High temperature superconductor field coil

Abstract

A method of manufacturing a high temperature superconductor (HTS) field coil from one or more HTS tapes. Each HTS tape includes a layer of HTS material. The method includes: winding the one or more HTS tapes around an axis to form a field coil including windings of HTS tape; and removing material from an axial edge of one or more of the HTS tapes around at least a portion of one or more of the windings to reduce a range of the one or more HTS tapes along the axis of the field coil.

Description

[0001] This application is a divisional application of application number 202180032673.3, which entered the national phase on November 2, 2022, and has the subject matter of "high temperature superconductor field coil". Technical Field

[0002] This invention relates to high-temperature superconductor (HTS) field coils. In particular, this invention relates to HTS field coils comprising HTS strips. Background Technology

[0003] Superconducting materials are typically classified into "high-temperature superconductors (HTS)" and "low-temperature superconductors (LTS)." LTS materials, such as Nb and NbTi, are metals or metal alloys whose superconductivity can be described by BCS theory. All low-temperature superconductors have a critical temperature below approximately 30 K (above this temperature, the material cannot superconduct even in a zero magnetic field). The behavior of HTS materials is not described by BCS theory, and such materials can have critical temperatures above approximately 30 K (although it should be noted that HTS and LTS materials are defined by the physical differences in composition and superconducting operation, not the critical temperature). The most commonly used HTS material is the "cuprate superconductor"—a ceramic based on cuprates (compounds containing copper oxide groups), such as BSCCO or ReBCO (where Re is a rare earth element, typically Y or Gd). Other HTS materials include iron pnictides (e.g., FeAs and FeSe) and magnesium diboride (MgB2).

[0004] ReBCO is typically manufactured as strips, having properties such as Figure 1The structure is shown. Such a strip 100 is typically about 100 micrometers thick and includes a substrate 101 (typically an electropolished nickel-molybdenum alloy, such as Hastelloy™, about 50 micrometers thick), on which a series of buffer layers (referred to as buffer stacks 102) of about 0.2 micrometers thick are deposited by ion beam assisted deposition (IBAD), magnetron sputtering, or other suitable techniques. An epitaxial ReBCO-HTS layer 103 (deposited by metal oxide chemical vapor deposition (MOCVD) or other suitable techniques) covers the buffer stack and is typically 1 micrometer thick. A silver layer 104 of 1 to 2 micrometers 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. A silver layer 104 and a copper stabilizer layer 105 are also deposited on the sides of the strip 100 and the substrate 101, such that these layers extend continuously around the strip 100, thereby allowing electrical connection from either side of the strip 100 to the ReBCO-HTS layer 103. Therefore, these layers 104 and 105 can also be referred to as "cladding". Typically, the silver cladding has a uniform thickness of about 1 to 2 micrometers on both sides and edges of the strip. Providing a silver layer 104 between the HTS layer 103 and the copper layer 105 prevents the HTS material from contacting copper, which could lead to copper poisoning of the HTS material. For clarity, in Figure 1 Parts of the silver layer 104 and the copper stabilizer layer 105 on the side of the strip 100 are not shown, but in Figure 9 This section is shown in the cross-sectional view provided. Figure 1 The silver layer 104 extending beneath the substrate 101 is also not shown, which is the conventional case (see, for example, [reference]). Figure 9 The silver layer 104 forms a low resistivity electrical interface with the ReBCO layer 103 and forms a hermetically protected seal around the ReBCO layer 103, while the copper layer 105 enables external connection to the strip (e.g., allows soldering) and provides a parallel conductive path for electrical stability.

[0005] Substrate 101 provides a mechanical backbone that can be fed via fabrication lines and allows for the growth of subsequent layers. Buffer stack 102 provides a biaxially textured crystal template on which the HTS layer is grown and prevents chemical diffusion of elements from the substrate into the HTS, which would impair the superconducting properties of the HTS. Silver layer 104 provides a low-resistance interface from ReBCO-HTS layer 103 to stabilizer layer 105, and stabilizer layer 105 provides an alternative current path in the event that superconductivity ceases at any point in the ReBCO (enters a "normal" state).

[0006] In addition, “stripped” HTS strips can be manufactured, which lack a substrate (e.g., a Hastelloy™ substrate) and buffer stack, but typically have a silver “surround coating”—a layer on both sides and at the edges of the HTS layer. Strips with a substrate will be referred to as “substrate-backed” HTS strips.

[0007] HTS strips can be arranged in HTS cables. An HTS cable comprises one or more HTS strips connected along its length by a conductive material (typically copper). HTS strips can be stacked (i.e., arranged such that the HTS layers are parallel), or the HTS strips can have other strip arrangements that can vary along the length of the cable. A significant special case of HTS cables is single HTS strips and HTS pairs. An HTS pair comprises a pair of HTS strips arranged such that the HTS layers are parallel. When using strips with a substrate, the HTS pair can be type 0 (HTS layers facing each other), type 1 (HTS layer of one strip facing the substrate of another strip), or type 2 (substrates facing each other). Cables comprising more than two strips can have some or all of the strips arranged in HTS pairs. Stacked HTS strips can include various different arrangements of HTS pairs, most commonly stacks of type 1 pairs or stacks of type 0 pairs and (or equivalently, stacks of type 2 pairs). HTS cables may include a mixture of strips with a substrate and stripped strips.

[0008] When describing coils in this document, the following terms will be used:

[0009] • "HTS cable" – A cable that includes one or more HTS strips. In this definition, a single HTS strip is an HTS cable.

[0010] • "Turn" - The section of HTS cable enclosing the inside of the coil (i.e., it can be modeled as a complete loop).

[0011] • "Arc" - the continuous length of the coil that is less than the entire field coil.

[0012] • "Inner radius / outer radius" - the distance from the center of the coil to the inside / outside of the HTS cable.

[0013] • "Inner circumference / outer circumference" - the distance measured around the inside / outside of the coil.

[0014] • "Thickness" - the radial depth of all turns of the coil, i.e., the difference between the inner radius and the outer radius.

[0015] • “Critical Current” (I C — The current at which the HTS becomes normal under a given temperature and external magnetic field (whereby the HTS is considered to "become normal" at the characteristic point of the superconducting transition, where the strips produce E0 volts per meter. The choice of E0 is arbitrary, but it is usually taken as 10 microvolts or 100 microvolts per meter).

[0016] • “Critical Temperature” – The temperature at which the HTS will become normal under a given magnetic field and current.

[0017] • “Peak critical temperature” – the temperature at which the HTS becomes normal without a given external magnetic field and negligible current.

[0018] • Electrically insulating materials – possessing more than approximately 10 6 Materials with resistivity in the ohm-meter range, such as insulators like MgO and diamond, each have a resistivity (at room temperature) exceeding approximately 10. 12 Ohm-meter resistivity.

[0019] • Electrical conductor material – having a density of less than approximately 10 -6 Materials with ohmic-meter resistivity.

[0020] Broadly speaking, there are two structural types for HTS field coils—through winding or assembling multiple segments. For example... Figure 2 As shown, the wound coil is manufactured by wrapping the HTS cable 201 (as shown by solid lines) in a continuous spiral around the formwork 202. The formwork is shaped to provide the required inner circumference of the coil and can be a structural part of the final wound coil, or it can be removed after winding. Figure 3 The segmented coil, schematically shown, comprises multiple segments 301, each segment potentially containing multiple cables or pre-formed busbars 311 (as shown by solid lines), and forming the arc of the entire coil. The segments are connected via connectors 302 to form a complete coil. Although for clarity, Figure 2 and Figure 3 The turns of the coil are shown as spaced apart, but there is usually material connecting the turns of the coil—for example, the turns of the coil can be bonded together by encapsulating them with epoxy resin.

[0021] Coils can be “insulated”—meaning the turns of the coil have an electrically insulating material between them (e.g., resulting in an inter-turn resistance of about 1 ohm or greater)—or they can be “non-insulated”, where the turns of the coil are electrically connected radially (i.e., connected by an electrically conductive material) and electrically connected along a cable (e.g., by welding or direct contact connecting copper stabilizer layers of the cable). Insulated HTS coils can be used in applications requiring large and rapid changes in the magnetic field, such as plasma control in fusion magnets. In contrast, non-insulated coils are generally not suitable for large field coils due to their very long ramp-up times.

[0022] The intermediate grounding option is a "partially insulated" coil, wherein the material between the turns has a resistance between that of a conventional electrical conductor (e.g., metal) and that of a conventional electrical insulator (e.g., ceramic or organic insulator), for example, having a resistivity 100 times that of copper and 10 times that of copper. 16 Resistivity between 10 and 10 times -6 Ohm-meter and 10 8 Resistivity between ohms and meters. Partially insulated HTS magnets, i.e., HTS magnets with partially conductive inter-turn connections (i.e., having 10 ohms). -6 Ohm-meter and 10 8 The inter-turn connection of a material with an "intermediate" resistivity between ohms and meters has a lower field scan rate but provides increased thermal and electrical stability under operating conditions, for example, because the coil allows heat and / or current to be conducted around the windings of the coil and between the windings of the coil. Partial insulation can be achieved by selecting a material with an appropriate resistivity or by providing a structure with partial insulation having the desired resistance. Such structures are described in detail in WO 2019 / 150123 A1, which is incorporated herein by reference.

