CN113035487A

CN113035487A - Device for improving excitation efficiency of superconducting closed coil

Info

Publication number: CN113035487A
Application number: CN202110262720.5A
Authority: CN
Inventors: 黄振
Original assignee: Shanghai Jiaotong University
Current assignee: Shanghai Jiaotong University
Priority date: 2020-03-11
Filing date: 2021-03-10
Publication date: 2021-06-25
Anticipated expiration: 2041-03-10
Also published as: WO2021180146A1; CN113035487B

Abstract

The invention discloses a device for improving the excitation efficiency of a superconducting closed coil, and belongs to the field of superconducting closed coil excitation. The apparatus includes a length of superconducting tape connected to an excitation superconducting coil, the superconducting tape including a conductive layer, a superconducting layer, and a substrate, the conductive layer being configured to have a pattern structure that blocks passage of current. The conductive layer is a single layer or multiple layers. The material of the conductive layer is copper and/or silver. The material of the superconducting layer is REBCO. The device further comprises a buffer layer which is made of dielectric materials and is basically insulated. The pattern structure comprises geometrical shapes, preferably grooves. The slot is configured to be in the plane of the conductive layer, the length of the slot being the same as or less than the width of the substrate. The trench is configured to be in the plane of the conductive layer, the depth of the trench being the same as or less than the thickness of the conductive layer. The device excites the closed superconducting coil through an external power supply or a magnetic flux pump. The device surface is covered with a material of insulating or weakly conductive properties. The device of the invention improves the excitation efficiency of the superconducting closed coil in a stable and efficient manner.

Description

Device for improving excitation efficiency of superconducting closed coil

Technical Field

The invention relates to the field of superconducting closed coil excitation, in particular to a device for improving the excitation efficiency of a superconducting closed coil.

Background

The superconducting closed coil excitation technology is one of key technologies in superconducting magnet application, and is applied to the fields of magnetic resonance imaging, nuclear magnetic resonance spectrometer, high-speed superconducting magnetic suspension and the like. Ideally, the normal state resistance of the persistent current switch should be infinite, but in reality, persistent current switches are classified as either an on, normal state (or resistive state) or an off, non-resistive state, with resistive and non-resistive being most common to achieve through temperature control. The resistance should be large enough in the normal state that the current flowing through the persistent current switch is no more than 10% of the coil operating current. Since the resistance of the persistent current switch to the normal state and the current flowing through it will generate dissipated energy in addition to the heater. The field loss on the persistent current switch generally needs to be less than 1W, and in any case at most not more than a few watts. This requirement is relatively mature for Low Temperature Superconducting (LTS) switches, such as: the low-temperature superconducting switch can use a special composite NbTi wire and a Cu-Ni alloy matrix to increase the resistivity and the like. Because the surface of the coated conductor such as the second generation high temperature superconducting material (REBCO) is coated with a micron-sized silver coating layer and a copper stabilizing layer, if the original strip is directly used for a continuous current switch, the conductivity of the coated conductor is relatively strong, especially at low temperature. The conventional method is to directly use the resistance of the superconducting material when the superconducting material is quenched, and can also improve the resistance value of the switch in a normal state by winding a sensing or non-sensing coil and using a longer material length, but the effect of the method for improving the resistance is still not obvious.

In the prior art, a superconducting Current Switch is disclosed in article 1 ("a REBCO periodic-Current Switch (PCS): Test Results and Switch Heater Performance", Philip c. michael, et al, ieee transmission ON APPLIED superconducting Current, vol.27, No.4, JUNE 2017), and its technical scheme is to increase the resistance of the Current Switch in the normal state by simply increasing the physical length, and the Switch length in the actual device is as long as 10 cm. In article 2 ("Characteristics of a HTS superconducting Current Switch System switching the n-Value", Yong Soo Yoon, et al IEEE TRANSACTIONS ON APPLIED SUPERCONNECTION VITY, VOL.16, NO.2, JUNE 2006), a high temperature superconducting Current Switch is disclosed, which is a technical solution to assemble longer strips into a coil form in order to increase the normal state resistance and reduce the volume.

