High-temperature superconductor magnets

Abstract

To provide a method and a HTS magnet for inductively supporting a flying lead and moving it from a winding pack to a joining fixture.SOLUTION: A high temperature superconductor HTS magnet has a coil formed of nested concentric windings, and each of the windings includes an HTS material, the HTS magnet further has an electrical contact surface for supplying an electrical current to a portion of at least one of the windings, and the surface provides an electrical contact between a conductive element and an axial end of the coil approximately around the path of at least one of the windings.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present application relates to high-temperature superconductor (HTS) magnets. In particular, the present application relates to supplying current to HTS magnets. [Background Art]

[0002] Superconducting materials are generally divided into "high-temperature superconductors" (HTS) and "low-temperature superconductors" (LTS). LTS materials include materials such as Nb and NbTi, which are metals or metal alloys whose superconductivity can be described by BCS theory. All low-temperature superconductors have a critical temperature of less than about 30 K, above which the material loses its superconductivity even in zero magnetic field. The behavior of HTS materials cannot be described by BCS theory, and such materials can have a critical temperature exceeding about 30 K, provided it should be noted that HTS materials are defined not by critical temperature, but by physical differences in superconducting operation and composition. The most commonly used HTS are "cuprate superconductors", which are ceramics of cuprate systems, that is, compounds containing copper oxide groups, such as BSCCO or ReBCO, wherein Re is a rare earth element, usually Y or Gd. Other HTS materials include iron pnictides (e.g., FeAs and FeSe) and manganese diboride (MgB2).

[0003] ReBCO is typically manufactured as a tape having the structure shown in Figure 1. Such a tape 100 typically has a thickness of about 100 μm and has a substrate 101 (typically electropolished "Hastelloy" with a thickness of about 50 μm), on which a series of buffer layers, known as a buffer stack 102, with a thickness of about 0.2 μm, are deposited by IBAD, magnetron sputtering, or other preferred techniques. An epitaxial ReBCO-HTS layer 103 (deposited by MOCVD or other preferred techniques) is placed on top of the buffer stack, which is typically 1 μm thick. A silver layer 104 of 1-2 μm is deposited on the HTS layer by sputtering or other preferred techniques, and a copper stabilizing layer 105 (or "cladding") is deposited on the tape by electroplating or other preferred techniques. This often completely covers the tape. Current is typically coupled to the tape 100 through the cladding.

[0004] The substrate 101 provides a mechanical framework and is fixed through the manufacturing line, allowing for the subsequent growth of layers. The buffer stack 102 needs to provide a biaxially textured crystallization template on which the HTS layer grows, suppressing the chemical diffusion of elements from the substrate to the HTS, which affects its superconducting properties. The silver layer 104 needs to provide a low-resistance interface from the ReBCO to the stabilizing layer, and the stabilizing underlayer 105 provides an alternative current path in case any part of the ReBCO ceases to be superconducting (enters a "normal" state).

[0005] HTS magnets can be formed into coils using wound HTS tape, such as the ReBCO tape 100 mentioned above. A common problem with such HTS magnets is the portion where individual tapes or cables separate from the winding pack and enter the junction (i.e., electrical connection) area.

[0006] Figure 2 schematically shows a "conventional" electrical connection to a coil 201 having an HTS tape 100. The outer windings of the coil 201 are partially pulled away from the winding pack to form a "flying lead" 202. An electrical connection fixture 203 is installed on the flying lead 202 to supply current to the coil 201.

[0007] In flying lead connections as shown in Figure 2, the HTS tape is affected by repeated movement under electromagnetic (EM) force and thermal contraction, leading to degradation during normal operation. Furthermore, these "exposed" sections of the HTS tape are often at further risk because there are no adjacent HTS sections (winding sections) to share the current with during critical current degradation. This means that these sections do not benefit from proximity to the main winding pack for heat and / or current dissipation.

[0008] Furthermore, individual tapes are fragile and easily bend due to mishandling, making these flying lead areas vulnerable to damage during the magnetic winding and assembly process. In addition, the flying lead system often requires the fabrication of expensive, precisely machined parts to guide and support the flying leads and move them from the winding pack to the connecting fixtures.

[0009] Another problem that can occur with superconducting magnets is quenching. Quenching occurs when a portion of the superconducting wire or coil enters a resistive state. This can be caused by fluctuations in temperature or magnetic field, or by physical damage or defects in the superconductor (for example, by neutron radiation if the magnet is used in a melting reactor). Due to the high current present in the magnet, even a small portion of the superconductor becoming resistive will cause a rapid increase in temperature. As mentioned earlier, superconducting wires are provided with a copper stabilizer to protect against quenching. When the superconductor returns to its normal state, the copper provides an alternative path for the current. The more copper included, the slower the temperature rise at the hot spot that forms around the quenched conductor region. [Overview of the project] [Problems that the invention aims to solve]

[0010] Therefore, there is a need for HTS magnets that can avoid or mitigate some or all of these problems.

[0011] The object of the present invention is to provide an HTS magnet that addresses, or at least mitigates, the aforementioned problems. [Means for solving the problem]

[0012] In a first aspect of the present invention, an HTS magnet is provided. The HTS magnet is a coil formed of nested concentric windings, each winding comprising a coil having an HTS material and a conductor element having an electrical contact surface that supplies current to at least one portion of the winding. The surface provides an electrical contact between the conductor element and the axial end of the coil substantially around the at least one path of the winding.

[0013] Each winding comprises an HTS tape and a cladding electrically connected to the HTS tape, and the electrical contacts may be provided on the cladding.

