Superconducting magnet device and cooling device for superconducting magnet device

Abstract

A superconducting magnet device (100) comprises: a superconducting coil device (110) provided with a superconducting coil (112) and a current introduction line (114) connected to the superconducting coil (112); a cryogenic device (120) that is provided with at least one cryogenic refrigerator (10) and that cools the superconducting coil device (110); at least one temperature sensor (130) provided to the superconducting coil device (110) or the cryogenic device (120); and a controller (140) configured to set a temperature target value on the basis of a state parameter pertaining to the superconducting magnet device (100), determine an operating parameter of the cryogenic refrigerator (10) on the basis of a comparison between a measured temperature from the temperature sensor (130) and the temperature target value, and operate the cryogenic refrigerator (10) using the determined operating parameter.

Description

Superconducting magnet device and cooling device for superconducting magnet device

[0001] The present invention relates to a superconducting magnet device and a cooling device for the superconducting magnet device.

[0002] Conventionally, there is known a superconducting magnet device that is cooled using a cryogenic refrigerator equipped with inverter control for energy conservation. In this superconducting magnet device, when the device is started up and cooled from an ambient temperature (e.g., room temperature) to a cryogenic set temperature (e.g., 10 K), if the measured temperature of the superconducting magnet device is higher than the set temperature, the output frequency of the inverter is increased to increase the refrigeration capacity of the cryogenic refrigerator. On the other hand, if the measured temperature of the superconducting magnet device is lower than the set temperature, the output frequency of the inverter is decreased to decrease the refrigeration capacity of the cryogenic refrigerator.

[0003] Japanese Patent Application Laid-Open No. 2000-121192

[0004] As a result of extensive research into superconducting magnet devices, the inventors have come to recognize the following problem. A superconducting magnet device must be cooled to an extremely low temperature below its critical temperature in order to exhibit superconductivity. The critical temperature can change depending on the state of the superconducting magnet device, such as the magnitude of the current flowing through the superconducting coils. In existing temperature control of superconducting magnet devices, the set temperature is set to a constant temperature that is sufficiently low so that the cooling temperature of the superconducting magnet device does not exceed the critical temperature even if the critical temperature changes. This means that even when the critical temperature changes and becomes relatively high depending on the state of the superconducting magnet device, the superconducting magnet device can be maintained at the set temperature, i.e., a temperature significantly lower than the increased critical temperature. In such a situation, the energy consumption required for cooling can undesirably be greater than necessary.

[0005] One exemplary object of an embodiment of the present invention is to improve energy conservation in a superconducting magnet device.

[0006] According to one aspect of the present invention, a superconducting magnet apparatus includes a superconducting coil apparatus including a superconducting coil and a current lead-in line connected to the superconducting coil; a cryogenic device including at least one cryogenic refrigerator for cooling the superconducting coil apparatus; at least one temperature sensor provided in the superconducting coil apparatus or the cryogenic device; and a controller configured to set a temperature target value based on state parameters related to the superconducting magnet apparatus, determine operating parameters of the cryogenic refrigerator based on a comparison between a measured temperature from the temperature sensor and the temperature target value, and operate the cryogenic refrigerator using the determined operating parameters.

[0007] According to one aspect of the present invention, a cooling device for a superconducting magnet device includes a cryogenic device having at least one cryogenic refrigerator for cooling a superconducting coil device, and a controller configured to set a temperature target value based on state parameters related to the superconducting magnet device, determine operating parameters for the cryogenic refrigerator based on a comparison between a measured temperature of the superconducting coil device and the temperature target value, and operate the cryogenic refrigerator using the determined operating parameters.

[0008] Any combination of the above components or mutual substitution of the components or expressions of the present invention between methods, devices, systems, computer programs, recording media, etc. are also valid aspects of the present invention.

[0009] According to the present invention, it is possible to improve the energy saving performance of a superconducting magnet device.

[0010] FIG. 1 is a diagram schematically showing a superconducting magnet device according to an embodiment. FIG. 2 is a diagram schematically showing a superconducting magnet device according to an embodiment. FIG. 3 is a diagram schematically showing a cryogenic refrigerator according to an embodiment. FIG. 4 is a graph schematically showing an exemplary relationship between the critical temperature of a superconducting coil and the magnetic field generated by the superconducting coil according to an embodiment. FIG. 5 is a graph schematically showing an example of setting a temperature target value in a superconducting magnet device according to an embodiment. FIGS. 6( a) and 6(b) are diagrams schematically showing a superconducting magnet device according to an embodiment. FIG. 7 is a graph schematically showing an example of setting a temperature target value in a superconducting magnet device according to an embodiment. FIGS. 8( a) and 8(b) are diagrams schematically showing a superconducting magnet device according to an embodiment.

[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 schematic diagram showing a superconducting magnet device 100 according to an embodiment. The superconducting magnet device 100 is installed in high-magnetic field 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 equipment (not shown), and can generate the high magnetic field required for the equipment.

[0013] The superconducting magnet device 100 includes a superconducting coil device 110, a cryogenic device 120, at least one temperature sensor 130, a status monitoring sensor 132, and a controller 140. The superconducting coil device 110 includes a superconducting coil 112, a current introduction line 114, and an excitation power supply 116. The cryogenic device 120 includes a vacuum vessel 122, a cryogenic refrigerator 10, and a heat shield 124.

[0014] The superconducting coil 112 is disposed in a vacuum vessel 122. The superconducting coil 112 is thermally coupled to the cryogenic refrigerator 10 installed in the vacuum vessel 122, and is used in a state where it is cooled to a cryogenic temperature below its critical temperature. The superconducting coil 112 is configured to generate a strong magnetic field when current is applied to it in this cooled state. The superconducting coil 112 may be a known superconducting coil (for example, a so-called low-temperature superconducting coil).

[0015] The vacuum vessel 122 is an insulated vacuum vessel, also called a cryostat, that provides a cryogenic vacuum environment suitable for bringing the superconducting coil 112 into a superconducting state. Typically, the vacuum vessel 122 has a cylindrical shape or a hollow cylindrical shape with a central cavity. The vacuum vessel 122 thus has a generally flat, circular or annular top plate 122a and bottom plate 122b, and a cylindrical side wall 122c (a cylindrical outer wall, or coaxially arranged cylindrical outer and inner walls) connecting the top plate 122a and bottom plate 122b. The cryogenic refrigerator 10 may be installed on the top plate 122a of the vacuum vessel 122. The vacuum vessel 122 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 cryogenic refrigerator 10 is configured to cool the thermal shield 124 to a first cooling temperature and to cool the superconducting coil 112 to a second cooling temperature that is lower than the first cooling temperature. In this embodiment, the cryogenic refrigerator 10 is a two-stage cryogenic refrigerator and includes a first cooling stage 33 and a second cooling stage 35. The first cooling temperature may be in a temperature range of about 20 K to about 100 K, for example, in a temperature range of about 30 K to about 50 K, and the second cooling temperature may be in a temperature range of about 3 K to about 20 K, for example, about 4 K. An exemplary configuration of the cryogenic refrigerator 10 is described below with reference to FIGS. 2 and 3.

[0017] The heat shield 124 is disposed within the vacuum vessel 122 to surround the superconducting coil 112. The heat shield 124 is formed of a metallic material such as copper or another material with high thermal conductivity. The heat shield 124 is directly attached to the first cooling stage 33 of the cryocooler 10 and thermally coupled to the first cooling stage 33. Alternatively, the heat shield 124 may be attached to the first cooling stage 33 via a flexible or rigid heat transfer member. During operation of the superconducting magnet device 100, the heat shield 124 is cooled to a first cooling temperature by the first cooling stage 33. The heat shield 124 can thermally protect low-temperature parts, such as the second cooling stage 35 of the cryocooler 10 and the superconducting coil 112, which are disposed inside the heat shield 124 and cooled to a lower temperature than the heat shield 124, from radiant heat from the vacuum vessel 122.

[0018] In this embodiment, the superconducting magnet device 100 is configured as a so-called conduction-cooled type in which the superconducting coil 112 is directly cooled by the cryogenic refrigerator 10. The superconducting coil 112 is thermally coupled to the second cooling stage 35 via a heat transfer member 126. The heat transfer member 126 is formed of a metal material such as copper or another material with high thermal conductivity, and connects the superconducting coil 112 to the second cooling stage 35. The heat transfer member 126 may be a rigid member that rigidly connects the superconducting coil 112 and the second cooling stage 35, or it may be flexible and connect the superconducting coil 112 and the second cooling stage 35 to allow relative displacement between them. Alternatively, the superconducting coil 112 may be directly attached to the second cooling stage 35 and thermally coupled to it. During operation of the superconducting magnet device 100, the superconducting coil 112 is cooled to the second cooling temperature by the second cooling stage 35.

