Superconducting magnet device and method for raising the temperature thereof

Abstract

To promptly rise temperature of a superconducting magnet device.SOLUTION: A superconducting magnet device 10 comprises: a superconducting coil 12; a vacuum case 14 housing the superconducting coil 12; a gas bomb 22 arranged outside the vacuum case 14; and a gas introduction line 24 that connects the gas bomb 22 to the vacuum case 14 so that gas can be introduced to the vacuum case 14 from the gas bomb 22. A gas filling amount of the gas bomb 22 is set in such a manner that vacuum level of the vacuum case 14 is reduced from a high vacuum to a middle vacuum.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a superconducting magnet device and a method for raising the temperature thereof. [Background technology]

[0002] Cryopumps are used to evacuate the vacuum vessel. Because cryopumps are gas-trapping vacuum pumps, they require periodic regeneration to expel trapped gas. To regenerate a cryopump, heating with an electric heater or supply of purge gas can be used to raise the temperature of the cryogenic surface where the gas is condensed to room temperature. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-44107 A Summary of the Invention [Problem to be solved by the invention]

[0004] A superconducting magnet device generally includes a vacuum vessel, also called a cryostat, and a superconducting coil cooled to an extremely low temperature within the cryostat. For maintenance of the superconducting magnet device, the superconducting coil may be heated by an electric heater to raise the temperature from an extremely low temperature to room temperature. To raise the temperature in a short time, it is desirable to pass a large current through the heater and the electrical wiring to the heater. However, this increases the risk of problems such as excessive heating by the heater or melting of the electrical wiring, posing safety concerns.

[0005] Other methods for accelerating the temperature increase include opening the cryostat to the atmosphere or supplying high-pressure gas into the cryostat, which fills the cryostat with gas at pressures above atmospheric pressure and promotes heat transfer from the ambient environment to the superconducting coils within the cryostat. However, introducing large amounts of gas in this way often results in the entire cryostat being cooled by the superconducting coils and the surrounding radiation shield, which can lead to condensation on the cryostat surface. Cryostats in superconducting magnet systems are often at least partially surrounded by an iron magnetic shield to reduce magnetic field leakage to the outside. There is a concern that condensation may adhere to the magnetic shield and cause rust.

[0006] One exemplary objective of certain aspects of the present invention is to rapidly heat up a superconducting magnet device. [Means for solving the problem]

[0007] According to one aspect of the present invention, a superconducting magnet device includes a superconducting coil, a vacuum vessel that houses the superconducting coil, a gas cylinder that is arranged outside the vacuum vessel and whose gas filling amount is determined so as to reduce the vacuum level of the vacuum vessel from a high vacuum to a medium vacuum, and a gas inlet line that connects the gas cylinder to the vacuum vessel so as to allow gas to be introduced from the gas cylinder into the vacuum vessel.

[0008] According to one aspect of the present invention, there is provided a method for raising the temperature of a superconducting magnet apparatus. The superconducting magnet apparatus includes a superconducting coil and a vacuum vessel containing the superconducting coil. The method includes connecting a gas cylinder to the vacuum vessel and introducing gas from the gas cylinder into the vacuum vessel. The gas cylinder is filled with gas at a level that reduces the degree of vacuum in the vacuum vessel from a high vacuum to a medium vacuum. [Effects of the Invention]

[0009] According to the present invention, the temperature of the superconducting magnet device can be raised quickly. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a side view schematically showing a superconducting magnet apparatus according to an embodiment. [Figure 2] 3 is a flowchart showing an example of a method for raising the temperature of a superconducting magnet device according to an embodiment. [Figure 3] FIG. 10 is a diagram showing a first modified example of the gas introduction unit according to the embodiment. [Figure 4] 4(a) to 4(c) are diagrams showing a second modified example of the gas introduction unit according to the embodiment. [Figure 5] FIG. 10 is a diagram showing a third modified example of the gas introduction unit according to the embodiment. [Figure 6] FIG. 10 is a diagram showing a fourth modified example of the gas introduction unit according to the embodiment. [Figure 7] FIG. 10 is a diagram showing a fifth modified example of the gas introduction unit according to the embodiment. [Figure 8] 10A and 10B are diagrams illustrating countermeasures against condensation on a vacuum container. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the description and drawings, identical or equivalent components, parts, and processes are designated by the same reference numerals, and redundant explanations will be omitted as appropriate. The scale and shape of each part shown in the drawings are set for convenience to facilitate explanation, and should not be interpreted as limiting unless otherwise specified. The embodiments are merely examples and do not limit the scope of the present invention in any way. All features and combinations thereof described in the embodiments are not necessarily essential to the invention.

