High temperature superconducting field coil, method for winding a high temperature superconducting field coil, device for placing high temperature superconducting tape on an HTS field coil, and method for manufacturing a high temperature superconducting field coil

Abstract

A high temperature superconducting (HTS) field coil. The HTS field coil includes a plurality of HTS tapes arranged to form windings of the HTS field coil and a substrate separating each winding. The windings form a coiled path around an inner circumference of the field coil, and the distance from the inner circumference of the field coil increases monotonically with movement in a first direction along the coiled path. For each HTS tape except for the radially innermost HTS tape, each end of the HTS tape is offset in the first direction from a corresponding end of an adjacent HTS tape that is radially inward of the HTS tape, and the HTS tape overlaps the adjacent HTS tape over at least 50% of the length of the adjacent HTS tape. The length of each HTS tape is less than the circumference of the coil plus the magnitude of the offset between one end of the HTS tape and the corresponding end of the adjacent HTS tape that is radially outward of the HTS tape.

Description

[Technical field]

[0001] The present invention relates to the field of high temperature superconducting magnets or HTS magnets. In particular, the present invention relates to a winding method for an HTS coil, a coil obtained by said winding method, and an apparatus arranged to perform said winding method. [Background technology]

[0002] Superconducting materials are typically classified as "high temperature superconductors" (HTS) and "low temperature superconductors" (LTS). LTS materials, such as Nb and NbTi, are metals or metal alloys whose superconductivity can be described by the BCS theory. All low temperature superconductors have a self-field critical temperature (the temperature above which they cannot become superconducting even in the absence of zero external magnetic field) below about 30 K. The behavior of HTS materials is not described by the BCS theory, and such materials may have a self-field critical temperature above about 30 K (it should be noted, however, that it is the physical differences in composition and superconducting behavior, not the self-field critical temperature, that define HTS and LTS materials). The most commonly used HTS are "copper oxide superconductors", which are ceramics based on copper oxides (compounds containing a copper oxide group) such as BSCCO or ReBCO (where Re is a rare earth element, typically Y or Gd). Other HTS materials include iron pnictides (eg, FeAs and FeSe) and magnesium diborate (MgB2).

[0003] ReBCO is typically manufactured as a tape having the structure shown in Figure 1. Such a tape 100 is generally approximately 100 microns thick and comprises a substrate 101 (typically an electropolished nickel-molybdenum alloy (e.g. Hastelloy® approximately 50 microns thick)) on which a series of buffer layers, known as a buffer stack 102, approximately 0.2 microns thick, is deposited by IBAD, magnetron sputtering, or other suitable technique. An epitaxial ReBCO·HTS layer 103 (deposited by metal oxide chemical vapor deposition (MOCVD) or other suitable technique) overlies the buffer stack and is typically 1 micron thick. A 1-2 micron silver layer 104 is deposited on the HTS layer by sputtering or other suitable technique, and a copper stabilizer layer 105 is deposited on the tape by electroplating or other suitable technique, often completely encapsulating the tape. The silver layer 104 and the copper stabilizer layer 105 are also deposited on the sides of the tape 100 and the substrate 101 so that they extend continuously around the tape 100, allowing electrical connection to be made from either side of the tape 100 to the ReBCO·HTS layer 103. These layers 104, 105 are therefore also referred to as "cladding". Typically, the silver cladding has a uniform thickness of approximately 1-2 microns on both sides and edges of the tape. The silver layer 104 between the HTS layer 103 and the copper layer 105 prevents the HTS material from contacting the copper, which could result in contamination of the HTS material by the copper. Portions of the silver layer 104 and the copper stabilizer layer 105 on both sides of the tape 100 are not shown in FIG. 1 for the sake of clarity. FIG. 1 also does not show the silver layer 104 extending under the substrate 101, as is typically the case. The silver layer 104 provides a low resistance electrical interface to the ReBCO layer 103 and provides a hermetic protective seal around the ReBCO layer 103, while the copper layer 105 allows for external connection to the tape (e.g., allows soldering) and provides a parallel conductive path for electrical stabilization.

[0004] In addition, "peeled" HTS tapes can be produced, which lack the substrate and buffer stack, but have a "perimeter coating", typically of silver, i.e., a layer on both sides and edges of the HTS layer. Tapes with a substrate are referred to as "substrate-attached" HTS tapes.

