High-temperature superconducting coil with resistance dipping winding and manufacturing method of high-temperature superconducting coil

Abstract

The invention relates to a high-temperature superconducting coil with a resistive dip winding and to a method for the production thereof, said high-temperature superconducting coil (HTSC) comprising:-a strip (HTS-TP) made of a high-temperature superconducting material, said strip being wound into a plurality of turns; -a resistive layer (RL) arranged between and in contact with the plurality of turns; characterised in that the resistive layer (RL) comprises: a grid (MSH) made of a metal-based material having a first electrical resistivity, and an impregnating material (IM) having a second electrical resistivity different from the first electrical resistivity, the impregnating material filling the grid; or a strip (TP) made of a metal-based material having a first electrical resistivity, said strip being formed with a through-hole (TO), and an impregnating material (IM) having a second electrical resistivity different from the first electrical resistivity, said impregnating material filling said through-hole.

Description

Field of the Invention

[0001] The present invention relates to the field of superconducting magnets and, more particularly, to high-temperature superconducting magnets. Background Art

[0002] For superconducting magnets, an important aspect to consider is the irreversible state transition from the superconducting state to the resistive state, known as "quench". Superconducting magnets need to be protected against this phenomenon because it can cause irreversible damage (especially the thermal effects due to the expansion of the resistive regions within the superconducting magnet).

[0003] This is a common problem for all superconducting magnets, but it becomes more critical when considering high-temperature superconductors (HTS).

[0004] In fact, when a HTS magnet quenches, the expansion rate of the resistive regions (i.e., the "normal" regions, non-superconducting regions) is very slow, and thus the associated resistive voltage rise is also very slow. This typically results in a voltage detection lag for the quench and a high risk of thermally induced local damage in the HTS magnet.

[0005] Solutions have been proposed to avoid such situations, especially for HTS coils:

[0006] A method of protecting HTS coils during local resistance transitions is to remove any electrical insulation between turns. This is achieved by allowing current to flow from one turn to (radially) another turn, enabling the current to automatically bypass the resistive regions of the HTS coil. This is a proven and effective method of protection against thermal damage. However, the main drawback of this solution is the large electrical time constant of the radial current, especially during the charging of the magnet. Another drawback is that the turns are not mechanically connected together (this aspect is also referred to as "dry winding technology" in the literature). These two drawbacks can cause complex mechanical behavior (some turns of the coil may lose their contact, thus limiting the self-protection characteristics), heat dissipation problems, and loss of magnetic field quality when the coil is charged and discharged. In addition, due to fluctuations in the thickness and width of the superconducting cable, "voids" are formed inside the winding, so "dry winding technology" is not optimal for the internal cooling of the coil. An alternative solution is based on "Metal-as-Insulation technology" (MI), which involves adding a resistive layer made essentially of metal strips between the turns of the HTS coil. The metal strips increase the resistance due to their material itself and the contact surface with the coil turns. This can reduce current bypass under normal operating conditions and, at the same time, reduce the associated electrical time constant. Therefore, this solution significantly reduces the inter-turn current bypass, thereby limiting the unnecessary unbalanced and torque forces between the internal components of the coil. The resistance can be set by choosing the metal material and thickness of the metal strips. The effectiveness of this solution in strong magnetic fields has been verified in recent studies, for example, see the article by Ph. Fazilleau et al., "38mm diameter cold bore metal-as-insulation HTS insert reached 32.5T in a background magnetic field generated by resistive magnet", Cryogenics, Volume 106 (2020) (A1).

[0007] To more conveniently set the resistance value of the metal strips, specific designs have also been proposed.

[0008] For example, in the field of PI technology, WO 2019 / 150123A1 (A2) proposed a partial insulation structure composed of a metal strip sandwiched between two insulating layers. Each insulating layer includes windows through which electrical contact can be made with the turns of the HTS coil, and the windows are further staggered from one insulating layer to the other. The number of windows in each insulating layer and the amount of staggering of the windows from one insulating layer to the other can set the resistance value of the partial insulating layer. In this document, solutions for ensuring the mechanical connection between the metal strip and the HTS coil are also proposed, such as by adhesives (such as epoxy resin) or mechanically. In this way, the disadvantages of the "dry winding technology" will no longer exist.

