Insulation of HTS links for HTS field coils

Abstract

A high-temperature superconducting (HTS) excitation coil. The HTS excitation coil includes: a plurality of turns comprising HTS material and a metal stabilizer; and a partial insulating layer separating the turns, enabling current sharing among the turns via the partial insulating layer. The partial insulating layer includes an insulating region and a plurality of conductive paths passing through the insulating region, wherein current can be shared among the turns via the plurality of conductive paths. Each conductive path includes an HTS bridge comprising HTS material, wherein the HTS bridge is connected in series with the normal conductive material of the conductive path.

Description

Technical Field

[0001] The present invention relates to an HTS excitation coil. Background Art

[0002] The challenges of producing fusion energy are complex. Many alternatives to tokamaks have been proposed, but none have yet produced results comparable to the best currently operating tokamaks (e.g., JET).

[0003] Global fusion research has entered a new phase with the start of construction on ITER, the largest and most expensive tokamak ever built (approximately €15 billion). A successful path to commercial fusion reactors requires long pulses, stable operation, and the high efficiency required to make electricity production economical. These three conditions are particularly difficult to achieve simultaneously, and the planned project will require years of experimental research, as well as theoretical and technological research, at ITER and other fusion facilities. It is widely expected that a commercial fusion reactor developed along this path will not be built until 2050.

[0004] To achieve the fusion reactions required for economical power generation (i.e., output power much greater than input power), conventional tokamaks must be huge (as exemplified by ITER) so that the energy confinement time (which is roughly proportional to the plasma volume) can be large enough so that the plasma can be hot enough for thermal fusion to occur.

[0005] WO 2013 / 030554 describes an alternative approach involving the use of a compact spherical tokamak as a neutron or energy source. The low-aspect-ratio plasma shape in a spherical tokamak improves particle confinement time and allows for net power generation in a much smaller machine. However, the small diameter central column required presents challenges in the design of the plasma confinement magnet. High-temperature superconductor (HTS) field coils are a promising technology for such magnets.

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

[0007] Another similar therapy is proton boron capture therapy (PBCT), in which boron-11 is introduced to the target site and a proton beam is used to induce p+ 11 B→3α reaction. The same device can be used to deliver proton beams for PBT or PBCT.

[0008] The proton beams used for PBT and PBCT are generated by particle accelerators such as cyclotrons or linear accelerators. Accelerators commonly used for PBT and PBCT typically produce protons with energies in the range of 60 MeV 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 designs for PBT equipment that allow for varying beam angles. In the first type of design, e.g. Figure 1 As shown, the accelerator 3001 is mounted on a gantry 3002, which allows it to rotate (typically around a horizontal axis) around a patient 3003. The patient is placed on a movable bed 3004, which provides more degrees of freedom (e.g., translational movement and rotation around a vertical axis).

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

[0011] Both designs require a gantry equipped with electromagnets capable of controlling protons at beam energies up to 400 MeV. This requires very high magnetic fields, so using HTS excitation coils can significantly reduce the mass and size of the electromagnets and the gantry required to move them. HTS excitation coils can be used in accelerators, quadrupole magnets for steering magnets, or dipole magnets for steering magnets.

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

[0013] ReBCO is usually manufactured as strips with a structure such as Figure 3As shown. This strip 100 is typically about 100 microns thick and comprises a substrate 101 (typically an electropolished Hastelloy alloy about 50 microns thick) on which a series of buffer layers, referred to as a buffer stack 102, are deposited by IBAD, magnetron sputtering, or other suitable techniques. This series of buffer layers is referred to as a buffer stack 102 and has a thickness of about 0.2 microns. An epitaxial ReBCO-HTS layer 103 (deposited by MOCVD or other suitable techniques) covers the buffer stack and is typically 1 micron thick. A 1 to 2 micron silver layer 104 is deposited on the HTS layer by sputtering or other suitable techniques, and a copper stabilizer layer 105 is deposited on the strip by electroplating or other suitable techniques, typically completely encapsulating the strip.

[0014] The substrate 101 provides a mechanical backbone that can be transported through the production line and allows the growth of subsequent layers. The buffer stack 102 is needed to provide a biaxially textured crystal template on which the HTS layer is grown and to prevent chemical diffusion of elements from the substrate into the HTS, which would destroy the superconducting properties of the HTS. The silver layer 104 is needed to provide a low-resistance interface from the ReBCO to the stabilizer layer, and the stabilizer layer 105 provides an alternative current path in the event that any part of the ReBCO stops superconducting (enters a "normal" state).