[0014] The electrical contact surface may provide electrical contact to the shaft end of the coil over more than 20%, more than 50%, or more than 80% of at least one of the winding paths. The electrical contact surface may be ring-shaped.

[0015] The HTS magnet has a plate extending over one or more other windings, and the conductive element may be formed integrally with the plate or on top of the plate. The conductive element protrudes from the surface of the plate, and the plate may further have a dielectric layer or electrical resistance layer that electrically insulates the surface of the plate from one or more portions of the other windings.

[0016] In this application, the “electrical resistance” layer means a layer having an electrical resistance greater than the electrical resistance between the conductor element and the coil, and the electrical resistance between the windings of the coil (i.e., the radial electrical resistance of the coil). The electrical resistance layer may be thermoconductive, and therefore heat may be conducted more efficiently from (or to) the coil. The electrical resistance layer may or may not be a dielectric layer. A non-dielectric electrical resistance layer is preferred when the dielectric is subject to radiation damage, for example, when the coil is part of a tokamak fusion reactor.

[0017] The HTS magnet has an interfacial conductor layer extending over one or more other windings, and heat and / or current may be transferred from the windings or the ends of each winding. The interfacial conductor layer may be brass and / or stainless steel. Other “solderable” metals, i.e., metals to which solder adheres, may also be used to provide electrical contacts. The interfacial conductor layer may be patterned by varying its thickness, for example, to form a “spiderweb” pattern.

[0018] The coil may have an electrical insulator between the windings.

[0019] The HTS magnet may have one or more sensors and / or one or more heaters positioned between the plate and the coil.

[0020] The electrical contact surface may provide electrical contact to either the innermost or outermost winding of the coil. The electrical contact surface may provide discontinuous electrical contact across the windings. For example, if a coil is formed from two full-length HTS tapes, the electrical contact surface may function as an electrical junction connecting the tapes in series.

[0021] The HTS magnet may further have another conductive element, the conductive element having an electrical contact surface that receives current from another or at least one portion of the winding. The surface substantially provides electrical contact to the shaft end or another shaft end of the coil around another or at least one path of the winding.

[0022] The electrical contact surface may provide electrical contact to the opposing surface of the coil.

[0023] The HTS magnet further comprises one or more additional coils, each of which has a conductive element providing electrical contact to an opposing surface of the coil, and the coils may be stacked axially and electrically connected to each other via their respective conductive elements. The adjacent axially stacked coils may be wound in opposite directions.

[0024] The HTS magnet has two or more concentric nested coils, each having its own conductive element, and each coil may be electrically connected to an adjacent coil by an electrical connection between the conductive elements of the respective coils. The electrical connections may be flexible and adapt to the movement of the coils relative to each other. The HTS magnet may have one or more intervening supports positioned between adjacent coils to block radial forces.

[0025] Each HTS tape in adjacent coils may differ in thickness, composition, width, and number by one or more.

[0026] In a second aspect of the present invention, there is provided an HTS magnet comprising: first and second coils, each coil being formed of nested concentric windings, each winding comprising an HTS material; and first and second conductor elements, each conductor element providing an electrical connection between said coils. Each conductor element comprises: a first electrical contact surface across which current moves to or from at least a portion of at least one of said windings of the first coil; and a second electrical contact surface across which current moves to or from at least a portion of at least one of said windings of the second coil. Each surface substantially extends around at least a portion of the path of the winding to provide electrical contact between the respective conductor element and an axial end of the respective coil.

[0027] The electrical resistance of the electrical connection provided by the first conductor element divided by the electrical resistance of the electrical connection provided by the second conductor element may be greater than 1.5, greater than 3, or greater than 10. An area of the electrical contact surface of the second conductor element may be larger than an area of the electrical contact surface of the first conductor element.

[0028] The first conductor element may be arranged radially outwardly from the second conductor element. In this case, it becomes possible to arrange the first conductor element in a region of low magnetic field.

[0029] The first or second conductor element may comprise a variable resistor or a switch. The variable resistor or switch may comprise an HTS tape.

[0030] In a third aspect of the present invention, there provided a tokamak comprising the aforementioned HTS magnet. The HTS magnet is configured to provide a toroidal magnetic field or a poloidal magnetic field.

[0031] A fourth aspect of the present invention provides a method for forming a semi-sustaining current in the aforementioned HTS magnet. The method comprises the steps of preparing each of the coils in a superconducting state, connecting a power supply in parallel across the coils, and disconnecting the power supply.

[0032] The second conductive element may have an HTS material, and the method may include the step of switching the HTS material from a normal state to a superconducting state after the step of connecting a power supply in parallel across the coil.

[0033] A fifth aspect of the present invention provides a method for forming an electrical connection in an HTS magnet having a coil composed of nested concentric windings, wherein each winding is made of HTS material. The method comprises the steps of: installing a dielectric layer or an electrical resistance layer that partially covers the surface of the coil; installing a conductor plate on the dielectric layer or electrical resistance layer; and forming an electrical contact between the conductor plate and the axial end of the coil substantially around the periphery of the at least one path of the winding.

[0034] The method further comprises the step of placing an interfacial conductor layer between the dielectric layer or electrical resistance layer and the coil, wherein the interfacial conductor layer extends over one or more other windings and transfers heat or current from the windings or the ends of each winding.

[0035] A sixth aspect of the present invention provides a conductor plate for supplying current to the shaft end of a coil composed of nested concentric windings. The conductor plate has a ring-shaped conductor element formed integrally with the plate or provided on the plate. The conductor element has an electrical contact surface that provides electrical contact between the conductor element and the coil. The conductor element further has a dielectric layer or electrical resistance layer on the conductor plate that provides an electrical insulating barrier adjacent to the electrical contact surface.

