Superconducting magnet

Abstract

The goal is to suppress temperature rise when the cooling unit is not functioning properly, while simultaneously ensuring cooling efficiency. [Solution] The superconducting magnet of the embodiment comprises a cryogenic section, a heat shield, a thermal resistance section, and a heat capacity section. The cryogenic section includes a superconducting coil and is cooled by a cooling section. The heat shield covers the cryogenic section. The thermal resistance section is connected to the contacted section, which is either the cryogenic section or the heat shield. The heat capacity section is connected to the thermal resistance section. The heat capacity section has a different thermal contraction rate than the contacted section. At a first temperature, the heat capacity section is in thermal contact with the contacted section to a first degree. At a second temperature higher than the first temperature, the heat capacity section is either not in contact with the contacted section or is in thermal contact with the contacted section to a second degree less than the first degree. The thermal resistance section has a greater thermal resistance than the portion of the contacted section to which the thermal resistance section is connected.

Description

[Technical Field]

[0001] The embodiments disclosed in the present specification and drawings relate to superconducting magnets. [Background Art]

[0002] Superconducting magnets used in magnetic resonance imaging (MRI) devices and the like are known (see, for example, Patent Document 1). A superconducting magnet includes, for example, a superconducting coil and a heat shield covering the superconducting coil. The superconducting coil is cooled to an extremely low temperature by a cooling unit. Examples of the cooling unit include a refrigerator system including an expander (cold head) and a compressor.

[0003] When the cooling unit does not operate normally, such as when the power supply for driving the cooling unit is lost due to a power outage, the temperature of the heat shield and the superconducting coil rises due to heat intrusion. In this case, recooling is required before quenching or re-excitation, which takes time. It is also conceivable to use an uninterruptible power supply or the like in preparation for a power loss, but the period for which power loss can be handled is limited depending on the capacity of the power supply, and if the period is exceeded, the above problem recurs.

[0004] In order to suppress the temperature rise of the heat shield and the superconducting coil, a method of increasing the heat capacity of the heat shield and the superconducting coil is conceivable. However, increasing the heat capacity of the heat shield and the superconducting coil means that the time required for cooling the heat shield and the superconducting coil increases. Therefore, the cooling efficiency of the superconducting magnet decreases. [Prior Art Literature] [Patent Literature]

[0005] [Patent Document 1] Japanese Patent Laid-Open No. 2011-131073 [Summary of the Invention] [Problem to be Solved by the Invention]

[0006] The problem that the embodiments disclosed in this specification and drawings aim to solve is to achieve both suppression of temperature rise when the cooling unit does not operate normally and ensuring cooling efficiency. However, the problem that the embodiments disclosed in this specification and drawings aim to solve is not limited to the above problem. Problems corresponding to the effects of each configuration shown in the embodiments described later can also be positioned as other problems. [Means for solving the problem]

[0007] The superconducting magnet of the embodiment comprises a cryogenic section, a heat shield, a thermal resistance section, and a heat capacity section. The cryogenic section includes a superconducting coil and is cooled by a cooling section. The heat shield covers the cryogenic section. The thermal resistance section is connected to the contacted section, which is either the cryogenic section or the heat shield. The heat capacity section is connected to the thermal resistance section. The heat capacity section has a different thermal contraction rate than the contacted section. At a first temperature, the heat capacity section is in thermal contact with the contacted section to a first degree. At a second temperature higher than the first temperature, the heat capacity section is either not in contact with the contacted section or is in thermal contact with the contacted section to a second degree less than the first degree. The thermal resistance section has a greater thermal resistance than the portion of the contacted section to which the thermal resistance section is connected. [Brief explanation of the drawing]

[0008] [Figure 1] A diagram showing a superconducting magnet 1 according to the first embodiment. [Figure 2] A cross-sectional view along line II-II shown in Figure 1. [Figure 3] A cross-sectional view showing a superconducting magnet 1 after cryogenic cooling. [Figure 4] An enlarged view of region AR1 shown in Figure 3, when the superconducting magnet 1 is equipped with an expandable portion 42. [Figure 5] A cross-sectional view showing a superconducting magnet 2 according to the second embodiment. [Figure 6] A cross-sectional view showing superconducting magnet 2 after cryogenic cooling. [Figure 7] A cross-sectional view showing a superconducting magnet 3 according to the third embodiment. [Figure 8] A cross-sectional view showing the superconducting magnet 3 after cryogenic cooling. [Modes for carrying out the invention]

[0009] The superconducting magnet according to an embodiment will be described below with reference to the drawings.

