than all of the plurality of turns.

[0263] (79) The method of (78), wherein the at least some neighboring ones of the plurality of turns comprises fewer than half of the plurality of turns. (80) The method of (78), wherein the at least some neighboring ones of the plurality of turns comprises fewer than one third of the plurality of turns.

[0264] (81) The method of any of (69)-(81), wherein the non-insulated superconducting magnet comprises at least one cable comprising the at least one heating element.

[0265] (82) The method of (81), wherein the at least one cable comprises a first cable comprising a first heating element and a second cable comprising a second heating element, wherein the second cable is disposed end-to-end with the first cable.

[0266] (83) The method of (80), wherein the at least one cable further comprises a third coaxial cable comprising a third heating element and disposed adjacent to the first cable and a fourth cable comprising a fourth heater and disposed adjacent to the second cable and disposed end-to-end with the third cable.

[0267] (84) The method of any of (69)-(83), wherein the plurality of turns are asymmetrical about at least one axis defining a plane of the plurality of turns.

[0268] (85) A method for operating a reactor comprising a non-insulated superconducting magnet configured to generate a toroidal magnetic field and comprising at least one heating element, a second magnet configured to generate a poloidal magnetic field, and a third magnet comprising a solenoid, the method comprising: reducing a current in the second magnet to zero; reducing a current in the third magnet to zero; and inducing a quench of the non-insulated superconducting magnet at least in part by heating the noninsulated superconducting magnet, wherein the at least one heating element is configured to heat the non-insulated superconducting magnet asymmetrically.

[0269] (86) A non-insulated superconducting magnet comprising: a first plate having at least one groove arranged in a plurality of turns; and a conductor disposed in the at least one groove, wherein a resistivity of the conductor varies along a length of the conductor.

[0270] (87) The non-insulated superconducting magnet of (86), wherein a material of the conductor varies along the length of the conductor.

[0271] (88) The non-insulated superconducting magnet of (87), wherein the material of the conductor varies between first and second types of copper alloys along the length of the conductor.

[0272] (89) The non-insulated superconducting magnet of any of (86)-(88), wherein a cross-sectional area of the conductor varies along the length of the conductor.

[0273] (90) The non-insulated superconducting magnet of any of (86)-(89), wherein the plurality of turns are asymmetrical about a first axis defining a plane of the first plate such that a first side of the plurality' of turns is closer to a center of the plurality of turns than a second side of the plurality of turns.

[0274] (91) The non-insulated superconducting magnet of (90), wherein a resistivity of portions of the conductor running along the first side of the plurality of turns is lower than a resistivity of portions of the conductor running along the second side of the plurality of turns.

[0275] (92) The non-insulated superconducting magnet of (91). wherein a cross- sectional area of the portions of the conductor running along the first side of the plurality of turns is larger than a cross-sectional area of the portions of the conductor running along the second side of the plurality of turns.

[0276] (93) The non-insulated superconducting magnet of (91). wherein a material of the portions of the conductor running along the first side of the plurality of turns has a lower resistivity' than a material of the portions of the conductor running along the second side of the plurality of turns.

[0277] (94) A method for inducing a preemptive quench in a non-insulated (NI) superconducting magnet, the method comprising directly heating portions of a superconducting material in the NI superconducting magnet to induce a quench in a portion of the NI superconducting magnet such that remaining portions of the superconducting material are inductively driven to have a non-superconducting resistance characteristic in a manner which results in a substantially uniform distribution of heat energy' in the magnet thereby resulting in a desired temperature distribution in the magnet during a quench event.

[0278] (95) A non-insulated (NI) superconducting magnet comprising means for inducing a preemptive quench by directly heating portions of a superconducting material in the NI superconducting magnet to induce a quench in a portion of the NI superconducting magnet such that remaining portions of the superconducting material are inductively driven to have a non-superconducting resistance characteristic in a manner which results in a substantially uniform distribution of heat energy in the NI superconducting magnet thereby resulting in a desired temperature distribution in the NI superconducting magnet during a quench event.

