Non-planar HTS coils and manufacturing techniques.

Abstract

The stellarator structure includes an HTS cable including a coil former having at least one channel and a tape stack within the at least one channel of the coil former, the at least one channel and the tape stack being stranded along a longitudinal direction.

Description

[Technical field]

[0001] Related Applications This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 63 / 191,066, entitled "NON-PLANAR HTS COILS AND MANUFACTURING TECHNIQUES," filed on May 20, 2021, and U.S. Provisional Patent Application No. 63 / 310,709, entitled "NON-PLANAR HTS COILS AND MANUFACTURING TECHNIQUES," filed on February 16, 2022, the entire contents of each of which are incorporated herein by reference.

[0002] The apparatus and techniques described herein relate to non-planar High Temperature Superconductor (HTS) cables and fabrication techniques for forming non-planar HTS cables that can provide magnetic confinement in stellarators or that can be used in other applications. [Background technology]

[0003] Nuclear fusion for power generation may use magnetic confinement to contain the plasma within the reactor. Apart from tokamaks, stellarators are the only other reliable magnetic confinement concept to date. Currently, energy containment within stellarators is not as good as tokamaks, but stellarators have some attractive features, such as lack of disruption and steady-state operation. The most advanced stellarators attempt to exploit the quasi-symmetry of the magnetic field to improve particle containment, but this may require extreme three-dimensional non-planar coils with precise geometric shapes to generate the required magnetic field structure. Standard niobium-titanium alloy superconductors have been used successfully in the construction of these large-scale three-dimensional non-planar coils for the W7-X stellarator, which has a maximum on-axis magnetic flux density of 3 Tesla. Summary of the Invention [Means for solving the problem]

[0004] Some embodiments relate to a high temperature superconductor (HTS) cable comprising a winding former having at least one channel and at least one HTS tape stack, a first HTS tape stack of the at least one HTS tape stack disposed in a first channel of the at least one channel, the first HTS tape stack and the first channel being twisted along a longitudinal direction of the HTS cable, and the first HTS tape stack having a twist pitch at a first location of the HTS cable that is shorter than a bend radius of the HTS cable at the first location.

[0005] The twist pitch may be less than 100 mm, and the bending radius may be 100 mm or less.

[0006] The HTS cable may have a non-planar geometry.

[0007] The HTS cable may have a stellarator conductor geometry.

[0008] Some embodiments relate to a stellarator comprising a high temperature superconductor (HTS) cable including a former having at least one channel and at least one HTS tape stack, a first HTS tape stack of the at least one HTS tape stack disposed in a first channel of the at least one channel, the first HTS tape stack and the first channel being stranded along a longitudinal direction of the HTS cable, and the first HTS tape stack having a lay pitch at a first location of the HTS cable that is shorter than a bend radius of the HTS cable at the first location.

[0009] Some aspects relate to a method of forming a high temperature superconductor (HTS) cable, the method including placing an HTS tape stack in a channel of a winding former and securing a plurality of compression structures on the HTS tape stack in the channel at a plurality of discrete locations along the channel to retain the HTS tape stack in the channel.

[0010] The method may include removing the plurality of compression structures from the channel.

[0011] The method may include fitting a cable jacket over the former and the HTS tape stack.

[0012] The multiple compression structures may be secured together by strings or straps.

[0013] Some embodiments relate to a method of forming a cable, the method including twisting a former having at least one channel to produce a first lay pitch, annealing the former after twisting the former to produce the first lay pitch, and twisting the former to produce a second lay pitch less than the first lay pitch after annealing the former.

[0014] The method may include disposing an HTS tape stack in a first channel of the at least one channel after twisting the former to produce a second twist pitch.

[0015] Some embodiments relate to a method of forming a high temperature superconductor (HTS) cable, the method including coupling an extension to an end of a former that also includes at least one channel, affixing at least one HTS tape stack to the extension, and inserting a first HTS tape stack of the at least one HTS tape stack into the channel while the first HTS tape stack is affixed to the extension.

[0016] The bonding step may include attaching at least one HTS tape stack to the extension under tension.

[0017] The method may include cutting an end of at least one HTS tape stack that is attached to an extension, and removing the extension after the cutting step.

