PLURALITY OF SUPERCONDUCTING FILAMENTS

Abstract

A method for forming a plurality of filaments, such that each filament is superconducting. The method includes providing a substrate having first and second sides. The substrate has a plurality of grooves in the first side of the substrate having a coating of a superconducting material so that for each groove within the plurality of grooves. A first part of the coating on a first side of a feature of the groove is separated from a second part of the coating on a second side of the feature of the groove. The second side of the feature of the groove is opposite of the first side of the groove, with removing from the second side of the substrate, at least a part of the substrate, to remove at least a connection from the first part of the coating to the second part of the coating via the substrate.

Claims

1.-33. (canceled)

34. A method for forming a plurality of filaments, wherein each filament is superconducting, said method comprising, such as sequentially comprising: providing a substrate, such as wherein the substrate comprises metal, such as the substrate being a planar metal substrate, wherein the substrate has a first side and a second side, such as wherein the first side is opposite the second side, and wherein the substrate comprises a plurality of grooves in the first side of the substrate, applying on the substrate a coating, wherein the coating is comprising a superconducting material, such as said coating being a high-temperature superconductor stack, so that for each groove within the plurality of grooves, i. a first part of the coating on a first side of a feature of the groove, such as the groove, is separated, such as disconnected, such as physically disconnected, from ii. a second part of the coating on a second side of the feature of the groove, such as the groove, wherein the second side of the feature of the groove is opposite of the first side of the feature of the groove, removing from the second side of the substrate, such as via electropolishing and/or etching, at least a part of the substrate, so as to remove at least a connection from the first part of the coating to the second part of the coating via the substrate, such as so as to provide the plurality of filaments, such as wherein portions of the substrate previously joining the filaments have been removed.

35. The method according to claim 34, further comprises prior to removing from the second side of the substrate at least a part of the substrate: applying on some or all of the first part of the coating and on some or all of the second part of the coating, such as on the first part and/or the second part of the coating, a protective covering, such as a resist, such as a protective covering layer, such as wherein the protective covering layer partially or wholly fills vacant space in the grooves.

36. The method according to claim 34, wherein removing from the second side of the substrate at least a part of the substrate is carried out via electropolishing and/or etching, such as electro-etching.

37. The method according to claim 36, wherein the electropolishing and/or etching is stopped before a liquid utilized for said electropolishing and/or etching reaches the first part of the coating and/or the second part of the coating.

38. The method according to claim 34, wherein removing from the second side of the substrate at least a part of the substrate is carried out via grinding and/or laser.

39. The method according to claim 34, wherein the removing from the second side of the substrate at least a part of the substrate, such as the electropolishing and/or etching, is stopped while each part of the coating, such as the first part of the coating and the second part of the coating, is adjoining a remaining part of the substrate.

40. The method according to claim 34, wherein the method is further comprising: twisting the plurality of filaments, or multiple pluralities of filaments, wherein each filament is twisted around its own axis and/or wherein a plurality of filaments are twisted around their common axis, such as wherein optionally twisted bundles of filaments are twisted around each other, thereby providing one or more superconducting structure each comprising a plurality of twisted filaments, such as wherein each filament has a helical shape with a center axis within one or more other helical shaped filaments, and/or transposition of the plurality of filaments, or multiple pluralities of filaments thereby providing one or more superconducting structures each comprising a plurality of transposed filaments.

41. The method according to claim 34, wherein the method is further comprising: forming a superconducting wire by providing one or more superconducting structures with a core and/or a capping.

42. The method according to claim 34, wherein a distance between a plane being parallel with a surface of the first side of the substrate, such as being tangential with the protrusions between the grooves, and a plane being tangential to a bottom of the plurality of grooves, such as a depth of the grooves as measured in a direction orthogonal to the plane of the first side of the substrate, is at least 1 m.

43. The method according to claim 34, wherein providing a substrate comprises providing the substrate, such as a tape, in a reel-to-reel setup.

44. The method according to claim 34, wherein applying on the substrate a coating comprises applying on the substrate, such as a tape, a coating in a reel-to-reel setup.

45. The method according to claim 34, wherein removing from the second side of the substrate at least a part of the substrate comprises removing from the second side of the substrate at least a part of the substrate, such as a tape, in a reel-to-reel setup.

46. The method according to claim 34, wherein each groove in the plurality of grooves comprises one or more undercuts.

47. The method according to claim 34, said method comprising: forming, such as via etching, one or more undercuts at each groove.