[0019] In another embodiment, the superconducting magnet device 100 may be configured as an immersion-cooled type in which the superconducting coils 112 are immersed in a cryogenic liquid refrigerant such as liquid helium. In this case, the cryogenic refrigerator 10 is used to cool, i.e., re-condense, the liquid refrigerant. The cryogenic refrigerator 10 can cool the superconducting coils 112 via the liquid refrigerant.

[0020] The superconducting coil 112 is connected to an excitation power supply 116 arranged outside the vacuum vessel 122 by a current introduction line 114. A current (hereinafter also referred to as an excitation current) is supplied from the excitation power supply 116 to the superconducting coil 112 through the current introduction line 114. This enables the superconducting magnet device 100 to generate a strong magnetic field.

[0021] The current introduction line 114 includes an external wiring 114a, a feedthrough terminal 114b, an outer current lead 114c, and an inner current lead 114d, and forms a current path from the excitation power supply 116 to the superconducting coil 112. Typically, one current introduction line 114 on the positive side and one current introduction line 114 on the negative side are provided.

[0022] An external wiring 114a arranged outside the vacuum vessel 122 connects the excitation power supply 116 to a feedthrough terminal 114b provided on the wall of the vacuum vessel 122. The external wiring 114a may be an appropriate power supply cable. The feedthrough terminal 114b is an airtight terminal for introducing current into the vacuum vessel 122, and connects the external wiring 114a to internal wiring (i.e., the outer current lead 114c and the inner current lead 114d) inside the vacuum vessel 122. The feedthrough terminal 114b allows the current introduction line 114 to pass through the wall of the vacuum vessel 122 while maintaining the airtightness of the vacuum vessel 122.

[0023] The outer current lead 114c is disposed outside the heat shield 124 within the vacuum vessel 122, and connects the feedthrough terminal 114b to the inner current lead 114d. The outer current lead 114c is formed of a metal material with excellent conductivity, such as pure copper, such as oxygen-free copper. The low-temperature end of the outer current lead 114c, connected to the inner current lead 114d, is thermally coupled to the heat shield 124. The low-temperature end of the outer current lead 114c is fixed to the heat shield 124 or connected to the heat shield 124 via an appropriate heat transfer member, and is cooled to the first cooling temperature, similar to the heat shield 124. However, the outer current lead 114c is electrically insulated from the heat shield 124. For example, the outer current lead 114c may be attached to a fixed part, such as the heat shield 124 or the heat transfer member, by sandwiching an insulating material (e.g., a sheet of insulating resin material) between the outer current lead 114c and the fixed part.

[0024] The inner current lead 114d is disposed inside the heat shield 124 and connects the outer current lead 114c to the superconducting coil 112. The inner current lead 114d may be a high-temperature superconducting current lead formed of, for example, a copper-oxide superconductor or other high-temperature superconducting material. The hot end of the inner current lead 114d, which is connected to the outer current lead 114c, is thermally coupled to the heat shield 124 and is cooled to a first cooling temperature similar to the heat shield 124. The cold end of the inner current lead 114d, which is connected to the superconducting coil 112, is cooled to a second cooling temperature similar to the superconducting coil 112.

[0025] 2 and 3 are diagrams that schematically show a cryogenic refrigerator 10 according to an embodiment. FIG. 2 shows the appearance of the cryogenic refrigerator 10 together with a schematic block diagram, and FIG. 3 shows the internal structure of the cryogenic refrigerator 10. As an example, the cryogenic refrigerator 10 is a two-stage Gifford-McMahon (GM) refrigerator. As will be described in detail later, as shown in the figures, the cryogenic refrigerator 10 and a controller 140 constitute a cooling device for a superconducting magnet apparatus 100 according to an embodiment.

[0026] The cryogenic refrigerator 10 includes a compressor 12 and an expander 14. The compressor 12 is configured to recover the working gas of the cryogenic refrigerator 10 from the expander 14, increase the pressure of the recovered working gas, and supply the working gas again to the expander 14. The working gas, also referred to as a refrigerant gas, is typically helium gas, although other suitable gases may be used.

[0027] Generally, the pressure of the working gas supplied from the compressor 12 to the expander 14 and the pressure of the working gas recovered from the expander 14 to the compressor 12 are both significantly higher than atmospheric pressure, and can be referred to as a first high pressure and a second high pressure, respectively. For ease of explanation, the first high pressure and the second high pressure are also simply referred to as a high pressure and a low pressure, respectively. Typically, the high pressure is, for example, 2 to 3 MPa. The low pressure is, for example, 0.5 to 1.5 MPa, e.g., approximately 0.8 MPa. For ease of understanding, the flow direction of the working gas is indicated by arrows.

[0028] The compressor 12 includes a compressor body 22 and a compressor housing 23 that houses the compressor body 22. The compressor 12 is also referred to as a compressor unit.

[0029] The compressor body 22 is configured to compress the working gas drawn in through its intake port and discharge the compressed gas from its discharge port. The compressor body 22 may be, for example, a scroll type, a rotary type, or any other type of pump that pressurizes the working gas. The compressor body 22 may be configured to discharge a fixed, constant flow rate of the working gas. Alternatively, the compressor body 22 may be configured to vary the flow rate of the working gas that it discharges. The compressor body 22 is sometimes referred to as a compression capsule.

[0030] The compressor 12 also includes a compressor motor 24 and a compressor inverter 25 that controls the operating frequency, i.e., the rotation speed, of the compressor motor 24. The compressor motor 24 is a drive source that drives the compressor main body 22 and is, for example, an electric motor driven by three-phase AC. The compressor inverter 25 is configured to convert AC input from a power source 46 to AC with a different frequency and supply the converted AC to the compressor motor 24. The power source 46 may be an external power source such as a commercial power source (three-phase AC power source). The operating frequency of the compressor motor 24 may be controlled by the compressor inverter 25 within a range of 30 Hz to 100 Hz or a range of 40 Hz to 70 Hz.

[0031] As is known, the compressor 12 may have various other components not shown. For example, an oil separator, an absorber, etc. may be provided in the working gas flow path on the discharge side. A storage tank and other components may be provided in the working gas flow path on the suction side. The compressor 12 may also be provided with an oil circulation system that cools the compressor body 22 with oil, a cooling system that cools the oil with cooling water, etc.

[0032] The expander 14 includes an expander cylinder 16 and a displacer assembly 18. The expander cylinder 16 guides the linear reciprocating motion of the displacer assembly 18, and forms expansion chambers (32, 34) for the working gas between the expander cylinder 16 and the displacer assembly 18. The expander 14 also includes a pressure switching valve 40 that determines the timing at which the working gas starts to be drawn into the expansion chamber and the timing at which the working gas starts to be exhausted from the expansion chamber.

[0033] In this document, for convenience in explaining the positional relationship between the components of the cryogenic refrigerator 10, the side closer to the top dead center of the displacer's axial reciprocating motion will be referred to as "top" and the side closer to the bottom dead center will be referred to as "bottom." The top dead center is the position of the displacer where the volume of the expansion space is maximum, and the bottom dead center is the position of the displacer where the volume of the expansion space is minimum. During operation of the cryogenic refrigerator 10, a temperature gradient occurs in which the temperature decreases from top to bottom in the axial direction, so the top side can also be referred to as the high-temperature side and the bottom side as the low-temperature side.

[0034] The expander cylinder 16 includes a first cylinder 16a and a second cylinder 16b. The first cylinder 16a and the second cylinder 16b are, for example, cylindrical members, and the second cylinder 16b has a smaller diameter than the first cylinder 16a. The first cylinder 16a and the second cylinder 16b are arranged coaxially, and the lower end of the first cylinder 16a is rigidly connected to the upper end of the second cylinder 16b.

[0035] The displacer assembly 18 includes a first displacer 18a and a second displacer 18b that are connected to each other and move together. The first displacer 18a and the second displacer 18b are, for example, cylindrical members, and the second displacer 18b has a smaller diameter than the first displacer 18a. The first displacer 18a and the second displacer 18b are arranged coaxially.

[0036] The first displacer 18a is accommodated in the first cylinder 16a, and the second displacer 18b is accommodated in the second cylinder 16b. The first displacer 18a is reciprocatingly movable in the axial direction along the first cylinder 16a, and the second displacer 18b is reciprocatingly movable in the axial direction along the second cylinder 16b.

[0037] 3, the first displacer 18a accommodates a first regenerator 26. The first regenerator 26 is formed by filling a cylindrical main body of the first displacer 18a with a wire mesh made of copper or other suitable first regenerator material. The upper and lower covers of the first displacer 18a may be provided as separate members from the main body of the first displacer 18a, and the upper and lower covers of the first displacer 18a may be fixed to the main body by suitable means such as fastening or welding, thereby accommodating the first regenerator material in the first displacer 18a.

