Superconducting excitation device and method

Abstract

This invention provides a superconducting excitation device and method, comprising: a superconducting tape; the superconducting tape includes a first superconducting tape and a second superconducting tape; one end of the long side of the first and second superconducting tapes is connected, and the other end is not connected; the superconducting tape is connected to a superconducting load to form a closed loop, a first terminal is connected to one end of the superconducting load, and a second terminal is connected to the other end of the load; a transmission current flows into the first superconducting tape through the first terminal and flows out from the second terminal, with the transmission currents in opposite directions on the first and second superconducting tapes; when the superconducting tape is placed in a changing magnetic field, when the transmission current is greater than the superconducting load current and the direction of the transmission current is the same as the direction of the load current, under the action of the opposite-direction transmission currents on the first and second superconducting tapes, the magnetic flux of the changing magnetic field links with the closed loop, thereby increasing the current of the superconducting load, so as to regulate the current of the superconducting load through the linked magnetic flux. This invention can achieve high-precision regulation of the superconducting load current.

Description

Technical Field

[0001] This invention belongs to the field of superconductivity, and more specifically, relates to a superconducting excitation device and method. Background Technology

[0002] In nuclear magnetic resonance (NMR), the resonant frequency is positively correlated with the magnetic flux density; higher magnetic flux density results in better spectral resolution. Low-temperature superconducting magnets are widely used in NMR. Due to the limitation of the critical magnetic field of low-temperature superconductors, the highest magnetic flux density currently achievable with low-temperature superconducting NMR magnets is 21.2 T (corresponding to a resonant frequency of 900 MHz). High-temperature superconductors, compared to low-temperature superconductors, possess a higher upper critical magnetic field, higher critical current density, and higher critical temperature, making them widely used in the manufacture of powerful magnets. High-temperature superconducting NMR magnets are essential for achieving NMR magnets with resonant frequencies greater than 1 GHz.

[0003] Due to the presence of junction resistance and flux creep, high-temperature superconducting magnets cannot operate in closed-loop constant-current mode. The decay of current in a closed-loop high-temperature superconducting magnet causes its magnetic field to change over time, thus requiring an external power supply to drive the magnet. For NMR, achieving high spectral resolution places high demands on the temporal stability of its magnetic field; specifically, the change in magnetic flux density within a few seconds must be less than one part per billion (10⁻⁶). -9 For power electronic constant current sources, achieving such high time stability is very difficult. Furthermore, using a power electronic constant current source to drive a high-temperature superconducting magnet inevitably introduces large current leads, resulting in significant heat loss.

[0004] Due to the shortcomings of the aforementioned power electronic constant current sources, researchers have begun to explore the use of high-temperature superconducting flux pumps without electrical contact to excite high-temperature superconducting magnets. The work described in the paper Walsh RM, Slade R, Pooke D and Hoffmann C, 2014 IEEE Trans. Appl. Supercond. 24:4600805, uses a high-temperature superconducting flux pump based on a traveling wave magnetic field to drive a 2T high-temperature superconducting NMR main magnet, causing the magnetic field of the magnet to change by 18 parts per million (18*10⁻⁸) within 25 seconds. -6However, the time stability of this magnetic field is lower than that provided by a power electronic constant current source, and naturally cannot meet the time stability requirements of NMR and MRI. The main problem with high-temperature superconducting flux pumps based on traveling wave magnetic fields is that using a large-area traveling wave magnetic field on the surface of the superconducting thin film results in a large mutual inductance between the traveling wave magnetic field and the superconducting magnet circuit, causing a large AC induction component to be superimposed on the DC magnetic field of the magnet. Therefore, maintaining a high-time-stability magnetic field in a closed high-temperature superconducting magnet using a traveling wave flux pump remains challenging.

[0005] Chinese patent document CN107924744A and paper Geng J, Coombs T A. Applied Physics Letters, 2015, 107(14):142601 propose a high-temperature superconducting flux pump based on a transformer-rectifier. This high-temperature superconducting flux pump applies a vertically varying magnetic field to the surface of a second-generation high-temperature superconducting tape carrying current, causing the high-temperature superconducting tape to enter a flux motion state, thereby linking the magnetic flux with the high-temperature superconducting magnet and achieving the effect of magnetizing the high-temperature superconducting magnet. The advantages of this type of high-temperature superconducting flux pump are: 1. Compared with traveling wave flux pumps, it reduces the mutual inductance between the varying magnetic field and the superconducting magnet circuit, reducing the interference of the varying magnetic field on the superconducting magnet's magnetic field. 2. The circuit structure is clear, facilitating the design of circuit parameters. 3. Compared with traveling wave flux pumps, it has higher magnetization accuracy. However, since the area of ​​the magnetic field acting perpendicularly on the superconducting tape is still relatively large, the number of magnetic flux movements is also relatively large. When precisely controlling the current of a small inductance high-temperature superconducting load, the control precision is insufficient, making it difficult to achieve precise control of the current of the shimming coil and the single-turn magnetic shielding coil in high-temperature superconducting NMR.

[0006] In summary, the main problems with existing technologies are as follows: 1. When using a power electronic constant current source to excite the main magnet of high-temperature superconducting NMR and high-resolution MRI, on the one hand, the current-time stability of the power electronic constant current source is limited and cannot meet the requirements of NMR and high-resolution MRI for the time stability of the magnet's magnetic field. On the other hand, it introduces large current leads into the system, resulting in significant heat loss. 2. Using the aforementioned traveling wave flux pump to excite the high-temperature superconducting magnet can reduce heat loss, but its output current time stability is lower than that of the power electronic constant current source. 3. Using the transformer-rectifier high-temperature superconducting flux pump provided in the aforementioned patent documents to excite the high-temperature superconducting magnet can reduce heat loss and achieve a certain degree of output current time stability. However, in the aforementioned application scenarios, the output current accuracy still cannot meet the application requirements, and the accuracy of the device's output current needs further improvement. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the purpose of this invention is to provide a superconducting excitation device and method, which aims to solve the problem of low load current control accuracy of existing high-temperature superconducting excitation devices.