[0005] HTS cables include one or more HTS tapes connected along their length via a conductive material (usually copper). The HTS tapes may be stacked (i.e. arranged so that the HTS layers are parallel) or have other tape arrangements that may vary along the length of the cable. Notable special cases of HTS cables are single HTS tapes and HTS pairs. An HTS pair includes a pair of HTS tapes arranged so that the HTS layers are parallel. If backed tapes are used, the HTS pair can be type 0 (HTS layers facing each other), type 1 (HTS layer of one tape facing the backing of the other tape), or type 2 (backings facing each other). Cables that include more than two tapes can have some or all of the tapes arranged in HTS pairs. Backed HTS tapes can include various arrangements of HTS pairs, most commonly either a stack of type 1 pairs or a stack of type 0 pairs (or equivalently type 2 pairs). HTS cables can include a mix of backed and peeled tapes.

[0006] Superconducting magnets are formed by arranging multiple HTS cables (or individual HTS tapes, which for the purposes of this description can be treated as a single tape cable) into coils, either by winding the HTS cables or by providing sections of coils made from HTS cables and bonding them together. HTS coils fall into three broad classes:

[0007] · Insulated, having electrically insulating material between the windings (so that current can only flow in the “helical path” through the HTS cable). Non-insulated, the windings are electrically connected radially and not just along the cable. Partially insulated, the windings are radially connected to a controlled resistance, either by using a high resistivity material (compared to copper for example) or by providing intermittent insulation between the coils.

[0008] An uninsulated coil can also be considered as a low resistance case of a partially insulated coil.

[0009] HTS coils are typically manufactured by providing a spool 201 of HTS cable 210 with a magnetic brake 202 for tensioning, as shown in Figure 2. The cable is then wound into the coil, turn by turn, by moving the spool around the coil (starting from a former or support structure 203 that defines the shape of the coil) or by rotating the coil about its axis while keeping the spool stationary. Additional layers of insulation, partial insulation layers (i.e., insulation with a current path through it, or material with a resistance intermediate between a typical insulator and a conductor), quench detection components, etc. may be wound with the HTS cable.

[0010] This is not suitable for all coil shapes and cable constructions. In particular, laminated tape cables (including several parallel HTS tapes running tangentially to the coil at all points) cannot be wound in this manner into coils with sharp turns, as this would result in severe distortion of the tapes on the outside of the turns. For such coils, an alternative winding method may be used, as shown in FIG. 3, in which a laminated tape cable is assembled in situ by providing several spools 301a-e of HTS tape, which are wound simultaneously from several spools onto a coil 302. The HTS tapes may be coated with flux as they are wound, and the coils may later be impregnated with solder to bond the HTS tapes together, or the HTS tapes may be soldered together as they are wound. The latter is generally preferred for larger coils, to avoid long periods of time for the entire coil to be held at high temperatures, which would risk degradation of the HTS tapes. As in the previous case, other components may be wound between the layers of HTS tapes that form each cable.

[0011] It is generally difficult to obtain a sufficient length of HTS tape such that each spool of HTS tape in FIG. 3 can hold enough tape for the entire coil. However, the HTS tapes may be replaced as each one runs out, or in a predetermined pattern. This results in a fixed pattern of "butt" joints from tape end to tape end (the coil is "straightened" and significantly shortened in length), as shown diagrammatically in FIG. 4, where each layer of HTS tape includes a butt joint 401 where the HTS tape ends, and the HTS tape 402 of the other layer overlaps this butt joint, resulting in an overall pattern similar to typical brickwork. As mentioned above, the length in FIG. 4 is significantly shorter. Typically, the length of each HTS tape is on the order of a few meters to a few hundred meters, and the thickness is on the order of a hundredth to a tenth of a millimeter.

[0012] One drawback of the winding method using individual tapes is that the soldering is done in one go. The time that the coil must be held at high temperature increases with the size of the coil and the cross-sectional area of ​​the winding. This can lead to problems with degradation of the HTS critical current if the recognized limits on the integral of temperature over time are exceeded. It also makes soldering errors difficult to detect and repair. In addition, the number of individual tape spools poses challenges when building a winding scheme for coils carrying high currents or operating in extreme environments requiring a large number of tapes.

[0013] Both of these winding methods make it difficult to introduce "grading" of the coil, i.e., HTS coils with zero field critical currents that vary around the coil (typically to compensate for non-uniform fields, temperatures, or distortions in the coil during use) while producing a substantially uniform coil. This can be mitigated to some extent by including additional HTS cable or tape along a given arc, but this requires additional tooling.