[0279] (96) The NI superconducting magnet of (95) wherein the means for inducing a preemptive quench comprises graded superconducting material and one or more heating elements distributed about the NI superconducting magnet to directly heat only selected portions of the NI superconducting magnet.

[0280] (97) The NI superconducting magnet of (96) wherein the superconducting material is a high temperature superconductor (HTS).

[0281] Having thus described several aspects and embodiments of the technology set forth in the disclosure, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be within the spirit and scope of the technology described herein. For example, those of ordinary skill in the art will readily envision a variety of other means and / or structures for performing the function and / or obtaining the results and / or one or more of the advantages described herein, and each of such variations and / or modifications is deemed to be within the scope of the embodiments described herein. Aspects described in one embodiment may be combined in any manner with aspects described in other embodiments. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described. In addition, any combination of two or more features, systems, articles, materials, kits, and / or methods described herein, if such features, systems, articles, materials, kits, and / or methods are not mutually inconsistent, is included within the scope of the present disclosure.

[0282] The above-described embodiments can be implemented in any of numerous ways. One or more aspects and embodiments of the present disclosure involving the performance of processes or methods may utilize program instructions executable by a device (e.g., a computer, a processor, or other device) to perform, or control performance of, the processes or methods. In this respect, various inventive concepts may be embodied as a computer readable storage medium (or multiple computer readable storage media) (e.g.. a computer memon, one or more floppy discs, compact discs, optical discs, magnetic tapes, flash memories, circuit configurations in Field Programmable Gate Arrays or other semiconductor devices, or other tangible computer storage medium) encoded with one or more programs that, when executed on one or more computers or other processors, perform methods that implement one or more of the various embodiments described above. The computer readable medium or media can be transportable, such that the program or programs stored thereon can be loaded onto one or more different computers or other processors to implement various ones of the aspects described above. In some

[0283] The terms “program” or “software” are used herein in a generic sense to refer to any type of computer code or set of computer-executable instructions that can be employed to program a computer or other processor to implement various aspects as described above. Additionally, it should be appreciated that according to one aspect, one or more computer programs that when executed perform methods of the present disclosure need not reside on a single computer or processor, but may be distributed in a modular fashion among a number of different computers or processors to implement various aspects of the present disclosure.

[0284] Computer-executable instructions may be in many forms, such as program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Typically the functionality of the program modules may be combined or distributed as desired in various embodiments.

[0285] Also, data structures may be stored in computer-readable media in any suitable form. For simplicity of illustration, data structures may be shown to have fields that are related through location in the data structure. Such relationships may likewise be achieved by assigning storage for the fields with locations in a computer-readable medium that convey relationship between the fields. However, any suitable mechanism may be used to establish a relationship between information in fields of a data structure, including through the use of pointers, tags or other mechanisms that establish relationship between data elements.

[0286] The above-described embodiments of the present technology can be implemented in any of numerous ways. For example, the embodiments may be implemented using hardware, software or a combination thereof. When implemented in software, the software code can be executed on any suitable processor or collection of processors, whether provided in a single computer or distributed among multiple computers. It should be appreciated . that any component or collection of components that perform the functions described above can be generically considered as a controller that controls the abovedescribed function. A controller can be implemented in numerous ways, such as with dedicated hardware, or with general purpose hardware (e.g., one or more processor) that is programmed using microcode or software to perform the functions recited above, and may be implemented in a combination of ways when the controller corresponds to multiple components of a system.

[0287] Further, it should be appreciated that a computer may be embodied in any of a number of forms, such as a rack-mounted computer, a desktop computer, a laptop computer, or a tablet computer, as non-limiting examples. Additionally, a computer may be embedded in a device not generally regarded as a computer but with suitable processing capabilities, including a Personal Digital Assistant (PDA), a smartphone or any other suitable portable or fixed electronic device.

[0288] Also, a computer may have one or more input and output devices. These devices can be used, among other things, to present a user interface. Examples of output devices that can be used to provide a user interface include printers or display screens for visual presentation of output and speakers or other sound generating devices for audible presentation of output. Examples of input devices that can be used for a user interface include keyboards, and pointing devices, such as mice, touch pads, and digitizing tablets. As another example, a computer may receive input information through speech recognition or in other audible formats.