[0008] To achieve the above objectives, in a first aspect, the present invention provides a superconducting excitation device, comprising: a superconducting tape;

[0009] The superconducting tape includes a first superconducting tape and a second superconducting tape; the long side, wide side, and thick side of the first superconducting tape and the second superconducting tape are parallel, respectively; one end of the long side of the first superconducting tape and the second superconducting tape are connected, and the other end is not connected; the ends of the long sides of the first superconducting tape and the second superconducting tape that are not connected are respectively designated as a first terminal and a second terminal; the width of the first superconducting tape and the second superconducting tape is greater than their thickness;

[0010] The superconducting tape is connected to the superconducting load to form a closed loop, with the first terminal connected to one end of the superconducting load and the second terminal connected to the other end of the load.

[0011] The transmission current flows into the first superconducting tape through the first terminal and flows out from the second terminal of the second superconducting tape. The directions of the transmission current in the first superconducting tape and the second superconducting tape are opposite.

[0012] When the superconducting tape is placed in a changing magnetic field, when the transmission current is greater than the current of the superconducting load and the direction of the transmission current is the same as the direction of the load current, under the action of the opposite transmission current on the first and second superconducting tapes, the magnetic flux of the changing magnetic field links with the closed loop, thereby increasing the current of the superconducting load, so as to regulate the current of the superconducting load through the linked magnetic flux.

[0013] In one possible example, when the superconducting tape is placed in a changing magnetic field, causing the superconducting tape to be in a state of magnetic flux motion, if the transmission current is less than the current of the superconducting load, the transmission current is 0, or the direction of the transmission current is opposite to the direction of the load current, then the magnetic flux linked with the closed loop decreases, thereby reducing the current of the superconducting load.

[0014] In one possible example, when the direction of the changing magnetic field is parallel to the wide and thick surface of the superconducting tape, the angle between the magnetic field direction and the wide side is defined as a first angle, the first angle ranging from 0 degrees to 60 degrees; or

[0015] When the direction of the changing magnetic field is parallel to the length and width of the superconducting tape, the angle between the magnetic field direction and the long side is defined as the second angle, which ranges from 0 degrees to 360 degrees.

[0016] In one possible example, the smaller the absolute value of the first angle of the direction of the changing magnetic field, the higher the precision of the magnetic flux control.

[0017] In one possible example, the changing magnetic field has a DC component to ensure that the amplitude of the changing magnetic field meets the requirements;

[0018] Under the influence of a changing magnetic field, the amount of magnetic flux passing through the superconducting tape per alternating cycle is related to the following factors:

[0019] Proportional to the amplitude of the changing magnetic field;

[0020] The thickness of the superconducting tape is proportional to the change in magnetic field acting on it.

[0021] It is proportional to the length of the superconducting tape subjected to the changing magnetic field;

[0022] Proportional to the magnitude of the transmitted current;

[0023] It is inversely proportional to the critical current of the superconducting tape.

[0024] In one possible example, the precision of flux control in the superconducting load is also related to the following factors:

[0025] The larger the transmission current, the lower the precision of the control of the superconducting load flux, and the faster the control speed.

[0026] The greater the thickness or length of the superconducting tape under the influence of the changing magnetic field, the lower the control precision of the superconducting load flux and the faster the control speed.

[0027] When the first angle is not 0 degrees, the wider the changing magnetic field acts on the superconducting tape, the lower the control precision of the superconducting load magnetic flux and the faster the control speed.

[0028] The greater the rate of change of the magnetic field strength of the changing magnetic field, the lower the control precision of the superconducting load flux and the faster the control speed.

[0029] The larger the DC magnetic field bias of the changing magnetic field, the lower the critical current of the first and second superconducting tapes, the lower the control precision of the superconducting load flux, and the faster the control speed.

[0030] The longer the changing magnetic field acts over a period of time, the greater the average rate of increase in the superconducting load magnetic flux.

[0031] In one possible example, the superconducting tape is made of rare earth barium copper oxide (ReBCO), bismuth strontium calcium copper oxide (BSCCO), or magnesium diboride (MgB2) material.

[0032] Secondly, the present invention provides a superconducting excitation method, comprising the following steps:

[0033] A superconducting tape is defined; the superconducting tape includes a first superconducting tape and a second superconducting tape; the long side, wide side, and thick side of the first superconducting tape and the second superconducting tape are parallel, respectively; one end of the long side of the first superconducting tape and the second superconducting tape are connected, and the other end is not connected; the ends of the long sides of the first superconducting tape and the second superconducting tape that are not connected are respectively designated as a first terminal and a second terminal; the width of the first superconducting tape and the second superconducting tape is greater than their thickness;

[0034] The superconducting tape is connected to the superconducting load to form a closed loop, with the first terminal connected to one end of the superconducting load and the second terminal connected to the other end of the load.

[0035] The control transmission current flows into the first superconducting tape through the first terminal and flows out from the second terminal of the second superconducting tape; the transmission current flows in opposite directions on the first and second superconducting tapes;

[0036] When the superconducting tape is placed in a changing magnetic field, when the transmission current is greater than the current of the superconducting load and the direction of the transmission current is the same as the direction of the load current, under the action of the opposite transmission currents on the first and second superconducting tapes, the magnetic flux of the changing magnetic field links with the closed loop, thereby increasing the current of the superconducting load and regulating the current of the superconducting load through the linked magnetic flux.

[0037] In one possible example, the method also includes the following steps:

[0038] When the superconducting tape is placed in a changing magnetic field, and the superconducting tape is in a state of magnetic flux motion, if the transmission current is less than the current of the superconducting load, the transmission current is 0, or the direction of the transmission current is opposite to the direction of the load current, then the magnetic flux linked with the closed loop decreases, thereby reducing the current of the superconducting load.