The conventional method for manufacturing a thermal control superconducting switch composed of a superconducting coated conductor is to use a section of superconducting material or to wind the superconducting material into an inductive or non-inductive coil, and to use a longer length of material to increase the resistance value of the switch when the switch is changed into a normal state, so that the manufactured superconducting switch composed of the superconducting coated conductor has a limited resistance value in a normal state, occupies a larger space in a coil type superconducting switch form, is troublesome to manufacture, wastes superconducting tapes, and even may form a heat island in a normal state. Superconducting switches made with inductive or non-inductive coils are relatively slow to open and close because of their large bulk heat capacity. The REBCO superconducting switch with sapphire as the substrate has a complex process and is difficult to make with some joints at the superconducting coil junction.

Accordingly, those skilled in the art have been devoted to developing a device for improving the excitation efficiency of the superconducting closed coil in order to improve the excitation efficiency of the superconducting closed coil in a stable and efficient manner.

Disclosure of Invention

In view of the above-mentioned drawbacks of the prior art, the technical problem to be solved by the present invention is how to improve the excitation efficiency of a superconducting closed coil in a simple, stable and efficient manner.

To achieve the above object, the present invention provides an apparatus for improving excitation efficiency of a superconducting closed coil, the apparatus comprising a length of superconducting tape connected to an exciting superconducting coil, the superconducting tape comprising a conductive layer, a superconducting layer and a substrate, the conductive layer being configured to have a pattern structure for blocking passage of current.

Further, the pattern structure has one or more geometric shapes on the surface of the conductive layer, and the cross section of the conductive layer is in a groove shape.

Further, individual said machine geometries include vertical lines, diagonal lines, curved lines, closed polygons.

Further, the length of the pattern structure is the same as or shorter than the width of the conductive layer.

Further, the depth of the pattern structure is the same as or less than or more than the thickness of the conductive layer.

Further, the side of the superconducting tape also has the conductive layer, and the conductive layer of the side is also configured to have the pattern structure that blocks the passage of current.

Further, the width of the geometric shape on the superconducting surface is smaller than or equal to the width of the geometric shape on the side conductive layer.

Further, the geometric shapes on the superconducting surfaces are joined end to end with the geometric shapes on the side conductive layers.

Furthermore, the method for manufacturing the pattern structure comprises one or more of etching, laser ablation, chemical corrosion or mechanical processing.

Further, the etching is wet etching or dry etching.

Further, the device excites the closed superconducting coil through an external power supply or a magnetic flux pump.

Further, the superconducting tape is wound in the form of a coil.

Further, the substrate is also configured to have the pattern structure that blocks the passage of current.

Further, the conductive layer is a single layer and/or a plurality of layers.

Further, the material of the conductive layer is copper and/or silver and/or stainless steel and/or alloys thereof.

Further, the material of the superconducting layer is REBCO or an iron-based superconductor.

Further, the device also comprises a buffer layer which is made of dielectric materials.

Further, the device excites the closed superconducting coil through an external power supply and/or a magnetic flux pump.

Further, the geometric figures are covered with materials with insulating or weak conductive properties.

The technical scheme of the invention solves the problem that the resistance of the superconducting switch composed of a single superconducting coated conductor and a coil type is smaller when the superconducting switch is changed into a normal state, and solves the problems that the superconducting switch composed of the superconducting coated conductor of the coil type occupies larger space, is troublesome to manufacture and wastes superconducting tapes, and even a heat island can be formed in the normal state; the problem that the speed of a coil type superconducting switch composed of a superconducting coating conductor is relatively low in the process of mutual switching between a resistive state and a non-resistive state because the overall heat capacity of the superconducting switch is relatively large due to the fact that relatively more materials for manufacturing the superconducting switch are used is solved; the problems that joints at the connecting parts of the REBCO superconducting switch and the superconducting coils with sapphire as the substrate are difficult to manufacture and the switching process is complex are solved.

The conception, the specific structure and the technical effects of the present invention will be further described with reference to the accompanying drawings to fully understand the objects, the features and the effects of the present invention.