[0018] The step of coupling the extension may include inserting a rod into a central cooling channel of the former and into the extension.

[0019] Some embodiments relate to a method of forming a high temperature superconductor (HTS) cable, the method including manufacturing a former having at least one channel on a surface of the former, the channel being wider than the HTS tape stack and / or having sidewalls at an angle greater than 90 degrees, stranding the former to have a first strand pitch, and after the stranding, inserting the HTS tape stack into the first of the at least one channel.

[0020] The phrases "HTS material" or "HTS superconductor" refer to a superconducting material that has a critical temperature above 30° K in a self-field. An example of a ceramic HTS is a rare-earth based superconductor (REBCO: Rare-Earth Barium Copper Oxide). The HTS superconductor may be formed into a tape or tape stack that includes several layers of various materials. The HTS material may be a REBCO, specifically a yttrium based superconductor (YBCO: Yttrium Barium Copper Oxide).

[0021] In the drawings, each identical or nearly identical component illustrated in various figures is represented by a similar reference numeral. For purposes of clarity, not every component may be labeled in every figure. The drawings are not necessarily drawn to scale, emphasis instead being placed on illustrating various aspects of the techniques and apparatus described herein. [Brief description of the drawings]

[0022] [Figure 1] FIG. 2 illustrates an example cable according to some embodiments. [Diagram 2] 1A-1C illustrate examples of at least one cable in at least one plate according to some embodiments. [Diagram 3] FIG. 2 illustrates a support case for at least one cable according to some embodiments. [Figure 4A] 4A-4D are diagrams illustrating examples of cable twist pitches according to some embodiments. [Figure 4B] 4A-4D are diagrams illustrating examples of bend radii of cables according to some embodiments. [Figure 5A] 1A-1C illustrate examples of tears in a winding form according to some embodiments. [Figure 5B] 11A-11C illustrate examples of non-uniform twisting of channels in a winding former according to some embodiments. [Figure 5C] FIG. 13 shows an example flow chart of a method that includes performing an annealing operation before twisting the former more tightly. [Figure 6A] 1A-1C are diagrams illustrating examples of small bend radii for cables according to some embodiments. [Figure 6B] FIG. 2 is a plot illustrating critical current according to some embodiments. [Figure 6C] FIG. 2 is a plot illustrating critical current according to some embodiments. [Figure 7A] FIG. 1 is a cross-sectional view of a former according to some embodiments. [Figure 7B] FIG. 1 is a cross-sectional view of a former according to some embodiments. [Figure 7C] FIG. 7B is a side view of the former embodiment of FIG. 7A juxtaposed with the former embodiment of FIG. 7B according to some embodiments. [Figure 7D] FIG. 13 illustrates a flowchart of a method of forming an HTS cable that includes forming channel sidewalls having an angle greater than 90° prior to twisting the former. [Figure 8A] 1 illustrates an example of at least one compression block fastened with cable ties according to some embodiments. [Figure 8B] FIG. 13 shows an example of a flowchart of a method that includes securing an HTS tape stack in a groove with a compression structure. [Figure 9A] 1A-1C illustrate examples of tape stacks being wound onto a winding former according to some embodiments. [Figure 9B] 1A-1C illustrate examples of a main cable and a core extension according to some embodiments. [Figure 9C] 1A-1C illustrate examples of tape stacks and formers with at least one wire wrap according to some embodiments. [Figure 9D] FIG. 13 is a perspective view of at least one temporary wire wrap around a former and a tape stack according to some embodiments. [Figure 9E] FIG. 2 illustrates an example of a cable without a core extension according to some embodiments. [Figure 9F] 1A-1C illustrate examples of cables partially covered by jacket tubes according to some embodiments. [Figure 9G] FIG. 13 shows a flowchart of a method that includes bonding an extension to an end of a coil former and affixing an HTS tape stack to the extension. [Figure 10A] 1A-1D illustrate examples of end portions of a cable without a core extension according to some embodiments. [Figure 10B] 1A-1D illustrate examples of end portions of a cable without a core extension according to some embodiments. [Figure 11] FIG. 2 is a plot illustrating a differential voltage according to some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The apparatus and techniques described herein relate to the formation of HTS cables with small bend radii and / or complex three-dimensional geometries. Such techniques may be used to form three-dimensional highly non-planar stellarator coils using HTS materials. The apparatus and techniques described herein enable the fabrication of three-dimensional non-planar coils using high temperature superconductors (HTS), which has the potential to significantly improve the fusion performance of the stellarator reactor concept by raising the achievable magnetic fields to provide greatly improved fusion performance.