[0015] Additionally, "stripped" HTS tapes can be made that lack the substrate and buffer stack, but instead have silver layers on both sides of the HTS layer. The tapes with substrates will be referred to as "substrate" HTS tapes.

[0016] HTS tapes can be arranged in an HTS cable. An HTS cable comprises one or more HTS tapes connected along their length via a conductive material (typically copper). The HTS tapes can be stacked (i.e., arranged so that the HTS layers are parallel), or they can have some other tape arrangement that can vary along the length of the cable. Notable exceptions to HTS cables are single HTS tapes and HTS pairs. An HTS pair comprises a pair of HTS tapes arranged so that the HTS layers are parallel. When using a base tape, the HTS pair can be Type 0 (HTS layers facing each other), Type 1 (the HTS layer of one tape faces the base of another tape), or Type 2 (the bases face each other). Cables comprising more than two tapes can have some or all of the tapes arranged as HTS pairs. Stacked HTS tapes can include various arrangements of HTS pairs, the most common being a stack of Type 1 pairs or a stack of Type 0 pairs (and / or, equivalently, Type 2 pairs). An HTS cable can include a mix of base tapes and stripping tapes.

[0017] When describing coils in this document, the following terminology will be used:

[0018] “HTS Cable” – a cable comprising one or more HTS tapes. For the purposes of this definition, a single HTS tape is an HTS cable.

[0019] "Turn" - a section of HTS cable within a coil that surrounds the interior of the coil (i.e., it can be modeled as a complete loop)

[0020] "Arc length" - the continuous length of the coil, which is less than the entire excitation coil

[0021] “Inner Radius / Outer Radius” – distance from the center of the coil to the inside / outside of the HTS cable

[0022] "Inner Circumference / Outer Circumference" - the distance measured around the inside / outside of the coil

[0023] "Thickness" - the radial depth of all turns of the coil, i.e. the difference between the inner and outer radius

[0024] “Critical current” (I C ) – The current at which an HTS becomes normal at a given temperature and external magnetic field (where an HTS is said to "become normal" at the characteristic point of the superconducting transition, where the ribbon produces E0 volts per meter. The choice of E0 is arbitrary but is usually considered to be 10 or 100 microvolts per meter.)

[0025] "Critical temperature" - the temperature at which HTS will become normal under a given magnetic field and current

[0026] “Peak critical temperature” – the temperature at which the HTS will become normal in the absence of an external magnetic field and with negligible current.

[0027] Broadly speaking, HTS field coils can be constructed in two ways – by winding, or by assembling several segments. Figure 4 As shown, a wound coil is manufactured by winding the HTS cable 201 in a continuous spiral around a former 202. The former is shaped to provide the desired inner circumference of the coil and can be a structural part of the final wound coil or can be removed after winding. Figure 5 As shown schematically, the segmented coil is composed of several segments 301, each of which may contain several cables or preformed busbars 311 and will form the arc length of the entire coil. These segments are connected by joints 302 to form a complete coil. Although for the sake of clarity, Figure 2 and Figure 3 The coil turns in FIG are shown separated, but there is usually material connecting the coil turns - for example, they can be reinforced by potting with epoxy resin.

[0028] The coil can be "insulated" - with electrical insulation between the coil turns, or "uninsulated" in which the coil turns are electrically connected radially and along the cable (e.g., by welding or by direct contact with the cable's copper stabilization layer). Uninsulated coils are not suitable for large field coils due to the extremely high acceleration times and the tendency for a quench to cause the entire cross-section of the coil to become normal before the energy from the magnet has been significantly dissipated - resulting in all the magnetic energy being dumped into a small volume.

[0029] An intermediate ground option is a "partially insulated" coil, where the resistance of the material between the turns is between the resistance of a conventional conductor (e.g., metal) and a conventional insulator (e.g., ceramic or organic insulator, e.g., with a resistivity 100 to 10 times that of copper). 15 times or in 10 -6 and 10 8 The resistance between the ohm-meter and the ...