[0289] Such computers may be interconnected by one or more networks in any suitable form, including a local area network or a wide area network, such as an enterprise network, and intelligent network (IN) or the Internet. Such networks may be based on any suitable technology7and may operate according to any suitable protocol and may include wireless networks, wired networks or fiber optic networks.

[0290] Also, as described, some aspects may be embodied as one or more methods. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.

[0291] All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and / or ordinary meanings of the defined terms. The indefinite articles “a’' and “an,"’ as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.’’

[0292] The phrase “and / or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and / or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and / or” clause, whether related or unrelated to those elements specifically identified. Thus, as anon-limiting example, a reference to “A and / or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

[0293] As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as anon- limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and / or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one. optionally including more than one, B (and optionally including other elements); etc.

[0294] Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," or "having," “containing,” “involving,” and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. In the claims, as well as in the specification above, all transitional phrases such as "‘comprising,” “including.” “carry ing,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of’ and “consisting essentially of’ shall be closed or semi-closed transitional phrases, respectively.

[0295] The terms “substantially”, “approximately”, and “about” may be used to mean within ±20% of a target value in some embodiments, within ±10% of a target value in some embodiments, within ±5% of a target value in some embodiments, within ±2% of a target value in some embodiments. The terms “approximately” and “about” may include the target value.

[0296] Use of ordinal terms such as “first,” “second,” “third,” etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

Claims

CLAIMS1. A non-insulated superconducting magnet, comprising: at least one heating element configured to induce a quench of the non-insulated superconducting magnet by heating the non-insulated superconducting magnet, wherein the at least one heating element is configured to heat the non-insulated superconducting magnet asymmetrically.

2. The non-insulated superconducting magnet of claim 1, wherein the at least one heating element is configured to heat the non-insulated superconducting element asymmetrically by heating the non-insulated superconducting magnet such that at least a portion of a first turn of a plurality of turns of a conductor of the non-insulated superconducting magnet transitions from a superconducting state to a non- superconducting state before at least a portion of a second turn of the plurality of turns transitions from the superconducting state to the non-superconducting state.

3. The non-insulated superconducting magnet of claim 2, wherein the at least a portion of the second turn transitions to the non-superconducting state in response to inductive coupling of the second turn with the first turn.

4. The non-insulated superconducting magnet of any of claims 1-3, wherein the at least one heating element is configured to heat the non-insulated superconducting magnet radially asymmetrically.

5. The non-insulated superconducting magnet of any of claims 1-4, wherein the noninsulated superconducting magnet comprises a conductor arranged in a plurality of turns including a first turn, a second turn, and a third turn, w herein the first turn is inside of the second turn and the second turn is inside of the third turn.

6. The non-insulated superconducting magnet of claim 5, wherein the at least one heating element is disposed radially between the first turn and the third turn.

7. The non-insulated superconducting magnet of claim 5, wherein the at least one heating element is disposed radially between at least some neighboring ones of the plurality of turns.

8. The non-insulated superconducting magnet of claim 7, wherein the at least some neighboring ones of the plurality of turns comprises fewer than all of the plurality of turns.

9. The non-insulated superconducting magnet of claim 7, wherein the at least some neighboring ones of the plurality of turns comprises fewer than half of the plurality of turns.

10. The non-insulated superconducting magnet of claim 7, wherein the at least some neighboring ones of the plurality of turns comprises fewer than one third of the plurality of turns.

11. The non-insulated superconducting magnet of claim 7, wherein the plurality of turns comprises at least ten turns and the at least some neighboring ones of the plurality of turns comprises less than five of the plurality of turns.

12. The non-insulated superconducting magnet of claim 7, wherein the at least some neighboring ones of the plurality of turns are disposed closest to a center of the plurality of turns relative to others of the plurality of turns.

13. The non-insulated superconducting magnet of any of claims 1-12, wherein the at least one heating element comprises a cable.

14. The non-insulated superconducting magnet of claim 13, wherein the at least one heating element comprises a first coaxial cable and a second coaxial cable disposed end- to-end with the first coaxial cable.