[0023] Insulated and partially insulated magnets require components to be introduced into the coil to insulate the turns (windings) from each other or to provide inter-turn connections. Insulated magnets are typically made by co-winding HTS strips with an insulating material such as polyimide. Partially insulated magnets are made in various ways, such as co-winding with metal strips (e.g., stainless steel strips), applying an edge coating, or co-winding with a specially designed flexible printed circuit board (PCB) containing conductive traces.

[0024] Each of these manufacturing methods has one or more drawbacks. For example, co-winding HTS strips with other types of strips (or PCBs) reduces the current density in the magnet windings. Introducing organic insulators (such as polyimide) can also reduce the mechanical properties of the coil, such as lowering the Young's modulus. Because the magnet windings are not bonded together (the windings are "unbonded"), poor mechanical properties can also occur in some cases, leading to reliance on inter-turn contact pressure to provide inter-turn contact. For example, dry, non-insulated or metallically insulated coils have shown tapering deformation (i.e., deformation that causes the coil to adopt a tapered geometry) due to the induced shielding current generated when the coil is operated. These organic insulators may also be a poor choice for use in fusion applications due to their poor neutron tolerance.

[0025] Another problem with existing methods of fabricating insulated or partially insulated coils is that the inter-turn resistivity may be too low to be implemented in large (high-inductance) coils. Since the electromagnetic time constant associated with a coil is determined by the ratio of the coil's inductance to its resistance (L / R), high-inductance coils require correspondingly "high" inter-turn resistance so that the coil can respond to changes in current / magnetic field on the appropriate time scale. Another problem is that, in some cases, the geometry of the inter-turn connection, or its limited thermal connection to the magnet, can lead to ohmic overheating during discharge, resulting in electrical burnout of the connection. This can occur, for example, when forming a partially insulated magnet by introducing a PCB between the turns: the thin metal traces of the PCB are typically thermally isolated from the rest of the magnet by polyimide insulation.

[0026] Figure 4 The diagram shows a radial cross-section of a specific type of wound coil referred to as a "pancake coil," in which HTS cable (strip) 401 is wrapped in a manner similar to a spool to form a flat coil. Pancake coils can be made to have an inner periphery that is any two-dimensional shape. Typically, pancake coils are configured as "double pancake coils," such as... Figure 5 As shown in the radial cross-section, it comprises two pancake coils 501, 502 wound in opposite directions to each other, with insulation 503 between the pancake coils, and internal terminals connected together 504. This configuration means that only a voltage (which is usually more accessible) needs to be supplied to the external terminals 521, 522 to drive the current through the turns of the coils, thereby generating a magnetic field.

[0027] One application of HTS field coils is in the plasma chamber of a tokamak device (“tokamak device”). Tokamak devices are characterized by a combination of a strong circumferential magnetic field, high plasma flow, and typically large plasma volume, along with significant auxiliary heating to provide a thermally stable plasma in which fusion can occur. Auxiliary heating (e.g., by injecting high-energy hydrogen, deuterium, or tritium through a neutral beam of tens of megawatts) is necessary to raise the temperature to sufficiently high values ​​required for nuclear fusion to occur and / or to maintain the plasma flow.

[0028] The problem with using HTS field coils in the plasma chamber of a tokamak device is that the construction and operation costs are high due to the typically large size, large magnetic field and high plasma flow required, and the engineering must be robust to cope with the large energy storage present in the magnet system and plasma, which carries the risk of “disruption”—in cases of severe instability, megaampere current can drop to zero in milliseconds.

[0029] This situation can be improved by shrinking the donut-shaped torus of a conventional tokamak device to its limit, making it resemble an apple with a core—a 'spherical' tokamak (ST). This concept, first realized at the START tokamak device in Culham, demonstrated a significant increase in efficiency—the magnetic field required to contain the hot plasma could be reduced by a factor of 10. Furthermore, plasma stability was improved, and construction costs could be reduced.

[0030] In order to achieve the fusion reaction required for economical power generation (i.e., output power much greater than input power), conventional tokamak devices must be very large so that the energy confinement time (roughly proportional to the plasma volume) is long enough for the plasma to be hot enough for thermal fusion to occur.

[0031] WO 2013 / 030554 describes an alternative approach involving the use of a compact spherical tokamak device as a neutron or energy source. The low aspect ratio plasma shape in a spherical tokamak device improves particle confinement time and allows for net power generation in a smaller machine. However, the need for a small-diameter central pillar poses challenges to the design of the plasma confinement container and associated magnets.

[0032] The magnet coils in a tokamak device can be divided into two groups. The poloidal field coils are horizontal, circular coils wound with their center located on the central pillar of the tokamak device, generating the poloidal field (i.e., a magnetic field substantially parallel to the central pillar). The circumferential field coils ("return legs") are wound vertically through the central pillar and around the outside of the plasma chamber to generate the circumferential field (i.e., a circular magnetic field around the central pillar). The combination of the poloidal and circumferential fields generates a helical magnetic field within the plasma chamber that keeps the plasma confined.

[0033] The current required to generate a circumferential field is extremely large. Therefore, the design of tokamak devices increasingly involves the use of superconducting materials in the field coils. For compact spherical tokamak devices, the diameter of the central column should be as small as possible. This presents a contradictory requirement, since the current density achievable even with superconducting materials is limited.

[0034] Figure 6 A vertical cross-section of a spherical tokamak device 600 is shown, comprising a toroidal field (TF) magnet 602 and multiple poloidal field (PF) magnets 605A-605F. The toroidal field (TF) magnet 602 consists of multiple D-shaped TF coils 603A, 603B arranged around a central post 604 oriented along axis A-A'. Figure 6 (Only two coils are shown in the diagram) are formed, each of the plurality of poloidal magnetic field magnets 605A-605F surrounding the central pillar 604. The current applied to the TF magnet and PF magnets 603A, 603B, 605A-605F generates a closed magnetic field that, when the tokamak device is in use, confines, shapes, and controls the hot plasma 607 inside the circumferential vacuum container 608.

[0035] Figure 7 A cross-section of the center post 604 is shown, which includes multiple current-carrying components through which the center post section of the TF coil passes. The space within the center post 603 is occupied by current-carrying components and non-current-carrying components, including, for example:

[0036] • Neutron shield 702 – used to prevent heating of the central pillar and degradation of the critical current of the superconductor in the central pillar;

[0037] • Electrical insulation component 703 — used to electrically insulate current-carrying components from each other;

[0038] • Coolant passage 704 – used to remove heat from the center column (e.g., using refrigerant);

[0039] • Cooling ribs 705 – used to carry heat from the various current-carrying components to the coolant passages 704.

[0040] Figure 8A sector of sector 701 of the central post 604 is shown. Sector 701 includes three current-carrying components 801A-801C, which constitute the TF coil 602. Each component includes one or more HTS field coils 801, such as pancake coils or bipancake coils. Figure 8 As can be seen, the rectangular cross-section of the HTS field coil does not fit well with the arc-shaped cross-section of sector 701, and a significant amount of space is wasted, making it unsuitable for other components such as additional cooling channels or sensors. The arrangement of the current-carrying components 801A-801C within sector 701 also results in high stress at the corners of the HTS coil's cross-section (as shown below regarding...). Figure 19 (As discussed).

[0041] Another problem with the current-carrying components 801A-801C in sector 701 is that the current-carrying components 801A and 801C closest to the tapered side of sector 701 have fewer turns than the current-carrying component 801B located at the center. These differences in the number of turns in the HTS strip will result in a high level of "ripple" in the magnetic field (as discussed below). Figure 21 (As discussed), this causes the magnetic field inside and near the central column to deviate from the desired circular symmetry.

[0042] Therefore, an alternative structure for the TF coil in the center column is needed to avoid these effects. Summary of the Invention

[0043] The purpose of this invention is to provide an HTS field coil that solves or at least alleviates the problems described above.

[0044] According to a first aspect of the invention, a method is provided for manufacturing a high-temperature superconductor (HTS) field coil from one or more HTS strips. Each HTS strip includes a layer of HTS material. The method includes: winding the one or more HTS strips around an axis to form a field coil comprising a winding of HTS strips; and removing material from at least a portion of the one or more windings from the axial edges of the one or more HTS strips to reduce the extent of the one or more HTS strips along the axis of the field coil.

[0045] Removing material from the axial edge of the one or more HTS strips may include reducing the extent of the HTS material layer along the axis of the field coil.

[0046] In HTS strips with a layered structure (e.g., Figure 1In the embodiment of the HTS strip 100 shown, the HTS strip is typically wound such that the layers are parallel to the axis of the field coil, i.e., the strip is wound such that the layers are arranged concentrically around the axis of the field coil. In this arrangement, removing material from the axial edge of the HTS strip (e.g., by mechanical means such as machining) may include removing material from each of the layers simultaneously. For HTS strips with a rectangular cross-section (e.g., ... Figure 1 The HTS strip 100 shown typically corresponds to the smaller side of a rectangular cross-section, that is, the edge of the HTS strip that corresponds to the “thickness” of the HTS strip.