Drawings

FIG. 1 is a schematic diagram of a prior art superconducting switch constructed from superconducting coated conductors;

FIG. 2 is a schematic view of a prior art flux pump comprised of a transformer or DC power source and an AC core coil;

FIG. 3 is a schematic cross-sectional view of a conventional REBCO high temperature superconducting bare tape (i.e., tape without encapsulation);

FIGS. 4 a-4 i are schematic diagrams of a metal scribe in the main region of action of an alternating field (or traveling field) of a superconducting switch or flux pump formed of superconducting coated conductors according to a preferred embodiment of the present invention;

FIG. 5 is a schematic view of a superconducting coated conductor with copper and/or silver coated on the side during the fabrication process;

fig. 6 a-6 e are schematic diagrams of superconducting surfaces of the main regions of the superconducting switch formed by superconducting coated conductors generating the main position of resistance or the effect of the flux pump alternating field (or traveling wave field) in the normal state according to a preferred embodiment of the present invention.

Detailed Description

The technical contents of the preferred embodiments of the present invention will be more clearly and easily understood by referring to the drawings attached to the specification. The present invention may be embodied in many different forms of embodiments and the scope of the invention is not limited to the embodiments set forth herein.

In the drawings, structurally identical elements are represented by like reference numerals, and structurally or functionally similar elements are represented by like reference numerals throughout the several views. The size and thickness of each component shown in the drawings are arbitrarily illustrated, and the present invention is not limited to the size and thickness of each component. The thickness of the components may be exaggerated where appropriate in the figures to improve clarity.

As shown in fig. 1, which is a working schematic diagram of using a superconducting persistent current switch (abbreviated as a superconducting switch) to excite or supplement magnetism to a superconducting closed coil, all or part of superconducting materials in the superconducting switch are part of the superconducting closed coil, the left diagram shows that the superconducting switch is heated to make the superconducting materials quench, i.e. change from a superconducting state to a Normal state (also called a resistive state), and then the resistance at the superconducting switch after quenching is multiplied by the flowing current to generate a voltage, and the value of the voltage is a voltage value when the superconducting coil (the superconducting material around which the superconducting coil is wound can be any superconducting material) is excited; the right diagram shows that when the heating of the superconducting material at the superconducting switch is finished after the excitation is finished and the superconducting material is restored to be below the critical temperature of the superconducting material and is changed into a superconducting state, the input and/or the output of the current source are disconnected, and the current can be operated in a closed loop in the closed coil.

In another embodiment of the present invention, rather than requiring quenching of the superconducting material during excitation of the superconducting switch, the closed coil may be excited or supplemented by flux pumping techniques (e.g., flux pumps of the somewhat commutated type or of the traveling wave field type, etc.). One of the characteristics is that an alternating current electromagnet is arranged at the superconducting switch of the figure 1 to provide an external alternating magnetic field to match with a transformer or a direct current power supply (as shown in figure 2) or to generate voltage at the closed position of the superconducting coil by utilizing the action of a traveling wave field to carry out excitation or magnetic compensation.

The preparation routes of superconducting materials are generally divided into deposition of superconducting thin films on metal substrates (generally called Coated conductors) and Powder-in-tube methods, the present example being directed to superconducting Coated conductors. Fig. 3 is a schematic cross-sectional view of a superconducting coated conductor, i.e., a REBCO high-temperature superconducting bare tape (bare tape is a tape without encapsulation, a superconducting coated conductor with an encapsulation tape is also applicable to the present invention, and the encapsulation tape is generally made of a conductive material such as Copper or stainless steel), which includes a Copper Stabilizer (Copper Stabilizer), a Silver capping layer (Silver Overlayer), a high-temperature superconducting layer ((RE) BCO-HTS), a Buffer layer (Buffer Stack), a Substrate (Substrate), and the like. When the superconducting layer is in a normal state (a resistance state), the copper stabilizing layer and the silver covering layer are relatively high-conductivity layers; the superconducting layer, the buffer layer and the substrate are layers having relatively weak conductivity. The buffer layer is theoretically substantially insulating, but may have weak conductivity. There are some minor differences between REBCO superconducting bare tapes from different manufacturers (e.g., the silver capping layer of the non-superconducting surface may not be present, the copper stabilizing layer of the superconducting and/or non-superconducting surfaces may not be present, etc.), but the basic structural principles are similar. Besides REBCO superconducting tapes, superconducting coated conductors include other types of superconductors like Iron-based superconductors (Iron-based superconductors); the same is that the superconducting coated conductors are basically composed of a conductive layer (which may be composed of a copper stabilizer layer and/or a silver capping layer and/or an alloy layer thereof and/or a series of materials with better conductivity such as stainless steel) and/or a superconducting layer and/or a buffer layer and/or a substrate, and the like, and the difference is that the materials constituting the superconducting layer are different. The following conductive layers are exemplified by copper and/or silver, and the like, for example, other materials with better conductivity.

