Multiple superconducting filaments

Abstract

There is provided herein a method (100) for forming a plurality of filaments (242), where each filament is superconducting, the method comprising: providing a substrate (230), where the substrate has a first side (231) and a second side (232), and where the substrate comprises a plurality of grooves (234) in the first side of the substrate; applying (108) a coating (238) on the substrate, where the coating comprises a superconducting material such that, for each of the plurality of grooves, a first portion of the coating on a first side of the groove feature is separated from a second portion of the coating on a second side of the groove feature, where the second side of the groove feature is opposite the first side of the groove feature; at least a portion of the substrate is removed (112) from the second side of the substrate to at least remove a connection from the first portion of the coating via the substrate to the second portion of the coating.

Description

Technical Field

[0001] The present invention relates to a method for forming a plurality of electrically conductive filaments, more particularly to a plurality of superconducting filaments, and also to a plurality of filaments and uses thereof. Background Art

[0002] Superconducting structures may be considered advantageous because they are able to conduct electrical current, such as direct current, without resistive electrical losses. Therefore, superconducting structures, such as superconducting tapes, are being used in several applications, such as electromagnets, generators, and transformers. However, methods for forming superconducting structures may be complex and impractical for industrial-scale manufacturing, and, although superconducting structures may have excellent performance when carrying direct current, they may exhibit high energy losses when used in alternating current (AC) applications.

[0003] It would therefore be advantageous to have a method for forming a superconducting structure that reduces, minimizes or eliminates losses when used in alternating current (AC) applications, that is simpler and / or has increased suitability for industrial scale manufacturing. Summary of the invention

[0004] It can be seen that an object of the present invention is to provide a method for forming a plurality of filaments, a corresponding plurality of filaments and uses thereof, such as for achieving a method of manufacturing that reduces, minimizes or eliminates energy losses when used in applications such as alternating current (AC), thereby providing a simpler and / or increased suitability for industrial scale manufacturing. Another object of the present invention is to provide an alternative to the prior art.

[0005] Therefore, in a first aspect of the present invention, the above objects and several other objects are intended to be achieved by providing a method for forming a plurality of filaments, wherein each filament is superconducting, such as high temperature superconducting (HTS), the method comprising, such as comprising in sequence:

[0006] providing a substrate, such as wherein the substrate comprises metal, such as the substrate is 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,

[0007] applying a coating on the substrate, wherein the coating comprises a superconducting material, such as the coating is a multilayer structure comprising a superconducting material optionally comprising rare earth barium copper oxide (also referred to as REBCO), such as the coating is a superconductor stack, such as the coating is a high temperature superconductor stack, such that for each groove within the plurality of grooves, the following two portions are separated, such as disconnected, such as physically disconnected:

[0008] i. A first portion of the coating on a first side of a groove feature (such as a groove), with

[0009] ii. a second portion of the coating on a second side of a groove feature (such as a groove), wherein the second side of the groove feature is opposite to the first side of the groove feature,

[0010] Removing at least a portion of the substrate from a second side of the substrate, such as by electropolishing and / or etching, to remove at least connections from the first portion of the coating via the substrate to the second portion of the coating, such as to provide a plurality of filaments, such as where portions of the substrate previously engaging the filaments have been removed.

[0011] The present invention may be particularly advantageous, but not exclusively advantageous, for providing a method for forming a plurality of filaments, which method is capable of achieving one or more of the following: reducing, minimizing or eliminating energy losses when used for alternating current (AC) applications; improving magnetic field stability; reducing magnetic field-related forces, the method being simpler and / or increasing suitability for industrial-scale manufacturing. Another possible advantage is that twistable filaments may be provided, such as described in the peer-reviewed academic review article "Multifilamentary coated conductors for ultra-high magnetic field applications", Anders Christian Wulff et al., Supercond. Sci. Technol. 34 (2021) 053003 Fig. 9 The filaments may be twisted individually, in pairs or in bundles comprising more than two filaments.

[0012] In an embodiment, the method comprises twisting the filaments individually, in pairs or in the form of bundles comprising more than two filaments. Advantages may be that it achieves minimization of energy losses, transposition (e.g., see the article "How filaments can reduce AC losses in HTS coated conductors: a review", Francesco Grilli and Anna Kario, Supercond. Sci. Technol. 29 (2016) 083002 (15 pp), the entire contents of which are hereby incorporated by reference, and spatially (and statistically) distributing joints.

[0013] The present invention may be particularly advantageous in that it provides a method for forming an electrical conductor or cable having narrow or thin filaments made of high temperature and / or ceramic-based superconductors.

[0014] By providing superconducting elements in the form of filaments, AC losses can be reduced and the magnet can be stabilized, such as described in the peer-reviewed academic review article "Multifilamentary coated conductors for ultra-high magnetic field applications", Anders Christian Wulff et al., Supercond. Sci. Technol. 34 (2021) 053003, the entire contents of which are incorporated herein by reference, and / or in the peer-reviewed academic article "How filaments can reduce AC losses in HTS coated conductors: a review" Grilli and Kairo, Supercond. Sci. Technol. 29 (2016) 083002, the entire contents of which are also incorporated herein by reference.

[0015] Another possible advantage of forming narrow superconducting filaments is that it becomes possible to effectively cover or stabilize the filaments, such as where, for example, the amount of coverage or stabilizing material (such as the proportion of stabilizing material) on the sides of the filament becomes significantly or relatively larger (relative to the width of the filament) compared to a wide flat tape that is typically a few millimeters wide (such as 2-12 mm). By increasing the cross-sectional ratio of the stabilizer material relative to the corresponding proportion of the superconductor layer, a superconducting tape / wire structure can be provided that has more stabilizing material per unit area of ​​superconducting material and can therefore be more resistant to quenching, such as local heating, such as local loss of superconducting properties. Adding stabilizing material (such as a material selected from the group including the following items: silver, copper, nickel, tin and / or zinc), such as silver or copper, to the first and second sides of the superconducting material can improve the thermal and electrical stability of the superconducting material (such as a composite material). Adding stabilizing material at the edges of a standard wide band does not significantly increase the stabilizer ratio to superconductor material ratio of the wide band (such as a 4 mm or 12 mm wide band). For example, for a narrower tape, such as a 70 μm wide and 50 μm thick tape with a 1 μm HTS layer, adding 10 μm of stabilizer material on all sides of the tape produces an aspect ratio of stabilizer to HTS layer width of approximately 40, which is two (2) times higher than a 12 mm wide and 50 μm thick tape with the same stabilizer layer thickness.

[0016] In an embodiment, the method further comprises adding a covering layer and / or a stabilizing material as part of and / or on top of the coating. "Covering layer" and "stabilizing material" are understood as known in the art.

[0017] The method relies on, and this necessity and / or in an embodiment only relies on, method steps that are suitable for large-scale manufacturing and / or are actually suitable for industrial-scale manufacturing, that is, the method according to an embodiment of the present invention can be actually suitable for industrial-scale manufacturing. For example, each of the following steps is a step that can be actually applied on an industrial scale: providing a substrate (such as a tape provided in a roll-to-roll arrangement), optionally applying grooves (such as applying grooves in a rolling process and / or a lithography process (such as by lithography and subsequent etching)), applying a coating, optionally providing a resist and removing (such as etching from the back).

[0018] It is believed that the inventors have gained the insight that a process for providing a plurality of superconducting filaments can be realized by (such as only by) industrially applicable method steps.

[0019] It can also be seen as an advantage that methods according to embodiments of the present invention are suitable for large-scale manufacturing, such as being very suitable for large-scale manufacturing because they can be relatively simple and / or efficient. For example, long filaments can be obtained (optionally in large quantities) in a relatively fast manner and / or in a manner that requires relatively few resources (such as relatively few equipment, manpower, energy and / or materials). Therefore, through embodiments of the present invention, large-scale manufacturing is possible, and in addition, this can be possible while minimizing resources (such as the use of resources).

[0020] Embodiments of the present invention may also be viewed as being effective in providing substrates for superconducting structures that promote relatively large critical currents due to the ability to obtain substrates having few or no damaged regions (such as, where damaged regions may be understood as portions of the superconducting material that are no longer functional, which in turn may reduce the critical current).

[0021] "Filament" is understood to mean the common meaning in the art, such as an optional flexible elongated element, such as a solid elongated element. "Elongated" may be understood to mean that something has a larger dimension in a first direction (such as a direction referred to as the length direction), such as being significantly longer, such as 2, 5, 10, 100, 1000, 10000 or 100000 times longer than one or both of the other two directions (such as directions referred to as the width and height) orthogonal to the first direction. "Solid element" may be understood to mean an element comprising a solid phase, such as an element consisting of a solid phase.

[0022] "Superconducting" is understood to have the common meaning in the art, such as the ability of a material to conduct electric current with substantially zero resistance, such as zero resistance, optionally when cooled below a characteristic transition temperature.

[0023] "Superconducting material" is understood to have the common meaning in the art, such as in the context of "superconducting" described in the previous paragraph. The superconducting material may include, such as consist of, rare earth barium copper oxide (also referred to as REBCO).

[0024] "High temperature superconductivity (HTS)" (or high H c ) is understood to have the common meaning in the art, such as the ability of a material to become superconducting at temperatures above 30 Kelvin, such as above a temperature corresponding to the boiling point of liquid nitrogen, which is about 77 Kelvin.

[0025] "Substrate" may be understood as "a substrate suitable for supporting a superconducting element", which in turn may be understood as a solid element on which a superconducting material may be placed (such as deposited), such that the substrate and the superconducting element may together form a superconducting element. The substrate may include, such as consisting of, one or more metallic elements (such as metals, semimetals, semiconductors and / or metalloids) or alloys. The substrate may include non-metals, such as, such as, such as, the substrate may consist of. The substrate may include a substantially flat surface.

[0026] The solid element can have any shape, where shape is understood to be a geometric shape seen in a cross section in a plane orthogonal to the length axis (such as corresponding to an axis parallel to the current delivery direction), such as an arbitrary shape, such as any one of a strip, a rectangle (such as a square shape), a triangle, an ellipse (such as a circle).

[0027] According to an embodiment, a method includes forming a Rutherford cable from a plurality of filaments.

[0028] Optionally, the substrate is shaped to achieve a twist pitch, such as a single element twist, such as a pair twist, such as a ROEBEL configuration (see reference "Supercond. Sci. Technol. 22 (2009) 034003", the entire content of which is hereby incorporated by reference), such as a conductor on a circular core (see reference "Supercond. Sci. Technol. 27 (2014) 125008", the entire content of which is hereby incorporated by reference), or such as a geometric shape that enables the superconducting element placed on the substrate to be transposed. The shaping can be given by a piecewise linear shape such as a zigzag shape.

