High Temperature Superconducting (HTS) Field Coil

Abstract

A high-temperature superconducting (HTS) field coil includes multiple turns containing an HTS material and a metal stabilizer, and a partial insulation layer separating the turns so that current can be shared between the turns through the partial insulation layer. The partial insulation layer includes an insulating region and multiple conductive paths through the insulating region, allowing current to be shared between the turns through the conductive paths. Each conductive path includes an HTS bridge containing an HTS material, and the HTS bridge is in series with the normal conducting material of the conductive path.

Description

[Technical field]

[0001] The present invention relates to an HTS field coil. [Background technology]

[0002] Fusion power generation is an extremely complex task, and many alternative non-tokamak devices have been proposed, but none have yet achieved results comparable to the best currently operating tokamaks, such as JET.

[0003] Global fusion research has entered a new phase after the start of construction of ITER, the largest and most expensive (15 billion euros) tokamak ever built. A successful route to a commercial fusion reactor requires long-pulse, stable operation combined with the high efficiency needed to make power production economical. Achieving these three conditions simultaneously is particularly difficult, and the planned program will require many years of theoretical and technological research, as well as experimental studies on ITER and other fusion facilities. It is widely expected that a commercial fusion reactor developed along this route will not be built before 2050.

[0004] To obtain the fusion reaction necessary for economical electricity generation (i.e., power output much greater than power input), a conventional tokamak must be massive (as exemplified by ITER) so that the energy confinement time (roughly proportional to the plasma volume) can be made long enough for the plasma to become hot enough for thermonuclear fusion to occur.

[0005] US Patent No. 5,399,633 describes an alternative approach involving the use of compact spherical tokamaks for use as neutron or energy sources. The low aspect ratio plasma shape in spherical tokamaks improves particle confinement times and allows for net power generation in a much smaller machine. However, a small diameter central column is required, which presents challenges for the design of plasma confinement magnets. High temperature superconductor (HTS) field coils are a promising technology for such magnets.

[0006] Another potential application for HTS field coils is in proton beam therapy devices. Proton beam therapy (also known as proton beam therapy) is a type of particle beam therapy used to treat cancer (and other diseases that respond to radiation therapy). In PBT, a beam of protons is directed at the treatment site (e.g., a tumor).

[0007] Another similar treatment involves introducing boron-11 into the target area and then using protons to create p+ 11 The first is proton-boron capture therapy (PBCT), which initiates the B→3α reaction. The same equipment can be used to deliver protons for either PBT or PBCT.

[0008] Proton beams for PBT and PBCT are generated by particle accelerators such as cyclotrons or linear accelerators. Accelerators typically used for PBT and PBCT produce protons with energies typically ranging from 60 to 250 MeV, with the most powerful facilities currently in operation having a maximum energy of 400 MeV.

[0009] Broadly speaking, there are two types of PBT machine designs that allow for beam angle variation. In the first type of design, as shown in Figure 1, the accelerator 3001 is mounted on a gantry 3002 that allows the accelerator 3001 to rotate (usually around a horizontal axis) around the patient 3003. The patient is placed on a movable bed 3004 that provides additional degrees of freedom (e.g. translation and rotation around a vertical axis).

[0010] The second type of design is shown in Figure 2. The accelerator 4001 is stationary and the beam is directed towards the patient through steering electromagnets 4002 (which typically include both quadrupole and dipole magnets), at least some of which are positioned on a gantry 4003 so that the beam can be rotated (e.g. about a horizontal axis) around the patient 4004. The patient is placed on a movable bed 4005.

[0011] Both designs require the gantry to carry electromagnets capable of steering protons at beam energies as high as 400 MeV. This requires very high magnetic fields, so the use of HTS field coils can significantly reduce the mass and size of the electromagnets and the gantry required to move them. HTS field coils can be used in the accelerator, the steering magnet quadrupole magnets, or the steering magnet dipole magnets.