[0012] 1 is a diagram schematically illustrating a superconducting magnet device 10 according to an embodiment. The superconducting magnet device 10 is mounted in high-magnetic-field-utilizing equipment as a magnetic field source for, for example, a single crystal pulling device, an NMR (Nuclear Magnetic Resonance) system, an MRI (Magnetic Resonance Imaging) system, an accelerator such as a cyclotron, a high-energy physics system such as a nuclear fusion system, or other high-magnetic-field-utilizing equipment (not shown), and can generate the high magnetic field required for the equipment.

[0013] The superconducting magnet device 10 includes a superconducting coil 12 , a vacuum vessel 14 , a magnetic shield 15 , a radiation shield 16 , a cryogenic refrigerator 18 , a vacuum pumping system 19 , and a gas introduction unit 20 .

[0014] The superconducting coil 12 is disposed within a vacuum vessel 14. The superconducting coil 12 is thermally coupled to a cryogenic refrigerator 18, such as a two-stage Gifford-McMahon (GM) refrigerator, installed within the vacuum vessel 14, and is used in a state cooled to a cryogenic temperature below the superconducting transition temperature. In this embodiment, the superconducting magnet device 10 is configured as a so-called conduction-cooled type in which the superconducting coil 12 is directly cooled by the cryogenic refrigerator 18. Note that in other embodiments, the superconducting magnet device 10 may be configured as an immersion-cooled type in which the superconducting coil 12 is immersed in a cryogenic liquid refrigerant such as liquid helium.

[0015] The vacuum vessel 14 is an insulated vacuum vessel, also called a cryostat, that provides a cryogenic vacuum environment suitable for bringing the superconducting coil 12 into a superconducting state. Typically, the vacuum vessel 14 has a cylindrical shape or a hollow cylindrical shape with a central cavity. The vacuum vessel 14 thus has a generally flat, circular or annular top plate 14a and bottom plate 14b, and a cylindrical side wall (a cylindrical outer wall, or coaxially arranged cylindrical outer and inner walls) connecting them. The cryogenic refrigerator 18 may be mounted on the top plate 14a of the vacuum vessel 14. The vacuum vessel 14 is formed of a metallic material, such as stainless steel, or other suitable high-strength material to withstand ambient pressure (e.g., atmospheric pressure).

[0016] The magnetic shield 15 covers the top plate 14a, bottom plate 14b of the vacuum vessel 14, and the cylindrical side wall (at least the outer peripheral wall) connecting them, in order to prevent the magnetic field generated by the superconducting coil 12 from leaking to the outside. The magnetic shield 15 is made of a magnetic material such as iron. In this embodiment, the magnetic shield 15 is provided as a separate member from the vacuum vessel 14 and is fixed to the outside of the vacuum vessel 14. However, in other embodiments, at least a portion of the magnetic shield 15 may be integrated with the vacuum vessel 14. For example, at least a portion of the top plate 14a, bottom plate 14b of the vacuum vessel 14, and the side wall connecting them may be made of a magnetic material so as to function as the magnetic shield 15.

[0017] The radiation shield 16 is disposed within the vacuum vessel 14 to surround the superconducting coil 12. The radiation shield 16 has a top plate 16a and a bottom plate 16b that face the top plate 14a and the bottom plate 14b of the vacuum vessel 14, respectively. The top plate 16a and the bottom plate 16b of the radiation shield 16 have a generally flat circular or annular shape, similar to the vacuum vessel 14. The radiation shield 16 also has a cylindrical side wall (a cylindrical outer wall, or coaxially arranged cylindrical outer and inner walls) connecting the top plate 16a and the bottom plate 16b. The radiation shield 16 is formed, for example, from pure copper (e.g., oxygen-free copper, tough pitch copper, etc.) or other highly thermally conductive metals. The radiation shield 16 blocks radiant heat from the vacuum vessel 14 and can thermally protect low-temperature parts, such as the superconducting coil 12, that are located inside the radiation shield 16 and cooled to a lower temperature than the radiation shield 16, from the radiant heat.

[0018] The first cooling stage of the cryocooler 18 is thermally coupled to the top plate 16a of the radiation shield 16, and the second cooling stage of the cryocooler 18 is thermally coupled to the superconducting coil 12 inside the radiation shield 16. During operation of the superconducting magnet device 10, the radiation shield 16 is cooled to a first cooling temperature, for example, 30 K to 70 K, by the first cooling stage of the cryocooler 18, and the superconducting coil 12 is cooled to a second cooling temperature lower than the first cooling temperature, for example, 3 K to 20 K (e.g., approximately 4 K), by the second cooling stage of the cryocooler 18. The superconducting coil 12 cooled to a cryogenic temperature in this manner is supplied with power from a coil power supply (not shown) located outside the vacuum vessel 14, thereby generating a desired high magnetic field.