[0009] As another example, recently, alternative solutions for MI technology have been proposed. This solution is based on using a resistive layer made of charged conductive epoxy resin between the turns of the coil. We can refer to Bouloukakis et al., "Discharge Behaviour and Modelling of a 1.5T REBCO Magnet With QuenchTolerant Coils Impregnated With Conductive Epoxy", IEEE Transactions onApplied Superconductivity, Vol. 31, No. 5, pp. 1-5, August 2021, Article No. 4601105, doi: 10.1109 / TASC.2021.3059975 (A3). This solution, like MI technology, introduces resistance between the turns of the coil. The resistance value can be set during the manufacturing process by adjusting the different components of the epoxy resin solution. In addition, as mentioned above, the epoxy resin solution (resin) forms an adhesive once dried, thus achieving the mechanical connection of the turns of the HTS coil.

[0010] T. Lécrevisse et al. provided a state-of-the-art review of the prior art in the article Supercond. Sci. Technol., 35 (2022), 074004 (page 18) (A4).

[0011] The object of the present invention is to propose another solution. Summary of the Invention

[0012] To achieve this object, the present invention proposes a high-temperature superconducting coil, which comprises:

[0013] - a strip made of a high-temperature superconducting material, the strip being wound into a plurality of turns;

[0014] - A resistive layer, which is disposed between and in contact with the plurality of turns; characterized in that the resistive layer comprises: a grid and an impregnating material, the grid being made of a metal-based material having a first resistivity, the impregnating material being dielectric or conductive but having a second resistivity different from the first resistivity, and the impregnating material filling the grid; or a strip and an impregnating material, the strip being made of a metal-based material having a first resistivity, the strip being formed with through holes, the impregnating material being dielectric or conductive but having a second resistivity different from the first resistivity, and the impregnating material filling the through holes.

[0015] Other features (considered individually or in combination) of the coil according to the present invention are also provided as:

[0016] - The grid is a fabric such as a woven fabric or a knitted fabric;

[0017] - The strip formed with through holes is made of a serrated strip;

[0018] - The metal-based material for the grid or the strip formed with through holes is selected from the following materials: steel, stainless steel or non-stainless steel, copper or copper alloy, aluminum or aluminum alloy;

[0019] - The impregnating material is a dielectric material or a metal-based material, and the dielectric material is selected from resins such as epoxy resins, waxes, oxide pastes;

[0020] - The grid or the strip formed with through holes is covered with a coating to adjust the contact resistance between the grid or the strip formed with through holes and the strip made of a high-temperature superconducting material;

[0021] - The second resistivity of the impregnating material is different from the first resistivity of the metal-based material constituting the grid or the strip formed with through holes.

[0022] The present invention also provides a method for manufacturing a high-temperature superconducting coil according to the present invention, the method comprising the following steps:

[0023] a) Construct a laminate by the following sub-steps:

[0024] a1) Provide a strip made of a high-temperature superconducting material;

[0025] a2) Provide a grid or a strip formed with through holes made of a metal-based material having a first resistivity;

[0026] a3) Place the grid or the strip formed with through holes on the strip made of a high-temperature superconducting material;

[0027] a4) Impregnating the grid or the strip provided with through-holes with an impregnating material having a second resistivity different from that of the metal-based material of the grid or strip;

[0028] The grid or the strip provided with through-holes is used together with the impregnating material to form the resistive layer;

[0029] b) Wrapping the laminate itself to form turns;

[0030] c) Curing the impregnating material of the laminate.

[0031] Other features of the method according to the invention (considered individually or in combination) are also provided as:

[0032] - Sub-step a3) and sub-step a4) are carried out simultaneously;

[0033] - Step b) is carried out simultaneously with sub-step a4);

[0034] - Step b) is carried out between sub-step a3) and sub-step a4). Description of the Drawings

[0035] Other features and advantages of the invention will become apparent by reading the following detailed description and referring to the accompanying drawings, in which:

[0036] - Figure 1 is a picture of a high-temperature superconducting coil according to the invention;

[0037] - Figure 2 is a cross-sectional view of the high-temperature superconducting coil according to the invention between two turns of the coil;

[0038] - Figure 3 shows a top view of a grid that can be used for the resistive layer of the coil;

[0039] - Figure 4 shows an alternative, in which the grid is replaced by a strip provided with through-holes, Figure 4(a) is a perspective view according to the first embodiment, Figure 4(b) is a perspective view according to the second embodiment, and Figure 4(c) is a top view according to the third embodiment;

[0040] - Figure 5 shows another alternative, in which the grid (shown in a cross-sectional view according to its thickness) is covered with a coating to further adjust the contact resistance with the high-temperature superconducting tape;

[0041] - Figure 6 is a schematic diagram of different steps of a possible manufacturing method of a high-temperature superconducting coil according to the invention.