The technical scheme of the embodiment is that a copper stabilizing layer and/or a silver covering layer with relatively strong conductivity in the superconducting coated conductor is blocked on a current path, the current is forced to flow through a superconducting layer with relatively weak conductivity (in a normal state/a resistance state) as far as possible, and the buffer layer is basically insulated, so that the current is greatly prevented from flowing from the superconducting layer to a substrate through the buffer layer. The substrate with relatively weak conductivity can also be optionally provided with a current barrier. The technical scheme of the embodiment is that the through-current capacity of the copper stabilizing layer and/or the silver covering layer and/or the substrate is reduced or removed on the whole, so that the resistance of the superconducting switch in a normal state is improved, the loss of the switch during the excitation of the closed coil is reduced, and the excitation efficiency of the superconducting closed coil is improved.

In another embodiment of the invention, which is excited by a flux pump, the flux barrier of the copper stabilizer layer and/or the silver cover layer can weaken the superposition effect of a shielding current field and an external field generated in a conductive metal layer of an action area of the external alternating field (or traveling wave field) when the flux pump works, wherein the action area is positioned at the closed position of the superconducting coil, and the excitation or complementary magnetic efficiency of the superconducting closed coil can also be improved.

The barriers described in the above embodiments may be the conductive layers completely separated (as shown in fig. 4a, 4b, 4d and 4i for trench 2/trench 3) or partially separated (partially separated means that there may still be copper and/or silver etc. in the separated trenches, partially separated may be in the conductive layers, i.e. the width of the trenches is less than the width of the substrate (as shown in fig. 4c, 4e, 4f, 4g, 4h) and/or in the plane perpendicular to the conductive layers, i.e. the depth of the trenches is less than the thickness of the copper stabilising layer and/or silver capping layer, as shown in fig. 4i for trench 1). The number of grooves is greater than or equal to 1 and the scoring pattern is not limited to that shown in fig. 4 b-4 h. The separation means is preferably a wet (e.g. chemical) or dry (e.g. plasma) etching or laser ablation and/or scoring and/or grooving and/or scribing method or a method using machining or dicing saw dicing or cutting or chemical etching, etc. (hereinafter only the scribing groove is used instead of these methods). The substrate current barrier option is arranged similarly to the conductive layer, but with copper and/or silver or the like being the substrate material.

The schematic drawing of the groove in the main region of the superconducting switch or flux pump alternating field (or travelling wave field) formed by the superconducting coated conductor is shown in fig. 4 a-4 i (but the groove drawing pattern is not limited to the form shown in fig. 4 a-4 i, and the groove drawing pattern is feasible, such as vertical straight line, horizontal straight line, oblique straight line, radial straight line, curve, discontinuous line, etc., as long as the current capacity of the copper stabilization layer and/or silver coating layer and/or substrate can be reduced), so that when the thermal control superconducting switch is in the normal state, the current can flow through the superconducting layer and/or buffer layer and/or substrate with relatively weak conductivity (i.e., relatively high resistivity), thereby improving the overall resistance value of the superconducting switch when the normal state is achieved; and can also be used to reduce the path and/or area of the shield current circulating in the relatively more conductive layer when acted upon by the alternating field (or traveling field).