48. A plurality of filaments, wherein each filament is superconducting, such as high-temperature superconducting (HTS), and wherein each filament is not being connected to the one or more other filaments via the substrate, such as wherein each filament is physically disconnected from one or more other parts of the substrate.

49. The plurality of filaments, wherein each filament is superconducting, such as high-temperature superconducting (HTS), and wherein each filament is not being connected to the one or more other filaments via a substrate, such as wherein each filament is physically disconnected from one or more other parts of the substrate.

50. The plurality of filaments according to claim 48, where each filament comprises a substrate.

51. The plurality of filaments according to claim 48, wherein the substrate is a solid element upon which a superconducting material may be placed, such as deposited, so that the substrate and the superconducting element may together form a superconducting element.

52. The plurality of filaments according to claim 51, wherein the solid element comprises a material selected from the group comprising: a nickel-based alloy, a copper based alloy, a chrome based alloy, iron, aluminum, silicon, titanium, tungsten (also known as wolfram (W)), silver, Hastelloy, Inconel and stainless steel.

53. The plurality of filaments according to claim 48, wherein each filament is comprising superconducting material comprising, such as consisting of rare-earth barium copper oxide.

54. The plurality of filaments according to claim 48, wherein each filament is comprising superconducting material, such as high-temperature superconducting (HTS) material, and furthermore comprising a part of the substrate adjoining the superconducting material.

55. The plurality of filaments according to claim 54, wherein each filament comprises superconducting material on, such as partially or fully covering each of, two or more sides of the substrate, such as wherein each of said sides are non-parallel, such as orthogonal, with respect to at least one other side within the two or more sides as observed in a cross-sectional view orthogonal to a longitudinal direction of each of the filament.

56. The plurality of filaments according to claim 54, wherein an angular extent of the superconducting material as observed in a cross-sectional view orthogonal to a longitudinal direction of each of the filament around a geometrical center of the substrate is 90 or more.

57. The plurality of filaments according to claim 48, wherein the substrate is roll-processed, such as metal or metal-alloy, such as Hastelloy, stainless steel, an austenitic nickel-chromium-based superalloys, such as Inconel, or nickel-tungsten.

58. The plurality of filaments according to claim 48, wherein the plurality of filaments are connected by a protective covering, and where the protective covering is only partially covering each filament.

59. The plurality of filaments according to claim 48, wherein a width, such as a maximum dimension in a direction orthogonal to a longitudinal direction of each filament and optionally furthermore being parallel with an interface between superconducting material and substrate material, of each filament is equal to or less than 200 micrometer.

60. The plurality of filaments according to claim 48, wherein a width, such as a maximum dimension in a direction orthogonal to a longitudinal direction of each filament and optionally furthermore being parallel with an interface between superconducting material and substrate material, of each filament is equal to or more than 1 micrometer.

61. The plurality of filaments according to claim 48, wherein a length, such as a maximum dimension in a longitudinal direction of each filament, of each filament is equal to or larger than 1 m.

62. The plurality of filaments according to claim 48, wherein a thickness, such as a maximum dimension in a direction orthogonal to a longitudinal direction of each filament and optionally furthermore being orthogonal to an interface between superconducting material and substrate material, such as wherein said dimension is being orthogonal to one or both of the dimensions along which width and length are measured, is at least 1 m.

63. The plurality of filaments according to claim 48, wherein an engineering current density JE of each filament at a temperature of 77 Kelvin and at zero applied magnetic field is at least 103 A/cm2, wherein the engineering current density is defined as the current density for a cross-sectional area including superconducting material and substrate including if present buffer layer or buffer-stack and stabilizing layer, wherein each filament is optionally having a width being equal to or less than 500 micrometer.

64. The plurality of filaments according to claim 48, wherein a distance, such as an average distance, from an edge, such as an edge at a side, of the filament and into the filament, wherein superconducting properties of the superconducting material has deteriorated, is equal to or less than 100 micrometer.

65. A wire, provided according to claim 34.

66. Use of the plurality of filaments as provided according to claim 34 for conducting a current, such as conducting a current at superconducting conditions.

Description

BRIEF DESCRIPTION OF DRAWNGS

[0121] The first, second, and third aspect according to the invention will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

[0122] FIG. 1 is a flowchart illustrating a method according to an embodiment of the invention.

[0123] FIGS. 2-7 shows schematic illustrations depicting steps in a method according to an embodiment of the invention.

[0124] FIG. 8 shows a superconducting wire.

[0125] FIG. 9 illustrates a method of forming a plurality of filaments according to an embodiment.

[0126] FIG. 10 shows a Hastelloy substrate with grooves formed in a 2LUPS process with a CC stack 1038.