[0012] Superconducting materials are usually divided into "high temperature superconductors" (HTS) and "low temperature superconductors" (LTS). LTS materials, such as Nb and NbTi, are metals or metal alloys whose superconductivity can be explained by the BCS theory. All low temperature superconductors have a critical temperature (the temperature above which the material does not become superconducting even in zero magnetic field) below about 30 K. The behavior of HTS materials is not explained by the BCS theory, and such materials may have critical temperatures above about 30 K (it should be noted, however, that it is the physical differences in composition and superconducting behavior, not the critical temperature, that define HTS and LTS materials). The most commonly used HTS are "cuprate superconductors", ceramics based on copper oxides (compounds containing a copper oxide group), such as BSCCO or ReBCO (where Re is a rare earth element, usually Y or Gd). Other HTS materials include iron pnictides (e.g., FeAs and FeSe) and magnesium diborate (MgB2).

[0013] ReBCO is typically manufactured as a tape with a structure as shown in Figure 3. Such a tape 100 is typically about 100 microns thick and includes a substrate 101 (typically electropolished Hastelloy about 50 microns thick) on top of which is deposited by IBAD, magnetron sputtering, or other suitable technique a series of buffer layers known as a buffer stack 102 about 0.2 microns thick. An epitaxial ReBCO-HTS layer 103 (deposited by MOCVD or other suitable technique) covers the buffer stack and is typically 1 micron thick. A 1-2 micron silver layer 104 is deposited on the HTS layer by sputtering or other suitable technique, and a copper stabilization layer 105 is deposited on the tape by electroplating or other suitable technique, which often completely encapsulates the tape.

[0014] The substrate 101 provides a mechanical backbone that can be fed through a manufacturing line and allows for the growth of subsequent layers. The buffer stack 102 is required to provide a biaxially oriented crystalline template on which to grow the HTS layers, preventing chemical diffusion of elements from the substrate into the HTS that would impair its superconducting properties. The silver layer 104 is required to provide a low resistance interface from the ReBCO to the stabilization layer, and the stabilization layer 105 provides an alternative current path in case any part of the ReBCO stops superconducting (becomes "normal").

[0015] Additionally, a "peeled-off" HTS tape can be fabricated that lacks the substrate and buffer stack, but instead has a silver layer on either side of the HTS layer. The tape with the substrate is referred to as a "substrate-attached" HTS tape.

[0016] HTS tapes can be arranged in HTS cables. HTS cables contain one or more HTS tapes connected along their length by a conductive material (usually copper). The HTS tapes can be stacked (i.e. arranged so that the HTS layers are parallel) or they can have other arrangements of tapes that can vary along the length of the cable. A notable special case of HTS cables is a single HTS tape and HTS pair. An HTS pair contains a pair of HTS tapes arranged so that the HTS layers are parallel. When using substrate-attached tapes, the HTS pair can be type 0 (HTS layers facing each other), type 1 (HTS layer of one tape facing the substrate of the other tape), or type 2 (substrates facing each other). Cables containing three or more tapes can have some or all of the tapes arranged in HTS pairs. Laminated HTS tapes can contain either various arrangements of HTS pairs, most commonly a stack of type 1 pairs, or a stack of type 0 pairs (or equivalently type 2 pairs). HTS cables can contain a mixture of substrate-attached and release tapes.

[0017] When describing coils herein, the following terminology is used: "HTS Cable" - a cable containing one or more HTS tapes. For purposes of this definition, a single HTS tape is an HTS cable. "Turn" - the portion of the HTS cable within the coil that surrounds the inside of the coil (i.e., the portion that can be modeled as a complete loop). "Arc" - A continuous length of coil that is less than the entire field coil. "Inner Radius / Outer Radius" - Distance from the center of the coil to the inside / outside of the HTS cable "Circumference / Outer Circumference" - Distance measured around the inside / outer circumference of the coil "Thickness" - the radial depth of all the turns of the coil, i.e. the difference between the inner and outer radii ·“Critical current” (I C) - the current at which the HTS becomes normally conducting at a given temperature and external magnetic field. (Here, the HTS is considered to have "become superconducting" at the characteristic point of the superconducting transition where the tape produces E0 volts per meter. The choice of E0 is arbitrary, but is usually taken to be 10 or 100 microvolts per meter.) "Critical Temperature" - The temperature at which the HTS becomes normally conductive for a given magnetic field and current. · "Peak Critical Temperature" - The temperature at which the HTS becomes normally conducting in the absence of an external magnetic field and with negligible current.