[0024] FIG. 1 is a perspective view of a stellarator coil. As shown in FIG. 1, one embodiment of the disclosed HTS cable has the same shape and size as one of the actual copper coils of the University of Wisconsin HSX stellarator device. However, it will be understood that the techniques and devices described herein are not limited to such shapes or specific sizes, and the coils may be made in other suitable shapes and sizes. The disclosed coils may have highly non-planar geometries as well as extremely small bends with bend radii of 100 mm or less. Layered winding of the HTS tape stack would not work in this geometry because the tape would strain well beyond the strain limit of about 0.4% at which it breaks. To avoid high strain on the HTS conductors, the HTS tape stack may be stranded along its length with a suitable twist pitch. The stranded laminated tape cable (VIPER) concept developed for the SPARC PF coil may be used with appropriate modifications. As long as the twist pitch is smaller than the bending radius, the helix and construction method of the cable former will avoid bending the tape in the constrained direction, so that the distortion of the tape after bending can be almost zero, since the tape is redistributed along the pitch. Since the minimum bending radius of the proposed coil is 100 mm, the twist pitch of the cable former can be reduced to less than 100 mm, which is about half the length of the VIPER design.

[0025] As an example, two cables, each about 10 m long, may be bent into the precise three-dimensional non-planar shape of the stellarator using automated equipment, for example, to form two coils. Each of the two cables may have four turns of about 2 m circumference. At least 20 cm of HTS cable may be left at each end of the cable as a joint and lead attachment. After verifying the correctness of the geometry (e.g., about 1 mm relative to the geometric center of the conductor), the HTS tape may be fixed in place. For example, a solder filling process, such as a Vacuum Pressure Impregnation (VPI) process, may fill the voids in the tape stack with a suitable solder alloy. An example of a suitable VPI process is described in U.S. Patent Application Publication No. 2022 / 0013256, which is incorporated herein by reference in its entirety.

[0026] FIG. 2 illustrates an example of an HTS cable 1 disposed between multiple plates 4. The HTS cable 1 may include a former 3 having at least one channel 6 with one or more HTS tape stacks 8 disposed therein. Although four channels 6 are illustrated, each containing at least one HTS tape stack, this is by way of example and the apparatus and techniques described herein are not limited to four channels with HTS tape stacks, but may have more or fewer channels, each of which may contain one or more HTS tape stacks. The HTS cable 1 may include a central cooling channel 5. In some embodiments, the HTS cable 1 is a two-turn coil, and two four-turn coils 1 may be sandwiched within at least one semicircular groove 27 of two precision-fabricated three-dimensional non-planar stainless steel "radial" plates 4 to form a coil containing two pancakes of four turns each, as illustrated in FIG. 2. The two pancake plates may be coupled (e.g., bolted) together along their inner and outer peripheries. The two pancake coils may be internally coupled with clamp-like low resistance electrical junctions (eg, about 3 nΩ) and fluid cryogen junctions such as those developed for SPARC.

[0027] Since superconducting stellarator coils operate in steady state with near zero voltage except during quenches, there is an option to electrically insulate the HTS cable from the radial support plates. If insulated, one option is to wrap the cable in an epoxy-impregnated layer and then clamp it into the grooves of the radial plates. A heating cycle at relatively low temperatures (much lower than the soldering temperature) may then be applied to the entire radial plate assembly to cure the insulation in situ. Another option is to wrap the cable in a thin layer of a compressible material compatible with cryogenic temperatures, such as silicone rubber. The insulating layer may also have the additional function of providing flexibility to fit the formed HTS cable coil into the radial support plates within certain geometric tolerances.

[0028] If no insulation is used, thin sheets of copper felt metal (as used in the sliding toroidal field magnetic joints of the Alcator C-Mod tokamak) may be used and soldered into the semicircular grooves of the radial plates to assist in current sharing between the HTS cable and the plates during a quench. Soldering of the felt metal into the semicircular grooves may be done before the HTS cable is clamped, thereby avoiding an additional vacuum pressure impregnation (VPI) soldering step. The copper felt metal may also provide flexibility for fitting the HTS cable coil into the radial support plates within certain geometric tolerances.