[0039] In one possible example, when the direction of the changing magnetic field is parallel to the wide and thick surface of the superconducting tape, the angle between the magnetic field direction and the wide side is defined as a first angle, the first angle ranging from 0 degrees to 60 degrees; or

[0040] When the direction of the changing magnetic field is parallel to the length and width of the superconducting tape, the angle between the magnetic field direction and the long side is defined as the second angle, which ranges from 0 degrees to 360 degrees.

[0041] In summary, the technical solutions conceived by this invention have the following beneficial effects compared with the prior art:

[0042] This invention provides a superconducting excitation device and method. This invention controls magnetic flux movement based on a principle different from existing technologies, enabling higher precision control of the linkage between the magnetic flux and the superconducting load. Compared to existing technologies, this invention primarily regulates the load current by applying a varying magnetic field parallel to the wide edge of the superconducting tape. By changing the direction and amplitude of the varying magnetic field, the precision of the regulated current, voltage, and resistance can be controlled. Compared to existing technologies, this invention can regulate the current in the superconducting load with a precision of approximately 2.067 x 10⁻⁶. -15 A*H.

[0043] This invention provides a superconducting excitation device and method, which can precisely control the voltage across the ends of a superconducting tape, with an accuracy of approximately 1*10. -15 V. This invention can precisely control the resistance of superconducting tapes, with an accuracy of approximately 1*10⁻⁶. -18 Ω. This invention can control the precision of the regulating current, regulating voltage, and regulating resistance by controlling the amplitude and direction of the transmitted current and changing the frequency of the magnetic field, and the regulation methods are rich. Attached Figure Description

[0044] Figure 1 A schematic diagram of a superconducting excitation device for regulating current provided in the first embodiment of the present invention;

[0045] Figure 2A This is a schematic diagram of the direction of a changing magnetic field applied to the superconducting excitation device provided in the first embodiment of the present invention.

[0046] Figure 2B This is a schematic diagram of another changing magnetic field direction applied to the superconducting excitation device provided in the first embodiment of the present invention;

[0047] Figure 3A A cross-sectional view of the first and second length portions of the superconducting excitation device provided in a first embodiment of the present invention;

[0048] Figure 3B This is a schematic diagram showing that the magnetic flux of the superconducting excitation device provided in the first embodiment of the present invention does not link with the closed loop during operation;

[0049] Figure 4A Another cross-sectional view of the first and second length portions of the superconducting excitation device provided in the first embodiment of the present invention;

[0050] Figure 4B A schematic diagram showing the linkage of magnetic flux with a closed loop during operation of the superconducting excitation device provided in the first embodiment of the present invention;

[0051] Figure 4CThis is a schematic diagram showing the superconducting excitation device provided in the first embodiment of the present invention, during operation, where the magnetic flux links with the closed loop and the device is in a state where the magnetic flux does not move;

[0052] Figure 5A A schematic diagram of a superconducting excitation device for regulating current provided in a second embodiment of the present invention;

[0053] Figure 5B A cross-sectional view of the first and second length portions of the superconducting excitation device provided in a second embodiment of the present invention;

[0054] Figure 6 An equivalent circuit diagram of the superconducting excitation device provided by the present invention during operation;

[0055] Figure 7 This is a closed-loop diagram of the superconducting excitation device provided in the first embodiment of the present invention;

[0056] Figure 8A Another cross-sectional view of the first and second length portions of the superconducting excitation device provided in the first embodiment of the present invention;

[0057] Figure 8B Another cross-sectional view of the first and second length portions of the superconducting excitation device provided in the second embodiment of the present invention;

[0058] Figure 8C For the present invention in Figure 8A and Figure 8B The equivalent circuit diagram of the superconducting excitation device under the operating mode;

[0059] Figure 9 This is an experimental data diagram of the superconducting excitation device provided in the first embodiment of the present invention;

[0060] In all the figures, the same reference numerals are used to denote the same elements or structures, wherein: 100 is the superconducting excitation device provided in the first embodiment; 101 is the superconducting tape shown in the first embodiment; 102 is the superconducting load; 103 is the transmission current; 104 is the magnetic field; 105 is the magnetic flux; 106 is the first length portion shown in the first embodiment; 107 is the second length portion shown in the first embodiment; 108 is the magnetic flux pre-linked with the closed loop; 109 is the magnetic field generator; 110 is the current source; 111 is the width; 112 is the thickness; 113 is the length; 116 is the current path; 117 is the current return path; 118 is the current terminal; 119 is the load current; 200 is the superconducting excitation device provided in the second embodiment; 201 is the superconducting tape shown in the second embodiment; 206 is the first length portion shown in the second embodiment; 207 is the second length portion shown in the second embodiment. Detailed Implementation

[0061] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0062] The superconducting excitation device includes a current source, a magnetic field generator, and a superconducting tape.

[0063] like Figure 1 As shown, the superconducting tape has a length, a width, and a thickness, with the width being greater than the thickness. A portion of the length and width of the superconducting tape lie in the same plane. The superconducting tape has a first length portion and a second length portion.

[0064] like Figure 1 As shown, the aforementioned current source is used to provide transmission current to the superconducting tape. When the superconducting tape has a first length portion and a second length portion, the current forms a current path in the first length portion and a current return path in the second length portion.

[0065] like Figure 1 , Figure 2A , Figure 2B As shown, the aforementioned magnetic field generator is used to selectively apply a changing magnetic field to the superconducting tape. This changing magnetic field is parallel to the length and width planes of the superconducting tape or at a certain angle to the length and width planes.

[0066] like Figure 3A , Figure 3B As shown, when the first length portion and the second length portion of the superconducting tape are adjacent and the length and width of the first length portion are on the same plane as the length and width of the second length portion, a changing magnetic field parallel to its width is applied to the superconducting tape. At this time, the changing magnetic field will act on the first length portion and the second length portion of the superconducting tape simultaneously, and the superconducting tape will enter a state of magnetic flux motion.

