Stellarators with layered superconductors with improved alignment sensitivity

Abstract

A stellarator, comprising a non-planar magnetic field coil including at least one winding of a high temperature superconductor, HTS, cable (500), the HTS cable (500) comprising in a first cross-section (530): - first multiple layers of superconductor material (100) with: a first geometric orientation (110, 111), a first magnetic orientation (120), and a first angle (310) between the first geometric orientation (110) and the first magnetic orientation (120); - second multiple layers of superconductor material (200) with: a second geometric orientation (210, 211), a second magnetic orientation (220), and a second angle (320) between the second geometric orientation (210) and the second magnetic orientation (220); with a third angle (330) between the first magnetic orientation (120) and the second magnetic orientation (220), wherein the third angle (330) is larger or smaller than o°.

Description

FIELD OF THE INVENTION

[0001] The present invention generally relates to high temperature superconductor, HTS, cables with multiple layers of superconductor materials for magnetic field coils, in particular for non-planar magnetic field coils in stellarators and related methods that use cables with multiple layers of superconductor material that have a field alignment sensitivity.BACKGROUND

[0002] Stellarators are developed for magnetic confinement of plasmas to provide energy based on fusion reactions which occur inside the confined plasma. To provide magnetic confinement, stellarators require non-planar magnetic field coils with windings of a cable, often using superconductor cable. The use of superconductor cables allows a positive energy balance of the stellarator as the current in the cable has no electrical resistance, thereby avoiding losses. Further, the use of superconductor cable allows strong magnetic fields which improves the power balance of a stellarator. The non-planar magnetic field coils often have complex geometries. Thus, the design and manufacturing are an engineering challenge.

[0003] Recently, the use of novel high temperature superconductor, HTS, materials for HTS cables in stellarator non-planar magnetic coils is investigated. Some HTS cables, for example HTS cables comprising multiple layers of superconductor material, may have a strong alignment-dependent magnetic field sensitivity, for example for a critical current that the multiple layers of superconductor material can carry. However, the complex magnetic requirements of stellarators may make it difficult to design non-planar magnetic field coils in a way that the field alignment sensitivity of the multiple layers of superconductor material is accounted for. As a result, the constraint of the field alignment sensitivity makes the HTS cable use less efficient, potentially requiring more HTS material and consequently increasing size and costs or decreasing the maximum amount of magnetic field possible, thus decreasing stellarator performance. Thus, a need exists for HTS cables which use multiple layers of superconductor material with a decreased field alignment sensitivity.SUMMARY

[0004] An embodiment according to the invention is a stellarator, comprising a non-planar magnetic field coil including at least one winding of a high temperature superconductor, HTS, cable. The HTS cable comprises in a first cross-section:

[0005] First multiple layers of superconductor material with a first geometric orientation, a first magnetic orientation, and a first angle between the first geometric orientation and the first magnetic orientation.

[0006] The HTS cable may further comprise in the first cross-section: Second multiple layers of superconductor material with a second geometric orientation, a second magnetic orientation, and a second angle between the second geometric orientation and the second magnetic orientation.

[0007] The HTS cable may further comprise in the first cross-section a third angle between the first magnetic orientation and the second magnetic orientation. The third angle may be larger or smaller than 0°.

[0008] Such a HTS cable may have the advantage that the third angle between the magnetic orientations of the first and second multiple layers of superconductor material may reduce the alignment-dependent magnetic field sensitivity of the HTS cable. This effect may be increased by optimization based on a) choice of first and / or second geometric orientation of the multiple layers of superconductor material in the HTS cable and / or b) selection of suited materials of the multiple layers of superconductor material with first angle and second angle as material properties. In other words, the geometric orientations of the multiple layers of superconductor material and the combination of different HTS materials with different angles between geometric and / or magnetic orientation provides various degrees of freedom for optimizing the field alignment sensitivity of the HTS cable.

[0009] This will be detailed in the following after a couple of optional definitions are provided.

[0010] The geometric orientation of multiple layers of superconductor material may be specified by a normal vector of the multiple layers of superconductor material in a plane of the first cross-section. In addition, the geometric orientation may be specified by a vector describing the direction in which the multiple layers of superconductor material extend perpendicular to the plane of the first cross-section, for example a local vector along the direction in which the multiple layers of superconductor extend.

[0011] A magnetic orientation may be defined as the plane in which the multiple layers of superconductor material have the lowest sensitivity to an external magnetic field. For some layers of superconductor material this plane may be the ab-plane of a crystal structure of the superconductor material.

[0012] An angle as used herein may be defined as the angle with the smallest angular value between the sides defining the angle. For example, if an angle between the sides defining an angle could be described as either 30° or 330°, the angle may be described as 30°. The same may apply for angles between a vector and a plane.

[0013] The first multiple layers of superconductor material and / or the second multiple layers of superconductor material may comprise one of the following number of layers: between 2 and 55, between 15 and 45, between 25 and 35, 30.

[0014] The first multiple layers of superconductor material and / or the second multiple layers of superconductor material may comprise one of the following number of layers: between 125 and 175, between 135 and 165, between 145 and 155, 150.

[0015] The first multiple layers of superconductor material and / or the second multiple layers of superconductor material may comprise one of the following number of layers: between 2 and 200, between 40 and 160, between 80 and 120.

[0016] In the following, different embodiments with different values for the third angle are disclosed.

[0017] In some embodiments, the third angle is at least one of: larger than 0° and less than 180°, larger than 0° and less than 90°, larger than 0° and less than 60°, larger than 0° and less than 45°, larger than 0° and less than 35°, larger than 0° and less than 30°, larger than 0° and less than 25°, larger than 0° and less than 20°, larger than 0° and less than 10°, larger than 0° and less than 5°.

