Co-wound coaxial voltage sensors for quench detection in grooved, stacked-plate, no-insulation superconducting coils

Abstract

A magnet has a co-wound voltage sensor for high temperature superconductor (HTS) quench detection that is mechanically robust, has excellent electrical noise rejection, and can be readily integrated into existing manufacturing methods. The magnet includes one or more stackable, electrically conductive plates having several grooves into which are wound a magnet coil conductor comprising HTS tape, and in which are co-wound, proximate to the coil conductor, an insulated, two-conductor cable forming the voltage sensor. Several such cables may be co-wound along all or a portion of the coil to provide redundant or spatial measurement of normal zone formation. The grooves also may include one or more quench heaters that form part of a quench protection system (QPS) which induces a controlled magnet quench when the voltage sensor detects a normal zone having non-zero resistance within the coil conductor.

Description

[0001] CO-WOUND COAXIAL VOLTAGE SENSORS FOR QUENCH DETECTION IN GROOVED, STACKED-PLATE, NO-INSULATION SUPERCONDUCTING COILS

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit of U.S. Provisional Application No. 63 / 617,550, filed January 4, 2024, the entire contents of which is incorporated by reference herein.

[0004] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH Not applicable.

[0005] BACKGROUND

[0006] Non-insulated (NI), high-temperature superconducting (HTS) magnets can be exceptionally strong mechanically and exhibit excellent stability against the formation of normal (i.e., non-superconducting) zones that lead to a quench. The grooved, stacked-plate superconducting NI magnet design of, e.g., U.S. Patent 11,810,712 has facilitated 20 Tesla DC performance in a large bore magnet suitable for fusion energy applications. This magnet design is readily adaptable to handle the unique environment of the SPARC tokamak, including coolant channels to handle the neutron heat loads; see Creely, A. J. et al., “Overview of the SPARC tokamak”, Journal of Plasma Physics 86 (2020) 865860502.

[0007] Despite robustness, there are situations that can cause NI magnets to become thermally unstable, resulting in quench. The formation of a persistent normal zone caused by of lack of sufficient cooling in the presence of localized heating (e.g., fusion neutron heat load) can cause thermal instability and quench. Failure of support systems can force NI magnets to quench. Such failures can include: (1) loss of terminal current causing radial current flow and joule heating that exceeds cryogenic cooling capacity, (2) loss of cryogenic cooling and / or (3) loss of thermal insulation such as via loss of cryostat vacuum. Such support system failures could be precipitated by loss of power.

[0008] SUMMARY OF DISCLOSED EMBODIMENTS

[0009] Described are methods and structures to implement a co-wound voltage sensor for HTS quench detection in grooved, stacked plate, no-insulation superconducting coils that is mechanically robust, has excellent electrical noise rejection and can be readily integrated into existing manufacturing methods.

[0010] One purpose of the co-wound voltage sensor is to detect the formation of a normal zone within a coil and to facilitate a successful preemptive quench action, if necessary. Grooved, stacked-plate, NI coils can readily accommodate coaxial co-wind voltage sensors, taking advantage of the soldered conductor unit cell that is employed.

[0011] Thus, a first embodiment is a magnet comprising an electrically conductive plate having a plurality of grooves; a coil conductor wound through the grooves of the plate; and a voltage sensor co-wound through the grooves of the plate, the voltage sensor comprising an insulated, two-conductor cable.

[0012] In some embodiments, the coil conductor comprises a high temperature superconductor (HTS) tape.

[0013] In some embodiments, the plurality of grooves comprises a copper cap that is soldered to the coil conductor and to the voltage sensor.

[0014] In some embodiments, the plurality of grooves further comprises one or more copper co-wound tapes.

[0015] In some embodiments, the insulated, two-conductor cable comprises a coaxial cable having magnesium oxide (MgO) insulation.

[0016] In some embodiments, the plurality of the grooves provides a base surface, wherein the coil conductor and the insulated, two-conductor cable are in physical and electrical contact with the base surface.

[0017] In some embodiments, the plurality of the grooves provides a base surface and a side cut surface, wherein the coil conductor is in physical and electrical contact with the base surface, and wherein the cable is in physical and electrical contact with the side cut surface. In some embodiments, the electrically conductive plate comprises a first plate, the magnet further comprising second and third electrically conductive plates, each of the plates having a respective plurality of grooves and a respective coil conductor wound through its grooves between an inner joint pad and an outer joint pad, wherein the inner joint pad of the first plate is electrically coupled to the inner joint pad of the second plate, and wherein the outer joint pad of the first plate is electrically coupled to the outer joint pad of the third plate.

[0018] In some embodiments, the voltage sensor comprises a plurality of insulated, two- conductor cables.

[0019] In some embodiments, the plurality of insulated, two-conductor cables is co-wound along the entire length of the coil conductor to provide redundant measurement of normal zone formation.

[0020] In some embodiments, the plurality of insulated, two-conductor cables is co-wound along a portion of the coil conductor to provide spatial information regarding normal zone formation within the portion.

