HTS Tapes with Improved Lateral Conductivity

Abstract

A high temperature superconducting (HTS) tape. The HTS tape comprises a superconducting layer formed from an HTS material, a substrate, and one or more buffer layers separating the superconducting layer from the substrate. The HTS tape further comprises a plurality of holes penetrating at least the superconducting layer and the one or more buffer layers, and a conductive material in each hole. The conductive material penetrates the one or more buffer layers via the holes to provide an electrical connection to the superconducting layer.

Description

[Technical field]

[0001] The present invention relates to high temperature superconductors, and in particular to high temperature superconducting ReBCO tapes. [Background technology]

[0002] Superconducting materials are usually classified as "high temperature superconductors" (HTS) and "low temperature superconductors" (LTS). LTS materials, such as Nb and NbTi, are metals or metal alloys whose superconductivity can be explained by BCS theory. All low temperature superconductors have a self-field critical temperature (the temperature above which the material does not become superconducting even in the absence of an external magnetic field) below about 30 K. The behavior of HTS materials is not explained by BCS theory, and such materials may have a self-field critical temperature above about 30 K. The most commonly used HTS are "cuprate superconductors", ceramics based on cuprates (compounds containing a copper oxide group), such as BSCCO or ReBCO (where Re is a rare earth element, usually Y or Gd). Other HTS materials include iron pnictides (e.g., FeAs and FeSe) and magnesium diborate (MgB2).

[0003] ReBCO superconductors are typically manufactured as tapes with a thickness of about 100 micrometers and a width of 2 mm to 12 mm. A typical tape structure is shown in FIG. 1 and includes a substrate 101 (typically an electropolished nickel-molybdenum alloy, e.g. Hastelloy®, about 50 micrometers thick), on which a series of buffer layers, known as a buffer stack 102, with a thickness of about 0.2 micrometers, are deposited. An epitaxial ReBCO-HTS layer 103 covers the buffer stack, typically 1 micrometer thick. A 1-2 micrometer silver layer 104 and a copper stabilizing layer 105 are deposited on the tape, often completely encapsulating it. The silver layer 104 and the copper stabilizing layer 105 extend continuously around the periphery of the tape 100 (not shown in FIG. 1 for clarity) and are therefore also referred to as "cladding". The silver layer 104 forms a low resistance electrical interface to the ReBCO layer 103 and a hermetic protective seal around the ReBCO layer 103, while the copper layer 105 allows external connections to be made to the tape from either side (e.g., by soldering) and provides a parallel conductive path for electrical stabilization.

[0004] A "peeled" HTS tape can be produced that lacks the substrate and buffer stack, but has a "periphery coating", usually of silver. The tape with the substrate can be referred to as a "substrate-attached" HTS tape.

[0005] HTS cables comprise one or more HTS tapes connected along their length via a conductive material (usually copper). The HTS tapes can be stacked (i.e. arranged so that the HTS layers are parallel) or have other arrangements of the tapes that can vary along the length of the cable. Notable special cases of HTS cables are single HTS tapes and HTS pairs. HTS pairs comprise a pair of HTS tapes arranged so that the HTS layers are parallel. When substrate-attached tapes are used, the HTS pairs can be type 0 (HTS layers face each other), type 1 (HTS layer of one tape faces the substrate of the other tape), or type 2 (substrates face each other). Cables with three or more tapes can have some or all of the tapes arranged in HTS pairs. Stacked HTS tapes can comprise either various arrangements of HTS pairs, most commonly a stack of type 1 pairs or a stack of type 0 pairs (or equivalently type 2 pairs). HTS cables can comprise a mix of substrate-attached and release tapes.

[0006] Superconducting magnets are formed by arranging HTS cables (or individual HTS tapes, which for the purposes of this description can be treated as a single-tape cable) into a coil, either by winding the HTS cable or by providing multiple sections of coils made from HTS cables and joining them together. The turns of the coil can be insulated, uninsulated, or partially insulated, for example by having a controlled resistance between the turns, as described in U.S. Pat. No. 5,399,323.