15. The non-insulated superconducting magnet of claim 13, wherein the at least one heating further comprises a third coaxial cable disposed adjacent to the first coaxial cable and a fourth coaxial cable disposed adjacent to the second coaxial cable and end-to-end with the third coaxial cable.

16. The non-insulated superconducting magnet of claim 5, wherein the conductor comprises a high-temperature superconductor (HTS) tape stack.

17. The non-insulated superconducting magnet of claim 5, further comprising a first plate having a first groove in which the conductor is arranged in the plurality of turns.

18. The non-insulated superconducting magnet of claim 17, further comprising a second plate having a second groove in which the conductor is arranged in a second pl ural i ty of turns and at least one second heating element configured to heat the noninsulated superconducting magnet asymmetrically.

19. The non-insulated superconducting magnet of claim 5, wherein the plurality of turns are asymmetrical about at least one axis defining a plane of the plurality of turns.

20. The non-insulated superconducting magnet of any of claims 1-19, wherein the at least one heating element comprises a plurality of heating elements each having a length of less than 20 meters.

21. The non-insulated superconducting magnet of claim 5, further comprising a first plate on which the conductor is arranged in the plurality of turns and a joint pad for coupling the conductor of the first plate to a second plate.

22. The non-insulated superconducting magnet of claim 21, wherein the joint pad comprises a plurality of cuts along the joint pad, wherein the plurality of cuts reduce a conductivity7of the joint pad.

23. The non-insulated superconducting magnet of claim 21, wherein the conductor comprises an increased taper at a point where the conductor couples to the joint pad.

24. The non-insulated superconducting magnet of claim 21, wherein the joint pad comprises a first end being coupled to the conductor and a second end distal to the first end, and wherein the second end is extended in length relative to the first end.

25. The non-insulated superconducting magnet of claim 5, wherein the conductor comprises a stack of high-temperature superconductor (HTS) tape and at least one portion of the conductor comprises at least one additional layer of HTS tape to increase a width of the at least one portion of the conductor.

26. The non-insulated superconducting magnet of claim 25, wherein the at least one additional layer of HTS tape has a length that is shorter than a length of the conductor.

27. The non-insulated superconducting magnet of claim 5, wherein a resistivity of the conductor varies along a length of the conductor.

28. The non-insulated superconducting magnet of claim 27, wherein a material of the conductor varies along the length of the conductor.

29. The non-insulated superconducting magnet of claim 28, wherein the material of the conductor varies between first and second types of copper alloys along the length of the conductor.

30. The non-insulated superconducting magnet of claim 27, wherein a cross-sectional area of the conductor varies along the length of the conductor.

31. The non-insulated superconducting magnet of claim 27, wherein the plurality of turns are asymmetrical about a first axis defining a plane of the plurality of turns such that a first side of the plurality of turns is closer to a center of the plurality of turns than a second side of the plurality of turns.

32. The non-insulated superconducting magnet of claim 31, wherein a resistivity' of portions of the conductor running along the first side of the plurality of turns is lower than a resistivity of portions of the conductor running along the second side of the plurality of turns.

33. The non-insulated superconducting magnet of claim 32, wherein a cross-sectional area of the portions of the conductor running along the first side of the plurality of turns is larger than a cross-sectional area of the portions of the conductor running along the second side of the plurality of turns.

34. The non-insulated superconducting magnet of claim 32, wherein a material of the portions of the conductor running along the first side of the plurality of turns has a lower resistivity than a material of the portions of the conductor running along the second side of the plurality of turns.

35. A non-insulated superconducting magnet, comprising: at least one cable comprising at least one heating element configured to induce quench of the non-insulated superconducting magnet by heating the non-insulated superconducting magnet.

36. The non-insulated superconducting magnet of claim 35, wherein the at least one cable comprises a coaxial cable.

37. The non-insulated superconducting magnet of any of claims 35-36, wherein the at least one cable comprises: a first cable comprising a first heating element; and a second cable disposed comprising a second heating element and positioned end- to-end with the first cable.

38. The non-insulated superconducting magnet of claim 37, wherein the at least one cable further comprises: a third cable comprising a third heating element positioned adjacent to the first cable; and a fourth cable comprising a fourth heating element positioned adjacent to the second cable and positioned end-to-end with the third cable.