[0018] In some embodiments, the third angle is at least one of: larger than 5° and less than 180°, larger than 5° and less than 90°, larger than 5° and less than 60°, larger than 5° and less than 45°, larger than 5° and less than 35°, larger than 5° and less than 30°, larger than 0° and less than 25°, larger than 5° and less than 20°, larger than 5° and less than 10°, 7.5°.

[0019] In some embodiments, the third angle is at least one of: larger than 10° and less than 180°, larger than 10° and less than 90°, larger than 10° and less than 60°, larger than 10° and less than 45°, larger than 10° and less than 35°, larger than 10° and less than 30°, larger than 10° and less than 25°, larger than 10° and less than 20°, 10°, 15°,20°,

[0020] In some embodiments, the third angle is at least one of: larger than 20° and less than 180°, larger than 20° and less than 90°, larger than 20° and less than 60°, larger than 20° and less than 45°, larger than 20° and less than 35°, larger than 20° and less than 30°, larger than 20° and less than 25°, 22.5°, 25°.

[0021] In some embodiments, the third angle is at least one of: larger than 25° and less than 180°, larger than 25° and less than 90°, larger than 25° and less than 60°, larger than 25° and less than 45°, larger than 25° and less than 35°, larger than 25° and less than 30°, 30°.

[0022] In some embodiments, the third angle is at least one of: larger than 30° and less than 180°, larger than 30° and less than 90°, larger than 30° and less than 60°, larger than 30° and less than 45°, larger than 30° and less than 35°, 35°, larger than 35° and less than 90°, larger than 35° and less than 60°, larger than 35° and less than 45°, 45°.

[0023] In some embodiments, the third angle is at least one of: larger than 45° and less than 180°, larger than 45° and less than 90°, larger than 45° and less than 60°, 60°, larger than 60° and less than 90°, 90°.

[0024] Selecting the third angle as described above may reduce the alignment-dependent magnetic field sensitivity of the HTS cable.

[0025] In some embodiments, the third angle is about 30° or 30°. This may simplify the relationship between the first orientation and the second orientation while at the same time providing a significant reduction of the alignment-dependent magnetic field sensitivity of the HTS cable.

[0026] In some embodiments, at least one of the first angle and the second angle is at least one of: between 35° and 85°, between 45° and 75°, between 55° and 65°, 60°.

[0027] In some embodiments, at least one of the first angle and the second angle is at least one of: between -35° and -85°, between -45° and -75°, between -55° and -65°,-60°.

[0028] In some embodiments, at least one of the first angle and the second angle is at least one of: between 65° and 115°, between 75° and 105°, between 85° and 95°, 90°.

[0029] In some embodiments, at least one of the first angle and the second angle is at least one of: between -65° and -115°, between -75° and -105°, between -85° and -95°, 90°.

[0030] In some embodiments at least one of the first angle, the second angle, and the third angle is chosen so that a magnetic field alignment sensitivity of the HTS cable is less than a magnetic field alignment sensitivity of the first multiple layers of superconductor material and / or less than a magnetic field alignment sensitivity of the second multiple layers of superconductor material.

[0031] By aligning the first and second multiple layers of superconductor material as disclosed herein based on the material properties of the first and second multiple layers of superconductor material the magnetic field alignment sensitivity of the HTS cable may be reduced as will be described in detail. First and second angle are determined by material and manufacturing properties of the multiple layers of superconductor material used. For example, the first angle may be 30° or 90° in commercially available layers of superconductor material. However, different first angles may become available in the future and the teachings as disclosed herein may also be applied for combinations of multiple layers of superconductor material with different first angles or combinations of for example first and second multiple layers of superconductor material. This may also reduce the field alignment sensitivity of the HTS cable.

[0032] In some embodiments, the first multiple layers of superconductor material comprise: a first plurality of the first multiple layers of superconductor material and a second plurality of the first multiple layers of superconductor material.

[0033] In some embodiments, the second multiple layers of superconductor material are arranged between the first plurality of the first multiple layers of superconductor material and the second plurality of the first multiple layers of superconductor material.

[0034] In some embodiments, the second multiple layers of superconductor material are arranged adjacent the first plurality of the first multiple layers of superconductor material and the second plurality of the first multiple layers of superconductor material.

[0035] This allows to "sandwich" the multiple layers of superconductor material together as will be detailed further below.

[0036] In some embodiments, a third plurality of the first multiple layers of superconductor material is arranged inside a first plurality of recesses of the HTS cable. A fourth plurality of the second multiple layers of superconductor material may be arranged inside a second plurality of recesses of the HTS cable.

[0037] Using a cable with recesses may allow for improved properties of the cable, for example improved cooling or improved mechanical properties. The first and / or second plurality of recesses may be inside a solid material, for example a machined or 3D-printed material, for example copper or a copper alloy.

[0038] In some embodiments, in a first cross-section of the HTS cable the third plurality of the first multiple layers of superconductor material are arranged alternatingly with the fourth plurality of the second multiple layers of superconductor material.

[0039] Arranging the third plurality alternatingly with the fourth plurality may reduce the alignment sensitivity of the HTS cable.

[0040] Alternatingly arranged may comprise that in rotational direction around the center of the HTS cable the first multiple layers of superconductor material alternate with the second multiple layers of superconductor material. However, other arrangements are possible.

[0041] In some embodiments, the third plurality of the first multiple layers of superconductor material and the fourth plurality of the second multiple layers of superconductor material are arranged symmetrically inside the first cross section.

[0042] In some embodiments, the first multiple layers of superconductor material have a first width and the second multiple layers of superconductor material have a second width, wherein the first width is different from the second width.

[0043] Using different widths may allow that the ratio of the amount of superconductor material used in the HTS cable between the first and second multiple layers of superconductor material may be controlled.

