Superconducting magnet device

Abstract

An object of the present invention is to reduce the failure risk of the antifreeze heater in a superconducting magnet device. The superconducting magnet device (10) includes: a superconducting coil (12); a vacuum vessel (14) that houses the superconducting coil (12); current leads (16) that are connected to the superconducting coil (12) and are provided inside the vacuum vessel (14); a power supply cable (18) that is disposed outside the vacuum vessel (14) and is connected to the current leads (16); and a heater (20) that is separately disposed from the current leads (16) and heats the current leads (16) via the power supply cable (18).

Description

[0001] This application claims priority based on Japanese Patent Application No. 2021-025479 filed on February 19, 2021. The entire content of the Japanese application is incorporated herein by reference. Technical Field

[0002] The present invention relates to a superconducting magnet device. Background Art

[0003] Generally, a superconducting magnet device includes a superconducting coil and a vacuum vessel that houses the superconducting coil in a cryogenically cooled state. In order to supply power to the superconducting coil from the outside, coil electrodes are provided outside the vacuum vessel. The coil electrodes are cooled by heat conduction from the superconducting coil. Therefore, moisture in the air around the vacuum vessel may freeze on the coil electrodes. Conventionally, it has been known to prevent this by operating a heater installed on the coil electrodes to directly heat the coil electrodes.

[0004] Patent Document 1: International Publication No. 2017 / 170265

[0005] The present inventors have studied the above superconducting magnet device, and as a result, have recognized the following problems. The heater installed on the coil electrodes is affected by the leakage magnetic field caused by the strong magnetic field generated by the superconducting magnet device, and the risk of its failure increases. Moreover, when the superconducting magnet device is mounted on an accelerator, since the dose of radiation near the superconducting magnet device becomes high, the risk of failure of the heater further increases.

[0006] When the heater fails, maintenance operations such as repair or replacement of the heater are required. However, the leakage magnetic field or radiation hinders the operator from approaching, so it is difficult to perform maintenance operations while the superconducting magnet device is operating. Stopping the superconducting magnet device for maintenance operations results in downtime of the superconducting magnet device, so it is not recommended. Summary of the Invention

[0007] One exemplary object of an embodiment of the present invention is to reduce the failure risk of the anti-freezing heater in a superconducting magnet device.

[0008] According to an embodiment of the present invention, a superconducting magnet device includes: a superconducting coil; a vacuum vessel that houses the superconducting coil; current leads that are connected to the superconducting coil and are provided inside the vacuum vessel; a power supply cable that is disposed outside the vacuum vessel and is connected to the current leads; and a heater that is separately disposed from the current leads and heats the current leads via the power supply cable.

[0009] According to the present invention, the failure risk of the anti-freezing heater in a superconducting magnet device can be reduced. Brief Description of the Drawings

[0010] Figure 1 It is a schematic diagram showing the superconducting magnet device related to the embodiment.

[0011] Figure 2 It is a schematic diagram showing the superconducting magnet device related to another embodiment.

[0012] In the figure: 10 - superconducting magnet device, 12 - superconducting coil, 14 - vacuum vessel, 16 - current lead, 16a - airtight terminal, 18 - power supply cable, 20 - heater, 20a - heating element, 20b - temperature sensor, 24 - restricted access area. Detailed Embodiment

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the specification and drawings, the same or equivalent components, parts, and processes are denoted by the same reference numerals, and repeated descriptions are appropriately omitted. In each drawing, for convenience of explanation, the scales or shapes of each part are simply set, and unless otherwise specifically stated, they are not to be construed in a limiting sense. The embodiments are examples and do not limit the scope of the present invention in any way. All the features or combinations thereof described in the embodiments are not necessarily essential to the invention.

[0014] Figure 1 It is a schematic diagram showing the superconducting magnet device 10 related to the embodiment. The superconducting magnet device 10 includes a superconducting coil 12, which can be mounted as a magnetic field source for an accelerator such as a cyclotron or other high - magnetic - field utilization equipment in a high - magnetic - field utilization equipment, for example, and can generate the high magnetic field required by the equipment.