The grooving may be performed on one or both sides (as shown in fig. 3, the copper stabilizer layer and/or the silver coating layer may be present on both sides of the superconducting coated conductor), and if the one side is preferably a superconducting side as shown in fig. 4 (the superconducting tape is not of a symmetrical structure, and is referred to with reference to the intermediate substrate, the superconducting side being the outermost side of the substrate on which the superconducting coating layer is provided). The preferred positions of the scribing grooves can be a plurality of positions (as shown by dashed lines in fig. 6a, as mentioned above, the scribing groove pattern is not limited to straight lines, but is feasible as long as the scribing groove pattern capable of reducing the current capacity of the copper stabilizing layer and/or the silver coating layer and/or the substrate), and the width, the number and the size of the scribing groove position area can be reasonably selected according to the required normal state resistance value of the superconducting switch (when the superconducting switch is used for excitation) and the area covered by the alternating field (or the traveling field) (when the flux pump is used for excitation or magnetic compensation). If the number of the grooves is larger, which results in longer length of the superconducting tape used by the superconducting switch, the superconducting tape can be wound into a coil form.

As shown in FIG. 5, in the actual production process of the superconducting coated conductor, the side surface of the superconducting coated conductor may be wrapped with one or more materials such as copper and/or silver, etc. the same as the conductive layer, in order to prevent the conduction of the superconducting surface and the non-superconducting surface current through the copper and/or silver wrapped on the side surface, at this time, the partial or complete cutting of the copper and/or silver wrapped on the side surface of the main area where the superconducting switch or flux pump alternating field (or travelling field) is to be applied may be selected, i.e. the groove pattern applied on the superconducting surface may be completely applied to the conductive layer on the side surface of the superconducting tape, for example, the cut-off partial or complete cutting is shown in the plan views of FIG. 6a and FIG. 6e, FIGS. 6a and 6e are schematic diagrams of the superconducting surface where the overall size of the side groove pattern is larger than that of the superconducting surface groove pattern of the superconducting surface, where FIG. 6a shows the overall size of the superconducting switch or flux pump alternating field (or travelling Fig. 6e shows a case where the overall size of the side scribing groove pattern is smaller than that of the superconducting plane. The scribing groove pattern shown in fig. 4 a-4 i is preferably in the area of fig. 6a and 6e after the complete cutting, the dashed lines shown in fig. 6a and 6e being used for the scribing groove pattern shown in fig. 4 a-4 i. Because the critical current of the strip material at the action area of the alternating field (or traveling wave field) of the superconducting switch or the flux pump is generally larger than that of the superconducting coil, the side copper and/or silver coating can be cut into the superconducting layer selectively when the side copper and/or silver coating is removed.

When the thermal control superconducting switch is heated to enable the switch to be in a normal state, the heating range needs to cover a part or all of the scribing groove; when the magnetic flux pump works, the alternating field (or traveling wave field) needs to cover a part of or all the scribing grooves (the schematic diagram of the scribing grooves is shown in a dashed line in fig. 6a and 6 e).

Fig. 6b shows another variant of fig. 6a, in which the copper and/or silver-coated side portions can be cut out in sections. The number of the cut-off segmented portions may correspond to one groove in the superconducting surface as shown in fig. 6a, or may correspond to a plurality of grooves in the superconducting surface as shown in fig. 6 c.

The three solutions shown in fig. 6 a-6 c are all represented by the alignment of the slot on the superconducting surface with the slot on the side surface at the joint of the two surfaces, where the alignment means that the width of the slot on the side surface is greater than or equal to the width of the slot on the superconducting surface, i.e. at this position, the slot on the superconducting surface is joined end to end with the slot on the conductive layer on the side surface, and when current flows through this position, the current is forced to enter the superconducting coating and/or substrate with higher resistance as much as possible, thus achieving the purpose of increasing resistance of this embodiment.