[0021] Some embodiments include coil state measuring electronics coupled to the voltage sensor, the coil state measuring electronics configured to measure a coil temperature and a coil operating current.

[0022] Some embodiments include a quench protection system (QPS) coupled to the coil state measuring electronics, the QPS having one or more coaxial quench heaters that are co-wound with the coil conductor.

[0023] In some embodiments, the QPS is configured to cause the one or more coaxial quench heaters to quench the magnet when both (a) the coil state measuring electronics measure or predict a thermally unstable state, and (b) the coil state measuring electronics measure a coil temperature and a coil operating current within given ranges. In some embodiments, the QPS is configured to cause the one or more coaxial quench heaters to quench the magnet when the coil state measuring electronics detect a normal zone of a given threshold size within the magnet.

[0024] It should be appreciated that in an embodiment, a magnet comprises an electrically conductive plate having a plurality of grooves; a coil conductor wound through the grooves of the plate; and a voltage sensor co-wound through the grooves of the plate, the voltage sensor comprising at least two electrically conductive wires with at least one of the two wires disposed against the coil conductor. In some embodiments, the coil conductor comprises an HTS tape stack. In some embodiments, one or both of the conductors are disposed adjacent an HTS tape stack. In some embodiments, one or both of the conductors are disposed in a groove of the plate adjacent an HTS tape stack in the groove. In some embodiments, one or both of the conductors are disposed in a groove of the plate and one or both of the conductors are mechanically and / or electrically coupled to an HTS tape stack in the groove. In some embodiments, the conductors are disposed in a groove of the plate and one or both of the conductors are soldered or otherwise electrically and mechanically coupled to an HTS tape stack in the groove.

[0025] It is appreciated that the concepts, techniques, and structures disclosed herein may be embodied in other ways not listed above. Therefore, the above summary of embodiments should not be viewed as limiting.

[0026] DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0027] The manner and process of making and using the disclosed embodiments may be appreciated by reference to the figures of the accompanying drawings. It should be appreciated that the components and structures illustrated in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the concepts described herein. Like reference numerals designate corresponding parts throughout the different views. Furthermore, embodiments are illustrated by way of example and not limitation in the figures, in which: Fig. 1 is a side view of a diagram of a stackable, grooved plate having a wound conductor and a co-wound two conductor voltage sensor in accordance with an embodiment of the concepts, structures, and techniques disclosed herein;

[0028] Fig. 2 is a schematic diagram of an equivalent electrical circuit for the conductor and voltage sensor shown in Fig. 1 ;

[0029] Fig. 3 is a top view of the stackable, grooved plate of Fig. 1;

[0030] Figs. 4A, 4B, and 4C are enlarged views of regions of the stackable, grooved plate shown in Fig. 3 ;

[0031] Fig. 5 shows a conceptual top view of an alternate embodiment of a stackable, grooved plate having windings in a direction opposite that of Fig. 3;

[0032] Figs. 6A and 6B show conceptual cross-sections of two implementations of stackable, grooved plates, each having a superconductor and a co-wound two conductor voltage sensor in accordance with embodiments; and

[0033] Fig. 7 shows a commercially available mineral insulated coaxial conductor that may be used in accordance with embodiments.

[0034] DETAILED DESCRIPTION

[0035] Left to quench on its own, a high energy NLHTS magnet will likely become damaged, as was experienced by the SPARC Toroidal Field Model Coil when it was deliberately quenched by forcing an open circuit condition; see Whyte, D.G. et al., “Experimental Assessment and Model Validation of the SPARC Toroidal Field Model Coil,” IEEE Transactions on Applied Superconductivity 34 (2024) 1. Consequently, high energy NLHTS magnets preferably implement active quench protection.

[0036] Normal zone detection is the primary means in which insulated superconducting coils are protected against quench damage. When a normal zone is detected, a fast discharge is triggered in which the stored energy is dumped into an external resistive load. For example, if a quench is detected in ITER (formerly the International Thermonuclear Experimental Reactor), a Fast Discharge (FD) is triggered, so that the magnetic energy remaining in the magnet can be discharged into external dump resistors. Coatanea- Gouachet, M., et al., “Electromagnetic Quench Detection in ITER Superconducting Magnet Systems,” IEEE Transactions on Applied Superconductivity 25 (2015) 1.

[0037] Although fiber optic sensors are now being considered due to significant technical advances, voltage sensors are presently the state-of-the art method to detect and react to normal zones in insulated coils. The aforementioned ITER reference accordingly states: “Fortunately, along with Joule heating comes an increase of resistance, and consequently, of the voltage across the quenched conductor. The Electromagnetic Quench Detection System will trigger the FD based on this voltage measurement.”

[0038] However, voltage sensors respond to both resistive and inductive voltages generated in the windings to varying degrees, depending how they are arranged within the coil. Inductive voltages can be large compared to resistive voltages, yet only the resistive component is of interest, being a direct measure of normal zone formation.