[0018] Broadly speaking, there are two types of construction for HTS field coils: by winding and by assembling multiple sections. Wound coils are manufactured by winding the HTS cable 201 in a continuous spiral around a former 202 as shown in FIG. 4. The former is shaped to provide the required inner circumference of the coil and can be a structural part of the final wound coil and can be removed after winding. Sectional coils are composed of several sections 301, each of which can contain several cables or preformed busbars 311, forming an arc of the entire coil, as shown diagrammatically in FIG. 5. These sections are connected by joints 302 to form a complete coil. The turns of the coils in FIG. 2 and FIG. 3 are shown spaced apart for clarity, but generally there is a material connecting the turns of the coil. For example, the turns can be solidified by potting with epoxy resin.

[0019] The coils can be either "insulated", which has electrically insulating material between the coil turns, or "non-insulated", where the coil turns are electrically connected radially as well as along the cable (e.g., by connecting the copper stabilization layers of the cable by soldering or direct contact). Non-insulated coils are not suitable for large field coils because they tend to have very long ramp-up times, with the entire cross section of the coil becoming normally conducting before quenching and significantly dissipating the energy from the magnet, resulting in all of the magnet energy being dumped into a small volume.

[0020] A compromise option is to have a material between the turns that has a resistance intermediate between that of a conventional conductor (e.g., metal) and that of a conventional insulator (e.g., ceramic or organic insulator), e.g., between 100 times the resistivity of copper and 10 15 times resistivity or 10 -6 Ohms to 10 8 The coil is a "partially insulated" coil, having a resistivity of ohms. Partial insulation can be achieved by selecting a material with the appropriate resistivity, or by providing a partially insulated structure that provides the required resistance. Such structures are described in detail in U.S. Pat. No. 5,393,363, which is incorporated herein by reference.

[0021] In the simplest case, as shown in Figures 6A and 6B, the partial insulating structure can be a metal strip 601 with an insulating layer 602 on each side, each insulating layer having one or more windows 603 through which electrical contact can be made to a second insulating layer. By offsetting the windows on each side of the strip and / or varying the size of the windows and their spacing along the strip, the effective resistance per unit length of the partial insulating structure can be controlled (and even varied along the structure) by changing the path 610 that the current takes between the windows. If such a partial insulating structure is wound between the turns of the coil and is in electrical contact with the HTS of both turns along the length of both turns (e.g., through the metal stabilization layers of both turns), the partially insulated coil can achieve any desired inter-turn resistance.

[0022] As a further example, a more complex structure can be provided as shown in Figures 7A to 7C. This structure includes five layers within an insulator 701: a first metal connection layer 711, a conductive layer 730, and a second metal connection layer 712. The first and second metal connection layers are provided on the surface of the insulator, and the conductive layer is provided inside the insulator and is electrically connected to the connection layer by vias 702. The conductive layer is divided into several regions, including lanes 703 that provide a conductive path between the two metal connection layers through the insulator. This adds another means of controlling the resistance of the layer, since the width and length of each "lane" affects the resistance. One advantage of this is that the window spacing can be made narrower (i.e., smoothing the resistance of the partial insulating layer) while compensating for resistance losses by extending the lane length and / or reducing the lane width. [Prior art documents] [Patent documents]

[0023] [Patent Document 1] International Publication No. 2013 / 030554 [Patent Document 2] International Publication No. 2019 / 150123 Summary of the Invention [Means for solving the problem]

[0024] According to a first aspect, there is provided a high temperature superconducting (HTS) field coil. The HTS field coil is made of HTS materials and metal stabilizers. Chemical materials and a partial insulation layer separating the turns such that current can be shared between the turns through the partial insulation layer. The partial insulation layer includes an insulating region and a plurality of conductive paths through the insulating region such that current can be shared between the turns through the conductive paths. Each conductive path includes an HTS bridge including an HTS material, the HTS bridge being in series with the normally conducting material of the conductive path.