[0044] In some embodiments, a ratio between the second width and the first width is at least one of the following: between .25 and .75, between .3 and .6, between .45 and .55, .5.

[0045] For example, a ratio of .5 may allow that the amount of the superconductor material used in the HTS cable between the first and second multiple layers of superconductor material is roughly or exactly the same. This may in addition or alternatively have the effect that the first and the second multiple layers of superconductor material have roughly or exactly the same current carrying capacity. This will be detailed below.

[0046] The first multiple layers of superconductor material and the second multiple layers of superconductor material may be electrically connected by a conductive material.

[0047] The conductive material may comprise a solder material. The conductive material may be a solder material.

[0048] The first multiple layers of superconductor material and the second multiple layers of superconductor material may have a short distance between each other in the first cross-section. This distance may be measured in the first cross-section from the closest distance between the first multiple layers of superconductor material and the second multiple layers of superconductor material. Said distance may be less than 10 cm, less than 5 cm, less than 2 cm, less than 1 cm, less than 7 mm, less than 5 mm, less than 2 mm, less than 1 mm, less than 500 µm, less than 300 µm, less than 100 µm, less than 80 µm, less than 60 µm, less than 40 µm, less than 20 µm, less than 10 µm, less than 5 µm, less than 1 µm.

[0049] A short distance may allow current sharing between the first and second multiple layers of superconductor material thus increasing performance. To illustrate: In cases where the conductive material between the first and second multiple layers of superconductor comprises solder material, the conductivity of the solder material may be about five times less than the conductivity of copper. Thus, a short distance between the first and second multiple layers of superconductor material may chosen as described elsewhere,

[0050] The first multiple layers of superconductor material and the second multiple layers of superconductor material maybe embedded within the same conductive material. For example, the embedding may be carried out by using in a soldering process and the embedding conductive material may be grown in subsequent soldering steps.

[0051] In some embodiments, no non-solder conductive material is present between the first multiple layers of superconductor material and the second multiple layers of superconductor material. For example, no machined or 3d printed material, for example no copper or copper alloy may be present.

[0052] Conductive material may be present between each of layers of the first and / or second multiple layers of superconductor material and may also be present between the first and / or second multiple layers of superconductor material.

[0053] The solder material may be a low temperature solder material. The melting temperature of the solder material may be chosen to be as high as possible but low enough so that the multiple layers of superconductor material are not adversely affected by the soldering process. The solder material may comprise lead and / or tin. For example, the solder material may be a solder with 60 weight-% lead and 40 weight-% tin. For example, ASTM B 32 Grade Sn60 may be used as a solder material with properties available at https: / / www.matweb.com / search / datasheet print.aspx?matguid=06a31d97bb734b50 9043d81cf131b280.

[0054] The first multiple layers of superconductor material and the second multiple layers of superconductor material may be electrically connected along a length of the HTS cable.

[0055] An electrical connection along a length of the HTS cable may allow current sharing between the first and second multiple layers of superconductor material thus increasing performance. Current sharing may be in particular enabled by a low distance between the first and second multiple layers of superconductor material as described elsewhere.

[0056] In some embodiments, the first multiple layers of superconductor material and / or the second multiple layers of superconductor material comprise rare earth barium copper oxide superconductor, ReBCO, tapes.

[0057] ReBCO tapes may be commercially available and have comparatively high performance, allowing manufacturing of high field non-planar magnetic field coils.

[0058] According to an embodiment, a method for providing a high temperature superconductor, HTS, cable for a non-planar magnetic field coil in a stellarator is provided. The method may comprise one or more of the following steps:

[0059] A step of providing first multiple layers of superconductor material, the first multiple layers of superconductor material comprising: a first geometric orientation, a first magnetic orientation, and a first angle between the first geometric orientation and the first magnetic orientation.

[0060] A step of fixing the first geometric orientation in a first cross-section of the HTS cable.

[0061] A step of providing second multiple layers of superconductor material, the second multiple layers of superconductor material comprising: a second geometric orientation, a second magnetic orientation, and a second angle between the second geometric orientation and the second magnetic orientation.

[0062] A step of fixing the second geometric orientation in the first cross-section of the HTS cable with a third angle between the first magnetic orientation and the second magnetic orientation, so that the third angle is larger or smaller than 0°.BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Fig. 1 shows a schematic view of a stellarator Fig. 2 shows first multiple layers of superconductor material. Fig. 3 shows the angular dependency of the field alignment sensitivity on a magnetic field. Fig. 4a shows a simplified view of the first multiple layers of superconductor material. Fig. 4b shows second multiple layers of superconductor material. Fig. 5a shows schematically a superposition of first multiple layers of superconductor material and second multiple layers of superconductor material according to an embodiment. Fig. 5b shows a plot of the field alignment sensitivity according to an embodiment. Fig. 6 shows a different embodiment. Fig. 7 shows a HTS cable according to an embodiment. Fig. 8 shows a HTS cable according to an embodiment. DETAILED DESCRIPTION

[0064] In the following, a detailed description with reference to the figures is provided. In the figures, identical reference signs refer to identical elements.

[0065] Fig. 1 shows a schematic view of a stellarator. In Fig. 1, a stellarator 10 is shown for magnetic confinement of a plasma 1. Some elements are removed for clarity. Inside the plasma 1, nuclear fusion reactions occur and release energy. The required magnetic confinement of the plasma 1 in stellarator 10 is achieved by a non-planar magnetic field coil 20 and further non-planar magnetic field coils 60 as well as additional magnetic field coils shown in Fig. 1 without reference numerals. As shown in Fig. 1, a combination of non-planar magnetic field coils and planar magnetic field coils may be used.

[0066] Fig. 2 shows first multiple layers of superconductor material 100. Multiple layers of superconductor material may be used inside the non-planar magnetic field coils of the stellarator shown in Fig. 1. The first multiple layers of superconductor material 100 may comprise rare earth barium copper oxide superconductor, ReBCO, tapes.