[0036] The conductive plate may further have an interfacial conductive layer that extends partially or completely across the dielectric layer or the electrical resistance layer. The interfacial conductive layer is configured to transfer heat or current from the winding or the ends of each winding.

[0037] A seventh aspect of the present invention provides a method for manufacturing a conductor plate that supplies current to the shaft end of a coil composed of nested concentric windings. The method comprises the steps of: providing a ring-shaped conductor element integrally formed with or provided on the plate, wherein the conductor element has an electrical contact surface that provides electrical contact between the conductor element and the coil; and curing a fiber-resistance composite on the conductor plate to form a dielectric layer or electrical resistance layer on the conductor plate that provides an electrical insulating barrier adjacent to the electrical contact surface.

[0038] The curing step may include heating the composite to a target temperature, maintaining the composite at the target temperature for a predetermined time, and then cooling the composite.

[0039] The heating rate may be less than 1°C / min, preferably less than 0.3°C / min. The cooling rate may be less than 1°C / min, preferably less than 0.4°C / min. The target temperature may be 180°C or higher. The predetermined time may be more than 1 hour, preferably more than 2 hours.

[0040] Also described is a method for forming an electrical and / or thermal connection on a copper surface, the method comprising the steps of providing a layer of silver on the copper surface and providing a layer of indium on the silver surface, thereby forming an electrical and / or thermal connection in the indium layer. Also described is an electrical and / or thermal connection having a copper surface, a layer of silver, and a layer of indium, the layer of silver being placed directly between the copper surface and the layer of indium. [Brief explanation of the drawing]

[0041] [Figure 1] This is a schematic perspective of conventional HTS tape technology. [Figure 2] This is a schematic front view of a conventional flying lead joint. [Figure 3A] This is a schematic front view of the HTS magnet. [Figure 3B] This is a schematic front view of the HTS magnet. [Figure 4] This is a schematic cross-sectional view of an HTS magnet. [Figure 5] This is a schematic cross-sectional view of an HTS magnet. [Figure 6] This is a schematic radial cross-sectional view of an HTS magnet with radial connections. [Figure 7] This is a schematic radial cross-sectional view of an HTS magnet having multiple "stacked" coils. [Figure 8] This is a schematic cross-sectional view of another HTS magnet. [Figure 9] Figure 8 is a schematic cross-sectional view of the HTS magnet, illustrating the current flowing through the magnet when the power supply is connected in parallel across the coil. [Figure 10] Figures 8 and 9 are schematic cross-sectional views of the HTS magnet, illustrating the current flowing through the magnet when the power supply is cut off. [Modes for carrying out the invention]

[0042] This invention proposes a solution to the aforementioned problems. An electrical connection is made to the HTS magnet coil through the axial end of the coil. Thus, current is supplied or received through the surface of the coil. In this form of connection, the dense winding pack of the HTS tape is protected, and no part of the HTS tape is separated from the coil. For example, the electrical connection is provided by a ring-shaped conductor positioned on the upper surface of the coil, and the conductor is in contact with the upward-facing end of the winding around the outer circumference of the coil. By using this arrangement or “ring joint”, the risk of magnet failure can be minimized both during assembly and operation. In addition, current can be supplied from or extracted from the HTS coil without requiring flying leads, the need for many auxiliary parts is eliminated, the cost and complexity of the HTS magnet are reduced, and manufacturing is simplified. Furthermore, as will be shown below, such a connection or joint improves the properties of the HTS magnet.

[0043] In this application, certain directions (e.g., up, down) or relative terms (e.g., top, upper side, lower, etc.) are referred to, but it should be understood that these terms are used solely for the purpose of providing examples of the concepts described herein. Similarly, in this disclosure, a “pancake” coil is used exemplary, i.e., a large flat coil formed of nested concentric windings, but it will be understood from the following discussion that this disclosure is not limited to such coils.

[0044] Furthermore, the integration of ring joints into larger structures (hereinafter referred to as the electrical-thermal interface "ETI" plate) allows for the provision of thermal connections, electrical insulation, and sensors—which are often traditionally installed separately on magnets—as a single unit. This simplifies the assembly process and makes it possible to manufacture these components independently of the HTS coil.

[0045] Figures 3A and 3B show schematic front views of two hypothetical embodiments of the ring joints 300A and 300B for the pancake coil 301.

[0046] Coil 301 has nested concentric windings of HTS tape 100, mostly arranged flat. The HTS tape 100 is wound "facing each other," and the opposing ends of the tape 100 protrude along the coil axis 303. Each complete winding corresponds to a complete rotation of the HTS tape 100 around the coil axis 303. The start and end points of the outermost windings are encoded as 301A and 301B in Figure 3A.

[0047] The ring joints 300A and 300B are formed by the respective ring conductors 304A and 304B. For clarity in showing the coil windings, for example, the ring conductors 304A and 304B are shown behind the coil 301. Each ring conductor 304A and 304B has a ring or ring made of a conductive material, preferably a metal such as copper. The ring conductors 200A and 200B contact the upper and lower ends of the windings, providing an electrical connection to the coil 201. Ring conductor 300A is positioned in the outer diameter of the coil 201, while ring conductor 200B is positioned in the inner diameter of the coil 201.

[0048] Each ring conductor 200A, 200B covers only a portion of the winding, so that current can be supplied to one end of coil 201 and thus circulate through the winding.