[0019] The vacuum pumping system 19 includes a vacuum pump 19a and a vacuum valve 19b and is configured to evacuate the vacuum vessel 14. The vacuum pumping system 19 is connected to a connection port 19c of the vacuum vessel 14. The vacuum pump 19a may be, for example, a turbomolecular pump, a rotary pump, or any other suitable vacuum pump, or a combination thereof. The vacuum valve 19b may be, for example, an on-off valve, and the vacuum pumping system 19 can evacuate the vacuum vessel 14 when both the vacuum pump 19a and the vacuum valve 19b are on. Note that the connection port 19c may include a vacuum valve separate from the vacuum valve 19b. When the superconducting magnet device 10 is operating, the vacuum valve at the connection port 19c may be closed, thereby maintaining a vacuum inside the vacuum vessel 14.

[0020] The gas introduction unit 20 includes a gas cylinder 22 and a gas introduction line 24 disposed outside the vacuum vessel 14. As will be described later, the gas filling amount of the gas cylinder 22 is determined so as to reduce the degree of vacuum in the vacuum vessel 14 from a high vacuum to a medium vacuum. The gas introduction line 24 connects the gas cylinder 22 to the vacuum vessel 14 so as to be able to introduce gas from the gas cylinder 22 into the vacuum vessel 14.

[0021] In this embodiment, the gas introduction line 24 includes a gas introduction pipe 26, a gas introduction valve 28, and a gas outlet 30. The gas introduction pipe 26 connects the gas cylinder 22 to the inlet side of the gas introduction valve 28. As will be described later, the gas introduction valve 28 closes the gas introduction line 24 when the superconducting coil 12 is in operation, and opens the gas introduction line 24 to raise the temperature of the superconducting coil 12 when the superconducting coil is not in operation. The gas outlet 30, which is the terminal end of the gas introduction line 24, is attached to the outlet side of the gas introduction valve 28.

[0022] The gas type filled in the gas cylinder 22 may be a low-boiling-point gas, for example, a gas having a boiling point of 100 K or less at atmospheric pressure, in order to prevent condensation due to contact with a cryogenic part. An inert gas is easy to handle and convenient. Therefore, in this embodiment, the gas cylinder 22 may be filled with helium gas. Alternatively, the gas cylinder 22 may be filled with nitrogen gas.

[0023] Generally, during operation of the superconducting magnet device 10, i.e., during the cooling operation of the cryocooler 18, the degree of vacuum within the vacuum vessel 14 is maintained at a high vacuum (typically, a pressure of less than 0.1 Pa, for example). This is because, after the vacuum vessel 14 is evacuated by the vacuum pumping system 19, gas remaining within the vacuum vessel 14 is captured by cryogenic surfaces (for example, the surfaces of the superconducting coil 12, the radiation shield 16, and the cryocooler 18) through cryotrapping. Therefore, the initial pressure within the vacuum vessel 14 before gas is supplied from the gas introduction unit 20 can generally be considered to be a high vacuum.

[0024] The amount of gas filled into the gas cylinder 22 is determined so as to reduce the degree of vacuum in the vacuum vessel 14 from a high vacuum to a medium vacuum. Here, the medium vacuum may be, for example, a pressure range of 0.1 to 3000 Pa or a pressure range of 0.1 to 100 Pa. Therefore, the gas filling amount into the gas cylinder 22 may be determined so as to increase the pressure in the vacuum vessel 14 from an initial pressure of less than 0.1 Pa to a set pressure of 3000 Pa or less, or to a set pressure of 100 Pa or less. From the viewpoint of achieving both promotion of heat transfer within the vacuum vessel 14 by gas introduction and miniaturization of the gas cylinder 22, this set pressure may preferably be selected from a pressure range of 1 to 10 Pa. Therefore, the gas filling amount into the gas cylinder 22 may be determined so as to increase the pressure in the vacuum vessel 14 from an initial pressure of less than 0.1 Pa to a set pressure of 10 Pa or less.

[0025] The vacuum vessel 14 is provided with a gas inlet port 32 that is connected to the gas inlet line 24 and that receives gas. In this example, the gas inlet port 32 is provided in the bottom plate 14b of the vacuum vessel 14, but this is not limitative and the gas inlet port 32 may be provided in another portion of the vacuum vessel 14, such as the top plate 14a or the side wall connecting the top plate 14a and the bottom plate 14b.

[0026] The gas introduction unit 20 is detachably attached to the vacuum vessel 14. The gas introduction port 32 and the gas outlet 30 of the gas introduction line 24 are joints that are airtightly coupled to each other. When the gas introduction port 32 and the gas outlet 30 of the gas introduction line 24 are coupled and the gas introduction valve 28 is opened, the gas stored in the gas cylinder 22 is supplied from the gas cylinder 22 into the vacuum vessel 14 through the gas introduction line 24 and the gas introduction port 32.