[0038] Similarly, the second displacer 18b accommodates a second regenerator 28. The second regenerator 28 is made of a non-magnetic regenerator material such as bismuth, HoCu, etc., housed in a cylindrical body of the second displacer 18b. ２The second displacer 18b is formed by filling it with a magnetic regenerator material such as a refrigerant or other suitable second regenerator material. The second regenerator material may be formed in a granular form. The upper and lower lids of the second displacer 18b may be provided as separate members from the main body of the second displacer 18b, and the upper and lower lids of the second displacer 18b may be fixed to the main body by suitable means such as fastening or welding, thereby containing the second regenerator material in the second displacer 18b.

[0039] The displacer assembly 18 defines an upper chamber 30, a first expansion chamber 32, and a second expansion chamber 34 inside the expander cylinder 16. The expander 14 includes a first cooling stage 33 and a second cooling stage 35 for heat exchange with a desired object or medium to be cooled by the cryogenic refrigerator 10. The upper chamber 30 is defined between the upper cover of the first displacer 18a and the top of the first cylinder 16a. The first expansion chamber 32 is defined between the lower cover of the first displacer 18a and the first cooling stage 33. The second expansion chamber 34 is defined between the lower cover of the second displacer 18b and the second cooling stage 35. The first cooling stage 33 is fixed to the lower part of the first cylinder 16a to surround the first expansion chamber 32, and the second cooling stage 35 is fixed to the lower part of the second cylinder 16b to surround the second expansion chamber 34. The first cooling stage 33 and the second cooling stage 35 are formed of, for example, pure copper (for example, oxygen-free copper, tough pitch copper, etc.) or other highly thermally conductive metal.

[0040] The first regenerator 26 is connected to the upper chamber 30 through a working gas passage 36a formed in the upper lid of the first displacer 18a, and is connected to the first expansion chamber 32 through a working gas passage 36b formed in the lower lid of the first displacer 18a. The second regenerator 28 is connected to the first regenerator 26 through a working gas passage 36c formed from the lower lid of the first displacer 18a to the upper lid of the second displacer 18b. The second regenerator 28 is also connected to the second expansion chamber 34 through a working gas passage 36d formed in the lower lid of the second displacer 18b.

[0041] A first seal 38a and a second seal 38b may be provided so that the flow of working gas between the first expansion chamber 32, the second expansion chamber 34 and the upper chamber 30 is directed to the first regenerator 26, the second regenerator 28, rather than through the clearance between the expander cylinder 16 and the displacer assembly 18. The first seal 38a may be attached to the top cover of the first displacer 18a so as to be positioned between the first displacer 18a and the first cylinder 16a. The second seal 38b may be attached to the top cover of the second displacer 18b so as to be positioned between the second displacer 18b and the second cylinder 16b.

[0042] 2, the expander 14 includes an expander housing 20 that houses the pressure switching valve 40. The expander housing 20 is coupled to the expander cylinder 16, thereby forming an airtight container that houses the pressure switching valve 40 and the displacer assembly 18. The expander housing 20 and the expander cylinder 16 are formed of a metal material, such as stainless steel, or other suitable high-strength material so that the airtight container can withstand the pressure difference between the inside and outside.

[0043] 3, the pressure switching valve 40 includes a high-pressure valve 40a and a low-pressure valve 40b, and is configured to generate periodic pressure fluctuations in the expander cylinder 16. The working gas discharge port of the compressor 12 is connected to the upper chamber 30 via the high-pressure valve 40a, and the working gas inlet port of the compressor 12 is connected to the upper chamber 30 via the low-pressure valve 40b. The high-pressure valve 40a and the low-pressure valve 40b are configured to selectively and alternately open and close (i.e., when one is open, the other is closed).

[0044] The pressure switching valve 40 may take the form of a rotary valve. That is, the pressure switching valve 40 may be configured so that the high-pressure valve 40a and the low-pressure valve 40b are alternately opened and closed by the rotational sliding of a valve disc relative to a stationary valve body. In this case, the expander motor 42 may be connected to the pressure switching valve 40 so as to rotate the valve disc of the pressure switching valve 40. For example, the pressure switching valve 40 is arranged so that the valve rotation axis is coaxial with the rotation axis of the expander motor 42.

[0045] Alternatively, the high pressure valve 40 a and the low pressure valve 40 b may be valves that can be controlled individually, in which case the pressure switching valve 40 does not need to be connected to the expander motor 42 .

[0046] The expander 14 includes an expander motor 42 and a motion conversion mechanism 43. The expander motor 42 is a drive source that drives the expander 14, and is, for example, an electric motor driven by three-phase AC. The expander motor 42 is attached to the expander housing 20. The motion conversion mechanism 43 is housed in the expander housing 20, similar to the pressure switching valve 40.

[0047] The expander motor 42 is connected to a displacer drive shaft 44 via a motion conversion mechanism 43, such as a Scotch yoke mechanism. The motion conversion mechanism 43 converts the rotational motion output by the expander motor 42 into linear reciprocating motion of the displacer drive shaft 44. The displacer drive shaft 44 extends from the motion conversion mechanism 43 into the upper chamber 30 and is fixed to the top lid of the first displacer 18a. The rotation of the expander motor 42 is converted into axial reciprocating motion of the displacer drive shaft 44 by the motion conversion mechanism 43, and the displacer assembly 18 reciprocates linearly in the axial direction within the expander cylinder 16.

[0048] The cryogenic refrigerator 10 is also provided with an expander inverter 45 that controls the operating frequency, i.e., the rotation speed, of the expander motor 42. In this example, the expander inverter 45 is mounted on the compressor 12, but is not limited to this and may be mounted on the expander 14. The expander inverter 45 is configured to convert AC input from the power source 46 to the expander inverter 45 into AC having a different frequency, and supply the converted AC to the compressor motor 24. The operating frequency of the expander motor 42 may be controlled by the expander inverter 45 within a range of 30 Hz to 100 Hz or a range of 40 Hz to 70 Hz.

[0049] Furthermore, a first temperature sensor 130a for measuring a first cooling temperature and a second temperature sensor 130b for measuring a second cooling temperature may be provided.

[0050] The first temperature sensor 130a may be arranged to measure the temperature of any portion of the superconducting magnet device 100 that is cooled to the first cooling temperature. For example, as shown in Fig. 2, the first temperature sensor 130a may be attached to the first cooling stage 33. Alternatively, as shown in Fig. 1, the first temperature sensor 130a may be attached to a portion of the current lead 114 that is cooled to the first cooling temperature (e.g., the high-temperature end of the inner current lead 114d or the low-temperature end of the outer current lead 114c). The first temperature sensor 130a may be attached to the heat shield 124.

[0051] The second temperature sensor 130b may be arranged to measure the temperature of any portion cooled to the second cooling temperature in the superconducting magnet device 100. For example, as shown in Fig. 2, the second temperature sensor 130b may be attached to the second cooling stage 35. Alternatively, as shown in Fig. 1, the second temperature sensor 130b may be attached to the superconducting coil 112 or the heat transfer member 126.

[0052] The first temperature sensor 130a and the second temperature sensor 130b are each communicatively connected to the controller 140 by wire or wirelessly, and can transmit information indicating the measured temperatures to the controller 140. A first temperature signal T1 indicating a first cooling temperature measured by the first temperature sensor 130a may be input from the first temperature sensor 130a to the controller 140. A second temperature signal T2 indicating a second cooling temperature measured by the second temperature sensor 130b may be input from the second temperature sensor 130b to the controller 140.

[0053] The condition monitoring sensor 132 is configured to measure a condition parameter related to the superconducting magnet device 100. The condition parameter may be a condition parameter related to the superconducting coil device 110 or a condition parameter related to the cryogenic device 120.

[0054] In this embodiment, the status monitoring sensor 132 may measure the current flowing through the superconducting coil 112 through the current introduction line 114 as a status parameter related to the superconducting coil device 110. In other words, the status monitoring sensor 132 may be a current sensor that measures the excitation current supplied to the superconducting coil 112. As shown in FIG. 1 , the status monitoring sensor 132 may be provided in the excitation power supply 116 to measure the excitation current to the superconducting coil 112. Alternatively, the status monitoring sensor 132 may be provided in the current introduction line 114 (e.g., external wiring 114 a) to measure the excitation current to the superconducting coil 112.