[0029] In an embodiment, the substrate is a "ribbon", i.e., an element whose thickness (length along the first dimension) is significantly smaller than its width (length along the second dimension), such as 10, 100 or 1000 times smaller, and whose width is significantly smaller than its length (length along the third dimension), such as 10, 100 or 1000 times smaller.

[0030] The solid element may include any material selected from the group consisting of: nickel-based alloys, copper-based alloys, chromium-based alloys, iron, aluminum, silicon, titanium, tungsten (also known as tungsten (W)), silver, Hastelloy, and stainless steel.

[0031] "Hastelloy" is understood to be an alloy whose main alloying component is nickel and to which other alloying components are added, such as the alloy containing one or more of the elements molybdenum, chromium, cobalt, iron, copper, manganese, titanium, zirconium, aluminum, carbon and tungsten in varying percentages. In a specific embodiment, Hastelloy is an alloy containing the elements Ni, Cr, Fe, Mo, Co, W, C. In a more specific embodiment, the alloy further contains Ni, Cr, Fe, Mo, Co, W, C and one or more of the elements Mn, Si, Cu, Ti, Zr, Al and B. In a more specific embodiment, the alloy is understood to contain about 47wt% Ni, 22wt% Cr, 18wt% Fe, 9wt% Mo, 1.5wt% Co, 0.6wt% W, 0.10wt% C, less than 1wt% Mn, less than 1wt% Si and less than 0.008wt% B. Hastelloy may be referred to in the art as a "high temperature alloy" or "high performance alloy".

[0032] "Stainless steel" is well known in the art. In certain embodiments, stainless steel is provided with nickel and / or chromium, such as to provide a stainless steel that is corrosion and / or oxidation resistant, mechanically stable, and non-magnetic at the operating temperature of the superconducting layer.

[0033] "Groove" is understood to have the common meaning in the art, such as an elongated depression, such as a depression relative to an adjacent portion of a substrate. The groove can be used to separate several portions of the surface of a substrate into portions on either side of the groove, so that deposition of material on the top of the substrate, such as in a line-of-sight process, produces portions of material separated (such as disconnected, such as physically disconnected) by the groove. A possible advantage of such separation can be that the distance from the first side to the second side (optional plane) of the substrate varies depending on the position of the first side, which in turn has the following advantages: to remove material from the second side of the substrate in a spatially non-specific manner (e.g., remove material everywhere, such as in substantially equal amounts everywhere on the optional plane), such as by etching or electropolishing, the entire thickness of material can first be removed from the first side to the second side of the substrate at the location of the groove, i.e., the portions having the groove can become disconnected from each other in a relatively simple and spatially non-specific removal step, such as by etching or electropolishing.

[0034] A "line of sight" process is understood to be any process that deposits material only at a position of the substrate that can be seen in a straight line from another position, such as a position above the substrate. Therefore, a "line of sight" process is broadly interpreted to include processes in which the deposited material follows a straight line before deposition and deposition processes with similar effects. In a specific embodiment, the line of sight process is any of die coating, bubble jet coating, and inkjet coating. In a specific embodiment, "line of sight" is understood to be a process in which the deposited material originates from a certain source and travels in a straight line from there to the position where it is deposited. In other words, the deposited material can only be at a position from which a straight line can be drawn to the source without passing through any obstacles. A possible advantage of using a line of sight process can be that it is able to deposit material on both sides of each groove while utilizing the groove feature to shield a certain portion, such as the bottom of the groove, so that no deposition occurs at the portion, thereby forming a destructive stripe in the deposited material. A "destructive stripe" can be understood as a missing line of coating material that divides the coating material into elongated strips of coating material on both sides of the destructive stripe. Destructive stripes can be regarded as gaps in an otherwise coherent coating material. If a coherent coating material, such as a layer of coherent coating material, is penetrated by the destructive stripe, the continuity of the coherent coating material is thereby disrupted into two separate materials (layers), such as two parts of coating material.

[0035] The grooves can be parallel to each other, such as parallel to each other. "Parallel" can be understood as parallel within 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 degrees. It is understood that although adjacent grooves can still be parallel, the grooves can be piecewise parallel, such as the grooves themselves are non-linear, such as curved, such as piecewise linear.

[0036] "Coating" is understood to have the common meaning in the art, such as a layer of material applied to a sub-state, such as a thin layer. The application of the coating can be implemented by several means, such as any of line-of-sight processes, such as die coating, bubble jet coating, and inkjet coating. The coating can optionally form a second generation high temperature superconductor coated conductor with at least a portion of the substrate.

[0037] The structure and / or texture of the superconducting material in the coating may be imparted to the superconducting layer by the substrate and / or by another layer in the coating, such as a buffer layer.

[0038] "Buffer (layer)" is understood as having the common meaning in the art, and may, for example, be understood as optionally providing structure and / or texture to the superconducting layer, and / or may, for example, be understood as providing an optional inert chemical barrier.

[0039] A "superconductor stack" may be understood as a layered construction, such as a multilayer structure, optionally with different layers, including a buffer layer (e.g. 0.1-2 microns) and a superconducting layer (e.g. rare earth based barium copper oxide (REBCO) with a thickness of e.g. 1-5 microns). The superconductor stack may be a high temperature superconductor stack.

[0040] "A first side of a groove feature" is understood to be the area on only one side of the groove feature.

[0041] A "groove feature" is understood to be a portion of a groove or the entire groove. For example, the entire groove can be used to separate, such as a break, such as a physical break, multiple portions of coating material applied in a line-of-sight process from directly above the groove (in this example, there is a portion on either side of the groove, where neither of these portions includes material in the groove). In another example, the edge of the groove or the side of the groove can be used to separate, such as a break, such as a physical break, multiple portions of coating material applied in a line-of-sight process from locations outside of a plane that is orthogonal to the surface containing the groove and parallel to the groove (in this example, such as in the bottom of the groove, a portion of the coating may include material in the groove).

[0042] "Separation" can be understood as that the separated elements are separated in space, such as the elements are separated by another material other than the material of the elements (for example, by having a non-solid material between the elements). In an embodiment, the separated elements can be connected to each other by the same material as the material of the elements (such as, the element portions at the top of the protrusions / protrusions on each side of the groove can be separated from each other, but connected by the same material as the material of the element extending from one protrusion / protrusion to another protrusion / protrusion). In an embodiment, due to the absence of the same material as the element material between the elements, the separated elements may be disconnected from each other, such as physically disconnected (for example, due to the absence of the same material as the material of the element extending from one protrusion / protrusion to another protrusion / protrusion, the elements on the top of the protrusions / protrusions on each side of the groove may be separated from each other and physically disconnected).

[0043] “Disconnected” may be understood as physically and / or electrically disconnected, such as where disconnected elements are not electrically connected by conductive material and / or not physically connected by materials of the elements.

[0044] "Removing from the second side of the substrate" may be understood as removing material from the surface of the second side of the substrate, such as removing material from the back side of the substrate relative to the front side including the groove, such as removing material sequentially, such as removing the outermost layer of material in each of a plurality of steps (these steps may follow each other in a substantially continuous manner, such as by etching, or may be discretized, such as when moving material in a plurality of milling or grinding steps). In addition, it may be understood that removing material from the second side of the substrate includes removing material from the second side of the substrate before removing material from the first side of the substrate and / or while material is still present on the first side of the substrate. When removing material from the second side of the substrate, the position of the surface of the second side of the substrate moves toward the first side of the substrate and / or portions of the coating.

[0045] “At least removing the connection from the first part of the coating to the second part of the coating via the substrate” can be understood as that material of the substrate is removed so that there is subsequently no physical connection from the first part of the coating to the second part of the coating via the substrate, such as the first part of the coating and the second part of the coating become detachable or separate from each other, and / or the first part and the second part of the coating are no longer connected via the substrate, such as at least in a cross-section orthogonal to the longitudinal direction of one or more or all of the filaments, such as for any part of the substrate, there is no path from the first part of the coating to the second part of the coating through the substrate.

[0046] In an embodiment, "removing at least a connection from the first portion of the coating to the second portion of the coating via the substrate" comprises splitting or breaking or severing or breaking a connection from at least the first portion of the coating to the second portion of the coating via the substrate.

[0047] The removal of material may be performed by, for example, electropolishing and / or etching (such as electroetching), a grinding process, a cutting process or a laser process.

[0048] The step of "removing at least a portion of the substrate from the second side of the substrate" may be performed by electropolishing and / or etching (such as electroetching). Possible advantages are that electropolishing and / or etching are well-established, suitable for industrial scale and / or suitable for removing some material (such as the substrate) while being gentle to the remaining material (such as the coating, especially if the remaining material is covered by a protective covering).

[0049] "Etching", "electroetching" or "electropolishing" may be understood as removing (substrate) material by etching, electroetching or electropolishing (such as using an etchant). In certain embodiments, the etchant may be in any of the following states of matter: plasma, liquid and gas. In certain embodiments, reactive ion etching (RIE) is used.

[0050] A "grinding process" is understood to be the removal of a portion of the (substrate) material by a grinding process or a polishing process, such as repeatedly scraping off tiny portions of the (substrate) material to be removed. In the present context, a "polishing process" is understood to be similar to a "grinding process".

[0051] A "cutting process" is understood to be a process in which material is displaced rather than removed. This can be achieved by using relatively sharp tools.

[0052] The step of “removing at least a portion of the substrate from the second side of the substrate” may be performed using a laser process, such as by laser marking and / or any one of laser engraving, laser etching and laser annealing.

[0053] It may be advantageous, for example, when using a spatially specific or spatially well-defined or spatially well-definable method (such as where material is removed or removable at spatially well-defined locations, such as even on a plane, such as where material at two locations with similar morphology is removed at significantly different rates, such as where the removal rate at one location is non-zero and at the other location is essentially zero), such as when using laser marking, that the grooves result in a smaller distance from the first side to the second side (at a location corresponding to the bottom of the grooves), which in turn results in less substrate material having to be removed to penetrate the substrate (compared to the case where there were no grooves).

[0054] According to an embodiment, a method is provided, the method further comprising, before removing at least a portion of the substrate from the second side of the substrate:

[0055] Applying a protective covering, such as a resist, such as a protective covering layer, over some or all of the first portion of the coating and over some or all of the second portion of the coating, such as over the first portion and / or the second portion of the coating, such as where the protective covering layer partially or completely fills the void in the recess.

[0056] A "protective covering" may be understood as a layer of material, such as a resist, which may, for example, protect (such as from mechanical deformation and / or thermal effects) (such as a coating) the underlying material during a step of removing at least a portion of the substrate from the second side of the substrate, such as during etching. An advantage of applying a protective covering may be that the material to which it is applied may be less damaged, such as no damage, during the step of removing at least a portion of the substrate from the second side of the substrate, which in turn may reduce, minimize or eliminate degradation of the superconducting properties of the resulting filament. The protective covering may be a photoresist, such as a liquid photoresist.