[0027] When the gas introduction valve 28 is opened, the entire amount of gas in the gas cylinder 22 is supplied to the vacuum vessel 14. The gas introduction unit 20 is a disposable gas source and is replaced after use. The used gas introduction unit 20 can be removed from the vacuum vessel 14 and replaced with a new unit.

[0028] The gas introduction line 24 is configured to be sufficiently airtight so that the gas in the gas cylinder 22 does not leak out of the gas introduction unit 20. The joint between the gas introduction pipe 26 and the gas cylinder 22 and the joint between the gas introduction pipe 26 and the gas introduction valve 28 are joined by a joining method that maintains sufficient airtightness, such as brazing or welding. Therefore, as long as the gas introduction valve 28 is closed, the gas stored in the gas cylinder 22 does not leak out.

[0029] Similarly, the gas inlet valve 28 and the gas outlet 30 are joined to maintain sufficient airtightness. Therefore, when the gas outlet 30 is airtightly joined to the gas inlet port 32, gas does not leak from the ambient environment of the vacuum vessel 14 into the vacuum vessel 14 through this joint or the joint between the gas inlet valve 28 and the gas outlet 30.

[0030] To ensure that gas leaks from the gas introduction unit 20 to the outside are prevented, a leak check may be performed on the gas introduction unit 20 in advance. As an example of an inspection method, the gas introduction unit 20 may be prepared before being attached to the vacuum vessel 14 and then carried into an inspection vacuum vessel connected to a leak detector. The presence or absence of a gas leak can be determined from the detection results of the leak detector before and after the gas introduction unit 20 is held in the evacuated inspection vacuum vessel for a predetermined time.

[0031] Furthermore, another test may be performed to ensure that gas leakage into the vacuum vessel 14 through the gas introduction unit 20 is prevented. The gas introduction unit 20 may be prepared before being attached to the vacuum vessel 14, and a pressure gauge may be connected to its gas outlet 30. The presence or absence of a gas leak can be determined from the pressure gauge measurement results before and after the gas introduction valve 28 is kept closed for a predetermined time.

[0032] By installing a gas introduction unit 20 that has passed these two tests in the vacuum vessel 14, the risk of gas leaks associated with the gas introduction unit 20 can be minimized.

[0033] 2 is a flowchart showing an example of a method for increasing the temperature of the superconducting magnet device 10 according to the embodiment. This method includes connecting the gas cylinder 22 to the vacuum vessel 14 (S10) and introducing gas from the gas cylinder 22 into the vacuum vessel 14 (S20).

[0034] The step (S10) of connecting the gas cylinder 22 may be performed at any time during the manufacture and use of the superconducting magnet device 10. For example, the gas introduction unit 20 may be pre-installed in the vacuum vessel 14 during the manufacturing process of the superconducting magnet device 10, and the superconducting magnet device 10 may be shipped and installed at the site of use in this state. Alternatively, the gas introduction unit 20 may not be pre-installed in the vacuum vessel 14, and the gas introduction unit 20 may be installed in the vacuum vessel 14 after the superconducting magnet device 10 is already operating at the site of use. The gas introduction unit 20 may also be installed in the vacuum vessel 14 when the operation of the superconducting magnet device 10 is stopped in preparation for maintenance on the superconducting magnet device 10. The installation of the gas introduction unit 20 in the vacuum vessel 14 may be performed by a serviceman dispatched by the manufacturer of the superconducting magnet device 10, or by the user of the superconducting magnet device 10.

[0035] The gas introduction valve 28 is closed when the gas introduction unit 20 is attached to the vacuum vessel 14. In particular, after the gas introduction unit 20 is attached to the vacuum vessel 14, the gas introduction valve 28 is always closed while the superconducting magnet device 10 is in operation. This blocks the gas introduction line 24, and prevents gas from flowing from the gas cylinder 22 into the vacuum vessel 14.

[0036] Once the superconducting magnet device 10 is started up, it is typically operated continuously for a considerable period of time (e.g., several years or more). After such a long period of normal operation, the superconducting magnet device 10 may undergo maintenance as needed. For maintenance, the operation of the superconducting magnet device 10 is stopped, i.e., the supply of current to the superconducting coils 12 is stopped, and the cooling operation of the cryogenic refrigerator 18 is also stopped. At this point, the components of the superconducting magnet device 10, such as the superconducting coils 12 and the cryogenic refrigerator 18, are still cooled to cryogenic temperatures, but it is desirable to return these components to room temperature so that workers can access them for maintenance. Therefore, in this embodiment, gas supplied from the gas introduction unit 20 to the vacuum vessel 14 is used to promote the temperature rise of the superconducting magnet device 10.