[0049] The ring conductors 300A and 300B each provide electrical contacts to different ends of the HTS tape 100, and they may be used as a pair to drive current radially from the outside to the inside (or vice versa) of the coil 301. For example, the coil 201 is provided (sandwiched) between the pair of ring conductors 304A and 304B to generate a magnetic field, so that current is supplied by one ring conductor 304A to one side (e.g., the top) of the coil 301 and flows through the windings of the coil 301. Then, the current is received by the other ring conductor 304B from the other side of the coil.

[0050] The selection of the radial width of the ring conductors 304A and 304B involves a trade-off between the number of turns between the junctions and the connection resistance. The connection resistance decreases by widening the ring conductors 304A and 304B, covering more turns of coil 301. However, this results in a decrease in the magnetic field generated by the magnet per unit current, because the number of turns carrying the complete magnetic current decreases. The reverse is also true when the radial width decreases.

[0051] Because the ring joint allows for a length on the order of the coil's circumference, a low-resistance connection is typically constructed using radially narrow ring conductors 304A and 304B, which do not significantly reduce the magnetic field generated by the magnet. In Figures 3A and 3B, the ring conductors 304A and 304B are shown to extend slightly outside the outer / inner ends of the coil 301. Alternatively, the shape of the ring conductors may be matched to closely resemble the radial profile of the coil 301, thereby minimizing the radial area of ​​the coil 301 and the ring joints 300A and 300B.

[0052] While Figures 3A and 3B use annular "pancake" coils to illustrate the characteristics of ring joints 300A and 300B, it is readily apparent that these types of joints may be applied to other coil shapes, such as "D" type toroidal magnetic field coils used in tokamaks. In such cases, the ring joints 300A and 300B do not need to be annular and may be shaped to follow the path of the coil winding. Similarly, the "ring conductors" 304A and 304B do not need to extend completely around the path of the coil winding; instead, they may extend only partially around the path of the coil winding. For example, in the case of magnets with large radii and / or thick HTS tape, it may be possible to form a low-resistance joint using ring conductors that extend only 20%, 50%, or 80% around the path of the winding. That is, the ring conductor may be defined by angles less than 360°. By introducing a "break" in the ring conductor (by preventing it from extending completely around the winding path), the formation of parasitic current loops within the ring conductor may be preferentially avoided. This is beneficial for applications such as nuclear magnetic resonance (NMR) or magnetic resonance imaging (MRI). In other applications, morphological constraints and / or the presence of other components, such as a tokamak (see below), may be required for such a break.

[0053] The ring joint may also be provided as part of a larger structure, which may be referred to as a conductive plate or electrical-thermal interface (ETI) plate. The ETI plate is typically a composite metal / insulator / sensor plate and is mounted to the end face of the HTS coil, performing several functions, as shown below: Means for forming electrical connections to and / or between HTS coils. A means of achieving "partial isolation" by introducing a control register in parallel with the HTS coil. The shape of the register is determined to adjust the dynamic electrical-thermal behavior of the coil. • Means for forming a thermal interface with the HTS coil for cooling. A means of introducing a thin electrical insulating layer between HTS coils and mechanically protecting the insulating layer from damage. A means of incorporating an accessory (sensor or heater) into an HTS magnet without interfering with the HTS winding.

[0054] Figure 4 shows a cross-section of an example magnet 400. The magnet has two ETI plates 400A and 400B mounted on a single pancake coil 401. In this example, the coil 401 has two full lengths of HTS tape 100 wound around each other around the magnet shaft 303. The tape 100 is a copper cladding as “type 0 set” (as described, for example, in WO2018 / 078326), and each winding has two tapes. An insulator 402 is provided between the windings of the HTS tape 100 to prevent current from flowing across the surface of the HTS tape. That is, current injected into one end of the HTS tape 100 is forced to circulate through the windings of the coil 401. The ETI plates 400A and 400B each have their respective ring conductors 404A and 404B, forming a ring joint at one end of the HTS tape 100. In this example, current is supplied to coil 401 via the bottom ETI plate 400B through the innermost radial end of the HTS tape 100. The current flows through a ring conductor 404A, around a series of windings in coil 301, before being received by the upper ETI plate 400A at the outermost radial end of the HTS tape 100.

[0055] The ETI plates 400A and 400B are electrically in contact with the coil 401 only through the ring conductors 404A and 404B, but the plates themselves extend radially across the coil, forming "base conductor" layers 405A and 405B, through which current is supplied to (or received from) the ring joint and a path is provided for heat conduction from the coil 301. In this example, the base conductors 405A and 405B are made of copper, but other conductive materials (e.g., metals) can also be used. The ring conductors 404A and 404B may be formed integrally with the base conductors 405A and 405B, or they may be fixed to them, for example, by solder.

[0056] By forming the ring conductors 404A and 404B on (or integrated with) the ETI plates 400A and 400B, they can be made extremely narrow in radial dimensions (sub-mm if necessary) while still remaining easy to handle. This is difficult to achieve if the ring conductors are independent components. The large surface area provided by the base conductors 405A and 405B allows heat to be efficiently dissipated from the coil 401, making it possible to arrange the electrical connection with the magnet more flexibly.

[0057] The base conductors 405A and 405B in the ETI plates 400A and 400B can be made thin to minimize the temperature rise across them. To avoid a weakening of the magnetic field strength, the coils can be made not to be spaced too far apart axially. Alternatively, heat can be easily extracted to a cooling bath at the outer or inner diameter of the coil 401, in which case the base conductors 405A and 405B need to be formed thick enough to meet the temperature requirements. The ETI plates 400A and 400B may also be structured so that one or more faces of the coil 401 are cooled sufficiently effectively (i.e., not relying on heat conduction at the radial ends of the coil). For example, the ETI plates 400A and 400B may have channels or pipes through which a gas or liquid coolant flows and heat is transferred away from the coil 401. Preferably, the channels or pipes may be provided on or inside one or more of the base conductors 405A and 405B.