[0057] According to an embodiment, a method is provided, the method further comprising, after removing at least a portion of the substrate from the second side of the substrate:

[0058] • Partially or completely removing the protective layer from some or all of the coating and the remainder of the substrate, such as to remove at least the connection from the first portion of the coating to the second portion of the coating via the protective covering.

[0059] Advantages of removing the protective covering may be, for example, to be able to separate the filaments and / or to be able to work with the filaments in order to construct a (optionally twisted and / or transposed) multi-filament superconducting element or a multi-filament superconducting wire without being hindered by the protective covering (optionally, where the individual filaments can be twisted in pairs and / or can be transposed relative to adjacent filaments).

[0060] According to an embodiment, a method is proposed in which the "partial removal of the protective covering" is performed by electropolishing and / or etching (such as electroetching or physical etching). Possible advantages are that electropolishing and / or etching are well-established, suitable for industrial scale and / or suitable for removing some material (such as the substrate) while being gentle to the remaining material (such as the coating, especially if the remaining material is covered by the protective covering).

[0061] According to an embodiment, a method is provided, wherein the method comprises providing a substrate by the following steps:

[0062] providing a substrate without recesses in a first side of the substrate, and

[0063] • Forming a plurality of grooves in the first side of the substrate.

[0064] The "forming of multiple grooves" can be implemented in several ways (such as by cutting or rolling shearing), which may be beneficial for applicability in industrial scenarios.

[0065] According to an embodiment, a method is presented wherein forming a plurality of recesses in a first side of a substrate comprises forming a plurality of trenches in the first side of the substrate in a roll-to-roll arrangement. A possible advantage is that it facilitates large scale processing.

[0066] According to an embodiment, a method is proposed, wherein the removal of at least a portion of the substrate from the second side of the substrate is stopped, such as electropolishing and / or etching, when portions of the coating (such as a first portion of the coating and a second portion of the coating) are adjacent to the remainder of the substrate. An advantage may be that by making portions of the coating adjacent to the remainder of the substrate, the remainder of the substrate may impart mechanical strength to the filament comprising the coating and the remainder of the substrate. In some embodiments, the substrate is a substrate that has undergone a rolling process, which may make the corresponding strength increase greater and may be greater than the strength increase imparted by adding material to the coating from which the (original) substrate has been completely removed. Another possible advantage of stopping may be the omission of the step of providing the substrate, i.e. providing the substrate, for example by deposition.

[0067] Another possible advantage is that the coating, such as the superconductor stack optionally including the protective cap and / or stabilizer material, adheres well to the optional metal substrate. For example, the superconducting stack in the coated conductor production can be epitaxially grown on the metal substrate, which can provide good mechanical strength between the metal substrate, the buffer layer and the superconducting layer in the superconducting stack. Good mechanical strength may be beneficial to avoid cracks in the coating, which in turn may be beneficial to prevent cracking of the coating.

[0068] According to an embodiment, a method is proposed, wherein electropolishing and / or etching is stopped before the liquid for said electropolishing and / or etching reaches the first part of the coating and / or the second part of the coating. A possible advantage may be to avoid the liquid from reaching the first part of the coating and / or the second part of the coating. The reason why this may be advantageous relative to the situation where the liquid reaches the first part of the coating and / or the second part of the coating is that if contact is formed between the liquid and the first part of the coating and / or the second part of the coating, the properties of the first part of the coating and / or the second part of the coating, such as the superconducting material of the first part of the coating and / or the second part of the coating may change, such as deteriorate. Another possible advantage is that if electropolishing and / or etching is stopped before the liquid for said electropolishing and / or etching reaches the first part of the coating and / or the second part of the coating, the liquid cannot move within the first part of the coating and / or the second part of the coating (which may be porous). In an embodiment, an undercut at a groove may be utilized to ensure that the deposited superconducting material (of the first portion of the coating and / or the second portion of the coating) does not extend to the sides of the groove, and forms a coherent structure of superconducting material extending from one side of the groove feature to the other side of the feature (such as extending from the top (protrusion) of the substrate adjacent to the groove to the side of the groove, or even to the bottom of the groove). Thus, for example, a coherent structure of superconducting material on the top (protrusion) of the substrate adjacent to the groove may be further away from the second side of the substrate (such as the distance between the second side of the substrate and the point where the coherent structure is closest to the second side of the substrate) than would be the case without the undercut. An undercut may be used to provide a physical break between the (sacrificial) superconducting material on one side of the groove feature (e.g., at the bottom of the groove) and the superconducting material on the other side of the groove feature (such as on the top (protrusion) of the substrate immediately adjacent to the groove).

[0069] According to an embodiment, a method is proposed, wherein removing at least a portion of the substrate from the second side of the substrate is performed by grinding and / or laser. Possible advantages of grinding may be that it is efficient, economical, fast and / or scalable. Possible advantages of laser may be that it is economical, controllable and / or spatially well-definable.

[0070] According to an embodiment, a method is provided, wherein each groove of the plurality of grooves comprises one or more undercuts. This may be advantageous for depositing superconducting material on a substrate, and utilizing the one or more undercuts to provide a physical break between portions of the superconducting material.

[0071] According to an embodiment, a method is proposed, wherein the method further comprises:

[0072] • Forming one or more undercuts at each recess, such as by etching, such as forming one or more undercuts in a two-level undercut process (2LUPS).

[0073] Undercuts may be formed, for example, by etching and / or electropolishing, such as described, for example, in WO13174380A1, the entire contents of which are hereby incorporated by reference. "Undercuts" may be understood as volumes at each recess, which volumes may be lower than the remainder of the substrate. Thus, the undercuts (volumes) may be obscured by overhanging portions of the substrate. The advantage is that when material is deposited on a substrate comprising recesses with undercuts from above the recesses using a line-of-sight process, material is not deposited on the shadowed undercut portions of the substrate. Such as described, for example, in WO13174380A1 (the entire contents of which are hereby incorporated by reference), more specifically in WO13174380A1. Figure 3 A to 3H and the additional description (which are incorporated herein by reference), the two-stage undercut profile substrate (2LUPS) process can be understood as providing an undercut in a process including a sandwich structure, wherein a destructive strip is formed in the outer layer. The 2LUPS process is described alternatively or additionally in the article "Multifilamentary coated conductors for ultra-high magnetic field applications", Anders Christian Wulff et al., Supercond. Sci. Technol. 34 (2021) 053003, such as in particular in Section 4.2, and the entire content of the article is incorporated herein by reference.

[0074] According to an embodiment, a method is proposed, wherein the method further comprises:

[0075] twisting a plurality of filaments or groups of a plurality of filaments, wherein each filament is twisted about its own axis, and / or wherein a plurality of filaments are twisted about their common axis, such as wherein bundles of optionally twisted filaments are twisted about each other, thereby providing one or more superconducting structures, each superconducting structure comprising a twisted plurality of filaments, such as wherein each filament has a helical shape with a central axis within one or more other helical filaments, and / or

[0076] - Transposing a plurality of filaments or groups of a plurality of filaments, thereby providing one or more superconducting structures, each superconducting structure comprising a transposed plurality of filaments.

[0077] "Twist" may be understood as a rotation of one portion of a filament (such as an end) relative to another portion (such as an opposite end) about a longitudinal axis, such as where the rotation spans at least half a turn or π (radians) or 180 degrees, such as n times π, where n is at least 1, such as at least 2 (corresponding to at least one full turn or at least 360 degrees), such as at least 5, such as at least 10, such as at least 50, such as at least 100, such as at least 1000. Each filament may be twisted around its own axis and / or a plurality of filaments (such as a bundle) twisted together. An advantage of twisting may be that it can reduce, minimize or eliminate instabilities and coupling losses. The repositioning of the filaments can effectively decouple the filaments, which can be achieved by twisting the filaments (see, for example, the article “How filaments can reduce AC losses in HTS coated conductors: a review”, Francesco Grilli and Anna Kario, Supercond. Sci. Technol. 29 (2016) 083002 (15 pp), in particular page 3, end of Section 2, the entire contents of which are incorporated herein by reference).

[0078] “Transposition” can generally be understood as the optional periodic exchange of the conductor positions of a transmission line, such as to reduce crosstalk and / or otherwise improve transmission, see, for example, the article “How filaments can reduce AC losses in HTS coated conductors: a review”, Francesco Grilli and Anna Kario, Supercond. Sci. Technol. 29 (2016) 083002 (15 pp), the entire contents of which are incorporated herein by reference).

[0079] Furthermore, it may be advantageous to deposit an additional cap, such as a metal, such as copper or silver, such as silver, before twisting the plurality of individual filaments around their own axis (longitudinal, rolling axis). The cap may also be added after twisting and / or after transposition and / or twisting with other filaments. The additional cap provides additional mechanical and thermal stability. The metallization may be applied by using electrodeposition, such as electroplating or sputtering.

[0080] According to an embodiment, a method is proposed, wherein the method further comprises:

[0081] • Forming a superconducting wire by providing a core and / or a cap for one or more superconducting structures.

[0082] A "core" may be understood as an optionally metallic (such as copper, stainless steel, gold or silver) element placed in the center, optionally with one or more superconducting structures twisted around the core. An advantage of the core may be that it provides mechanical strength to the resulting superconducting wire.

[0083] "Capping" can be understood as a material placed on the periphery. The advantage of the capping may be that it provides mechanical and / or thermal protection to the superconducting portion of the obtained superconducting wire. Another possible advantage of the capping may be that it produces additional mechanical strength for the obtained superconducting wire. It can also provide additional heat capacity, which can be used to prevent superconductor quenching (see "Multifilamentary coated conductors for ultra-high magnetic field applications", Anders Christian Wulff, etc., Supercond. Sci. Technol. 34 (2021) 053003, the entire contents of the article are incorporated herein by reference).

[0084] "Wire" is understood to be an electrically conductive and optionally flexible element comprising a plurality of superconducting filaments and one or more additional elements, such as a cap and / or a core. The wire may comprise at least 5 filaments, such as at least 10 filaments, such as at least 100 filaments, such as at least 500 filaments, such as at least 1000 filaments, such as at least 10000 filaments. The length of the wire may be at least 0.1 m, such as at least 1 m, such as at least 10 m, such as at least 100 m, such as at least 1000 m.

[0085] According to an embodiment, a method is provided, wherein the method further comprises forming a coil by winding one or more filaments, superconducting structures and / or superconducting wires. An advantage of providing a coil is that such a coil can be used for a variety of purposes, such as generating a magnetic field such as used in a nuclear magnetic resonance (NMR) scanner, a magnetic resonance imaging scanner, a fusion reactor poloidal or toroidal field magnet, a central column solenoidal magnet, a toroidal coil, a solenoid, an accelerator magnet or a racetrack coil magnet.