[0047] Material can be removed such that the HTS layer varies radially across the field coil along the axis of the coil, and / or circumferentially around one or more of the windings. Material removal can include removing material across the entire surface of the field coil. Material can be removed to provide at least one axial surface of a truncated cone for the field coil. Material removal can include removing a conductive cladding that is in electrical contact with the HTS material and extends across at least the axial edge of the HTS strip. The cladding can be removed from the axial edge of one or more HTS strips across the entire surface of the field coil to expose the HTS material layer located at the axial edge of one or more HTS strips.

[0048] The HTS strip, or each HTS strip, may include a flexible substrate (e.g., a substrate comprising Hastelloy™ or other metals or alloys) and an electrically insulating layer (e.g., buffer stack 102) disposed on the surface of the flexible substrate, wherein the HTS material layer is disposed on the electrically insulating layer. Alternatively, stripped strips may be used, in which case there is no electrically insulating layer, and the HTS material layer is disposed on the flexible substrate (e.g., it may be made of silver).

[0049] In a specific embodiment, the HTS strip or each HTS strip includes a flexible substrate, an intermediate layer disposed on a surface of the flexible substrate, an HTS material layer disposed on the intermediate layer, and a conductive cladding layer electrically contacting the HTS material and extending across at least the axial edges of the HTS strip. Removing material from the axial edges of the one or more HTS strips may include partially or completely removing the cladding layer from the axial edges of the one or more HTS strips around at least a portion of the one or more windings in the windings, to increase the resistance between the HTS material layer in the windings and the HTS material layers in adjacent windings. Removing the cladding layer from the edges of the one or more HTS strips may include removing the cladding layer to expose the HTS material layer located at the axial edges of the one or more HTS strips around at least a portion of the one or more windings in the windings.

[0050] The intermediate layer may be or may include an electrically insulating layer (e.g., buffer stack 102) or a semiconductor layer, such as a layer of silicon and / or gallium arsenide, which may optionally be incorporated into the buffer stack 102 as a single layer. The HTS field coil may be radially “insulating” or “partially insulating” (as described above) depending on the resistivity of the intermediate layer. For example, in some embodiments, the resistivity of the intermediate layer may be between 10⁻⁶ and 10⁻⁶. -6 Ohm-meter and 10 8 Between ohms and meters, to provide partial insulation for the coil.

[0051] The cladding may extend continuously around the entire periphery of the HTS strip before being partially or completely removed from the edges of one or more HTS strips.

[0052] The method may include attaching conductive elements to the cladding on the axial edge of one or more HTS strips before removing the metal cladding. The method may include partially removing the conductive elements to leave electrical contacts through which current is supplied to at least a portion of at least one winding of the windings via the axial edge of the one or more HTS strips.

[0053] In embodiments where the intermediate layer is an electrically insulating layer, for example, the electrically insulating layer may have a thickness of, for example, less than 3 micrometers or less than 1 micrometer, and preferably less than 0.3 micrometers. The electrically insulating layer may include one or more ceramic material layers. The substrate may have a thickness of less than 100 micrometers or less than 75 micrometers, and preferably less than 50 micrometers.

[0054] Generally, the HTS material layer may contain ReBCO material, where Re is a rare earth element such as Y or Gd. The HTS material layer may have a thickness of less than 10 micrometers or less than 1 micrometer. The conductive cladding may contain metals such as copper and / or silver. The HTS strip, or the conductive cladding of each HTS strip, may extend on each face of the HTS strip.

[0055] The windings of the HTS field coil can be arranged in two or more layers stacked along the axis of the field coil, and material is removed from the axial edge of one or more HTS strips in one or more of the layers. For example, the HTS field coil can be a double pancake coil.

[0056] Material can be removed entirely around one or more windings in a winding.

[0057] The HTS field coil may include two HTS strips arranged as a type 0 pair, wherein the HTS layers of the two HTS strips face each other, and the substrates of the HTS strips are separated by HTS layers.

[0058] The method may also include sealing the edges of one or more HTS strips in the HTS strip with an insulating or conductive material.

[0059] Removing material from the axial edges of one or more HTS strips can include mechanically removing the material, preferably by machining the axial edges of the one or more HTS strips. Mechanical material removal can include cutting; drilling, laser cutting, plasma cutting, water jet cutting, grinding, sanding, wire erosion, turning, laser ablation, ion milling, sputtering, and electrical discharge machining, or one or more of these methods.

[0060] Alternatively or additionally, material can be chemically removed partially or entirely from the axial edges of one or more HTS strips in the HTS strips. For example, if the cladding contains copper, the cladding can be chemically removed by dissolving the copper in a ferric chloride solution. If the cladding contains silver, the cladding can be (preferably) chemically removed by dissolving the silver in a solution containing an oxidizing agent (such as hydrogen peroxide).

[0061] The method may include cooling the HTS field coil during the step of removing material from the axial edges of the one or more HTS strips. For example, such cooling can prevent thermal damage or degradation of the HTS material layer.

[0062] The method may also include polishing the axial edges of the one or more HTS strips after material removal.

[0063] The method may also include removing material from another axial edge of one or more HTS strips, the other axial edge being disposed on a face of the field coil opposite to the face of the axial edge of the field coil.

[0064] Material removal may include cutting through the HTS field coil to divide it into two or more HTS field coils. For example, the HTS field coil can be divided by traveling through a cutting surface (e.g., a plane) of each of one or more HTS strips. For example, the HTS field coil can be divided by a cutting plane substantially perpendicular to the coil axis, which preferably bisects the coil. The method may also include forming one or more electrical connections between the two or more HTS field coils to form a solenoid.

[0065] Winding the one or more HTS strips around an axis to form a field coil may include a cable wound with two outer HTS strips having the one or more HTS strips and one or more inner HTS strips. The one or more inner HTS strips are disposed between the outer HTS strips and have a metal cladding that provides a conductive path between the HTS layers of the two outer HTS strips. Before and / or after material removal, the one or more inner HTS strips may be narrower than the outer HTS strips in a direction parallel to the axis of the coil. Before and / or after material removal, the respective axial edges of the one or more inner HTS strips and the outer HTS strips may be aligned with each other along the edges of the cable.

[0066] According to a second aspect of the invention, a method for manufacturing an electromagnet is provided. The electromagnet includes a high-temperature superconducting (HTS) field coil mounted within a recess or enclosed space. The method includes manufacturing the HTS field coil according to a first aspect of the invention, wherein the step of removing material from the axial edges of one or more HTS strips of the HTS field coil includes removing material to adapt the HTS field coil to fit the recess or the enclosed space. The method further includes mounting the HTS field coil into the recess or the enclosed space.

[0067] Fitting the HTS field coil within a recess or enclosed space allows the HTS field coil to contact (i.e., fit snugly) each surface defining the recess or enclosed space. Alternatively, the relative size of the HTS field coil to the recess or enclosed space allows for a small travel (e.g., less than 1 mm) within the recess or enclosed area. The recess or enclosed space can be housed in a support structure, such as a rigid housing or enclosure that provides mechanical support for some or all of the coil's windings. The support structure prevents or limits deformation of the field coil when it is operated.

[0068] According to a third aspect of the invention, a method is provided for manufacturing a toroidal field (TF) magnet comprising a plurality of high-temperature superconducting (HTS) field coils for a plasma chamber of a tokamak device. The method includes manufacturing a plurality of HTS field coils according to a method according to a first aspect of the invention. Each HTS field coil includes a segment in a corresponding sector for mounting to a central post of the TF magnet. The step of removing material from the axial edge of the one or more HTS strips of each HTS field coil includes removing material to adapt the cross-section of the segment of the HTS field coil to the cross-section of the sector. The method further includes:

[0069] The sections of each HTS field coil are installed into their respective sectors; and

[0070] The sectors are arranged around a central axis to form the central column of the TF magnet, wherein the windings within the segments of the HTS field coils mounted in the sectors are arranged parallel to the central axis.

[0071] Removing material to adapt the cross-section of the segment of the HTS field coil to the cross-section of the sector may include: removing material to cause the cross-section of the segment of the HTS field coil to taper toward and / or away from the central axis.

[0072] Each sector may include multiple HTS field coils, the axes of which are arranged parallel to each other and perpendicular to the central axis of the central column.

[0073] According to a fourth aspect of the invention, a high-temperature superconductor (HTS) field coil is provided, the HTS field coil comprising windings of one or more HTS strips around an axis of the coil. Each HTS strip comprises a flexible substrate, an intermediate layer disposed on a surface of the flexible substrate, and an HTS material layer disposed on the intermediate layer. At least one of the one or more HTS strips (and optionally all HTS strips) is configured such that there is no conductive path extending radially across the intermediate layer for one or more of the windings, whereby the HTS material layer in the at least one of the one or more HTS strips of the one or more windings is at least partially electrically insulated from the HTS layer in the adjacent windings through the intermediate layer.

