Superconducting coil and superconducting magnet device

Abstract

To provide a superconducting coil capable of preventing damage to the superconducting coil and persistent current switch in the event of emergency demagnetization in a high-temperature superconducting magnet device capable of persistent current operation.SOLUTION: A superconducting coil in which both ends of a superconducting coil winding 4 and a persistent current switch 5 are superconductively connected to each other includes a pair of power leads 6 for supplying current to the superconducting coil, and each end includes a superconducting wire (main wire 7) constituting the superconducting coil winding 4, a superconducting wire (PCS wire 8) constituting the persistent current switch 5, and a superconducting connection portion 9 for superconductively connecting them, which are arranged on the power lead 6, the superconducting wire constituting the superconducting coil winding 4 and the power lead 6 being electrically connected to each other. The superconducting coil includes a heater (emergency demagnetization heater 10) for heating the superconducting connection part 9. A diode 13 is arranged between the pair of power leads 6, and the power leads in the pair are electrically connected to each other via the diode.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a superconducting coil capable of being emergency demagnetized, and a superconducting magnet device using the same. [Background technology]

[0002] The basic circuit of a conventional superconducting electromagnet device consists of a superconducting coil, an excitation power supply that supplies current to the superconducting coil, a persistent current switch (PCS) that forms a closed circuit for persistent current operation, and a protective resistor and diode installed in parallel to the superconducting coil. The persistent current switch is heated to cause a normal conductive transition, and current is supplied to the superconducting coil from the excitation power supply. The persistent current switch is then cooled to a superconducting state, and the current supply from the excitation power supply is then stopped, resulting in persistent current operation in which current continues to flow in the closed circuit in the superconducting state consisting of the superconducting coil and the persistent current switch. This allows the superconducting electromagnet to maintain a magnetic field for a long period of time.

[0003] This property is utilized in devices such as MRI (Magnetic Resonance Imaging) and NMR (Nuclear Magnetic Resonance) devices.In addition, because it is possible to move the superconducting coil separately from the excitation power source, it is expected that it will also be used in rotating machines such as generators and motors.

[0004] When it becomes necessary to quickly eliminate the magnetic field in a conventional superconducting magnet, the superconducting coil or the persistent current switch is heated by a heater to cause a normal conductive transition. This diverts the current to the protective resistor and diode installed in parallel with the superconducting coil and the persistent current switch, and the coil current decays as energy is consumed by Joule heating, making it possible to quickly eliminate the magnetic field. This operation is called emergency demagnetization.

[0005] In the case of a device with multiple superconducting coils, a persistent current switch is placed in parallel with the multiple superconducting coils connected in series, and the connections between them are made using superconducting connections that have zero electrical resistance when cooled. This configuration makes it possible to realize persistent current operation that can maintain a magnetic field for a long period of time without current decay, even in a device with multiple superconducting coils. However, because superconducting connections cannot be redone like ordinary solder connections, if any of the multiple superconducting coils or persistent current switches break down, it is not possible to repair it by replacing only that one.

[0006] In view of this, a modular superconducting coil has been proposed in which both ends of one superconducting coil and one persistent current switch are superconductively connected (for example, Non-Patent Document 1). Even when multiple modular superconducting coils are used, persistent current operation in which current continues to flow in the closed circuit in each modular superconducting coil is possible if the operation is performed according to the above procedure. As described above, by using modular superconducting coils, it becomes possible to treat superconducting coils as interchangeable general-purpose parts. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Weijun Yao et al.,“MgB2 Coils for MRI Applications”, IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY,VOL.20,NO.3,JUNE 2010 DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0008] In conventional superconducting magnet devices, in the event of emergency demagnetization, a superconducting element such as a superconducting coil or a persistent current switch is heated by a heater to cause a normal conductive transition, and the current is attenuated by a protective resistor and a diode provided in parallel. However, when multiple superconducting coils are used, it is necessary to make the protective resistor larger or provide some kind of cooling means to prevent the protective resistor from being damaged by excessive Joule heat. In addition, when a high-temperature superconductor is used as a superconducting element, it is difficult to heat the entire element evenly to cause a normal conductive transition because of its high critical temperature. If only a part of the superconducting element were to undergo a normal conductive transition, there is a possibility that local Joule heat would be generated and the element would be damaged.