[0010] <First Embodiment> Figure 1 shows a superconducting magnet 1 according to the first embodiment. Figure 2 is a cross-sectional view taken along the line II-II shown in Figure 1. Note that Figure 2 is a cross-sectional view showing the superconducting magnet 1 before cryogenic cooling. As shown in Figures 1 and 2, the superconducting magnet 1 has a generally cylindrical shape. The superconducting magnet 1 may be used, for example, in a magnetic resonance imaging (MRI) device. In this case, the space S enclosed by the cylindrical shape of the superconducting magnet 1 is used as an imaging area for imaging a subject.

[0011] In the following explanation, the direction parallel to the central axis O of the superconducting magnet 1 is referred to as the Z direction or axial direction Z. A cross-section perpendicular to the axial direction Z is referred to as a transverse plane. The direction perpendicular to the central axis O of the superconducting magnet 1, as viewed from the axial direction Z, is referred to as the radial direction R. Along the radial direction R, the direction approaching the central axis O is referred to as the "inside" direction in the radial direction R, and the direction moving away from the central axis O is referred to as the "outside" direction in the radial direction R. The direction circumferential around the central axis O, as viewed from the axial direction Z, is referred to as the circumferential direction.

[0012] As shown in Figures 1 and 2, the superconducting magnet 1 comprises a cryogenic section 10, a heat shield 20, a thermal resistance section 30, a heat capacity section 41, a vacuum vessel 50, and a cooling section 60. Note that the thermal resistance section 30 and the heat capacity section 41 are not shown in Figure 1.

[0013] The cryogenic section 10 includes at least one superconducting coil 11 (superconducting coils 11a to 11g in the example in Figure 1) and a helium container 12. The cryogenic section 10 is cooled to an extremely low temperature by the cooling section 60. "Extremely low temperature" means, for example, a temperature below the superconducting transition temperature of the superconducting coil 11 (for example, around a few Kelvin).

[0014] The superconducting coil 11 has a roughly annular shape with the central axis O as its central axis. The superconducting coil 11 generates a magnetic field (for example, a static magnetic field) in space S. The cryogenic section 10 may include, for example, a superconducting coil 11 that forms the main magnetic field (superconducting coils 11a to 11e in the example of Figure 1) and superconducting coils 11 that reduce the leakage magnetic field (superconducting coils 11f and 11g in the example of Figure 1).

[0015] In the example shown in Figure 1, the superconducting coils 11a to 11e are spaced apart in the axial direction Z. The superconducting coils 11f and 11g are spaced apart in the axial direction Z and are located outside of the superconducting coils 11a to 11e in the radial direction R. However, the number and arrangement of the superconducting coils 11 included in the cryogenic section 10 can be changed as appropriate.

[0016] The helium container 12 has a roughly cylindrical shape with a central axis O as its central axis. In the example in Figure 1, the helium container 12 has an inner wall 12a, an outer wall 12b, and a pair of side walls 12c. The outer wall 12b is located radially outward from the inner wall 12a in the direction R. The pair of side walls 12c extend radially in the direction R and connect both ends of the inner wall 12a in the axial direction Z to both ends of the outer wall 12b in the axial direction Z. The superconducting coils 11a to 11e are arranged along the inner wall 12a. The superconducting coils 11f and 11g are arranged along the outer wall 12b. However, the specific shape of the helium container 12 and the positional relationship between the helium container 12 and the superconducting coils 11 can be changed as appropriate.

[0017] The helium container 12 holds helium (liquid helium and gaseous helium). Helium is held in the internal space 12s of the helium container 12. In the example of Fig. 1, the internal space 12s is a space surrounded by an inner wall 12a, an outer wall 12b, and a pair of side walls 12c. The helium container 12 may have a pipe 12d for supplying helium to the internal space 12s and discharging helium from the internal space 12s.

[0018] The superconducting coil 11 is provided in the internal space 12s. In other words, the helium container 12 accommodates (encloses) the superconducting coil 11. A winding former (not shown) for wiring, arranging and fixing the superconducting coil 11 may be provided in the internal space 12s. The phrase "superconducting coil 11" in the present specification may also intend a configuration including both the coil body and the winding former.