[0067] like Figure 2A As shown, the direction of the aforementioned changing magnetic field can be parallel to the wide and thick surface of the superconducting tape, with an angle α between it and the width 111 ranging from 0 to ±60 degrees. Figure 2B As shown, the direction of the aforementioned changing magnetic field can be parallel to the length and width of the superconducting tape, and the angle β between it and the length 113 is 0 to 360 degrees.

[0068] like Figure 1 As shown, when the superconducting tape is connected to a superconducting load to form a closed loop, and a current source is used to provide transmission current to the superconducting tape, if the transmission current is greater than the load current in the superconducting load and the superconducting tape is in a state of magnetic flux motion, the superconducting tape exhibits a "cross-magnetic field" effect. Figure 3B , Figure 4A , Figure 4B As shown, the magnetic flux of a changing magnetic field will link with a closed loop. According to Faraday's law: Δi L As can be seen from ΔΦ / L, the increased linkage flux in the superconducting load circuit leads to an increase in the current within the circuit, thus enabling control of the superconducting load current. The precision of this control can reach 2.067*10⁻⁶. -15 A*H. At this point, the output voltage across the two ends of the superconducting tape can also be controlled, with a control precision of 1*10. -15 At this point, the superconducting tape can also be considered as a controllable resistor, and its resistance adjustment accuracy can reach 1*10. -18 Ω. If the transmission current is less than the load current in the superconducting load, or the transmission current is 0, or the direction is opposite to the load current and the superconducting tape is in a state of magnetic flux motion, the magnetic flux will not link with the load, thereby reducing the load loop current.

[0069] like Figure 4C As shown, if no changing magnetic field is applied to the superconducting tape, the superconducting tape is in a non-magnetic flux motion state. At this time, the magnetic flux in the closed loop is conserved, and the magnetic flux cannot disappear or link with the closed loop.

[0070] like Figure 5A , Figure 5B As shown, the length and width of the first length portion of the superconducting tape can also be parallel to the length and width of the second length portion, and the length and width of the first length portion is located above or below the length and width of the second length portion. In this case, the magnetic field generator selectively applies a changing magnetic field to the superconducting tape. The direction of this magnetic field can be parallel to the width of the superconducting tape, or it can be at a certain angle to the superconducting tape. Figure 2A , Figure 2B The described angle range is consistent. At this time, the superconducting tape enters a state of magnetic flux motion. By reasonably setting the magnitude and direction of the transmission current, the magnetic flux can be linked or not linked to the load circuit, thereby controlling the current in the superconducting load, the voltage across the superconducting tape, and the equivalent resistance of the superconducting tape.

[0071] like Figure 6 The diagram shows the equivalent circuit of the superconducting excitation device with the magnetic field direction indicated in the two operating modes described above.

[0072] like Figures 1 to 4C The first embodiment of the invention is shown. The superconducting excitation device 100 includes a superconducting tape 101, a superconducting load 102, a current source 110, and a magnetic field generator 109. The superconducting tape 101 has a width 111 and a thickness 112, with the width 111 being greater than the thickness 112. A portion of the length 113 of the superconducting tape 101 is located in the same plane as the width 111.

[0073] like Figure 7The superconducting tape 101 shown is a second-generation superconducting thin film or tape, with a thickness 112 of approximately 1*10. -6 m. In other experimental setups, the thickness may also be 1*10 m. -9 m and 1*10 -3 Between m.

[0074] The width 111 can be 4mm, 6mm, 10mm or 12mm.

[0075] The current source 110 provides transmission current 103 to the superconducting tape 101 through the current terminal 118.

[0076] refer to Figure 1 , Figure 3A as well as Figure 4A The superconducting tape 101 is composed of a first length portion 106 and a second length portion 107. The first length portion 106 is adjacent to the second length portion 107. The first length portion 106 is approximately parallel to the second length portion 107, and the lengths 113 and widths 111 of the first length portion 106 and the second length portion 107 are located on the same plane.

[0077] The transmission current 103 forms a current path 116 in the first length portion 106 and a current return path 117 in the second length portion 107. The current flowing through the superconducting tape passes through the current path 116 and the current return path 117. The relative positions of the first length portion 106 and the second length portion 107 cause the current flowing through the current path 116 and the current return path 117 to be substantially opposite in direction.

[0078] refer to Figure 1 It can be seen that the current path 116 of the first length portion 106 flows to the left end, and the current return path 117 of the second length portion 107 flows to the right end. (Reference) Figure 3A and Figure 4A The current path 116 of the first length portion 106 flows out of the plane, and the current return path 117 of the second length portion 107 flows inward. The relative position and structure of the current path 116 of the first length portion 106 and the current return path 117 of the second length portion 107 can reduce the inductance of the superconducting tape 101.

[0079] The transmission current 103 can be a constant current or a time-varying current. The transmission current 103 is delivered to the superconducting tape 101 through a superconducting material or a partially resistive conductive material. The current source 110 can be any device that can output current, such as a power electronic power supply, a transformer, or a flux pump. To reduce the ripple of the magnetic field and current in the superconducting load 102, a flux pump can be used as the current source 110 to provide a highly stable transmission current 103.

[0080] The magnetic field generator 109 is used to selectively apply a changing magnetic field 104 to the superconducting tape 101. That is, the changing magnetic field 104 can be applied to the superconducting tape 101 at any time, or it can be applied to the superconducting tape 101 at preset time intervals. The magnetic field generator 109 can apply the changing magnetic field 104 by program control or by user control.

[0081] A variable magnetic field 104 is selectively applied to a first length portion 106 and a second length portion 107. The variable magnetic field 104 is applied such that the magnetic flux 105 is parallel to the plane formed by a portion of the length 113 and width 111 of the superconducting tape 101.

[0082] refer to Figure 1 , Figure 3A and Figure 4A In a first embodiment, magnetic flux 105 is selectively applied to a first length portion 106 and a second length portion 107, the direction of which is parallel to the width 111 of the first length portion 106 and the width 111 of the second length portion 107. The magnetic flux 105 in the first embodiment interacts with the first length portion 106 and the second length portion 107, resulting in a "cross-field" effect.