[0074] The intermediate layer may be or may include an electrically insulating layer or a semiconductor layer (e.g., Si and / or GaAs). As mentioned above with respect to the first aspect of the invention, the HTS field coil may therefore be radially "insulating" or "partially insulating" depending on the resistivity of the intermediate layer. In other words, the HTS material layer in at least one HTS strip of the one or more HTS strips of the one or more windings in the winding may be electrically insulated or partially electrically insulated from the HTS layer in the adjacent winding through the intermediate layer.

[0075] The HTS field coil can be formed according to the method described above for the first aspect.

[0076] The term "radial" means a direction extending perpendicular to the axis of the coil (i.e., the axis around which the coil windings encircle) and toward or away from that axis. No conductive path extending radially across the interlayer (e.g., an electrically insulating layer) means that no one or more electrically conductive materials extend continuously across (e.g., across) the interlayer in a radial direction. Therefore, the interlayer (e.g., an electrically insulating layer) radially electrically insulates (i.e., provides radial electrical insulation) or at least partially radially electrically insulates (i.e., provides radial electrical insulation) of the HTS material layer in at least one HTS strip of one or more HTS strips in one or more windings from the HTS layer in the adjacent winding.

[0077] The HTS strip, or each HTS strip, may include a conductive cladding electrically connected to the HTS material layer. In some examples, the cladding does not extend radially across the intermediate layer, at least in a radial portion radially outside the first current connection point and radially inside the second current connection point.

[0078] The HTS field coil may include an electrically insulating material disposed on one or more axial edges of the one or more HTS strips. Alternatively or additionally, the HTS field coil may include a conductor material disposed on one or more axial edges of the one or more HTS strips.

[0079] The winding may include a winding having a cable, the cable including two outer HTS strips having the one or more HTS strips and one or more inner HTS strips, the one or more inner HTS strips being disposed between the outer HTS strips and having a metal cladding, the metal cladding providing a conductive path between the HTS layers of the two outer HTS strips.

[0080] The conductive path provided by the metal cladding between the HTS layers of the two outer HTS strips may (in some embodiments) extend radially across one or more of the intermediate layers of the one or more inner HTS strips on only one side.

[0081] The HTS field coil may include a conductor element having an electrical contact surface through which current is supplied to a portion of at least one of the windings. The surface provides electrical contact between the conductor element and an axial edge of the field coil.

[0082] An HTS field coil may include an electrical conductor disposed between intermediate layers of HTS strips in adjacent windings. The HTS material layer is radially separated from the electrical conductor through the intermediate layer. The electrical conductor may include two or more electrical contacts that can be electrically connected to measure the voltage across a radially separated portion of the conductor.

[0083] According to a fifth aspect of the invention, an electromagnet is provided, the electromagnet comprising one or more HTS field coils according to a fourth aspect of the invention, or comprising one or more HTS field coils manufactured by a method according to a first aspect of the invention.

[0084] According to a sixth aspect of the invention, a system is provided comprising a plasma container and a set of field coils for generating a magnetic field within the plasma container, each field coil being an HTS field coil according to a fourth aspect of the invention, or an HTS field coil manufactured by a method according to a first aspect of the invention.

[0085] According to a seventh aspect of the invention, a satellite, aircraft, or unmanned aerial vehicle is provided, which includes one or more HTS field coils according to a third aspect of the invention, or includes one or more HTS field coils manufactured by a method according to a first aspect of the invention. Attached Figure Description

[0086] Figure 1 This is a schematic perspective view showing the internal structure of the ReBCO stripe;

[0087] Figure 2 It is a schematic top view of a wound coil;

[0088] Figure 3 This is a schematic top view of a segmented coil;

[0089] Figure 4 This is a schematic radial cross-sectional view of a pancake-shaped coil;

[0090] Figure 5 This is a schematic radial cross-sectional view of a double pancake coil;

[0091] Figure 6 This is a schematic vertical cross-sectional view of a tokamak device;

[0092] Figure 7 It is the cross-section of the central column;

[0093] Figure 8 yes Figure 7 The cross-section of the sector of the central column;

[0094] Figure 9 This is a schematic cross-sectional view of ReBCO strips;

[0095] Figure 10 It is a schematic radial cross-sectional view of the coil of a cable formed by two ReBCO strips;

[0096] Figure 11 According to an embodiment of the present invention, by means of... Figure 10 A schematic radial cross-sectional view of a coil formed by removing the metal cladding from the axial edge of the coil;

[0097] Figure 12 yes Figure 11 The coil was modified to include a schematic radial cross-sectional view of the electrical contact portion between the windings of the inserted coil;

[0098] Figure 13 This is a schematic radial cross-sectional view of a coil including a pair of conductor plates extending along the axial edge of the coil, which comprises a cable formed by two ReBCO strips; and

[0099] Figure 14This is a schematic radial cross-sectional view of a coil according to an embodiment of the present invention, wherein... Figure 13 The portion of the coil with its metal cladding and conductor plate removed;

[0100] Figure 15 It is a schematic radial cross-sectional view of a coil of cable formed by four ReBCO strips; and

[0101] Figure 16 This is a schematic radial cross-sectional view of a coil formed by removing the metal cladding from the axial edge of the coil according to an embodiment of the present invention;

[0102] Figure 17 This is a flowchart of the method for manufacturing HTS coils.

[0103] Figure 18 This is a cross-section of a sector of an exemplary central column;

[0104] Figure 19 The results of stress simulation of the HTS stack in the TF magnet are shown;

[0105] Figure 20 The results of stress simulation of an HTS stack in an exemplary TF magnet are shown;

[0106] Figure 21 It is the cross-section of the central column, showing the magnetic field;

[0107] Figure 22 This is a flowchart of the method for manufacturing HTS coils; and

[0108] Figure 23 This is a flowchart of a method for manufacturing a TF magnet comprising multiple HTS field coils for use in the plasma chamber of a tokamak device. Detailed Implementation

[0109] This paper proposes solutions to some of the problems mentioned above, wherein an HTS field coil is modified by removing material from the axial edges of one or more HTS strips after winding. For example, in one embodiment, HTS material is removed from the HTS strip to alter the superconducting properties of the strip in different regions of the coil. In another embodiment, material removal causes the buffer stack of the HTS strip to provide turn-to-turn electrical insulation in an insulated or partially insulated field coil. Such a field coil can be produced by completely or partially removing the metal cladding from the edges of the HTS strip, for example, after the HTS strip has been wound into the coil. The resulting coil may be referred to as a "Buffer Layer Insulator (BLI)" coil.

[0110] Figure 9 A radial cross-section through a ReBCO strip 900 is shown, which is similar to... Figure 1 ReBCO strip 100. With Figure 1 The same elements in the strips are given the same reference numerals. However, in this example, the copper stabilizer layer 105 and the silver layer 104 can be seen extending around the other layers of the strip 900 to completely enclose it, that is, the copper stabilizer layer 105 and the silver layer 104 act as cladding for the layered structure of the strip 900.

[0111] As mentioned above, substrate 101 is typically Hastelloy™ and has a thickness of approximately 50 μm to 75 μm. Buffer stack 102 is a series of four layers of ceramic material, such as MgO, LaMaO3, YSZ, etc., typically with a combined thickness of approximately several hundred nanometers to several micrometers. The details of the composition and thickness of each layer of buffer stack 102 typically vary depending on the supplier. Copper cladding 105 is typically approximately 10 μm to 20 μm thick (including at the edges). Buffer stacks with more (or fewer) ceramic layers can also be used.

[0112] Figure 10 A radial cross-sectional view of a pancake coil 1000 formed by winding two ReBCO strips 900A and 900B around axis Z (the axis of the coil) is shown. For clarity, only the two windings 1002 and 1004 of strips 900A and 900B are shown in the figure, but any number of windings can be used (see, for example, [reference needed]). Figure 13The windings 1002 and 1004 of coil 1000 are nested within each other to form a generally planar coil 1000. In this specific example, strips 900A and 900B are arranged in an O-type configuration such that their ReBCO planes face each other, which allows some current to be shared between the two strips 900A and 900B when the coil 1000 is operated. Other configurations are, of course, also possible, as discussed above. Coil 1000 is typically solder-encapsulated, for example, with PbSn solder, to form a non-insulated coil.

[0113] Figure 11 A radial cross-sectional view of coil 1100 is shown, showing the layered structure of ReBCO strip 900 exposed by removing the copper and silver cladding layers 104, 105 from both sides of coil 1000.