[0055] Because the strength of the magnetic field generated by the superconducting coil 112 is approximately linearly correlated with the excitation current to the superconducting coil 112, the status monitoring sensor 132 may measure the magnetic field (e.g., magnetic flux density) generated by the superconducting coil 112 as a status parameter for the superconducting coil device 110. Such a magnetic field sensor may be disposed anywhere in the region where the superconducting coil 112 generates a magnetic field. For example, the magnetic field sensor may be disposed outside the vacuum vessel 122, such as by being attached to the outer surface of the vacuum vessel 122. Alternatively, the magnetic field sensor may be disposed inside the vacuum vessel 122, such as by being attached to or located near the superconducting coil 112.

[0056] The condition monitoring sensor 132 is communicatively connected to the controller 140 by wire or wirelessly and can transmit information indicative of the measured condition parameter to the controller 140. A condition signal S indicative of the condition parameter measured by the condition monitoring sensor 132 may be input from the condition monitoring sensor 132 to the controller 140.

[0057] The controller 140 is configured to set a temperature target value based on the output from the condition monitoring sensor 132. Details of this setting will be described later.

[0058] In addition, the controller 140 is configured to determine operating parameters of the cryogenic refrigerator 10 based on a comparison between the measured temperature from the temperature sensor 130 (e.g., the first temperature sensor 130a or the second temperature sensor 130b) and the target temperature value, and to operate the cryogenic refrigerator 10 using the determined operating parameters.

[0059] For example, the controller 140 may be configured to determine a temperature error based on a comparison of the measured temperature from the temperature sensor 130 with a temperature target value, and to determine operating parameters of the cryogenic refrigerator 10 based on the temperature error. The controller 140 may include a feedback control system that determines the operating parameters of the cryogenic refrigerator 10 to reduce or minimize the temperature error.

[0060] The operating parameter of the cryogenic refrigerator 10 may be the operating frequency of the compressor motor 24 or the operating frequency of the expander motor 42. The controller 140 may be configured to generate a compressor command signal B1 indicating a command value for the operating frequency of the compressor motor 24 based on a comparison between the temperature measured by the temperature sensor 130 and a temperature target value, and output the signal to the compressor inverter 25. The compressor inverter 25 can drive the compressor motor 24 at the operating frequency of the command value in accordance with the compressor command signal B1. The controller 140 may also be configured to generate an expander command signal B2 indicating a command value for the operating frequency of the expander motor 42 based on a comparison between the temperature measured by the temperature sensor 130 and a temperature target value, and output the signal to the expander inverter 45. The expander inverter 45 can drive the expander motor 42 at the operating frequency of the command value in accordance with the expander command signal B2.

[0061] The internal configuration of the controller 140 is realized as a hardware configuration by elements and circuits such as a computer CPU and memory, and as a software configuration by a computer program, etc., but in the figure it is depicted as appropriate as functional blocks realized by the cooperation of these. Those skilled in the art will understand that these functional blocks can be realized in various ways by combining hardware and software.

[0062] For example, the controller 140 can be implemented as a combination of a processor (hardware) such as a CPU (Central Processing Unit) or a microcomputer, and a software program executed by the processor (hardware). Such a hardware processor may be configured, for example, as a programmable logic device such as an FPGA (Field Programmable Gate Array), or may be a control circuit such as a programmable logic controller (PLC). The software program may be a computer program that causes the controller 140 to control the superconducting magnet device 100 or the cryogenic refrigerator 10.

[0063] 1 and 2, the controller 140 may be located separately from the excitation power supply 116 of the superconducting magnet device 100 and the cryogenic refrigerator 10. Alternatively, the controller 140 may be incorporated into the excitation power supply 116. Alternatively, the controller 140 may be mounted on a component of the cryogenic refrigerator 10 (e.g., the compressor 12 or the expander 14). Alternatively, the controller 140 may be located remotely from the superconducting magnet device 100 and the cryogenic refrigerator 10 and communicatively connected thereto.

[0064] With the above configuration, when the compressor 12 and the expander motor 42 are operated, the cryogenic refrigerator 10 generates periodic volume fluctuations and synchronized pressure fluctuations of the working gas in the first expansion chamber 32 and the second expansion chamber 34. Typically, during the intake stroke, the low-pressure valve 40b closes and the high-pressure valve 40a opens, causing high-pressure working gas to flow from the compressor 12 through the high-pressure valve 40a into the upper chamber 30, be supplied to the first expansion chamber 32 through the first regenerator 26, and be supplied to the second expansion chamber 34 through the second regenerator 28. In this way, the pressures of the first expansion chamber 32 and the second expansion chamber 34 are increased from low to high. At this time, the displacer assembly 18 is moved upward from bottom dead center to top dead center, increasing the volumes of the first expansion chamber 32 and the second expansion chamber 34. The intake stroke ends when the high-pressure valve 40a closes.

[0065] During the exhaust stroke, the high-pressure valve 40a closes and the low-pressure valve 40b opens, opening the high-pressure first and second expansion chambers 32 and 34 to the low-pressure working gas inlet of the compressor 12. The working gas expands in the first and second expansion chambers 32 and 34, and the resulting low-pressure working gas is discharged from the first and second expansion chambers 32 and 34 through the first and second regenerators 26 and 28 into the upper chamber 30. At this time, the displacer assembly 18 is moved downward from top dead center to bottom dead center, reducing the volumes of the first and second expansion chambers 32 and 34. The working gas is recovered from the expander 14 to the compressor 12 through the low-pressure valve 40b. The exhaust stroke ends when the low-pressure valve 40b closes.

[0066] In this manner, a refrigeration cycle, such as a GM cycle, is configured, and the first and second cooling stages 33 and 35 are cooled to a desired cryogenic temperature. The first cooling stage 33 can be cooled to a first cooling temperature, for example, in the range of approximately 30 K to approximately 70 K. Portions of the current introduction line 114 thermally coupled to the first cooling stage 33 (e.g., the low-temperature end of the outer current lead 114 c and the high-temperature end of the inner current lead 114 d) and the heat shield 124 are also cooled to the first cooling temperature. The second cooling stage 35 can be cooled to a second cooling temperature (e.g., approximately 1 K to approximately 4 K) lower than the first cooling temperature. The superconducting coil 112 is cooled to the second cooling temperature by the second cooling stage 35. In this manner, the cryocooler 10 can cool the superconducting coil 112 below its critical temperature, enabling the superconducting magnet device 100 to operate.

[0067] When the superconducting magnet device 100 is started up, an excitation current is supplied to the superconducting coil 112 from the excitation power supply 116 through the current introduction line 114, thereby exciting the superconducting coil 112. The excitation power supply 116 may increase the excitation current from zero to the rated current value of the superconducting coil 112 at a predetermined current increase rate (e.g., a constant current increase rate). The excitation power supply 116 may maintain the excitation current at the rated current value during operation of the superconducting magnet device 100. Furthermore, when the superconducting magnet device 100 is shut down, the excitation power supply 116 may decrease the excitation current of the superconducting coil 112 from the rated current value to zero at a predetermined current decrease rate (e.g., a constant current decrease rate). In this way, the superconducting coil 112 can generate a magnetic field in response to the excitation current.

[0068] 4 is a graph according to an embodiment, which schematically illustrates an exemplary relationship between the critical temperature of the superconducting coil 112 and the magnetic field generated by the superconducting coil 112. The vertical axis of the graph represents the critical temperature Tc of the superconducting coil 112, and the horizontal axis represents the maximum value of the self-magnetic field generated within the superconducting coil 112. Because the maximum value of the self-magnetic field within the superconducting coil 112 is roughly proportional to the current flowing through the superconducting coil 112, the horizontal axis of the graph can also be considered to represent the excitation current to the superconducting coil 112.

[0069] The critical temperature of the superconducting coil 112 depends on the maximum value of the self-magnetic field in the superconducting coil 112 and the excitation current to the superconducting coil 112. As shown in Fig. 4, the critical temperature of the superconducting coil 112 is approximately linear with respect to the maximum value of the self-magnetic field in the superconducting coil 112, and the larger the magnetic field, the lower the critical temperature.

[0070] If the cooling temperature of the superconducting coil 112 exceeds the critical temperature, a quench (loss of superconductivity) may occur. Therefore, the temperature target value Tt for the second cooling temperature for cooling the superconducting coil 112 should be set so as not to exceed the critical temperature Tc. To reduce the risk that the cooling temperature of the superconducting coil 112 accidentally exceeds the critical temperature Tc, the temperature target value Tt may be set to a temperature value that is lower than the critical temperature Tc by a certain temperature margin TM. The larger the temperature margin TM is set and the lower the temperature target value Tt is set relative to the critical temperature Tc, the easier it is to prevent quenching of the superconducting coil 112.