[0083] The magnetic field generator 109 can be a constant conductor electromagnet, a superconducting electromagnet, a movable permanent magnet, or any device capable of generating a changing magnetic field. If the changing magnetic field 104 is generated by a changing current, the field strength of the changing magnetic field 104 can be changed by altering the changing current. To ensure that the amplitude of the changing magnetic field 104 is sufficiently large, a DC component will also be present in the changing magnetic field 104. The amount of magnetic flux 105 passing through the superconducting tape 101 per AC cycle is related to the following factors:

[0084] 1. Proportional to the amplitude of the changing magnetic field 104;

[0085] 2. The thickness of the superconducting tape under the action of a changing magnetic field is 112.

[0086] 3. The length 113 is proportional to the length of the first length portion 106 and the second length portion 107 under the action of the changing magnetic field;

[0087] 4. Proportional to the magnitude of the current passing through current path 116 and current return path 117;

[0088] 5. The critical current of the superconductor is inversely proportional to that of the first length portion 106 and the second length portion 107.

[0089] refer to Figure 6 , Figure 6 This is the equivalent circuit diagram of the superconducting excitation device. Figure 6The directions of the magnetic fields applied to the first length portion 106 and the second length portion 107 are shown in the figure. When current flows through the first length portion 106 of the superconducting tape 101, the magnetic flux 105a acts unidirectionally on the current. Figure 6 In the example shown, the magnetic flux 105a is directed to the right. When current flows through the second length portion 107 of the superconducting tape 101, the magnetic flux 105b acts unidirectionally on the current. Figure 6 In the example shown, the magnetic flux 105b is oriented to the left. In this case, the actual direction of motion of the magnetic flux is perpendicular to both magnetic fluxes 105a and 105b. That is, the magnetic flux 105a applied to the first length portion 106 moves out of the plane, while the magnetic flux 105b applied to the second length portion 107 moves inward into the plane. According to Faraday's law, the magnetic flux moves in opposite directions in the first length portion 106 and the second length portion 107, thus inducing voltages in the same direction in both length portions 106 and 107.

[0090] refer to Figure 1 , Figure 3B , Figure 4B , Figures 4C to 6 The superconducting load 102 is connected to the superconducting tape 101 to form a closed loop. This closed loop can be fully superconducting or it can have partial resistance. The resistance of this closed loop may be the resistance of the weld joint or the equivalent resistance generated by the magnetic flux creep effect of the high-temperature superconductor.

[0091] The superconducting load 102 can be of any shape and size. (Reference) Figure 1 The superconducting load 102 is a coil; reference Figure 7 The superconducting load 102 is a thin superconducting sheet or a thin superconducting tape. The load current 119 flowing through the superconducting load 102 can be adjusted.

[0092] The superconducting load 102 can be made of rare earth barium copper oxide (ReBCO), bismuth strontium calcium copper oxide (BSCCO), magnesium diboride (MgB2), and other materials.

[0093] Ideally, the superconducting load 102 is fully superconducting. However, in practical engineering, the superconducting load 102 is often not fully superconducting and contains a small local equivalent resistance.

[0094] The load current 119 flowing through the superconducting load 102 can be controlled, with a control resolution of approximately 2.067*10. -15 A*H.

[0095] The control device and method for regulating the load current 119 are applicable to the precise control of current in all types of superconducting magnets, especially high-temperature superconducting magnets. The control device and method for regulating the load current 119 can be used to regulate the current in the main magnet, padding coil, and shielding coil in nuclear magnetic resonance imaging (NMR). It can also be used in magnetic resonance imaging (MRI), superconducting quantum interference devices (SQIs), gravimeters, scientific magnets, micro-instruments, or other devices containing fully superconducting magnets or magnets with low equivalent resistance. For superconducting quantum interference device (SQI) sensors, regulating their load current 119 can remove trapped magnetic flux, thereby improving the signal-to-noise ratio and magnetic field detection sensitivity.

[0096] The transmission current 103 flows into the superconducting tape 101 and the superconducting load 102. That is, the transmission current 103 is equal to the sum of the current in the superconducting tape 101 and the load current 119 in the superconducting load 102. The current flowing into the superconducting tape 101 and the current flowing into the superconducting load 102 are inversely proportional to their respective self-inductances. Since the self-inductance of the superconducting load 102 is significantly greater than that of the superconducting tape 101, in this case, when the transmission current 103 is applied to the superconducting excitation device 100, the vast majority of the transmission current 103 will flow into the superconducting tape 101.

[0097] The position of the current terminal 118 into the closed loop, through which the transmission current 103 flows, determines which part of the loop is the superconducting tape 101 and which part is the superconducting load 102. For example... Figure 7 The figure shows the experimental setup of the superconducting excitation device 100 provided in the first embodiment. The superconducting tape and the superconducting load are made of the same material, forming a single-turn closed loop. Figure 7 The superconducting load 102 is located to the right of the current terminal 118 in the closed loop where the transmission current 103 flows, and the superconducting tape 101 is located to the left of the current terminal 118. In order to ensure that the transmission current 103 mainly flows into the superconducting tape 101, the loop area of ​​the superconducting load 102 is larger than that of the superconducting tape 101, so that the loop of the superconducting load 102 has a larger self-inductance.

[0098] The resolution of flux control in the superconducting load 102 can be adjusted by controlling one or more of the following options:

[0099] 1. The magnitude and direction of the transmission current 103, or the magnitude and direction of the current flowing into current path 116 and current return path 117. The larger the transmission current 103, the greater the rate of change of the regulated magnetic flux, and the lower the regulation resolution.

[0100] 2. Dimensions and shape of the superconducting tape 101. Specifically, the thickness 112 or the width 111 of the superconducting tape. The larger the thickness 112 or the width 111, the lower the precision of magnetic flux control. The width 111 only affects the precision of magnetic flux control when the changing magnetic field 104 is not parallel to the length and width of the superconducting tape 101.