[0037] The step (S20) of introducing gas from the gas cylinder 22 can be performed at any timing after the step (S10) of connecting the gas cylinder 22 and while the superconducting magnet device 10 is not operating. In this step, the gas introduction valve 28 is operated and opened. The gas stored in the gas cylinder 22 is supplied to the vacuum vessel 14 through the gas introduction line 24 and the gas introduction port 32. The introduction of gas from the gas introduction unit 20 into the vacuum vessel 14 may be performed by a serviceman dispatched by the manufacturer of the superconducting magnet device 10, or may be performed by the user of the superconducting magnet device 10.

[0038] The vacuum vessel 14 is pressurized from an initial high vacuum pressure to a set medium vacuum pressure. For example, the vacuum vessel 14 is pressurized from an initial pressure of less than 0.1 Pa to a set pressure of 3000 Pa or less, or 100 Pa or less, by gas supplied from the gas cylinder 22. Preferably, the vacuum vessel 14 is pressurized by gas supplied from the gas cylinder 22 to a set pressure selected from a pressure range of 1 to 10 Pa.

[0039] The gas supplied to the vacuum vessel 14 contributes to heat transfer between the outer surface of the vacuum vessel 14, which is exposed to the ambient environment (e.g., room temperature), and the object to be cooled, such as the superconducting coil 12, inside the vacuum vessel 14, thereby efficiently raising the temperature of the object to be cooled inside the vacuum vessel 14 toward the ambient temperature. According to the inventor's investigations, in order to obtain this advantage, it is sufficient to raise the pressure level inside the vacuum vessel 14 to a medium vacuum of about several Pa. Therefore, according to the embodiment, the superconducting magnet device 10 can be heated more quickly than if it were heated naturally.

[0040] After the temperature rise is complete, necessary maintenance can be performed on the components of the superconducting magnet device 10, such as the superconducting coil 12 and the cryogenic refrigerator 18. After the maintenance is completed, the vacuum vessel 14 is evacuated by the vacuum pumping system 19, and then the cryogenic refrigerator 18 is operated again. The superconducting coil 12 and radiation shield 16 are re-cooled, and the superconducting magnet device 10 can start operating again.

[0041] High-pressure gas cylinders widely used in industry usually have a large volume of several hundred to several thousand liters and are filled with gas at a high pressure of 1 MPa or more. When gas is supplied from such a gas cylinder to a vacuum vessel, the pressure inside the vacuum vessel easily rises above atmospheric pressure. It is practically difficult to adjust the pressure inside the vacuum vessel to an intermediate pressure (e.g., medium vacuum) below atmospheric pressure. In addition, cylinders are large and occupy a large space.

[0042] In contrast, according to the embodiment, a significantly smaller amount of gas can be filled into the gas cylinder 22. According to the inventor's calculations, a sufficient amount of gas to raise the pressure from a high vacuum to a medium vacuum in a large-volume vacuum vessel 14 of, for example, 10,000 L class, can be provided by a gas cylinder 22 with an internal volume of about 0.1 L at a filling pressure of 0.6 MPa at room temperature. Such a gas cylinder 22 can be a cylindrical vessel with a height of only about 10 cm.

[0043] Therefore, by simply opening the gas introduction valve 28, an appropriate amount of gas can be introduced into the vacuum vessel 14. There is no need for the highly difficult pressure adjustment inside the vacuum vessel 14 that would be required if an existing large gas cylinder were used. In addition, because a small cylinder can be used, the gas introduction unit 20 also saves space.

[0044] Furthermore, as mentioned above, if an excess amount of gas is supplied to the vacuum vessel 14 to create atmospheric pressure or higher, the vacuum vessel 14 is cooled overall via the gas by the superconducting coil 12 and other cryogenic parts, often resulting in condensation or freezing on the outer surface of the vacuum vessel 14. Since the superconducting magnet device 10 is usually covered with an iron magnetic shield 15, there is a concern that the condensed water will adhere to the magnetic shield 15 and cause rust.

[0045] In contrast, in the embodiment, the amount of gas filled in the gas cylinder 22 is limited to a specified small amount, so that excessive pressure buildup in the vacuum vessel 14 can be avoided, and as a result, the above-mentioned problem can be addressed in advance.

[0046] The present invention has been described above based on examples. It will be understood by those skilled in the art that the present invention is not limited to the above-described embodiments, and that various design changes and modifications are possible, and that such modifications are also within the scope of the present invention. Various features described in relation to one embodiment can also be applied to other embodiments. A new embodiment created by combining embodiments will have the combined effects of the respective combined embodiments.

[0047] 3 is a diagram showing a first modified example of a gas introduction unit 20 according to the embodiment. As in the above-described embodiment, the gas introduction unit 20 includes a gas cylinder 22 and a gas introduction line 24, which includes a gas introduction pipe 26, a gas introduction valve 28, and a gas outlet 30. The gas outlet 30 is connected to a gas introduction port 32 of the vacuum vessel 14.