[0086] According to an embodiment, a method is proposed, wherein the superconducting wire includes a reinforcing element, such as a reinforcing element including Hastelloy and / or carbon fiber, and wherein the reinforcing element is optionally embedded in a cap. A possible advantage is to increase the strength of the resulting superconducting wire. The reinforcing element can be a fiber material (optionally having a diameter of 50-500 microns (such as 100 to 300 microns, such as 150 to 250 microns, such as approximately 200 microns)), such as Hastelloy fiber or carbon fiber wrapped or wound around one or more filaments, and optionally embedded in a cap by optionally being plated into a cap (such as a copper cap, such as produced by copper plating).

[0087] According to an embodiment, a method is proposed, wherein the distance between a plane parallel to the surface of the first side of the substrate (such as tangent to the protrusions (such as the tops of the protrusions) between the grooves) and a plane tangent to the bottom of the plurality of grooves, such as the depth of the grooves measured in a direction orthogonal to the plane of the first side of the substrate, is at least 1 μm, such as at least 10 μm, such as at least 25 μm, such as at least 50 μm, such as at least 100 μm. By having a minimum distance (depth), the tolerance for subsequent removal of the substrate is correspondingly larger. This in turn can simplify the removal step and / or reduce the risk of failure or damage to the remaining components.

[0088] According to an embodiment, a method is presented, wherein providing a substrate comprises providing the substrate, such as a tape, in a roll-to-roll arrangement. A possible advantage is that it facilitates large-scale processing.

[0089] According to an embodiment, a method is presented wherein applying a coating on a substrate comprises applying the coating on a substrate, such as a tape, in a roll-to-roll arrangement. A possible advantage is that it facilitates large-scale processing.

[0090] According to an embodiment, a method is provided wherein removing at least a portion of the substrate from the second side of the substrate comprises removing (such as by any one or more of electropolishing, etching, grinding and / or laser removal) at least a portion of a substrate (such as a tape) from the second side of the substrate in a roll-to-roll arrangement. A possible advantage is that it facilitates large-scale processing.

[0091] According to a second aspect of the invention, a plurality of filaments is provided, wherein each filament is superconducting, such as a high temperature superconductor (HTS), and wherein each filament is not connected to 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 (such as each filament comprises a portion of the substrate, such as a (original) substrate).

[0092] According to an alternative second aspect of the invention which replaces the second aspect of the invention, a plurality of filaments are provided, wherein each filament is superconducting, such as a high temperature superconductor (HTS), and wherein each filament is not connected to one or more other filaments through a substrate, such as wherein each filament is physically disconnected from one or more other portions of the substrate.

[0093] According to an embodiment, a plurality of filaments is provided, wherein each filament comprises a substrate. A possible advantage is that this may increase the strength and / or robustness of the filaments. This may be utilized, for example, when the filaments are integrated into a wire.

[0094] According to an embodiment, a plurality of filaments is presented, wherein the substrate is a solid element on which a superconducting material may be placed (such as deposited), such that the substrate and the superconducting element may together form a superconducting element.

[0095] According to an embodiment, a plurality of filaments are provided, wherein the solid element comprises a material selected from the group consisting of: nickel-based alloys, copper-based alloys, chromium-based alloys, iron, aluminum, silicon, titanium, tungsten (also known as tungsten (W)), silver, Hastelloy, and stainless steel.

[0096] According to an embodiment, a plurality of filaments is provided, wherein each filament comprises a superconducting material including, such as consisting of, rare earth barium copper oxide.

[0097] According to an embodiment, a plurality of filaments are presented, wherein each filament comprises a superconducting material, such as a high temperature superconducting (HTS) material, and further comprises (such as after a step of removing at least a portion of the substrate from a second side of the substrate is completed) a portion of the substrate adjacent to the superconducting material, and optionally further comprises a buffer layer and / or one or more metal layers (which together can be considered to form a superconductor stack, such as an HTS stack).

[0098] According to an embodiment, a plurality of filaments are provided, wherein each filament comprises superconducting material on two or more sides of a substrate (such as partially or completely covering each of said sides), such as wherein each of said sides is non-parallel, such as orthogonal, with respect to at least one other of the two or more sides when viewed in a cross-sectional view orthogonal to the longitudinal direction of each of the filaments. A possible advantage may be that a larger area of ​​each filament (such as not just the top side) may be used to carry superconducting material, which in turn may enable each filament to carry more current.

[0099] According to an embodiment, each filament includes a superconducting material, wherein the angular range of the superconducting material around the geometric center of the substrate observed in a cross-sectional view orthogonal to the longitudinal direction of each of the filaments is 90° or greater, such as at least 135°, such as 180° or greater, such as greater than 181°, such as greater than 185°, such as greater than 190°, such as greater than 200°, such as at least 225°, such as at least 270°, such as 315°. As an example, for a square cross-section filament with superconducting material only on one side, the angular range is 90°. As another example, for a filament with a circular cross-section of superconducting material only on one side (such as the upper side, with reference to, for example, a cross section through the middle of the sphere in the northern hemisphere), the angular range is 180°. The advantage of a relatively large angular range may be that a larger portion of the filament surface can be used to carry superconducting material, which in turn can carry more current. In an embodiment, the angular range is less than 360° (such as not completely around, such as less than 355°).

[0100] According to an embodiment, a plurality of filaments are provided, wherein the substrate is subjected to a rolling process, such as the substrate is a metal or a metal alloy, such as the metal alloy is Hastelloy, stainless steel, such as An advantage of a metal or metal alloy that has been subjected to a rolling process (such as warm roll or cold roll processing) may be that it has high strength, such as relative to a material such as a metal or metal alloy that has been deposited (e.g., by electron beam evaporation, thermal evaporation, sputtering deposition, or electrochemical deposition). In an embodiment, the substrate is annealed after the rolling process, such as subjected to a heat treatment. The (substrate) material that has been subjected to the rolling process will have a characteristic grain structure that is visible, for example, in a scanning electron microscope (SEM).

[0101] According to an embodiment, a plurality of filaments are provided, wherein the plurality of filaments are connected by a protective covering, and wherein the protective covering only partially covers each filament, such as covering a superconducting coating, but does not cover all remaining portions of the filaments. An advantage of having a protective covering may be that a portion of the filaments, such as a superconducting coating, may be protected, such as during storage and transportation. Another possible advantage is that the protective covering may be used to hold the filaments together in a fixed spatial relationship, such as to maintain control over the relative spatial positioning of the filaments.

[0102] According to an embodiment, a plurality of filaments are provided, wherein the width of each filament, such as the maximum dimension in a direction orthogonal to the longitudinal direction of each filament and optionally also parallel to the interface between the superconducting material and the substrate material, is equal to or less than 2 mm, such as equal to or less than 1 mm, such as equal to or less than 750 microns, such as equal to or less than 500 microns, such as equal to or less than 400 microns, such as equal to or less than 300 microns, such as equal to or less than 250 microns, such as equal to or less than 200 microns, such as equal to or less than 150 microns, such as equal to or less than 100 microns. An advantage of a relatively small width may be that it enables the presence of multiple filamentary superconductors in a superconducting structure, which may reduce or minimize the shielding field amplitude and / or hysteresis energy losses (Q) of each filament. h ). Another advantage is that mechanical bending (including twisting about the longitudinal axis of the filament) becomes easier the narrower the filament. A possible advantage of twisting may be that it enables transposition (such as transposition) with reduced, minimized or zero in-plane bending relative to wider filaments (where in-plane bending may generally be disadvantageous, such as degrading superconducting properties). Another possible advantage is that the metal coverage of each individual filament is increased and therefore thermal stability is improved. Another possible advantage is that smaller filaments reduce the amount of Joule heating in the event of a single filament crack / break.

[0103] The width of a filament may be understood as the dimension in a direction orthogonal to the longitudinal direction of each filament and parallel to the interface between the superconducting material and the substrate material.

[0104] According to an embodiment, a plurality of filaments are proposed, wherein the width of each filament, such as the maximum dimension in a direction orthogonal to the longitudinal direction of each filament and optionally also parallel to the interface between the superconducting material and the substrate material, is equal to or less than 200 microns, such as equal to or less than 150 microns, such as equal to or less than 100 microns, such as equal to or less than 50 microns, such as equal to or less than 25 microns, such as equal to or less than 10 microns.

[0105] According to an embodiment, a plurality of filaments are provided, wherein the width of each filament, such as the maximum dimension in a direction orthogonal to the longitudinal direction of each filament and optionally also parallel to the interface between the superconducting material and the substrate material, is equal to or greater than 1 micron, such as equal to or greater than 10 microns, such as equal to or greater than 25 microns, such as equal to or greater than 50 microns, such as equal to or greater than 100 microns, such as equal to or greater than 200 microns, such as equal to or greater than 500 microns. A possible advantage is that this minimum width may be advantageous in overcoming the problem of grain size (e.g., REBCO with a grain size of about 50 nm) becoming comparable to the width. Another possible advantage is that it allows current to dissipate into the surrounding material (such as a copper matrix).

[0106] According to an embodiment, a plurality of filaments are proposed, wherein the length of each filament, such as the maximum dimension in the longitudinal direction of each filament, is equal to or greater than 1 meter, such as equal to or greater than 10 meters, such as equal to or greater than 100 meters, such as equal to or greater than 1 kilometer, such as equal to or greater than 10 kilometers, such as equal to or greater than 100 kilometers, such as equal to or greater than 1000 kilometers. The length of each filament can be understood as the maximum dimension of the filament. It is understood that the length is to be measured along the filament and / or for the filament configuration with the largest length (such as, for example, the length of the filament will be the length of the rolled filament, rather than the length or diameter of the coil including the rolled filament). In a specific embodiment, the length can be 1m, such as 100m, such as 1km, such as 20km, such as 100km, such as greater than 100km, such as within 1m to 30km, such as within 1km to 30km.

[0107] According to an embodiment, a plurality of filaments is proposed, wherein the length of each filament, such as the maximum dimension in the longitudinal direction of each filament, is equal to or less than 1 km, such as equal to or less than 100 m, such as equal to or less than 25 m, such as equal to or less than 10 m.