[0007] Due to the layered structure of the HTS tape, low resistance joints can only be made on the surface of the tape closest to the HTS layer (i.e., the "HTS side"). The opposite surface closest to the substrate (the "substrate side") will necessarily have a higher resistance between the HTS and any joints on that surface. FIG. 2 shows an HTS tape 200 having a first joint to a first conductor 210 and a second joint to a second conductor 220. The HTS tape comprises an HTS layer 201, a substrate 202, a buffer layer (not shown) separating the HTS layer from the substrate, and a copper clad or other metal clad 203. Silver layers as described above and other layers may also be present. The first conductor 210 is located on the HTS side of the tape 200 and allows current to flow directly from the HTS layer 201 to a path 211 through the entire surface of the copper clad 203 on the HTS side. In contrast, current to the second conductor 220 cannot flow directly from the HTS layer 201 to the substrate 202 and then to the copper cladding and second conductor because the buffer layer of the HTS tape 200 is insulating. Therefore, the current follows a path 221 through the copper cladding at the edge of the tape. This path 221 is longer and has a smaller cross-sectional area than the path 211 taken by the current flowing in the first conductor 210, and therefore has a higher resistance. This limits the ability to create low resistance joints for certain configurations of the HTS tape. This effect also increases the turn-to-turn resistance of uninsulated and partially insulated coils.

[0008] One option to overcome this problem is the use of release tape, as mentioned above, however release tapes are generally more fragile than substrate-attached tapes and are expensive to obtain in significant lengths. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 2019 / 150123 Summary of the Invention [Means for solving the problem]

[0010] According to a first aspect, a high temperature superconducting (HTS) tape is provided. The HTS tape comprises a superconducting layer formed from an HTS material, a substrate, and one or more buffer layers separating the superconducting layer from the substrate. The HTS tape further comprises a plurality of holes penetrating at least the superconducting layer and the one or more buffer layers, and a conductive material within each hole. The conductive material provides an electrical connection of the superconducting layer to the HTS material through the one or more buffer layers via the holes.

[0011] According to a second aspect, a method of modifying an HTS tape is provided. An HTS tape is provided having a superconducting layer formed from an HTS material, a substrate, and one or more buffer layers separating the superconducting layer from the substrate. A plurality of holes are formed through at least the superconducting layer and the buffer layers of the HTS tape. A conductive material is provided within the holes such that the conductive material penetrates the one or more buffer layers through the holes to provide an electrical connection to the HTS material of the superconducting layer. For example, the conductive material is electrically connected to the substrate and the HTS layer.

[0012] According to a third aspect, a method for manufacturing a high temperature superconducting (HTS) tape is provided. A substrate is provided, the substrate having a plurality of holes extending from a first surface of the substrate at least part way through the substrate. One or more buffer layers are deposited on the first surface of the substrate. A high temperature superconducting (HTS) material is deposited on the buffer layers. The buffer layers and the HTS material are not deposited on the substrate holes. A conductive material is provided in the holes such that the conductive material penetrates the one or more buffer layers through the holes to provide an electrical connection to the HTS material of the superconducting layer. For example, the conductive material is electrically connected to the substrate and the HTS material.

[0013] According to a fourth aspect, there is provided a high temperature superconductor (HTS) field coil comprising one or more HTS tapes wound around an axis of the coil, each HTS tape being an HTS tape according to the first aspect or an HTS tape modified or manufactured according to the second or third aspect, respectively.

[0014] According to a fifth aspect, there is provided a high temperature superconducting (HTS) cable comprising a plurality of HTS tapes according to the first aspect or a plurality of HTS tapes modified or manufactured according to the second aspect or the third aspect, respectively.

[0015] HTS tapes embodying the invention typically also include at least one conductive layer, e.g., a metal layer such as the silver-clad and / or copper-clad layers shown in Figure 1. The conductive layer can cover either the substrate or the superconducting layer, or both, on the side opposite an intervening buffer layer.

[0016] In use, embodiments of the present invention provide a path by which electrical current can flow from the HTS material, through the conductive material, and through holes provided in the at least one buffer layer. [Brief description of the drawings]

[0017] [Figure 1] The structure of the HTS tape is shown. [Diagram 2] 1 shows an HTS tape bonded to two conductors. [Figure 3A] 1 shows an HTS tape with multiple holes. [Figure 3B] 3B shows the HTS tape of FIG. 3A after being filled with a conductive material. [Figure 4A-4C] 1 shows various hole configurations for HTS tapes. [Diagram 5] 1 shows an HTS tape with blind holes in the substrate. [Figure 6] A cross section of the HTS coil is shown. [Figure 7] 1 illustrates directional terms used herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] To reduce the resistance to electrical current flow between the HTS side and the substrate side of the tape, an HTS tape is proposed herein having holes through at least the HTS layer and the electrically insulating buffer layer. The holes are at least partially filled with a conductive material, such as a metal or metal alloy. The conductive material provides a path for electrical current to flow from the substrate side of the tape, through the holes, through one or more electrically insulating buffer layers, and to the HTS layer.