[0114] The cladding can be mechanically removed using various methods, including turning or wire erosion. In a preferred embodiment, a copper plate is welded across the face of coil 1000, and then the plate is machined away by milling, grinding, turning (e.g., on a lathe) or other mechanical metal removal means to leave one or more metal bonding rings for injecting current into coil 1000 through the edges of HTS strips 900A, 900B. In this case, a cutting tool penetrates the metal plate and continues into HTS strips 900A, 900B to remove approximately 0.5 mm of the edges of HTS strips 900A, 900B. Of course, this process can be performed on one or both surfaces of coil 1000, depending on the desired inter-turn resistance of coil 1000 (which is maximized by completely removing the cladding from both surfaces). The inter-turn resistance can also be varied by changing the thickness of one or more layers 104 of the buffer stack in HTS strips 900A and 900B (e.g., a thinner buffer stack can be used to make coils that are only partially insulated). Other types of metal plates (other than copper) can also be used. Current can also be injected into the coil by means other than an "edge-connected" plate. For example, by metal parts (contacts) to which the cable is terminated (e.g., by welding) at the inner and / or outer diameter of the coil.

[0115] Alternatively or additionally, chemical processes can be used to dissolve the copper and silver cladding. For example, a ferric chloride (FeCl3) solution can be used to dissolve the copper cladding 105. To dissolve the silver cladding 104, a solution of 1 part ammonium hydroxide and 1 part hydrogen peroxide can be used, optionally diluted with methanol to reduce the reaction rate. Other reagents can also be used to dissolve the silver cladding, including nitric acid and / or hydrochloric acid, or a hydrogen peroxide solution in combination with an acid or base. Removing the copper and silver cladding 104, 105 using a solution of hydrogen peroxide and ammonium hydroxide generally does not affect the surface of the ReBCO layer 103. In some cases, removing the silver cladding 104 using other reagents may dissolve or react with the exposed edges of the ReBCO layer 103. However, minor degradation of the edges of the ReBCO layer 103 is generally acceptable for many applications. Optionally, an insulating material, such as epoxy resin, can be used to seal the edges to prevent contaminants from entering the exposed strip edges and to allow for thermal contact. The portion of the coil at the inner and outer diameters can be omitted during the edge processing so that the metal layer is left in place for current injection purposes (not shown).

[0116] Other methods for removing the copper and silver cladding layers 104, 105 include sputtering (e.g., using ion milling) and / or laser ablation.

[0117] The structure of the BLI coil 1100 offers numerous advantages. Because the BLI coil 1100 is wound solely with ReBCO (HTS) strips, the current density of the magnet is maximized (compared to other types of insulated or partially insulated magnets made by winding the HTS strips together with another strip or PCB). In particular, the buffer layers of strips 900A and 900B exhibit highly efficient inter-turn resistance due to their thinness, maximum cross-sectional area, and close thermal contact with the ReBCO (HTS) layer 103. Because the coil 1100 contains (essentially) only HTS strips, the Young's modulus of the BLI coil 1100 and the structural integrity of the coil are also maintained at a high level.

[0118] The buffer stack forms an insulating barrier between the turns of coil 600, eliminating the need for additional insulating material layers between the windings, such as low-modulus organic insulators. This allows the insulated coil to have a high Young's modulus and a high turn density, essentially determined solely by the thickness of the HTS strip. This high (e.g., maximum) turn density allows coil 600 to deliver a higher current density compared to other coils with additional material incorporated between the windings of the HTS strip. The cross-sectional area of ​​the inter-turn connections is also the largest, spanning the entire width of the HTS strip, thus maximizing the opportunity for heat transfer between the windings, such as in the case of quenching. The stiffness of coil 600 and the consolidation of the windings also reduce or minimize strain (or strain variation) within the HTS strip, for example, preventing degradation of the HTS material when the coil is used and / or making coil 600 easier to maintain. The absence of additional material (such as organic insulators) within the coil also avoids the possibility of degradation of that additional material, which could be of particular concern if the coil is exposed to high neutron fluxes (such as those produced in fusion reactors).

[0119] Figure 12 A schematic radial cross-section through coil 1200 is shown, which is identical to coil 1100 except that electrical contacts 1201 have been fabricated to a central electrical conductor region located between the centers (in the radial direction) of the respective windings 1002, 1004. The central region includes a metal cladding (i.e., copper cladding 105 and silver cladding 104) and a substrate 101 for each strip 900A, 900B (i.e., strip 900B of winding 1004 and strip 900A of winding 1002). The metal cladding 104, 105 and substrate 101 of each strip 900A, 900B in the electrical conductor region 1202 are electrically connected to each other, but electrically insulated from the HTS layer 103 of each strip 900A, 900B immediately adjacent to the conductor region by a buffer stack 102. In other words, the electrical contact 1201 is formed in the central region of the windings 1002, 1004 that is electrically insulated from the HTS layer (in the radial direction) of the strip. When the coil 1200 is being wound, the electrical contact 1201 can be formed by inserting a metal (e.g., copper) contact between the windings 1002, 1004. Alternatively or additionally, the electrical contact 1201 can be formed by welding a metal contact to the axially facing edge of the conductor region 1202.

[0120] When current is supplied to the HTS layer 103 of windings 1002, 1004, an induced voltage is generated within coil 1200. This voltage is “picked up” by the electrical conductor region 1202 and can be measured using a potentiometer connected between this electrical contact 1201 and another electrical contact formed into another part of the electrical conductor region 1202 (e.g., a contact formed into the innermost or outermost radial turn of coil 1200). The induced voltage measured between the two contacts can then be subtracted from the voltage measured across coil 1200 as a whole (i.e., between the innermost and outermost turns of coil 1200, including HTS layer 103). Therefore, the remaining voltage contributes resistively (rather than inductively) to the voltage drop across coil 1200, which is a good indicator of whether HTS layer 103 is superconducting. In other words, the difference between the voltage across coil 1200 and the induced voltage measured for the electrical conductor region 1202 indicates the resistive voltage formed in coil 1200, which in itself indicates a non-superconducting region that is forming or has already formed in the HTS material, which may lead to rapid heat generation (i.e., quenching) within the coil.

[0121] Figure 13 A radial cross-sectional view of coil 1300 is shown, which includes multiple windings of HTS strip 1301 and two annular conductors 1303A and 1303B. The multiple windings of HTS strip 1301 are arranged to form a main planar pancake coil. The two annular conductors 1303A and 1303B cover the face of the coil across the edges of HTS strip 1301 on both sides of coil 1300. Each annular conductor 1303A and 1303B includes an annular element or ring made of a conductive material, preferably a metal such as copper, which extends radially across the coil to form an electrical connection between the windings of coil 1300. The annular conductors 1303A and 1303B are soldered to the face of coil 1300 to provide good electrical contact to the edges of HTS strip 1301.

[0122] Figure 14 It shows how to get from Figure 13The diagram shows a radial cross-sectional view of coil 1400 obtained by removing the toroidal conductors 1303A and 1303B and cladding 105 from a portion of coil 1300. For example, material in the toroidal conductors and cladding can be machined away to leave portions of the toroidal conductors 1403A and 1403B bonded to cladding 105, while exposing the HTS layer 103 at the edge of the HTS strip 1401. Current can be supplied to coil 1400 through the radially innermost end of the HTS strip 1401 using the top toroidal conductor 1403A. Current flows through successive windings of coil 1400 and is then received by the bottom toroidal conductor 1403B at the radially outermost end of the HTS strip 1401, i.e., the toroidal conductors 1403A and 1403B serve as electrical contacts (or "current connection points") through which current is transferred to or from coil 1400. It is believed that during the initial phase of current injection, the current injected into coil 1400 penetrates the turns covered by toroidal conductor 1403A (which acts as a small “non-insulated” coil), thereby producing a current distribution that minimizes the impedance on the turns. Over time, the current distribution within coil 1400 then adjusts from (i) an initial distribution that reduces the induced voltage (such that current flows from the outermost radial edge of the top toroidal conductor 1403A through the turns of the coil between the two toroidal conductors 1403A, 1403B and out through the innermost radial edge of the bottom toroidal conductor 1403B) to (ii) a current distribution that minimizes the ohmic voltage (such that current will penetrate all turns of toroidal conductors 1403A, 1403B uniformly).

[0123] In some examples, coil 1400 may have ring conductors 1403A, 1403B on only one side. Although ring conductors 1403A, 1403B are shown on opposite sides of coil 1400, they may be arranged on the same side, in which case current may be injected or removed from only one side of the coil, which may be advantageous, for example, in space-constrained environments.

[0124] Although it is preferred to remove the metal cladding after the HTS strips 900A, 900B, 1301, and 1401 have been wound into coils, the BLI coil can also be formed by removing the metal cladding from the side of the HTS strip before winding the coil.

[0125] The coils 1000, 1100, 1200, 1300, and 1400 described above are formed by winding cables with two HTS strips arranged in an O-type configuration (where the HTS layers face each other), which allows current to be shared between the two HTS strips 900A and 900B. Coils can also be formed from cables including more than two HTS strips 900A and 900B. However, for these types of coils, removing the copper cladding 105 and silver cladding 104 from the axial edges of the strips 900A and 900B prevents current from being shared among all the strips 900A and 900B in the cable. This is because removing the cladding means that current is shared only between the strips where an O-type configuration exists (i.e., HTS layers 103 face each other). A solution to this problem is achieved by winding coils from cables including HTS strips of different widths, as described below.