[0042] - Figure 7 is a schematic diagram of an experimental device for testing a high-temperature superconducting coil;

[0043] - Figure 8 is a curve obtained by using the Figure 7 experimental setup, which shows the variation of the central magnetic induction intensity (unit: mT) of the coil with time (unit: ms) after a 20 A discharge in multiple tests;

[0044] - Figure 9 is a curve obtained by using the Figure 7 experimental setup, which shows the variations of the current (unit: A), voltage (unit: V) and central magnetic induction intensity (unit: mT) of the coil with time (unit: seconds) to test the stability of the coil under quench conditions;

[0045] - Figure 10 is a curve obtained by using the Figure 7 experimental setup, which shows the variations of the current (unit: A), voltage (unit: V) and central magnetic induction intensity (unit: mT) of the coil with time (unit: seconds) to test the robustness of the coil against pulsed quenches. DETAILED DESCRIPTION

[0046] The high-temperature superconducting coil HTSC according to the present invention is shown in Figure 1 (overall view) and Figure 2 (cross-sectional view).

[0047] The high-temperature superconducting coil HTSC includes a tape HTS-TP made of a high-temperature superconducting material and wound into a plurality of turns, and a resistance layer RL disposed between and in contact with the turns. As shown in Figure 2 , the resistance layer is shown between two consecutive turns of the tape HTS-TP.

[0048] The resistance layer RL can be formed in different ways.

[0049] In Figure 3 , the resistance layer RL includes a mesh MSH made of a metal-based material having a first resistivity, and an impregnating material IM having a second resistivity different from the first resistivity, and the impregnating material IM fills the mesh MSH.

[0050] The mesh MSH can in particular be a fabric such as a woven fabric or a knitted fabric. For example, a woven fabric (tissue) of stainless steel can be used.

[0051] In FIG. 4, the resistance layer RL includes a tape TP made of a metal-based material having a first resistivity, the tape being formed with through holes TO, and an impregnating material IM having a second resistivity different from the first resistivity, and the impregnating material fills the through holes.

[0052] More specifically, FIG. 4(a) shows a strip having through-holes that are identical (given dimensions) holes, and preferably evenly distributed along the strip.

[0053] FIG. 4(b) shows a strip having through-holes with variable dimensions, and ultimately unevenly distributed along the strip.

[0054] FIG. 4(c) shows a strip having through-holes formed by the zigzag shape of the strip.

[0055] In any case, the metal-based material for the grid MSH or the strip TP formed with through-holes TO can be selected from the following materials: steel, stainless steel, copper and copper alloys (including beryllium copper alloys, brass, etc.), aluminum and aluminum alloys.

[0056] Also in any case, the impregnating material IM can be a dielectric material or a metal-based material, and the dielectric material is selected from the following materials: resin (such as epoxy resin), wax, oxide paste). In particular, resin is particularly suitable due to its adhesion properties and high dielectric properties.

[0057] The grid MSH or the strip TP formed with through-holes TO can be covered by a coating CTG. The coating CTG can help to adjust the contact resistance between the grid MSH or the strip TP formed with through-holes TO and the strip HTS-TP made of a high-temperature superconducting material.

[0058] For example, Figure 5 shows the deposition position of the coating in the case of using a grid within the resistive layer.

[0059] Of course, for any alternative (not shown in the drawings) shown in FIGS. 4(a) to 4(d), the coating can also be deposited on the surface of the strip TP having through-holes TO that is intended to contact the high-temperature superconducting strip HTS-TP.

[0060] The coating can be deposited by an atomic layer deposition (ALD) process, and its thickness is generally between 100 nanometers and 1 micrometer. For example, the coating can be made of alumina or a mixture of alumina and zinc oxide.

[0061] Figure 6 Shows a possible manufacturing method of the high-temperature superconducting coil HTSC according to the present invention.

[0062] The first step 100 includes constructing a laminate by the following sub-steps:

[0063] - Sub-step 101: Providing a strip HTS-TP made of a high-temperature superconducting material,

[0064] - Sub-step 102: Provide a grid MSH made of a metal-based material having a first resistivity or a strip TP formed with vias TO;

[0065] - Sub-step 103: Place the grid MSH or the strip TP formed with vias TO on a strip made of a high-temperature superconducting material;

[0066] - Sub-step 104: Impregnate the grid MSH or the strip TP formed with vias TO with an impregnating material IM having a second resistivity different from that of the metal-based material of the grid MSH or the strip TP.