[0014] In addition, the above winding methods are difficult to implement for complex coil shapes, such as HTS coils that are not convex in a single plane. For non-convex shapes, special measures must be taken at any concave sections to prevent the HTS tape from "bridging" across those sections. Also, for non-planar coils, the movement of the HTS spool (or the coil itself) can become significantly more complicated.

[0015] Finally, both methods rely on having long lengths of HTS tape so that the coil can be wound from as few sections of tape or cable as possible. In general, a longer HTS tape will be more expensive than a shorter HTS tape of the same overall length. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] US Patent Application Publication No. 2003 / 213611 [Patent Document 2] US Patent Application Publication No. 2016 / 216348 [Patent Document 3] International Publication No. 2015 / 011491 [Patent Document 4] International Publication No. 2018 / 078326 [Patent Document 5] International Publication No. 2019 / 150095 Summary of the Invention

[0017] [Scheduled for completion once new claims are finalized] According to a first aspect, a high temperature superconducting (HTS) field coil is provided. The HTS field coil includes a plurality of HTS tapes arranged to form windings of the HTS field coil and a substrate separating each winding. The windings form a coiled path around an inner circumference of the field coil, and the distance from the inner circumference of the field coil increases monotonically with movement in a first direction along the coiled path. For each HTS tape except for a radially innermost HTS tape, each end of the HTS tape is offset in the first direction from a corresponding end of an adjacent HTS tape that is radially inward of the HTS tape, and the HTS tape overlaps the adjacent HTS tape over at least 50% of the length of the adjacent HTS tape. The length of each HTS tape is less than the circumference of the coil plus the magnitude of the offset between one end of the HTS tape and the corresponding end of the adjacent HTS tape that is radially outward of the HTS tape.

[0018] According to a second aspect, a method of winding a high temperature superconducting (HTS) field coil is provided. A former is provided that defines an inner circumference of the field coil. A first HTS tape is placed on the former. A plurality of HTS tapes are sequentially placed to form windings of the HTS field coil. Each HTS tape overlaps a previous HTS tape over at least 50% of the length of the previous HTS tape such that each end of the HTS tape is offset in a first direction around the circumference of the field coil from a corresponding end of the previous HTS tape. During the placement of the plurality of HTS tapes, a substrate is wrapped around the field coil to separate the windings formed by the HTS tapes. The length of each HTS tape is less than the circumference of the field coil plus the magnitude of the offset between one end of an HTS tape and the corresponding end of a next HTS tape.

[0019] According to a third aspect, an apparatus for placing a high temperature superconducting (HTS) tape onto an HTS magnetic field coil is provided. The apparatus includes a spool, a feeding mechanism, a tape cutter, a propulsion system, and a controller. The spool is configured to hold the HTS tape. The feeding mechanism is configured to deliver the HTS tape from the spool onto the HTS magnetic field coil. The tape cutter is configured to separate the HTS tape placed on the magnetic field coil from the HTS tape on the spool. The propulsion system is configured to move the apparatus in both directions around the circumference of the HTS magnetic field coil. The controller is configured to: causing a feeding mechanism to feed the HTS tape onto the HTS field coil while a propulsion system is moving the apparatus in a first direction about the circumference; after a specified length of the HTS tape has been dispensed, causing a tape cutter to separate the dispensed HTS tape from the HTS tape on the spool; causing the propulsion system to move the apparatus in a second direction about the circumference; and The method is configured to repeat the steps of delivering an HTS tape, separating the delivered tape, and moving back in the second direction so that each HTS tape is delivered at a starting position that is offset in the first direction from the starting position of the previous HTS tape.

[0020] Further embodiments are set out in claims 2 et seq. [Brief description of the drawings]

[0021] The drawings are presented solely for the purpose of illustrating certain concepts and should not be construed as precise representations of particular devices, methods, or results of methods. Unless otherwise indicated, elements in the drawings are not presented to scale, and only those elements necessary for the purpose of understanding the presented concepts are shown (e.g., supporting structures are generally omitted).