[0039] Inductive voltage compensation can be employed using separate pick-up coils and real-time data processing. But co-wound voltage sensors - which are wound alongside the HTS winding - are most effective in minimizing the inductive voltage contribution because, by design, the flux coupling to the sensor is very similar, if not identical, to that of the winding, which provides direct cancellation.

[0040] For this reason, ITER employs co-wound voltage sensors, in addition to inductive voltage compensation schemes, as an essential part of its magnet quench detection system. The aforementioned ITER reference continues: “The [Central Solenoid] detection system is composed of two parallel systems: The first one uses co-wound tapes (CWT), which capture the magnetic flux collected by the conductors of each double pancake. Excellent coupling between the conductor and the co-wound tape allows reducing the inductive voltage by a factor of 105. The second one uses [Mutual Inductance Compensation] MIK cancellation, whose principle is as follows: on the one hand, it measures the quantity (voltage) within which the resistive voltage signal hides, including noise (coupled signals). On the other hand, it calculates the real time noise which should be rejected.”

[0041] The key to minimizing unwanted inductive voltage contributions is to route the cowound voltage sensor wire very close to the conductor. For ITER, the co-wound tapes (CWT) are steel tapes embedded in the turn insulation and twisted around the conductor - akin to wrapping the conductor with electrical tape. Consequently, the inductive coupling of the co-wound tape and the superconductor to time varying magnetic fields that pass among them is not identical. See Martovetsky, N.N. et al., “Detection of the normal zone with cowound sensors in cable -in-conduit conductors,” IEEE Transactions on Applied Superconductivity 7 (1997) 451, and Martovetsky, N.N. et al., “ITER CS Quench Detection System and Its Qualification by Numerical Modeling,” IEEE Transactions on Applied Superconductivity 24 (2014) 1.

[0042] In this regard, a better scheme is to employ a co-wound sensor that is internal to the cable, as was proposed for the Tokamak Physics Experiment (TPX) tokamak, see Schultz, J., “Feasibility of the TPX Internal Voltage-Sensor Quench Detection System,” 1997, M.I.T. Plasma Science and Fusion Center report PSFC / RR-97-3. There, it was proposed to embed coaxial co-wind voltage sensors directly within the TPX low temperature superconducting (LTS) cable-in-conduit conductor. Calculations showed that this scheme had excellent inductive voltage cancellation, leading the authors to state: the information leads us to conclude that an internally co-wound voltage sensor system alone should be adequate to protect the TPX magnets, in the event of a quench.” However, the internally co-wound voltage sensor of the TPX tokamak was envisioned for use with an LTS conductor producing magnetic fields attainable in 1997, not an HTS conductor that produces a 20 T magnetic field, and the forces and electrical noise associated with such a large field.

[0043] Non-insulated, high temperature superconducting (NI-HTS) quench protection systems (QPS) employ heaters to preemptively quench high temperature superconducting (HTS) magnets included in such systems; that is, to actively drive a quench in a way that does not lead to magnet damage. Quench protection systems protect NI-HTS magnets by forcing large sections of coils to quench substantially at the same time (and ideally at precisely the same time). However, a QPS must be activated at a point in time that prevents magnet damage. If the QPS is activated too soon, e.g., when the ratio of the operating current normalized to the critical current (Iop / Ic) is too low, the heaters may not be capable of quenching large sections of the coils. Conversely, if the QPS is activated too late, a localized normal zone may thermally run away, causing so-called “hot spot” damage in the before the remainder of the coil can be quenched.

[0044] Therefore, one component of an NI-HTS QPS is coil state monitoring combined with normal zone detection. The QPS is activated when: (1) the NI magnet is measured to be, or is predicted to become, thermally unstable due to external or internal causes and there is no means to recover, and (2) the NI magnet is in a state (i.e., within temperature and operating current range) in which the QPS will drive a successful quench. Regardless of coil state, the QPS must be engaged if a normal zone of a threshold size is detected within the magnet.

[0045] Disclosed embodiments include a coaxial, co-wound quench detection cable in a grooved, stacked-plate superconducting coil.

[0046] Referring now to Fig. 1, shown is a conceptual side view of a single, grooved plate 100 containing a portion of a superconducting coil. The structure of Fig. 1 enables measurement of a resistive voltage of a coil conductor 110, which typically includes a high temperature superconductor (HTS) tape among other materials. In some embodiments, the coil conductor 110 may be about 150 meters long, but in other embodiments the length of the coil conductor 110 may be longer or shorter than 150 meters. The particular length of an HTS tape to use in the coil conductor of a particular application will depend upon the needs of the particular application.

[0047] The plate 100 is structural and non-insulated (that is, electrically conducting throughout), and includes the coil conductor 1 10 wound through its grooves between an inner joint pad 120 and an outer joint pad 130. The inner joint pad 120 of the depicted plate 100 is electrically coupled to an inner joint pad of a neighboring plate in the stack, e.g., a plate “below” (not shown). Likewise, the outer joint pad 130 of the plate 100 is electrically coupled to an outer joint pad of a different neighboring plate in the stack, e.g., a plate “above” (not shown).