[0019] Helium held in the helium container 12 is cooled to an extremely low temperature by the cooling unit 60. The superconducting coil 11 accommodated in the helium container 12 is cooled to an extremely low temperature by coming into contact with the helium cooled in this manner.

[0020] The heat shield 20 has a substantially cylindrical shape centered on the central axis O. The heat shield 20 in the example of Fig. 1 has an inner wall 20a, an outer wall 20b, and a pair of side walls 20c. The outer wall 20b is located outward of the inner wall 20a in the radial direction R. The pair of side walls 20c extend in the radial direction R and connect both end portions of the inner wall 20a in the axial direction Z and both end portions of the outer wall 20b in the axial direction Z. However, the specific shape and the like of the heat shield 20 can be appropriately changed.

[0021] The heat shield 20 covers the cryogenic section 10 (the helium container 12). That is, the heat shield 20 accommodates (encloses) the cryogenic section 10 (the helium container 12). In other words, the cryogenic section 10 (the helium container 12) is disposed in the internal space 20s of the heat shield 20.

[0022] In the example shown in Figure 1, the internal space 20s is a space enclosed by an inner wall 20a, an outer wall 20b, and a pair of side walls 20c. The inner wall 20a is located radially R inward from the inner wall 12a of the helium container 12. The outer wall 20b is located radially R outward from the outer wall 12b of the helium container 12. The pair of side walls 20c are located axially Z outward from the pair of side walls 12c of the helium container 12. Gaps are provided between the inner walls 12a, 20a, between the outer walls 12b, 20b, and between the side walls 12c, 20c.

[0023] The heat shield 20 plays a role in reducing heat intrusion into the cryogenic section 10 due to radiant heat. For this purpose, metal materials with high heat transfer properties, such as aluminum alloys (hereinafter also referred to as aluminum materials) and copper alloys (hereinafter also referred to as copper materials), are generally used for the heat shield 20. Non-magnetic materials may also be used for the heat shield 20.

[0024] The vacuum vessel 50 has a generally cylindrical shape with the central axis O as its central axis. In the example in Figure 1, the vacuum vessel 50 has an inner wall 50a, an outer wall 50b, and a pair of side walls 50c. The outer wall 50b is located radially outward from the inner wall 50a in the direction R. The pair of side walls 50c extend radially in the direction R and connect both ends of the inner wall 50a in the axial direction Z to both ends of the outer wall 50b in the axial direction Z. However, the specific shape of the vacuum vessel 50 can be changed as appropriate.

[0025] The vacuum vessel 50 covers the heat shield 20. That is, the vacuum vessel 50 houses (encloses) the heat shield 20. In other words, the heat shield 20 is located in the internal space 50s of the vacuum vessel 50.

[0026] In the example shown in Figure 1, the internal space 50s is a space enclosed by an inner wall 50a, an outer wall 50b, and a pair of side walls 50c. The inner wall 50a is located radially inward R from the inner wall 20a of the heat shield 20. The outer wall 50b is located radially outward R from the outer wall 20b of the heat shield 20. The pair of side walls 50c are located axially outward Z from the pair of side walls 20c of the heat shield 20. Gaps are provided between the inner walls 20a, 50a, between the outer walls 20b, 50b, and between the side walls 20c, 50c.

[0027] The vacuum vessel 50 maintains a vacuum in its internal space 50s. As a result, the components located within the internal space 50s (i.e., the heat shield 20 and the cryogenic section 10) are vacuum-insulated.

[0028] A gradient magnetic field coil 81 (not shown in Figure 2) for generating a gradient magnetic field in space S may be provided inside the inner wall 50a of the vacuum container 50. A support base 82 (not shown in Figure 2) for supporting the vacuum container 50 may be provided outside the outer wall 50b of the vacuum container 50.

[0029] The cooling unit 60 cools the cryogenic section 10. For example, the cooling unit 60 maintains a thermal equilibrium state in which liquid helium and gaseous helium coexist in the internal space 12s of the helium container 12 by cooling the internal space 12s to an extremely low temperature. That is, the cooling unit 60 removes heat from the internal space 12s, thereby suppressing the evaporation of liquid helium and the temperature rise of gaseous helium caused by radiant heat from the outside and heat conduction. As a result, the cooling unit 60 maintains the temperature of the cryogenic section 10 and the heat shield 20 at a constant level (e.g., extremely low).