[0067] The first multiple layers of superconductor material 100 shown in Fig. 2 have a first geometric orientation 110, 111. Here, the geometric orientation is indicated by the normal vector 110 and a vector 111 describing the direction in which the first multiple layers of superconductor material 100 extend perpendicular to the plane of the first cross section shown in Fig. 2. In the example of Fig. 2, vector 111 points away from the viewer into the figure.

[0068] The first magnetic orientation 120 shown in Fig. 2 may be defined as the plane in which the first multiple layers of superconductor material 100 have the lowest sensitivity to an external magnetic field. In case of Fig. 2, the first magnetic orientation 120 is the plane of the ab-plane of a crystal structure of the first multiple layers of superconductor material 100. The first magnetic orientation may be perpendicular to a vector 122. In the example of Fig. 2 vector 122 corresponds to the c-axis of a crystal structure of the first multiple layers of superconductor material 100.

[0069] The dashed lines in Fig. 2 indicate angle steps of 30°. Thus, the c-axis is tilted by 30° with respect to the geometric orientation 110. Fig. 2 shows a first angle 310 between the first geometric orientation 110 and the first magnetic orientation 120. As indicated by the dashed lines, the first angle 310 shown in Fig. 2 is 60°

[0070] In Fig. 3, a plot of the field alignment sensitivity is shown in arbitrary units. In detail, Fig. 3 shows a field alignment sensitivity 600 of the first multiple layers of superconductor material shown in Fig. 2. Axis 901 shows an angle of a magnetic field with steps of 30° indicated by dashed lines. Axis 902 shows the critical current curve 903 of the first multiple layers of superconductor material 100 for a given external magnetic field. As can be seen from Fig. 3, the critical current 903 has a sharp maximum 903a at the angle of the magnetic orientation 120. As also shown Fig. 3, the critical current 903 has a strong dependence on alignment, significantly dropping when the magnetic field is not aligned with the first magnetic orientation 120. As will be discussed later, a significant drop occurs for a third angle 330 which is 30° in the example of Fig. 3. The width of the significant drop may depend on several factors, for example magnetic field strength. Further, the behavior and curve 903 is an example and different layers of superconductor material may exhibit different behavior with different curves. However, many layers of superconductor material exhibit similar behavior although for different angles and with different shapes, for example different widths of the peak 903a shown in Fig. 3.

[0071] Thus, if materials like the first multiple layers of superconductor material 100 or other materials with similar characteristics are used it is desirable to broaden the peak of the sharp maximum 903a shown in Fig. 3. Embodiments that achieve this are discussed herein.

[0072] Fig. 4a shows a simplified view of the first multiple layers of superconductor material shown in Fig. 2 for comparison with Fig. 4b. Regarding Fig. 4a, less details than in Fig. 2 are shown. Notably, the vector 122 of the c-axis and the angle to the c-axis 311 are not shown for simplicity. The description of Fig. 2 is not repeated here but applies to Fig. 4a as well.

[0073] Fig. 4b shows second multiple layers of superconductor material. The second multiple layers of superconductor material 200 a second geometric orientation 210, 211, a second magnetic orientation 220, and a second angle 320 between the second geometric orientation 210 and the second magnetic orientation 220.

[0074] The second geometric orientation 210, 211 may be defined like the first geometric orientation described with respect to Fig. 2. Also, the second magnetic orientation 220 may be defined like the first magnetic orientation described with respect to Fig. 2.

[0075] The second multiple layers of superconductor material 200 may be similar to the first multiple layers of superconductor material 100. However, the second multiple layers of superconductor material 200 and the first multiple layers of superconductor material 100 may be different. As shown in Fig. 4b, the second geometric orientation 210, 211 is different from the first geometric orientation 110, 111 shown in Fig. 4a for comparison. Namely, the second multiple layers of superconductor material 200 are rotated by 90° to the left as indicated by arrow 210. In addition, the second multiple layers of superconductor material 200 are reversed, i.e. the vector 211 of Fig. 4b points towards the viewer while the vector 111 in Fig. points away from the viewer. Combining the first and the second multiple layers of superconductor material allows to reduce the angular sensitivity as will be explained with reference to Fig. 5a and Fig. 5b.

[0076] Fig. 5a shows schematically a superposition of first multiple layers of superconductor material and second multiple layers of superconductor material. In Fig. 5a, first multiple layers of superconductor material 100 are oriented as shown in Fig. 4a with identical reference signs. The first angle 310 is omitted for clarity. Further, second multiple layers of superconductor material 200 are oriented as shown in Fig. 4b. As shown in Fig. 5a, a third angle 330 between the first magnetic orientation 120 and the second magnetic orientation 220 is observed. The third angle 330 is larger or smaller than 0°. In the embodiment of Fig. 5a, the third angle 330 is 30°. As discussed with respect to Fig. 3, an angle of 30° may be related to the width of the peak 903 shown in Fig. 3. This will be explained in detail with respect to Fig. 5b below.

[0077] Fig. 5b shows a plot of the field alignment sensitivity according to an embodiment. Fig. 5b is based on Fig. 3. For brevity, the description of Fig. 3 will not be repeated and applies correspondingly to Fig. 5b. In addition, Fig. 5b shows the critical current curve 904 of an embodiment of the invention according to Fig. 5a. Namely, the critical current curve 904 is the superposition of the critical current curve 903 of the first multiple layers of superconductor material 100 and the critical current curve not shown of the second multiple layers of superconductor material 200. critical current curve 904 is scaled with respect to critical current curve 904 for clearer presentation. As can be seen, the critical current curve has two peaks 904a and 904b, corresponding to the first magnetic orientation 120 and the second magnetic orientation 220, respectively. Thus, by combining first multiple layers of superconductor material 100 and second multiple layers of superconductor material 200 HTS cables may be provided which use multiple layers of superconductor material with a decreased field alignment sensitivity.