[0030] In the simplest case, such as Figure 6A and Figure 6B As shown, a partially 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 metal strip and / or varying their size and spacing along the strip, the effective resistance per unit length of the partially insulating structure can be controlled (and even varied along the structure) by varying the path 610 taken by current between the windows. If such a partially insulating structure is wound between coil turns and makes electrical contact with the HTS of both turns along its length (e.g., via their metal stabilization layers), a partially insulating coil with any desired inter-turn resistance can be achieved.

[0031] As another example, 7A to 7CAs shown, a more complex structure can be provided. The structure includes five layers within the insulating body 701 - a first metal connection layer 711; a conductive layer 730; and a second metal connection layer 712. The first metal connection layer and the second metal connection layer are arranged on the surface of the insulating body, and the conductive layer is arranged inside the insulating body and electrically connected to the connection layer through the through hole 702. The conductive layer is divided into several regions, including a channel 703, which provides a conductive path through the insulating body between the two metal connection layers. This adds another way to control the resistance of the layer, because the width and length of each "channel" will affect the resistance. One advantage of doing this is that the windows can be spaced more closely (i.e., the resistance of part of the insulating layer is smoothed) while compensating for the loss of resistance by extending the length of the channels and / or reducing their width. Summary of the Invention

[0032] According to a first aspect, a high-temperature superconducting (HTS) excitation coil is provided. The HTS excitation coil comprises a plurality of turns comprising HTS material and a metal stabilizer; and a partial insulating layer separating the turns such that current can be shared between the turns via the partial insulating layer. The partial insulating layer comprises an insulating region and a plurality of conductive paths passing through the insulating region, wherein current can be shared between the turns via the conductive paths. Each conductive path comprises an HTS bridge comprising HTS material, wherein the HTS bridge is connected in series with the normal conductive material of the conductive path.

[0033] Further embodiments are defined in claim 2 et seq. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A first PBT device is shown;

[0035] Figure 2 A second PBT device is shown;

[0036] Figure 3 shows the structure of the ReBCO tape;

[0037] Figure 4 It is a schematic diagram of a wound coil;

[0038] Figure 5 It is a schematic diagram of a segmented coil;

[0039] Figure 6A and Figure 6B shows a portion of an insulating layer according to WO 2019 / 150123 A1;

[0040] 7A to 7C An alternative partial insulation layer according to WO 2019 / 150123 A1 is shown;

[0041] Figure 8shows the simulation results of a partially insulated TF coil during a quench;

[0042] Figure 9 is a side cross-sectional view of an exemplary portion of an insulating layer;

[0043] Figure 10 is a diagram of another exemplary portion of an insulating layer;

[0044] Figure 11A 、 Figure 11B 、 Figure 11C 、 Figure 11D and Figure 11E Yet another exemplary partial insulation layer is shown;

[0045] Figure 12 is a circuit diagram of a general exemplary portion of an insulating layer. DETAILED DESCRIPTION

[0046] While the partial insulation structure described in the background is suitable for most coils, it has been found that some parts of the coil have a higher I / I than others. C In fractionally operated coils, local hot spots will still occur. This hot spot will not appear where the quench initially begins, but rather at the point in the coil with the maximum I / I C To explain why this happens, it is helpful to first explain what happens during a quench in a partially insulated field coil.

[0047] Figure 8 Simulation results for a single, partially insulated, D-shaped TF coil during a quench are shown. The upper portion of the figure shows the (local) average current in the coil over a series of time steps (from left to right, starting from the time a portion of the coil becomes normal), and the lower portion shows the temperature in the coil over the same time steps. When a portion of a single turn of the field coil becomes normal (or nearly normal), the current in that turn will quickly drop to zero 801—because it becomes more favorable for the current to follow a radial path around the turn (through the partial insulation) rather than through the turn's helical path (through the HTS). This has two effects—first, the temperature of the single turn and adjacent turns will begin to rise 802 due to resistive heating from the radial path, and second, because the coil's inductance opposes the change in magnetic field, the current in the remaining turns will increase 803. In a symmetrical coil, the temperature increase will radiate outward from the single turn, causing the adjacent turns to become normal, which will then increase the current in the radial path, causing further heating until the entire coil becomes normal. This process occurs rapidly and dissipates the stored energy essentially evenly across the field coil.