[0025] Further embodiments are defined in claims 2 et seq. [Brief description of the drawings]

[0026] [Figure 1] A first PBT device is shown. [Diagram 2] A second PBT device is shown. [Diagram 3] The structure of the ReBCO tape is shown. [Figure 4] FIG. 2 is a schematic diagram of a winding coil. [Diagram 5] FIG. 2 is a schematic diagram of a section coil. [Figure 6] 6A and 6B show a partial insulating layer according to Patent Document 2. [Figure 7] 7A to 7C show an alternative partial insulating layer according to US Pat. No. 5,399,633. [Figure 8] Simulation results of a partially insulated TF coil during a quench are presented. [Figure 9] 1 is a side cross-sectional view of an exemplary partial insulating layer. [Figure 10] FIG. 13 is a diagram of a further exemplary partial insulating layer. [Figure 11A-C] 11A, 11B and 11C show further exemplary partial insulating layers. [Fig. 11D-E] 11D and 11E show further exemplary partial insulating layers. [Figure 12] FIG. 2 is a circuit diagram of a typical exemplary partial insulating layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Although the partial insulation structure described in the background is suitable for most coils, some parts of the coil have a higher I / I than other parts. C It has been found that localized hot spots can still occur in coils operating at I / I ratios. These hot spots are located not where the quench first started, but in the I / I ratio of the coil. C To explain why this happens, it is helpful to first explain what happens during the quench of a partially insulated field coil.

[0028] Figure 8 shows the results of a simulation of a single partially insulated D-shaped TF coil during a quench. The top of the figure shows the (local) average tape current in the coil over a series of time steps (starting from the point when part of the coil becomes normal, going from left to right), and the bottom of the figure shows the temperature in the coil over the same series of time steps. When part of a single turn of the field coil becomes normal (or approaches normal), the current in that turn drops rapidly to zero (801). This is because it becomes more favorable for the current to follow a radial path and bypass the turn (through the partial insulation) than to follow the helical path of the turn (through the HTS). This has two effects. First, the temperature of the single turn and the adjacent turns starts to rise due to resistive heating from the radial path (802), and second, the current in the remaining turns increases due to the inductance of the coil opposing the change to the magnetic field (803). In a symmetrical coil, the temperature rise radiates out from a single turn, causing adjacent turns to become normally conducting, which then increases the current in the radial path, causing further heating, until the entire coil becomes normally conducting. This process occurs quickly, dissipating the stored energy substantially evenly throughout the field coil.

[0029] However, asymmetric coils, i.e., I / I C For coils whose ratio varies around the field coil, the field coil will not be heated uniformly due to the equal redistribution of current and the initial uniform heating of the field coil as the field coil is completely quenched. This is due to the I / I C The low ratio region, e.g., the central column 810, is I / I C This is because it quenches before the high ratio regions, which simply cannot support the same current before they generate too much resistance (and therefore heat). CThe lower ratio regions become normal more rapidly, eventually reaching a point where the entire cross section of the coil becomes resistive. At this stage, similar to the previous description of a quench in a non-insulated field coil, the resistive portions of the coil heat up rapidly (804) and the current in the helical path decreases rapidly (805) as the current in the helical path is dumped into the resistive portions and resistive radial paths. This reduces the I / I C The temperature in the low ratio area will be much higher than the temperature in the rest of the coil, potentially damaging that portion of the coil.

[0030] A simple solution to this problem is to C By designing the coil so that I / I is substantially constant around the circumference of the coil (e.g., by varying the number of HTS tapes at different points of the coil), or C The primary goal of the HTS coil is to provide additional cooling in areas where the HTS tape is low. However, in many applications, such areas arise because there is not enough space in that area of ​​the HTS coil for more HTS tape or more cooling (or the increased space required would result in an unacceptable trade-off). One example is the central column of a spherical tokamak, where there is a tendency to make the central column diameter as small as possible because this increases the efficiency of the tokamak, and most of the central column is taken up by a portion of the toroidal field coil.