[0048] In the first modification, a restricting tool 34 is provided to restrict access to the gas introduction valve 28 when the superconducting coil 12 is in operation. The restricting tool 34 is made of a magnetic material such as iron, and is attracted toward the superconducting coil 12 by the magnetic field B when the superconducting coil 12 generates the magnetic field B. The magnetic shield 15 may be removed near the restricting tool 34 and the gas introduction unit 20 so that the magnetic field B can be effectively applied to the restricting tool 34.

[0049] To position the restrictor 34, a pair of positioning members 36a, 36b are provided on both sides of the gas inlet valve 28. These positioning members 36a, 36b may be a pair of opposing positioning plates or may be fixed to the gas inlet pipe 26 so that they are parallel to each other. One of the positioning members, 36a, is disposed between the gas inlet valve 28 and the gas outlet 30. As shown in FIG. 3 , when the restrictor 34 is attracted by the magnetic field B, the restrictor 34 abuts against the positioning member 36a and is positioned so as to surround the gas inlet valve 28. The other positioning member, 36b, is disposed below the opposing positioning member 36a and between the gas inlet valve 28 and the gas cylinder 22. This positioning member 36b catches the restrictor 34 that falls due to gravity when the superconducting coil 12 is not operating and does not generate the magnetic field B.

[0050] The restrictor 34 has a ring-like or short cylindrical shape and is large enough to surround the gas introduction valve 28. When the restrictor 34 surrounds the gas introduction valve 28, the restrictor 34 can restrict the user's access to the gas introduction valve 28. To inform the user of its function, the restrictor 34 may have warning signs such as "Always closed" or "Do not operate" on a surface visible to the user, such as the outer surface.

[0051] Therefore, when magnetic field B is generated during operation of the superconducting coil 12, the restrictor 34 is attracted by magnetic field B, hits the positioning member 36a, and surrounds the gas introduction valve 28. The restrictor 34 blocks access to the gas introduction valve 28, preventing the user from operating the gas introduction valve 28. This reduces the risk that the user will mistakenly operate the gas introduction valve 28 while the superconducting magnet device 10 is in operation and inadvertently introduce gas from the gas introduction unit 20 into the vacuum vessel 14. On the other hand, when the superconducting coil 12 is not operating, magnetic field B is not generated, and the restrictor 34 is separated from the gas introduction valve 28. The user can operate the gas introduction valve 28 and introduce gas from the gas introduction unit 20 into the vacuum vessel 14 without being blocked by the restrictor 34.

[0052] In this embodiment, the restricting device 34 is actuated by utilizing the magnetic force generated by the superconducting coil 12, but is not limited to this. The restricting device 34 may be movable by other power or manually between a restricting position that restricts access to the gas introduction valve 28 and an open position that allows access.

[0053] Alternatively, the restricting device 34 may restrict access to the gas introduction valve 28 by being attached to seal the gas introduction valve 28, such as a seal attached to the gas introduction valve 28 to prevent operation of the gas introduction valve 28.

[0054] 4(a) to 4(c) are diagrams showing a second modified example of the gas introduction unit 20 according to the embodiment. As in the above-described embodiment, the gas introduction unit 20 includes a gas cylinder 22 and a gas introduction line 24, which includes a gas introduction pipe 26, a gas introduction valve 28, and a gas outlet 30. The gas outlet 30 is connected to a gas introduction port 32 of the vacuum vessel 14.

[0055] In the second modification, a flow path resistance 38 that suppresses the flow rate of gas flowing from the gas inlet port 32 into the vacuum vessel 14 is provided in the gas inlet line 24, in this example, the gas inlet pipe 26. A multilayer insulation (MLI) 40 is often provided inside the vacuum vessel 14. The multilayer insulation 40 is usually installed between the vacuum vessel 14 and the radiation shield 16 to improve the thermal insulation of the vacuum vessel 14. The multilayer insulation 40 is positioned opposite the gas inlet port 32 inside the vacuum vessel 14. The multilayer insulation 40 has a delicate film structure.

[0056] As shown in Fig. 4(a), the flow path resistance portion 38 may be a narrowed portion 38a provided in the gas introduction pipe 26. Alternatively, as shown in Fig. 4(b), the flow path resistance portion 38 may be a porous portion 38b provided in the gas introduction pipe 26. As yet another example, the flow path resistance portion 38 may be provided in the gas introduction port 32, as shown in Fig. 4(c). For example, the flow path resistance portion 38 may be provided at the tip of the gas introduction port 32 located in the vacuum vessel 14.

[0057] In this way, by providing the flow path resistance portion 38 in the gas inlet line 24 or the gas inlet port 32, it is possible to reduce the flow rate of the gas blown out from the gas inlet port 32 into the vacuum vessel 14. This reduces the risk that the multilayer insulation 40 facing the gas inlet port 32 will be damaged by the blown out gas.