[0009] In view of the above, an object of the present invention is to provide a superconducting coil and a superconducting magnet device capable of persistent current operation, which makes it possible to omit protective resistors and their cooling devices that are installed outside the device, and which can prevent damage to the superconducting coil and persistent current switch in the event of emergency demagnetization. [Means for solving the problem]

[0010] In order to solve the above problems, the superconducting coil of the present invention has a pair of power leads for supplying a current to the superconducting coil, in which both ends of a superconducting coil winding and a persistent current switch are superconductively connected, and each end of the superconducting coil has a superconducting wire constituting the superconducting coil winding, a superconducting wire constituting the persistent current switch, and a superconducting joint that superconductively connects them, the superconducting wire constituting the superconducting coil winding and the power lead are electrically connected, a heater is provided for heating the superconducting joint, a diode is arranged between the pair of power leads, and the pair of power leads are electrically connected via the diode. Other aspects of the present invention will be described in the embodiments described later. Effect of the Invention

[0011] According to the present invention, in a high-temperature superconducting magnet device capable of persistent current operation, it is possible to omit the protective resistor and its cooling device that are provided outside the device, and to prevent damage to the superconducting coil and persistent current switch in the event of emergency demagnetization. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a diagram showing a schematic diagram of a circuit configuration of a superconducting magnet apparatus according to the first embodiment. [Diagram 2] FIG. 2 is a diagram showing wiring on a power lead according to the first embodiment. [Diagram 3] 2 is a cross-sectional view of a superconducting joint according to the first embodiment. FIG. [Figure 4] 1 is a diagram showing a schematic external view of a module-type superconducting coil according to a first embodiment. [Diagram 5] 1 is a schematic diagram showing a cross section of a module-type superconducting coil according to a first embodiment. [Figure 6] FIG. 4 is a diagram illustrating an example of operation during a first emergency demagnetization. [Figure 7] FIG. 11 is a diagram showing wiring on a power lead according to the second embodiment. [Figure 8] FIG. 11 is a cross-sectional view of wiring on a power lead according to a second embodiment. [Figure 9] FIG. 11 is a diagram showing wiring on a power lead according to the third embodiment. [Figure 10] FIG. 11 is a cross-sectional view of a superconducting joint according to a third embodiment. [Figure 11] FIG. 13 is a diagram illustrating a schematic circuit configuration according to a fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Next, an embodiment of the present invention will be described in detail with reference to the drawings as appropriate. (First embodiment) A first embodiment to which the present invention is applied will be described below with reference to Fig. 1 to Fig. 6. Fig. 1 is a diagram showing a schematic circuit configuration of a superconducting magnet device according to the first embodiment. A superconducting magnet device 1 to which the present invention is applied is composed of a modular superconducting coil 3 contained in a cryostat 2, an excitation power supply 11 provided outside the cryostat 2, a circuit breaker 12, and a diode 13 that electrically couples the power leads.

[0014] The modular superconducting coil 3 is composed of a superconducting coil winding 4, a persistent current switch 5 provided in parallel therewith, a PCS heater 14 in thermal contact with the persistent current switch, power leads 6 (power leads 6a, 6b) for supplying current to the modular superconducting coil, a wire for the superconducting coil (hereinafter referred to as a main wire 7), a wire for the persistent current switch (hereinafter referred to as a PCS wire 8), a superconducting joint 9 (superconducting joints 9a, 9b) for connecting them in a superconducting state, and an emergency demagnetization heater 10 in thermal contact with the superconducting joint. All the superconducting elements contained in the cryostat 2 are kept below the critical temperature by a cooling means (not shown) and in a superconducting state. The superconducting materials applied to the above superconducting elements may be bismuth-based wire, rare earth-based wire, magnesium diboride, etc.