[0126] Figure 15 A radial cross-section of coil 1500 is shown, which includes windings 1502 and 1504 consisting of a cable comprising four HTS strips 1501A-1501D. The central axis Z of the coil (not shown) is located at... Figure 15 The right side of the coil section shown in the diagram. Two strips 1501A and 1501D have a wider width than the other two strips 1501B and 1501C. Figure 15 and Figure 16 In the middle, because Figure 15 and Figure 16 The radial cross-section through the coil is shown, so the “width” (i.e., the second short dimension of the strip) of strips 1501A-1501D extends vertically. Each narrower strip 1501B, 1501C is disposed in the cable between the wider strips 1501A, 1501D, and is arranged in an O-type configuration with a corresponding strip of the wider strips 1501A, 1501D, i.e., the wider strips 1501A, 1501D are oriented such that their HTS layer 103 is closer to the center of the cable than their buffer stack 102, while the narrower strips 901B, 901C are oriented such that their HTS layer 103 is farther from the center of the cable than their buffer stack 102. The windings of coil 1500 (as exemplified by windings 1502 and 1504) are aligned on one side 1506A of coil 1500 (in a direction transverse to the radial and circumferential directions) to give the coil a flat surface on that side (bottom side) 1506A and a radially "serrated" surface on the other side (top side) 1506B of coil 1500, due to the wider strips 1501A and 1501D protruding from coil 1500 relative to the narrower strips 1501B and 1501C. The silver cladding 104 and copper cladding 105 in coil 1500 are intact.

[0127] Figure 16 A radial cross-section of coil 1600 is shown. Coil 1600 is obtained by removing the silver cladding 104 and copper cladding 105 from the flat surface of coil 1000 on the bottom side 1006B of coil 1500 and from the wider strips 1501A and 1501D on the top side 1506B of coil 1500 (“narrower” and “wider” here refer to the extent of the strips along the axis of coil 1600). The cladding 104 and 105 of the narrow strips 1501B and 1501C are not removed on the top side 1506B. Therefore, a conductive path is provided through the cladding 104 and 105 between the narrow strips 1501B and 1501C, allowing current to be shared between the narrow strips 1501B and 1501C, and thus between each of the strips 1501A and 1501D constituting the cable. However, there is no conductive path between adjacent windings 1502 and 1504, therefore coil 1600 is a BLI coil.

[0128] Alternatively, coil 1500 may not have an edge aligned with the HTS strip on one side 1506A, i.e., the two sides of coil 1500 may be stepped or “zigzag”. In this case, it may not be necessary to remove either of the cladding 104, 105 from the narrower HTS strips 1501B, 1501C.

[0129] This approach (i.e., using HTS strips of different widths) allows the construction of insulated or partially insulated coils using cables that include more than two HTS strips, thus extending the scalability of this manufacturing method to larger coils.

[0130] In some cases, coil 1500 can be "encapsulated" with solder to fill the gap between the wider strips 1501A and 1501D, as this facilitates the removal of cladding 104 and 105 from the wider strips 1501A and 1501D on the top side 1506B of coil 1500. The solder covering the narrower strips 1501B and 1501C provides radial mechanical stability to the wider strips 1501A and 1501D, thereby preventing damage to the wider strips 1501A and 1501D when machining the top side 1506B of coil 1500 to remove cladding 104 and 105.

[0131] In one specific example, the wider strips 1501A and 1501D have a width of 12 mm, while the narrower strips 1501B and 1501C have a width of 11 mm or 10 mm. Preferably, the HTS layer 103 and buffer stack 102 of the wider strips 1501A and 1501D should extend over the narrower strips 1501B and 1501C, such that the cladding 104 and 105 can be removed from the wider strips 1501A and 1501D without damaging the cladding 104 and 105 of the narrower strips 1001B and 1001C. In some cases, the cladding 104 and 105 of strips 1500A-1500D may extend about 10 micrometers beyond the HTS layer 103 and buffer stack 102, requiring the removal of about 10 micrometers of material (i.e., cladding) from either side of the coil 1500 to produce the insulated coil 1600. However, in practice, the variation in HTS strip width and the alignment of the windings relative to each other (i.e., the flatness of the coil) means that it is preferable to remove 100 micrometers or more of material from each side of the coil (i.e., the cladding and some of the HTS layer 103 and the buffer stack 102) to ensure that the coil is completely insulated.

[0132] Insulated coils can also be produced using cables that include more than four HTS strips, provided that the outer HTS strips 1501A and 1501D of the cable are wider than the HTS strips 1501B and 1501C which are closer to the center of the cable.

[0133] Figure 17 This is a flowchart of a method for manufacturing an HTS coil using one or more HTS strips. Each HTS strip includes a flexible substrate, an electrically insulating layer (e.g., buffer stack 102) disposed on a surface of the flexible substrate, an HTS material layer disposed on the electrically insulating layer, and a conductive cladding layer electrically contacting the HTS material and extending across at least the edges of the HTS strip. The electrically insulating layer may only be "partially insulating," in which case the electrically insulating layer may have a resistance between 100 and 10 times that of, for example, copper. 16 Resistivity between 10 and 10 times, or with a resistivity between 10 and 10 times. -6 Ohm-meter and 10 8 Resistivity between ohms and meters, etc.

[0134] Step 1701 of the method includes: winding one or more HTS strips around an axis to form a field coil comprising a winding of HTS strips.

[0135] Step 1702 of the method includes: partially or completely removing the cladding from the axial edge of one or more HTS strips in the HTS strips around at least a portion of one or more windings in the winding to increase the resistance between the HTS material layer in the winding and the HTS material layer in the adjacent winding.

[0136] While the above discussion focuses on removing the cladding from one or more axial edges of HTS field coils 1000, 1100, and 1200, it is also possible to remove more or other material from one or more axial edges to reduce the width of the field coil (i.e., the extent along the coil axis). Surprisingly, it has been found that HTS field coils can be highly resilient to physical damage, allowing for significant alterations to the coil's shape even after winding. For example, it has been found that an HTS field coil can still function effectively even after drilling several holes through it or after shaping it using standard machining techniques such as sawing, grinding, and sanding. In particular, current can continue to circulate around the HTS material of such coils even when there is an interruption or damage within some of the coil windings. This is likely a result of current sharing between adjacent windings, allowing the current to "bypass" the affected portion of the winding. As long as the total current does not exceed the minimum critical current of the HTS material in any part of the coil, or if the inter-turn resistance is low enough and cooling is provided to cool the resistive heat load so that the total current may even potentially exceed the minimum critical current, the current can continue to circulate around the windings of the coil.

[0137] These findings offer significant opportunities for applications requiring easily assembled pancake-shaped coils, but the rectangular cross-section of such coils presents drawbacks, such as in the central column of a toroidal field coil (as described above). (See below for further details.) Figure 18 The discussed point is that, after winding (and preferably after encapsulating the coil in, for example, solder or epoxy), the cross-section of the coil can be modified to better fit within the desired space. "Encapsulating" a coil refers to filling (or wrapping) the coil with a material (e.g., solder or epoxy) after it has been formed by winding one or more lengths of HTS strip (cable). The encapsulation material fills the gaps in the coil structure and improves the structural integrity of the coil, for example, reducing the likelihood of loosening or damage to windings facing the inner or outer radius of the coil during machining. Encapsulation with a conductive material (e.g., solder) can also improve the electrical connection between the coil turns. Encapsulating the coil with a structurally effective material (such as resin or solder) provides efficient transfer of radial stress, allowing a higher current to be supplied to the coil to generate a stronger magnetic field without exceeding the coil's strain limit. Furthermore, the rigidity of the encapsulated coil can reduce the amount of support required for the coil. For example, the encapsulated coil can be supported only at the outer radius of the encapsulated coil (or conversely, at the inner radius of the encapsulated coil) by a rigid support structure.

[0138] By varying the width of the HTS material layer 103 (i.e., the extent along the field coil axis), the superconducting properties of the HTS field coils 1000, 1100, and 1200, such as the critical current, can be altered. Other materials removed typically include material from the axial edges of each layer in the HTS strip 100, namely the substrate 101, buffer stack 102, HTS material layer 103, and cladding layers 104 and 105. Other materials can be removed by machining one or both sides of the HTS field coils 200 and 500 after removing cladding layers 104 and 105 from one or more of the axial edges of the field coils 1000, 1100, and 1200. Alternatively (or additionally), the reduced-width HTS field coils can be fabricated by cutting through the HTS field coil, for example, across the HTS field coils 1000, 110, and 1200 in a plane perpendicular to the coil axis Z, thereby dividing the coil into two reduced-width HTS field coils. This plane bisects the field coils 1000, 1100, and 1200, such that each of the narrower field coils has a width approximately half the width of the original field coils 1000, 1100, and 1200. For example, one or more 12mm wide HTS strips can be wound into pancake coils, and then this pancake coil can be divided into two pancake coils, each with a width of approximately 6mm. Cutting through the field coils 1000, 1100, and 1200 can be accomplished, for example, by electrical discharge machining (also known as spark machining or wire erosion). The axial edges(s) of the HTS field coil(s) can be polished after machining to ensure no “short circuits” (i.e., no radial electrical connections between the windings) and / or to gently remove any edges damaged by the cutting process.