[0067] The grid MSH or the strip TP formed with vias TO together with the impregnating material IM are used to form a resistance layer RL.

[0068] The second step 200 includes winding the laminate itself to form turns.

[0069] The third step 300 includes curing the impregnating material IM of the laminate.

[0070] The manufacturing method may be carried out continuously in the above order, but it is not necessary.

[0071] For example, sub-steps 103 and 104 may be carried out simultaneously.

[0072] As another example, step 200 may be carried out simultaneously with sub-step 104.

[0073] As another example, step 200 may be carried out between sub-step 103 and sub-step 104.

[0074] Proof of concept

[0075] A high-temperature superconducting coil was manufactured as described above.

[0076] The selected high-temperature superconducting tape (“HTS tape”) is 6 mm wide and 76 μm thick, and a total of 25.5 m is required to wind a flat coil.

[0077] The resistance layer is made of a stainless-steel grid filled with epoxy resin as the impregnating material. More specifically, the grid is a woven fabric (gauze). The fabric uses 30-μm strands, which results in a total thickness of 60 μm. The open area (%) through which the epoxy resin of the grid can pass is 49%. The length and width of the grid correspond to the length and width of the HTS tape. For the proof-of-concept flat coil, a room-temperature-curing epoxy resin with a thermal shrinkage coefficient close to that of the HTS material was used.

[0078] The winding of the superconducting tape and the grid and impregnation are carried out synchronously.

[0079] The inner diameter of the flat coil is 60 mm and the outer diameter is 99.1 mm, with approximately 100 turns. The coil inductance is 1.035 mH, and the coil magnetic constant is 1.617 mT / A.

[0080] Experimental Setup and Results

[0081] To verify the self - protection characteristics of the coil detailed in the "Proof of Concept", its characteristics have been tested through an experimental setup.

[0082] For this purpose, the coil HTSC was immersed in a liquid nitrogen (LN2) bath BTH at 77 K. The voltage U and current I of the coil (which can be achieved by adding two welded taps at both ends of the coil) were monitored, and the central magnetic induction intensity of the coil was monitored using a Hall sensor (Arepoc).

[0083] A schematic diagram of the experimental setup is shown in Figure 7 (the Hall sensor is not shown).

[0084] Approximately 60 tests were carried out using this coil, which included three thermal cycle tests from room temperature to liquid nitrogen bath conditions (77 K) and multiple quench tests.

[0085] Figure 8 Shows the variation of the central magnetic induction intensity (unit: mT) with time (unit: s) in the case of a sudden discharge of a 20 A current for 16 out of the 60 tests carried out.

[0086] First, the coil HTSC was charged to 20 A in a ramp manner by the power supply PS, at which time the mechanical contactor MC was closed. Subsequently, the mechanical contactor MC was suddenly opened. Finally, starting from the moment when the mechanical contactor MC was opened (t = 0 s), the variation of the magnetic field with time was monitored.

[0087] This kind of test can evaluate the contact resistance between the high - temperature superconducting tape and the resistive layer.

[0088] We can see that Figure 7 the curves of all the tests shown in are similar, which means that the contact resistance is constant. Therefore, even after thermal cycling and quenching, we can expect the repeatable characteristics of the coil during charging and discharging. This also indirectly indicates that the contact between the high - temperature superconducting tape and the resistive layer (grid + epoxy resin) is maintained. In fact, thanks to the epoxy resin, the resistive layer is bonded between two turns of the high - temperature superconducting tape.

[0089] Figure 9Shows the variation of the current I (A), voltage U (V), and central magnetic induction intensity B (mT) of the coil with time (s) in the first test case. First, the coil is charged with a current below the quench current of 2 A (ramping up in the interval of 0 - 20 s; the current is 70 A). Subsequently, the power supply voltage is kept constant at a lower value to passively protect the coil for approximately 60 s (the interval of 20 - 78 s) - the current intensity remains constant at 70 A in the same time interval. After that, the current is increased in steps of 1 A until quench (the interval of 88 - 92 s; quenching at 72 A). Subsequently, at t = 92 s, a discharge phenomenon can be observed, and the current drops sharply and suddenly to 32 A, indicating the self - protection ability of the coil against quench. While the current is decreasing, the voltage rises to 0.7 V (the limit value applied by the power supply). At t = 145 s, the current is gradually cut off by ramping down. It should be noted that the variation of the central magnetic induction intensity is similar to that of the current, and due to Figure 9 the scale selected in Figure 9 only two curves can actually be distinguished in

[0090] Figure 10 Shows the variation of the current I (A), voltage U (V), and central magnetic induction intensity (mT) of the coil with time (s) in another test case.