[0058] 5 is a diagram showing a third modified example of the gas introduction unit 20 according to the embodiment. As in the above-described embodiment, the gas introduction unit 20 includes a gas cylinder 22 and a gas introduction line 24, which includes a gas introduction pipe 26, a gas introduction valve 28, and a gas outlet 30. The gas outlet 30 is connected to a gas introduction port 32 of the vacuum vessel 14.

[0059] In the third modification, the gas introduction port 32 includes an additional gas introduction valve 42 that opens and closes the gas introduction port 32, and a joint 44 that is coupled to the gas outlet 30 of the gas introduction line 24. In this way, the gas introduction valve 28 of the gas introduction unit 20 and the additional gas introduction valve 42 are connected in series, which more reliably prevents the accidental introduction of gas from the gas cylinder 22 into the vacuum vessel 14.

[0060] Furthermore, the gas introduction line 24, for example, the gas introduction pipe 26, may be provided with a pressure gauge 46. In this way, a leak check can be performed before introducing gas from the gas introduction unit 20 into the vacuum vessel 14.

[0061] A leak check can be performed, for example, by the following procedure. First, with gas inlet valve 42 of gas inlet port 32 closed, gas inlet valve 28 of gas inlet unit 20 is opened. This fills the space from joint 44 of gas inlet port 32 to gas cylinder 22. In this state, the measured pressure of pressure gauge 46 is monitored for a predetermined period. If no pressure fluctuation is detected, it can be determined that there is no leak at the joint between gas outlet 30 and joint 44, so gas inlet valve 42 is opened and gas is introduced from gas inlet unit 20 into vacuum chamber 14. If pressure fluctuation is detected, gas inlet valve 28 is closed, gas inlet unit 20 is removed, and it can be replaced with a new gas inlet unit 20.

[0062] 6 is a diagram showing a fourth modified example of the gas introduction unit 20 according to the embodiment. As in the above-described embodiment, the gas introduction unit 20 includes a gas cylinder 22 and a gas introduction line 24, and the gas introduction line 24 includes a gas introduction pipe 26, a gas introduction valve 28, and a gas outlet 30. The gas introduction port 32 of the vacuum vessel 14 includes an additional gas introduction valve 42 that opens and closes the gas introduction port 32, and a joint 44 that is coupled to the gas outlet 30 of the gas introduction line 24.

[0063] In the fourth modification, a vacuum exhaust valve 48 is provided in the gas introduction port 32. The gas introduction port 32 includes an additional gas introduction valve 42 and an intermediate part 50 that can be attached thereto. The intermediate part 50 has a joint part 44 and the vacuum exhaust valve 48. The joint part 44 and the vacuum exhaust valve 48 are provided so as to branch off from the gas introduction valve 42 when the intermediate part 50 is attached to the gas introduction valve 42. Thus, the vacuum exhaust valve 48 is branched and connected between the gas introduction valve 28 of the gas introduction line 24 and the additional gas introduction valve 42 of the gas introduction port 32. The vacuum exhaust valve 48 is connected to a vacuum pump (for example, the vacuum pump 19a shown in FIG. 1).

[0064] In this case, the gas introduction unit 20 and the intermediate part 50 can be attached to the vacuum vessel 14, for example, by the following procedure. First, the intermediate part 50 is attached to the gas introduction valve 42, and the gas outlet 30 of the gas introduction unit 20 is attached to the joint 44 of the intermediate part 50. Alternatively, the gas introduction unit 20 may be attached to the gas introduction valve 42 with the intermediate part 50 already attached. Next, the vacuum exhaust valve 48 is opened, and the space from the gas introduction valve 42 of the gas introduction port 32 to the gas introduction valve 28 of the gas introduction unit 20 is evacuated. Then, the vacuum exhaust valve 48 is closed. In this manner, the gas introduction unit 20 can be easily attached to a superconducting magnet apparatus 10 that has not yet had the gas introduction unit 20 attached, while the apparatus is in operation.

[0065] 1, or in addition to it, can be used to evacuate the vacuum vessel 14. In this case, since a large amount of gas can flow from the vacuum vessel 14 to the gas inlet valve 42 and the vacuum exhaust valve 48, the Cv values ​​of the gas inlet valve 42 and the vacuum exhaust valve 48 may be larger than the Cv value of the gas inlet valve 28.

[0066] 7 is a diagram showing a fifth modified example of the gas introduction unit 20 according to the embodiment. In the fifth modified example, the gas introduction unit 20 includes, in addition to the gas cylinder 22, an additional gas cylinder 52 filled with a gas different from that of the gas cylinder 22. The additional gas cylinder 52 may be filled with a gas having a higher boiling point than the gas cylinder 22, such as nitrogen gas.