39. The non-insulated superconducting magnet of any of claims 35-38, further comprising a conductor, wherein the at least one cable is disposed adjacent to at least a portion of the conductor and configured to heat the at least the portion of the conductor.

40. The non-insulated superconducting magnet of claim 39, further comprising a first plate having at least one groove arranged in a plurality7of turns, wherein the conductor is disposed in the at least one groove and the at least one cable is disposed in the at least one groove adjacent to the at least the portion of the conductor.

41. The non-insulated superconducting magnet of claim 40, further comprising:a second plate having at least one second groove arranged in a second plurality of turns, wherein the conductor is disposed in the at least one second groove of the second plate; and at least one second cable comprising at least one heating element disposed adjacent to a second portion of the conductor and configured to heat the second portion of the conductor.

42. The non-insulated superconducting magnet of claim 40, wherein the conductor is arranged in a plurality of turns and the at least the portion of the conductor comprises fewer than half of the plurality of turns.

43. The non-insulated superconducting magnet of claim 40, wherein the conductor is arranged in a plurality’ of turns and the cable is disposed along a portion of the plurality of turns disposed closest to a center of the plurality7of turns relative to others of the plurality of turns.

44. The non-insulated superconducting magnet of claim 40, wherein the conductor is arranged in a plurality of turns including a first turn, a second turn, and a third turn, wherein the first turn is inside of the second turn and the second turn is inside of the third turn.

45. The non-insulated superconducting magnet of claim 44, wherein the at least one heating element is disposed radially between the first turn and the third turn.

46. The non-insulated superconducting magnet of claim 39, wherein the conductor comprises a high-temperature superconductor (HTS) tape stack.

47. The non-insulated superconducting magnet of claim 44, wherein the plurality of turns are asymmetrical about at least one axis defining a plane of the plurality of turns.

48. The non-insulated superconducting magnet of any of claims 35-48, wherein the at least one cable comprises a plurality of cables each having a length of less than 20 meters.

49. The non-insulated superconducting magnet of claim 39, further comprising: a first plate on which the conductor is arranged in a first plurality of turns;a second plate on which the conductor is arranged in a second plurality' of turns; and a joint pad for coupling the conductor from the first plate to the second plate.

50. The non-insulated superconducting magnet of claim 49, wherein the joint pad comprises a plurality of cuts along the joint pad, wherein the plurality of cuts reduce a conductivity of the joint pad.

51. The non-insulated superconducting magnet of claim 49, wherein the conductor comprises an increased taper at a point where the conductor couples to the joint pad.

52. The non-insulated superconducting magnet of claim 49, wherein the joint pad comprises a first end being coupled to the conductor and a second end distal to the first end, and wherein the second end is extended in length relative to the first end.

53. The non-insulated superconducting magnet of claim 39, wherein the conductor comprises a stack of high-temperature superconductor (HTS) tape and at least one portion of the conductor comprises at least one additional layer of HTS tape to increase a width of the at least one portion of the conductor.

54. The non-insulated superconducting magnet of claim 53, wherein the at least one additional layer of HTS tape has a length that is shorter than a length of the conductor.

55. The non-insulated superconducting magnet of claim 39, wherein a resistivity of the conductor varies along a length of the conductor.

56. The non-insulated superconducting magnet of claim 55, wherein a material of the conductor varies along the length of the conductor.

57. The non-insulated superconducting magnet of claim 56, wherein the material of the conductor varies between first and second types of copper alloys along the length of the conductor.

58. The non-insulated superconducting magnet of claim 55, wherein a cross-sectional area of the conductor varies along the length of the conductor.

59. The non-insulated superconducting magnet of claim 55, wherein the conductor is arranged in a plurality of turns that are asymmetrical about a first axis defining a plane of the plurality of turns such that a first side of the plurality of turns is closer to a center of the plurality of turns than a second side of the plurality of turns.

60. The non-insulated superconducting magnet of claim 59, wherein a resistivity' of portions of the conductor running along the first side of the plurality of turns is lower than a resistivity of portions of the conductor running along the second side of the plurality of turns.