[0071] The risk of quenching the superconducting coil 112 varies depending on the state of the superconducting magnet device 100. For example, the risk of quenching increases when the excitation current is changing (e.g., increasing) compared to when the excitation current is maintained constant. This is because, for example, AC losses can cause the superconducting coil 112 to heat up and rise in temperature during magnetization or demagnetization. AC losses are caused by the time rate of change of the excitation current to the superconducting coil 112 (in other words, the magnetic field generated by the superconducting coil 112). Furthermore, during magnetization or demagnetization, a stick-slip phenomenon can occur due to deformation of the superconducting coil 112. Such mechanical disturbances can cause instantaneous localized heating within the superconducting coil 112, which can ultimately lead to a quench.

[0072] To address this issue, existing superconducting coil temperature management typically selects a relatively large temperature margin TM, so that the superconducting coil is cooled to a constant cooling temperature that is sufficiently lower than the critical temperature throughout its entire operation period, from energization to deenergization. While this is effective in preventing quenching, it may require more energy to cool the superconducting coil.

[0073] Therefore, in this embodiment, the controller 140 is configured to set the target temperature value Tt based on the output (e.g., the status signal S) from the status monitoring sensor 132. The controller 140 is configured to determine the operating parameters of the cryogenic refrigerator 10 based on a comparison between the measured temperature from the temperature sensor 130 and the target temperature value Tt, and to operate the cryogenic refrigerator 10 using the determined operating parameters.

[0074] In this way, it is possible to set the target temperature value Tt according to the state of the superconducting magnet device 100 detected by the state monitoring sensor 132, and adjust the cooling capacity of the cryogenic refrigerator 10. It is expected that this will enable improved energy conservation in the superconducting magnet device 100, compared to the existing method of maintaining a constant cooling temperature that is sufficiently lower than the critical temperature.

[0075] The controller 140 may be configured to determine the measured value of the state parameter and the amount of change over time thereof based on the output from the state monitoring sensor 132. For example, the controller 140 may receive a state signal S from the state monitoring sensor 132 and determine the measured value of the state parameter based on the state signal S. The controller 140 may also determine the amount of change over time of the state parameter by calculation from the acquired measured value of the state parameter.

[0076] When the status monitoring sensor 132 measures the excitation current to the superconducting coil 112, the controller 140 determines the excitation current and its time-dependent change amount (for example, its time derivative, i.e., the sweep rate of the excitation current) based on the output from the status monitoring sensor 132. When the status monitoring sensor 132 measures the magnetic field generated by the superconducting coil 112, the controller 140 determines the magnetic field and its time-dependent change amount based on the output from the status monitoring sensor 132.

[0077] The controller 140 may be configured to set the temperature target value Tt according to a predetermined relationship between the measured value and the time change of the state parameter and the temperature target value Tt. As described above, the critical temperature Tc depends on the state parameter, and the risk of quenching can be reflected in the time change of the state parameter. In this way, it is possible to set the temperature target value Tt so as not to exceed the critical temperature Tc while taking into account the risk of quenching.

[0078] The predetermined relationship may be determined such that the larger the measured value of the state parameter, the smaller the target temperature value Tt. In this way, the target temperature value Tt can be set in accordance with the tendency of change in the critical temperature Tc, which decreases as the state parameter increases, as illustrated in FIG.

[0079] The predetermined relationship may be determined such that the greater the change in the state parameter over time, the smaller the target temperature value Tt. In this way, the target temperature value Tt can be set according to the risk of quenching, which increases as the change in the state parameter over time increases.

[0080] 5 is a graph according to an embodiment, schematically illustrating an example of setting a temperature target value Tt in the superconducting magnet device 100. The graph shows an example of the time change of the excitation current I to the superconducting coil 112, the time change of the critical temperature Tc of the superconducting coil 112 determined according to the excitation current, and the time change of the temperature target value Tt set based on the excitation current. The vertical axis of the graph represents the excitation current or the temperature of the superconducting coil 112, and the horizontal axis represents the elapsed time. However, in the graph, the excitation current and the elapsed time are normalized as normalized current and normalized time, respectively, normalized by a ratio to a certain reference value.

[0081] 5 , the normalized current to the superconducting coil 112 is supplied over a normalized time period from time 1 to time 5. More specifically, the excitation of the superconducting coil 112 extends over a normalized time period from time 1 to time 2. Thus, the normalized current increases from 0 to 1 over a normalized time period from time 1 to time 2. The normalized current value of 1 may correspond to the rated current of the superconducting coil 112. The superconducting coil 112 is in normal operation over a normalized time period from time 2 to time 4, during which the normalized current is maintained constant at a value of 1 (i.e., the rated current is supplied to the superconducting coil 112). Then, over a normalized time period from time 4 to time 5, the normalized current is decreased from 1 to 0, and the superconducting coil 112 is demagnetized.

[0082] As described above, the critical temperature Tc of the superconducting coil 112 decreases as the excitation current I to the superconducting coil 112 increases. Therefore, during the normalized time from time 0 to time 1 and from time 5 to time 6 when no excitation current is supplied to the superconducting coil 112, the critical temperature Tc has a relatively large first temperature value (approximately 9.5 K in the illustrated example). During the normalized time from time 2 to time 4 when the superconducting coil 112 is in operation, the critical temperature Tc has a relatively small second temperature value (approximately 6.5 K in the illustrated example). During the normalized time from time 1 to time 2 when the superconducting coil 112 is being excited, the critical temperature Tc decreases from the first temperature value to the second temperature value as the current increases. During the normalized time from time 4 to time 5 when the superconducting coil 112 is being demagnetized, the critical temperature Tc increases from the second temperature value to the first temperature value as the current decreases.

[0083] The temperature target value Tt for the second cooling temperature for cooling the superconducting coil 112 is set to a temperature value lower than the critical temperature Tc of the superconducting coil 112. The temperature target value Tt is set in conjunction with the critical temperature Tc. In other words, if the critical temperature Tc increases (or decreases), the temperature target value Tt also increases (or decreases). In this embodiment, the temperature margin TM is not constant regardless of the state of the superconducting coil 112. The temperature margin TM differs depending on the state of the superconducting coil 112.

[0084] 5 , the temperature target value Tt is set to a temperature value that is lower than the critical temperature Tc by a first temperature margin TM1 during the normalized times from time 0 to time 1 and from time 5 to time 6 when no excitation current is supplied to the superconducting coil 112. The first temperature margin TM1 may be selected, for example, from a range of 1 K to 2 K. In this example, the first temperature margin TM1 is 1.5 K, and the temperature target value Tt is set to 8 K.

[0085] From time 2 to time 4 in the normalized time during which the superconducting coil 112 is in operation, the temperature target value Tt is set to a temperature value that is lower than the critical temperature Tc by the second temperature margin TM2. In this way, the temperature target value Tt is also reduced in accordance with the reduction in the critical temperature Tc that accompanies the application of current to the superconducting coil 112. The second temperature margin TM2 may be the same as the first temperature margin TM1. In this case, in this example, the temperature target value Tt is set to 5 K. Alternatively, the second temperature margin TM2 may be different from the first temperature margin TM1.

[0086] During the normalized time from time 1 to time 2 during which the superconducting coil 112 is excited, the temperature target value Tt is set to a temperature value lower than the critical temperature Tc by a third temperature margin TM3. As shown in FIG. 5 , the third temperature margin TM3 is greater than the first temperature margin TM1 (and the second temperature margin TM2). In other words, during the excitation of the superconducting coil 112, the temperature margin TM is increased compared to before the excitation (and during operation after the excitation), and the temperature target value Tt is reduced by a greater amount. The third temperature margin TM3 may be selected, for example, from a range of 2 K to 5 K.

[0087] Similarly, during the normalized time from time 4 to time 5 during which the superconducting coil 112 is being demagnetized, the target temperature value Tt is set to a temperature value that is lower than the critical temperature Tc by a fourth temperature margin TM4. The fourth temperature margin TM4 is also greater than the first temperature margin TM1 (and the second temperature margin TM2). The fourth temperature margin TM4 may be equal to or different from the third temperature margin TM3.

[0088] As described above, the risk of quenching increases when the excitation current is changing, such as during excitation of the superconducting coil 112. By temporarily lowering the temperature target value Tt while the excitation current is changing, the temperature margin TM can be increased to address the increased risk of quenching. Furthermore, when no excitation current is being supplied or a constant excitation current is being supplied, the risk of quenching decreases. In such a situation, the refrigeration capacity that the cryocooler 10 should provide can be reduced by setting the temperature target value Tt higher. This improves the energy efficiency of the superconducting magnet device 100.

[0089] An exemplary method for setting such a temperature target value Tt according to the state of the superconducting coil 112 can use the following general formula, which includes a function of the excitation current and a function of the time derivative of the excitation current: Tt=f(I)+g(dI / dt)+T ０ where f is a function of the excitation current I, and g is a function of the time differential of the excitation current I (i.e., the current sweep rate). ０ is a temperature constant.