[0029] 3 illustrates a support case 9 for supporting at least one HTS cable 1a-1d in a stellarator configuration. In a complete stellarator assembly, the support case 9 may be fabricated by precision three-dimensional fabrication (e.g., additive manufacturing) to precisely hold multiple non-planar coils (e.g., 1a-1d) in the precise relative geometric shapes required, as illustrated in FIG.

[0030] The completed stellarator coil may be cooled to 77K by completely immersing the entire coil assembly in a pool of liquid nitrogen (LN2). To verify the integrity of the cable, the superconducting properties (critical current and exponent) may be measured and compared to theoretical calculations. To verify the precision of the geometry in the coil fabrication, a Hall probe may be used to perform a three-dimensional mapping of the magnetic flux density around the coil and compared to the desired magnetic field configuration.

[0031] The coil may also be deliberately subjected to multiple quenches to verify its remaining functionality and to determine if a drop in Ic occurs. Quenches can be induced by limiting the LN2 cooling or by increasing the operating current. One or more small electric heaters may also be placed on the coil to induce localized quenches. The quench induces a voltage in the coil leads due to both the resistance of the copper former and the finite inductance of the coil as the current decreases. Voltage taps on the leads and other critical locations, such as interpancake junctions, may monitor the voltage.

[0032] Stellarator coils may also be tested at approximately 20 K using the test facilities at the Massachusetts Institute of Technology (MIT) Plasma Science and Fusion Center (PSFC). At this lower temperature, the current carrying capacity of the HTS is much greater than at 77 K, and self-induced electromagnetic forces on the coil (e.g., HTS cable 1) become significant. Since quench tests performed under these conditions result in a greater release of magnetic energy and its conversion to thermal energy, temperature measurements may be included in these tests. The performance of the coils may be compared to detailed design models.

[0033] The processes for fabricating straight sections of HTS VIPER cables up to 12 m in length have already been developed and proven in the SPARC project, but adapting the VIPER cable design to meet the requirements of a three-dimensional non-planar stellarator coil has created several challenges that have led to changes in the cable design and some of the fabrication methods.

[0034] One difference in HTS stellarator coils is that the twist pitch of the extruded copper core (form) can be short (e.g., down to 100 mm or less) to meet the desired small radius bends of the cable. Figure 4A illustrates twist pitch P of HTS cable 1 in the longitudinal direction along with former 3 and tape stack 8. The twist pitch P is the distance along the length of HTS cable 1 between sections of HTS tape stack 8 with the same twist angle.

[0035] 4B is a diagram illustrating the bend radius R of the HTS cable 1 at a particular location along the HTS cable 1. The bend radius R is the radius of an imaginary circle having the same curvature as the HTS cable 1 at the particular location. In some embodiments, the lay pitch P is less than the bend radius R of the HTS cable 1.

[0036] The extra tight twist caused some problems, and some modifications and changes were made to solve them. One problem was that the excess torque distorted the copper extrusion in an unacceptable way. Figure 5A shows an example of a torn former 11. Figure 5B shows an example of uneven twist 12a, 12b in the former. Another problem that arose was that the width of the channel in the extruded copper core (e.g., former) was narrowed to the point where it was impossible to insert a 4 mm wide HTS tape.

[0037] These problems can be reduced or eliminated by applying an intermediate annealing step in a vacuum oven, as illustrated in FIG. 5C. First, for example, the former is twisted to produce a first twist pitch (e.g., 200 mm). Then, an annealing step is performed. An example of suitable annealing parameters is a temperature of 600° C. for 4 hours in a vacuum. However, the techniques described herein are not limited to a particular annealing temperature, time, or environment. Following the annealing step, the former (e.g., 3) may be twisted to produce a second twist pitch (e.g., 100 mm) that is shorter than the first twist pitch. To limit the longitudinal shrinkage, pins that do not significantly distort the copper may be used. Following the twisting and annealing steps, the HTS tape stack may be inserted into the channels of the former and fixed in place.