[0048] In Fig. 1, an operating current Iopenters the plate 100 at the inner joint pad 120 from a first neighboring plate, travels along the conductor 1 10 to the outer joint pad 130, and exits the plate 100 to a second neighboring plate. In both neighboring plates, current would flow in the opposite direction, i.e., from an outer joint pad to an inner joint pad. In this way, a single operating current Iopcan travel through a stack of plates from a first terminal of the magnet coil to a second terminal of the coil.

[0049] In accordance with various embodiments, two conductors 140 (e.g., a two- conductor cable 140) are co-wound with the coil conductor 110 through the grooves of the plate 100. In embodiments, the two conductors 140 are disposed in a groove of the plate adjacent an HTS tape stack in the groove. In embodiments, the two conductors 140 are disposed in a groove of the plate and one or both of the two conductors 140 are mechanically and / or electrically coupled to an HTS tape stack in the groove. In embodiments, the two conductors 140 are disposed in a groove of the plate and one or both of the two conductors 140 are soldered to an HTS tape stack in the groove.

[0050] In embodiments, the two conductors 140 may be implemented as an insulated, two-conductor cable, as a coaxial cable, as a conductor-coated ribbon, as a pair of insulated wires (e.g. a twisted pair), individual non-insulated wires, individual insulated wires, or in any other suitable form or configuration. After reading the disclosure provided herein, one of ordinary skill in the art will appreciate how to select a configuration of the two conductors 140.

[0051] In one illustrative embodiment, the two conductors 140 may be implemented as an insulated coaxial cable. An example of an example coaxial cable is depicted in more detail in Fig. 4C and Fig. 7. In a coaxial cable embodiment, the coaxial cable comprises a center wire 142 (or center conductor 142) and a conducting sheath 144 (or outer conductor 144), separated by an insulating layer 143. In one embodiment, the coaxial cable is disposed in a groove of the plate and mechanically and / or electrically coupled to an HTS tape stack in the groove. In embodiments, the coaxial cable is soldered to an HTS tape stack in the groove.

[0052] In the example embodiment of Fig. 1, the two conductors 140 have one end 146 that is grounded, i.e., a first conductor (or wire) 142 electrically connects to the second conductor (or wire) 144 at end 146. A grounding region 170 proximate the inner joint pad 120, showing the end 146 of the two conductors 140, is also shown in Figs. 3 and 4A, and is described below.

[0053] The two conductors 140 travels along the conductor 110 all the way to the outer joint pad 130, where the coil conductor 110 ends, and is not insulated along this path. The two conductors 140 continue beyond the end of the outer joint pad 130.In embodiments, a portion of at least one or the two conductors may be wrapped in an external electrically insulating material 148 (e.g. as in an insulated wire). This insulating material 148 could be Kapton, Teflon, or an electrically insulating coating could be used. Externally-insulated portions 149 of the two conductors 140 are routed in its own groove in the radial plate until it exits the plate. A transitional region 180 between the uninsulated conductor (or wire) leaving the outer joint pad 130 and the insulated conductor (or wire) routed in the groove is also shown in Fig. 4B and is described below.

[0054] Upon exiting from the plate 100, the two conductors 140 are electrically connected to two conductors 150a, 150b, which may, for example, be provided as a twisted pair cable or a separate coaxial cable with an externally-insulated sheath, carrying the electrical signal to measurement electronics 160 that are external to the coil. The measurement electronics 160 should preferably be provided having a high input impedance (e.g., an input impedance larger, and ideally significantly larger, than the impedance of the circuit being measured such that the measurement electronics 160 do not affect (or have a negligible effect upon) the circuit being measured). The coupling region 190 proximate the exit of the plate 100 is shown in Fig. 4C and described below.

[0055] The electrical function of the example structure in Fig. 1 may be represented by an equivalent electrical circuit as shown in Fig. 2. Referring now to Fig, 2, the equivalent electrical circuit illustrates that a high impedance voltage measurement records the voltage drop, VR, only along the conductor 110, represented by resistance, R, because the measurement itself causes negligible current flow in the first conductor (or wire) 142 or the second conductor (or wire). In embodiments in which the first conductor and second conductor are arranged to form a coaxial cable, the first conductor 142 may correspond to a center conductor (or center wire)of the coaxial cable and the second conductor 144 may correspond to an outer conductor (or wire or sheath) of the coaxial cable. For the same reason, the electrical resistance along the center wire 142 or sheath 144 (or changes in that resistance as a function of time or temperature) does not affect the measurement.

[0056] Because the two conductors 140 are placed adjacent to the path of the coil conductor 110, the first one of the conductors and the coil conductor 110 have substantially identical inductive coupling to time varying magnetic fields that pass among them. This provides for cancellation of inductive voltages, leaving only the resistive component to be recorded as VR. For example, when the two conductors 140 are arranged in a coaxial cable configuration a center conductor of the coaxial cable (e.g. conductor 142) and the coil conductor 110 have substantially identical inductive coupling to time varying magnetic fields that pass among them.