[0078] Fig. 6 shows a different embodiment. Fig. 6 corresponds to Fig. 5a. Thus, the description will not be repeated here and applies to Fig. 6 as well. Different from Fig. 5a, the second orientation 110, 211 of the second multiple layers of superconductor material 200 is different. While the normal vector 210 is identical in both Fig. 5a and Fig. 6, the vector 211 is different. While vector 211 in Fig. 5a points toward the viewer, vector 211 in Fig. 6 points away from the viewer, so that vector 211 and vector 111 are both pointing away from the viewer in Fig. 6. As shown in Fig. 6, this has the effect that the third angle 330 is 60° in the embodiment of Fig. 5a, while the third angle 330 is 30° in the embodiment of Fig. 5a. Thus, the embodiment according to Fig. 6 may achieve a larger third angle when desired, for example for further broadening the peak even more as shown in Fig. 5b.

[0079] Further, combinations of the first and second orientations shown in Fig. 5a and Fig. 6 may be used, for example by using more than first and second multiple layers of superconductor materials, for example by combining the first and second multiple layers of superconductor material shown in Fig. 5a with the second multiple layers of superconductor material 200 shown in Fig. 6. Also, the second multiple layers of superconductor material 200 shown in Fig. 5a may be combined with the second multiple layers of superconductor material 200 shown in Fig. 6 and so on. This will be further explained by the following embodiment.

[0080] The HTS cable may further comprise in the first cross-section: third multiple layers of superconductor material with: a third geometric orientation, a third magnetic orientation, and a fourth angle between the second geometric orientation and the second magnetic orientation, with a fifth angle between the third magnetic orientation and the first magnetic orientation, wherein the fifth angle (330) is larger or smaller than 0°.

[0081] In some embodiments, the first multiple layers of superconductor material and / or the second multiple layers of superconductor material and / or the third multiple layers of superconductor material may be arranged alternatingly. In addition or alternatively, a first group of layers of the first multiple layers of superconductor material and / or the second multiple layers of superconductor material and / or the third multiple layers of superconductor material may be arranged in between a second group of layers of the first multiple layers of superconductor material and / or the second multiple layers of superconductor material and / or the third multiple layers of superconductor material.

[0082] For example, a first layer of the first multiple layers of superconductor material may be followed by a first layer of the second multiple layers of superconductor material followed by a first layer of the third multiple layers of superconductor material followed by a second layer of the first multiple layers of superconductor material followed by a second layer of the second multiple layers of superconductor material followed by a second layer of the third multiple layers of superconductor material and so on. This is only an example. Other orders or combinations can be chosen. The different layers of superconductor may be mixed with each other. The first multiple layers of superconductor material and / or the second multiple layers of superconductor material and / or the third multiple layers of superconductor material may be mixed with each other. In other embodiments, the different multiple layers of superconductor material may be kept separate, for example arranged on top of each other, next to each other or adjacent to each other.

[0083] Also, the number of layers may be different for the first multiple layers of superconductor material and / or the second multiple layers of superconductor material and / or the third multiple layers resulting in different alternating arrangements.

[0084] As an exemplary embodiment, a third angle may be 30° and / or a fifth angle may be 60°. In another embodiment, the third angle may be between 10° and 50° and / or the fifth angle may be between 40° and 80°. In another embodiment, the third angle may be between 20° and 40° and / or the fifth angle may be between 50° and 70°.

[0085] The geometric orientation of the first, second and / or third multiple layers of superconductor material may be essentially identical. In some embodiments the geometric orientation of the first, second and / or third multiple layers of superconductor material is identical. A stack of multiple layers of superconductor material may be formed in which the geometric orientation of the first, second and / or third multiple layers of superconductor material is essentially identical. The first, second and / or third multiple layers of superconductor material may be arranged alternatingly.

[0086] The described concept of combining first, second, and / or third multiple layers of superconductor material may be expanded to additional multiple layers of superconductor material, for example fourth, fifth and so on multiple layers of superconductor material. The different multiple layers of superconductor material may have different geometric orientation and / or magnetic orientations. The different multiple layers of superconductor material may be from different manufacturers and / or have a different critical current. By using these combinations, a reduced alignment sensitivity of the HTS cable may be achieved.

[0087] Fig. 7 shows a HTS cable according to an embodiment. Fig. 7 shows a first cross-section 530: of a high temperature superconductor, HTS, cable 500 according to an embodiment. The HTS cable 500 comprises first multiple layers of superconductor material 100 and second multiple layers of superconductor material 200 as described with respect to the embodiments above. Further, the first multiple layers of superconductor material 100 comprise a first plurality 151 of the first multiple layers of superconductor material 100 and a second plurality 152 of the first multiple layers of superconductor material 100. As shown in Fig. 7, the second multiple layers of superconductor material 200 are arranged between the first plurality 151 of the first multiple layers of superconductor material 100 and the second plurality 152 of the first multiple layers of superconductor material. As also shown in Fig. 7, the first multiple layers of superconductor material have a first width 140 and the second multiple layers of superconductor material have a second width 240, wherein the first width is different from the second width. In the embodiment shown in Fig. 7, a ratio between the second width 240 and the first width 140 is 0.5, but other ratios are possible. In Fig. 7, the first multiple layers of superconductor material 100 and the second multiple layers of superconductor material 200 are electrically connected by a conductive material 700, wherein the conductive material 700 comprises a solder material. As shown in Fig. 7, the first and second layers of superconductive material have a short distance between each other, thus facilitating current sharing between the multiple layers of superconductor materials as described above.