[0038] In the first few tests of tightly twisted stellarator cables containing stacks (e.g., 8) of HTS tapes, the critical current of the tapes inside the stack at 77 K was reduced by up to 50% compared to virgin tapes. Figure 6A illustrates an example of a small bend radius for an HTS cable (e.g., the small bend radius R shown in Figure 4B).

[0039] Figure 6B is a plot illustrating the decrease in critical current inside the turns, and Figure 6C is a plot illustrating that by further widening the extruded core channel by opening the channel wall or sidewall angle beyond 90° to ±15° above 90°, virtually all of the decrease is eliminated.

[0040] FIG. 7A illustrates a cross section of a former 3a having at least one channel 6a with sidewall 26a and a central cooling channel 15a. FIG. 7A illustrates at least one sidewall 26a of at least one channel 6a at 90°. FIG. 7B illustrates a cross section of a former 3b having at least one channel 6b with sidewall 26b and a central cooling channel 15b. FIG. 7B illustrates at least one sidewall 26b of at least one channel 14b at more than 90°±15°. Also, the width of at least one channel 6b of the former 3b, i.e., the extruded copper core, has been widened from 5.0 mm to 6.0 mm. FIG. 7C illustrates the formers 3a, 3b illustrated in FIG. 7A (left) and FIG. 7B (right) arranged side by side, i.e., the copper core. FIG. 7D illustrates a flow chart of a method of forming an HTS cable including forming channel sidewalls with an angle greater than 90° before twisting the former.

[0041] Manually winding entire stacks of tapes, especially stainless steel "dummy" tapes, onto tightly twisted extrusion cores (e.g., formers) proved labor intensive and technically difficult early on. The stacks of tapes (e.g., 8) tend to bulge beyond the height of the channels (e.g., 6a, 6b), resulting in irreparable damage when the wound core is inserted into the tight jacket tube. The basic problem is that the tightly twisted stacks of HTS or steel tapes act like strong springs and will bulge unless forced to stay within the channels. Initially, this problem was addressed by applying strong tension along the tape stack, but this method proved problematic for longer cables. Any unintentional release of tension during the winding process, even momentarily, would cause the stack to protrude and have to be completely removed and discarded. Two techniques substantially facilitate the winding procedure, thereby reducing the time it takes and ensuring a high success rate.

[0042] The first technique was to temporarily insert small custom compression blocks, fastened with cable ties, on top of each tape stack at intervals of approximately 50 cm along the length of the cable as the tape stack is wound into the channel, as illustrated in FIG. 8A. FIG. 8A shows an example of a compression block 18 fastened to a channel of a coil former 3 with cable ties 17a, 17b around the circumference of the compression block 18, tape stack 8, and coil former 3. However, any suitable spacing may be used, and the compression block 18 or other compression structure may be held or fastened by any suitable device or structure, not limited to cable ties 17a, 17b or straps. The compression block 18 is narrow enough to fit into the channel of the coil former and thick enough to press securely onto the HTS tape stack 8. The specific dimensions of the compression block 18 selected for use with the copper core (e.g., coil former) described herein are 6.0 mm wide x 12.5 mm long x 3.2 mm thick. However, the size of the compression block 18 is not limited to such dimensions. The choice of material for the compression block 18 is not critical. Preferably, the compression block 18 comprises a rigid material. In some embodiments, the material of the compression block 18 may be G10 (glass epoxy impregnated). However, the compression block 18 described herein is not limited to a particular material. In some embodiments, the edges of the compression block 18 may be chamfered to avoid damaging the HTS tape stack 8. The compression block 18 effectively prevents bulging of the tape stack 8 even when tension in the stack 8 is released. FIG. 8B shows an example of a flow chart illustrating such a technique.