[0031] Given the advantages of partially insulated HTS coils, particularly those having a partial insulation layer as described above, there is a need to find a solution to the problem of non-uniform quenching without significantly increasing the thickness of the HTS coil (compared to a comparable coil having a partial insulation layer as described in the background).

[0032] This can be achieved by providing the HTS element within the partial insulation layer such that it is in series with at least a portion of the conductive path through the partial insulation layer. The HTS element acts as a current limiter for the radial path. Therefore, in areas where the coil becomes normal faster, the current that can be shunted through the radial path is limited (because the HTS element also becomes normal faster, increasing the local resistance of the partial insulation layer). This means that more current is shunted through the radial path in areas of the coil that become normal more slowly, which increases the heating in these areas and therefore equalizes the loss rate of the superconducting around the coil. This allows more energy to be released elsewhere in the coil, thus reducing the I / I C The temperature of the hot spots in the high temperature areas decreases.

[0033] FIG. 9 shows a side cross-sectional view of an exemplary partial insulation layer 900, which includes an insulator 901 (generally in the form of a long strip for co-winding with the HTS turns, running side to side as shown), a metal connection layer 902, and an HTS bridge 903. The HTS bridges are spaced along the insulator (regularly in this example, but may be closer spaced in some areas than others) and provide electrical connections between the metal connection layers. As mentioned above, the HTS bridges effectively act as current limiters, since their resistance increases rapidly once the radial current reaches a critical current. The critical current of the HTS bridge depends on internal factors, such as the properties of the HTS material and the dimensions of the HTS material (especially the width), and external factors, such as local temperature, local magnetic field, and strain. Identifying the critical current required during operation of a coil including a partial insulation layer can be done by simulation, as is common in the field.

[0034] When the radial current per HTS bridge exceeds the critical current of the HTS bridge, the HTS bridge becomes normally conducting with a high resistance. There may still be paths of moderate resistance (e.g., through any metallization or substrate of the HTS, through normally conducting lanes provided through the insulator, or through other paths, e.g., through the solder if the coil is soldered), but the overall effect is a significant increase in the resistance of the partial insulation layer in the area where the HTS bridge has become normally conducting. This directs the current to other parts of the partial insulation layer that have lower resistance (causing more heating in these parts). For currents close to but not exceeding the critical current, the resistance of the HTS bridge increases as the current increases. Thus, for a partially insulated coil with a uniformly constructed partial insulation layer, the redistribution of current tends toward an equilibrium where both the radial current and the critical current of the HTS bridge are the same around the coil. This occurs because areas with high critical current have low resistance, which causes more current to flow through these areas, which causes additional heating, which in turn lowers the critical current of the HTS bridge.

[0035] If a portion of the coil (e.g., a high I / I in the helical path of that portion of the coil) C When the I / I ratio in the HTS bridge is heated (by creating a hot spot as described above), this reduces the critical current of the HTS bridge in that area and diverts the radial current to other parts of the coil, causing them to heat up. C The same effect that causes leveling of the heating in the turns of the HTS as the field coil quenches also levels out the heating in the turns of the HTS as the field coil quenches, thus distributing the energy released during quench more evenly.

[0036] Figure 10 shows an exemplary partial insulating layer incorporating an HTS bridge in a design similar to Figures 6A and 6B. As in Figure 6B, the partial insulating layer includes a metal strip 1001 with an insulating layer 1002 on each side and multiple windows on each side of the insulating layer, the windows being offset from one another to provide a current path 1010 through the partial insulating layer. In this case, the partial insulating layer also includes an HTS bridge 1003 in the window on one side and a connecting element 1004 in the window on the other side, which connect the metal strip to a connecting layer 1005.