Fig. 6d shows a further variant of fig. 6b, in which the slot on the superconducting side is not joined to the slot on the side at the joint between the two sides, but is offset to some extent, in which case part of the conductive layer of the superconducting side will communicate with the conductive layer of the side, which solution does not provide the same increase in electrical resistance as the three solutions shown in fig. 6 a-6 c.

Since oxide superconducting materials (such as REBCO) are very sensitive to water and decompose quickly when exposed to water, they are converted to non-superconducting materials, and in order to prevent the exposed oxide superconducting layer from reacting with water, it is preferable to cover the surface of the exposed oxide superconducting layer in the trench with an insulating or weakly conductive material.

The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the present teachings without departing from the inventive concepts. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined by the claims.

Claims

1. An apparatus for increasing the excitation efficiency of a superconducting closed coil, the apparatus comprising a length of superconducting tape connected to an exciting superconducting coil, the superconducting tape comprising a conductive layer, a superconducting layer and a substrate, the conductive layer being configured to have a patterned structure that blocks the passage of current.

2. An apparatus for increasing excitation efficiency of a superconducting closed coil according to claim 1, wherein the pattern structure has one or more geometric shapes on the surface of the conductive layer and has a groove shape in the cross section of the conductive layer.

3. An apparatus for increasing excitation efficiency of a superconducting closed coil according to claim 2, wherein the single geometric shape comprises a vertical line, an oblique line, a curved line, or a closed polygon.

4. An apparatus for increasing excitation efficiency of a superconducting closed coil according to claim 1, wherein the length of the pattern structure is the same as or shorter than the width of the conductive layer.

5. An apparatus for increasing excitation efficiency of a superconducting closed coil according to claim 1, wherein the depth of the pattern structure is the same as or less than or more than the thickness of the conductive layer.

6. The apparatus for improving excitation efficiency of a superconducting closed coil according to claim 2, wherein the side surface of the superconducting tape also has the conductive layer, and the conductive layer of the side surface is also configured to have the pattern structure for blocking current.

7. An apparatus for increasing excitation efficiency of a superconducting closed coil according to claim 6, wherein the width of the geometric shape on the superconducting surface is less than or equal to the width of the geometric shape on the side conductive layer.

8. An apparatus for increasing excitation efficiency of a superconducting closed coil according to claim 6, wherein the head and/or tail of the geometric shape on the superconducting surface is engaged with the geometric shape on the side conductive layer.

9. The apparatus for improving excitation efficiency of a superconducting closed coil according to claim 1, wherein the pattern structure is formed by one or more of etching, laser ablation, chemical etching or mechanical processing.

10. The apparatus for improving excitation efficiency of a superconducting closed coil according to claim 9, wherein the etching is wet etching or dry etching.

11. The apparatus for increasing excitation efficiency of a superconducting closed coil according to claim 9, wherein the apparatus excites the closed superconducting coil by an external power source or a flux pump.

12. An apparatus for increasing excitation efficiency of a superconducting closed coil according to claim 1, wherein the superconducting tape is wound in a coil form.

13. An apparatus for increasing excitation efficiency of a superconducting closed coil according to claim 1, wherein the material of the conductive layer is copper and/or silver and/or stainless steel and/or alloys thereof.

14. The apparatus of claim 1, wherein the substrate is also configured to have the pattern structure that blocks current from passing.

15. An apparatus for increasing excitation efficiency of a superconducting closed coil according to claim 1, wherein the conductive layer is a single layer and/or a plurality of layers.

16. The apparatus for increasing excitation efficiency of a superconducting closed coil according to claim 1, wherein the material of the superconducting layer is REBCO or an iron-based superconductor.

17. An apparatus for increasing excitation efficiency of a superconducting closed coil according to claim 1, wherein the apparatus further comprises a buffer layer, the buffer layer being a dielectric material.

18. An apparatus for increasing the excitation efficiency of a superconducting closed coil according to claim 1, wherein the apparatus excites the closed superconducting coil by an external power source and/or a flux pump.

19. An apparatus for increasing the excitation efficiency of a superconducting closed coil according to claim 2, wherein the geometric figure is covered with a material with insulating or weak conductive properties.