61. The non-insulated superconducting magnet of claim 60, wherein a cross-sectional area of the portions of the conductor running along the first side of the plurality of turns is larger than a cross-sectional area of the portions of the conductor running along the second side of the plurality of turns.

62. The non-insulated superconducting magnet of claim 60, wherein a material of the portions of the conductor running along the first side of the plurality of turns has a lower resistivity than a material of the portions of the conductor running along the second side of the plurality of turns.

63. A system comprising: a plurality of non-insulated superconducting magnets, each of the non-insulated superconducting magnets being configured to produce a toroidal magnetic field and comprising: at least one heating element configured to induce quench of the respective non-insulated superconducting magnet, wherein the at least one heating element is configured to heat the non-insulated superconducting magnet asymmetrically; and circuitry coupled to the plurality of non-insulated superconducting magnets, wherein the circuitry' is configured to control the at least one heating element of each of the non-insulated superconducting magnets to induce quench of the respective noninsulated superconducting magnets.

64. The system of claim 63, wherein the circuitry is configured to control the at least one heating element of each of the non-insulated superconducting magnets to initiate heating at a same time.

65. The system of any of claims 63-64, further comprising: a second magnet configured to produce a poloidal magnetic field; and a third magnet comprising a solenoid.

66. A system comprising: a plurality of non-insulated superconducting magnets, each of the non-insulated superconducting magnets being configured to produce a toroidal magnetic field and comprising: at least one cable comprising at least one heating element configured to induce quench of the respective non-insulated superconducting magnet by heating the respective non-insulated superconducting magnet; and circuitry coupled to the plurality of non-insulated superconducting magnets, wherein the circuitry is configured to control the at least one heating element of each of the non-insulated superconducting magnets to induce quench of the respective noninsulated superconducting magnets.

67. The system of claim 66, wherein the circuitry is configured to control the at least one heating element of each of the non-insulated superconducting magnets to initiate heating at a same time.

68. The system of any of claims 66-67, further comprising: a second magnet configured to produce a poloidal magnetic field; and a third magnet comprising a solenoid.

69. A method for inducing quench in a non-insulated superconducting magnet comprising a conductor and at least one heating element, the method comprising: controlling the non-insulated superconducting magnet to quench at least in part by heating, with the at least one heating element, the conductor asymmetrically such that at least a portion of a first turn of a plurality of turns of the conductor transitions from asuperconducting state to a non-superconducting state before at least a portion of a second turn of the plurality of turns transitions form the superconducting state to the non- superconducting state.

70. The method of claim 69, wherein the first turn of the plurality of turns is closer to a center of the plurality of turns than the second turn of the plurality of turns.

71. The method of any of claims 69-70, wherein controlling the non-insulated superconducting magnet to quench further comprises heating, wi th the at least one heating element, the conductor asymmetrically such that the at least the portion of the second turn of the plurality of turns transitions from the superconducting state to the non- superconducting state before at least a portion of a third turn of the plurality of turns transitions from the superconducting state to the non-superconducting state.

72. The method of claim 71, wherein the first turn is closer to a center of the plurality of turns than the second turn, and the second turn is closer to the center of the plurality of turns than the third turn.

73. The method of any of claims 69-72, wherein the controlling is performed by control circuitry for the non-insulated superconducting magnet in response to the control circuitry receiving a command to shut down the non-insulated superconducting magnet.

74. The method of any of claims 69-73, wherein the conductor of the non-insulated superconducting magnet comprises a high temperature superconductor (HTS) tape stack.

75. The method of any of claims 69-74, wherein prior to the controlling the noninsulated superconducting magnet to quench, a resistance between respective turns of the plurality of turns is less than 1 megaohm.

76. The method of any of claims 69-75, wherein the at least one heater is disposed along fewer than half of the plurality of turns.

11. The method of any of claims 69-76. wherein the at least one heating element is disposed radially between at least some neighboring ones of the plurality of turns.

78. The method of claim 77, wherein the at least some neighboring ones of the plurality of turns comprises fewer than all of the plurality of turns.