[0022] [Figure 1] FIG. 1 is a diagram of a high-temperature superconducting (HTS) tape. [Diagram 2] FIG. 1 is a diagram of a known winding method. [Diagram 3] FIG. 2 is a diagram of an alternative known winding method. [Figure 4] 1 is a simplified cross-section of a known HTS cable. [Figure 5A-5E] 5A-5E show an exemplary method of placing an HTS tape onto an HTS coil. [Figure 6] 1 shows HTS coils placed with variable offsets. [Figure 7] 11 is a cross section of a further exemplary HTS coil winding showing certain substrate options. [Figure 8] FIG. 1 is a schematic diagram of an apparatus for placing an HTS tape on an HTS coil. [Figure 9] FIG. 1 is a schematic diagram of an apparatus for winding an HTS coil. [Figure 10] 13 is a schematic diagram of a further exemplary method of placing an HTS tape on an HTS coil. [Figure 11]FIG. 11 is a schematic diagram of the windings of an HTS coil placed according to FIG. 10. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Rather than using the winding process described in the Background, a winding process is described herein that uses multiple relatively short lengths of HTS tape that are laid down in an overlapping "shingle" pattern.

[0024] 5A-5E are schematic diagrams of a simplified method of laying HTS tape onto a coil, which is represented as a flat line for ease of illustration, but it will be understood that the same principles apply to wound wire coils.

[0025] In Figure 5A, a first HTS tape 501 is placed on a substrate 500. The substrate separates the windings of the HTS coil once constructed and may be conductive, insulating, or partially insulating as required for the final coil design and may also include additional components such as quench detection components, sensors, etc. The substrate may be changed during winding of the coil, for example, for the first winding the substrate may be a coil former or support structure and then changed to a substrate with suitable properties to separate the windings before winding the second winding begins.

[0026] 5B, a second HTS tape 502 is placed over the first HTS tape such that it overlaps a significant portion of the length of the HTS tape 502, with a distance S1 between the beginning of the first HTS tape and the beginning of the second HTS tape, and a distance E1 between the end of the first HTS tape and the end of the second HTS tape. Distances S1 and E1 may be substantially equal (i.e., the first and second HTS tapes may be the same length) or may be different (i.e., the HTS tapes may be different lengths), but at least in this example, the beginning of the second HTS tape is further around the coil than the beginning of the first HTS tape, and the end of the second HTS tape is further around the coil than the end of the second HTS tape. Note that although the HTS tape is shown flat and horizontal in this figure and in Figures 5A and 5C, this is merely for convenience of illustration, and the HTS tape may be placed such that a portion of region E1 resides on the substrate.

[0027] 5C, a third HTS tape 503 is placed over the second HTS tape in substantially the same manner as the second HTS tape was placed over the first HTS tape, i.e., the third HTS tape overlaps a significant portion of the second HTS tape and has distances S2 and E2 between the beginning of the second and third HTS tapes and the end of the second and third HTS tapes, respectively.

[0028] 5D shows the result after multiple HTS tapes 510 have been laid down. In each case, the "nth" HTS tape is laid down on top of the "n-1th" HTS tape, with a significant portion of the distance S between the start of the n-1th HTS tape 511 (i.e., the previously laid HTS tape) and the nth HTS tape 512 (i.e., the most recently laid HTS tape). n-1 , and the distance E between the end point of the n-1th HTS tape and the nth HTS tape n-1 The result is a "shingle" pattern of HTS tape, with each tape overlapping several previously wrapped tapes and several subsequently wrapped tapes.

[0029] In Figure 5E, substrate 500 is laid down over previously laid HTS tape 510 up to the beginning of the next laid down HTS tape (note that because this figure is a linear representation of the HTS coil, point X on the substrate shown laying down over an HTS tape may be the same as point Y on the substrate that is laid down under an HTS tape further down in the figure). By successively laying down additional substrates and further HTS tapes, an HTS coil may be built up to any desired number of turns.

[0030] The winding method illustrated in FIG. 5 results in an HTS field coil including a plurality of HTS tapes arranged to form windings and a substrate separating each winding. The windings form a coiled path around the inner circumference of the field coil, with the distance from the inner circumference increasing monotonically as one moves in a first direction along the coiled path. For each HTS tape, except for the innermost tape, each end of the HTS tape is offset in the first direction from the corresponding end of an adjacent HTS tape that is radially inward of the HTS tape, such that the HTS tape overlaps an adjacent HTS tape by at least 50% of its length. Since a 50% overlap provides a coil with only two tapes at any given cross-section of the winding, in coils with significant current requirements, the overlap may be at least 90% (10 tapes per winding cross-section) or at least 95% (20 tapes per winding cross-section). The length of each HTS tape is less than the circumference of the coil plus the magnitude of the offset relative to the next tape (i.e., the adjacent tape radially outward). This will be the maximum length that allows the next tape to be placed where the substrate has not yet been laid down. Especially for highly overlapping coils, i.e. coils where the overlap is short and on the order of the minimum bending radius of the substrate, the maximum length can be considered as the circumference of the coil.