[0015] In the persistent current operation, first, the persistent current switch 5 is heated by a heater to cause a normal conductive transition, and then a current is supplied from the excitation power supply 11 to the modular superconducting coil 3. After that, the heater is stopped, and the persistent current switch 5 is returned to a superconducting state, and the current supply from the excitation power supply 11 is stopped, resulting in persistent current operation in which the current continues to flow through the closed circuit consisting of the superconducting coil winding 4 and the persistent current switch 5 with almost no attenuation. This allows the superconducting magnet device 1 to maintain a magnetic field for a long period of time. On the other hand, to cancel the persistent current operation, current is supplied again from the excitation power supply 11 while the persistent current switch 5 is in a superconducting state, and then the persistent current switch is heated by a heater to cause a normal conductive transition, thereby directly connecting the excitation power supply 11 and the superconducting coil winding 4, and canceling the persistent current mode.

[0016] When emergency demagnetization is required to quickly eliminate the magnetic field of a superconducting magnet device due to some factor, in a conventional superconducting magnet device, the superconducting coil or persistent current switch is heated by a heater to cause a normal conductive transition, and the current is attenuated by consuming energy in a protective resistor and a diode provided in parallel with the superconducting coil. However, when multiple superconducting coils are used, in order to prevent the protective resistor from being damaged by excessive Joule heat, it is necessary to make the protective resistor itself larger or to provide some kind of cooling means. In addition, when high-temperature superconductors are used for the superconducting coil and persistent current switch, it is difficult to heat the entire element evenly to cause a normal conductive transition because of the high critical temperature. If only a part of the superconducting element undergoes a normal conductive transition, local Joule heat may occur, damaging the element.

[0017] Therefore, in this embodiment, as shown in FIG. 1, a main line 7, a PCS line 8, and a superconducting connection portion 9 are arranged on a power lead 6 that supplies current to a modular superconducting coil 3.

[0018] Fig. 2 is a diagram showing wiring on a power lead 6 according to the first embodiment. Fig. 3 is a cross-sectional view (A-A' cross section) of a superconducting joint according to the first embodiment. Fig. 4 is a diagram showing a schematic appearance of a modular superconducting coil 3 according to the first embodiment.

[0019] 2, the main line 7 and the PCS line 8 are electrically connected to a power lead 6 made of a good conductor such as copper in a section just before entering the superconducting connection 9. The superconducting connection 9 is provided with a heater for causing a normal conductive transition (hereinafter, the superconducting connection heater (emergency demagnetization heater 10)).

[0020] As shown in the cross-sectional view of Fig. 3, inside the superconducting joint 9, the main line 7 and the PCS line 8 are connected via the superconducting bulk 70 inside a joint container (superconducting joint container 71) made of stainless steel or the like. To start emergency demagnetization during persistent current operation, it is possible to first use the emergency demagnetization heater 10 to quickly heat the superconducting joint, which has a relatively small heat capacity, to cause a normal conductive transition. As a result, the current flowing through the current path 51 shown in Fig. 2 starts to flow through the power lead as shown in current path 52.

[0021] As shown in Figures 1 and 4, a pair of power leads 6 (between power lead 6a and power lead 6b) are electrically coupled via a diode 13. The above electrical coupling is achieved by using solder 21 for the main line 7 and PCS line 8, and by bolting a current cable made of good conductor to the diode. Current is supplied from outside the device by bolting a current cable 26 made of good conductor onto the power leads, as shown in Figures 1 and 4.

[0022] 5 is a schematic diagram showing cross sections (cross sections B-B' and C-C' in FIG. 4) of the modular superconducting coil 3 according to the first embodiment. As shown in FIG. 5, the main wires 7 and the PCS wires 8 other than those on the power leads 6 are fixed with epoxy resin or the like to a cooling copper plate 23 that cools the superconducting coil winding 4 in a coil bobbin 24, and are kept at or below the critical temperature, similar to the superconducting coil winding 4.

[0023] The operation during emergency demagnetization in this embodiment will be described with reference to FIG. Fig. 6 is a diagram showing a schematic diagram of the operation during the first emergency demagnetization. To start emergency demagnetization during persistent current operation, first, the emergency demagnetization heater 10 is used to quickly heat the superconducting joint 9, which has a relatively small heat capacity, so that it can transition to normal conduction. As a result, the current flowing through the current path 51 shown in Fig. 2 starts to flow through the power lead 6 as shown in the current path 52. After that, the main line 7 and the PCS line 8 are heated by Joule heat of the current flowing through the power lead 6, and the normal conduction region expands, and the voltage across the diode 13 increases.

