A superconducting magnet with ultra-high current density and its wireless excitation device

Abstract

This invention discloses an ultra-high current density superconducting magnet and its wireless excitation device. The superconducting magnet includes superconducting magnet coil units and multiple superconducting strips connected in parallel. Each superconducting magnet coil unit includes a magnet coil frame and magnet coils wound on the frame. The superconducting magnet coil units are stacked, with one end connected to a busbar of one superconducting strip and the other end connected to a busbar of another superconducting strip. The two busbars are connected by superconducting flying wires. This invention uses a parallel connection to automatically distribute current among the coils. When the operating current of one coil exceeds its critical current, the current automatically flows to other coils, causing the current in coils whose operating current has not reached the critical current to continue to increase. Ultimately, all coils can operate close to their respective critical currents, increasing the operating current of each coil and significantly improving the engineering current density of the magnet.

Description

Technical Field

[0001] This invention belongs to the field of superconducting magnet technology, and more specifically, relates to a superconducting magnet with ultra-high current density and its wireless excitation device. Background Technology

[0002] Strong magnetic field environments are among the most important extreme experimental conditions in scientific research, and are also essential requirements in fields such as MRI, terahertz technology, and electromagnetic shaping. Superconducting materials, due to their excellent current-carrying capacity in the superconducting state, have become important current-carrying materials for generating strong magnetic fields.

[0003] High-temperature superconducting magnets operating in low-temperature environments rely on power electronic power supplies operating at room temperature to supply power through thick metal current leads. The heat conduction and ohmic losses of the leads will generate a large heat load in the low-temperature environment, which not only poses a challenge to the cooling system, but also easily causes temperature rise that can induce superconducting magnets to lose quench.

[0004] To reduce the low-temperature thermal load from the current leads, the operating current of the superconducting magnet must be reduced to decrease the diameter of the current leads. Therefore, superconducting magnets often employ a multi-coil series operation mode. However, the critical current density J of superconducting materials, especially high-temperature superconducting tapes represented by ReBCO and Bi2223, is relatively high. c The magnetic field B and the angle θ between the magnetic field and the strip surface are significantly affected. The magnetic field B and the angle θ are different at different positions of the coil, so the critical current density J of the strip at different positions of the magnet is different. c Unlike other magnets, the angle θ at the magnet's end is close to 90°, resulting in a very small critical current in the superconducting tape and a significant decrease in the current-carrying capacity of the end coils. The series connection method clamps the magnet's operating current to the end coil with the smallest critical current, greatly limiting the overall current density of the magnet. Furthermore, in a magnet with multiple coils operating in series, if one coil fails, the others will also malfunction, leading to low safety margins and poor reliability. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an ultra-high current density superconducting magnet and its wireless excitation method and device, which aims to solve the problem of limited operating current density of the magnet caused by series power supply of the superconducting magnet, further improve the current density and electrothermal stability of the magnet, and reduce the low-temperature thermal load.

[0006] This invention provides an ultra-high current density superconducting magnet, comprising superconducting magnet coil units connected in parallel and multiple superconducting strips; the superconducting magnet coil unit includes a magnet coil frame and a magnet coil wound on the magnet coil frame; the superconducting magnet coil units are stacked, and one end of the superconducting magnet coil unit is connected to a superconducting strip busbar, and the other end of the superconducting magnet coil unit is connected to another superconducting strip busbar, and the two superconducting strip busbars are connected by a flying wire.

[0007] During operation, due to the parallel structure of the superconducting magnet coil units, the current is automatically distributed among the various superconducting magnet coil units, allowing each superconducting magnet coil unit to have a different operating current. When the operating current of one superconducting magnet coil unit exceeds its critical current, the current will automatically flow to other superconducting magnet coil units, causing the current of the superconducting magnet coil units whose operating current has not reached the critical current to continue to increase. Ultimately, all superconducting magnet coil units can operate close to their respective critical currents, thereby increasing the operating current of each coil and improving the engineering current density.

[0008] More preferably, when four superconducting magnet coil units are stacked, the equivalent circuit of the superconducting magnet includes: a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a first inductor L1, a second inductor L2, a third inductor L3, and a fourth inductor L4; the first resistor R1 is connected in series with the first inductor L1; the second resistor R2 is connected in series with the second inductor L2; the third resistor R3 is connected in series with the third inductor L3; the fourth resistor R4 is connected in series with the fourth inductor L4; the non-series connection terminals of the first resistor R1, the second resistor R2, and the third resistor R4 are connected in series with the fourth inductor L4. The non-series connection terminal of 3 and the non-series connection terminal of the fourth resistor R4 are connected in parallel to the positive terminal of the induced current i. The non-series connection terminals of the first inductor L1, the second inductor L2, the third inductor L3, and the fourth inductor L4 are connected in parallel to the negative terminal of the induced current i. Wherein, the first inductor L1, the second inductor L2, the third inductor L3, and the fourth inductor L4 represent the inductances of the four coils, the first resistor R1, the second resistor R2, the third resistor R3, and the fourth resistor R4 represent the nonlinear resistances of the superconducting tape, and i represents the current of the equivalent excitation current source of the superconducting magnet.