[0019] FIG. 3A shows an HTS tape 310 having a substrate 311, an HTS layer 312, a silver coating 313, a copper cladding 314, and at least one electrically insulating buffer layer 315 between the HTS layer and the substrate. The HTS tape has a number of holes 320 that penetrate the entire thickness of the HTS tape. Each hole 320 is shown to have a consistent size and shape throughout the HTS tape 310, although tapered holes, conical holes, or holes that are otherwise non-uniform throughout their depth are also possible. FIG. 3B shows the same HTS tape 310 after the holes have been filled with a metal or other conductive material 316 to form a conductive path through the buffer layer 315.

[0020] The holes can have any suitable size, shape, spacing, spatial density, arrangement, or geometry. Each of these characteristics, as well as the depth of the blind holes, may be constant across the surface of the tape, or may vary regularly or irregularly. For example, FIG. 4A shows an HTS tape 401 having an array of substantially circular holes 402 penetrating the HTS tape 401, although other shapes are possible. The array may be, for example, a square, rectangular, or hexagonal grid to simplify both modeling of expected results and formation of the holes. Each hole may have a cross-section in which both linear dimensions are substantially uniform and have equal or nearly equal proportions. Alternatively, the holes may be elongated, with one dimension extending significantly further than the other. For example, FIG. 4B shows an HTS tape 403 divided into filaments by a series of elongated linear holes 404 (i.e., grooves) extending along the HTS tape. As yet another example, Figure 4C shows an HTS tape 405 having a series of elongated linear holes 406, each extending a short distance along the HTS tape. The elongated holes may also follow curved or other non-linear paths. The depth of the elongated blind holes into the substrate 311 may vary over their length or may be through holes over some range (as described in more detail below in connection with Figure 5).

[0021] The holes are small, or in the case of elongated holes, narrow in width compared to the width of the tape. Thus, FIG. 3A, as well as all figures, is not drawn to scale. For example, the holes generally have a minimum or small width (e.g., diameter of a substantially circular hole or width of a slot) of 1 micrometer to 1 millimeter, more preferably 10 to 100 micrometers. The spacing between the centers of adjacent holes can be, for example, 2 to 10 times their diameter.

[0022] In general, to ensure that a superconducting path exists along the tape, it is desirable that all remaining ReBCO or other HTS material be electrically connected at least to the ends of the tape through other ReBCO (e.g., in a grooved tape having grooves that run the entire length of the tape) and / or that the remaining ReBCO form a connected surface, i.e., a surface where each point can be connected to each other point without leaving the surface. Geometries that do not follow any of these restrictions are possible and may be desirable, for example, for specific joint configurations or to provide isolated regions of superconductor within the tape for other purposes. Arranging the holes along the tape such that there are no blocked or restricted superconducting paths (e.g., no dead ends) in the direction of current flow ensures minimal reduction in current density or critical current of the HTS tape. Control of current density throughout the tape and other desired effects can be provided by intentionally creating a serpentine path through the superconducting material along the tape. For example, the holes can be arranged in a regular lattice at an angle to the length of the tape to provide a serpentine current path along the tape.

[0023] As shown in Figure 5, it is also possible to provide an HTS tape in which the holes penetrate (from the HTS side) the HTS layer 312 and the buffer layer 315 of the tape 310 without penetrating completely through the substrate 311, i.e. the holes are blind holes into the substrate 311. Similar to the through holes of Figures 3A and 3B, the blind holes are filled with a conductive material 516 that provides an electrical connection between the HTS layer 312 and the substrate 311 through the buffer layer 315. Since typical metal alloy substrates are conductive, this still provides the advantage of reducing resistance by providing an alternative current path.

[0024] The resistance across the tape depends on the size, spacing, geometry, and number of holes provided. This can be modeled analytically and / or numerically using techniques known in the art. The resistance also depends on the depth of the holes and the material used to fill the holes. That is, a highly resistive material in the holes will produce a greater resistance across the tape than a less resistive material for the same hole geometry. Also, if the substrate is more resistive than the material used to fill the holes, the deeper the holes extend into the substrate, the lower the resistance will be (and vice versa if the substrate is less resistive than the material filling the holes).

