Classifications

• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21B—FUSION REACTORS
  • G21B1/00—Thermonuclear fusion reactors
  • G21B1/11—Details
  • G21B1/21—Electric power supply systems, e.g. for magnet systems, switching devices, storage devices, circuit arrangements
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21B—FUSION REACTORS
  • G21B1/00—Thermonuclear fusion reactors
  • G21B1/05—Thermonuclear fusion reactors with magnetic or electric plasma confinement
  • G21B1/057—Tokamaks
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B12/00—Superconductive or hyperconductive conductors, cables, or transmission lines
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B12/00—Superconductive or hyperconductive conductors, cables, or transmission lines
  • H01B12/02—Superconductive or hyperconductive conductors, cables, or transmission lines characterised by their form
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F6/00—Superconducting magnets; Superconducting coils
  • H01F6/06—Coils, e.g. winding, insulating, terminating or casing arrangements therefor
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E30/00—Energy generation of nuclear origin
  • Y02E30/10—Nuclear fusion reactors
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
  • Y02E40/60—Superconducting electric elements or equipment; Power systems integrating superconducting elements or equipment

Definitions

• the present invention relates to high temperature superconductors (HTS).
• HTS high temperature superconductors
• the present invention relates to cables comprising HTS tapes.
• High temperature superconductors HTS
• low temperature superconductors LTS materials
• All low temperature superconductors have a critical temperature (the temperature above which the material cannot be superconducting even in zero magnetic field) below about 30K.
• the behaviour of HTS material is not described by BCS theory, and such materials may have critical temperatures above about 30K (though it should be noted that it is the physical differences in superconducting operation and composition, rather than the critical temperature, which define HTS material).
• HTS cuprate superconductors
• cuprates compounds containing a copper oxide group
• BSCCO compounds containing a copper oxide group
• ReBCO where Re is a rare earth element, commonly Y or Gd
• Other HTS materials include iron pnictides (e.g. FeAs and FeSe) and magnesium diborate (MgB 2 ).
• ReBCO is typically manufactured as tapes, with a structure as shown in Figure 1.
• Such tape 500 is generally approximately 100 microns thick, and includes a substrate 501 (typically electropolished hastelloy approximately 50 microns thick), on which is deposited by IBAD, magnetron sputtering, or another suitable technique a series of buffer layers known as the buffer stack 502, of approximate thickness 0.2 microns.
• An epitaxial ReBCO-HTS layer 503 overlays 15 the buffer stack, and is typically 1 micron thick.
• a 1 -2 micron silver layer 504 is deposited on the HTS layer by sputtering or another suitable technique, and a copper stabilizer layer 505 is deposited on the tape by electroplating or another suitable technique, which often completely encapsulates the tape.
• the substrate 501 provides a mechanical backbone that can be fed through the manufacturing line and permit growth of subsequent layers .
• the buffer stack 502 is required to provide a biaxially textured crystalline template upon which to grow the HTS layer, and prevents chemical diffusion of elements from the substrate to the HTS which damage its superconducting properties.
• the silver layer 504 is required to provide a low resistance interface from the ReBCO to the stabiliser layer, and the stabiliser layer 505 provides an alternative current path in the event that any part of the ReBCO ceases superconducting (enters the“normal” state).
• Figure 2 shows a ReBCO tape 200, illustrating an x,y,z coordinate system which will be used in this document.
• the y axis is along the length of the tape (i.e. in the direction of the current when the tape is in use)
• the x axis is along the width of the tape (i.e. in the plane of the tape, perpendicular to the y axis)
• the z axis is perpendicular to the x and y axes (i.e. normal to the plane of the tape).
• FIG 3 shows a cross section of an exemplary ReBCO tape in the x/z plane.
• the ReBCO layer itself is crystalline, and the principal axes of the ReBCO crystal are shown for one point in the tape.
• the ReBCO tape is shown in simplified form with an HTS layer 301 , a copper cladding 302, and a substrate 303.
• the crystal structure of ReBCO has three principal axes which are mutually perpendicular, referred to in the art as a, b, and c.
• a/b plane of the ReBCO layer 301 is shown as a single line 310, perpendicular to the c-axis 320.