[0031] FIG. 6 shows the distance S at which the HTS tapes 610 overlap each other. n and E n6 shows how coil grading is achieved by varying the offset distance. In region 601, the offset distance is such that there are three HTS tapes in the cross section of the coil. In region 602, the offset distance is increased, downgrading the coil to have only two HTS tapes in the given cross section. In region 602, the offset distance is decreased, upgrading the coil to have five HTS tapes in the given cross section. Generally, in areas of the coil where these distances are large, the number of HTS tapes in a given cross section of the cable is reduced, and where these distances are small, the number of HTS tapes in a given cross section of the cable is increased. This results in the grading of the coil, since the zero field critical current at a given temperature depends on the amount of HTS conductor in the cross section of the winding. In general, the offset distance may vary around the coil, and in certain instances may vary such that the average offset is greater for all windings of the coil in a first arc of the coil (which reduces the current density in that arc) than in a second arc of the coil (which increases the current density in that arc) (i.e., such that the grading of a given arc is similar for all windings).

[0032] Depending on the desired properties of the final coil, the substrate may be an insulator, a conductive material connecting the windings, a semiconductor, or any combination of these (e.g., an insulating strip with conductive paths passing through it to radially connect the windings with a pre-determined resistance). The substrate may include a conductive material with a channel therein, and the HTS tape may be placed in the channel. In this case, the substrate may additionally include an insulating layer on the outside of the conductive material to separate the windings, which may or may not have conductive paths passing through it.

[0033] The current flowing through the coil has to travel between the HTS tapes at each tape end. The substantial overlap between the tapes means that the resistance introduced by this is very low, and the slight increase in Joule losses can be compensated for by additional cooling of the HTS coil by methods well known in the art. The tapes are fixed by a conductive fixing medium (e.g. solder or conductive resin such as conductive epoxy resin, or resin impregnated with a conductive material), and most of the current transfer between the tapes occurs in this medium and in the conductive (e.g. copper) cladding on the individual tapes. A further improvement in resistance can be obtained by providing an additional conductive path bridging the sides of all the tapes. This means that the current flowing from the "bottom" of the tape stack to the "top" of the tape stack only needs to pass through that conductive path, rather than through each HTS tape in between. This conductive path may be provided by a separately bonded conductive element, or the substrate may include a U-shaped copper channel 701 in which the HTS tape 702 is placed, as shown in FIG. 7, which is an end cross-sectional view of a winding of the coil. Here, the sides of the U-shape form the conductive path. The substrate may include additional elements 703, 704 to separate the windings and / or insulate the outer edges of the U-shaped channel.

[0034] The HTS tape may be fixed in place after winding by impregnating the coil with solder or other fixing medium (e.g., a conductive resin). Alternatively, the solder or other fixing medium may be co-wound with the HTS tape and melted, cured, or otherwise induced to fix the tape during winding. This latter process reduces the time the HTS material spends at high temperature and also allows each HTS tape joint to be monitored for defects as it is wound, allowing errors to be detected and potentially corrected (e.g., by reflowing the solder or by reversing the joint and rewinding that section of the tape) during the winding process.

[0035] FIG. 8 shows an exemplary apparatus for laying down HTS tape for the winding method described above. The apparatus has a guide 801 that follows the path of the coil (including the substrate 850 and the already laid HTS tape 851) and maintains alignment with the coil. The apparatus has an HTS tape spool 802 that houses the HTS tape 803. The HTS tape 803 is laid down on the coil as the apparatus moves in a first direction (to the right in the figure, hereafter referred to as "above the coil", but this should be recognized only as a relative direction) and is fed off the spool 802 by a feeding mechanism. The feeding mechanism includes a pusher 804 and / or a motor configured to rotate the HTS tape spool, and a roller 805 or other similar means that may be spring-loaded or similarly biased to press the HTS tape against the tape (or substrate) of the already laid coil. A bonding agent, for example solder paste, resin such as epoxy resin, conductive epoxy, or solder flux, is applied from the roller via a nozzle or other dispenser 806 positioned above the coil. This allows the deposited bonding agent to end up between the HTS tape 803 and the already laid HTS tape 851. A bonding agent activator 807 is present (if necessary) down the coil from the roller to provide the necessary heating, curing, or other activation for the bonding agent. For example, the bonding agent activator may be a heater that heats the solder to a temperature sufficient to melt. A number of sensors 808 may be used down the coil from the roller, for example on either side of the bonding agent activator, to measure whether the bond between the HTS tape 803 and the already laid HTS tape 851 is acceptable or not. These sensors may include cameras, electrical sensors, thermal sensors (e.g., thermal cameras or temperature probes), or any other suitable sensors. The determination of whether the bond is acceptable or not may be based on pre-calibrated values, a determination via machine learning based on known good and known bad samples, or human monitoring of the sensor output or samples thereof.