[0058] The use of cooling ETI plates 400A and 400B provides an alternative approach to methods using thermal conductive pastes. Thermal conductive pastes have inferior thermal conductivity compared to solder, are difficult to apply suitably to thin layers, and complicate the manufacturing process.

[0059] Furthermore, the ETI boards 400A and 400B have dielectric layers 406A and 406B, which electrically insulate the ends of the HTS tape 100 from the base conductor portions 405A and 405B of the board. The dielectric layers 406A and 406B are composed of a dielectric material, such as a glass fiber / resin composite, like a "prepreg".

[0060] Furthermore, the ETI boards 400A and 400B have interfacial conductor layers 407A and 407B, which can be soldered to the coil 401 for superior thermal and electrical contact. This layer acts as a radial resistor, controlling the thermal and electrical behavior of the coil 401. The introduction of such “partial insulation,” i.e., a controlled “turn-to-turn” resistor, provides a desired balance between thermal stability and coil ramp time in the HTS coil. The interfacial conductor layer is composed of a conductive material, preferably brass or steel, because these materials can be soldered and have a higher electrical resistivity than copper. This allows for thicker layers, and thus makes it easier to control the thickness. The introduction of such “partial insulation,” (PI), i.e., a controlled “turn-to-turn” resistor, provides a desired balance between thermal stability and coil ramp time in the HTS coil. In particular, the use of a layer extending across the coil windings eliminates the need for other forms of partial insulation and the need for a “wrap-around” layer of metal such as stainless steel.

[0061] In some cases, the interfacial conductor layers 407A and 407B are bonded to the dielectric layers 406A and 406B by an adhesive. However, the adhesive must withstand the soldering temperature without being structurally weakened. Otherwise, the layers tend to delaminate during soldering. One way to solve this problem is to use a glass fiber / resin composite, such as a "prepreg," as both the dielectric and bonding medium. For example, a composite such as "Prepreg MTC400" manufactured by "SHD Corporation" can be used. By performing a relatively long curing process, the glass transition temperature (T) of the composite can be reduced. g This allows the soldering temperature to be higher than that of a normal coil. For example, the composite may be “post-cured” by heating to 180°C at a rate of approximately 0.3°C / min, holding for 2 hours, and then cooling at a rate of 0.3°C / min. In this procedure, for example, 200°C T gThis allows the composite to withstand most soldering processes that occur at lower temperatures. However, performing such a curing process in-situ on the ETI board on the coil can be difficult because the heating temperature and time can damage the coil (due to the continuous degradation of the HTS tape, which occurs as a function of temperature and time), potentially damaging or degrading any already formed solder joints.

[0062] However, it is also possible to enhance the "turn-to-turn" resistance effect by using non-insulated coils and blocking the alternative low-resistance path between windings through the copper cladding of the HTS tape 100 by including insulator 402.

[0063] The thickness of ETI plates 400A and 400B (i.e., the total thickness including the ring conductor) is typically in the range of 0.25 to 1.00 mm, the thickness of the dielectric layer (if present) is typically in the range of 10 to 100 μm, and the thickness of the interface conductive layer (if present) is typically in the range of 10 to 100 μm.

[0064] The solder used to join the interface layers 407 and 407B to the windings of the coil 401 is typically PbSn. However, this material is highly conductive, and even a thin coating of PbSn on the interface layers 407A and 407B provides a sufficiently low-resistance current path, causing the current to bypass the interface layers 407A and 407B. To avoid this problem, the solder material is selected from those with high resistivity, preferably having a higher resistivity than PbSn. For example, when the coil is used as a magnet at a temperature lower than the critical temperature of the ReBCO tape, a solder material with a resistivity 10 times or more that of PbSn is preferred. For example, the solder material may be composed of PbBi, which has a resistivity about 50 times greater than PbSn. Similarly, PbBiSn can also be used. Compared to PbSn solder coatings, high resistivity solder with PbBi (or PbBiSn) coatings means that more current flows within the interface layers 407A and 407B.

[0065] Partially insulated ETI boards often have the advantage of high flexibility. Turn-to-turn resistance can be controlled by the thickness and composition of the interface conductor. To block inductive spirals that provide long-range radial current or impedance, the shape of the interface conductor layer can be modified by using lithography, such as etching a subdivided spiderweb pattern. In any of these cases, a balance can be achieved between charging time and thermal-electrical stability.

[0066] Thin electrical insulation between pancake coils is preferable because it provides the necessary dielectric properties without causing a large temperature rise due to the heat flowing through it. However, many common dielectric materials (such as polyimide sheets) are soft and therefore susceptible to breakage under electromagnetic stress during magnet operation and assembly. The risk of breakage is minimized by embedding an insulator inside the ETI plate and protecting the insulators on both sides with metal sheets.

[0067] Since the ETI plate is a separate component from the coil, it can be substituted to alter the coil's behavior. For example, initially, an ETI plate with a thick interfacial conductor layer may be installed to safely operate the coil and define its critical current. Once the maximum operating current is determined, the ETI plate can be changed to one that provides the ability to ramp the magnet more quickly within the known characteristic range of the magnet.