[0108] A possible advantage of relatively short lengths of filament sections can be that, for example, shorter fabricated coated conductors (such as HTS tapes) can be spliced ​​together, which conductors have a width of, for example, 4 mm or 12 mm and a length of, for example, 100 m. The span length of the spliced ​​section can be, for example, 1 to 100 cm, such as 10 cm or 50 cm, or several meters, such as 1 to 10 m, such as 1 m or 5 m. Splicing can be produced industrially by electrodeposition (such as copper plating, such as silver plating) or welding (such as tin welding). The filaments can be twisted mechanically into a transposition matrix and then, for example, copper plated or welded to adhere to the filaments. The longer the spliced ​​section, the lower the resistance of the splice or joint. This solution solves the problem of joining superconducting (SC) (such as high temperature superconducting) tapes, where the tapes are usually welded together only in a local short section at the ends of the tape. Using shorter components from SC, such as HTS, manufacturing can make it possible to overlap the joints completely or partially, for example, by several meters, which means that the joints will no longer constitute so-called weak points. The use of shorter production pieces in HTS manufacturing simplifies the production of coated conductors and allows a larger span of superconductor properties because multiple filaments can be transposed along the entire length of the superconductor wire or cable, and the quality (such as superconductor properties) of the individual filaments can vary, as long as the individual filaments with low, medium, and high performance (such as Ic or Tc) are evenly distributed, that is, statistically uniformly distributed along the entire wire or cable length.

[0109] This means that multiple filament transposed wires or cables can be produced with typically lower HTS production standards, and may even benefit from using HTS tapes from different suppliers, such as to provide leveled performance along the entire wire by varying superconducting performance levels.

[0110] According to an embodiment, a plurality of filaments are proposed, wherein the thickness, such as the maximum dimension in a direction orthogonal to the longitudinal direction of each filament and optionally also orthogonal to the interface between the superconducting material and the substrate material (such as wherein the dimension is orthogonal to one or both of the dimensions measuring width and length), is at least 1 μm, such as at least 10 μm, such as at least 25 μm, such as at least 50 μm, such as at least 100 μm, such as at least 200 μm, such as at least 500 μm. A possible advantage is that such a dimension may produce strength and / or robustness. Such a dimension may be provided by a method according to the first aspect with a corresponding groove depth and uniform etching. Alternatively, such a dimension may be provided by a method according to the first aspect utilizing spatially confined etching.

[0111] The thickness of the filaments may be understood as the dimension in a direction normal to the longitudinal direction of each filament and normal to the interface between the superconducting material and the substrate material.

[0112] According to an embodiment, a plurality of filaments are provided, wherein the engineering current density J of each filament at a temperature of 77 Kelvin and zero applied magnetic field is E For at least 10 5 A / cm 2 , such as at least 3*10 5 A / cm 2 , such as at least 5*10 5 A / cm 2 , such as at least 10 6 A / cm 2 , such as at least 3*10 6 A / cm 2 , such as at least 10 7 A / cm 2 , wherein the engineering current density is defined as the current density for a cross-sectional area including the superconducting material and the substrate, including a buffer layer or buffer stack if present and a stabilization layer, wherein the width of each filament is optionally equal to or less than 500 microns, such as equal to or less than 400 microns, such as equal to or less than 300 microns, such as equal to or less than 250 microns, such as equal to or less than 200 microns, such as equal to or less than 150 microns, such as equal to or less than 100 microns. "Engineering current density" is understood to have the common meaning in the art.

[0113] An example of the width of the superconducting filament is 20 μm.

[0114] According to an embodiment, a plurality of filaments are proposed, wherein the distance from the edge of the filament (such as the edge at the side of the filament) to the superconducting performance of the superconducting material in the filament where the superconducting performance is degraded, such as the average distance, is equal to or less than 100 microns, such as equal to or less than 50 microns, such as equal to or less than 25 microns, such as equal to or less than 20 microns, such as equal to or less than 15 microns, such as equal to or less than 10 microns, such as equal to or less than 5 microns, such as equal to or less than 1 micron. "Degradation" is understood as a performance change that has a negative impact on superconducting performance, such as delamination, phase change and / or cracking. The distance can be observed and measured, for example, by a scanning electron microscope (SEM) image obtained from above the superconducting coating portion and / or a cross-sectional image obtained from a cross section orthogonal to the longitudinal direction of the filament. The advantage is that a relatively small degradation distance can maintain a relatively high engineering current density.

[0115] Since cracks may lead to the breaking of the coating, such as where the coating comprises a high temperature superconducting (HTS) layer, the absence of cracks or as few cracks as possible is considered advantageous.

[0116] According to an embodiment, a plurality of filaments are provided, wherein the ratio t / w of the thickness t of the substrate adjacent to the superconducting material (wherein the thickness is optionally measured in a direction orthogonal to the longitudinal direction and to the interface between the superconducting coating and the substrate) to the width w (wherein the width is optionally measured in a direction orthogonal to the longitudinal direction and to the thickness direction and / or to the interface between the superconducting material and the substrate material) is at most equal to or less than 20: 1, such as equal to or less than 10: 1, such as equal to or less than 5: 1, such as equal to or less than 2: 1. An advantage may be to have a relatively low ratio t / w of width to thickness, for example because a lower ratio makes it simpler to integrate the filaments into a superconducting structure.

[0117] According to a third aspect of the present invention, a use is provided of a plurality of filaments provided according to the first aspect and / or according to the second aspect for conducting electric current, such as conducting electric current under superconducting conditions.

[0118] According to a fourth aspect of the present invention, a conductor is provided, such as a cable (such as comprising a plurality of conductors), such as a power cable (such as a cable capable of transmitting at least 10 kV of electricity and / or transmitting at least 100 amperes of current), the conductor comprising a plurality of filaments provided according to the first aspect and / or according to the second aspect. "Cable" is understood to be a conductive structure comprising a plurality of conductors, such as one in which the conductors are twisted around their own axis and / or a common axis. The length of the cable may be at least 0.1 m, such as at least 1 m, such as at least 10 m, such as at least 100 m, such as at least 1000 m. The cable may comprise at least 5 filaments, such as at least 10 filaments, such as at least 100 filaments, such as at least 500 filaments, such as at least 1000 filaments, such as at least 10000 filaments.

[0119] According to alternatives to other aspects of the invention, any of a coil comprising multiple filaments according to the first aspect and / or according to the second aspect, a generator, a transformer, a nuclear magnetic resonance (NMR) scanner, a magnetic resonance imaging scanner, a fusion reactor poloidal or toroidal field magnet, a central column solenoid magnet, a toroidal coil, a solenoid, an accelerator magnet or a racetrack coil magnet is proposed. BRIEF DESCRIPTION OF THE DRAWINGS

[0120] The first, second and third aspects according to the present invention will now be described in more detail with reference to the accompanying drawings. The drawings represent one way of implementing the invention and should not be construed as limiting other possible embodiments falling within the scope of the appended claims.

[0121] Figure 1 is a flow chart illustrating a method according to an embodiment of the present invention.

[0122] Figures 2 to 7 Shown is a schematic diagram describing steps in a method according to an embodiment of the present invention.

[0123] Figure 8 A superconducting wire is shown.

[0124] Fig. 9 A method of forming a plurality of filaments according to an embodiment is shown.

[0125] Fig.10 1 shows a Hastelloy substrate with grooves formed in a CC stack 1038 in a 2LUPS process.

[0126] Fig.11 express Fig.10 Zoomed view of the .

[0127] Fig.12 A single filament 1242 is shown etched.

[0128] Fig.13 Represents the I / V setup used to characterize the superconducting properties of the filaments.

[0129] Fig.14 Indicates immersion in liquid nitrogen Fig.13 I / V settings.

[0130] Figures 15-16 Scanning electron microscope (SEM) image showing 3D etched Hastelloy substrate.

[0131] Fig.17 Scanning electron microscope image showing a focused ion beam milled HTS stack deposited on a 3D etched Hastelloy substrate.

[0132] Fig.18A collage of two images representing filaments.

[0133] Fig.19 Represents the result of twisting multiple filaments. DETAILED DESCRIPTION

[0134] Figure 1 1 is a flow chart showing a method according to an embodiment of the present invention, the method being a method 100 for forming a plurality of filaments and also forming a superconducting structure and providing a superconducting wire, wherein each filament is superconducting, such as a high temperature superconductor (HTS), the method comprising, in sequence:

[0135] Providing 102 a substrate that is 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:

[0136] i. providing a substrate without a groove in a first side of the substrate,

[0137] ii. forming 104 a plurality of grooves in the first side of the substrate, and

[0138] iii. forming 106 one or more undercuts at each recess by etching and / or electropolishing, and optionally in a two-stage undercut process (2LUPS) (although it should be noted that alternative embodiments are contemplated, such as embodiments similar to the present embodiment in all other respects but in which undercuts are not present or formed),

[0139] Applying 108 a coating on the substrate, wherein the coating comprises a high temperature superconducting stack such that for each groove within the plurality of grooves, the following two portions are separated, such as disconnected, such as physically disconnected:

[0140] i. a first portion of a coating on a first side of a groove feature (such as a groove); and

[0141] ii. a second portion of the coating on a second side of a groove feature (such as a groove), wherein the second side of the groove feature is opposite to the first side of the groove feature,

[0142] applying 110 a protective covering, such as a resist, over some or all of the first portion of the coating and over some or all of the second portion of the coating, such as over the first portion and / or the second portion of the coating, wherein the protective covering partially or completely fills the voids in the recesses,

[0143] removing 112 at least a portion of the substrate from the second side of the substrate by electropolishing and / or etching to remove at least connections from the first portion of the coating via the substrate to the second portion of the coating, such as to provide a plurality of filaments, such as where portions of the substrate previously engaging the filaments have been removed,

[0144] stopping 114 to remove at least a portion of the substrate from the second side of the substrate while portions of the coating, such as the first portion of the coating and the second portion of the coating, are adjacent to the remaining portion of the substrate,

[0145] partially or completely removing 116 the protective covering from some or all of the coating and the remainder of the substrate, such as to remove at least a connection from a first portion of the coating to a second portion of the coating via the protective covering,

[0146] twisting 118 a plurality of filaments or groups of a plurality of filaments, wherein each filament is twisted about its own axis and / or wherein a plurality of filaments are twisted about their common axis, such as wherein bundles of optionally twisted filaments are twisted about each other, thereby providing one or more superconducting structures, each superconducting structure comprising a twisted plurality of filaments, such as wherein each filament has a helical shape with a central axis located within one or more other helical filaments,

[0147] • Forming 120 a superconducting wire by providing a core and a covering for one or more superconducting structures.

[0148] Figures 2 to 7 A schematic diagram depicting steps in a method 100 for forming a plurality of filaments and also forming a superconducting structure and providing a superconducting wire, wherein each filament is superconducting, such as a high temperature superconductor (HTS), according to an embodiment of the present invention is shown.

[0149] Figure 2 A substrate 228 is shown 102 , the substrate 228 being a planar metal substrate without grooves in a 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.

[0150] Figure 3 The substrate 230 is shown after forming 104 a plurality of recesses 234 in the first side of the substrate, and after forming 106 one or more undercuts 236 at each recess (as indicated by the dashed lines defining the shaded undercut portions of each recess).