[0009] The value of the induced current i is equal to the sum of the operating currents of the four superconducting magnet coil units.

[0010] The present invention also provides a wireless excitation device based on the above-mentioned ultra-high current density superconducting magnet, comprising: a rotor and a stator; a permanent magnet for generating a rotating magnetic field is provided on the rotor; the stator is composed of flying wires of superconducting tape, and the flying wires of superconducting tape are connected to both ends of each superconducting tape busbar to form a parallel connection, thereby forming a closed loop.

[0011] More preferably, the flying wires of the superconducting tape are arranged in a uniform circumferential distribution.

[0012] During operation, the rotor rotates, and the magnetic field of the permanent magnet cuts the stator superconducting tape flying wire. Due to the self-rectification effect of the superconducting tape, a DC electromotive force is generated on the superconducting tape, which in turn generates a DC current in the superconducting tape, providing wireless power to the closed superconducting magnet.

[0013] Furthermore, the rotor is positioned in the ambient temperature region, while the stator and the superconducting magnet are positioned in the cryogenic region. The ambient temperature region and the cryogenic region can be separated by a ring-shaped Dewar breaker, with the cryogenic region inside the ring-shaped Dewar breaker and the ambient temperature region outside the ring-shaped Dewar breaker.

[0014] Compared with the prior art, the present invention has the following technical advantages based on the above-described technical solutions:

[0015] (1) The present invention adopts a parallel connection method so that the current can be automatically distributed in each coil. When the working current of one coil exceeds its critical current, the current will automatically flow to other coils, so that the current of the coil whose working current has not reached the critical current continues to increase. In the end, all coils can work at close to their respective critical currents, thereby solving the bottleneck problem that the working current of the traditional series connection method between magnet coils is limited by the coil with a smaller critical current, increasing the working current of each coil and significantly improving the engineering current density of the magnet.

[0016] (2) In this invention, since the magnet coils are connected in parallel, when a coil fails to quench, the resistance of the coil branch increases significantly, and its current can be automatically distributed to other coils that have not failed to quench, preventing the thermal load generated by the large current in the failure branch from having a negative impact on the magnet and the refrigeration system, and further enhancing the electrothermal stability of the magnet.

[0017] (3) This invention can be applied to non-insulated magnets, so that the coil works in a saturated state and the current fills the entire area of ​​the superconducting layer of the strip, which can eliminate problems such as excessive stress and magnetic field configuration distortion caused by shielding current. Attached Figure Description

[0018] Figure 1 This is a three-dimensional structural diagram of the ultra-high current density superconducting magnet provided in the embodiment of the present invention;

[0019] Figure 2(a) is a top view of the superconducting magnet with ultra-high current density provided in the embodiment of the present invention; (b) is a three-dimensional structural view of the superconducting magnet with ultra-high current density provided in the embodiment of the present invention from different angles.

[0020] Figure 3 This is an equivalent circuit diagram of a superconducting magnet with ultra-high current density provided in an embodiment of the present invention;

[0021] Figure 4 This is a schematic diagram of the structure of the wireless excitation device based on a superconducting magnet with ultra-high current density provided in the embodiment of the present invention, wherein (a) and (c) represent two three-dimensional structural views of the wireless excitation device from two different angles, and (b) is a top view of the wireless excitation device.

[0022] Figure 5 This is a cross-sectional schematic diagram of the room temperature region and the low temperature region provided in the embodiment of the present invention. The dots and crosses indicate the direction of current flow in the superconducting magnet coil. The dots indicate that the current flow is outward from the paper and the crosses indicate that the current flow is inward from the paper.

[0023] Figure 6 This is a schematic diagram of the structure of a non-insulated superconducting magnet system based on an ultra-high current density superconducting magnet provided in an embodiment of the present invention. (a) and (c) are two three-dimensional structural views of the non-insulated superconducting magnet system from two different angles, and (b) is a bottom view of the non-insulated superconducting magnet system.

[0024] In the diagram, the same number indicates the same physical meaning. Among them, 1 is the stator superconducting tape flying wire, 2 is the magnet coil skeleton, 3 is the superconducting magnet coil, 4 is the superconducting tape busbar, 5 is the rotor, 6 is the permanent magnet, 7 is the rotating motor rotor prime mover, 8 is the outer wall of the transmission structure, 9 is the stator outer wall, 10 is the copper thermally conductive outer reinforcement plate, 11 is the Dewar, and 100 is the parallel superconducting magnet. Detailed Implementation

[0025] 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.