[0057] When the coil conductor 110 is superconducting along its entire length, the resistance, R, will be zero and the voltage reading, VR, will be zero. However, when a normal zone forms anywhere along the conductor 110, the resistance, R, will be non-zero in that zone. A voltage reading of VR = Iopx R will be recorded, where R is the sum of resistance from all normal zones present along the coil conductor 110.

[0058] Based on the magnitude of VR and its persistence in time, measurement electronics 160 may trigger an alert system 201 to provide an alert signal 200 (e.g. in the form of an electrical signal) that a normal zone has been detected within that coil. Appropriate corrective or mitigative action can then be taken, by a device or system coupled to the alert signal 200, such as activating a preemptive quench protection system. For example, an alert system 201 may receive and / or monitor the magnitude of VR and its persistence in time and issue an alert signal 201 which results in a preemptive quench. Alert system 201 may, for example, comprise one or more processors and / or processing elements. Referring now to Fig. 3, shown is a conceptual top view of the stackable, grooved plate of Fig. 1. In this plate 100, the windings follow a spiral path between inner joint pad 120 and outer joint pad 130, and the voltage sensor is connected to conductors 150a, 150b that exit the plate 100 at a desired azimuthal location 310 (shown in more detail in Fig. 4C).

[0059] In the example embodiment shown in Fig. 3, a single coaxial co-wound quench detection cable 140 is placed aside the conductor 110, running along its entire length within the plate 100. It is contemplated to have more than one cable 140 to provide redundancy of measurement of normal zone formation anywhere in the conductor 110, if desired, or to provide a coaxial quench heater cable that facilitates a preemptive quench; various configurations are shown in Fig. 6A and 6B and described below. It is also contemplated to run one or more coaxial co-wound quench detection cables 140 along a single portion of the conductor 110 (e.g., along only a small number of the outer turns) so as to provide spatial information on where a normal zone is forming, should it form.

[0060] By cutting or otherwise providing a dedicated groove for cable exit, the cables 140 can be made to exit at substantially the same azimuthal location 310 for all plates in a stack, regardless whether they wind counterclockwise (Fig. 3) or clockwise (Fig. 5) starting from the inner joint pad. Multiple dedicated grooves for coaxial cable exit at the desired azimuthal location 310 can accommodate multiple coaxial co-wound quench detection cables 140, if desired.

[0061] Fig. 4A is an enlarged portion of the grounding region 170 in Figs. 1 and 3. Fig. 4A shows that the coaxial sensor cable 140 terminates within the boundary of the inner joint pad 120, thereby electrically connecting its center conductor with its outer conductor. Due to this connection, the coaxial cable 140 forms a closed circuit in which any voltage drop along the outer conductor is due to resistive and inductive voltages along the coil conductor 110, while voltage drop along the center conductor is due to inductive voltages only. The voltage that appears at end of the cable 140 (as shown in Fig. 4C) is the difference between the two. Thus, the voltage measurement records voltage due to current flow through one or more resistive sections of the coil conductor 110 (i.e., normal zones), should any be present. Fig. 4B is an enlarged portion of the transitional region 180 in Figs. 1 and 3. Fig. 4B shows that some portions (e.g., portion 330) of the coaxial cable 140 are insulated over its outer sheath 144, while other portions (e.g., portion 340) may not be so insulated. In particular, there is no insulation surrounding the outer sheath 144 when the cable 140 is co-wound with the coil conductor 110, so that the outer sheath 144 can be made in good electrical contact with the conductor 110, thereby permitting the cable 140 to be used as a voltage sensor in accordance with embodiments.

[0062] Fig. 4C is an enlarged portion of the coupling region 190 in Figs. 1 and 3. Fig. 4C shows in particular detail a coupling of external twisted pair wires 150a, 150b to a coaxial quench detection cable 140 in accordance with an embodiment. Notably, the twisted pair wires 150a, 150b are insulated except where they are electrically coupled to the coaxial cable 140. Thus, the signal produced by the coaxial cable 140 is shielded from electrical noise in the environment while it is conveyed to the voltage measurement electronics 160.

[0063] As described above, if the coil conductor 1 10 is superconducting, then no resistive voltage exists. In this case, the center conductor 142 and outer conductor 144 have the same electrical potential (i.e., the same voltage) due to their direct electrical coupling at the inner joint pad 120 and the inductive components along them that are substantially identical but of opposite sign and therefore cancel. However, if the coil conductor 1 10 has one or more regions that are normally conducting, the outer sheath (or outer conductor) 144 will have a different voltage along it than the center wire (or center conductor) 142. This non-zero voltage difference may be measured by an external voltmeter (or other measuring means 160) attached, for example, by the twisted pair wires 150a, 150b as shown in Figs. 1, 3, and 4C.

[0064] There may be an advantage in continuing the insulated coaxial cable geometry (rather than twisted pair shown in Fig. 4C) all the way out to the location of the voltage measurement means 160. This can be accommodated by appropriate extension cables.