[0090] In fact, in the example of FIG. 5, the temperature target value Tt of the superconducting coil 112 is determined by the following formula: Tt=C １ I+C ２ (dI / dt) ２ +T ０ Here, the coefficient C １ , C ２ Both are negative values. ０ is predetermined to be the critical temperature Tc when no exciting current is supplied to the superconducting coil 112.

[0091] Therefore, when no excitation current is supplied to the superconducting coil 112, Tt=T ０ That is, the temperature target value Tt is set to the critical temperature Tc when no excitation current is supplied to the superconducting coil 112. When a constant excitation current is supplied to the superconducting coil 112, dI / dt=0, and therefore Tt=C １ I+T ０ Coefficient C １is a negative value, the set temperature target value Tt is T ０ For example, the coefficient C is set to correspond to the proportional constant of the linear relationship between the critical temperature Tc and the excitation current as shown in FIG. １ By setting the temperature target value Tt to be lower than the critical temperature Tc, the set temperature target value Tt can be made lower than the critical temperature Tc.

[0092] When the excitation current is changing, such as during excitation of the superconducting coil 112, Tt=C １ I+C ２ (dI / dt) ２ +T ０ Coefficient C ２ is a negative value, and (dI / dt) ２ is a positive value, the set temperature target value Tt is １ I+T ０ Therefore, as illustrated in FIG. 5, when the excitation current is changing, the temperature target value Tt can be lowered compared to when the excitation current is not changing.

[0093] The advantage of setting the target temperature value Tt using a single formula like this is that the user does not need to determine the state of the superconducting magnet device 100 and change the target temperature value Tt depending on that state. Regardless of various states such as non-excitation, excitation, operation at a constant current, and demagnetization, the target temperature value Tt can be automatically set using a single formula. The operating state of the cryogenic refrigerator 10 can be changed depending on the setting of the target temperature value Tt, thereby improving the energy saving performance of the superconducting magnet device 100.

[0094] Note that the amount of change over time of the state parameter may be omitted when setting the target temperature value Tt. Therefore, the controller 140 may be configured to determine the measured value of the state parameter based on the output from the state monitoring sensor 132, and set the target temperature value in accordance with a predetermined relationship between the measured value of the state parameter and the target temperature value.

[0095] Such an alternative setting method may be used to set a temperature target value for the first cooling temperature when the current introduction line 114 has a high-temperature superconducting current lead. If the cooling temperature of the high-temperature superconducting current lead exceeds its critical temperature (e.g., about 60 K to 70 K), a quench may occur in the high-temperature superconducting current lead. However, unlike the superconducting coil 112, the high-temperature superconducting current lead does not have the risk of quenching due to changes in the excitation current. Therefore, as an example, the temperature target value for the first cooling temperature is Tt=f(I)+T ０ , more specifically, for example, Tt=C １ I+T ０ It may be set by:

[0096] In the above-described embodiment, the target temperature value Tt is set based on the measured value of the state parameter (and / or its change over time), but instead, the controller 140 may be configured to set the target temperature value based on the command value of the state parameter. Ideally, the command value and the measured value of the state parameter match, so the target temperature value can also be set using the command value of the state parameter.

[0097] For example, the controller 140 may store a command value for the excitation current to the superconducting coil 112 and transmit this command value to the excitation power supply 116. The excitation power supply 116 may supply the excitation current to the superconducting coil 112 in accordance with the command value from the controller 140. The controller 140 may set a temperature target value Tt based on the command value for the excitation current to the superconducting coil 112.

[0098] The superconducting magnet device 100 may be configured to generate a charged particle beam. For example, the superconducting magnet device 100 may be a superconducting accelerator, such as a superconducting cyclotron, or a part thereof. When the charged particle beam hits a structure, such as an obstacle, in the superconducting accelerator, a loss of beam current may occur. Neutrons may be generated and scattered in proportion to the magnitude of this loss. Neutrons that hit the superconducting coil 112 may impart energy to the superconducting coil 112, causing the temperature of the superconducting coil 112 to increase. In this way, heat input to the superconducting coil 112 may occur in proportion to the beam current.

[0099] Therefore, the controller 140 may be configured to set the temperature target value Tt based on the beam current of the charged particle beam generated by the superconducting accelerator as a state parameter. The controller 140 may set the temperature target value Tt based on a command value of the beam current. Alternatively, the state monitoring sensor 132 may be a beam current sensor that measures the beam current of the charged particle beam as a state parameter. The controller 140 may set the temperature target value Tt based on the measured value of the beam current.

[0100] In the above-described embodiment, the controller 140 is configured to set a temperature target value for either the first cooling temperature or the second cooling temperature based on the output from the condition monitoring sensor 132. Alternatively, temperature target values ​​may be set for both the first cooling temperature and the second cooling temperature.

[0101] Therefore, the controller 140 may be configured to set a first temperature target value and a second temperature target value based on the output from the condition monitoring sensor 132. The first temperature target value is a temperature target value for the first cooling temperature, and the second temperature target value is a temperature target value for the second cooling temperature. The first temperature target value and the second temperature target value can each be set by the exemplary setting method described above.

[0102] The controller 140 may be configured to determine a first candidate value for an operating parameter of the cryogenic refrigerator 10 based on a comparison between a measured value of a first cooling temperature from the first temperature sensor 130a and a first target temperature value, to determine a second candidate value for an operating parameter of the cryogenic refrigerator 10 based on a comparison between a measured value of a second cooling temperature from the second temperature sensor 130b and a second target temperature value, and to determine the operating parameter of the cryogenic refrigerator 10 based on the first candidate value and the second candidate value.

[0103] For example, the controller 140 may select a candidate value that brings about a higher cooling capacity for the cryogenic refrigerator 10 from among first and second candidate values ​​for the operating parameters of the cryogenic refrigerator 10, and determine the selected candidate value as the operating parameter of the cryogenic refrigerator 10. When the operating frequency of the compressor motor 24 (or the expander motor 42) is used as the operating parameter of the cryogenic refrigerator 10, the controller 140 may use the higher operating frequency value from the first and second candidate values. In this manner, it is expected that it will be possible to satisfy the temperature target values ​​for both the first cooling temperature and the second cooling temperature.

[0104] Furthermore, the controller 140 may be configured to determine the operating frequency of one of the compressor motor 24 and the expander motor 42 as an operating parameter of the cryogenic refrigerator 10 based on a comparison between the measured temperature from the temperature sensor 130 and a temperature target value, and to determine the operating frequency of the other of the compressor motor 24 and the expander motor 42 based on the determined operating frequency. For example, the controller 140 may be configured to determine the operating frequency of the compressor motor 24 as an operating parameter of the cryogenic refrigerator 10 based on a comparison between the measured temperature from the temperature sensor 130 and a temperature target value, and to determine the operating frequency of the expander motor 42 based on the determined operating frequency.

[0105] In this case, the controller 140 may use a predetermined relationship between the operating frequency of the compressor motor 24 and the operating frequency of the expander motor 42 to determine the operating frequency of one of the compressor motor 24 and the expander motor 42. The predetermined relationship may be an operating frequency f of the compressor motor 24 that is optimized to achieve effective cooling by the cryogenic refrigerator 10. ｃｏｍｐ and the operating frequency f of the expander motor 42 ＣＨ Such an optimized relationship can be appropriately set based on the designer's empirical knowledge or experiments or simulations. The predetermined relationship can be, for example, ＣＨ = a × f ｃｏｍｐ +f ０ (T2), the operating frequency f of the compressor motor 24 ｃｏｍｐ and the operating frequency f of the expander motor 42ＣＨ It may have a linear relationship with f ０ (T2) is a function of the second cooling temperature.

[0106] If the operating frequency of the expander motor 42 calculated from the operating frequency of the compressor motor 24 according to a predetermined relationship deviates from the range of possible operating frequencies of the expander motor 42, the maximum (or minimum) value of the range of possible operating frequencies may be used instead of the calculated value of the operating frequency. The same applies when determining the operating frequency of the compressor motor 24 from the operating frequency of the expander motor 42.

[0107] 6(a) and 6(b) are diagrams schematically illustrating a superconducting magnet device 100 according to an embodiment. While one cryogenic refrigerator 10 is shown as an example in Fig. 1, the superconducting magnet device 100 may include multiple cryogenic refrigerators 10 for cooling one and the same superconducting coil 112, as shown in Fig. 6(a) and 6(b), as necessary, for example, when the superconducting coil 112 is large.

[0108] In this case, the superconducting magnet device 100 may be provided with a plurality of temperature sensors 130 that measure the temperature of the superconducting coil 112. Each of the plurality of temperature sensors 130 may be associated with a different one of the plurality of cryogenic refrigerators 10. In the illustrated example, two cryogenic refrigerators 10 and two temperature sensors 130 are provided, one temperature sensor 130 associated with one cryogenic refrigerator 10, and the other temperature sensor 130 associated with the other cryogenic refrigerator 10.