[0068] Figure 5 shows a cross-section of the magnet 500. The magnet 500 has two axially stacked magnets 400, each having pancake coils 401A and 401B. The thermal and electrical connection between coils 401A and 401B is achieved after stacking by connecting the base copper layers of adjacent ETI boards 402A and 402B to each other. This can be done by pressing the magnets 400 axially (i.e., along the axis 503 of the magnets) and, if necessary, by adding an elastic conductive layer 504, such as an indium layer, between the magnets 400, or by soldering (although this requires heating the entire magnet). Alternatively, "NanoBond" (RTM) technology may be used, in which a multilayer foil is inserted between the ETI boards 402A and 402B, a chemical reaction is initiated within the foil, heat is generated, and the foil is soldered to each of the boards.

[0069] Since the thermal and / or electrical connection between adjacent ETI plates 402A and 402B is effective, the surface condition of the plates is preferably good, for example, free of oxides. One way to achieve this is to provide a base copper layer of ETI plates 402A and 402B having a layer (e.g., coating) of a noble metal such as silver. The silver layer is preferred because silver has a low affinity for oxygen and is chemically comparable to indium. In this case, a flexible indium layer 504 is used to form a high-quality pressed joint.

[0070] Additional plates 505A, 505B, such as copper plates, may be provided at either axial end of the magnet 500 to provide additional cooling or electrical connections to the magnet 500.

[0071] A power supply (not shown) is connected across plates 505A and 505B to supply current to the magnet 500. In this example, the ring joints for each face of the magnet are located at the outermost radial ends of the coils, while the ring joint connecting the two coils is located at the innermost radial ends of the coils. Thus, the current flows radially inward through one winding of the coil, then axially between the coils, and then radially outward through the winding of the outer coil. As current flows in opposite directions through each coil, coils 401A and 401B are wound in opposite directions (i.e., clockwise / counterclockwise), and as a result, the magnetic fields generated by each of the magnets 400 have the same polarity, thereby generating a sufficiently large magnetic field. For example, coils 401A and 401B are prepared similarly (i.e., wound in the same direction), and one coil is "reversed" relative to the other before stacking to form the magnet 500. With this method, it is clear that another ETI board can be placed between them to stack another pancake coil.

[0072] As mentioned above, the ETI plates may have channels or pipes through which gas or liquid flows and heat is transferred from the coils. Such arrangements are particularly effective for cooling magnets 400 stacked in the axial direction, as shown in Figure 5. In particular, by providing cooling channels or pipes to the ETI plates 402A and 402B placed between the coils, heat can be effectively transferred from the "bodies" of the coils 401A and 401B.

[0073] Furthermore, an electrical connection can be formed between nested / concentric pancake coils using a ring conductor in the ETI board. That is, as mentioned above, a joint can be formed that carries current radially rather than axially. For example, the pancake coil may be expanded by winding a second length of HTS tape around it. In this case, an electrical joint can be formed between the ends of two HTS tapes, preferably in the ETI board, using a ring conductor. That is, the ring conductor is used to provide a joint that crosses a discontinuity or break in the winding. An example where this is beneficial is stress reduction in deep coils (when the value of outer diameter divided by inner diameter is large, for example, greater than about 3 times). In such situations, it is beneficial to subdivide the coil into multiple nested coils and isolate the forces generated by each to suppress stress accumulation in the winding. In this case, the radial connection between the nested coils can be made by a suitable ring conductor in the ETI board.

[0074] Figure 6 shows a radial cross-section of the HTS magnet 600. The HTS magnet 600 has two ring conductors 604A and 604B, providing a radial connection between the inner coil 601 and the outer coil 602. A mechanical support 607, such as a cylinder, is provided between the inner coil 601 and the outer coil 602 to block the radial forces between them.

[0075] Figure 7 shows a radial cross-section of the HTS magnet 600. The HTS magnet 600 is compact, robust, and capable of generating a straight, high-power magnetic field.

[0076] The HTS magnet 700 has radially nested stacks 701, 702, and 703 of the aforementioned HTS magnet 400. For example, the outermost radial stack has HTS magnets 400A to F arranged axially, and adjacent magnets are electrically connected via their ETI plates. The ring joints formed by the ETI plates are arranged so that current flows alternately between axial flow (between adjacent coils) and radial flow (around the windings of each coil), which is represented by the arrows superimposed on the HTS magnets 400A to F in Figure 6. In the case of the HTS magnet 400 as shown with reference to Figure 4, the coils of adjacent magnets are wound in opposite directions, and the magnetic field along the axis 704 of the magnet is maximized. The other two nested magnet stacks 702 and 703 have a similar configuration and reinforce the magnetic field generated by the outer stack 701. Radial junctions / connections 705 and 706 are formed between the terminal ETI plates of adjacent stacks, allowing current to flow from one stack to the next. In the example shown in Figure 6, the current is supplied to magnet 700 through the upper ETI plate of the HTS magnet 400A at the top of the outer stack 701. As previously mentioned, after the current flows through stack 701, it flows radially through junction 705 and enters the outer nested stack 702. Similarly, after flowing through this stack 702, the current flows radially and enters the inner nested stack 703 through junction 706. Finally, after the current flows through the inner nested stack 703, it is derived from magnet 700 through the bottom ETI plate of the HTS magnet at the bottom of the inner nested stack 703.

[0077] In the example magnet 700 shown in Figure 7, there are three stacks 701, 702, and 703, each having six HTS coils. However, of course, any number of stacks and / or coils can be used. Furthermore, the stacks may have different numbers of coils, providing even greater flexibility in the magnet design.

[0078] Composing the HTS magnet 700 from many small HTS magnets ("coil subdivisions") offers numerous advantages. In particular, as shown below, coil subdivisions overcome challenges related to stress limitations in the HTS tape, and the "grading" of the subdivision coils by their arrangement within the magnet 700 enables a more optimal magnet design.