[0048] However, in an asymmetric coil (i.e., I / I Cfraction varies around the field coil), the uniform redistribution of current and the initial uniform heating of the field coil will not result in uniform heating of the field coil at the time of complete quench. This is because with a lower I / I C The regions with higher I / I scores (e.g., center column 810) will be C fraction of the region before quenching - this is simply because such a region cannot hold that much current before developing significant resistance (and therefore heat). c The fractional area will become normal more quickly, eventually reaching a point where the entire cross-section of the coil is resistive. At this stage, similar to the previous description of a quench in a non-insulated field coil, the resistive portion of the coil will heat up rapidly 804, and the current in the spiral path will decrease rapidly 805 as the current in the spiral path is dumped into the resistive portion and the resistive radial path. This results in a coil with a lower I / I c The temperature in the fractional area rises more than the temperature of the rest of the coil, possibly causing damage to the coil in that portion.

[0049] A simple way to solve this problem is to design the coil so that I / I c substantially constant around the coil (e.g., by varying the amount of HTS tape at different points in the coil), or to a value with low I / I c The HTS coils are located in a region of the HTS coils that provides additional cooling. However, in many applications, such regions arise because there is insufficient space in that region of the HTS coils to accommodate more HTS ribbon or more cooling (or increasing the required space would result in an unacceptable compromise). An example is in the central column of a spherical tokamak, where there is a drive to make the diameter of the central column as small as possible because this improves the efficiency of the tokamak - and most of the central column is taken up by portions of the toroidal field coils.

[0050] In view of the advantages of partially insulated HTS coils (and in particular partially insulated HTS coils with a partial insulation layer as described above), it is desirable to find a solution to the problem of non-uniform quenching without significantly increasing the thickness of the HTS coil (compared to an equivalent coil with a partial insulation layer as described in the background).

[0051] This can be achieved by providing an HTS element within a portion of the insulating layer, such that the HTS element is in series with at least a portion of the conductive path through the portion of the insulating layer. The HTS element acts as a current limiter for the radial path - so that in areas of the coil that become normal more quickly the current that can be shunted through the radial path is limited (because the HTS element also becomes normal more quickly, thereby increasing the local resistance of the portion of the insulating layer). This means that in areas of the coil that become normal more slowly more current will be shunted through the radial path, which will increase heating in these areas, thereby evening out the rate of superconducting losses around the coil. This in turn will reduce the rate of superconducting losses in areas with high I / I c The temperature of any hot spots in the area will be increased because more energy will be dumped elsewhere in the coil.

[0052] Figure 9 A side cross-sectional view of an exemplary partial insulation layer 900 is shown, comprising an insulation body 901 (typically in the form of an elongated strip for co-winding with HTS turns, extending to the left and right as shown), a metal connection layer 902, and an HTS bridge 903. The HTS bridges are spaced apart along the insulation body (regularly in this example, although they may be more closely spaced in some areas than in others) and provide electrical connections between the metal connection layers. As described above, the HTS bridges will effectively act as current limiters because their resistance will increase rapidly when the radial current reaches its critical current. The critical current of the HTS bridge will depend on internal factors such as the properties of the HTS material and the dimensions of the HTS material (particularly the width), as well as external factors such as the local temperature, local magnetic field, and strain. The critical current required during operation of a coil comprising a partial insulation layer can be determined via simulation, which is common in the art.

[0053] When the radial current in each HTS bridge exceeds the critical current of the HTS bridge, the HTS bridge will become normal and have a high resistance. A moderately resistive path may still exist (e.g., through any HTS cladding or base, through a normal conductive path provided by the insulation body, or through other routes, such as solder if the coil is solder-potted), but the overall effect will be a significant increase in the resistance of the partial insulation layer in the area where the HTS bridge has become normal. This shifts current to other parts of the partial insulation layer with lower resistance (causing more heating in these areas). At currents approaching, but not exceeding, the critical current, the resistance of the HTS bridge will increase as the current increases. Therefore, for partially insulated coils with uniformly constructed partial insulation layers, the current redistribution will tend to equilibrium, where the radial current and the critical current of the HTS bridge are the same around the coil. This occurs because areas with higher critical currents will have lower resistance, which causes more current to flow through them, resulting in additional heating and, consequently, a lowering of the critical current of the HTS bridge.

[0054] If a portion of the coil becomes hot (e.g. due to a high I / I in the spiral path of that portion of the coil C fraction leads to hot spots as described above), this will reduce the critical current of the HTS bridge in this area, thereby transferring radial current to other parts of the coil and causing them to heat up. C The same effect of equalization also results in equalized heating in the HTS turns during a quench in the field coil, and thus a more even distribution of the energy dumped during the quench.