[0101] 3. The angle between the changing magnetic field 104 and the superconducting tape 101. (Reference) Figure 2A When the changing magnetic field 104 is parallel to the wide and thick surface of the superconducting tape 101, the angle between the changing magnetic field 104 and the width 111 is α, and the angle range is from 0 degrees to 60 degrees. The smaller the absolute value of the angle α, the smaller the rate of change of the controlled load magnetic flux, and the higher the control precision.

[0102] 4. The length of the superconducting tape 101 subjected to the changing magnetic field 104. That is, the length 113 of the first length portion 106 and the second length portion 107 of the superconducting tape 101. The longer this length, the greater the rate of change of the controlled magnetic flux, and the lower the control precision.

[0103] 5. The rate of change of the changing magnetic field 104. The frequency of the changing current affects the rate of change of the changing magnetic field 104. The higher the frequency of the changing current or the higher the rate of change of the changing magnetic field 104, the greater the rate of change of the controlled load magnetic flux, and the lower the control accuracy.

[0104] 6. Amplitude of the changing magnetic field 104. The larger the amplitude, the greater the rate of change of the controlled load magnetic flux. When a DC bias exists in the changing magnetic field 104, both the amplitude of the AC magnetic field and the amplitude of the DC magnetic field will affect the rate of change of the load magnetic flux. The DC magnetic field bias will affect the critical current of the first length portion 106 and the second length portion 107 of the superconducting tape 101. The larger the DC magnetic field bias, the lower the critical current, and the lower the accuracy of load magnetic flux control.

[0105] 7. Duration of the changing magnetic field 104. When the changing magnetic field 104 is alternately applied to the superconducting tape 101, the duration of its application affects the rate of change and the precision of the controlled magnetic flux. Specifically, within a 10s period, if the 100Hz changing magnetic field 104 is applied for 1s, the load current 119 will increase by 1A. If the 100Hz changing magnetic field 104 is applied for 2s, the load current 119 will increase by 2A. In the above example, the average rate of current increase within 10s is 0.1A / s and 0.2A / s, respectively.

[0106] 8. Temperature of superconducting tape 101 and superconducting load 102 or superconducting excitation device 100.

[0107] The magnetic field generator 109 is used to regulate the speed and accuracy of magnetic flux injection into the load. In a first embodiment, two magnetic field generators 109 are used to regulate the load magnetic flux at different speeds. One magnetic field generator applies a magnetic field with an α angle of 0 degrees to achieve higher magnetic flux regulation accuracy. The other magnetic field generator applies a magnetic field with an α angle of 60 degrees to achieve lower magnetic flux regulation accuracy. The regulation accuracy of the load magnetic flux can be controlled by coordinating the two magnetic field generators. One magnetic field generator can be turned on while the other is turned off, or both magnetic field generators can be turned on simultaneously.

[0108] The superconducting excitation device 100 may also consist only of a superconducting tape 101, a current source 110, and a magnetic field generator 109. Specifically, the current source 110 is connected to the superconducting tape 101 via a current terminal 118 but not to the superconducting load 102. In this case, the superconducting tape 101 does not form a closed loop with the superconducting load 102. In this scenario, the superconducting excitation device 100 becomes a high-precision voltage source. When a changing magnetic field 104 is applied to the superconducting tape 101, a high-precision controllable voltage will exist across the current terminal 118 in the superconducting tape 101. That is, the superconducting excitation device 100 can regulate the potential difference across the current terminal 118 in the superconducting tape 101, rather than the current in the superconducting load 102. The regulation accuracy of the voltage across the current terminal 118 is approximately 1*10^6. -15 V.

[0109] When the superconducting excitation device 100 consists only of the superconducting tape 101 and the magnetic field generator 109, the superconducting tape 101 itself can function as a high-precision controllable resistor. The resistance adjustment precision of the superconducting tape 101 is approximately 1*10⁻⁶. -18 Ω. By controlling the waveform of the changing magnetic field 104, the resistance of the superconducting tape 101 can be made quasi-constant. The superconducting tape 101 with highly controllable resistance can be applied to filters or other applications.

[0110] refer to Figure 1 , Figure 3A and Figure 4C A first embodiment of the superconducting excitation device 100 includes providing a transmission current 103 to the superconducting tape 101, forming a current path 116 in a first length portion 106 of the superconducting tape 101, and forming a current return path 117 in a second length portion 107. Specifically, the transmission current 103 is direct current.

[0111] A variable magnetic field 104 is selectively applied to the superconducting tape 101, such that the magnetic flux 105 is parallel to the width 111 of the superconducting tape 101. The variable magnetic field is simultaneously applied to the first length portion 106 and the second length portion 107. The load current 119 is regulated by controlling the amount of magnetic flux linked to the closed loop through the transmission current 103 and the variable magnetic field 104. The variable magnetic field 104 can be applied or not applied at any time or at fixed time intervals. The application of the variable magnetic field 104 can be controlled by a program or by a user.

[0112] When a changing magnetic field 104 is applied to the superconducting tape 101, the superconducting tape 101 is in a state of magnetic flux motion. When the superconducting tape 101 is in a state of magnetic flux motion, the magnetic flux 105 may or may not link to a closed loop. The amount of magnetic flux linking to the closed loop depends on the magnitude of the transmission current 103 and the magnitude of the load current 119 in the superconducting load 102. The magnitude of the regulated load current 119 in the superconducting load 102 is proportional to the amount of magnetic flux linking to the closed loop. According to Faraday's law of electromagnetic induction: Δi L =ΔΦ / L, the change Δi of the load current 119 in the superconducting load 102 L Based on the change ΔΦ of the magnetic flux linked with the closed loop, and L being the inductance of the superconducting load 102, an increase in the magnetic flux linked with the closed loop will lead to an increase in the load current 119 in the superconducting load 102, and vice versa.