[0025] To further fine-tune the resistance, an insulating layer can be provided on the side of the holes (i.e., before filling each hole with conductive material) between the conductive material filling each hole and the substrate. This means that the resistance depends more simply on the geometry of the holes and the resistivity of the material filling them, without having to consider the lateral flow of current through the substrate.

[0026] The greatest reduction in resistance is generally obtained by increasing the total cross-sectional area of ​​the holes in the HTS tape. However, as the area of ​​the holes increases, the critical current of the HTS tape also decreases, since there is less ReBCO to provide a superconducting path. Thus, the desired geometry is a balance between the resistance and critical current required for the tape, both of which can be modeled in a manner known in the art. As mentioned above, the placement of the holes should not result in actual breaks in the tape. For example, holes that extend across the entire width of the HTS tape are not preferred, as this would result in a break in the superconducting path. Instead, the holes should be such that each region of ReBCO on the tape is connected, via a continuous path through the ReBCO, at least to each end of the tape, and optionally to each other region of ReBCO.

[0027] In addition to providing a resistive path through the tape, holes in the tape also act to reduce shielding currents in a manner similar to grooved tape; that is, the holes create obstacles in the superconducting material that limit the length and width of the shielding currents generated in the HTS. An array of holes arranged to create a meandering current path along the tape can be used in place of narrow grooves for substantially the entire length of the tape as a technique for reducing shielding currents. This effect occurs whether or not the holes are filled with conductive material.

[0028] The pattern of the holes, including the number, spacing, size, or other characteristics of the holes, can be varied along the length of the tape, for example, to provide different resistance or critical current characteristics in different areas of the tape.

[0029] If the holes extend into the substrate, a large cross-sectional area of ​​the holes may be undesirable due to mechanical considerations, i.e., cutting the tape too much may weaken it too much, however this can be mitigated by providing a specific hole pattern (e.g. the pattern in FIG. 4C is stronger than the pattern in FIG. 4B due to increased links between uncut areas) or by the choice of material to fill the holes.

[0030] The holes can be formed by any suitable technique, for example: Ablative cutting (e.g. laser cutting, electron beam cutting, ion beam cutting) can be used to cut the HTS tape to the desired depth. This will cause some thermal damage to the surrounding areas of the HTS depending on the type, strength, and pulse duration of the ablative cut used. It has been found that 20 micrometer diameter through holes in the HTS tape can be created with little damage to the surrounding ReBCO. Mechanical punching, drilling, scribing, or slitting of the tape can be used to create holes about 100 micrometers wide, which results in some cracking of the ReBCO. Chemical etching can be used to create holes with 10 to 100 micrometer precision (even smaller with advanced photolithography processes) and dissolve metals (e.g., copper or silver) and ReBCO with minimal damage to the surrounding materials. However, because the buffer layer is generally not susceptible to chemical attack, chemical etching may be used in combination with any of the above methods, i.e., by etching the outer cladding layer of the tape and HTS to expose the buffer layer for the holes, and then using alternative methods (e.g., mechanical cutting or laser cutting) to create holes through the buffer layer within the holes created by chemical etching. The holes created through the buffer layer can be smaller than those created by chemical etching to avoid thermal or mechanical stress to the ReBCO layer during their creation.

[0031] Different hole forming techniques can create tapered holes or holes that are non-uniform in size as they pass through the HTS tape. For example, using a lower power or intensity laser during ablation cutting can result in a larger hole where the laser enters the HTS tape than at the exit point for a through hole or the bottom of a blind hole. In general, the greater the intensity of the laser or other cutting beam, the closer the sides of the hole will be to parallel. When cutting tapered holes from the substrate side of the HTS tape, the widest part of the hole will be in the substrate 311, minimizing damage to and removal of material from the HTS layer 312.

[0032] Instead of cutting holes in the HTS tape, the HTS tape can be created with holes drilled in situ. This can be achieved, for example, by providing a substrate with holes in predetermined locations and depositing the buffer layer and HTS material on this substrate, resulting in an HTS tape with the required holes. The holes can then be filled with a suitable conductive material. If some conduction through the substrate is desired, the initial holes in the substrate can be blind holes. Besides providing the substrate, the deposition of the buffer layer and the HTS layer is performed according to conventional techniques, for example, pulsed laser deposition (PLD), chemical vapor deposition (CVD), chemical solution deposition (CSD), reactive co-evaporation (RCE), etc. In all cases, a macroscopically uniform film of material with a thickness on the nanometer to micrometer scale is grown on the tape surface.