[0151] Figure 3 The dimensions of the groove 234 are also shown. Figure 3The distance 233a between a plane parallel to the (upper (in the figure)) surface of the first side of the substrate (such as tangent to the protrusion between the grooves 234) and a plane tangent to the bottom of the plurality of grooves and a plane (as shown by the lower horizontal dashed line) is shown, that is, the depth of the groove measured in a direction orthogonal to the plane of the first side of the substrate (that is, measured in the vertical / up and down direction within the drawing plane). The distance 233a or depth is non-zero, such as at least 100nm, such as at least 1μm, such as at least 10μm, such as at least 25μm, such as at least 50μm, such as at least 100μm. The distance 233a or depth can also be at most 4mm, such as at most 2mm, such as at most 1mm. The distance 233a or depth may be within ]10 nm; 4 mm[, such as within ]1 μm; 2 mm[, such as within ]10 μm; 1 mm[ (herein, the open brackets "]x,; y[ indicate that neither x nor y is included in the interval, but all the numbers therebetween are included). In addition, the size or width 233b of the groove is also indicated, i.e., from the edge of the protrusion on one side of the groove (such as the starting point of the edge, such as the end of the planar portion of the substrate outside the groove) to the direction parallel to the plane of the first side of the substrate and orthogonal to the longitudinal direction of the groove (i.e., on the plane of the drawing) The distance from the edge of the protrusion on the other side of the groove (measured in the horizontal and left-right directions within the plane). The size or width 233b can be at least 1 micron, such as at least 2 microns, such as at least 5 microns, such as at least 10 microns, such as at least 30 microns, such as at least 100 microns, such as at least 200μm. The size or width 233b can be at most 1mm, such as at most 500μm, such as at most 200μm, such as at most 100μm. The size or width 233b can be in the range of 1 micron to 1 mm, such as in the range of 10μm to 500μm. Figure 3 Also shown in is a distance 233c between adjacent grooves measured in the same direction as width 233b. Distance 233c may be at least 100 μm. Distance 233c may be at most 2 mm. Distance 233c may be within]100 μm; 2 mm[, such as within]200 μm; 1 mm[.

[0152] Figure 4 The substrate 230 is shown after applying 108 a coating 238 including a high temperature superconductor stack on the substrate such that, for each groove within a plurality of grooves, a first portion of the coating on a first side of the groove is physically disconnected from a second portion of the coating on a second side of the groove, wherein the second side of the groove feature is opposite the first side of the groove feature. Additionally, portions of the coating material can be seen in the grooves.

[0153] Figure 5Represents a substrate 230 having a protective covering 240 applied 110 as a resist over some or all of the first portion of the coating and some or all of the second portion of the coating, such as over the first portion and / or the second portion of the coating, wherein the protective covering partially or completely fills the voids in the recesses.

[0154] Figure 6 A plurality of filaments 242 are shown after the following operations: at least a portion of the substrate is removed 112 from a second side of the substrate (where substrate 230 is no longer present and the dashed rectangle 244 represents the location previously held by substrate 230) by electropolishing and / or etching to at least remove the connection from the first portion of the coating to the second portion of the coating via the substrate, such as to provide a plurality of filaments 242, each of which is superconducting, such as where portions of the substrate that previously joined the filaments (such as through the superconducting coating) have been removed. Figure 6 Also represented is the result of stopping 114 removing at least a portion of the substrate from the second side of the substrate while portions of the coating (such as the first portion of the coating and the second portion of the coating) abutting the remaining portion 246 of the substrate.

[0155] Figure 7 Plurality of filaments 242 is shown after partially or completely removing 116 protective covering 240 from some or all of the coating and the remainder of the substrate, such as to remove at least a connection from a first portion of the coating to a second portion of the coating via the protective covering. Figure 7 Also shown are the width 248 and thickness 250 of the filament. The length is the dimension normal to the plane of the paper.

[0156] Figure 8 A plurality of filament groups are shown, wherein each filament is twisted around its own axis, and wherein the plurality of filaments in each filament group is twisted around their common axis, thereby providing a plurality of superconducting structures 256, each superconducting structure 256 comprising a plurality of twisted filaments, wherein each filament has a spiral shape, and wherein these superconducting structures have been provided 120 in the form of a superconducting wire 252 having a core 254 and a cap 258.

[0157] Example

[0158] According to an embodiment, a method of forming a plurality of filaments is provided, wherein each filament is superconducting, the method comprising the following detailed description (and in Fig. 9 Steps 1 to 9 (schematically shown in FIG. 1 ):

[0159] In steps 1 to 5, a substrate including a plurality of grooves is provided, and in steps 2 to 5, a plurality of grooves are formed in a first side (such as an upper side, top side or front side) of the substrate (wherein the first side is opposite to a second side (such as a lower side, bottom side or back side)):

[0160] Step 1: Start with a substrate without grooves in the form of a polished Hastelloy strip 4 mm wide, 100 μm thick and 50 m long with a surface roughness below 10 nm (here, the surface roughness is 10×10 μm 2 Arithmetic surface roughness value of atomic force microscope scan). The surface quality applies to the coating conductor (CC) chemical vapor deposition (CVD) / metal organic chemical vapor deposition (MOCVD), physical vapor deposition (PVD) or chemical deposition of buffer layers and superconducting layers. Polishing can be achieved by electrochemical polishing in a phosphorus and sulfuric acid mixture solution according to standard procedures in the literature (see, for example, Wulff et al. 2015, Supercond. Sci. Technol. 28 (2015) 072001, page 2, section 2).

[0161] Fig. 9 Sub-figure (a) of shows a cross-sectional view of the belt in a plane orthogonal to the longitudinal direction of the belt.

[0162] Step 2: Apply a masking material as described in Wulff et al. 2015, Supercond. Sci. Technol. 28 (2015) 072001, page 2, section 2.

[0163] This can be a masking tape, e.g. film, photoresist or the like. It is understood that Membrane refers to DuPont TM A well-known product of , which is a film of poly (4,4′-oxydiphenylene-diammonium pyromellitic acid).

[0164] Fig. 9 Sub-figure (b) of shows a cross-sectional view of the strip in a plane orthogonal to the longitudinal direction of the strip with the masking material.

[0165] Step 3: Remove a portion of the mask material by using mechanical scribing, wet / dry chemical lithography processes, or laser scribing. Here, standard photolithography steps are used to completely remove the mask material in the areas where the grooves are to be etched.

[0166] Fig. 9 Sub-figure (c) of shows a cross-sectional view of the tape in a plane orthogonal to the longitudinal direction of the tape, wherein a portion of the masking material is removed.

[0167] Step 4: Apply 0.01 to 1 A / cm 2 A mixture of phosphorus and sulfuric acid is used to etch the substrate until grooves are formed.

[0168] Fig. 9 Sub-figure (d) of shows a cross-sectional view of a tape in a plane orthogonal to the longitudinal direction of the tape, the tape having grooves formed by etching.

[0169] Step 5: Remove the mask material using an organic solvent (such as acetone) or a stripper (such as sodium hydroxide).

[0170] In step 6, the following operations are performed: applying a coating on the substrate, wherein the coating (coated conductor (CC) stack) is a high temperature superconductor stack, so that for each groove in the plurality of grooves, a first portion of the coating on a first side of the groove is separated (such as separated, but still physically connected, such as as shown in Figure 5) from a second portion of the coating on a second side of the groove. Fig. 9 (e)), wherein the second side of the groove feature is opposite to the first side of the groove feature.

[0171] Step 6: Deposit a superconducting coated conductor (CC) stack on the material, referring to the method described in, for example, 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.

[0172] Fig. 9 Sub-figure (e) of shows a cross-sectional view of the tape in a plane orthogonal to the longitudinal direction of the tape, wherein the remaining parts of the masking material are removed and a superconducting CC stack is deposited on the tape.

[0173] In step 7, a protective covering (protective material) is applied over some or all of the first portion of the coating and some or all of the second portion of the coating, the protective covering partially or completely filling the voids in the grooves.

[0174] Step 7: Apply protective material, such as liquid photoresist, and cover the top of the tape and CC stack (and in this embodiment also the sides, such as to avoid etching the sides of the substrate and / or the sides of the outer CC stack) to protect the superconducting stack. The grooves should also be fully or partially covered with protective material. The protective material can be applied in several ways, such as liquid photoresist applied by inkjet (e.g., firmly fixing the opposite side of the tape to a solid element to avoid photoresist on said opposite side), liquid photoresist applied by brush or dip coating (such as with, for example, Scotch The opposite side of the temporarily covered tape is dip coated).

[0175] Fig. 9 Sub-figure (f) of shows a cross-sectional view of the tape with the protective material applied in a plane orthogonal to the longitudinal direction of the tape.

[0176] In step 8, the following operation is performed: at least a portion of the substrate is removed from a second side (such as the back side or bottom side) of the substrate by etching, such as electrochemical etching, or by electropolishing to at least remove connections from the first portion of the coating to the second portion of the coating via the substrate, such as to provide a plurality of filaments, wherein portions of the substrate previously joined to the filaments have been removed.

[0177] Step 8: Etch from the back side of the ribbon structure using a mixture of phosphorus and sulfuric acid. Etching can continue until they are physically connected only by the protective material.

[0178] Fig. 9 Sub-figure (g) of FIG. 1 shows a cross-sectional view of the plurality of filaments obtained after removing a portion of the substrate from the back side, in a direction orthogonal to the longitudinal direction of the plurality of filaments (with Fig. 9 The views in sub-figure (g) are in the same plane) connected by a protective cover.

[0179] In step 9, the protective covering is partially or completely removed from some or all of the coating and the remainder of the substrate, such as to remove at least the connection from the first portion of the coating to the second portion of the coating via the protective covering.

[0180] Step 9: Remove the protective material mechanically by stripping the material, or dissolving in an organic solvent (such as ethanol or acetone) or a stripping solvent (such as sodium hydroxide).

[0181] Fig. 9 Sub-figure (h) of represents a cross-sectional view of the resulting plurality of filaments no longer connected by the protective covering in a plane orthogonal to the longitudinal direction of the plurality of filaments, ie after the protective covering has been removed.

[0182] Fig.10 A Hastelloy substrate 1030 is shown with recesses formed in a CC stack 1038 (without undercut) in a 2LUPS process. Fig.10 can be considered as corresponding to Figure 4 and / or Fig. 9 Schematic diagram in subfigure (e) of .

[0183] Fig.11 Show Fig.10 Zoomed view of the .

[0184] Fig.12 A single filament 1242 is shown etched out, but with the remaining portion 1246 of the substrate, where the width (i.e., the size in the left-right horizontal dimension, i.e., the size within the paper, is about 500 μm, i.e., the image depicts a filament 1242 of about 500 μm wide with CC stacking). The thickness of the filament (the dimension in the up-down direction in the paper) is about 80 μm. Fig.12 can be considered as corresponding to Figure 7 and / or Fig. 9 Schematic diagram in subfigure (h).