[0127] FIG. 11 shows a zoom view of FIG. 10.

[0128] FIG. 12 shows a single filament 1242 etched out.

[0129] FIG. 13 shows I/V setup for characterizing superconducting performance of a filament.

[0130] FIG. 14 shows the I/V setup of FIG. 13 immersed in liquid nitrogen.

[0131] FIGS. 15-16 show Scanning Electron Microscope (SEM) images of 3D etched Hastelloy substrate.

[0132] FIG. 17 shows Scanning Electron Microscope image of Focused Ion Beam milled HTS stack deposited on a 3D etched Hastelloy substrate.

[0133] FIG. 18 shows a collage of two images of filaments.

[0134] FIG. 19 shows the result of twisting a plurality of filaments.

DETAILED DISCLOSURE OF THE INVENTION

[0135] FIG. 1 is a flowchart illustrating a method according to an embodiment of the invention, said method being a method 100 for forming a plurality of filaments, wherein each filament is superconducting, such as high-temperature superconducting (HTS), and furthermore forming a superconducting structure and providing a superconducting wire, said method sequentially comprising: [0136] Providing 102 a substrate being a planar metal substrate, wherein the substrate has a first side and a second side, such as wherein the first side is opposite the second side, wherein providing the substrate comprises: [0137] i. Providing the substrate without grooves in the first side of the substrate, [0138] ii. forming 104 a plurality of grooves in the first side of the substrate, and [0139] iii. forming 106 via etching and/or electropolishing, and optionally in a two-level undercut process (2LUPS), one or more undercuts at each groove (although it is noted that alternative embodiments are conceivable, such as embodiments being similar in all other regards to the present embodiment, but wherein undercuts are not present or formed), [0140] Applying 108 on the substrate a coating, wherein the coating is comprising a high-temperature superconductor stack, so that for each groove within the plurality of grooves, [0141] i. a first part of the coating on a first side of a feature of the groove, such as the groove, [0142] is separated, such as disconnected, such as physically disconnected, from [0143] ii. a second part of the coating on a second side of the feature of the groove, such as the groove, wherein the second side of the feature of the groove is opposite of the first side of the feature of the groove, [0144] Applying 110 on some or all of the first part of the coating and on some or all of the second part of the coating, such as on the first part and/or the second part of the coating, a protective covering, such as a resist, wherein the protective covering partially or wholly fills vacant space in the grooves, [0145] Removing 112 from the second side of the substrate via electropolishing and/or etching at least a part of the substrate, so as to remove at least a connection from the first part of the coating to the second part of the coating via the substrate, such as to provide the plurality of filaments, such as wherein portions of the substrate previously joining the filaments have been removed, [0146] Stopping 114 the removing from the second side of the substrate at least a part of the substrate, while each part of the coating, such as the first part of the coating and the second part of the coating, is adjoining a remaining part of the substrate, [0147] Removing 116 the protective covering partially or wholly from some or all of the coating and remaining portions of the substrate, such as so as to remove at least a connection from the first part of the coating to the second part of the coating via the protective covering, [0148] Twisting 118 the plurality of filaments, or multiple pluralities of filaments, wherein each filament is twisted around its own axis and/or wherein a plurality of filaments are twisted around their common axis, such as wherein optionally twisted bundles of filaments are twisted around each other, thereby providing one or more superconducting structures each comprising a plurality of twisted filaments, such as wherein each filament has a helical shape with a center axis within one or more other helical shaped filaments, [0149] Forming 120 a superconducting wire by providing one or more superconducting structures with a core and a capping.

[0150] FIGS. 2-7 shows schematic illustrations depicting steps in a method according to an embodiment of the invention, said method being a method 100 for forming a plurality of filaments, wherein each filament is superconducting, such as high-temperature superconducting (HTS), and furthermore forming a superconducting structure and providing a superconducting wire.

[0151] FIG. 2 shows 102 a substrate 228 being a planar metal substrate without grooves in the first side, wherein the substrate has a first side 231 and a second side 232, such as wherein the first side is opposite the second side.

[0152] FIG. 3 shows the substrate 230 after forming 104 a plurality of grooves 234 in the first side of the substrate, and after forming 106 one or more undercuts 236 at each groove (as indicated by the dashed lines delimiting the shadowed, undercut portions of each groove).