[0015] The superconducting coil 12 is thermally connected to, for example, a two - stage Gifford - McMahon (GM) refrigerator or other forms of cryogenic refrigerators (not shown), and is used in a cryogenic state cooled below the superconducting transition temperature. In the present embodiment, the superconducting magnet device 10 is configured as a so - called conduction - cooled type directly cooled by a cryogenic refrigerator, rather than immersing the superconducting coil 12 in a cryogenic liquid refrigerant such as liquid helium. In addition, the superconducting coil 12 can also be cooled by an immersion - cooling method of immersing it in a cryogenic liquid refrigerant.

[0016] Furthermore, the superconducting magnet device 10 includes: a vacuum vessel 14 that houses the superconducting coil 12; a current lead 16 that is connected to the superconducting coil 12 and is provided on the vacuum vessel 14; a power supply cable 18 that is disposed outside the vacuum vessel 14 and is connected to the current lead 16; and a heater 20 that is separately disposed from the current lead 16 and heats the current lead 16 via the power supply cable 18.

[0017] The internal space of the vacuum vessel 14 provides a cryogenic vacuum environment suitable for maintaining the superconducting coil 12 in a superconducting state. The vacuum vessel 14 is, for example, a cryostat. As an example, the superconducting coil 12 has an annular shape, and the vacuum vessel 14 has an annular shape surrounding the superconducting coil 12. To withstand ambient pressure (e.g., atmospheric pressure), the vacuum vessel 14 is made of a metal material such as stainless steel or other suitable high-strength materials, for example.

[0018] The current lead 16 connects the superconducting coil 12 and the power supply device 22 via the power supply cable 18. At least a pair (positive electrode side and negative electrode side) of current leads 16 is provided. An airtight terminal 16a that penetrates the wall portion of the vacuum vessel 14 and is used to introduce current into the vacuum vessel 14 is provided at the end of the current lead 16 on the ambient side (room temperature side). In the illustrated example, the airtight terminal 16a is provided on the upper surface of the vacuum vessel 14, but is not limited to this configuration. The end of the current lead 16 on the side opposite to the room temperature side (low temperature side) is connected to the superconducting coil 12.

[0019] The power supply cable 18 has a first end 18a, a second end 18b, and a flexible wire portion 18c connecting the first end 18a and the second end 18b. The first end 18a is connected to the airtight terminal 16a by, for example, connector connection or other appropriate connection methods. The second end 18b is connected to the power supply device 22 by an appropriate connection method.

[0020] The power supply cable 18 defines an upper limit value of the operating temperature based on the physical properties of the power supply cable 18 (such as the heat resistance temperature of the synthetic resin material forming the sheath of the flexible wire portion 18c). Therefore, it is recommended that the power supply cable 18 be used in an operating environment not exceeding this upper limit value of the operating temperature.

[0021] The heater 20 includes: a heating element 20a mounted on the power supply cable 18; a temperature sensor 20b for measuring the temperature of the power supply cable 18; and a controller 20c for controlling the output power of the heater 20 so that the measured temperature becomes equal to or lower than the upper limit value of the operating temperature of the power supply cable 18 based on the measured temperature of the power supply cable 18 measured by the temperature sensor 20b.

[0022] The heating element 20a is, for example, a contact heating element such as a rubber heater, and is mounted on the flexible wire portion 18c of the power supply cable 18. The heating element 20a may also be mounted on the flexible wire portion 18c in a manner of being wound around the sheath of the flexible wire portion 18c. Therefore, the heating element 20a is disposed separately from the airtight terminal 16a on the power supply cable 18, and is not mounted on the airtight terminal 16a.

[0023] For ease of replacement, the heating element 20a may also be detachably mounted on the power supply cable 18.

[0024] The temperature sensor 20b is a general-purpose temperature sensor, and it is installed on the power supply cable 18 to measure the temperature of the heated part of the power supply cable 18 based on the heating element 20a. The temperature sensor 20b is installed between the heating element 20a and the cord part 18c on the cord part 18c, or at a position adjacent to or close to the heating element 20a.

[0025] The controller 20c is electrically connected to the temperature sensor 20b to receive the temperature signal output by the temperature sensor 20b. This temperature signal represents the measured temperature of the heated part of the power supply cable 18 based on the heating element 20a. Further, the controller 20c is electrically connected to the heating element 20a to send a control signal for controlling the heating element 20a to the heating element 20a. The output power of the heating element 20a is controlled according to this control signal. The controller 20c controls the output power of the heater 20 by a known control method such as PID control and based on the measured temperature of the power supply cable 18 so that the measured temperature is below the upper limit value of the operating temperature of the power supply cable 18.