[0033] Suitable conductive materials for filling the holes include metals or metal alloys (e.g., silver, copper, additional cladding materials, or solders), semiconductors, metal-insulator transition materials, or composite materials. The conductive material 316 can be applied in a liquid or molten state. High temperatures can damage the HTS layer 312, so it is beneficial to use a solder with a low melting point. Using a solder or other liquid-state material with low surface tension helps ensure that the holes are substantially filled with material and have few voids to provide a good electrical path through the buffer layer 315. Electroplating and similar techniques can also be used to at least partially fill the holes with the conductive material.

[0034] Some conductive materials may react with different layers of the HTS tape after filling the holes. For example, some solders will react with silver over time and dissolve. To prevent long-term damage to the silver coating 313, solders with higher silver content, closer to their saturation point, can be used.

[0035] The formation of holes and their subsequent filling can damage the superconducting material around the holes. For example, the area around the holes is damaged by the heat generated during laser cutting, while solder and other filling materials damage any superconducting material with which they are in physical contact. The damaged superconducting material becomes insulating and cannot conduct electrical current even at cryogenic temperatures. In such cases, an alternative current path formed through the insulating buffer layer is from the undamaged superconducting material 312 into the overlying metal layers 313, 314 to bypass the damaged area, and from the metal layers 313, 314 to the conductive material 316 in the holes (or vice versa). Tests have shown that damage to the superconducting material caused by laser cutting and subsequent filling of the holes with solder is limited to an area of ​​approximately 10 to 20 micrometers wide surrounding each hole.

[0036] When used to form high temperature superconducting magnets or HTS cables, the HTS tapes described above improve electrical conductivity between stacked HTS tapes. For example, when wound into a pancake coil (i.e., a simple coil in which the HTS is wound in a manner similar to a single turn of ribbon), the HTS tapes described above reduce the radial resistance between the turns of the coil, which can be easily controlled as described above.

[0037] Such HTS tapes can be used to form buffer-layer insulated HTS coils as described in WO 2021 / 224279, resulting in a buffer-layer insulated coil that is a partially insulated coil similar to that described in WO 2021 / 224279. The result is an HTS coil as shown in FIG. 6, where each turn 601 has a radial conductive path to the other turns through holes 602 and the copper cladding and / or substrate (e.g., if the holes are blind holes to the substrate). The coil may be insulated at the ends such that the buffer layer extends to each side of the insulator or coil, meaning that the only conductive radial path through the buffer layer is through the conductive elements in each hole. A similar structure can be applied to HTS cables formed from the tape, i.e., the only conductive path across or through the buffer layer of each HTS tape in the cable is through the conductive elements, eliminating the need for conductive edging to connect the turns of the cable.

[0038] When terms such as "length," "width," "depth," or similar terms are used herein, they refer to specific directions relative to the HTS tape as conventionally used in the art and as shown in FIG. 7. "Length," "Along," or similar terms refer to features or measurements that extend along the longest major axis of the HTS tape, parallel to the plane of the HTS material layers in the tape (701). "Width," "Across," or similar terms refer to a direction perpendicular to the "length," but still parallel to the plane of the HTS material layers (702). "Thickness," "Through," or similar terms refer to a direction perpendicular to both the "width" and "length," and perpendicular to the plane of the HTS material layers (703). The sides of the HTS tape separated in the length direction 701 are "ends" 710, the sides of the HTS tape separated by the width dimension 702 are "edges" 720, and the sides separated by the thickness dimension 703 are "faces" 730. These are defined relative to a flat HTS tape, but apply equally when the tape is curved. For example, if a tape is wrapped in a circle about an axis parallel to its width, the length of the tape extends around the circle and each face forms a cylinder.

[0039] While the above has primarily referred to ReBCO tapes, it should be understood that similar techniques can be applied to similarly constructed HTS tapes using alternative HTS materials, such as those using iron-based superconductors.