[0043] The cable ties and compression blocks may be finally removed when the wound core is inserted into a tight jacket tube, which may help to ensure that the ends of the tape stacks are secured under tension. Direct securing at the end of the desired core may not be feasible due to mechanical interference between the stacks when winding multiple stacks around the core. To allow for secure securing of multiple stacks, short core extensions are fitted onto the end of the desired core by sliding them over temporary copper bars inserted in the central coolant channel (e.g., 15a, 15b), as illustrated in Figures 9A-9D. Figure 9A shows an example of a tape stack 8 wound on a coil former 3. Figure 9B illustrates the main cable 16 and the core extensions 21. The core extensions 21 may be shorter lengths of the same stranded copper extrusions used to form the copper core (e.g., coil former 3), as illustrated in Figure 9B. These core extensions 21 are temporary, removable, and fully reusable. The tape stacks are secured to the extensions using the compression blocks 18 and cable ties 17a, 17b described above. The core extensions 21 are long enough (e.g., about 140 mm or more, such as 150 mm) to accommodate multiple tape stacks 8 without mechanical interference between the stacks 8. This allows a high tension to be maintained on all tape stacks 8. A permanent bond may be achieved at the desired core end by a wire wrap process in a shallow groove machined near the end of the core. FIG. 9C illustrates the former 3 and tape stack 8 with at least one wire wrap 22. As illustrated in FIG. 9C, a temporary wire wrap process is performed on the opposing ends of the temporary extensions. FIG. 9D is a perspective view of the temporary wire wrap 22 around the former 3 and tape stack 8. This wire wrap process was previously developed for VIPER cables, but the use of temporary core extensions (e.g., 21) enhances the process.

[0044] After wire wrapping, a cut-off wheel may be used to cut the tape stack (e.g., 8) between the end of the core (e.g., former 3) and the opposing end of the extension (e.g., 21), thereby removing the extension (e.g., 21) for removal and reuse. FIG. 9E illustrates the main cable 16 without the extension (e.g., 21). FIG. 9E shows the protruding rod 25 over which the extension (e.g., 21) slides in use. FIG. 9F illustrates the main cable 16 without the extension (e.g., 21) with a cable jacket 23 (e.g., copper tube) partially covering the tape stack 8 and former 3. FIG. 9G illustrates a flow chart of a method including coupling the extension to the end of the former and affixing the HTS tape stack to the extension.

[0045] As shown in Figures 10A and 10B, the use of the cut-off wheel and removal of the extensions results in a much cleaner cable end compared to the original VIPER process. Figure 10A shows an example of the end of the main cable 16 and the rod 25 protruding therefrom after use of the cut-off wheel (not shown). Figure 10B shows a perspective view of the main cable 16 and central cooling channel 15 after use of the cut-off wheel (not shown). The combination of the compression block 18 and temporary extension 21 provides a significant improvement to the process of manually winding multiple tape stacks 8. This combination allows the procedure to be effectively performed by only two people and allows the wound core (e.g., former 19) to be successfully inserted into the coherent copper jacketed tube 23, eliminating the wasteful loss of tape stacks 8 that are ejected. However, such techniques need not be used in combination in all cases, so in some embodiments, the compression block 18 or temporary extension 21 may be used alone rather than in combination.

[0046] After the wound core (e.g., former 3) is inserted into the cable jacket 23, the subsequent roll forming and VPI soldering processes may remain unchanged from those previously developed for VIPER cables. The procedure for testing in liquid nitrogen to determine the critical current characteristics (Ic and "n" index) at 77K is also unchanged. Excellent results have been obtained in several stellarator cable samples, with measured values ​​of Ic=5.8kA and n≈21, which are in close agreement with theoretical calculations, as shown in FIG. 11.

[0047] Although the techniques and structures described herein may be used in stellarator coils, the disclosure is not so limited, as the techniques and structures described herein may be used in any superconducting cable, particularly a superconducting cable having an HTS tape stack regardless of bend radius R.

[0048] An example of a VIPER cable is described in U.S. Patent No. 8,437,819, which is incorporated herein by reference in its entirety, which introduces a Twisted Stacked Tape Cable (TSTC), including a version with multiple grooves on the coil former.

[0049] The use of HTS in three-dimensional non-planar coils allows operation at significantly stronger magnetic fields, thereby improving fusion power generation from stellarator reactors and / or allowing for smaller reactor sizes.

[0050] Various aspects of the apparatus and techniques described herein may be used singly, in combination, or in various configurations not specifically discussed in the embodiments described in the preceding description, and therefore the application is not limited to the details and configurations of components described in the preceding description or illustrated in the drawings. For example, aspects described in one embodiment may be combined in any manner with aspects described in other embodiments.