[0139] The axial edges (or potentially all outer surfaces) of the HTS field coil can preferably be hermetically sealed to prevent contaminants from entering the exposed layered structure. This can be achieved by applying an insulating coating such as ceramic or resin (e.g., epoxy). An insulating coating is preferred to avoid the formation of undesirable electrical connections between turns. However, in some cases, such as when the HTS field has a low inter-turn resistivity (e.g., a "partially insulated" coil), one or more metal layers (or applied beneath the insulating coating) can be applied alternatively to protect the individual layers of the HTS strip. For example, a nickel layer can be applied to the HTS coil, deposited onto the surface of the HTS field coil, for example, by electroplating or other chemical or physical deposition methods.

[0140] The method for manufacturing HTS field coils with reduced width contrasts with conventional methods, where the HTS field coil is manufactured by selecting or preparing an HTS strip 100 with a width corresponding to the desired width of the field coil. Specifically, cutting the field coils 1000, 1100, and 1200 to the desired width after winding the coil avoids the limitation of the coil width on the width of the HTS strip 100 available from the manufacturer. It also avoids the need to produce narrower HTS strips, which is typically time-consuming, difficult to be precise, and can lead to edge damage (cracks) that can cause long-term conductor degradation, especially in high-field coils, by cutting the commercially available HTS strip 100 to the required dimensions. Cutting through the HTS strip 100 after winding it into the field coils 1000, 1100, and 1200 also allows the HTS field coil profile to be shaped into a more complex geometry than a planar pancake coil. For example, when viewed along the axis of the coil, one or both axial surfaces of the field coil can be convex or concave. In some examples, one or both axial surfaces of the field coil can be flat-conical, i.e., shaped such that vectors perpendicular to the outer axial surface of the field coil diverge from or converge toward the axis. In some examples, only one axial surface is non-planar. Changing the width of the HTS field coil in this way allows for alteration (or “grading”) of the superconducting properties of the field coil for different windings. The magnetic field generated by the coil during use can also be shaped to some extent by changing the width of the field coil, which can be useful in applications requiring fine control of the magnetic field, such as in magnetic resonance imaging (MRI).

[0141] For example, HTS field coils with reduced widths produced by the above method can be electrically connected to each other, for example, to form a double pancake coil. One or more HTS field coils with reduced widths can be incorporated into an HTS solenoid formed by a stack of pancake coils. Preferably, the width of the coil (i.e., the range along the axis of the solenoid) can be adjusted according to its position in the stack. For example, coils located in or near the midplane of the HTS solenoid can have a reduced width compared to coils located far from the midplane of the solenoid. Typically, the width of the coil can increase with increasing distance from the midplane of the solenoid. It is preferable to place the thinner coil closer to the midplane because the magnetic field in this part of the solenoid is parallel to the HTS layer 103, and therefore the critical current density tends to be higher, unlike at the end of the solenoid where the field angle deviates from parallel, and the critical current density is typically lower. Therefore, it is desirable that the inner pancake coil (i.e., the pancake coil near the middle plane of the solenoid) is thin and the outer pancake coil is wider in order to balance the critical current of all pancake coils and to make optimal use of the conductor throughout the solenoid.

[0142] The above discussion regarding HTS field coils with reduced widths pertains to the manufacture of coils using "conventional" HTS strips including cladding 104, 105. However, in some cases, HTS field coils with reduced widths pertain to HTS strips 100 that do not include cladding 104, 105. Alternatively, in other examples, the HTS strip may include cladding 104, 105 that does not extend along the axial edges of the HTS strip.

[0143] Figure 18 Sector 1800 of an exemplary central column is shown. (Compared to...) Figure 8 Similar to sector 701 shown, sector 1800 is a cross-section through a D-shaped HTS coil comprising six pancake coils arranged as three double pancake coils. The HTS coil has been cut to provide a cross-section that is annular within the central column. In this example, this is achieved by leaving the four pancake coils 1801 facing the center of the sector unmodified, and cutting two pancake coils 1802 at the left and right sides of sector 1800 with bevels 1803 and 1804, such that the cross-section of the pancake coils 1802 tapers towards and away from the central axis of the central column. Figure 8 Compared to the coil in the previous example, bevels 1803 and 1804 are formed such that the pancake coil 1802 (and the other half of the corresponding double pancake coil) can be made larger, that is, the extent of the coil along the axis toward the central post can be increased (i.e., more windings can be accommodated), wherein bevel 1803 fits (i.e., is close to) the boundary of sector 1800. Bevels 1803 and 1804 can be cut exclusively in the straight portion of coil 1802 that passes through the central post (i.e., the “post” of each D-shaped coil), wherein the “return leg” (i.e., the portion outside the central post) remains unmodified.

[0144] Multiple such coils can be arranged to form a TF magnet, wherein the annular sector 1800 of the central column section of each coil 1802, 1801 is brought together to form the central column of the TF magnet.

[0145] Will Figure 18 and Figure 8 In comparison, the external double pancake coil 1802 has an area increased by approximately 50% in its cross-section, even considering the area loss due to the bevel cutting, and the total cross-sectional area of ​​the pancake coils 1801 and 1802 in the current-carrying elements is increased by approximately 25%. Figure 8 Compared to the current-carrying element, this significantly increases the current density of the current-carrying element. Further shaping of the coil and / or adding more shaped coils (e.g., adding to one or more gaps 1805) may potentially allow for even further improvements.

[0146] Figure 19 The results of stress simulations for the cross-section 1901 of the TF magnet are shown, illustrating the winding of the HTS strip 1902 of a single pancake coil with a rectangular (i.e., unmodified) cross-section. The stress at the radial interior of the HTS strip 1902 is unacceptably high (exceeding 500 MPa in some places, compared to the maximum acceptable compressive stress of 450 MPa for typically available HTS strips) and will lead to degradation and possible permanent damage to the HTS strip.

[0147] Figure 20 The results of stress simulation of the cross-section 2001 of the TF magnet are shown, along with the winding of the HTS strip 2002 with a single pancake-shaped coil cut into an oblique surface 2003. Compare this to... Figure 19 The comparison shows that the stress is significantly reduced—the stress of the entire structure is less than 330 MPa.

[0148] Coils 1802, 2002 (and the HTS field coils 1000, 1100, 1200 described above) can be cut and shaped by virtually any suitable method for cutting metal or metal composites, such as electrical discharge machining (EDM), grinding, sanding, etching, laser cutting, plasma cutting, waterjet cutting, etc. Shaping methods that generate significant heat can cause localized degradation of the HTS material near the cut, and if the HTS material reaches a temperature above the degradation temperature, which depends on the exact HTS material and manufacturer, but is typically from approximately 150 degrees Celsius to several hundred degrees Celsius. This degradation can be mitigated or avoided by providing appropriate cooling (e.g., water cooling) while the coil is being cut / shaped. Furthermore, the high thermal conductivity of partially insulated coils (especially if solder-encapsulated) means that it acts as an effective heat sink during the cutting process. In many cases, EDM is preferred because it minimizes damage to the strip and allows for easy adaptation to the resulting curved geometry through proper shaping of the electrodes used to generate the discharge. These methods can also be combined as needed. For example, bulk material can be removed by a method that may damage the axial edges of the HTS strip (which may be called a "roughing" process), and another method (which may be called a "finishing" process) can be used to remove the remaining damaged material after the roughing process.

[0149] Typically, HTS coils are particularly suitable for the cutting and shaping described above if the coil is as follows:

[0150] • Non-insulated or partially insulated, i.e., constructed such that current can be shared radially across substantially all of its length between the turns of the coil (e.g., coils comprising radially spaced current paths).

[0151] • Encapsulated, for example, encapsulated in solder or epoxy resin—that is, immersed in a material that will subsequently harden to provide additional structure for the coil (and, if conductive, provide additional current paths).

[0152] The coil can then be cut as described above to form any desired shape, provided that once cut, there is at least one current path around the winding of the coil, i.e., from the outermost radial end of the HTS strip (cable) to the innermost radial end of the HTS strip.

[0153] While the above examples pertain to TF coils in tokamak devices, it is understood that the techniques for cutting and shaping HTS coils can be applied to any application of HTS coils, and are particularly useful in applications where available space for the coil is limited and / or its shape is irregular, such as in aircraft and / or spacecraft. Furthermore, although the above description focuses on pancake-shaped coils, the method is equally applicable to other partially insulated or non-insulated coil structures, such as jointed coils.

[0154] As described above, another advantage of shaped HTS field coils is that the magnetic field generated by the coil can be better controlled. Figure 21 A contour plot showing the magnitude of the magnetic field generated near the central pillar 2100 of a TF magnet comprising 12 TF coils 2101 with rectangular cross-sections is shown. While the magnetic field far from the central pillar 2100 is substantially circularly symmetrical, the magnetic field near and within the central pillar exhibits a high level of “ripples” (i.e., a lack of symmetry). Shaping the coils 2101 into a “wedge” shape allows them to be packed more tightly together, thus significantly reducing the ripples. The uses of the shaped coils 2101 described herein are not limited to the central pillar of tokamak devices, but can also include other types of plasma chambers (e.g., star generators) or devices for generating precisely controlled magnetic fields, such as MRI machines, NMR spectrometers, and charged particle accelerators.