[0185] Fig.13 An I / V setup for characterizing the superconducting properties of a filament 1342 in liquid nitrogen is shown, the I / V setup comprising a current lead 1360 and a voltage tap 1362. The dimensions can be retrieved from a ruler 1364 (numbers are in centimeters, the distance between adjacent smaller line marks is 1 mm). The washer 1366 is generally circular, indicating that the scale provided by the ruler applies in both horizontal and vertical directions.

[0186] Fig.14 Indicates immersion in liquid nitrogen Fig.13 The I / V setup. Current ramp tests were performed by immersing the filament in liquid nitrogen while measuring the voltage drop between the contact points, and the results showed that no transition to normal conduction was shown when the current exceeded 3A at zero applied magnetic field and 77K. When the width of the substrate and CC stack was estimated to be 500μm and the total thickness was estimated to be 80μm, the engineering current density was estimated to be 9375A / cm at zero applied magnetic field and 77K. 2 . The reference coated conductor sample has a recorded average Ic=97A at zero applied magnetic field at 77K for a 4mm bandwidth, corresponding to an expected Ic of over 12A for a 500μm wide filament. Note that the engineering current density can be improved by at least 3-5 times using another selected superconducting material. In addition, by reducing the thickness of the substrate, such as by continuing the etching to remove the substrate from the back for a longer time (such as making the thickness of the substrate, for example, less than half the current substrate thickness), an increase of at least (such as another) 2 times can be achieved, such as by leaving only a small part of the substrate (with a thickness of about 4μm), an increase of about 20 times can be achieved, such as estimated when the substrate is completely etched away. Taking into account possible improvements in materials and reductions in substrate thickness, about 1.8MA / cm can be achieved at zero magnetic field and 77K. 2 It should also be noted that as the operating temperature decreases, such as at 50 K, such as at 30 K, such as at 20 K or at 4.2 K, the expected current density is higher. In contrast, as the applied magnetic field increases, the expected current density is lower.

[0187] Fig.15 Scanning electron microscope (SEM) image showing a 3D etched Hastelloy substrate (view: perpendicular to the tape plane). Fig.15 can be considered as corresponding to Figure 3 Schematic diagram in (except undercut) and / or Fig. 9 Sub-image (d) of (excluding remaining mask material).

[0188] Fig.16Scanning electron microscope image (view: tilted) of a 3D etched Hastelloy substrate showing 3D etching and focused ion beam milling. The image shows a protrusion (or elongated "bump") formed between two grooves (on the left and right of the protrusion), where the width of the protrusion (left and right on the paper) is about 18 μm. Fig.16 (except for the cuts made by focused ion beam milling) can be considered as corresponding to Figure 3 Schematic diagram in (except undercut) and / or Fig. 9 Sub-image (d) of (excluding remaining mask material).

[0189] Fig.17 Scanning electron microscope image showing a focused ion beam milled 3D etched Hastelloy substrate with CC stacking in the form of a substrate 1771 of Hastelloy C276, a 1-2 μm thick buffer layer 1772 of yttrium stabilized zirconia (YSZ) with 50 nm ceria (as in Wulff et al. 2015, Supercond. Sci. Technol. 28 (2015) 072001), a 1-2 μm thick yttrium barium copper oxide (YBCO) layer 1773 and a 1-2 μm thick silver layer 1774. All thicknesses refer to the dimensions in the vertical / up-down direction in the figure, i.e., orthogonal to the plane of the layers. The width of the superconducting filament is about 25 μm. Fig.17 can be considered as corresponding to Figure 4 Schematic diagram in (except undercut) and / or Fig. 9 Subgraph (e).

[0190] Fig.18 Collage of two images representing filaments (filaments in the right image are held by a human hand), where the substrate has been etched from the back to remove the connections between the filaments through the substrate in a plane orthogonal to the longitudinal direction of the substrate. The length of the filaments, such as the free part of the filaments, spans several centimeters. The (full) width of the substrate is 4 mm (such as shown in the up-down direction in the upper right corner of the left sub-image).

[0191] Fig.19 Represents the result of twisting a plurality of filaments, wherein the plurality of filaments are twisted around their common axis, and wherein each filament is thereby also twisted around its own axis (the 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 central axis within one or more other helical filaments, and wherein a conductor is provided by setting a core. A belt is provided at each end, and The distance between the bands is 5 cm.

[0192] Although the present invention has been described in conjunction with specified embodiments, the present invention should not be interpreted as being limited in any way to the examples presented. The scope of the present invention is set forth by the appended claims. In the context of the claims, the terms "comprise" or "include" do not exclude other possible elements or steps. In addition, references such as "individual" or "kind" should not be interpreted as excluding multiple. The reference numerals used in the claims regarding the elements shown in the drawings should also not be interpreted as limiting the scope of the present invention. In addition, the individual features mentioned in different claims may be advantageously combined, and the mention of these features in different claims does not exclude that the combination of features is impossible and advantageous.

[0193] Terms

[0194] Furthermore, a method for forming a plurality of filaments, a plurality of filaments and a use of a plurality of filaments are proposed according to the following clauses, which may be combined with any of the preceding embodiments and / or with 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), the method comprising, such as sequentially comprising:

[0196] providing (102) a substrate (230), such as wherein the substrate comprises metal, such as the substrate is 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) a coating (238) on the substrate, wherein the coating comprises a superconducting material, such as the coating being a high temperature superconductor stack, such that for each groove within the plurality of grooves, the following two portions are separated, such as disconnected, such as physically disconnected:

[0198] i. a first portion of a coating on a first side of a groove feature (such as a groove); and

[0199] ii. a second portion of the coating on a second side of a groove feature (such as a groove), wherein the second side of the groove feature is opposite to the first side of the groove feature,

[0200] · Removing (112) at least a portion of the substrate from a second side of the substrate, such as by electropolishing and / or etching, to at least remove connections from a first portion of the coating to a second portion of the coating via the substrate, such as to provide a plurality of filaments, such as where portions of the substrate previously joined to the filaments have been removed.

[0201] 2. The method (100) according to any of the preceding clauses, further comprising, before removing at least a portion of the substrate from the second side of the substrate:

[0202] Applying (110) a protective covering (240), such as a resist, such as a protective covering layer, over some or all of the first portion of the coating and over some or all of the second portion of the coating (238), such as over the first portion and / or the second portion of the coating, such as where the protective covering layer partially or completely fills the void in the recess.

[0203] 3. The method (100) according to any of the preceding clauses, wherein removing at least a portion of the substrate from the second side (232) of the substrate (230) is performed by electropolishing and / or etching, such as electroetching.

[0204] 4. A method (100) according to any of the preceding clauses, wherein removing at least a portion of the substrate from the second side of the substrate is stopped (114), such as by stopping electropolishing and / or etching, when portions of the coating, such as a first portion of the coating and a second portion of the coating, are adjacent to a remaining portion (246) of the substrate.

[0205] 5. The method (100) according to any one of the preceding clauses, wherein the method further comprises:

[0206] twisting (118) a plurality of filaments (242) or groups of a plurality of filaments, wherein each filament is twisted about its own axis, and / or wherein a plurality of filaments are twisted about their common axis, such as wherein bundles of optionally twisted filaments are twisted about each other, thereby providing one or more superconducting structures (256), each superconducting structure comprising a twisted plurality of filaments, such as wherein each filament has a helical shape with a central axis within one or more other helical filaments, and / or

[0207] • Transposing a plurality of filaments (242) or groups of a plurality of filaments, thereby providing one or more superconducting structures (256), each superconducting structure comprising a transposed plurality of filaments.

[0208] 6. The method (100) according to clause 5, wherein the method further comprises:

[0209] • Forming (120) a superconducting wire (252) by providing one or more superconducting structures (256) with a core (254) and / or a cap (258).

[0210] 7. A plurality of filaments (242), wherein each filament is superconducting, such as a high temperature superconductor (HTS), and wherein each filament is not connected to one or more other filaments via a substrate, such as wherein each filament is physically disconnected from one or more other portions of the substrate.

[0211] 8. The plurality of filaments of clause 7, wherein each filament comprises a superconducting material, such as a high temperature superconducting (HTS) material, and further comprises a portion of the substrate that is adjacent to the superconducting material.

[0212] 9. A plurality of filaments (242) according to any one of clauses 7 to 8, wherein the substrate is subjected to a rolling process, such as the substrate is a metal or a metal alloy, such as the metal alloy is Hastelloy, stainless steel, such as Austenitic nickel-chromium based super alloys such as nickel-tungsten.

[0213] 10. A plurality of filaments (242) according to any one of clauses 7 to 9, wherein the plurality of filaments are connected by a protective covering (240), and wherein the protective covering only partially covers each filament.

[0214] 11. A plurality of filaments (242) according to any one of clauses 7 to 10, wherein the width (248) of each filament, such as the maximum dimension in a direction orthogonal to the longitudinal direction of each filament and optionally also parallel to the interface between the superconducting material and the substrate material, is equal to or less than 200 microns, such as equal to or less than 150 microns, such as equal to or less than 100 microns, such as equal to or less than 50 microns, such as equal to or less than 25 microns, such as equal to or less than 10 microns.

[0215] 12. A plurality of filaments (242) according to any one of clauses 7 to 11, wherein the length of each filament, such as the maximum dimension in the longitudinal direction of each filament, is equal to or greater than 1m, such as equal to or greater than 10m, such as equal to or greater than 100m, such as equal to or greater than 1km, such as equal to or greater than 10km, such as equal to or greater than 100km, such as equal to or greater than 1000km.

[0216] 13. A plurality of filaments (242) according to any one of clauses 7 to 12, wherein the engineering current density J of each filament at a temperature of 77 Kelvin and zero applied magnetic field is E For at least 10 3 A / cm 2 , such as at least 3*10 3 A / cm 2 , such as at least 10 4 A / cm 2 , such as at least 18750A / cm 2 , such as at least 3*10 4 A / cm 2 , such as at least 10 5 A / cm 2 , such as at least 3*10 5 A / cm 2 , such as at least 5*105 A / cm 2 , such as at least 10 6 A / cm 2 , such as at least 3*10 6 A / cm 2 , such as at least 10 7 A / cm 2 , where the engineering current density is defined as the current density for a cross-sectional area including the superconducting material and the substrate, the substrate including a buffer layer or buffer stack if present and a stabilization layer, wherein the width of each filament is optionally equal to or less than 500 microns, such as equal to or less than 400 microns.