[0026] In addition, as a hardware structure, the controller 20c is implemented by components or circuits represented by a computer's CPU or memory, and as a software structure, the controller 20c is implemented by a computer program or the like, but is appropriately drawn as a functional module realized by their cooperation in the figure. Those skilled in the art should understand that these functional modules can be implemented in various forms by a combination of hardware and software.

[0027] In the present embodiment, the vacuum vessel 14 (i.e., the superconducting coil 12) is disposed within the restricted access area 24. The power supply device 22 is disposed outside the restricted access area 24, and the power supply cable 18 is led out from the hermetic terminal 16a within the restricted access area 24 to the outside of the restricted access area 24. The heater 20 is disposed outside the restricted access area 24, and the heating element 20a is assembled on the power supply cable 18 outside the restricted access area 24 as described above.

[0028] The restricted access area 24 is preset around the superconducting coil 12 as an area where a magnetic field and / or radiation dose exceeding a reference may be generated, and at least during the operation of the superconducting coil 12, people are restricted from entering this area. The restricted access area 24 may be a radiation management area.

[0029] During the operation of the superconducting magnet device 10, the exciting current is supplied from the power supply device 22 to the superconducting coil 12 through the power supply cable 18 and the current lead 16. Thus, the superconducting magnet device 10 can generate a strong magnetic field. At this time, the superconducting coil 12 is cooled to an extremely low temperature, so the hermetic terminal 16a is also cooled due to the heat conduction of the current lead 16. Since the hermetic terminal 16a is exposed to the ambient environment of the vacuum vessel 14, moisture in the surrounding air may condense or frost on the hermetic terminal 16a. Depending on the situation, the moisture may even freeze on the hermetic terminal 16a.

[0030] However, according to the embodiment, the heater 20 heats the vacuum vessel 14 via the power supply cable 18. The power supply cable 18 serves as a heat conduction path from the heating element 20a to the hermetic terminal 16a, and the heat generated by the heating element 20a is transferred to the hermetic terminal 16a via the power supply cable 18 (especially via the wires inside the cable). In this way, the temperature drop of the hermetic terminal 16a can be suppressed, and thus condensation, frosting or even freezing on the hermetic terminal 16a can be prevented or alleviated.

[0031] The heater 20 is separately arranged from the current lead 16 (i.e., the superconducting coil 12). By keeping a distance from the superconducting coil 12, the heater 20 can be arranged at a position where the influence of the leakage magnetic field or radiation that may be generated by the superconducting coil 12 is relatively low (for example, outside the restricted access area 24). Thus, compared with the case where the heater 20 is directly mounted on the current lead 16, the failure risk of the heater 20 caused by the leakage magnetic field or radiation can be reduced.

[0032] Moreover, if the heater 20 is arranged outside the restricted access area 24, even during the operation of the superconducting magnet device 10, the operator can approach the heater 20 to perform maintenance operations such as inspection. Assuming that the heater 20 fails, it is also easy to handle.

[0033] In the above embodiment, the heater 20 adopts a form of using the temperature sensor 20b and the controller 20c to control the temperature regulation of the heating element 20a, but it is not limited to this. The heating element 20a can also heat the power supply cable 18 with a constant output power. At this time, the heater 20 may not have the temperature sensor 20b and the controller 20c.

[0034] Figure 2FIG. 0 is a schematic view showing a superconducting magnet device 10 according to another embodiment. Similarly to the above-described embodiment, the superconducting magnet device 10 includes: a superconducting coil 12; a vacuum vessel 14 that houses the superconducting coil 12; current leads 16 that are connected to the superconducting coil 12 and are disposed within the vacuum vessel 14; a power supply cable 18 that is disposed outside the vacuum vessel 14 and is connected to the current leads 16; and a heater 20 that is separately disposed from the current leads 16 and heats the current leads 16 via the power supply cable 18. The heater 20 is disposed outside a restricted access area 24.

[0035] In the present embodiment, the heater 20 controls the output power of the heater 20 according to the energization state of the superconducting coil 12. Accordingly, a controller 20c is electrically connected to a power supply device 22 to receive a signal indicating the energization state of the superconducting coil 12 from the power supply device 22. Based on this signal, the controller 20c grasps the energization state of the superconducting coil 12, such as conduction and disconnection of the superconducting coil 12 or the magnitude of the current supplied to the superconducting coil 12.