[0153] FIG. 3 also illustrates dimensions of the grooves 234. FIG. 3 is indicated a distance 233a between a plane (as indicated with the upper horizontal dashed line) being parallel with an (upper (in the figure)) surface of the first side of the substrate, such as being tangential with the protrusions between the grooves 234, and a plane (as indicated with the lower horizontal dashed line) and a plane being tangential to the bottom of the plurality of grooves, i.e., a depth of the grooves as measured in a direction orthogonal to the plane of the first side of the substrate (i.e., measured in the vertical/up-down direction in the plane of the paper of the figure). Said distance 233a or depth is non-zero, such as at least 100 nm, such as at least 1 m, such as at least 10 m, such as at least 25 m, such as at least 50 m, such as at least 100 m. Said distance 233a or depth may furthermore be at most 4 mm, such as at most 2 mm, such as at most 1 mm. Said distance 233a or depth may be within ]10 nm; 4 mm[, such as within ]1 m; 2 mm[, such as within ]10 m; 1 mm[(where the open brackets ]x,;y[indicate that neither x nor y is included in the interval, yet all numbers therebetween are included). Furthermore is indicated a dimension or width 233b of the grooves, i.e., the distance from an edge (such as the beginning of an edge, such as the end of the planar portion of the substrate outside of the groove) of a protrusion on one side of groove to an edge of a protrusion on another side of a groove as measured in a direction parallel with the plane of the first side of the substrate and orthogonal to a longitudinal direction of the grooves (i.e., measured in the horizontal and left-right direction in the plane of the paper of the figure). The dimension or width 233b may be at least 1 micrometer, such as at least 2 micrometer, such as at least 5 micrometer, such as at least 10 micrometer, such as at least 3 0micrometer, such as at least 100 micrometer, such as at least 200 m. The dimension or width 233b may be at most 1 mm, such as at most 500 m, such as at most 200 m, such as at most 100 m. The dimension or width 233b may be within 1 micrometer-1 mm, such as within 10 m-500 m. There is in FIG. 3 furthermore indicated a distance 233c between adjacent grooves which is measured in the same direction as the width 233b. The distance 233c may be at least 100 m. The distance 233c may be at most 2 mm. The distance 233c may be within ]100 m; 2 mm[, such as within ]200 m; 1 mm[.

[0154] FIG. 4 shows the substrate 230 after applying 108 on the substrate a coating 238 comprising a high-temperature superconductor stack, so that for each groove within the plurality of grooves a first part of the coating on a first side of the groove is physically disconnected, from a second part of the coating on a second side of the groove, wherein the second side of the feature of the groove is opposite of the first side of the feature of the groove. Furthermore, portions of coating material can be seen in the grooves.

[0155] FIG. 5 shows the substrate 230 Applying 110 on some or all of the first part of the coating and on some or all of the second part of the coating, such as on the first part and/or the second part of the coating, a protective covering 240, being a resist, wherein the protective covering partially or wholly fills vacant space in the grooves.

[0156] FIG. 6 shows the a plurality of filaments 242 after removing 112 from the second side of the substrate (where the substrate 230 is no longer present, and where dotted rectangle 244 indicates the position previously held by substrate 230) via electropolishing and/or etching at least a part of the substrate, so as to remove at least a connection from the first part of the coating to the second part of the coating via the substrate, such as so as to provide the plurality of filaments 242 wherein each filament is superconducting, such as wherein portions of the substrate previously joining the filaments have been removed, such as via the superconducting coating. FIG. 6 also shows the result of stopping 114 the removing from the second side of the substrate at least a part of the substrate, while each part of the coating, such as the first part of the coating and the second part of the coating, is adjoining a remaining part 246 of the substrate.

[0157] FIG. 7 shows the plurality of filaments 242 after removing 116 the protective covering 240 partially or wholly from some or all of the coating and remaining portions of the substrate, such as so as to remove at least a connection from the first part of the coating to the second part of the coating via the protective covering. FIG. 7 also indicates a width 248 and a thickness 250 of a filament. Length is a dimension orthogonal to the plane of the paper.

[0158] FIG. 8 shows a plurality of groups of filaments, wherein each filament is twisted around its own axis and wherein a plurality of filaments in each group of filaments are twisted around their common axis thereby providing a plurality of superconducting structures 256 each comprising a plurality of twisted filaments wherein each filament has a helical shape and wherein these superconducting structures have been provided 120 in a superconducting wire 252 with a core 254 and a capping 258.