[0065] The above discussion in connection with Fig. 3 applies to the similar, but counterwound embodiment shown in Fig. 5. Thus, in Fig. 5 shown is a counter-wound plate 100’ having a coil conductor 1 10’ wound between an inner joint pad 120’ and an outer joint pad 130’, co-wound with a two-conductor cable 140’. Fig. 5 shows a grounding region 170’, a transitional region 180’, and a coupling region 190’. However, in accordance with the embodiment shown in Fig. 5, the operating current Iopflows through the conductor coil 110' from the outer joint pad 130’ to the inner joint pad 120’, exactly opposite of the flow in the embodiment of Fig. 3. Thus, in various embodiments, plates according to the designs of Figs. 3 and 5 may be stacked repeatedly on top of each other in an alternating fashion with their joint pads aligned, to thereby provide a single conductor coil enabling a continuous flow of the operating current between the plates and throughout the stack.

[0066] Referring now to Fig. 6A and 6B, there are shown conceptual cross-sections of two different implementations of stackable, grooved plates, each having a conductor and a voltage sensor in accordance with embodiments. The embodiment 600 of Fig. 6A includes a plate 610 having multiple channels 620a, 620b, 620c, and 620d of a rectangular groove. Of course, implementations may have any number of such channels in cross-section, and it should be appreciated that the depiction of exactly four such channels is not limiting. While the depictions herein show a single, continuous, spiraling groove, implementations of embodiments may have any number of grooves.

[0067] Each channel 620a-d retains a portion of a single coil conductor, e.g., conductor 622. That is, the single conductor 622 winds through the spiraling groove and thus appears in multiple locations in the cross-section of Fig. 6A. The conductor 622 illustratively may be comprised of a composite tape stack having one or more HTS tapes co-wound with copper tapes, Hastelloy tapes, stainless steel tapes, or other useful or needful co-wind tapes.

[0068] The groove is covered by an electrically conductive cap 624, which appears in multiple portions 624a, 624b, 624c, 624d of the cross-section of Fig. 6. In embodiments, cap 624 may comprise or be provided from copper. Other materials (e.g., materials having mechanical and electrical characteristics the same as or similar to copper) may also be used as the cap 624. Cap 624 provides at least structural retention of the conductor 622 within the channels of the groove. The conductor 622 and the cap 624 are themselves structurally coupled using solder 626. While the cap 624 extends substantially across the width of each channel, the conductor 622 does not, so there exists in the groove a solder flow channel 626 into which additional material may be placed. Thus, a voltage sensor as described above (e.g., implemented using one or more co-wound, coaxial quench detection cables 628) may be placed into the solder flow channel 626 prior to soldering. Fig. 6A shows two such cables 628a, 628b, a portion of each of which appears in cross-section in each of the four channels.

[0069] As discussed above, a coaxial quench heater may be placed proximate to the coil conductor 622 to facilitate a preemptive quench. This coaxial quench heater may be implemented using a coaxial cable, as substantially described above. Therefore, in some embodiments, the coaxial cable most proximate to the conductor 622 (i.e., cable 628b) may be used not as a duplicate voltage sensing cable, but instead as a coaxial quench heater. It should be appreciated that, in such embodiments, the relative dimensions of the two cables 628a and 628b may be different due to their different purposes and design currents, and thus that Fig. 6A is not necessarily to scale.

[0070] In Fig. 6B is shown a similar embodiment 640, including a plate 650, four channels 660a, 660b, 660c, 660d, a single coil conductor 662, a cap 664, and a solder flow channel 666. However, it may be appreciated that, unlike the embodiment shown in Fig. 6A, the coil conductor 662 shown in Fig. 6B extends substantially across the width of each channel. Thus, the groove in the plate 650 is not purely rectangular, but includes a side cut 667 into which two quench detection cables 668a, 668b have been inserted. As before, once the cables 668a, 668b are properly placed, the entire assembly may be soldered to provide structural and electrical stability.

[0071] Referring now to Fig. 7, there is shown a commercially available coaxial cable 700 that may be used in conjunction with embodiments of the concepts, techniques, and structures disclosed herein. The cable shown has a single, oxygen-free, copper-center wire

[0072] 702 (or center conductor 702) of diameter d. Surrounding the copper wire is high purity, compacted magnesium oxide (MgO) powder for insulation 703. Surrounding the insulator

[0073] 703 is a conductive sheath 704 (or outer conductor 704) of thickness t, which may, for example, be provided as 316 stainless steel. Other electrically conductive materials may, of course, also be used. In embodiments, the cable may be Nickel plated and may have an outer diameter D and a length L. The particular dimensions d, t, D, L of coaxial cable 700 as well as the particular materials from which coaxial cable 700 is made may be selected to suit the needs of a particular application. After reading the disclosure provided herein, one of ordinary skill in the art will appreciate howto select the particular dimensions (i.e., physical dimensions), materials, and electrical characteristics of a coaxial cable to suit the needs of a particular application.