[0036] The apparatus includes a tape cutter 809, e.g., a knife, located above the coil from the roller, which cuts the tape when the apparatus reaches the position where a given tape should end.

[0037] During tape laying, the machine lays each HTS tape starting at a first end, and continues laying the tape by moving up the coil until it reaches the desired end of the tape, at which point the tape is cut and the machine continues moving all the way to the end without feeding additional tape, until the HTS tape is spliced ​​to the previously laid HTS tape. The machine then moves back down the coil to the start of the next HTS tape and repeats the process. In this manner, the machine can lay several HTS tapes along the coil, as described with reference to Figures 5A-5E.

[0038] A position sensor 810 may be used to monitor the amount of tape being dispensed from the HTS tape spool 801 and determine if enough tape remains to dispense the next HTS tape onto the coil. A further position sensor 811 may be used to determine where the device is located over the coil and when to start and stop laying the HTS tape according to a pre-set laying pattern for the desired coil.

[0039] In effect, the device "rides" the coil like a cart on a roller coaster moving back and forth with the tape resting on it as it moves "up" the coil, then the tape is cut and the device moves "down" the coil to the start of the next tape. The device may include a propulsion system such as motorized wheels, or multiple guides may alternately grip the coil or its support structure and move the device so that it can "crawl" along the coil. Alternatively, the propulsion system may be external to the main device, such as a gantry configured to suitably move the device around the coil.

[0040] The operation of the apparatus is controlled by a controller, which may be integral to the apparatus or may be a remote device that sends appropriate inputs to the apparatus. The controller causes the various components of the apparatus to perform the tape deposition method described above. In some implementations, the controller may be distributed over several components, for example as a distributed computing architecture or as separate electrical or mechanical control systems for the individual parts that may be coordinated by a central controller.

[0041] To ensure that the beginning of the HTS tape is properly bonded to the coil, the machine may move to deposit a patch of bonding agent at the beginning of the HTS tape and then deliver the HTS tape over the patch of bonding agent to form an initial strong bond before continuing to deliver the tape.

[0042] The device shown above lays down the HTS tape according to the example of Figures 5A-5E, but does not lay down the substrate itself. As shown in Figure 9, this can be done by a separate spool 901 moving continuously around the coil 902, for example at the average speed of the HTS tape laying device. This is so that there is always a substrate 910 for the HTS tape to be laid at the end of the length of the HTS tape (where it does not overlap with the previous tape), and also so that the substrate is not laid down on top of the start of a tape that has not yet been laid down. The device 903 of Figure 8 then follows this spool, moving back and forth to lay down the individual HTS tapes.

[0043] An alternative "hybrid" winding method is shown diagrammatically in FIG. 10. This method combines features of the conventional winding method shown in FIG. 2 or FIG. 3 with features of the novel winding method shown in FIG. 5A-5E, and may be advantageous, for example, in situations where the additional resistance introduced by the winding method of FIG. 5A-5E is unacceptable. In the hybrid winding method, the coil is initially wound according to the conventional method shown in FIG. 2 or FIG. 3, or according to any other continuous winding method for winding the HTS cable to form the field coil. During this winding method (either simultaneously with the winding of the HTS cable or during pauses in the winding of the HTS cable), layers of tape are laid down along the arc of the field coil, in electrical contact with the HTS cable, using the winding method shown in FIG. 5A-5E. These layers of tape act as a "shunt" for the HTS cable. The "shunt" is in electrical contact with the cable and can share current with the HTS cable, providing additional current paths (and therefore additional current carrying capacity) along the arc of the field coil.

[0044] The shunt functions similarly to that described in EP 3747034, except that instead of a single HTS tape or a conventional HTS tape stack, the HTS shunt has an overlapping arrangement of tapes as described above. That is, the start and end of each HTS tape in the shunt is offset in one direction around the coil from the start and end of the HTS tape radially inward of the coil. Similar modifications may be made to the tapes in the HTS shunt as described above for a coil wound entirely using the method of FIG. 5. For example, the spacing of the HTS tapes in the HTS shunt may be varied to control the amount of HTS in any given cross section of the field coil, or additional conductive paths may be provided on the sides of the HTS shunt, or any of the other modifications described above.