Claims

1. 1. A high temperature superconducting (HTS) tape comprising: a superconducting layer formed from an HTS material; A substrate; one or more buffer layers separating the superconducting layer from the substrate; a plurality of holes extending through at least the superconducting layer and the one or more buffer layers; a conductive material in each hole that passes through the one or more buffer layers and provides an electrical connection to the superconducting layer through the hole; An HTS tape comprising:

2. The HTS tape of claim 1 , wherein each hole extends completely through the substrate.

3. The HTS tape of claim 1 , wherein each hole extends at most partially into the substrate.

4. 4. The HTS tape according to claim 1, wherein the holes are arranged such that the HTS of the superconducting layer forms a connection surface and / or such that all parts of the HTS are electrically connected to the ends of the tape via the HTS layer.

5. Each hole is A hole having a substantially circular cross section; a groove extending along the HTS tape; or A groove extending only partially along the HTS tape 5. The HTS tape according to claim 1 , wherein

6. 6. The HTS tape of claim 1 , wherein one or more of the size, shape, spatial density and / or spacing of the holes varies along the length of the HTS tape.

7. 7. The HTS tape of claim 1, wherein the conductive material substantially fills each hole.

8. 8. The HTS tape of claim 1, wherein the conductive material provides an electrical connection between the superconducting layer and the substrate through the holes.

9. 9. The HTS tape of claim 1, wherein the conductive material is any of a metal, a metal alloy, silver, copper, a solder, a semiconductor, a metal-insulator transition material, or a composite material.

10. 10. The HTS tape of any one of claims 1 to 9, wherein each hole has a minimum width of from 1 micrometer to 1 millimeter, more preferably from 10 micrometers to 100 micrometers.

11. 1. A method for modifying an HTS tape, comprising: An HTS tape, a superconducting layer formed from an HTS material; A substrate; one or more buffer layers separating the superconducting layer from the substrate; providing an HTS tape having forming a plurality of holes through at least the HTS layer and the buffer layer of the HTS tape; providing a conductive material in each hole such that the conductive material passes through the hole and through the one or more buffer layers to provide an electrical connection to the superconducting layer; The method includes:

12. forming the plurality of holes Chemical etching of the HTS layer and / or the buffer layer, Mechanical etching of the HTS layer and / or the buffer layer, Ablative cutting of the HTS tape and / or buffer layer The method of claim 11 , comprising one or more of the following:

13. 13. The method of claim 12, wherein forming the plurality of holes comprises chemically etching the HTS layer to form a plurality of first holes, and ablatively cutting or mechanically etching the buffer layer and optionally the substrate to form a plurality of second holes, each second hole having a cross-sectional area smaller than a cross-sectional area of ​​a respective first hole in the HTS layer, and each second hole being located at a bottom of a respective first hole in the HTS layer.

14. 14. The method of claim 12 or 13, wherein providing a conductive material within the hole comprises substantially filling the hole with a conductive material.

15. 15. The method of claim 12, wherein the conductive material provides an electrical connection between the superconducting layer and the substrate through the holes.

16. 11. A high temperature superconductor (HTS) field coil, the HTS field coil comprising a winding of one or more HTS tapes about an axis of the coil, the or each HTS tape being an HTS tape according to any one of claims 1 to 10.

17. 17. The HTS field coil of claim 16, wherein at least one of the one or more HTS tapes is configured such that the only conductive path extending radially across or through the buffer layer for the one or more windings is the conductive material in each hole.

18. 18. An HTS field coil as claimed in claim 16 or 17, wherein the or each HTS tape has a higher density of holes in areas of the HTS field coil which include joints between the HTS tapes or cables than in areas of the HTS field coil which do not include joints.

19. 20. The HTS field coil of claim 18, wherein the or each HTS tape has no holes in areas of the HTS field coil that do not include joints.

20. 1. A method for producing a high temperature superconducting (HTS) tape, comprising: providing a substrate having a plurality of holes extending from a first surface of the substrate at least part way through the substrate; depositing one or more buffer layers on a first surface of the substrate; depositing a high temperature superconducting (HTS) material on the buffer layer; preventing the buffer layer and HTS material from being deposited over holes in the substrate; providing a conductive material within the holes, such that the conductive material passes through the holes and through the one or more buffer layers to provide an electrical connection to the HTS material; The method includes:

21. 11. A high temperature superconducting (HTS) cable comprising a plurality of HTS tapes according to any one of claims 1 to 10.

22. 22. The HTS cable of claim 21, wherein at least one of the one or more HTS tapes is configured such that the only conductive path extending across or through the buffer layer for one or more of the HTS tapes is the conductive material in each hole.

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