Example

[0159] According to an embodiment, there is presented a method of forming a plurality of filaments, wherein each filament is superconducting, said method comprising steps 1-9 as described in detail below (and schematically illustrated in FIG. 9):

[0160] A substrate which comprises a plurality of grooves is provided in steps 1-5, with forming the plurality of grooves in a first side (such as an over-side, a top side or a frontside) of the substrate in steps 2-5 (with the first side being opposite a second side, such as an under-side, a bottom side or a backside):

[0161] Step 1: Start with a substrate without grooves in the form of a polished 4 mm wide, 100 m thick and 50 m long Hastelloy tape with surface roughness below 10 nm (where surface roughness is arithmetic surface roughness value over a 1010 m.sup.2 atomic force microscopy scan). The surface quality is suitable for coated conductor (CC) chemical vapor deposition (CVD)/metal organic chemical vapor deposition (MOCVD), physical vapor deposition (PVD) or chemical deposition of buffer layers and superconducting layer. Polishing can be achieved by electrochemical polishing in a solution of phosphorous and sulfuric acid mixture following standard procedures from the literature, see, e.g., Wulff et al. 2015, Supercond. Sci. Technol. 28(2015) 072001, page 2, section 2.

[0162] Subfigure (a) of FIG. 9 shows a cross-sectional view of the tape in a plane being orthogonal to a longitudinal direction of the tape.

[0163] Step 2: Apply a masking material as described in Wulff et al. 2015, Supercond. Sci. Technol. 28 (2015) 072001, page 2, section 2.

[0164] This could be a masking tape, such as a Kapton film, a photoresist or similar. It is understood that Kapton film refers to the well-known product from DuPont which is a film of poly(4,4-oxydiphenylene-pyromellitimide).

[0165] Subfigure (b) of FIG. 9 shows a cross-sectional view of the tape in a plane being orthogonal to a longitudinal direction of the tape with masking material.

[0166] Step 3: Remove part of the masking material using mechanical scribing, a wet/dry chemical lithography process, or by laser scribing. Here it is done using standard lithography steps to fully remove the masking material in areas where grooves are to be etched.

[0167] Subfigure (c) of FIG. 9 shows a cross-sectional view of the tape in a plane being orthogonal to a longitudinal direction of the tape with part of the masking material removed.

[0168] Step 4: Etch into the substrate using a mixture of phosphorous and sulfuric acid applying a current density between 0.01-1 A/cm.sup.2 until grooves have been formed.

[0169] Subfigure (d) of FIG. 9 shows a cross-sectional view of the tape in a plane being orthogonal to a longitudinal direction of the tape with grooves formed by etching.

[0170] Step 5: Remove the masking material using an organic solvent (such as acetone) or a stripping agent such as sodium hydroxide.

[0171] Applying on the substrate a coating, wherein the coating (coated conductor (CC) stack) is a high-temperature superconductor stack, so that for each groove within the plurality of grooves, a first part of the coating on a first side of the groove, is separated (such as separated, but still physically connected, e.g., as depicted in FIG. 9(e)), from a second part of the coating on a second side of the groove, wherein the second side of the feature of the groove is opposite of the first side of the feature of the groove, is carried out in step 6.

[0172] Step 6: Deposit a superconducting coated conductor (CC) stack on the material, cf., e.g., a method as described in Wulff et al 2015, Supercond. Sci. Technol. 28 (2015) 072001, page 2, section 2, or Insinga et al 2018, IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 28, NO. 4, June 2018, page 2, section 2.

[0173] Subfigure (e) of FIG. 9 shows a cross-sectional view of the tape in a plane being orthogonal to a longitudinal direction of the tape with the remaining parts of the masking material removed and a superconducting CC stack deposited on the tape.

[0174] Applying on some or all of the first part of the coating and on some or all of the second part of the coating a protective covering (protective material), which partially or wholly fills vacant space in the grooves is carried out in step 7.

[0175] Step 7: Apply a protective material, such as liquid photoresist and cover the top (and in this embodiment also covering the sides, such as to avoid etching of the sides of the substrate and/or the sides of the outer CC stacks) of the tape and CC stack so as to protect the superconducting stack. The grooves should also be fully or partly covered with protective material. The protective material can be applied in several ways, e.g., liquid photoresist applied with an inkjet (e.g., with an opposite side of the tape held firmly against a solid element to avoid photoresist on said opposite side), with a brush or with dip-coating (such as dip-coating with an opposite side of the tape temporarily covered, e.g., with Scotch tape).

[0176] Subfigure (f) of FIG. 9 shows a cross-sectional view of the tape in a plane being orthogonal to a longitudinal direction of the tape with the protective material applied.

[0177] Removing from the second side (such as the backside or bottom side) of the substrate via etching, such as electrochemical etching, or via electropolishing, at least a part of the substrate, so as to remove at least a connection from the first part of the coating to the second part of the coating via the substrate, such as so as to provide the plurality of filaments, wherein portions of the substrate previously joining the filaments have been removed, is carried out in step 8.