[0055] Figure 10 shows the incorporation of an HTS bridge into a Figure 6A and Figure 6B An exemplary partial insulation layer in the design of Figure 6B Similarly, the partial insulating layer includes a metal strip 1001 with an insulating layer 1002 on each side and a plurality of 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 within the window on one side and a connecting element 1004 within the window on the other side, the connecting element 1004 connecting the metal strip to a connecting layer 1005.

[0056] Figures 11A to 11E shows the incorporation of an HTS bridge into a 7A to 7C The exemplary partial insulating layer in the design of . The drain insulating layer includes 5 layers, which are:

[0057] First metal connection layer 1111;

[0058] a first insulating layer 1121;

[0059] Conductive layer 1130;

[0060] a second insulating layer 1122;

[0061] A second metal connection layer 1112 .

[0062] Figures 11A to 11C The layouts of the first metal connection layer 1111 , the conductive layer 1130 , and the second metal connection layer 1122 are shown respectively. Figure 11D and Figure 11E It is along Figures 11A to 11C The section of lines D and E in .

[0063] There are connection layers to facilitate connection to the HTS cable by soldering. In this and previous examples, these can be omitted, or include several smaller areas that allow electrical contact to be made to the electrical connection through part of the insulation layer.

[0064] The conductive layer is divided into several conductive regions. These regions are of two types. Square regions 1131 (although they can be of any shape) are connected to only one of the metal connection layers via vias 1106. These regions do not affect the electrical properties of the portion of the 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 them and the metal connection layer, the thermal properties of the portion of the insulating layer can be varied independently of the electrical properties.

[0065] The other regions 1132 each connect the window 1101 of the first insulating layer 1121 to the window 1102 of the second insulating layer 1122. Each of the regions 1132 includes an HTS bridge 1107 that is connected in series with the rest of the region. The resistance between the windows when the HTS is superconducting can be controlled by changing the geometry of the region 1132 - for example, where the region 1132 contains Figure 11B As shown in the elongated track 1133, increasing the width of the track will reduce the resistance between the windows, and increasing the length of the track (e.g., by providing a nonlinear track, or by moving the windows) will increase the resistance between the windows. The radial current at which the HTS will stop superconducting can be controlled by changing the HTS material used (e.g., different ReBCO formulations or suppliers will typically have different critical currents) and / or changing the dimensions (particularly the width) of the HTS bridge - although the critical current will also depend on external factors such as temperature and magnetic field. As mentioned earlier, the desired HTS arrangement can be determined via simulation, which is common in HTS magnet design.

[0066] Window 1101 in the first insulating layer is formed by drilling holes through the first connection layer and the first insulating layer. These holes are then plated with metal 1103 (or other conductive material) to connect the first connection layer and the conductive layer. Window 1102 in the second insulating layer is formed by drilling a through-hole 1102 through all layers. The through-hole is then plated with metal 1104 (or other conductive material). To prevent window 1102 through the second insulating layer from forming a connection with the first connection layer, the first connection layer is etched around through-hole 1102 to electrically isolate it, and an insulating cap 1105 is placed at the end of through-hole 1102 to prevent bridging due to soldering or contact with the HTS cable.

[0067] As an alternative, the windows 1102 can be drilled from the other side of the partial insulating layer so that they pass through the second connection layer, the second insulating layer, and the conductive layer, and do not pass through (or do not completely pass through) the first insulating layer. As another alternative, all windows can be formed by through-holes passing through all layers, wherein etching of the second connection layer and insulating capping on the second connection layer are used for the windows 1101 of the first insulating layer.

[0068] As with the previous example, some of the electrical connections 1108 that span portions of the insulating layer may not include HTS bridges (i.e., may be connected to Figure 7B The channel 703 is basically the same as that of the HTS, so as to further control the upper limit of the resistance of the part of the insulating layer when the HTS quenches.

[0069] Figure 12 The circuit diagram of the general partial insulation layer is shown in FIG. 1 , and the above description provides a specific example of the general partial insulation layer. The HTS coil 1201 is connected by two groups of resistors. The first group is a variable resistor R connected in series with a resistor R1. HTS Variable resistor R HTS represents the resistance of the HTS bridge and will depend on the critical current ratio I / I of the HTS C (i.e., when I / I C When the resistance is less than about 0.8, it will be very low, and as I / I c The larger the resistance increases, and when I / I C If it is greater than 1, the resistance will be very high.) R1 represents the resistance of the other conductive element in series with the HTS bridge.