[0155] Figure 22 This is a flowchart of a method for manufacturing an HTS coil. In step 2201, a partially insulated coil is formed, for example by winding an HTS cable and a partially insulated layer around a molding die. In step 2202, the resulting coil is then encapsulated, for example, in solder or epoxy resin. In step 2203, the coil is machined into a desired shape by removing material (including the HTS material) such that a current path exists around the coil after molding.

[0156] Figure 23 This is a flowchart of a method for manufacturing a TF magnet comprising multiple HTS field coils for use in the plasma chamber of a tokamak device. The method includes:

[0157] • Step 2301: Following the method described above, manufacture multiple HTS field coils by removing material from one or more axial edges of the coil. Each HTS field coil (which may be a D-shaped coil, for example...) Figure 3 (As shown) includes the corresponding sectors for mounting to the central post of the TF magnet (e.g.) Figure 7 and Figure 8 The section (e.g., the current-carrying component shown) in the current-carrying component Figure 3 The “busbar” 311 shown in the diagram. Material is removed from the axial edge of the HTS strip of each HTS field coil so that the cross-section of that section of the HTS field coil is adapted to the cross-section of the sector;

[0158] • Step 2302: Install each HTS field coil segment into its respective sector; and

[0159] • Step 2303: Arrange sectors around the central axis to form the central pillar of the TF magnet. The windings within the HTS field coil sections installed in the sectors are arranged parallel to the central axis.

[0160] While various embodiments of the invention have been described above, it should be understood that they are presented by way of example and not limitation. It will be apparent to those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of the invention. For example, although the coil described above is described as having an HTS strip 100 arranged in a “Type 0” configuration, other configurations, such as “Type 1” and “Type 2” (e.g., described in WO2018 / 078326), may also be used. Similarly, although this disclosure refers to a “pancake” coil as an example, i.e., a generally planar coil formed by nested concentric windings, it will be understood from the above discussion that this disclosure is not limited to such coils. Similarly, although the above description relates to the ReBCO strip 100, other types of HTS strips consisting of one or more insulating (or partially insulating) buffer stacks may be used instead of or attached to the ReBCO strip 100. The properties of the buffer stacks, such as the composition of the layers and / or the thickness of the layers, may also be changed to make the coil insulating or partially insulating. For example, the buffer layer may be composed of or contain semiconductor materials, such as silicon and / or gallium arsenide. In some cases, the buffer layer stack may be composed of or contain one or more metal-insulator transition (MIT) materials, such as vanadium oxide (e.g., VO, V₂O₃, V₃O₅, V₄O₇, V₅O₉, etc.) to provide inter-turn resistance that may vary based on the metal-to-insulator phase transition within the material, for example, due to changes in the material's temperature.

[0161] The HTS field coils described above (or equivalently, HTS field coils manufactured according to the methods described above) are particularly suitable for use in aerospace applications. For example, HTS field coils can be incorporated into aircraft, unmanned aerial vehicles, satellites, spacecraft, rocket-propelled vehicles, and autonomous exploration vehicles. In such (and other) applications, removing material from the axial edges of one or more HTS strips allows for adjustment of the coil's shape, resulting in a smaller and lighter coil. This is particularly advantageous for technologies with space and weight constraints, such as in satellites. HTS field coils with buffer layer insulation are also advantageous in this regard, as they can provide partially insulated (PI) or fully insulated coils without the need to introduce additional insulating material layers between the windings, thus further reducing the coil's volume / weight. Furthermore, since the HTS strips are typically not modified when the HTS field coil is wound (material is removed after winding), a tightly wound, consolidated coil can be formed, capable of withstanding significant forces, such as those generated during aircraft takeoff or satellite launch. In contrast, producing HTS field coils with high mechanical stability using other manufacturing methods is generally more difficult. In other manufacturing methods, material is removed from the HTS strip before winding the coil, or additional layers need to be introduced between the windings.

[0162] Typically, HTS field coils are configured to generate a magnetic field with a specific intensity and spatial distribution. However, in some cases, material can be removed from the axial edges of one or more HTS strips to reduce the size and mass of the coil while largely preserving the intensity and / or spatial distribution generated by the coil. The amount and / or location of the material to be removed can be determined through trial and error, or preferably through computer simulations (e.g., finite element models) of the coil and its associated magnetic field. In the latter case, evolutionary or genetic algorithms can be used to optimize the material removal. For example, these algorithms may be subject to one or more constraints (e.g., acceptable tolerances) related to the intensity and spatial distribution of the magnetic field and / or the operating parameters of the coil (such as current and temperature).

[0163] The shape of the HTS field coil can also be modified (or alternatively) by removing material from the HTS strip to obtain a specific current distribution within the strip when the coil is used. For example, material can be removed from the HTS strip (e.g., by machining the coil) such that the ratio of current to critical current (I / Ic) is adjusted. CThe current is approximately constant for a specific region of the coil or the entire coil. This optimization reduces “excess” current (i.e., current exceeding the critical current) and allows the coil to operate in a “saturation” mode, where the current is essentially equal to the critical current, minimizing resistive heating within the coil. An example of this type of optimization is the HTS pancake coil, which is divided into two or more HTS field coils with reduced widths, i.e., a reduced range along the axis of the coil (see the discussion above on reduced-width HTS field coils), for example, by “wire-cutting” the pancake coil into two smaller (reduced-width) pancake coils. Another benefit associated with coils manufactured in this way is the reduction in the current required by the power supply, thus allowing the use of smaller and / or lighter power supplies and non-superconducting current-carrying components. The reduced power consumption of the HTS field coil can also extend the life of the power supply, which can be, for example, an electrochemical cell unit (battery).

[0164] As understood by those skilled in the art, in some cases, the technique for removing material from the HTS field coil can be selected based on the application using the HTS coil. However, any of the techniques described above can generally be used, such as EDM, grinding, sanding, etching, laser cutting, plasma cutting, waterjet cutting, chemical material removal, etc.

Claims

1. A method for manufacturing a high-temperature superconductor (HTS) field coil, the method comprising: An initial HTS field coil is formed by winding one or more HTS strips around an axis through multiple turns; and Cut through the initial HTS field coil to divide the initial HTS field coil into two or more HTS field coils.

2. The method according to claim 1, wherein, Each turn includes two or more HTS strips.

3. The method according to claim 2, wherein, The two or more HTS strips include at least two HTS strips, which are arranged such that the HTS planes of the two HTS strips face each other.

4. The method according to claim 1, wherein, The cutting includes cutting through the initial HTS field coil in a plane substantially perpendicular to the axis of the initial HTS field coil.

5. The method according to claim 4, wherein, The plane bisects the initial HTS field coil.

6. The method according to claim 1, wherein, The initial HTS field coil is a pancake coil.

7. The method according to claim 1, wherein, Forming the initial HTS field coil includes consolidating the initial HTS field coil by combining the turns together.

8. The method of claim 1, further comprising sealing one or more axial edges of the HTS field coil exposed by the cut.

9. The method according to claim 8, wherein, The seal includes sealing with an electrical insulating material.

10. The method according to claim 8, wherein, The seal includes sealing with an electrically conductive material.

11. The method of claim 1, further comprising cooling the initial HTS field coil during the cutting process.

12. The method of claim 1, further comprising forming one or more electrical connections between two or more HTS field coils to form a solenoid.

13. A high-temperature superconducting HTS field coil manufactured according to any one of the preceding claims.

14. A solenoid comprising two or more HTS field coils according to claim 13.

15. A method of manufacturing an electromagnet, the electromagnet comprising a high-temperature superconducting HTS field coil mounted in a recess or enclosed space, the method comprising: Obtain an HTS field coil comprising windings of one or more HTS strips around an axis; By removing material from the axial edges of the one or more HTS strips around at least a portion of the one or more windings to reduce the extent of the one or more HTS strips along the axis of the field coil, the HTS field coil is adapted to fit the recess or the enclosed space; and The HTS field coil is installed into the recess or the enclosed space.

16. A method for manufacturing a circumferential field TF magnet comprising a plurality of high-temperature superconducting (HTS) field coils having a central axis for a plasma chamber of a tokamak device, each HTS field coil comprising a winding of one or more HTS strips around the axis, the method comprising: By removing material from the axial edges of the one or more HTS strips around at least a portion of the one or more windings to reduce the extent of the one or more HTS strips along the axis of the field coils, a segment of each HTS field coil in the HTS field coils is adapted to mount the segment into a corresponding sector of the central post of the TF magnet. Each HTS field coil segment is installed into its respective sector; and The sectors are arranged around the central axis to form the central column of the TF magnet, wherein the windings within the segments of the HTS field coils mounted in the sectors are arranged parallel to the central axis.

17. The method according to claim 16, wherein, Removing the material causes the cross-section of the section of the HTS field coil to taper toward and / or away from the central axis.

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