[0024] Then, when the voltage across the diode 13 reaches the turn-on voltage, the current that had been flowing through the persistent current switch 5 is diverted to the diode 13 side. If the PCS heater 14 is turned ON in this state, it is possible to reduce Joule heat due to the normal conductive transition, and it becomes possible to prevent damage to the persistent current switch 5. After that, the persistent current switch 5 is heated to cause the normal conductive transition, and almost all of the current that had been flowing through the persistent current switch 5 is diverted to the diode 13 side. This allows the current in each modular superconducting coil 3 to be rapidly attenuated, making it possible to perform emergency demagnetization without providing a protective resistor outside the device.

[0025] If it is desired to advance the diode turn-on start time, the soldering area of ​​the PCS wire 8 is reduced as shown in FIG. 2. That is, the area of ​​the solder 21a electrically connecting the superconducting wire (PCS wire 8) constituting the persistent current switch 5 to the power lead 6 is smaller than the area of ​​the solder 21b electrically connecting the superconducting wire (main wire 7) constituting the superconducting coil winding 4 to the power lead 6. This increases the electrical resistance of the current path 52, and it is possible to increase the speed of expansion of the normal conductive part by increasing Joule heat. Also, the diode voltage shown in FIG. 6 decreases after turning on. This is due to the temperature dependency of the turn-on voltage, and indicates that the temperature of the diode 13 is rising due to Joule heat.

[0026] Second Embodiment Fig. 7 is a diagram showing wiring on a power lead 6 according to the second embodiment. Fig. 8 is a cross-sectional view (D-D' cross section) of the wiring on a power lead 6 according to the second embodiment. As shown in Figs. 7 and 8, the modular superconducting coil according to the second embodiment differs from the first embodiment in that the PCS wire 8 is electrically coupled to the power lead 6 via a metal material 54 having a high resistivity.

[0027] This not only provides the same effects as in the first embodiment, but also makes it possible to increase the Joule heat generated in the power lead 6 after the emergency demagnetization heater 10 is turned ON, thereby shortening the time required for the diode 13 to turn on.

[0028] (Third embodiment) Fig. 9 is a diagram showing wiring on a power lead 6 according to the third embodiment. Fig. 10 is a cross-sectional view (cross-section E-E' and cross-section F-F' in Fig. 9) of a superconducting joint 9 according to the third embodiment. As shown in Figs. 9 and 10, the modular superconducting coil 3 according to the third embodiment differs from the first and second embodiments in that the PCS wires 8 are not electrically coupled to the power leads 6 by solder connection.

[0029] This not only provides the same effects as those of the first and second embodiments, but also, while the main line 7 and the PCS line 8 are connected in a superconducting state via the superconducting bulk 70 provided inside the superconducting connection container 71 when the emergency demagnetization heater 10 is OFF, by turning the emergency demagnetization heater 10 ON and causing the superconducting bulk 70 to transition to normal conductivity, the current path changes from 51 via the superconducting bulk 70 to current path 52 via the superconducting connection container 71. This makes it possible to increase Joule heat more than when it is via the power lead 6, and shortens the time required for the diode 13 to turn on.

[0030] (Fourth embodiment) 11, the modular superconducting coil 3 according to the fourth embodiment is different from the first embodiment in that the number of the modular superconducting coils 3 is multiple, and each of the modular superconducting coils 3 is connected to a current cable 26 made of a good conductor. Also, the modular superconducting coils 3 are different in that the multiple emergency demagnetization heaters 10 are wired in series.

[0031] This allows a plurality of modular superconducting coils 3 to be operated simultaneously with persistent current in the same procedure as in the first to third embodiments. Furthermore, emergency demagnetization is possible in the same procedure as in the first to third embodiments, and the coil current is attenuated by the diode 13 of each modular superconducting coil. In other words, the energy consumption during emergency demagnetization is shared by each modular superconducting coil 3, making it possible to avoid the need to increase the size of protective resistors or add cooling means as in conventional superconducting magnets. Furthermore, by wiring multiple emergency demagnetization heaters 10 in series, it becomes possible to energize them simultaneously, and it becomes possible to emergency demagnetize multiple modular coils simultaneously.