[0109] The controller 140 may be configured to determine the operating parameters of each of the multiple cryogenic refrigerators 10 based on a comparison of the measured temperature from the temperature sensor 130 corresponding to the cryogenic refrigerator 10 among the multiple temperature sensors 130 with the target temperature value.

[0110] 6( a) shows a configuration in which multiple cryogenic refrigerators 10 are installed at positions thermally separated from one another. Multiple temperature sensors 130 are also arranged at positions separated from one another. In such a case, each of the multiple cryogenic refrigerators 10 may be individually controlled using the temperature measurements from the corresponding temperature sensors 130. Thus, the controller 140 may be configured to individually operate the multiple cryogenic refrigerators 10 using operating parameters determined for each of the multiple cryogenic refrigerators 10.

[0111] 6(b) shows a configuration in which a plurality of cryogenic refrigerators 10 are installed in close thermal proximity to one another. A plurality of temperature sensors 130 are also arranged in close proximity to one another. In such a case, if the cryogenic refrigerators 10 were controlled individually as in the configuration of FIG. 6(a), there is a concern that the control may become unstable, such as hunting occurring in the operating parameters of the cryogenic refrigerators 10, due to the plurality of cryogenic refrigerators 10 being strongly thermally coupled to one another.

[0112] Therefore, when multiple cryogenic refrigerators 10 are arranged in close thermal proximity as in the configuration of FIG. 6( b), the controller 140 may be configured to determine representative values ​​of operating parameters based on operating parameters determined for each of the multiple cryogenic refrigerators 10 and operate the multiple cryogenic refrigerators 10 using the determined representative values ​​of the operating parameters. For example, the controller 140 may use, as a representative value, an operating parameter value that provides a higher refrigeration capacity to the cryogenic refrigerator 10, among the operating parameter values ​​determined for each of the multiple cryogenic refrigerators 10. When the operating frequency of the compressor motor 24 (or the expander motor 42) is used as the operating parameter of the cryogenic refrigerator 10, the controller 140 may use, as a representative value, a higher operating frequency value, among the operating frequency values ​​determined for each of the multiple cryogenic refrigerators 10. In this way, the above-mentioned concerns, such as hunting, can be addressed.

[0113] The superconducting coil 112, particularly a large one, has a relatively large heat capacity, which may cause a delay in thermal response. As illustrated in Fig. 5, even if the temperature target value Tt is significantly reduced at the same time as the supply of the excitation current I to the superconducting coil 112 is started, it may take some time for the cooling temperature of the superconducting coil 112 to actually decrease to the reduced temperature target value Tt. Such a delay in the temperature reduction of the superconducting coil 112 may increase the risk of a quench occurring during excitation.

[0114] Therefore, the controller 140 may be configured to set a temperature target value so as to increase the refrigeration capacity of the cryogenic refrigerator 10 in advance of energizing the superconducting coil device 110. For example, the controller 140 may be configured to set the temperature target value Tt based on the state parameters ahead of the actual change in the state parameters.

[0115] Fig. 7 is a graph showing an example of setting the temperature target value Tt in the superconducting magnet device 100 according to the embodiment. The excitation current I and critical temperature Tc shown in Fig. 7 are the same as those in the example shown in Fig. 5. However, in the example shown in Fig. 7, the temperature target value Tt begins to change a time Δt before the start of supply of the excitation current I (i.e., time 1 in normalized time), as compared to Fig. 5.

[0116] To advance the setting of the temperature target value Tt in this manner, the controller 140 may include a timer. The timer counts an advance time t1 from a reference start time (e.g., time 0 in normalized time), and the controller 140 starts the advance setting of the temperature target value Tt when the advance time t1 has elapsed. The timer also counts a waiting time t2 from the reference start time until the start of excitation, and the controller 140 starts the supply of the excitation current I to the superconducting coil 112 when the waiting time t2 has elapsed. As shown in FIG. 7 , the difference between the advance time t1 and the waiting time corresponds to the time Δt. In this way, the temperature target value Tt is lowered prior to the start of the supply of the excitation current I, thereby reducing the delay in the thermal response of the superconducting coil 112 to the start of the supply of the excitation current I and addressing the above-mentioned concerns.

[0117] In the above-described embodiment, the superconducting magnet device 100 is configured as a so-called conduction-cooled type in which the superconducting coil 112 is directly cooled by the cryogenic refrigerator 10. However, the superconducting magnet device 100 may also be configured as a so-called immersion-cooled type in which the superconducting coil 112 is cooled by a cryogenic refrigerant such as liquid helium.

[0118] 8(a) and 8(b) are diagrams schematically showing a superconducting magnet device 100 according to an embodiment. Similar to the embodiment shown in Fig. 1, the superconducting magnet device 100 includes a superconducting coil device 110, a cryogenic device 120, at least one temperature sensor 130, a status monitoring sensor 132, and a controller 140. The superconducting coil device 110 includes a superconducting coil 112, a current introduction line 114, and an excitation power supply 116. The cryogenic device 120 includes a vacuum vessel 122, a cryogenic refrigerator 10, and a thermal shield (not shown).

[0119] 8( a), the cryogenic device 120 includes a cryogenic refrigerant tank 150 that cools the superconducting coil device 110 with a cryogenic refrigerant 152, and the vaporized cryogenic refrigerant 152 is re-condensed by at least one cryogenic refrigerator 10. The second cooling stage 35 of the cryogenic refrigerator 10 may be disposed in the cryogenic refrigerant tank 150.

[0120] The pressure in the cryogenic refrigerant vessel 150 is expected to change in correlation with the amount of heat generated by the superconducting coil 112 due to the supply of an excitation current to the superconducting coil 112. Therefore, the state monitoring sensor 132 may be a pressure sensor that measures the pressure in the cryogenic refrigerant vessel 150 as a state parameter. Similarly, the liquid level of the cryogenic refrigerant 152 in the cryogenic refrigerant vessel 150 is expected to change in correlation with the amount of heat generated by the superconducting coil 112 due to the supply of an excitation current to the superconducting coil 112. Therefore, the state monitoring sensor 132 may be a liquid level sensor that measures the liquid level of the cryogenic refrigerant 152 in the cryogenic refrigerant vessel 150 as a state parameter.

[0121] 8(b), the cryogenic device 120 may include a refrigerant circulation passage 154 that cools the superconducting coil device 110 with a cryogenic refrigerant 152. The refrigerant circulation passage 154 may include a refrigerator chamber 156 and a heat exchanger 158.

[0122] The refrigerator chamber 156 may be a vacuum vessel for the cryogenic refrigerator 10 that is separate from the vacuum vessel 122, as shown. Alternatively, the refrigerator chamber 156 may be part of the vacuum vessel 122. The second cooling stage 35 of the cryogenic refrigerator 10 may be located within the refrigerator chamber 156.

[0123] The heat exchanger 158 is thermally coupled to the superconducting coil 112 such that the cryogenic refrigerant 152 flowing through the heat exchanger 158 cools the superconducting coil 112. The heat exchanger 158 may be thermally coupled to the superconducting coil 112 via a heat transfer member.

[0124] The cryogenic refrigerant 152 that has cooled the superconducting coil 112 in the heat exchanger 158 is returned to the refrigerator chamber 156 through the refrigerant circulation path 154 and is cooled by the cryogenic refrigerator 10. The cooled cryogenic refrigerant 152 is supplied again to the heat exchanger 158 through the refrigerant circulation path 154 and cools the superconducting coil 112. In this way, the cryogenic refrigerant 152 circulates through the refrigerant circulation path 154.

[0125] The cryogenic refrigerant 152 may circulate through the refrigerant circulation passage 154 in a gaseous state, for example, a gaseous state pressurized to a high pressure (for example, a pressure of 10 to 20 atmospheres). Alternatively, the cryogenic refrigerant 152 may circulate through the refrigerant circulation passage 154 in a liquid state. Alternatively, the cryogenic refrigerant 152 may circulate through the refrigerant circulation passage 154 in a supercritical state.

[0126] The temperature, pressure, and flow rate of the refrigerant circulation passage 154 are expected to change in correlation with the amount of heat generated by the superconducting coil 112 due to the supply of an excitation current to the superconducting coil 112. Therefore, the condition monitoring sensor 132 may be a temperature sensor that measures the temperature of the refrigerant circulation passage 154 as a condition parameter. The temperature sensor may measure the temperature of the cryogenic refrigerant 152 at the inlet from the refrigerant circulation passage 154 to the refrigerator compartment 156 or at the outlet from the refrigerator compartment 156 to the refrigerant circulation passage 154. Alternatively, the condition monitoring sensor 132 may be a flow rate sensor that measures the flow rate of the refrigerant circulation passage 154 as a condition parameter. Alternatively, the condition monitoring sensor 132 may be a pressure sensor that measures the pressure of the refrigerant circulation passage 154 as a condition parameter. Alternatively, if a refrigerant circulation pump is provided in the refrigerant circulation passage 154, the condition monitoring sensor 132 may be a rotation speed sensor that measures the rotation speed of the refrigerant circulation pump as a condition parameter.