[0178] Step 8: Etch from the backside of the tape structure using mixture of phosphorous and sulfuric acid. Etching can be continued until these are only physically connected via the protective material.

[0179] Subfigure (g) of FIG. 9 shows a cross-sectional view of the resulting plurality of filaments, which are being connected by the protective covering in a plane being orthogonal to a longitudinal direction of the plurality of filaments (same view as in subfigure (g) of FIG. 9) after a portion of the substrate has been removed from the backside.

[0180] Removing the protective covering partially or wholly from some or all of the coating and remaining portions of the substrate, such as so as to remove at least a connection from the first part of the coating to the second part of the coating via the protective covering is carried out in step 9.

[0181] Step 9: The protective material is removed either mechanically by peeling off the material, or dissolving in an organic solvent, such as ethanol or acetone, or a stripping solvent such as sodium hydroxide.

[0182] Subfigure (h) of FIG. 9 shows a cross-sectional view of the resulting plurality of filaments, which are no longer being connected by the protective covering in a plane being orthogonal to a longitudinal direction of the plurality of filaments, i.e., after the protective covering has been removed.

[0183] FIG. 10 shows a Hastelloy substrate 1030 with grooves formed in a 2LUPS process with a CC stack 1038 (without undercut). FIG. 10 could be seen as corresponding to the schematic illustrations in FIG. 4 and/or subfigure (e) of FIG. 9.

[0184] FIG. 11 shows a zoom view of FIG. 10.

[0185] FIG. 12 shows a single filament 1242 etched out, but with a remaining part 1246 of substrate, where a width (i.e., a size in a horizontal dimension left-right, i.e., in the plane of the paper, being ca. 500 m, i.e., the image depicts a ca. 500 m wide filament 1242 with CC stack). A thickness (dimension up-down in the plane of the paper) of the filament is ca. 80 m. FIG. 12 could be seen as corresponding to the schematic illustrations in FIG. 7 and/or subfigure (h) of FIG. 9.

[0186] FIG. 13 shows I/V setup for characterizing superconducting performance of a filament 1342 in liquid nitrogen, including current lead 1360 and voltage tap 1362. The dimensions can be retrieved from the ruler 1364 (with numbers being centimeters and the distance between adjacent smaller line markings being 1 mm). The washer 1366 is substantially circular, which indicates that the scale provided by the ruler applies both horizontally and vertically.

[0187] FIG. 14 shows the I/V setup of FIG. 13 immersed in liquid nitrogen. An electrical current ramping test with the filament immersed in liquid nitrogen while measuring the voltage drop between the contacts points showed no transition to normal conducting at more than 3 A at zero applied magnetic field and 77 K. With a width of estimated 500 m and a total thickness of estimated 80 m of the substrate and CC stack, an engineering current density of 9375 A/cm.sup.2 at zero applied magnetic field and 77 K is estimated. A reference coated conductor sample had a recorded average Ic=97 A at zero applied magnetic field at 77 K for a 4 mm tape width corresponding to an expected Ic for the 500 m wide filament of more than 12 A. It is noted that an engineering current density could be improved with a factor of at least 3-5 with another choice of superconducting material. Furthermore, a (such as another) factor of at least 2 could be achieved by reducing a thickness of the substrate, such as by continuing for a longer time the etch removing the substrate from the backside (such as giving substrate being, e.g., less than half the thickness of the present substrate), such as a factor of approximately 20 by leaving only a small part of the substrate (about 4 m in thickness), such as estimated with a situation where the substrate is etched away completely. Taking both the possible improvement in materials and reduced substrate thickness into account, an engineering current density of approximately 1,8 MA/cm.sup.2 may be arrived at zero magnetic field and 77 K. It is also noted that additionally higher current densities at expected at decreased operating temperatures, such as 50 K, such as 30 K, such as 20 K or 4.2 K. In contrast, lower current densities are expected at increased applied magnetic fields.

[0188] FIG. 15 shows Scanning Electron Microscope (SEM) image (view: normal to tape flat surface) of 3D etched Hastelloy substrate. FIG. 15 could be seen as corresponding to the schematic illustration in FIG. 3 (except for the undercut) and/or subfigure (d) of FIG. 9 (except for the remaining masking material).