[0051] The use of ordinal terms such as "first," "second," "third," etc. in the claims to modify claim elements does not, by itself, imply any priority, precedence, or ordering of one claim element over other claim elements, or the chronological order in which acts of a method are performed, but is merely used as a label to distinguish one claim element having a particular name from other claim elements having the same name (but using ordinal terms) to distinguish the claim elements.

[0052] As used herein, the use of "including," "comprising," "having," "containing," "involving," and variations thereof, is meant to encompass the items listed thereafter, and equivalents thereof, as well as additional items.

[0053] The terms "approximately" and "about" may be used in some embodiments to mean within ±20% of a target value, in some embodiments to mean within ±10% of a target value, in some embodiments to mean within ±5% of a target value, and in some embodiments to mean within ±2% of a target value. The terms "approximately," "substantially," and "about" may be inclusive of the target value.

Claims

1. A high-temperature superconducting (HTS) cable, comprising: a wound type having at least one channel; at least one HTS tape stack, wherein a first HTS tape stack of the at least one HTS tape stack is disposed in a first channel of the at least one channel; the first HTS tape stack and the first channel are twisted along the longitudinal direction of the HTS cable, and the first HTS tape stack has a twist pitch shorter than the bending radius of the HTS cable at the first position at the first position of the HTS cable. A high-temperature superconducting (HTS) cable.

2. The HTS cable according to claim 1, wherein the twist pitch is less than 100 mm and the bending radius is 100 mm or less.

3. The HTS cable according to claim 1 or 2, wherein the HTS cable has a non-planar shape.

4. The HTS cable according to claim 3, wherein the HTS cable has a shape of a stellarator conductor.

5. A stellarator, comprising: a high-temperature superconducting (HTS) cable, comprising: a wound type having at least one channel; at least one HTS tape stack, wherein a first HTS tape stack of the at least one HTS tape stack is disposed in a first channel of the at least one channel; the first HTS tape stack and the first channel are twisted along the longitudinal direction of the HTS cable, and the first HTS tape stack has a twist pitch shorter than the bending radius of the HTS cable at the first position at the first position of the HTS cable. A stellarator.

6. A method of forming a high-temperature superconducting (HTS) cable, comprising: disposing an HTS tape stack in a channel of a wound type; fixing a plurality of compression structures on the HTS tape stack at a plurality of individual positions along the channel in the channel to hold the HTS tape stack in a groove.

7. The method according to claim 6, further comprising removing the plurality of compression structures from the channel.

8. The method according to claim 6 or 7, further comprising the step of fitting a cable jacket onto the coil type and the HTS tape stack.

9. The method according to claim 6 or 7, wherein the plurality of compression structures are fixed by a string or a strap.

10. A method of forming a cable, comprising: twisting a coil type having at least one channel so as to produce a first twist pitch; annealing the coil type after the step of twisting the coil type so as to produce the first twist pitch; twisting the coil type after the step of annealing the coil type so as to produce a second twist pitch shorter than the first twist pitch.

11. The method according to claim 10, further comprising the step of disposing an HTS tape stack in a first channel of the at least one channel after the step of twisting the coil type so as to produce the second twist pitch.

12. A method of forming a high temperature superconductor (HTS) cable, comprising: coupling an extension to an end of a coil type including at least one channel; fixing at least one HTS tape stack to the extension; inserting a first HTS tape stack of the at least one HTS tape stack into the channel while the first HTS tape stack is fixed to the extension.

13. The method according to claim 12, wherein the step of fixing includes attaching the at least one HTS tape stack to the extension under tension.

14. cutting an end of the at least one HTS tape stack fixed to the extension; removing the extension after the step of cutting. The method according to claim 12 or 13, further comprising

15. The method according to claim 12 or 13, wherein the step of coupling the extension includes inserting a rod into a central cooling channel of the coil type and the extension.

16. A method of forming a high temperature superconductor (HTS) cable, comprising: manufacturing the coil type having at least one channel on a surface of the coil type, the channel being wider than an HTS tape stack and / or having side walls at an angle greater than 90 degrees; twisting the coil type to have a first twist pitch; A method comprising, after the twisting step, inserting the HTS tape stack into a first channel of the at least one channel.

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