[0113] refer to Figure 3B In the example shown, initially there are three magnetic fluxes 108 linked to a closed loop. A magnetic field generator 109 applies a changing magnetic field 104 to the superconducting tape 101, thus placing the superconducting tape 101 in a state of magnetic flux motion. This produces... Figure 3B The single magnetic flux 105 of the changing magnetic field 104 shown in 4B and 4C.

[0114] When the transmission current 103 is greater than the load current 119 in the superconducting load 102, the single magnetic flux 105 links with the closed loop. (Reference) Figures 3A to 4B The single magnetic flux 105 was from Figure 3A The indicated position is dragged through the gap between the first length portion 106 and the second length portion 107. Figure 4A The position shown. The single magnetic flux 105 of the changing magnetic field 104 is... Figure 4B The method shown links with a closed loop.

[0115] Conversely, when the transmission current 103 is less than the load current 119 in the superconducting load 102, the magnetic flux 105 does not link with the closed loop. When the transmission current 103 is 0 or opposite in direction to the load current 119 in the superconducting load 102, the magnetic flux 105 does not link with the closed loop. In this case, the magnetic flux 105 from Figure 4A The position shown was pulled to Figure 3A The location shown. (As indicated) Figure 3B As shown, magnetic flux 105 does not link with the closed loop.

[0116] In some cases, even without a pre-linked magnetic flux 108 to the closed loop, the flux can still be pulled out of the closed loop so that it does not link with it. In this situation, the negative flux will link with the closed loop, and its direction of motion will be opposite to that of the positive flux. The direction of flux motion is determined by the direction of the current in the superconducting tape 101. According to Faraday's law: Δi L =ΔΦ / L, the movement of the magnetic flux 105 through the superconducting tape 101 generates a voltage. The direction of this voltage depends on the direction of the current in the superconducting tape 101.

[0117] According to Ampere's law: Φ = Li L The direction of the load current is determined by the magnetic flux linked with the load, where L is the inductance and i L This represents the amplitude and direction of the current.

[0118] refer to Figure 4C When the magnetic field generator 109 does not apply a changing magnetic field 104 or the magnetic field 104 is unchanged, the superconducting tape 101 is in a state of no magnetic flux movement. At this time, no new magnetic flux 105 will link with the closed loop, and the magnetic flux 108 linked with the closed loop cannot disappear or cannot be disconnected from the closed loop.

[0119] Therefore, refer to Figure 3B and Figure 4B Since the single magnetic flux 105 links with the closed loop, the total magnetic flux linked with the closed loop increases from the initial three magnetic fluxes 118 to four magnetic fluxes. This causes the load current 118 to increase.

[0120] refer to Figure 4B and Figure 4C When the magnetic field generator 109 stops applying the changing magnetic field 104 to the superconducting tape 101, the magnetic flux 108 that initially linked with the closed loop and the single magnetic flux 105 that later linked with the closed loop remain linked with the closed loop.

[0121] When the transmission current 103 is an alternating current, the magnetic field generator 109 selectively applies or does not apply a changing magnetic field 104 to the superconducting tape 101 according to the frequency of the alternating transmission current 103. Specifically, when the alternating transmission current 103 is greater than the load current 119, the changing magnetic field 104 is applied to the superconducting tape 101, thereby causing the magnetic flux 105 to link with the closed loop. When the alternating transmission current 103 is in the negative half-wave of its period or less than the load current 119, the changing magnetic field 104 is not applied to the superconducting tape 101, thereby preventing the magnetic fluxes 105 and 108 from not linking with the closed loop. The same logic applies to non-alternating transmission current 103.

[0122] Figure 5A and Figure 5B A second embodiment of the superconducting excitation device 200 of the present invention is shown. Except as described below, the structure, function and options of the superconducting excitation device 200 are the same as those of the superconducting excitation device 100 of the first embodiment.

[0123] In the second embodiment, the superconducting excitation device 200 includes a superconducting tape 201, which includes a first length portion 206 and a second length portion 207. The first length portion 206 is parallel to the second length portion 207, and the length 113 and width 111 of the first length portion 206 are located in the same plane, which is located above or below the plane containing the length 113 and width 111 of the second length portion 207. The special structure of the superconducting tape 201 in the superconducting excitation device 200 generates a "magnetic flux oscillation" effect. The equivalent circuit of the superconducting excitation device 200 is as follows: Figure 6 As shown.

[0124] refer to Figures 8A to 8C The figure illustrates the direction of the varying magnetic field 104 applied to the superconducting excitation devices 100 and 200 in the first and second embodiments. Magnetic flux 105 is selectively applied to the superconducting excitation devices 100 and 200. The magnetic field direction is parallel to the length 113 of the first length portions 106 and 206 and the length 113 of the second length portions 107 and 207. This varying magnetic field results in a "flux cutting" effect. Figure 8A and Figure 8B As shown, the direction of the magnetic flux 105 points inward into the plane, and is the same as the length direction of the first length portion 106, 206 and the second length portion 107, 207. Figure 8C Equivalent circuit diagrams of the two embodiments described above are shown, including the direction of the changing magnetic field, with the magnetic flux 105 having opposite directions in the first length portions 106, 206 and the second length portions 107, 207 of the superconducting tapes 101 and 201.

[0125] As proof of the effectiveness of the aforementioned superconducting excitation device and method, Figure 9Experimental data for the superconducting excitation device provided in the first embodiment are presented. This data shows the change in the linkage flux 108 of the superconducting load 102 as the number of operations of the magnetic field generator 109 increases, under different amplitudes of the varying magnetic field 104. The sensor for measuring the flux 108 is a Hall sensor. Figure 9 The slope of the data represents the number of magnetic fluxes 105 linked to a closed loop when a changing magnetic field 104 is applied. For example... Figure 9 It can be seen that the superconducting excitation device provided in the first embodiment achieves a load current regulation accuracy of 6.18*10. -14 A*H, through optimization of the experimental setup, is expected to achieve higher control precision.