[0189] FIG. 16 shows Scanning Electron Microscope image (view: angled) of 3D etched and Focused Ion Beam milled 3D etched Hastelloy substrate. The figure shows a protrusion (or elongated hill) formed between two grooves (on the left and right side of the protrusion), where the protrusion has a width (left-right in the plane of the paper) of ca. 18 m. FIG. 16 (except for the Focused Ion Beam milled cut-out) could be seen as corresponding to the schematic illustrations in FIG. 3 (except for the undercut) and/or subfigure (d) of FIG. 9 (except for the remaining masking material).

[0190] FIG. 17 shows Scanning Electron Microscope image of Focused Ion Beam milled 3D etched Hastelloy substrate with CC stack in the form of a substrate 1771 being Hastelloy C276, a 1-2 m thick buffer layer 1772 being Yttria-stabilized zirconia (YSZ) with 50 nm Cerium Oxide (as in Wulff et al. 2015, Supercond. Sci. Technol. 28 (2015) 072001), a 1-2 um thick layer 1773of Yttrium barium copper oxide (YBCO) layer and a silver layer 1774 being 1-2 m thick. All thicknesses refer to a dimension in the vertical/up-down direction in the figure, i.e., orthogonal to the plane of the respective layers. Width of the superconducting filament is ca. 25 m. FIG. 17 could be seen as corresponding to the schematic illustrations in FIG. 4 (except for the undercut) and/or subfigure (c) of FIG. 9.

[0191] FIG. 18 shows a collage of two images of filaments (with the filaments in the image on the right side being held by a human hand), where a substrate has been etched from the backside so as to remove a connection between the filaments through the substrate in a plane orthogonal to a longitudinal direction of the substrates. A length of the filaments, such as the free portion of the filaments, spans several centimeters. The (full) width of the substrate is 4 mm (such as the full width shown in the up-down direction in the upper right corner of the left sub-figure).

[0192] FIG. 19 shows the result of twisting a plurality of filaments wherein the plurality of filaments is twisted around their common axis and wherein each filament is thereby also twisted around its own axis (by an angular amount corresponding to the twisting of the plurality of filaments) thereby providing a structure comprising a plurality of twisted filaments wherein each filament is twisted around its own axis and furthermore has a helical shape with a center axis within one or more other helical shaped filaments, and wherein a wire has been provided by providing a core. Kapton tape is provided in each end, and a distance between the Kapton tapes is 5 cm.

[0193] Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms comprising or comprises do not exclude other possible elements or steps. Also, the mentioning of references such as a or an etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

Clauses

[0194] There is furthermore presented a method for forming a plurality of filaments, a plurality of filaments and use of the plurality of filaments according to the clauses below, which clauses may be combined with any of the preceding embodiments and/or any of the appended claims:

[0195] 1. A method (100) for forming a plurality of filaments (242), wherein each filament is superconducting, such as high-temperature superconducting (HTS), said method comprising, such as sequentially comprising: [0196] Providing (102) a substrate (230), such as wherein the substrate comprises metal, such as the substrate being a planar metal substrate, wherein the substrate has a first side (231) and a second side (232), such as wherein the first side is opposite the second side, and wherein the substrate comprises a plurality of grooves (234) in the first side of the substrate, [0197] Applying (108) on the substrate a coating (238), wherein the coating is comprising a superconducting material, such as said coating being a high-temperature superconductor stack, so that for each groove within the plurality of grooves, [0198] i. a first part of the coating on a first side of a feature of the groove, such as the groove, [0199] is separated, such as disconnected, such as physically disconnected, from [0200] ii. a second part of the coating on a second side of the feature of the groove, such as the groove, wherein the second side of the feature of the groove is opposite of the first side of the feature of the groove, [0201] Removing (112) from the second side of the substrate, such as via electropolishing and/or etching, at least a part of the substrate, so as to remove at least a connection from the first part of the coating to the second part of the coating via the substrate, such as so as to provide the plurality of filaments, such as wherein portions of the substrate previously joining the filaments have been removed.

[0202] 2. A method (100) according to any of the preceding clauses, further comprising prior to removing from the second side of the substrate at least a part of the substrate: [0203] Applying (110) on some or all of the first part of the coating and on some or all of the second part of the coating (238), such as on the first part and/or the second part of the coating, a protective covering (240), such as a resist, such as a protective covering layer, such as wherein the protective covering layer partially or wholly fills vacant space in the grooves.

[0204] 3. A method (100) according to any of the preceding clauses, wherein removing from the second side (232) of the substrate (230) at least a part of the substrate is carried out via electropolishing and/or etching, such as electro-etching.

[0205] 4. A method (100) according to any of the preceding clauses, wherein the removing from the second side of the substrate at least a part of the substrate, such as the electropolishing and/or etching, is stopped (114) while each part of the coating, such as the first part of the coating and the second part of the coating, is adjoining a remaining part (246) of the substrate.