[0036] For example, the controller 20c can turn on a heating element 20a when the superconducting coil 12 is disconnected, and turn off the heating element 20a when the superconducting coil 12 is conducting. When the superconducting coil 12 is conducting, current flows through the power supply cable 18 and the current leads 16 to generate Joule heat, thereby being able to heat the hermetic terminal 16a. When it is expected that icing of the hermetic terminal 16a can be prevented by this heating amount, the heating element 20a can be turned off.

[0037] Similarly, when the magnitude of the current supplied to the superconducting coil 12 is less than a threshold value (for example, when the superconducting coil 12 is idling), the controller 20c can turn on the heating element 20a. When the magnitude of the current supplied to the superconducting coil 12 is equal to or greater than the threshold value (for example, when the superconducting coil 12 is operating normally), the controller 20c can turn off the heating element 20a. The threshold value can be appropriately set according to the experience of the designer or experiments or simulation tests conducted by the designer.

[0038] Instead of turning on the heating element 20a, the heating element 20a can be made to operate at its maximum output power or a certain high first output power. Also, instead of turning off the heating element 20a, the heating element 20a can be made to operate at the maximum output power or a second output power lower than the first output power.

[0039] In this way, a temperature drop of the hermetic terminal 16a can also be suppressed, thereby being able to prevent or reduce dew condensation, frosting, or even icing on the hermetic terminal 16a. And the risk of failure of the heater 20 caused by leakage magnetic field or radiation from the superconducting coil 12 can be reduced.

[0040] In addition, the control of the heater 20 based on the energized state of the superconducting coil 12 can be used in parallel with the control of the heater 20 based on the measured temperature. For example, during the period when the heater 20 is turned on according to the energized state of the superconducting coil 12, the controller 20c can control the output power of the heater 20 based on the measured temperature of the power supply cable 18 by the temperature sensor 20b so that the measured temperature is below the upper limit value of the operating temperature of the power supply cable 18.

[0041] As described above, the present invention has been described based on the embodiments. Those skilled in the art should understand that the present invention is not limited to the above-described embodiments, and various design changes can be made, various modifications can exist, and such modifications are also within the scope of the present invention. The various features described in one embodiment can also be applied to other embodiments. The new embodiments produced by combination have the effects of the respective embodiments being combined.

[0042] In the case where the restricted access area 24 is not set, the heater 20 can be disposed near the hermetic terminal 16a to achieve effective heating. For example, the heating element 20a can be assembled on the first end portion 18a of the power supply cable 18. Further, even in the case where the restricted access area 24 is set, the heater 20 can be disposed within the restricted access area 24 to achieve more effective heating.

[0043] The heater 20 may also have a non-contact heating element such as an infrared heater or a circulator, and the power supply cable 18 can be heated by such a non-contact heating element.

[0044] As described above, the present invention has been described based on the embodiments and using specific statements. However, the embodiments are merely one way of expressing the principles and applications of the present invention, and within the scope not departing from the idea of the present invention defined by the technical solution, there can be many modifications or changes in the configuration of the embodiments.

Claims

1. A superconducting magnet device, characterized in that, Comprising: A superconducting coil; A vacuum vessel for accommodating the superconducting coil; Current leads connected to the superconducting coil and provided with airtight terminals passing through the vacuum vessel for introducing current into the vacuum vessel; A power supply cable disposed outside the vacuum vessel, with its first end connected to the airtight terminal and its second end connected to a power supply device; And A heater disposed outside the vacuum vessel, separated from the current leads and disposed at a position less affected by the leakage magnetic field or radiation generated by the superconducting coil, and heating the current leads via the power supply cable.

2. The superconducting magnet device according to claim 1, wherein: The heater has a heating element assembled on the power supply cable.

3. The superconducting magnet device according to claim 1 or 2, wherein: The superconducting coil is disposed within a restricted access area, The heater is disposed outside the restricted access area.

4. The superconducting magnet device according to claim 1 or 2, wherein: The heater has a temperature sensor for measuring the temperature of the power supply cable, and controls the output power of the heater according to the measured temperature of the power supply cable measured by the temperature sensor so that the measured temperature is below the upper limit value of the operating temperature of the power supply cable.

5. The superconducting magnet device according to claim 1 or 2, wherein: The heater controls the output power of the heater according to the energization state of the superconducting coil.

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