[0088] The arrangement shown in Fig. 7 is an example and other configurations may be used. In Fig. 7, the second multiple layers of superconductor material are arranged in an orthogonal angle with respect to the first multiple layers of superconductor material, see arrows 110 and 210. In one embodiment, the second multiple layers of superconductor material are arranged in a non-orthogonal angle with respect to the first multiple layers of superconductor material, for example with an angle of 20°, 30°, 45°, 50°, 60°, 70°, 80°, -20°, -30°, -45°, -50°, -60°, -70°, -80°.

[0089] In some embodiments the first multiple layers of superconductor material 100 are stacked on top of the second multiple layers of superconductor material 200 as shown with reference numerals 200 and 152 in Fig. 7 or vice versa.

[0090] Fig. 8 shows a HTS cable according to an embodiment. Fig. 8 shows a first cross-section 530: of a high temperature superconductor, HTS, cable 500 according to an embodiment. The HTS cable 500 comprises first multiple layers of superconductor material 100 and second multiple layers of superconductor material 200 as described with respect to the embodiments above. Further, in the embodiment, a third plurality 153 of the first multiple layers of superconductor material 100 is arranged inside a first plurality of recesses 510 of the HTS cable 500 and a fourth plurality 254 of the second multiple layers of superconductor material 200 is arranged inside a second plurality of recesses 520 of the HTS cable. The recess may be in a machined or 3d printed material, for example, copper or a copper alloy. in the first cross-section 530 of the HTS cable 500 the third plurality 153 of the first multiple layers of superconductor material are arranged alternatingly with the fourth plurality 254 of the second multiple layers of superconductor material. This is shown in a simple way with four different recesses in Fig. 8, but larger number of recesses are possible, for example 6, 8, 10, 12, 14, etc. In some examples, the numbers of recesses are arranged in a circular manner, but other arrangements are possible. Also, as shown in Fig. 8, the third plurality of the first multiple layers of superconductor material and the fourth plurality of the second multiple layers of superconductor material are arranged symmetrically inside the first cross-section. However, in other embodiments the arrangement is not symmetrical.

[0091] In some embodiments, the arrangement of the multiple layers of superconductor materials shown in Fig. 8 is arranged without any recesses in machined or 3d printed material as shown in Fig. 7. In these embodiments, the third plurality 153 of the first multiple layers of superconductor material and the fourth plurality 254 of the second multiple layers of superconductor material are arranged adjacent to each other, with a distance to each other and / or in direct contact to each other. Also combinations are possible with the embodiments described above. For example, Fig. 7 and Fig 8 show an essentially perpendicular angle between the multiple layers of superconductor material, but also non-orthogonal angles as described elsewhere are possible.

[0092] Both HTS cables of Fig. 7 and Fig. 8 have a square cross-section 530. Other shapes are possible as well. Some embodiments have non-circular shapes which facilitate alignment of the HTS cable. In some embodiments, is one or more of the following: non-circular, rectangular, square, hexagonal, octagonal, polygonal, a polygonal approximation of a circular shape, a polygonal approximation of an elliptical shape, an equiangular polygon, an equilateral polygon, a regular polygon, a convex polygon, a polygon with the following number of sides: between 3 and 100, between 3 and 50, between 3 and 64, between 3 and 32, between 4 and 16, between 4 and 12, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12; comprising at least one groove feature, comprising at least one ridge feature.

[0093] Fig. 9 shows a method according to an embodiment of the invention. Namely, Fig. 8 shows a method 800 for providing a high temperature superconductor, HTS, cable 500 for a non-planar magnetic field coil in a stellarator.

[0094] The method comprises a step 810 of providing first multiple layers of superconductor material 100, the first multiple layers of superconductor material 100. The first multiple layers of superconductor material 100 comprise: a first geometric orientation 110, 111, a first magnetic orientation 120, and a first angle 310 between the first geometric orientation 110 and the first magnetic orientation 120.

[0095] The method comprises a step 820 of fixing the first geometric orientation 110, 111 in a first cross-section 530 of the HTS cable 500. Fixing may be achieved for example by providing a solder material in a molten phase.

[0096] The method comprises a step 830 of providing second multiple layers of superconductor material 200, the second multiple layers of superconductor material 200 comprising: a second geometric orientation 210, 211, a second magnetic orientation 220, and a second angle 320 between the second geometric orientation 210 and the second magnetic orientation 220.

[0097] The method comprises a step 840 of fixing the second geometric orientation 110, 111 in the first cross-section 530 of the HTS cable 500 with a third angle 330 between the first magnetic orientation 120 and the second magnetic orientation 220, so that the third angle 330 is larger or smaller than 0°.

[0098] The fixing may be achieved by providing additional solder material. This may result in an arrangement of first and second multiple layers of superconductor material with a good electrical connection between the first and second multiple layers of superconductor material. The third angle may be chosen arbitrarily, for example as disclosed in the embodiments above. Thus, the method allows a simple manufacturing process of an HTS cable with reduced alignment sensitivity.

[0099] In some embodiments, the embodiments described before are combined. For example, the arrangement of the first and second multiple layers of superconductor material explained with respect to Fig. 7 may be combined with the embodiment explained with respect to Fig. 8. For example, in some recesses of the recesses 510, 520 the arrangement shown in Fig. 7 may be placed and so on. The same applies for the remainder of the description. Further, a larger number of multiple layers of superconductor material may be used to further reduce the alignment sensitivity of the HTS cable.