[0070] The second set of resistances is resistance R2, which represents the resistance of the current path around the HTS. This can include current passing through any cladding or substrate of the HTS bridge (and through any series components), or other electrical connections that do not include the HTS (e.g., through some insulating layers). Figure 11B The current path of the connection 1108).

[0071] Although various examples of insulation within a partial insulation layer have been presented above (e.g. Figure 10 The insulation layer, Figure 6B 11 ), it should be understood that the unifying concept of these examples is a partial insulating layer having an "insulating region" through which multiple conductive paths are provided. This also includes other examples not described in detail herein, such as a vacuum or gas gap within a partial insulating layer, or a gap in a partial insulating layer that is later filled with epoxy (e.g., when the coil is epoxy-potted).

[0072] Partial insulation layers are incorporated into the HTS field coils in a manner that allows current to be shared radially between turns. For example, in a wound field coil, the partial insulation layers may be co-wound with the cable, while in a segmented field coil, the segments may be constructed from alternating layers of partial insulation layers and HTS cable (or other HTS current-carrying components). External electrical connections to the partial insulation layers (e.g., metallic connection layers, or ends of conductive paths) may be connected to the turns via solder, by simple contacts, or by any other suitable method.

[0073] In a segmented coil, part of the insulation layer may or may not continue within the joint between segments—that is, part of the insulation layer may extend all the way to the end of the segment (to match the corresponding layer of the other segment at the joint), the joint may include an insulating region that prevents current from bypassing the part of the insulation layer within the joint, or the joint may have a conductor that allows current to bypass the part of the insulation layer within the joint.

[0074] The HTS bridge can be distributed throughout the field coils, or can be used only during normal operation of the magnet to have a high I / I C areas (with a normal conducting current path through partial insulation provided outside those areas).

[0075] The HTS bridge can be made of similar HTS material as the excitation coil, or can be made of an HTS material with a reduced critical current and / or a higher critical temperature. Providing an HTS bridge with a reduced critical current and / or a higher critical temperature allows the characteristics of the HTS bridge to be controlled, specifically, how quickly they will become normally conductive when required. Variation of the critical current can be achieved by providing an HTS bridge with a reduced HTS cross-section (e.g., reduced width) compared to the HTS material used for the magnet coil, providing an HTS bridge made of an HTS material with stripes or other variations in the amount and / or distribution of the HTS material compared to the magnet coil, or providing an HTS bridge made of an HTS material with an inherently lower critical current per unit volume. Variation of the critical temperature can be achieved by providing an HTS bridge made of an HTS material with an inherently higher critical temperature, or controlling the oxidation level of the ReBCO HTS material used in the HTS bridge, as the oxidation level of ReBCO is directly related to the critical temperature.

Claims

1. A high-temperature superconducting (HTS) excitation coil, comprising: Multiple turns, including HTS material and metal stabilizers; a partial insulating layer separating the plurality of turns so that current can be shared among the plurality of turns via the partial insulating layer; The partial insulating layer comprises: Insulation area, a plurality of conductive paths passing through the insulating region, wherein current can be shared between the plurality of turns via the plurality of conductive paths; Each conductive path comprises an HTS bridge comprising HTS material, wherein the HTS bridge is connected in series with the normally conductive material of the conductive path.

2. The HTS excitation coil according to claim 1, wherein: Each HTS bridge includes a metal stabilizer and / or a substrate bonded to and connected in parallel with the HTS material.

3. The HTS excitation coil according to claim 1, wherein: The plurality of conductive paths are evenly spaced along the portion of the insulating layer.

4. The HTS excitation coil according to claim 1, wherein: The partial insulating layer further comprises a plurality of other conductive paths passing through the insulating region, wherein current can also be shared between the plurality of turns via the plurality of other conductive paths, wherein the plurality of other conductive paths do not comprise HTS material.

5. The HTS excitation coil according to claim 4, wherein: The plurality of conductive paths including the HTS bridge are arranged in a first region of the excitation coil, and the plurality of other conductive paths are arranged at least outside the first region, wherein in the first region, a ratio I / I between an operating current of the excitation coil and a critical current per turn of the excitation coil during operation of the magnet is c higher than said ratio outside said first region.

6. The HTS excitation coil according to 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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