[0217] 14. A plurality of filaments (242) according to any one of clauses 7 to 13, wherein a distance from an edge of the filament, such as an edge at a side, to a position in the filament where the superconducting properties of the superconducting material deteriorate, such as an average distance, is equal to or less than 100 microns, such as equal to or less than 50 microns, such as equal to or less than 25 microns, such as equal to or less than 20 microns, such as equal to or less than 15 microns, such as equal to or less than 10 microns, such as equal to or less than 5 microns.

[0218] 15. A use of a plurality of filaments (242) according to any one of clauses 1 to 6 and / or according to any one of clauses 7 to 14 for conducting electric current, such as conducting electric current under superconducting conditions.

Claims

1. A method (100) for forming a plurality of filaments (242), wherein each filament is superconducting, such as high temperature superconducting (HTS), the method comprising, such as sequentially comprising: providing (102) a substrate (230), such as wherein the substrate comprises metal, such as the substrate is 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, Applying (108) a coating (238) on the substrate, wherein the coating comprises a superconducting material, such as the coating being a high temperature superconductor stack, such that for each groove within the plurality of grooves, the following two portions are separated, such as disconnected, such as physically disconnected: i. a first portion of the coating on a first side of a recessed feature such as a recess, and ii. a second portion of the coating on a second side of a groove feature, such as a groove, wherein the second side of the groove feature is opposite to the first side of the groove feature, · Removing (112) at least a portion of the substrate from a second side of the substrate, such as by electropolishing and / or etching, to at least remove connections from a first portion of the coating to a second portion of the coating via the substrate, such as to provide a plurality of filaments, such as where portions of the substrate previously joined to the filaments have been removed.

2. The method (100) according to any of the preceding claims, further comprising, before removing at least a portion of the substrate from the second side of the substrate: Applying (110) a protective covering (240), such as a resist, such as a protective covering layer, over some or all of the first portion of the coating and over some or all of the second portion of the coating (238), such as over the first portion and / or the second portion of the coating, such as where the protective covering layer partially or completely fills the void in the recess.

3. The method (100) according to any of the preceding claims, wherein removing at least a portion of the substrate from the second side (232) of the substrate (230) is performed by electropolishing and / or etching, such as electroetching.

4. The method (100) according to claim 3, wherein the electropolishing and / or etching is stopped before the liquid used for the electropolishing and / or etching reaches the first part of the coating and / or the second part of the coating.

5. The method (100) according to any of the preceding claims, wherein at least a portion of the substrate is removed from the second side (232) of the substrate (230) in real time by grinding and / or laser.

6. A method (100) according to any of the preceding claims, wherein removing at least a portion of the substrate from the second side of the substrate, such as electropolishing and / or etching, is stopped (114) when portions of the coating, such as a first portion of the coating and a second portion of the coating, abut against a remaining portion (246) of the substrate.

7. The method (100) according to any one of the preceding claims, wherein the method further comprises: twisting (118) the plurality of filaments (242) or groups of a plurality of filaments, wherein each filament is twisted about its own axis, and / or wherein a plurality of filaments are twisted about their common axis, such as wherein bundles of optionally twisted filaments are twisted about each other, thereby providing one or more superconducting structures (256), each superconducting structure comprising a twisted plurality of filaments, such as wherein each filament has a helical shape with a central axis within one or more other helical filaments, and / or - transposing the plurality of filaments (242) or groups of plurality of filaments, thereby providing one or more superconducting structures (256), each superconducting structure comprising a transposed plurality of filaments.

8. The method (100) according to any one of the preceding claims, wherein the method further comprises: • Forming (120) a superconducting wire (252) by providing one or more superconducting structures (256) with a core (254) and / or a cap (258).

9. A method (100) according to any one of the preceding claims, wherein the distance (233a) between a plane parallel to the surface of the first side of the substrate, such as a plane tangent to the protrusion between the grooves (234), and a plane tangent to the bottom of the plurality of grooves, such as the depth of the grooves measured in a direction orthogonal to the plane of the first side of the substrate, is at least 1 μm, such as at least 10 μm, such as at least 25 μm, such as at least 50 μm, such as at least 100 μm, such as at least 200 μm, such as at least 500 μm.

10. The method (100) according to any one of the preceding claims, wherein providing (102) a substrate (230) comprises: A substrate, such as a tape, is provided (102) in a roll-to-roll arrangement.

11. The method (100) of any one of the preceding claims, wherein applying (108) a coating (238) on a substrate comprises: The coating (238) is applied (108) to a substrate, such as a tape, in a roll-to-roll arrangement.

12. The method (100) of any one of the preceding claims, wherein removing (112) at least a portion of the substrate from the second side of the substrate comprises: At least a portion of the substrate, such as at least a portion of the tape, is removed (112) from the second side of the substrate in a roll-to-roll arrangement.

13. The method (100) according to any of the preceding claims, wherein each groove of the plurality of grooves comprises one or more undercuts.

14. The method (100) according to any one of the preceding claims, comprising: • Forming one or more undercuts at each recess, such as by etching.

15. A plurality of filaments (242), wherein each filament is superconducting, such as a high temperature superconductor (HTS), and wherein each filament is not connected to one or more other filaments via a substrate, such as wherein each filament is physically disconnected from one or more other portions of the substrate.

16. A plurality of filaments (242), wherein each filament is superconducting, such as a high temperature superconductor (HTS), and wherein each filament is not connected to one or more other filaments via a substrate, such as wherein each filament is physically disconnected from one or more other portions of the substrate.

17. A plurality of filaments according to any one of claims 15 to 16, wherein each filament comprises a substrate.

18. A plurality of filaments according to any one of claims 15 to 17, wherein the substrate is a solid element onto which the superconducting material can be placed, such as deposited, such that the substrate and the superconducting element can together form the superconducting element.

19. The plurality of filaments of claim 18, wherein the solid element comprises a material selected from the group consisting of: nickel-based alloys, copper-based alloys, chromium-based alloys, iron, aluminum, silicon, titanium, tungsten (also known as tungsten (W)), silver, Hastelloy, and stainless steel.

20. A plurality of filaments according to any one of claims 15 to 19, wherein each filament comprises a superconducting material comprising, such as consisting of, rare earth barium copper oxide.

21. A plurality of filaments according to any one of claims 15 to 20, wherein each filament comprises a superconducting material, such as a high temperature superconducting (HTS) material, and further comprising a portion of the substrate adjacent to the superconducting material.

22. A plurality of filaments (242) according to claim 21, wherein each filament comprises a superconducting material on two or more sides of a substrate, such as in a manner that partially or completely covers each of the two or more sides, such as wherein each of the sides is non-parallel, such as orthogonal, with respect to at least one other of the two or more sides as viewed in a cross-sectional view orthogonal to the longitudinal direction of each filament.

23. A plurality of filaments (242) according to any one of claims 21 to 22, wherein the angular range of the superconducting material around the geometric center of the substrate as viewed in a cross-sectional view orthogonal to the longitudinal direction of each filament is 90° or greater, such as 180° or greater.

24. The plurality of filaments (242) according to any one of claims 15 to 23, wherein the substrate is subjected to a rolling process, such as the substrate is a metal or a metal alloy, such as the metal alloy is Hastelloy, stainless steel, such as Austenitic nickel-chromium based super alloys such as nickel-tungsten.

25. The plurality of filaments (242) of any one of claims 15 to 24, wherein the plurality of filaments are connected by a protective covering (240), and wherein the protective covering only partially covers each filament.

26. A plurality of filaments (242) according to any one of claims 15 to 25, wherein the width (248) of each filament, such as the maximum dimension in a direction orthogonal to the longitudinal direction of each filament and optionally also parallel to the interface between the superconducting material and the substrate material, is equal to or less than 200 microns, such as equal to or less than 150 microns, such as equal to or less than 100 microns, such as equal to or less than 50 microns, such as equal to or less than 25 microns, such as equal to or less than 10 microns.

27. A plurality of filaments (242) according to any one of claims 15 to 26, wherein a width (248) of each filament, such as a maximum dimension in a direction orthogonal to a longitudinal direction of each filament and optionally also parallel to an interface between a superconducting material and a substrate material, is equal to or greater than 1 micron, such as equal to or greater than 10 microns, such as equal to or greater than 25 microns, such as equal to or greater than 50 microns, such as equal to or greater than 100 microns, such as at least 200 μm, such as at least 500 μm.

28. A plurality of filaments (242) according to any one of claims 15 to 27, wherein the length of each filament, such as the maximum dimension in the longitudinal direction of each filament, is equal to or greater than 1m, such as equal to or greater than 10m, such as equal to or greater than 100m, such as equal to or greater than 1km, such as equal to or greater than 10km, such as equal to or greater than 100km, such as equal to or greater than 1000km.

29. A plurality of filaments (242) according to any one of claims 15 to 28, wherein the thickness (250), such as the maximum dimension in a direction orthogonal to the longitudinal direction of each filament and optionally also orthogonal to the interface between the superconducting material and the substrate material, such as wherein the dimension is orthogonal to one or both of the dimensions along which the width and length are measured, is at least 1 μm, such as at least 10 μm, such as at least 25 μm, such as at least 50 μm, such as at least 100 μm, such as at least 200 μm, such as at least 500 μm.

30. The plurality of filaments (242) of any one of claims 15 to 29, wherein the engineering current density J of each filament at a temperature of 77 Kelvin and zero applied magnetic field is E For at least 10 3 A / cm 2 , such as at least 3*10 3 A / cm 2 , such as at least 10 4 A / cm 2 , such as at least 18750A / cm 2 , such as at least 3*10 4 A / cm 2 , such as at least 10 5 A / cm 2 , such as at least 3*10 5 A / cm 2 , such as at least 5*10 5 A / cm 2 , such as at least 10 6 A / cm 2 , such as at least 3*10 6 A / cm 2 , such as at least 10 7 A / cm 2 , where the engineering current density is defined as the current density for a cross-sectional area including the superconducting material and the substrate, the substrate including a buffer layer or buffer stack if present and a stabilization layer, wherein the width of each filament is optionally equal to or less than 500 microns, such as equal to or less than 400 microns.

31. A plurality of filaments (242) according to any one of claims 15 to 30, wherein a distance from an edge of the filament, such as an edge at a side, to a location in the filament where superconducting properties of the superconducting material deteriorate, such as an average distance, is equal to or less than 100 microns, such as equal to or less than 50 microns, such as equal to or less than 25 microns, such as equal to or less than 20 microns, such as equal to or less than 15 microns, such as equal to or less than 10 microns, such as equal to or less than 5 microns, such as equal to or less than 1 micron.

32. A conductor, such as a cable, such as a power cable, comprising a plurality of filaments (242) according to any one of claims 1 to 14 and / or provided according to any one of claims 15 to 31.

33. Use of a plurality of filaments (242) provided according to any one of claims 1 to 14 and / or according to any one of claims 15 to 31 for conducting electric current, such as conducting electric current under superconducting conditions.

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