• the critical current of the tape depends on the ReBCO crystal thickness and quality. It also has an approximately inverse dependence on the ambient temperature and also the magnitude of the applied magnetic field. Finally, the ReBCO HTS layer displays anisotropic critical current behaviour, ie: the critical current depends on the orientation of the applied magnetic field with respect to the c-axis. When the applied magnetic field vector lies in the a/b plane 310 the critical current is considerably higher than when the applied magnetic field vector is aligned along the c-axis 320. The critical current varies smoothly between these two extremes in “out of a/b plane” field orientation, as shown by the blue curve in Figure 6a. (In practice, there may be more than one angle at which critical current shows a peak. Furthermore, the amplitude and width of the peaks vary with both applied field and temperature, but for the purposes of this explanation we can consider a tape with a single dominant peak that defines the optimum orientation of applied B field that gives maximum critical current).
• ReBCO tapes are normally manufactured so that the c-axis is as close to perpendicular to the plane of the tape as possible.
• This offset is likely to comprise a fixed offset, plus a variable offset that changes with position along the tape.
• this angular offset between c-axis and z-axis leads to variation of the critical current along the tape.
• a cable for carrying electrical current in a coil of a magnet comprising a stack of tape assemblies.
• Each tape assembly has a length and a width, such that the length is much larger than the width, and each tape assembly comprises an FITS layer of anisotropic high temperature superconductor, FITS material, wherein a c-axis of the FITS layer is at a non-zero angle to a vector perpendicular to the plane of the FITS layer.
• the tape assemblies are stacked as a series of pairs, each pair comprising first and second FITS tape assemblies and a copper layer therebetween.
• the tape assemblies in each pair are arranged such that the c-axis of the FITS layer of the first FITS tape assembly of each pair have reflective symmetry to the c-axis of the FITS layer of the second FITS tape assembly of each pair about a plane which is parallel to and equidistant from each FITS layer.
• a method of manufacturing a cable for carrying electric current in a coil of a magnet comprising a high-strength metal substrate layer, and an FITS layer of anisotropic high temperature superconductor, FITS, material, wherein a c- axis of the FITS layer is at a non-zero angle to a vector perpendicular to the plane of the FITS layer.
• the first tape assembly is applied to a copper layer.
• the second tape assembly is applied to the copper layer, such that the FITS layer of the first tape and the FITS layer of the second tape are parallel and separated by the copper layer, and such that a c-axis of the second FITS tape assembly has reflective symmetry to the c- axis of the FITS layer of the second FITS tape assembly of each pair about a plane which is parallel to and equidistant from each FITS layer.
• Figure 1 is an illustration of the structure of ReBCO tape
• Figure 2 is a diagram showing a coordinate system for describing ReBCO tape
• Figure 3 is a pair of cross sections of a ReBCO tape, showing the principal axes of the ReBCO crystal
• Figure 4 is a cross sections of a type 0 pair
• Figure 5 is a cross sections of an exemplary type 0 pair
• Figures 6A, 6B, 6C, and 6D show the critical current variation with external magnetic field of the constructions of Figures 4A/B and 5A/B for different ReBCO tapes;
• Figure 7A shows the current ratio of ReBCO within a field coil constructed using the construction of Figure 4.
• Figure 7B shows the current ratio of ReBCO within a field coil constructed using the construction of Figure 5;
• the invention describes a method of combining pairs of FITS tapes such that any variation in the angle at which peak critical current occurs along the tape is averaged out in the pair, leading to a more consistent behaviour.
• Figure 4 shows an exemplary type-0 pair of ReBCO tapes in a cross section perpendicular to the axis of the tape.
• a type-0 pair comprises two tapes 410, 420, oriented such that the ReBCO layers 41 1 , 421 face each other, and with a copper lamination 430 between them.
• a flaw or“dropout” in critical current in one tape such as a crack
• this allows current to transfer between the ReBCO layers
• Each tape has a c-axis 412, 422 at an angle a from the perpendicular to the plane of the ReBCO layer (i.e. the z-axis), and a peak lc angle (i.e. the angle of applied magnetic field for which the critical current is greatest) which is perpendicular to the c- axis.
• the type-0 pair would be constructed by first applying the tape 410 from a spool of ReBCO tape to the copper lamination 430 from one end to the other and then applying the tape 420 from the same spool of HTS tape in the same direction on the opposite side of the copper lamination. This results in the c-axis of the ReBCO
• the type-0 pair can be constructed as shown in Figure 5, which is a cross section equivalent to Figure 4 for an exemplary type-0 pair construction.