[0045] In the example of Figure 10, a spool 1001 of HTS cable 1010 is used to provide a main winding 1011 in a manner similar to spool 201 and HTS cable 210 of Figure 2. An apparatus 1003 according to Figure 8 and related description moves along the main winding and lays down additional HTS tape 1020 in selected regions 1021 (in the illustrated example, in the central column section of the toroidal field coil) to form HTS shunts. The apparatus 1003 may follow the main winding spool 201 around the coil (i.e., move around the coil outside of region 1021 but do not lay down additional tape), or may be removed from the coil as the cable is wound from the main winding spool and reintroduced each time an additional section of HTS tape is laid down. Multiple HTS shunts may be added around the coil, and HTS shunts may be added to any number of turns of the main winding.

[0046] FIG. 11 shows a schematic close-up of a single winding in the area with additional tape after winding of the coil. The winding includes an HTS cable (only a cross section of which is shown) forming a field coil 1101. At arc 1110, an HTS shunt including an HTS tape 1111 is provided on the HTS cable. Although only four HTS tapes are shown in the figure, any number of HTS tapes may be used to form the HTS shunt, provided that for each HTS tape other than the radially inner HTS tape, each end of the HTS tape is offset in a first direction from the corresponding end of an adjacent HTS tape radially inward of said HTS tape.

[0047] Although there is some resistance between the main HTS coil and the HTS shunt, this resistance is very small because the current can pass to and from the shunt along the entire length of the shunt. This is also true if the coil is provided without insulation and the current can enter the shunt from either side. However, if the HTS shunt is made from HTS tape with a substrate, the resistance of the substrate side of the HTS shunt is higher than the resistance of the HTS side. Thus, if the current in the coil is such that the critical current of the main HTS cable alone is not sufficient to carry the transport current in the arc with the shunt, the excess current is easily shunted to the HTS shunt. At currents lower than the critical current of the main HTS cable in the graded region, the majority of the current flows mainly in the main HTS cable. When the HTS cable current approaches the critical current in the portion of the cable that is subject to high magnetic fields (or high temperatures, or magnetic field angles that are not very well aligned with the c-axis of the ReBCO HTS layer), the HTS generates a voltage that drives the excess current through the small resistance between the main cable and the shunt. Voltage generated per meter of HTS (E HTS )teeth

number

[0048] If the shunts are provided along the arc of the coil, they may be provided evenly on all windings of the HTS cable (e.g., each winding of the HTS cable may have an HTS shunt including two tapes), or the distribution of the shunts may vary across the cross section of the coil (e.g., all windings toward the outside of the central post of the TF coil may have shunts, and only all other windings may have shunts, and / or less HTS tape for windings toward the inside of the central post of the TF coil as the magnetic field gets lower).

[0049] While the above examples considered situations in which HTS shunts were laid down in a manner similar to that shown in Figures 5A-5E, the apparatus of Figure 8 may be used to lay down HTS shunts as more typical of stacked tape cables, such as where each tape overlaps a portion of the previously laid down tape (i.e., each tape is laid down with each edge offset toward the center of the tape relative to the previously laid down tape), or where each tape completely overlaps the previously laid down tape, or any other arrangement that may be formed by sequentially laying down HTS tapes.

Claims

1. A high temperature superconducting (HTS) field coil, a plurality of HTS tapes arranged to form windings of the HTS field coil, the windings forming a coiled path around an inner circumference of the HTS field coil, the distance from the inner circumference of the HTS field coil monotonically increasing as the plurality of HTS tapes move in a first direction along the coiled path; a substrate separating each of the windings; Including, For each HTS tape except the radially innermost HTS tape: each end of the HTS tape is offset in the first direction from a corresponding end of an adjacent HTS tape that is radially inward of the HTS tape; the HTS tape overlaps the adjacent HTS tape over at least 50% of the length of the adjacent HTS tape; an HTS field coil, wherein the length of each HTS tape is less than the circumference of the HTS field coil plus the magnitude of the offset between one end of the HTS tape and the corresponding end of the adjacent HTS tape that is radially outward of the HTS tape;

2. Each HTS tape is solder paste, solder flux, Resin, and Resin impregnated with conductive material 10. The HTS field coil of claim 1, wherein the HTS field coil is joined to an adjacent HTS tape by one of:

3. 10. The HTS field coil of claim 1, wherein the offset between each HTS tape and the adjacent HTS tape varies around the HTS field coil.