[0100] The above invention has been described with focus on use of the disclosed cables in non-planar magnetic field coils of a stellarator. However, the concepts described above may be used in other context, for example as cables and methods for the manufacturing thereof. For example, the invention described above may also be useful in other fields with unusual geometries and hence requiring complex field alignment, for example particle accelerator magnets or magnetic resonance tomography. This will be detailed below with the further examples.FURTHER EXAMPLES

[0101] Example 1. A high temperature superconductor, HTS, cable (500), the HTS cable (500) comprising in a first cross-section (530): first multiple layers of superconductor material (100) with: a first geometric orientation (110, 111), a first magnetic orientation (120), and a first angle (310) between the first geometric orientation (110) and the first magnetic orientation (120); second multiple layers of superconductor material (200) with: a second geometric orientation (210, 211), a second magnetic orientation (220), and a second angle (320) between the second geometric orientation (210) and the second magnetic orientation (220); with a third angle (330) between the first magnetic orientation (120) and the second magnetic orientation (220), wherein the third angle (330) is larger or smaller than 0°.

[0102] Example 2. The HTS cable (500) of example 1, wherein the third angle (330) is at least one of: larger than 0° and less than 180°, larger than 0° and less than 90°, larger than 0° and less than 60°, larger than 0° and less than 45°, larger than 0° and less than 35°, larger than 0° and less than 30°, larger than 0° and less than 25°, larger than 0° and less than 20°, larger than 0° and less than 10°, larger than 0° and less than 5°, larger than 5° and less than 180°, larger than 5° and less than 90°, larger than 5° and less than 60°, larger than 5° and less than 45°, larger than 5° and less than 35°, larger than 5° and less than 30°, larger than 0° and less than 25°, larger than 5° and less than 20°, larger than 5° and less than 10°, 7.5°, larger than 10° and less than 180°, larger than 10° and less than 90°, larger than 10° and less than 60°, larger than 10° and less than 45°, larger than 10° and less than 35°, larger than 10° and less than 30°, larger than 10° and less than 25°, larger than 10° and less than 20°, 100, 15°, 20°, larger than 20° and less than 180°, larger than 20° and less than 90°, larger than 20° and less than 60°, larger than 20° and less than 45°, larger than 20° and less than 35°, larger than 20° and less than 30°, larger than 20° and less than 25°, 22.5°, 25°, larger than 25° and less than 180°, larger than 25° and less than 90°, larger than 25° and less than 60°, larger than 25° and less than 45°, larger than 25° and less than 35°, larger than 25° and less than 30°, 30°, larger than 30° and less than 180°, larger than 30° and less than 90°, larger than 30° and less than 60°, larger than 30° and less than 45°, larger than 30° and less than 35°, 35°, larger than 35° and less than 180°, larger than 35° and less than 90°, larger than 35° and less than 60°, larger than 35° and less than 45°, 45°, larger than 45° and less than 180°, larger than 45° and less than 90°, larger than 45° and less than 60°, 60°, larger than 60° and less than 180°, larger than 60° and less than 90°. 90°.

[0103] Example 3. The HTS cable (500) of example 1 or example 2, wherein the third angle (330) is about 30°.

[0104] Example 4. The HTS cable (500) of one of the previous examples, wherein at least one of the first angle (310) and the second angle (320) is at least one of: between 35° and 85°, between 45° and 75°, between 55° and 65°, 60°, between -35° and -85°, between -45° and -75°, between -55° and -65°, -60°, between 65° and 115°, between 75° and 105°, between 85° and 95°, 90°, between -65° and -115°, between -75° and -105°, between -85° and -95°, 90°.

[0105] Example 5. The HTS cable (500) of one of the previous examples, wherein at least one of the first angle (310), the second angle (320), and the third angle (330) is chosen so that a magnetic field alignment sensitivity (600) of the HTS cable (500) is less than a magnetic field alignment sensitivity of the first multiple layers of superconductor material (100) and / or less than a magnetic field alignment sensitivity of the second multiple layers of superconductor material (200).

[0106] Example 6. The HTS cable (500) of one of the previous examples, wherein the first multiple layers of superconductor material (100) comprise: a first plurality (151) of the first multiple layers of superconductor material (100) and a second plurality (152) of the first multiple layers of superconductor material (100);

[0107] Example 7. The HTS cable (500) of example 6, wherein the second multiple layers of superconductor material (200) are arranged between the first plurality (151) of the first multiple layers of superconductor material (100) and the second plurality (152) of the first multiple layers of superconductor material.

[0108] Example 8. The HTS cable (500) of one of the previous examples, wherein a third plurality (153) of the first multiple layers of superconductor material

[0109] (100) is arranged inside a first plurality of recesses (510) of the HTS cable (500) and a fourth plurality (254) of the second multiple layers of superconductor material (200) is arranged inside a second plurality of recesses (520) of the HTS cable.

[0110] Example 9. The stellarator of example 8, wherein in the first cross-section (530) of the HTS cable (500) the third plurality (153) of the first multiple layers of superconductor material are arranged alternatingly with the fourth plurality (254) of the second multiple layers of superconductor material.

[0111] Example 10. The HTS cable (500) of one of examples 8 to 9, wherein the third plurality of the first multiple layers of superconductor material and the fourth plurality of the second multiple layers of superconductor material are arranged symmetrically inside the first cross section.

[0112] Example 11. The HTS cable (500) of one of the previous examples, wherein the first multiple layers of superconductor material have a first width (140) and the second multiple layers of superconductor material have a second width (240), wherein the first width is different from the second width.

[0113] Example 12. The HTS cable (500) of example 10, wherein a ratio between the second width (240) and the first width (140) is at least one of the following: between .25 and .75, between .3 and .6, between .45 and .55, .5.

[0114] Example 13. The HTS cable (500) of one of the previous examples, wherein the first multiple layers of superconductor material (100) and the second multiple layers of superconductor material (200) are electrically connected by a conductive material (700) and / or wherein the first multiple layers of superconductor material (100) and the second multiple layers of superconductor material (200) are electrically connected along a length of the HTS cable. and / or wherein the conductive material (700) comprises a solder material.