[0037] 11A-11E show an exemplary partial insulation layer incorporating an HTS bridge in a design similar to that of FIGS. 7A-7C. The leaky insulation layer includes five layers, which are, in order: a first metal connection layer 1111; a first insulating layer 1121, Conductive layer 1130, a second insulating layer 1122; Second metal connection layer 1112 It is.

[0038] Figures 11A-11C respectively show the layout of first metal contact layer 1111, conductive layer 1130, and second metal contact layer 1122. Figures 11D and 11E are cross-sectional views along lines D and E of Figures 11A-11C.

[0039] The connection layers are present to facilitate attachment to the HTS cable by soldering. In this and the previous examples, they may be omitted or may include several smaller areas that allow electrical contact with the electrical connections through the partial insulation layer.

[0040] The conductive layer is divided into a number of conductive regions. These regions are of two types: square regions 1131 (which may in fact be of any shape) that are connected to only one of the metal connection layers by vias 1106. These regions do not affect the electrical properties of the partial insulating layer, but provide a thermal path through the respective insulating layer. By varying the size of these regions and the number of connections between these regions and the metal connection layers, the thermal properties of the partial insulating layer can be varied independently of the electrical properties.

[0041] Each of the other regions 1132 connects a window 1101 in the first insulating layer 1121 to a window 1102 in the second insulating layer 1122. Each of the regions 1132 includes an HTS bridge 1107, which is connected in series with the rest of the region. The resistance between the windows while the HTS is superconducting can be controlled by varying the geometry of the region 1132. For example, if the region 1132 includes an elongated track 1133 as shown in FIG. 11B, increasing the width of the track decreases the resistance between the windows, and increasing the length of the track (e.g., by providing a non-straight track or by moving the window) increases the resistance between the windows. The radial current at which the HTS stops superconducting can be controlled by changing the HTS material used (e.g., different ReBCO formulations or suppliers generally have different critical currents) and / or by changing the dimensions (especially the width) of the HTS bridge. However, the critical current also depends on external factors such as temperature and magnetic field. As previously mentioned, the required geometry of the HTS can be determined by simulation, as is common in the design of HTS magnets.

[0042] A window 1101 in the first insulating layer is formed by the first connection layer and a via drilled through the first insulating layer, which is then plated with metal 1103 (or other conductive material) to connect the first connection layer and the conductive layer. A window 1102 in the second insulating layer is formed by drilling a via 1102 through all layers, which is then plated with metal 1104 (or other conductive material). To prevent a connection being made to the first connection layer through the window 1102 in the second insulating layer, the first connection layer is etched around the via 1102 to electrically insulate the via 1102, and an insulating cap 1105 is placed on the end of the via 1102 to ensure that no bridging occurs due to soldering or contact with the HTS cable.

[0043] As an alternative, the windows 1102 can instead be drilled from the other side of the partial insulating layer such that they pass through the second connecting layer, the second insulating layer, and the conductive layer, and do not pass through (or do not pass completely through) the first insulating layer. As a further alternative, all windows can be formed from vias that pass through all layers, with an etch of the second connecting layer and an insulating cap on the second connecting layer being used for the windows 1601 in the first insulating layer.

[0044] As with previous examples, some of the electrical connections 1108 across the partial insulation layer may not include an HTS bridge (i.e., may be essentially the same as lane 703 in FIG. 7B) to further control the upper limit of the resistance of the partial insulation layer when the HTS is quenched.

[0045] FIG. 12 shows a circuit diagram for a generic partial insulation layer for which the above description provides a concrete example. An HTS coil 1201 is connected by two sets of resistors. The first set is a variable resistor R in series with resistor R1. HTS The variable resistor R HTS represents the resistance of the HTS bridge, and the critical current ratio I / I C (i.e., I / I C is very low when I / I is less than about 0.8. C increases as I / I C(It will be very high if is greater than 1.) R1 represents the resistance of other conductive elements in series with the HTS bridge.

[0046] The second set of resistors is resistor R2, which represents the resistance of the current path that bypasses the HTS, which may include current passing through any metallization or substrate of the HTS bridge (and any components in series), or through other electrical connections through partial insulation layers that do not include the HTS, such as connection 1108 in FIG.