[0091] First, the coil is charged to 134 A at a ramp rate of 200 A / s (pulse current test). This current value corresponds to approximately 1.86 times the quench current (as mentioned before, the quench current is 72 A). Subsequently, a discharge phenomenon can be quickly observed, and the current drops sharply and suddenly to 32 A, indicating the self - protection ability of the coil against quench. At the same time, since the current pulse cannot heat a sufficient volume of the coil to keep the coil in the changed state (contrary to the test shown in Figure 9 ), the voltage also drops accordingly. At t = 17 s, the coil cooled by the cryogenic bath returns to the superconducting state again. Finally, at t = 34 s, a new current pulse is sent: the characteristics are the same. It should be noted that the variation of the central magnetic induction intensity is similar to that of the current, and due to Figure 10 the scale selected in Figure 10 only two curves can actually be distinguished in

Claims

1. A high temperature superconducting coil (HTSC), comprising: - A tape (HTS-TP) made of a high temperature superconducting material, the tape being wound into a plurality of turns; - A resistance layer (RL) disposed between and in contact with the plurality of turns; characterized in that the resistance layer (RL) comprises: · A mesh (MSH) and an impregnating material (IM), the mesh being made of a metal-based material having a first resistivity, the impregnating material being dielectric or conductive but having a second resistivity different from the first resistivity, the impregnating material filling the mesh; or · A tape (TP) and an impregnating material (IM), the tape being made of a metal-based material having a first resistivity, the tape being formed with through holes (TO), the impregnating material being dielectric or conductive but having a second resistivity different from the first resistivity, the impregnating material filling the through holes.

2. The high-temperature superconducting coil (HTSC) according to claim 1, wherein The mesh (MSH) is a fabric such as a woven fabric or a knitted fabric.

3. The high-temperature superconducting coil (HTSC) according to any one of the preceding claims, characterized in that, The tape (TP) formed with through holes (TO) is made of a serrated tape.

4. The high-temperature superconducting coil (HTSC) according to any one of the preceding claims, characterized in that, The metal-based material for the mesh (MSH) or the tape (TP) formed with through holes (TO) is selected from the following materials: steel, stainless steel or non-stainless steel, copper or copper alloy, aluminum or aluminum alloy.

5. The high temperature superconducting coil (HTSC) according to any one of the preceding claims, characterized in that, The impregnating material (IM) is a dielectric material or a metal-based material, and the dielectric material is selected from resins such as epoxy resin, wax, oxide paste.

6. The high-temperature superconducting coil (HTSC) according to any one of the preceding claims, characterized in that, The mesh (MSH) or the tape (TP) formed with through holes (TO) is covered with a coating (CTG) to adjust the contact resistance between the mesh (MSH) or the tape (TP) formed with through holes (TO) and the tape (HTS-TP) made of a high temperature superconducting material.

7. The high-temperature superconducting coil (HTSC) according to any one of the preceding claims, characterized in that, The second resistivity of the impregnating material is different from the first resistivity of the metal-based material constituting the mesh (MSH) or the tape (TP) formed with through holes (TO).

8. A method of manufacturing a high temperature superconducting coil (HTSC) according to any one of the preceding claims, comprising the following steps: a) Constructing a laminate by the following sub-steps: a1) Providing a tape (HTS-TP) made of a high temperature superconducting material, a2) Providing a mesh (MSH) or a tape (TP) formed with through holes (TO) made of a metal-based material having a first resistivity, a3) Placing the mesh (MSH) or the tape (TP) formed with through holes (TO) on the tape made of a high temperature superconducting material, a4) Impregnating the mesh (MSH) or the tape (TP) formed with through holes (TO) with an impregnating material (IM) having a second resistivity different from the first resistivity of the metal-based material of the mesh (MSH) or the tape (TP); The mesh (MSH) or the tape (TP) formed with through holes (TO) together with the impregnating material (IM) are used to form the resistance layer (RL); b) Winding the laminate itself to form turns, c) Curing the impregnating material (IM) of the laminate.

9. The method according to the preceding claim, wherein, Sub-step a3) and sub-step a4) are carried out simultaneously.

10. The method according to claim 8, wherein, Step b) is carried out simultaneously with sub-step a4).

11. The method according to claim 8, wherein, Step b) is carried out between sub-step a3) and sub-step a4).

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