[0032] As described above, the modular superconducting coil 3 of this embodiment is a modular superconducting coil in which the superconducting coil winding 4 and the persistent current switch 5 are superconductively connected at both ends, and a wire for a superconducting coil (hereinafter, a main wire 7), a wire for a persistent current switch (hereinafter, a PCS wire 8), and a superconducting connection portion that connects them in a superconducting state are arranged on the power lead 6 that supplies current to the modular superconducting coil. Both the main wire 7 and the PCS wire 8, or only the main wire 7, are electrically connected to the power lead in a section just before entering the superconducting connection portion 9. In addition, the pair of power leads 6 are electrically connected via a diode 13. A heating means (emergency demagnetization heater 10) is provided to cause the superconducting connection portion 9 to undergo a normal conductive transition.

[0033] With the above structure, the superconducting joint 9, which has a small heat capacity, can be quickly brought to a normal conductive transition during emergency demagnetization, and part of the current flowing through the persistent current switch 5 can be diverted to the diode 13 provided between the power leads 6. The persistent current switch 5 is then heated to bring about a normal conductive transition, and almost all of the current flowing through the persistent current switch 5 is diverted to the diode 13 side. This allows the current in each modular superconducting coil 3 to be quickly attenuated, and enables emergency demagnetization without providing a protective resistor outside the device. In addition, the persistent current switch 5 can be brought to a normal conductive transition while the current is sufficiently limited, making it possible to prevent damage due to excessive Joule heat. [Explanation of symbols]

[0034] 1. Superconducting magnet device 2. Cryostat 3. Modular superconducting coil (superconducting coil) 4 Superconducting coil winding 5 Persistent current switch 6,6a,6b Power Lead 7 Main wire (wire for superconducting coil) 8 PCS wire (wire for permanent current switches) 9,9a,9b Superconducting joint 10 Emergency demagnetization heater (heater) 11 Excitation power supply 12 Circuit Breaker 13. Diode 14 PCS heater 21, 21a, 21b Solder 23 Cooling copper plate 24 Coil bobbin 26 Current Cable 51 Current path (current path during persistent current operation) 52 Current path (current path during emergency demagnetization) 54 Metallic materials with high resistivity 70 Superconducting bulk 71 Superconducting joint container

Claims

1. In a superconducting coil in which both ends of a superconducting coil winding and a persistent current switch are superconductively connected, a pair of power leads for supplying a current to the superconducting coil; At each of the two ends, a superconducting wire constituting the superconducting coil winding, a superconducting wire constituting the persistent current switch, and a superconducting connection portion superconductively connecting them are disposed on the power lead; a superconducting wire constituting the superconducting coil winding and the power lead are electrically connected to each other, and a heater is provided for heating the superconducting joint; A diode is disposed between the pair of power leads, and the pair of power leads are electrically coupled via the diode. A superconducting coil comprising:

2. 2. The superconducting coil according to claim 1, The area of ​​the solder electrically connecting the superconducting wire constituting the persistent current switch and the power lead is smaller than the area of ​​the solder electrically connecting the superconducting wire constituting the superconducting coil winding and the power lead. A superconducting coil comprising:

3. 2. The superconducting coil according to claim 1, The superconducting wire constituting the persistent current switch and the power lead are electrically connected via a metal having a higher resistivity than the metal constituting the power lead. A superconducting coil comprising:

4. 2. The superconducting coil according to claim 1, the superconducting joint is composed of a superconducting bulk material and a superconducting joint container containing the superconducting bulk material, The superconducting wire constituting the superconducting coil winding arranged on the power lead and the superconducting wire constituting the persistent current switch are electrically connected at the superconducting joint via a superconducting bulk material and a superconducting joint container. A superconducting coil comprising:

5. A plurality of superconducting coils according to any one of claims 1 to 4 are disposed in a cryostat, and the plurality of superconducting coils are connected to each other by normal conducting current cables. A superconducting magnet device characterized by:

6. 6. The superconducting magnet apparatus according to claim 5, The heaters for heating the plurality of superconducting joints are connected in series. A superconducting magnet device characterized by:

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