4. 4. The HTS field coil of claim 3, wherein the offset is varied such that an average of the offset is greater in a first arc of the HTS field coil than in a second arc of the HTS field coil for all windings of the HTS field coil.

5. 10. The HTS field coil of claim 1, wherein the substrate comprises a conductive material having a channel therein, the HTS tape residing in the channel such that multiple sides of the channel electrically connect with each other.

6. 10. The HTS field coil of claim 1, wherein each HTS tape overlaps an adjacent HTS tape radially inward of the HTS tape over at least 90% of the length of the adjacent HTS tape.

7. 1. A method of winding a high temperature superconducting (HTS) field coil, comprising: providing a former defining an inner periphery of the HTS field coil; placing a first HTS tape on the former; sequentially placing a plurality of HTS tapes to form windings of the HTS field coil, each HTS tape overlapping a previous HTS tape over at least 50% of a length of the previous HTS tape such that each end of the HTS tape is offset from a corresponding end of the previous HTS tape in a first direction around a circumference of the HTS field coil; While the plurality of HTS tapes are positioned, winding a substrate around the HTS field coil to separate the windings formed by the HTS tapes; Including, The method, wherein the length of each HTS tape is less than the circumference of the HTS field coil plus the magnitude of the offset between one end of the HTS tape and the corresponding end of the next HTS tape.

8. 8. The method of claim 7, further comprising applying a bonding agent between each HTS tape and the previous HTS tape during or before placing each HTS tape.

9. The method of claim 8 , wherein the bonding agent is a solder.

10. The method of claim 7 , wherein the former includes an initial portion of the substrate, and the first HTS tape is placed on the initial portion of the substrate.

11. 8. The method of claim 7, wherein the offset distance between each end of each HTS tape and the corresponding end of an adjacent HTS tape varies around the HTS field coil.

12. 12. The method of claim 11 , wherein the offset is varied such that an average of the offset is greater in a first arc of the HTS field coil than in a second arc of the HTS field coil for all windings of the HTS field coil.

13. 1. An apparatus for placing a high temperature superconducting (HTS) tape onto an HTS field coil, comprising: a spool configured to hold the HTS tape; a feeding mechanism configured to deliver HTS tape from the spool to the HTS field coil; a tape cutter configured to separate the HTS tape placed on the HTS field coil from the HTS tape on the spool; a propulsion system configured to move the device in both directions around the circumference of the HTS field coil; Controller and Including, The controller causing the feeding mechanism to feed an HTS tape onto the HTS field coil while the propulsion system moves the apparatus in a first direction around the circumference; After a specified length of HTS tape has been dispensed, causing the tape cutter to separate the dispensed HTS tape from the HTS tape on the spool; causing the propulsion system to move the device in a second direction around the periphery; repeating the steps of feeding an HTS tape, separating the fed tape, and moving back in the second direction; An apparatus configured to:

14. A high temperature superconducting (HTS) field coil, an HTS cable arranged to form a helix having a plurality of windings; one or more HTS shunts; Including, Each HTS shunt: arranged between each pair of adjacent windings along an arc of the HTS field coil so that current can be shared between the HTS cable and at least one side of the HTS shunt; a plurality of HTS tapes, each HTS tape positioned within said arc; For each HTS tape except the radially innermost HTS tape of each HTS shunt: each end of the HTS tape is offset in a first direction along the circumference of the HTS field coil from a corresponding end of an adjacent HTS tape that is radially inward of the HTS tape; an HTS field coil, wherein the HTS tape overlaps the adjacent HTS tape over at least 50% of the length of the adjacent HTS tape;

15. 1. A method of manufacturing a high temperature superconducting (HTS) field coil, comprising: winding an HTS cable to provide a field coil having a plurality of windings; While winding the HTS cable, an HTS shunt is positioned adjacent to a previous winding of the field coil along an arc of the field coil; placing a first HTS tape onto the HTS cable; sequentially placing a plurality of HTS tapes to form the HTS shunt, each HTS tape overlapping a previous HTS tape over at least 50% of a length of the previous HTS tape such that each end of the HTS tape is offset from a corresponding end of the previous HTS tape in a first direction around the circumference of the field coil; and Winding the HTS cable so that the HTS shunt is sandwiched between the winding and the previous winding of the field coil, so that current is shared between the HTS shunt and the HTS cable. A method comprising:

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