[0127] An additional refrigerant circulation path may be provided between the refrigerant circulation path 154 and the superconducting coil 112. The additional refrigerant circulation path may be thermally coupled to the refrigerant circulation path 154 and the superconducting coil 112 so as to be cooled by the refrigerant circulation path 154 and cool the superconducting coil 112. In other words, the refrigerant circulation path 154 corresponds to the primary side, and the additional refrigerant circulation path corresponds to the secondary side. In this case, the temperature, pressure, or flow rate of the additional refrigerant circulation path may be used as the state parameter.

[0128] 8(a) and 8(b), the controller 140 is configured to set a temperature target value based on the measured or command value of a state parameter, as in the embodiment described above with reference to FIGS. 1 to 7. The controller 140 is also configured to determine operating parameters for the cryogenic refrigerator 10 based on a comparison between the measured temperature from the temperature sensor 130 and the temperature target value, and to operate the cryogenic refrigerator 10 using the determined operating parameters. In this way, as in the embodiment described above, it is expected that the energy saving performance of the superconducting magnet device 100 can be improved.

[0129] 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.

[0130] Although the above embodiment has been described as an example in which the cryocooler 10 is a GM refrigerator, the present invention is not limited thereto. In some embodiments, the cryocooler 10 may be another type of two-stage cryocooler having a first cooling stage 33 and a second cooling stage 35, such as a Solvay refrigerator, a Stirling refrigerator, or a pulse tube refrigerator.

[0131] 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.

[0132] The present invention can be used in the fields of superconducting magnet devices and cooling devices for superconducting magnet devices.

[0133] 10 cryogenic refrigerator, 12 compressor, 14 expander, 24 compressor motor, 33 first cooling stage, 35 second cooling stage, 42 expander motor, 100 superconducting magnet device, 110 superconducting coil device, 112 superconducting coil, 120 cryogenic device, 130 temperature sensor, 130a first temperature sensor, 130b second temperature sensor, 132 status monitoring sensor, 140 controller.

Claims

1. A superconducting magnet device comprising: a superconducting coil device having a superconducting coil and a current introduction line connected to the superconducting coil; a cryogenic device having at least one cryogenic refrigerator for cooling the superconducting coil device; at least one temperature sensor provided in the superconducting coil device or the cryogenic device; and a controller configured to set a temperature target value based on state parameters related to the superconducting magnet device, determine operating parameters of the cryogenic refrigerator based on a comparison between the temperature measured by the temperature sensor and the temperature target value, and operate the cryogenic refrigerator using the determined operating parameters.

2. The superconducting magnet device according to claim 1, characterized in that the controller is configured to determine the value of the state parameter and its change over time, and to set the target temperature value in accordance with a predetermined relationship between the value of the state parameter, the change over time, and the target temperature value.

3. A superconducting magnet apparatus according to claim 2, wherein the relationship is predetermined such that the larger the amount of change in the state parameter over time, the smaller the target temperature value.

4. The superconducting magnet device of claim 1, wherein the controller is configured to determine the value of the state parameter and set the temperature target value according to a predetermined relationship between the value of the state parameter and the temperature target value.

5. A superconducting magnet device as described in any one of claims 1 to 4, characterized in that the cryogenic refrigerator comprises a first cooling stage that cools a portion of the current introduction line to a first cooling temperature and a second cooling stage that cools the superconducting coil to a second cooling temperature lower than the first cooling temperature, the at least one temperature sensor includes a first temperature sensor that measures the first cooling temperature and a second temperature sensor that measures the second cooling temperature, and the controller is configured to set the temperature target value for either the first cooling temperature or the second cooling temperature based on the state parameter.

6. The superconducting magnet device according to any one of claims 1 to 4, characterized in that the cryogenic refrigerator comprises a first cooling stage that cools a portion of the current introducing line to a first cooling temperature and a second cooling stage that cools the superconducting coil to a second cooling temperature lower than the first cooling temperature, the at least one temperature sensor includes a first temperature sensor that measures the first cooling temperature and a second temperature sensor that measures the second cooling temperature, and the controller is configured to set a first target temperature value and a second target temperature value based on the state parameter, determine a first candidate value for the operating parameter of the cryogenic refrigerator based on a comparison between the measured value of the first cooling temperature from the first temperature sensor and the first target temperature value, determine a second candidate value for the operating parameter of the cryogenic refrigerator based on a comparison between the measured value of the second cooling temperature from the second temperature sensor and the second target temperature value, and determine the operating parameter of the cryogenic refrigerator based on the first candidate value and the second candidate value.

7. A superconducting magnet device as described in any one of claims 1 to 4, characterized in that the cryogenic refrigerator comprises a compressor having a compressor motor and an expander having an expander motor, and the controller is configured to determine the operating frequency of one of the compressor motor and the expander motor as the operating parameter of the cryogenic refrigerator based on a comparison between the measured temperature from the temperature sensor and the target temperature value, and to determine the operating frequency of the other of the compressor motor and the expander motor based on the determined operating frequency.

8. A superconducting magnet device as described in any one of claims 1 to 4, characterized in that the cryogenic device comprises a plurality of cryogenic refrigerators, the at least one temperature sensor includes a plurality of temperature sensors, each of which is associated with a different one of the plurality of cryogenic refrigerators and measures the temperature of the superconducting coil, and the controller is configured to determine, for each of the plurality of cryogenic refrigerators, the operating parameters of that cryogenic refrigerator based on a comparison between the measured temperature from a temperature sensor of the plurality of temperature sensors corresponding to that cryogenic refrigerator and the temperature target value.

9. The superconducting magnet apparatus according to claim 8, wherein the controller is configured to operate the plurality of cryogenic refrigerators individually using the operating parameters determined for each of the plurality of cryogenic refrigerators.

10. The superconducting magnet device according to claim 8, characterized in that the controller is configured to determine a representative value of the operating parameter based on the operating parameter determined for each of the plurality of cryogenic refrigerators, and to operate the plurality of cryogenic refrigerators using the determined representative value of the operating parameter in common.

11. A superconducting magnet device as described in any one of claims 1 to 4, characterized in that the controller is configured to set the temperature target value so as to increase the refrigeration capacity of the cryogenic refrigerator in advance prior to energizing the superconducting coil device.

12. A superconducting magnet device as described in any one of claims 1 to 4, further comprising a state monitoring sensor for measuring the state parameter, wherein the state monitoring sensor measures, as the state parameter, the current flowing through the superconducting coil via the current introduction line or the magnetic field generated by the superconducting coil.

13. A superconducting magnet device as described in any one of claims 1 to 4, further comprising a state monitoring sensor for measuring the state parameter, wherein the cryogenic device comprises a cryogenic refrigerant tank for cooling the superconducting coil device with a cryogenic refrigerant, the cryogenic refrigerant being recondensed by the at least one cryogenic refrigerator, and the state monitoring sensor measures, as the state parameter, the pressure of the cryogenic refrigerant tank or the liquid level of the cryogenic refrigerant in the cryogenic refrigerant tank.

14. A superconducting magnet device as described in any one of claims 1 to 4, further comprising a condition monitoring sensor for measuring the condition parameter, wherein the cryogenic device comprises a refrigerant circulation passage for cooling the superconducting coil device with a cryogenic refrigerant, the cryogenic refrigerant being cooled by the at least one cryogenic refrigerator, and the condition monitoring sensor measures the temperature, pressure, or flow rate of the refrigerant circulation passage as the condition parameter.

15. A superconducting magnet device according to any one of claims 1 to 4, characterized in that the superconducting magnet device is configured to generate a charged particle beam, and the controller is configured to set the temperature target value based on the beam current of the charged particle beam as the state parameter.

16. A superconducting magnet apparatus according to any one of claims 1 to 4, wherein the controller is configured to set the temperature target value based on the command value of the state parameter.

17. A cooling device for a superconducting magnet device, the superconducting magnet device comprising a superconducting coil device, the cooling device comprising at least one cryogenic refrigerator for cooling the superconducting coil device, and a controller configured to set a temperature target value based on state parameters related to the superconducting magnet device, determine operating parameters of the cryogenic refrigerator based on a comparison between a measured temperature of the superconducting coil device and the temperature target value, and operate the cryogenic refrigerator using the determined operating parameters.

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