[0026] In this invention, the superconducting magnets are connected in parallel, and the current is automatically distributed among the coils, so that the operating current of each coil can be different. When the operating current of one coil exceeds its critical current, the current will automatically flow to other coils, so that the current of the coils whose operating current has not reached the critical current continues to increase. In the end, all coils can operate close to their respective critical currents, thereby increasing the operating current of each coil and improving the engineering current density.

[0027] Figure 1The structure of a superconducting magnet provided in an embodiment of the present invention is shown. The superconducting magnet consists of stacked superconducting coils and a parallel structure formed by multiple superconducting strip busbars shorted together. For ease of explanation, only the parts relevant to the embodiment of the present invention are shown, and are described in detail below:

[0028] The superconducting magnet provided in this embodiment of the invention is composed of multiple single-pane coils or double-pane coils stacked together. The ends of the coils are connected by multiple superconducting tape busbars, that is, one end of each coil wire is connected to one superconducting tape busbar and the other end is connected to another superconducting tape busbar, forming a parallel structure, as shown in the figure. Figure 1 and Figure 2 As shown. Parallel connection allows for automatic current distribution among the coils, meaning each coil can have a different operating current. When the operating current of one coil exceeds its critical current, the current automatically flows to other coils, causing the current in the coils whose operating current has not reached the critical current to continue to increase. Ultimately, all coils can operate close to their respective critical currents, thus increasing the operating current of each coil and improving the engineering current density.

[0029] Its equivalent circuit is as follows Figure 3 As shown, L1, L2, L3, and L4 represent the inductances of the four coils, R1, R2, R3, and R4 represent the nonlinear resistances of the superconducting tape, and i represents the induced current, which is the current generated by the rotor magnetic field cutting the stator superconducting tape flying wires. The value of i is equal to the sum of the operating currents of the four coils. The parallel connection allows for automatic current distribution among the coils, meaning each coil can have a different operating current. When the operating current of one coil exceeds its critical current, the current automatically flows to the other coils, causing the current in the coils whose operating current has not reached the critical current to continue to increase, ultimately enabling all coils to operate close to their respective critical currents.

[0030] In this embodiment of the invention, the superconducting magnet can be wirelessly excited. The wireless excitation system includes a rotor and a stator. The rotor is equipped with permanent magnets to generate a rotating magnetic field. The stator consists of superconducting tape flying wires, which are evenly distributed along the circumference and can be connected to both ends of each superconducting tape in the magnet busbar, forming a closed loop with the parallel magnets. The wireless excitation process of the superconducting magnet is as follows: When the rotor rotates, the magnetic field of the permanent magnet cuts the stator superconducting tape flying wires. Due to the self-rectification effect of the superconducting tape, a DC electromotive force is generated in the superconducting tape, which in turn generates a DC current, providing wireless power to the closed superconducting magnet. The structure of the wirelessly excited superconducting magnet is as follows: Figure 4 As shown.

[0031] In this embodiment of the invention, the entire device can be divided into a room temperature region and a low temperature region. The rotor and its transmission system are located in the room temperature region, while the superconducting part, including the superconducting magnet and the stator superconducting tape flying wire, is located in the low temperature region. A cross-sectional schematic diagram is shown below. Figure 5 As shown, the solid dots and crosses indicate the direction of current flow in the superconducting magnet coil. The dots indicate that the current flows outward from the paper, and the crosses indicate that the current flows inward from the paper. A ring-shaped Dewar 11 is used to set up a normal temperature zone and a low temperature zone. The inside of the ring-shaped Dewar is the low temperature zone, and the outside of the ring-shaped Dewar is the normal temperature zone. The temperature in the normal temperature zone is room temperature, and the temperature in the low temperature zone is below 77K.

[0032] The superconducting magnet provided in this embodiment of the invention can also be applied to non-insulating superconducting magnet systems. Figure 6 The structure of a non-insulated superconducting magnet system designed according to the above-described superconducting magnet according to an embodiment of the present invention is shown, wherein (a) and (c) are two three-dimensional structural views of the non-insulated superconducting magnet system from two different angles, and (b) is a bottom view of the non-insulated superconducting magnet system; for ease of explanation, only the parts related to the embodiment of the present invention are shown, and are now described in detail below:

[0033] The non-insulated superconducting magnet system consists of two parts: a rotating motor flux pump device and a non-insulated superconducting magnet. The rotating motor flux pump device supplies power to the non-insulated superconducting magnet. The rotating motor flux pump device can be further divided into a rotor and its transmission device and a stator superconducting strip flying wire.