[0067] The gas introduction line 24 is configured to be switchable between connecting the gas cylinder 22 and the vacuum vessel 14 and connecting the additional gas cylinder 52 and the vacuum vessel 14. For example, an additional gas introduction valve 54 may be provided to connect the additional gas cylinder 52 to the gas introduction pipe 26. The additional gas introduction valve 54 is connected to the gas introduction pipe 26 between the gas cylinder 22 and the gas introduction valve 28.

[0068] In this way, the type of gas used can be switched depending on the temperature. For example, in the initial stage of temperature rise, a low boiling point gas, such as helium gas, can be introduced into the vacuum vessel 14 from the gas cylinder 22, and when the temperature has risen to a certain level (for example, when the temperature has risen above the temperature of liquid nitrogen), a high boiling point gas, such as nitrogen gas, can be introduced into the vacuum vessel 14 from the additional gas cylinder 52.

[0069] Alternatively, the additional gas cylinder 52 may also be filled with the same type of gas as the gas cylinder 22. In this way, gas can be supplied to the vacuum vessel 14 in stages from these two gas cylinders.

[0070] 8 is a diagram illustrating a countermeasure against condensation on the vacuum vessel 14. When it is desired to deal with condensation on the surface (e.g., the side surface) of the vacuum vessel 14, a moisture absorbent 56 may be provided so as to cover at least the portion of the surface of the vacuum vessel 14 that needs to be addressed. Also, a water tray 58 may be placed below the vacuum vessel 14 to collect dripping condensed water. A water guide plate 60 may be provided on the surface of the vacuum vessel 14 to direct the condensed water into the water tray.

[0071] The present invention has been described using specific terms based on the embodiments, but the embodiments merely illustrate one aspect of the principles and applications of the present invention, and many modifications and changes in arrangement are permitted to the embodiments as long as they do not deviate from the concept of the present invention as defined in the claims. [Explanation of symbols]

[0072] 10 superconducting magnet device, 12 superconducting coil, 14 vacuum vessel, 22 gas cylinder, 24 gas inlet line, 28 gas inlet valve, 32 gas inlet port, 34 restrictor, 38 flow path resistance portion, 40 multilayer insulation material, 42 gas inlet valve, 48 vacuum exhaust valve, 52 gas cylinder, 54 gas inlet valve.

Claims

1. A superconducting coil; a vacuum vessel that houses the superconducting coil; a gas cylinder disposed outside the vacuum vessel, the gas filling amount of which is determined so as to reduce the degree of vacuum in the vacuum vessel from a high vacuum to a medium vacuum; a cryogenic refrigerator that cools the superconducting coil; a gas introduction line connecting the gas cylinder to the vacuum vessel so as to enable gas to be introduced from the gas cylinder into the vacuum vessel when the cryogenic refrigerator is not in operation.

2. the vacuum vessel includes a gas inlet port connected to the gas inlet line and configured to receive the gas; 2. The superconducting magnet apparatus according to claim 1, wherein the gas introduction line is provided with a gas introduction valve that closes the gas introduction line when the superconducting coil is in operation and opens the gas introduction line to heat up the superconducting coil when the superconducting coil is not in operation.

3. 3. The superconducting magnet apparatus according to claim 2, further comprising a restricting member for restricting access to said gas introduction valve when said superconducting coil is in operation.

4. 4. The superconducting magnet apparatus according to claim 2, wherein a flow resistance portion for suppressing a flow rate of the gas flowing from the gas inlet port into the vacuum vessel is provided in the gas inlet line or the gas inlet port.

5. 5. The superconducting magnet apparatus according to claim 4, further comprising a multi-layer heat insulating material disposed in the vacuum vessel opposite the gas inlet port.

6. 6. The superconducting magnet apparatus according to claim 2, wherein the gas introduction port is provided with an additional gas introduction valve for opening and closing the gas introduction port.

7. 7. The superconducting magnet apparatus according to claim 6, further comprising a vacuum exhaust valve branching and connected between the gas inlet valve of the gas inlet line and the additional gas inlet valve of the gas inlet port.

8. Further provided is an additional gas cylinder filled with a gas different from the gas cylinder; 8. The superconducting magnet apparatus according to claim 1, wherein the gas introduction line is configured to be switchable between connecting the gas cylinder to the vacuum vessel and connecting the additional gas cylinder to the vacuum vessel.

9. A method for raising the temperature of a superconducting magnet device, the superconducting magnet device including a superconducting coil, a vacuum vessel containing the superconducting coil, and a cryogenic refrigerator cooling the superconducting coil, the method comprising: connecting a gas cylinder to the vacuum vessel; introducing gas from the gas cylinder into the vacuum vessel when the cryogenic refrigerator is not operating; The method according to claim 1, wherein the gas charge of the gas cylinder is determined to reduce the vacuum level of the vacuum vessel from a high vacuum to a medium vacuum.

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