79. The method of claim 78, wherein the at least some neighboring ones of the plurality of turns comprises fewer than half of the plurality of turns.

80. The method of claim 78, wherein the at least some neighboring ones of the plurality of turns comprises fewer than one third of the plurality of turns.

81. The method of any of claims 69-81, wherein the non-insulated superconducting magnet comprises at least one cable comprising the at least one heating element.

82. The method of claim 81, wherein the at least one cable comprises a first cable comprising a first heating element and a second cable comprising a second heating element, wherein the second cable is disposed end-to-end with the first cable.

83. The method of claim 80, wherein the at least one cable further comprises a third coaxial cable comprising a third heating element and disposed adjacent to the first cable and a fourth cable comprising a fourth heater and disposed adjacent to the second cable and disposed end-to-end with the third cable.

84. The method of any of claims 69-83, wherein the plurality of turns are asymmetrical about at least one axis defining a plane of the plurality of turns.

85. A method for operating a reactor comprising a non-insulated superconducting magnet configured to generate a toroidal magnetic field and comprising at least one heating element, a second magnet configured to generate a poloidal magnetic field, and a third magnet comprising a solenoid, the method comprising: reducing a current in the second magnet to zero; reducing a current in the third magnet to zero; andinducing a quench of the non-insulated superconducting magnet at least in part by heating the non-insulated superconducting magnet, wherein the at least one heating element is configured to heat the non-insulated superconducting magnet asymmetrically.

86. A non-insulated superconducting magnet comprising: a first plate having at least one groove arranged in a plurality of turns; and a conductor disposed in the at least one groove, wherein a resistivity of the conductor varies along a length of the conductor.

87. The non-insulated superconducting magnet of claim 86, wherein a material of the conductor varies along the length of the conductor.

88. The non-insulated superconducting magnet of claim 87, wherein the material of the conductor varies between first and second types of copper alloys along the length of the conductor.

89. The non-insulated superconducting magnet of any of claims 86-88, wherein a cross-sectional area of the conductor varies along the length of the conductor.

90. The non-insulated superconducting magnet of any of claims 86-89, wherein the plurality of turns are asymmetrical about a first axis defining a plane of the first plate such that a first side of the plurality of turns is closer to a center of the plurality of turns than a second side of the plurality of turns.

91. The non-insulated superconducting magnet of claim 90, wherein a resistivity' of portions of the conductor running along the first side of the plurality of turns is lower than a resistivity of portions of the conductor running along the second side of the plurality' of turns.

92. The non-insulated superconducting magnet of claim 91, wherein a cross-sectional area of the portions of the conductor running along the first side of the plurality of turns is larger than a cross-sectional area of the portions of the conductor running along the second side of the plurality of turns.

93. The non-insulated superconducting magnet of claim 91, wherein a material of the portions of the conductor running along the first side of the plurality of turns has a lower resistivity than a material of the portions of the conductor running along the second side of the plurality of turns.

94. A method for inducing a preemptive quench in a non-insulated (NI) superconducting magnet, the method comprising directly heating portions of a superconducting material in the NI superconducting magnet to induce a quench in a portion of the NI superconducting magnet such that remaining portions of the superconducting material are inductively driven to have a non-superconducting resistance characteristic in a manner which results in a substantially uniform distribution of heat energy in the magnet thereby resulting in a desired temperature distribution in the magnet during a quench event.

95. A non-insulated (NI) superconducting magnet comprising means for inducing a preemptive quench by directly heating portions of a superconducting material in the NI superconducting magnet to induce a quench in a portion of the NI superconducting magnet such that remaining portions of the superconducting material are inductively driven to have a non-superconducting resistance characteristic in a manner which results in a substantially uniform distribution of heat energy7in the NI superconducting magnet thereby resulting in a desired temperature distribution in the NI superconducting magnet during a quench event.

96. The NI superconducting magnet of claim 95 wherein the means for inducing a preemptive quench comprises graded superconducting material and one or more heating elements distributed about the NI superconducting magnet to directly heat only selected portions of the NI superconducting magnet.

97. The NI superconducting magnet of claim 96 wherein the superconducting material is a high temperature superconductor (HTS).

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