[0115] Example 14. The HTS cable (500) of one of the previous examples, wherein the first multiple layers of superconductor material and / or the second multiple layers of superconductor material comprise rare earth barium copper oxide superconductor, ReBCO, tapes.

[0116] Example 15. A method (800) for providing a high temperature superconductor, HTS, cable (500), the method comprising: a step (810) of providing first multiple layers of superconductor material (100), the first multiple layers of superconductor material (100) comprising: a first geometric orientation (110, 111), a first magnetic orientation (120), and a first angle (310) between the first geometric orientation (110) and the first magnetic orientation (120); a step (820) of fixing the first geometric orientation (110, 111) in a first cross-section (530) of the HTS cable (500), a step (830) of providing second multiple layers of superconductor material (200), the second multiple layers of superconductor material (200) comprising: a second geometric orientation (210, 211), a second magnetic orientation (220), and a second angle (320) between the second geometric orientation (210) and the second magnetic orientation (220); a step (840) of fixing the second geometric orientation (110, 111) in the first cross-section (530) of the HTS cable (500) with a third angle (330) between the first magnetic orientation (120) and the second magnetic orientation (220), so that the third angle (330) is larger or smaller than 0°.

Claims

1. A stellarator, comprising a non-planar magnetic field coil including at least one winding of a high temperature superconductor, HTS, cable (500), the HTS cable (500) comprising in a first cross-section (530): - first multiple layers of superconductor material (100) with: a first geometric orientation (110, 111), a first magnetic orientation (120), and a first angle (310) between the first geometric orientation (110) and the first magnetic orientation (120); - second multiple layers of superconductor material (200) with: a second geometric orientation (210, 211), a second magnetic orientation (220), and a second angle (320) between the second geometric orientation (210) and the second magnetic orientation (220); with a third angle (330) between the first magnetic orientation (120) and the second magnetic orientation (220), wherein the third angle (330) is larger or smaller than 0°.

2. The stellarator of claim 1, wherein the third angle (330) is at least one of: larger than 0° and less than 180°, less than 0° and larger than -180°.

3. The stellarator of claim 1 or claim 2, wherein the third angle (330) is about 30°.

4. The stellarator of one of the previous claims, wherein at least one of the first angle (310) and / or the second angle (320) is at least one of: between 35° and 85°, between -35° and -85°, between 65° and 115°, between -65° and -115°.

5. The stellarator of one of the previous claims, wherein at least one of the first angle (310), the second angle (320), and the third angle (330) is chosen so that a magnetic field alignment sensitivity (600) of the HTS cable (500) is less than a magnetic field alignment sensitivity of the first multiple layers of superconductor material (100) and / or less than a magnetic field alignment sensitivity of the second multiple layers of superconductor material (200).

6. The stellarator of one of the previous claims, wherein the first multiple layers of superconductor material (100) comprise: - a first plurality (151) of the first multiple layers of superconductor material (100) and - a second plurality (152) of the first multiple layers of superconductor material (100).

7. The stellarator of claim 6, wherein the second multiple layers of superconductor material (200) are arranged between the first plurality (151) of the first multiple layers of superconductor material (100) and the second plurality (152) of the first multiple layers of superconductor material.

8. The stellarator of one of the previous claims, wherein a third plurality (153) of the first multiple layers of superconductor material (100) is arranged inside a first plurality of recesses (510) of the HTS cable (500) and a fourth plurality (254) of the second multiple layers of superconductor material (200) is arranged inside a second plurality of recesses (520) of the HTS cable.

9. The stellarator of claim 8, wherein in the first cross-section (530) of the HTS cable (500) the third plurality (153) of the first multiple layers of superconductor material are arranged alternatingly with the fourth plurality (254) of the second multiple layers of superconductor material.

10. The stellarator of one of claims 8 to 9, wherein the third plurality of the first multiple layers of superconductor material and the fourth plurality of the second multiple layers of superconductor material are arranged symmetrically inside the first cross section.

11. The stellarator of one of the previous claims, wherein the first multiple layers of superconductor material have a first width (140) and the second multiple layers of superconductor material have a second width (240), wherein the first width is different from the second width.

12. The stellarator of claim 10, wherein a ratio between the second width (240) and the first width (140) is at least one of the following: between .25 and .75, between .3 and .6, between .45 and .55, .5.

13. The stellarator of one of the previous claims, wherein the first multiple layers of superconductor material (100) and the second multiple layers of superconductor material (200) are electrically connected by a conductive material (700) and / or wherein the first multiple layers of superconductor material (100) and the second multiple layers of superconductor material (200) are electrically connected along a length of the HTS cable. and / or wherein the conductive material (700) comprises a solder material.

14. The stellarator of one of the previous claims, wherein the first multiple layers of superconductor material and / or the second multiple layers of superconductor material comprise rare earth barium copper oxide superconductor, ReBCO, tapes.

15. A method (800) for providing a high temperature superconductor, HTS, cable (500) for a non-planar magnetic field coil in a stellarator, the method comprising: a step (810) of providing first multiple layers of superconductor material (100), the first multiple layers of superconductor material (100) comprising: a first geometric orientation (110, 111), a first magnetic orientation (120), and a first angle (310) between the first geometric orientation (110) and the first magnetic orientation (120); a step (820) of fixing the first geometric orientation (110, 111) in a first cross-section (530) of the HTS cable (500) a step (830) of providing second multiple layers of superconductor material (200), the second multiple layers of superconductor material (200) comprising: a second geometric orientation (210, 211), a second magnetic orientation (220), and a second angle (320) between the second geometric orientation (210) and the second magnetic orientation (220); a step (840) of fixing the second geometric orientation (110, 111) in the first cross-section (530) of the HTS cable (500) with a third angle (330) between the first magnetic orientation (120) and the second magnetic orientation (220), so that the third angle (330) is larger or smaller than 0°.

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