[0034] The rotor and its transmission device are located in the ambient temperature region, while the stator superconducting strip flywires and the non-insulated superconducting magnet are located in the cryogenic region. The transmission system does not require cryogenic conditions; placing it in the ambient temperature region reduces the heat load on the cryogenic refrigeration system and avoids the impact of cryogenic temperatures on the transmission system, which operates normally at ambient temperature. The stator side contains a large amount of superconducting material, hence its placement in the cryogenic region. The non-insulated superconducting magnet consists of four single-pane YBCO coils stacked in parallel, with the inner core material of the coils being copper. The stator superconducting strip flywires consist of six 10mm wide YBCO strips, evenly distributed around the circumference and mounted on a G10 epoxy resin outer wall. One end of each stator superconducting strip flywire is welded to the copper core of the four coils, and the other end is welded to the outermost strip of the coils, thus forming a stacked parallel structure of non-insulated coils.

[0035] 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 magnet with ultra-high current density, characterized in that, Applied to a non-insulated superconducting magnet system, the non-insulated superconducting magnet system includes two parts: a rotating motor flux pump device and a non-insulated superconducting magnet. The rotating motor flux pump device supplies power to the non-insulated superconducting magnet and includes superconducting magnet coil units and multiple superconducting strips connected in parallel. The superconducting magnet coil unit includes a magnet coil frame and a single-disc magnet coil first wound on the magnet coil frame; The superconducting magnet coil units are stacked, with one end of each superconducting magnet coil unit connected to a superconducting tape busbar and the other end of each superconducting magnet coil unit connected to another superconducting tape busbar. The two superconducting tape busbars are connected by a superconducting flying wire. During operation, the current is automatically distributed among the various superconducting magnet coil units, allowing each superconducting magnet coil unit to have a different operating current. When the operating current of one superconducting magnet coil unit exceeds its critical current, the current will automatically flow to other superconducting magnet coil units, causing the current in the superconducting magnet coil units whose operating current has not reached the critical current to continue to increase. Ultimately, all superconducting magnet coil units can operate close to their respective critical currents, thereby increasing the operating current of each coil and improving the engineering current density. When four superconducting magnet coil units are stacked, the equivalent circuit of the superconducting magnet includes: a first resistor R1, a second resistor R2, a third resistor R3, and a fourth resistor R4. The first resistor R1, the second resistor R2, the third resistor R3, and the fourth resistor R4 represent the nonlinear resistances of the superconducting tape.

2. The ultra-high current density superconducting magnet as described in claim 1, characterized in that, The equivalent circuit of the superconducting magnet also includes: a first inductor L1, a second inductor L2, a third inductor L3, and a fourth inductor L4; The first resistor R1 is connected in series with the first inductor L1; The second resistor R2 is connected in series with the second inductor L2; The third resistor R3 is connected in series with the third inductor L3; The fourth resistor R4 is connected in series with the fourth inductor L4; The non-series connection terminals of the first resistor R1, the second resistor R2, the third resistor R3, and the fourth resistor R4 are connected in parallel to the positive terminal of the induced current i, and the non-series connection terminals of the first inductor L1, the second inductor L2, the third inductor L3, and the fourth inductor L4 are connected in parallel to the negative terminal of the induced current i. Wherein, the first inductor L1, the second inductor L2, the third inductor L3 and the fourth inductor L4 represent the inductances of the four coils, and i represents the current of the equivalent excitation current source of the superconducting magnet.

3. The ultra-high current density superconducting magnet as described in claim 2, characterized in that, The value of the current i of the equivalent excitation current source of the superconducting magnet is equal to the sum of the operating currents of the four superconducting magnet coil units.

4. A wireless excitation device based on the ultra-high current density superconducting magnet according to any one of claims 1-3, characterized in that, include: Rotor and stator; The rotor is equipped with a permanent magnet for generating a rotating magnetic field. When the permanent magnet rotates with the rotor, it generates a rotating magnetic field. The stator is composed of flying wires of superconducting tape, and the flying wires of superconducting tape are connected to both ends of each superconducting tape busbar to form a closed loop.

5. The wireless excitation device as claimed in claim 4, characterized in that, The flying wires of the superconducting tape are distributed uniformly along the circumference.

6. The wireless excitation device as claimed in claim 4, characterized in that, During operation, the rotor rotates, and the rotating magnetic field generated by the permanent magnet cuts the stator superconducting tape flying wire. Due to the self-rectification effect of the superconducting tape, a DC electromotive force is generated on the superconducting tape, which in turn generates a DC current in the superconducting tape, which serves as a power source to wirelessly power the closed superconducting magnet.

7. The wireless excitation device according to any one of claims 4-6, characterized in that, The rotor is located in the normal temperature range, while the stator and the superconducting magnet are located in the low temperature range.

8. The wireless excitation device as described in claim 7, characterized in that, The normal temperature zone and the low temperature zone are set by a ring-shaped Dewar, with the low temperature zone inside the ring-shaped Dewar and the normal temperature zone outside the ring-shaped Dewar.

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