[0079] Considering the stress limitations of the HTS tape, the maximum allowable lateral tensile strength of the HTS tape 100 is typically around 10-50 MPa, which provides a practical limit to the radial depth of the winding that can be used. However, this problem can be avoided by coil subdivision, which subdivides the coil into several radially nested coils, as shown in Figure 7, and by introducing mechanical supports 707, 708 between the coils. Similarly, axial forces can be blocked by subdivision along the axis of the magnet and by introducing axial support structures (not shown).

[0080] When considering the "grading" of sub-split coils, in high-field magnets, the magnetic field vector can vary significantly depending on the radial and / or axial arrangement of the magnets. In the case of HTS magnets, this means that parameters that characterize the operation of the magnet as a superconductor, such as critical current, also depend on the arrangement. Therefore, the optimal design of the magnet 700 can be obtained by grading the HTS tape 100 according to the arrangement of the magnets. For example, when achieving the maximum magnetic field, and in the case of quench magnets, it is desirable to maximize the ratio of current to critical current (gamma) (I / Ic) at all points in the magnet. Grading can be done by changing the number of HTS tapes per unit rotation / turn, the tape width or thickness, or the tape type (i.e., manufacturer or HTS material used).

[0081] Often, for monitoring purposes, it is necessary to embed sensors (such as temperature or strain probes) in the HTS magnet. Additional components, such as heaters, may be required for rapid cooling protection. It is desirable that the HTS coil and its associated components are separate parts, and that in case of failure, the two be manufactured separately and replaceable individually. Suitable ETI boards can be manufactured to accommodate multiple sensors or other components that do not need to be directly embedded in the HTS coil windings.

[0082] Figure 8 shows a cross-section of the HTS magnet 800. This magnet is similar to the HTS magnet 500 shown in Figure 5, but differs in that each of the adjacent ETI plates 801A and 801B has inner ring conductors 804A and 804B, and outer ring conductors 805A and 805B.

[0083] As shown in Figure 9, the introduction of two ring conductors on each plate provides two alternative paths 908, 909 for the current flowing through the magnet 800 when the power supply 907 is connected to the set of coils. One path 908 is the same as the path described with reference to Figure 4, i.e., the current flows around the windings of each coil 400 via the inner ring conductors 805A, 805B. The other path 909 “shorts out” or bypasses path 908 by providing an electrical connection between the outer windings of the coils 400. In this case, the current flows through the outer windings to one of the coils 400 and is led out of the coil via the outer ring conductor 804B instead of passing around the other winding of the coil. Similarly, the current flows through the outer ring conductor 804A through the outer winding of the other coil, between their axial ends, and is led out of the coil without passing around the other winding of the other coil.

[0084] The proportion of current flowing along each path 908, 909 is governed by the relative electrical resistance of the paths, which can be controlled by changing the electrical resistance of the outer and inner ring conductors 804A, 804B, 805A, 805B, and / or the electrical resistance of the electrical contacts formed by the ring conductors with respect to the windings of coil 400. By making the electrical resistance of the direct path 909 greater than that of the roundabout path 908, most of the current can flow to and from coil 400 radially, making the longer, roundabout path 908 more significant than the shorter, direct path 909. This is achieved, for example, by forming an area of ​​the outer ring conductors 804A, 804B that is smaller than the area of ​​the inner ring conductors 805A, 805B. Even if a small leakage current flows through path 909 and does not contribute to the magnetic field generated by the circulation of current through the windings of coil 400, coil 400 is charged to a full critical current in the inner winding, and any additional leakage current is carried by the outer winding because it has a high critical current in this low magnetic field region. Once magnet 800 is charged, power supply 907 is disconnected, and current flows around coil 400 in a closed loop.

[0085] Figure 10 shows the path 1010 of the "trapped" current flowing through the magnet 800 after the power supply 907 is disconnected. In this case, the current flows through the windings of coil 400, around the closed loop, and through each of the ring conductors 805B, 805A, 804A, and 804B. Because coil 400 is superconducting, the current can flow around path 1010 for a long period of time until it decays, i.e., it becomes a circulating current, and the magnetic field formed by it becomes "semi-persistent".

[0086] The time constant for the decay of circulating current is determined by the ratio (L / R) of the coil's magnetic self-inductance (L) to its electrical resistance (R). For example, consider a magnet with a coil having an inner diameter of 50 mm and an outer diameter of 98 mm. The self-inductance is ~2 mH, and the electrical junction typically has a resistance of approximately 1~5 nΩ under liquid nitrogen (i.e., an estimated combined resistance of ~10 nΩ for the inner and outer electrical junctions). The L / R time constant for this magnet is approximately 200,000 seconds, or 2.3 days.

[0087] Furthermore, a large time constant relates to a large "charging" time, i.e., the time it takes for a steady-state current distribution to be established between paths 908 and 909 when the power supply is connected. To minimize the charging time, it is beneficial to increase the resistance of path 908 during charging (i.e., the configuration shown in Figure 9). This can be achieved by a variable resistor or switch introduced into the outer electrical junction provided by the outer ring conductors 804A and 804B. For example, an HTS switch having HTS material may be provided between the outer ring conductors 804A and 804B. During charging, the switch is "off" (non-superconducting state), providing a large resistance, which in turn allows for rapid charging. This can be achieved, for example, by heating the HTS material to a temperature above its critical temperature. The switch is then switched "on" (e.g., no further heating or cooling), closing the current path 1010 and disconnecting the power supply.