[0074] For example, MgO-insulated, coaxial quench detection cables with diameters ~0.5 mm as shown in Fig. 7 are commercially available. This means they can be readily accommodated by the conductor unit cell. They can be placed in the bottom of a solder flow channel as shown in Fig. 6A, and / or a custom feature that is machined or otherwise provided into the plate so to accommodate them, such as a side-groove feature shown in Fig. 6B.

[0075] In some embodiments, coaxial quench detection cables may be disposed in only the first 3.5 inner turns of a grooved plate. In other embodiments, it may be desirable or even necessary to run coaxial quench detection cables the full distance of the conductor. The coaxial quench detection cables may be much smaller diameter (less than about 0.5 mm) than coaxial heater cables (typically about 2 mm).

[0076] To produce a signal without blind spots (i.e., that can detect a normal zone at any location in the HTS coil) there should be at least one quench detection cable that goes the full distance from inner to outer joint pad. In some embodiments, two cables are used better to provide redundancy.

[0077] In some embodiments, one or more cables go halfway from the outer joint pad to the inner joint pad. If a voltage is detected on the full length cable, it can be compared to that measured on the half-length cable. Thus, if the voltages are the same, it means the normal zone is locate somewhere along the length of the half-length cable. If there is no voltage on the half-length cable, it means the normal zone is located where there is no half-length cable. As the quench progresses and the quench protection system is engaged, comparison of voltages on full and half-length cables will provide information on the progression of normal zone formation and uniformity of normal zone formation along the winding, driven by the quench protection system. One could consider cables that go %, 7>, 74, and full length along the winding to resolve such details even finer, if desired.

[0078] Thus, the scheme described herein of insulated coaxial co-wound quench detection cable implementation in grooved, stacked plate no-insulation coils can be readily accommodated by existing manufacturing methods. In one embodiment, MgO may be used to insulate the quench detection cables, however it is appreciated that other insulators may be used in accordance with other embodiments.

[0079] Figs. 3-6 show example embodiments of coaxial co-wound quench detection cables implemented in a grooved, stacked plate HTS coil. That is, the special purpose conductor cable of Fig. 7 is placed in the grooves, either in contact with, or proximately aside conductor components such as an HTS tape or stack of such tapes, a copper cap, a copper co-wind, or other filler tapes. The entire structure is soldered together during the manufacture of individual pancake -wound coils (Figs. 3 and 5), and multiple pancake coils may then be stacked together to form a magnet. Embedded coaxial heaters may also be present in the conductor groove.

[0080] Any of the components described herein (e.g., any of the plates, conductors, cables such as twisted pair cables or coaxial cables) can exist in multiples. The descriptions herein are not meant to be limiting in quantity.

[0081] Various embodiments of the concepts, systems, devices, structures and techniques sought to be protected are described herein with reference to the related drawings. Alternative embodiments can be devised without departing from the scope of the concepts, systems, devices, structures and techniques described herein.

[0082] It is noted that various connections and positional relationships (e.g., over, below, adjacent, etc.) are set forth between elements in the description and in the drawings. These connections and / or positional relationships, unless specified otherwise, can be direct or indirect, and the described concepts, systems, devices, structures and techniques are not intended to be limiting in this respect. Accordingly, a coupling or connection of entities (e.g., elements, structures or layers) can refer to either a direct or an indirect coupling or connection of the entities. Furthermore, a positional relationship between entities can be a direct or indirect positional relationship.

[0083] As an example of an indirect positional relationship, references in the present description to forming element, structure or layer "A" over element, structure or layer "B" include situations in which one or more intermediate elements, structures or layers (e.g., structure or layer "C") is between element, structure or layer "A" and element, structure or layer "B" as long as the relevant characteristics and functionalities of element, structure or layer "A" and element, structure or layer "B" are not substantially changed by the intermediate element(s), structure(s) or layer(s).

[0084] The following definitions and abbreviations are to be used for the interpretation of the claims and the specification. As used herein, the terms "comprises," "comprising, "includes," "including," "has," "having," "contains" or "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, a mixture, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such composition, mixture, process, method, article, or apparatus.

[0085] Additionally, the term "exemplary" is used herein to mean "serving as an example, instance, or illustration. Any embodiment or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments or designs. The terms "one or more" and "one or more" are understood to include any integer number greater than or equal to one, i.e. one, two, three, four, etc. The terms "a plurality" are understood to include any integer number greater than or equal to two, i.e. two, three, four, five, etc.

[0086] The terms "connection," “coupling,” or variants thereof can include an indirect connection or coupling and a direct connection or coupling. Further, when a particular feature, structure, or characteristic is described with respect to a specific embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in other embodiments whether or not explicitly described.

[0087] References in the specification to "one embodiment, "an embodiment," "an example embodiment," etc., indicate that the embodiment described can include a particular feature, structure, or characteristic, but every embodiment can include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment.