[0126] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A superconducting excitation device, characterized in that, include: Superconducting tape; The superconducting tape includes a first superconducting tape and a second superconducting tape; the long side, wide side, and thick side of the first superconducting tape and the second superconducting tape are parallel, respectively; one end of the long side of the first superconducting tape and the second superconducting tape are connected, and the other end is not connected; the ends of the long sides of the first superconducting tape and the second superconducting tape that are not connected are respectively designated as a first terminal and a second terminal; the width of the first superconducting tape and the second superconducting tape is greater than their thickness; The superconducting tape is connected to the superconducting load to form a closed loop, with the first terminal connected to one end of the superconducting load and the second terminal connected to the other end of the load. The transmission current flows into the first superconducting tape through the first terminal and flows out from the second terminal of the second superconducting tape. The directions of the transmission current in the first superconducting tape and the second superconducting tape are opposite. When the superconducting tape is placed in a changing magnetic field, when the transmission current is greater than the current of the superconducting load and the direction of the transmission current is the same as the direction of the load current, under the action of the opposite transmission current on the first and second superconducting tapes, the magnetic flux of the changing magnetic field links with the closed loop, thereby increasing the current of the superconducting load, so as to regulate the current of the superconducting load through the linked magnetic flux.

2. The superconducting excitation device according to claim 1, characterized in that, When the superconducting tape is placed in a changing magnetic field, causing it to be in a state of magnetic flux motion, if the transmission current is less than the current of the superconducting load, the transmission current is 0, or the direction of the transmission current is opposite to the direction of the load current, then the magnetic flux linked with the closed loop decreases, thereby reducing the current of the superconducting load.

3. The superconducting excitation device according to claim 1, characterized in that, When the direction of the changing magnetic field is parallel to the wide and thick surface of the superconducting tape, the angle between the magnetic field direction and the wide side is defined as a first angle, and the range of the first angle is 0 degrees to 60 degrees; or When the direction of the changing magnetic field is parallel to the length and width of the superconducting tape, the angle between the magnetic field direction and the long side is defined as the second angle, which ranges from 0 degrees to 360 degrees.

4. The superconducting excitation device according to claim 3, characterized in that, The smaller the absolute value of the first angle of the direction of the changing magnetic field, the higher the precision of magnetic flux control.

5. The superconducting excitation device according to any one of claims 1 to 4, characterized in that, The changing magnetic field has a DC component to ensure that the amplitude of the changing magnetic field meets the requirements. Under the influence of a changing magnetic field, the amount of magnetic flux passing through the superconducting tape per alternating cycle is related to the following factors: Proportional to the amplitude of the changing magnetic field; The thickness of the superconducting tape is proportional to the change in magnetic field acting on it. It is proportional to the length of the superconducting tape subjected to the changing magnetic field; Proportional to the magnitude of the transmitted current; It is inversely proportional to the critical current of the superconducting tape.

6. The superconducting excitation device according to any one of claims 1 to 4, characterized in that, The precision of flux control in the superconducting load is also related to the following factors: The larger the transmission current, the lower the precision of the control of the superconducting load flux, and the faster the control speed. The greater the thickness or length of the superconducting tape under the influence of the changing magnetic field, the lower the control precision of the superconducting load flux and the faster the control speed. When the first angle is not 0 degrees, the wider the changing magnetic field acts on the superconducting tape, the lower the control precision of the superconducting load magnetic flux and the faster the control speed. The greater the rate of change of the magnetic field strength of the changing magnetic field, the lower the control precision of the superconducting load flux and the faster the control speed. The larger the DC magnetic field bias of the changing magnetic field, the lower the critical current of the first and second superconducting tapes, the lower the control precision of the superconducting load flux, and the faster the control speed. The longer the changing magnetic field acts over a period of time, the greater the average rate of increase in the superconducting load magnetic flux.

7. The superconducting excitation device according to any one of claims 1 to 4, characterized in that, The superconducting tape is made of rare earth barium copper oxide (ReBCO), bismuth strontium calcium copper oxide (BSCCO), or magnesium diboride (MgB2).

8. A superconducting excitation method, characterized in that, Includes the following steps: A superconducting tape is defined; the superconducting tape includes a first superconducting tape and a second superconducting tape; the long side, wide side, and thick side of the first superconducting tape and the second superconducting tape are parallel, respectively; one end of the long side of the first superconducting tape and the second superconducting tape are connected, and the other end is not connected; the ends of the long sides of the first superconducting tape and the second superconducting tape that are not connected are respectively designated as a first terminal and a second terminal; the width of the first superconducting tape and the second superconducting tape is greater than their thickness; The superconducting tape is connected to the superconducting load to form a closed loop, with the first terminal connected to one end of the superconducting load and the second terminal connected to the other end of the load. The control transmission current flows into the first superconducting tape through the first terminal and flows out from the second terminal of the second superconducting tape; the transmission current flows in opposite directions on the first and second superconducting tapes; When the superconducting tape is placed in a changing magnetic field, when the transmission current is greater than the current of the superconducting load and the direction of the transmission current is the same as the direction of the load current, under the action of the opposite transmission currents on the first and second superconducting tapes, the magnetic flux of the changing magnetic field links with the closed loop, thereby increasing the current of the superconducting load and regulating the current of the superconducting load through the linked magnetic flux.

9. The superconducting excitation method according to claim 8, characterized in that, It also includes the following steps: When the superconducting tape is placed in a changing magnetic field, and the superconducting tape is in a state of magnetic flux motion, if the transmission current is less than the current of the superconducting load, the transmission current is 0, or the direction of the transmission current is opposite to the direction of the load current, then the magnetic flux linked with the closed loop decreases, thereby reducing the current of the superconducting load.

10. The superconducting excitation method according to claim 8, characterized in that, When the direction of the changing magnetic field is parallel to the wide and thick surface of the superconducting tape, the angle between the magnetic field direction and the wide side is defined as a first angle, and the range of the first angle is 0 degrees to 60 degrees; or When the direction of the changing magnetic field is parallel to the length and width of the superconducting tape, the angle between the magnetic field direction and the long side is defined as the second angle, which ranges from 0 degrees to 360 degrees.

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