[0088] One important application of the aforementioned HTS magnets is a type of fusion reactor known as a tokamak. A tokamak is characterized by a strong toroidal magnetic field, a high plasma current, and a combination of a large plasma volume and large preheating, which provides a hot, stable plasma. This allows the tokamak to create the conditions under which nuclear fusion can occur. Preheating (e.g., by injecting a tens of megawatts of high-energy hydrogen, deuterium, or tritium neutron beam) is necessary to raise the temperature to a sufficiently high value required for fusion to occur and / or to maintain the plasma current.

[0089] The magnet coils of a tokamak can be divided into two groups. The poloidal field coil is a horizontal circular coil wound so that its center rests on the tokamak's central column, forming a poloidal field (i.e., substantially parallel to the central column). The toroidal field coil is wound perpendicularly through the central column and around the outside of the plasma chamber ("return rim"), forming a toroidal field (i.e., circulating around the central column). The combination of the poloidal and toroidal fields creates a helical field within the plasma chamber, which maintains the confined plasma.

[0090] The current required to form a toroidal field is extremely large. Therefore, the use of superconducting materials in the magnetic field coils is increasing in tokamak design. In small spherical tokamaks, the diameter of the central column must be as small as possible. This presents a conflicting requirement, as even superconducting materials have limits to the current density they can achieve.

[0091] The HTS material described herein is particularly suitable for use in tokamaks, especially spherical tokamaks, when forming either (or both) a poloidal field or a toroidal field.

[0092] As described above, various embodiments of the present invention have been explained, but it is important to understand that these are for illustrative purposes only and not to limit the invention. It will be apparent to those skilled in the art that various modifications of form and detail can be made without departing from the spirit and scope of the invention. For example, although the coil described above has an HTS tape 100 arranged in a "Type 0" configuration, other configurations such as "Type 1" and "Type 2" can also be used (for example, described in International Publication WO2018 / 078326). Similarly, in the above example, the coils are connected substantially in series across the power supply, but the coils can also be connected in parallel across the power supply. Accordingly, the present invention is not limited to any of the embodiments described above, but is defined solely by the appended claims and their equivalents.

Claims

1. A conductive plate that forms an electrical connection on the axial surface of a coil composed of nested concentric windings, Each winding contains high-temperature superconductor, HTS material. The conductor plate is, The base conductor layer, A conductor element integrally formed with the base conductor layer, or a conductor element disposed on the base conductor layer, having an electrical contact surface that provides electrical contact between the conductor element and the coil, An interfacial conductor layer that transmits heat and / or current from the coil, A dielectric layer or electrical resistance layer disposed on the surface of the base conductor layer between the base conductor layer and the interface conductor layer, wherein the dielectric layer or electrical resistance layer electrically insulates the interface conductor layer from the conductor element and the base conductor layer, and provides an electrical insulation barrier adjacent to the conductor element and the electrical contact surface, A conductive plate having [a certain characteristic].

2. The conductive plate according to claim 1, wherein the dielectric layer or electrical resistance layer is formed from a composite material of fibers and resin.

3. The conductive plate according to claim 2, wherein the composite material has a prepreg.

4. The conductive plate according to claim 2, wherein the composite material has a glass transition temperature higher than 150°C.

5. Furthermore, the base conductor layer has a silver layer, The conductor plate according to claim 1, wherein the silver layer and the dielectric layer or electrical resistance layer are located on both opposing axial surfaces of the base conductor layer.

6. The conductor plate according to claim 1, wherein the base conductor layer contains copper.

7. The conductor plate according to claim 1, wherein the conductor element has a ring-shaped conductor element.

8. The conductive plate according to claim 1, wherein the interfacial conductive layer includes a solderable metal.

9. The conductive plate according to claim 8, wherein the solderable metal includes brass and / or stainless steel.

10. The conductive plate according to claim 1, wherein the interfacial conductive layer is patterned by varying its thickness.

11. High-temperature superconductor (HTS) magnet, A coil formed by nested concentric windings, where each winding has HTS material, A conductive plate according to any one of claims 1 to 10, which is in contact with the axial surface of the coil, HTS magnets.

12. Furthermore, the HTS magnet according to claim 11, further comprising a second conductive plate according to any one of claims 1 to 10 that contacts the axial surface opposite to the coil.

13. A method for forming electrical contacts in a coil composed of nested concentric windings, wherein each winding comprises a high-temperature superconductor, an HTS material, This method is The steps include: applying an interfacial conductor layer so as to partially cover the axial surface of the coil, wherein the interfacial conductor layer is configured to transmit heat and / or current from the coil; The steps include: placing a dielectric layer or an electrical resistance layer on the interface conductor layer; The steps include: installing a base conductor layer on the dielectric layer or electrical resistance layer; It has, The base conductor layer comprises a conductor element integrally formed with the base conductor layer, or a conductor element disposed on the base conductor layer, and an electrical contact surface that provides electrical contact between the conductor element and the coil. A method comprising: the dielectric layer or electrical resistance layer being disposed on the surface of the base conductor layer between the base conductor layer and the interface conductor layer, electrically insulating the interface conductor layer from the conductor element and the base conductor layer, and providing an electrical insulating barrier adjacent to the conductor element and the electrical contact surface.

14. The method according to claim 13, further comprising the step of curing a composite of fibers and resin between the base conductor layer and the interface conductor layer to form a dielectric layer.

15. A method for forming an electrical connection in a coil composed of nested concentric windings, Each winding contains high-temperature superconductor, HTS material. This method is A step of obtaining a conductor plate according to any one of claims 1 to 10, The steps include: installing the interface conductor layer and the electrical contact surface of the conductor plate on the axial plane of the coil; A method having.

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