[0088] For purposes of the description hereinafter, the terms "upper," "lower," "right," "left," "vertical," "horizontal, "top," "bottom," and derivatives thereof shall relate to the described structures and methods, as oriented in the drawing figures. The terms "overlying," "atop," "on top, "positioned on" or "positioned atop" mean that a first element, such as a first structure, is present on a second element, such as a second structure, where intervening elements such as an interface structure can be present between the first element and the second element.

[0089] The term "direct contact" means that a first element, such as a first structure or layer, and a second element, such as a second structure or layer, are connected without any intermediary structures or layers at the interface of the two elements.

[0090] 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.

[0091] The terms “approximately,” “about,” “substantially,” and “substantially equal to” 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, and yet within ±2% of a target value in some embodiments. The terms “approximately,” “about,” “substantially,” and “substantially equal to” may include the target value. The terms “approximately,” “about,” “substantially and “substantially equal to” may also be used to refer to values that are within ±20% of one another in some embodiments, within ±10% of one another in some embodiments, within ±5% of one another in some embodiments, and yet within ±2% of one another in some embodiments.

[0092] The terms “approximately,” “about,” “substantially” and “substantially equal to” may also be used to refer to values that are within ±20% of a comparative measure in some embodiments, within ±10% in some embodiments, within ±5% in some embodiments, and yet within ±2% in some embodiments. For example, a first direction that is “substantially” perpendicular to a second direction may refer to a first direction that is within ±20% of making a 90° angle with the second direction in some embodiments, within ±10% of making a 90° angle with the second direction in some embodiments, within ±5% of making a 90° angle with the second direction in some embodiments, and yet within ±2% of making a 90° angle with the second direction in some embodiments.

[0093] It is to be understood that the disclosed subject matter is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The disclosed subject matter is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods, and systems for carrying out the several purposes of the disclosed subject matter. Therefore, the claims should be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the disclosed subject matter.

[0094] Although the disclosed subject matter has been described and illustrated in the foregoing exemplary embodiments, it is understood that the present disclosure has been made only by way of example, and that numerous changes in the details of implementation of the disclosed subject matter may be made without departing from the spirit and scope of the disclosed subject matter.

Claims

CLAIMSWhat is claimed is:

1. A magnet comprising: an electrically conductive plate having a plurality of grooves; a coil conductor wound through the grooves of the plate; and a voltage sensor co-wound through the grooves of the plate, the voltage sensor comprising an insulated, two-conductor cable.

2. The magnet of claim 1, wherein the coil conductor comprises a high temperature superconductor (HTS) tape.

3. The magnet of claim 1, wherein the plurality of grooves comprises a copper cap that is soldered to the coil conductor and to the voltage sensor.

4. The magnet of claim 1, wherein the plurality of grooves further comprises one or more copper co-wound tapes.

5. The magnet of claim 1, wherein the insulated, two-conductor cable comprises a coaxial cable having magnesium oxide (MgO) insulation.

6. The magnet of claim 1, wherein the plurality of the grooves provides a base surface, and wherein the coil conductor and the insulated, two-conductor cable are in physical and electrical contact with the base surface.

7. The magnet of claim 1, wherein the plurality of the grooves provides a base surface and a side cut surface, wherein the coil conductor is in physical and electrical contact with the base surface, and wherein the cable is in physical and electrical contact with the side cut surface.

8. The magnet of claim 1, wherein the electrically conductive plate comprises a first plate, the magnet further comprising second and third electrically conductive plates,each of the plates having a respective plurality of grooves and a respective coil conductor wound through its grooves between an inner joint pad and an outer joint pad, wherein the inner joint pad of the first plate is electrically coupled to the inner joint pad of the second plate, and wherein the outer joint pad of the first plate is electrically coupled to the outer joint pad of the third plate.

9. The magnet of claim 1, wherein the voltage sensor comprises a plurality of insulated, two-conductor cables.

10. The magnet of claim 9, wherein the plurality of insulated, two-conductor cables is co-wound along the entire length of the coil conductor to provide redundant measurement of normal zone formation.

11. The magnet of claim 9, wherein the plurality of insulated, two-conductor cables is co-wound along a portion of the coil conductor to provide spatial information regarding normal zone formation within the portion.

12. The magnet of claim 1, further comprising coil state measuring electronics coupled to the voltage sensor, the coil state measuring electronics configured to measure a coil temperature and a coil operating current.

13. The magnet of claim 12, further comprising a quench protection system (QPS) coupled to the coil state measuring electronics, the QPS having one or more coaxial quench heaters that are co-wound with the coil conductor.

14. The magnet of claim 13, wherein the QPS is configured to cause the one or more coaxial quench heaters to quench the magnet when both (a) the coil state measuring electronics measure or predict a thermally unstable state, and (b) the coil state measuring electronics measure a coil temperature and a coil operating current within given ranges.

15. The magnet of claim 13, wherein the QPS is configured to cause the one or more coaxial quench heaters to quench the magnet when the coil state measuring electronics detect a normal zone of a given threshold size within the magnet.

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