[0047] While the above has shown various examples of insulation within the partial insulating layer (e.g., an insulating layer as in FIG. 10, an insulator as in FIG. 6B, or an insulating layer as in FIG. 11), it will be understood that the unifying concept of these examples is a partial insulating layer having "insulating regions" in which multiple conductive paths are provided. This also includes other examples not described in detail herein, such as vacuum or gas gaps within the partial insulating layer, or gaps within the partial insulating layer that are subsequently filled with epoxy (e.g., when a coil is potted with epoxy resin).

[0048] Partial insulation layers are incorporated into the HTS field coil to allow current to be shared radially between the turns. For example, in a wound field coil, the partial insulation layers can be co-wound with the cable, and in a sectioned field coil, the sections can be constructed from alternating layers of partial insulation layers and HTS cable (or other HTS current carrying assemblies). The external electrical connections of the partial insulation layers (e.g., metal connection layers, or ends of conductive paths) can be connected to the turns through solder, by simple contact, or by any other suitable method.

[0049] In section coils, the partial insulation layer may or may not be continuous within the joints between sections: the partial insulation layer may extend to the end of the section (to match the corresponding layer of the other section at the joint), the joint may include an insulating region that prevents current from bypassing the partial insulation layer in the joint, or the joint may have a conductor that allows current to bypass the partial insulation layer in the joint.

[0050] The HTS bridges can be distributed across the field coil or can be I / I C can only be used in areas with high thermal conductivity (the normal current path through the partial insulation is provided outside these areas).

[0051] The HTS bridge can be made of the same HTS material as the electromagnetic coil, or it can be made of an HTS material with a reduced critical current and / or a higher critical temperature. By providing an HTS bridge with a reduced critical current and / or a higher critical temperature, the properties of the HTS bridge can be controlled, in particular how quickly it becomes normal when required. Altering the critical current can be achieved by providing an HTS bridge with a reduced HTS cross-sectional area (e.g. reduced width) compared to the HTS material used for the electromagnetic coil, by providing the HTS bridge made from an HTS material with striations or other changes in the amount and / or distribution of HTS material compared to the electromagnetic coil, or by providing an HTS bridge made of an HTS material with an inherently lower critical current per unit volume. Altering the critical temperature can be achieved by providing an HTS bridge made of an HTS material with an inherently higher critical temperature, or by controlling the oxygenation level of the HTS material of ReBCO used for the HTS bridge, as the oxygenation level of ReBCO is directly related to the critical temperature.

Claims

1. A high temperature superconducting (HTS) field coil, a plurality of turns including an HTS material and a metal stabilizer; a partial insulating layer separating the turns so that current can be shared between the turns through the partial insulating layer; Including, The partial insulating layer is an insulating region; a plurality of conductive paths through the insulating region, the conductive paths allowing current to be shared between the turns through the conductive paths; Including, An HTS field coil, wherein each conductive path includes an HTS bridge including HTS material, said HTS bridge in series with the normally conductive material of said conductive path.

2. 2. The HTS field coil of claim 1, wherein each HTS bridge includes a metal stabilizer and / or substrate bonded to and connected in parallel with the HTS material.

3. The HTS field coil of claim 1 , wherein the conductive paths are equally spaced along the partial insulation layer.

4. 2. The HTS field coil of claim 1, wherein the partial insulation layer further includes a plurality of additional conductive paths through the insulation region, the additional conductive paths also allowing current sharing between the turns, the additional conductive paths being free of HTS material.

5. The conductive path including the HTS bridge is provided within a first region of the HTS field coil, and the further conductive path is provided outside at least the first region of the HTS field coil, and the first region of the HTS field coil has a ratio I / I between an operating current of the HTS field coil during operation of the HTS field coil and a critical current of each turn of the HTS field coil. C 5. The HTS field coil of claim 4 wherein the ratio is higher outside the first region.

6. 2. The HTS field coil of claim 1, wherein the HTS material of the HTS bridge has a lower critical current and / or a higher critical temperature than the HTS material of the plurality of turns.

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