[0206] 5. A method (100) according to any of the preceding clauses, wherein the method is further comprising: [0207] Twisting (118) the plurality of filaments (242), or multiple pluralities of filaments, wherein each filament is twisted around its own axis and/or wherein a plurality of filaments are twisted around their common axis, such as wherein optionally twisted bundles of filaments are twisted around each other, thereby providing one or more superconducting structures (256) each comprising a plurality of twisted filaments, such as wherein each filament has a helical shape with a centre axis within one or more other helical shaped filaments, and/or [0208] Transposition of the plurality of filaments (242), or multiple pluralities of filaments thereby providing one or more superconducting structures (256) each comprising a plurality of transposed filaments.

[0209] 6. A method (100) according to clause 5, wherein the method is further comprising: [0210] Forming (120) a superconducting wire (252) by providing one or more superconducting structures (256) with a core (254) and/or a capping (258).

[0211] 7. A plurality of filaments (242), wherein each filament is superconducting, such as high-temperature superconducting (HTS), and wherein each filament is not being connected to the one or more other filaments via the substrate, such as wherein each filament is physically disconnected from one or more other parts of the substrate.

[0212] 8. The plurality of filaments according to clause 7, wherein each filament is comprising superconducting material, such as high-temperature superconducting (HTS) material, and furthermore comprising a part of the substrate adjoining the superconducting material.

[0213] 9. The plurality of filaments (242) according to any of clauses 7-8, wherein the substrate is roll-processed, such as metal or metal-alloy, such as Hastelloy, stainless steel, an austenitic nickel-chromium-based superalloys, such as Inconel, or nickel-tungsten.

[0214] 10. The plurality of filaments (242) according to any of clauses 7-9, wherein the plurality of filaments are connected by a protective covering (240), and where the protective covering is only partially covering each filament.

[0215] 11. The plurality of filaments (242) according to any of clauses 7-10, wherein a width (248), such as a maximum dimension in a direction orthogonal to a longitudinal direction of each filament and optionally furthermore being parallel with an interface between superconducting material and substrate material, of each filament is equal to or less than 200 micrometer, such as equal to or less than 150 micrometer, such as equal to or less than 100 micrometer, such as equal to or less than 50 micrometer, such as equal to or less than 25 micrometer, such as equal to or less than 10 micrometer.

[0216] 12. The plurality of filaments (242) according to any of clauses 7-11, wherein a length, such as a maximum dimension in a longitudinal direction of each filament, of each filament is equal to or larger than 1 m, such as equal to or larger than 10 m, such as equal to or larger than 100 m, such as equal to or larger than 1 km, such as equal to or larger than 10 km, such as equal to or larger than 100 km, such as equal to or larger than 1000 km.

[0217] 13. The plurality of filaments (242) according to any of clauses 7-12, wherein an engineering current density JE of each filament at a temperature of 77 Kelvin and at zero applied magnetic field is at least 10.sup.3 A/cm.sup.2, such as at least 3*10.sup.3 A/cm.sup.2, such as at least 10.sup.4 A/cm.sup.2, such as at least 18750 A/cm.sup.2, such as at least 3*10.sup.4 A/cm.sup.2, such as at least 10.sup.5 A/cm.sup.2, such as at least 3*10.sup.5 A/cm.sup.2, such as at least 5*10.sup.5 A/cm.sup.2, such as at least 10.sup.6 A/cm.sup.2, such as at least 3*10.sup.6 A/cm.sup.2, such as at least 10.sup.7 A/cm.sup.2, wherein the engineering current density is defined as the current density for a cross-sectional area including superconducting material and substrate including if present buffer layer or buffer-stack and stabilizing layer, wherein each filament is optionally having a width being equal to or less than 500 micrometer, such as equal to or less than 400 micrometer.

[0218] 14. The plurality of filaments (242) according to any of clauses 7-13, wherein a distance, such as an average distance, from an edge, such as an edge at a side, of the filament and into the filament, wherein superconducting properties of the superconducting material has deteriorated, is equal to or less than 100 micrometer, such as equal to or less than 50 micrometer, such as equal to or less than 25 micrometer, such as equal to or less than 20 micrometer, such as equal to or less than 15 micrometer, such as equal to or less than 10 micrometer, such as equal to or less than 5 micrometer.

[0219] 15. Use of the plurality of filaments (242) as provided according to any of clauses 1-6 and/or according to any of clauses 7-14 for conducting a current, such as conducting a current at superconducting conditions.