• the tapes 510, ReBCO layers 51 1 and copper lamination 530 are equivalent to the tape 410, ReCBO layer 51 1 , and copper lamination 430 of Figure 4.
• the tape 520 has been applied such that the ReBCO layer 421 faces the ReBCO layer 51 1 of the tape 510, and such that the c-axes 51 1 , 521 and a/b planes 512, 522 of each tape 510, 520 have reflective symmetry about a plane 501 which is parallel to and equidistant from each tape of the type-0 pair.
• the application of the tape to form the construction of Figure 5 can be done by first applying the tape 510 from a spool of ReBCO tape in one direction), and then applying the tape 520 from the same roll of ReBCO tape in the opposite direction along the y-axis.
• the ReBCO tape may be unwound from the spool between application of the tape 510 and application of the tape 520, and rewound in the opposite direction, then the tape 520 is applied in the same direction as the application of the tape 510.
• the tape 510 and the tape 520 may be applied in the same direction from different rolls, which have been wound in opposite senses, to produce the correct alignment of the c-axes.
• this can be achieved by spooling off one tape of greater than twice the required length, folding it in the middle about the x axis (i.e. end-to-end), and cutting off or otherwise removing a section containing the fold, to leave two tapes which are then arranged in a type-0 pair in a“flipped” orientation (or a type-2 pair if the tape is folded such that the substrates face each other).
• Figures 6A to 6D show plots of the critical current vs angle of magnetic field for type-0 pairs constructed according to Figure 4 (blue line) or Figure 5 (red line), for tapes with an angle between the c-axis and the perpendicular of the tape of approximately 1 degree (Figure 6A), 5 degrees (Figure 6B), 10 degrees (Figure 6C) and 35 degrees (Figure 6D).
• the flipped-pair arrangement has the beneficial effect of averaging out the impact of any changes in the angle at which peak critical current occurs at any position along the tape. This is because the peaks of the individual tapes in the pair are merge into one lower broader peak, as shown in Figure 6A (red curve). Small variations in the angular offset along the tape will cause the peak to broaden or sharpen. Furthermore, where the flipped pair is made from a single reel of tape, if the critical current at the start of the reel is lower or higher than at the end of the reel, as supplied, this will also be averaged out by the flipped type-0 orientation.
• the c-axis 320 diverges by as much as 30-35 degrees from the perpendicular to the plane of the tape.
• the flipped pair orientation is less useful with these tapes, because the peak lc becomes split into two peaks, both lower than the peak in the un-flipped arrangement of tape pairs. This is illustrated in figure 6D.
• FIG. 7A shows a chart of the ratio between current and critical current for a cross section of a pancake solenoid magnet coil constructed from a plurality of type-0 pairs according to the construction of Figure 4
• Figure 7B shows a chart of the ratio between current I and critical current lc for a cross section of a magnet coil constructed from a plurality of type-0 pairs according to the construction of Figure 5 (ie: the“flipped” orientation).
• Each coil is constructed from two spiral “pancake” windings of type-0 pairs, stacked on top of each other (i.e.
• the ReBCO tape used has an angle between the c-axis and the perpendicular to the plane of the tape (z-axis) of 35 degrees. As can be seen from the Figures, the arrangement of figure 7B is symmetrical. This leads to symmetric heating due to current sharing, which is more desirable from the perspective of understanding coil performance.
• type-0 pairs of HTS tapes similar arrangements may be used for type-1 pairs (i.e. where the HTS layer of one tape faces the substrate layer of the other, such that one HTS layer is between the substrates and one is not) or type-2 pairs (i.e. where the substrate layers face each other, such that they are between the HTS layers), arranged such that the c-axes of the HTS tapes have reflective symmetry about a plane parallel to the HTS layers.
• the above disclosure may also be applied to cases where one or both tapes in a pair are“exfoliated” HTS tape, i.e. HTS tape without a substrate.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Power Engineering (AREA)
• Plasma & Fusion (AREA)
• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Superconductors And Manufacturing Methods Therefor (AREA)
• Crystals, And After-Treatments Of Crystals (AREA)
• Containers, Films, And Cooling For Superconductive Devices (AREA)

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• 2018
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