[0030] The cooling unit 60 may be, for example, a refrigeration system including an expander (cold head) and a compressor. The cooling unit 60 is driven by power supplied by, for example, a power supply device (not shown).

[0031] As shown in Figure 2, the thermal resistance portion 30 is connected to the heat shield 20. That is, the thermal resistance portion 30 is in contact with the heat shield 20 and is fixed to the heat shield 20. Hereinafter, the object to which the thermal resistance portion 30 is connected will be referred to as the contacted portion 70. In this embodiment, the contacted portion 70 is the heat shield 20.

[0032] The thermal resistance section 30 is positioned on the opposite side of the heat shield 20 from the cryogenic section 10. In other words, the thermal resistance section 30 is connected to the heat shield 20 (outer wall 20b) from the side opposite to the cryogenic section 10. Specifically, the thermal resistance section 30 is located radially outward from the outer wall 20b of the heat shield 20 in the radial direction R. The thermal resistance section 30 is located radially between the outer wall 20b of the heat shield 20 and the outer wall 50b of the vacuum vessel 50.

[0033] The thermal resistance portion 30 has a greater thermal resistance than the portion of the heat shield 20, which is the contacted portion 70, to which the thermal resistance portion 30 is connected (hereinafter referred to as the connection portion 71). The thermal resistance portion 30 connects the connection portion 71 and the heat capacity portion 41, and also transfers heat between the connection portion 71 and the heat capacity portion 41. As long as the thermal resistance portion 30 has a greater thermal resistance than the connection portion 71 and can connect the connection portion 71 and the heat capacity portion 41, the specific structure of the thermal resistance portion 30 and the specific components constituting the thermal resistance portion 30 can be changed as appropriate.

[0034] The heat capacity section 41 is connected to the thermal resistance section 30. That is, the heat capacity section 41 is in contact with the thermal resistance section 30 and is fixed to the thermal resistance section 30. In other words, the heat capacity section 41 is connected to the connection section 71 via the thermal resistance section 30.

[0035] The heat capacity section 41 is positioned on the opposite side of the heat shield 20 from the cryogenic section 10. That is, the heat capacity section 41 is located radially outward from the outer wall 20b of the heat shield 20 in the radial direction R. Specifically, the heat capacity section 41 is located radially outward from the outer wall 20b of the heat shield 20 and the outer wall 50b of the vacuum vessel 50.

[0036] The heat-capacitating portion 41 has a shape that conforms to the heat shield 20, which is the contacted portion 70. Specifically, the heat-capacitating portion 41 has a roughly arc shape (for example, a roughly semicircular shape) in cross-sectional view. One end of the arc-shaped heat-capacitating portion 41 is connected to the thermal resistance portion 30.

[0037] The heat capacity portion 41 has a different thermal contraction rate than the heat shield 20, which is the contacted portion 70. Specifically, the heat capacity portion 41 has a larger thermal contraction rate than the heat shield 20. That is, the heat capacity portion 41 contracts more than the heat shield 20 when cooled.

[0038] Figure 3 is a cross-sectional view showing the superconducting magnet 1 after cryogenic cooling. As shown in Figure 3, the heat capacity portion 41 is in thermal contact with the heat shield 20, which is the contacted portion 70, to a first degree after cryogenic cooling (i.e., at a temperature below the first temperature).

[0039] The "first degree" and the "second degree" described later are indices indicating the magnitude of thermal contact (heat flow) between the contacted portion 70 and the heat capacity portion 41, with larger values ​​indicating greater thermal contact (heat flow). In the example in Figure 3, "thermal contact at the first degree" simply means "contact." The "first temperature" is the temperature at which the heat capacity portion 41 comes into thermal contact with the contacted portion 70 at the first degree, due to the difference in thermal contraction rates between the heat capacity portion 41 and the contacted portion 70.

[0040] Since one end of the heat capacity portion 41 is connected to the thermal resistance portion 30, the heat capacity portion 41 contracts starting from the thermal resistance portion 30. Therefore, after cryogenic cooling, the end of the heat capacity portion 41 opposite to the thermal resistance portion 30 comes into contact with the contacted portion 70.

[0041] On the other hand, as shown in Figure 2, the heat capacity portion 41 does not come into contact with the heat shield 20, which is the contacted portion 70, before cryogenic cooling (i.e., at a temperature of the second temperature or higher). Here, the "second temperature" is a temperature higher than the first temperature. The second temperature may be, for example, a temperature higher than the superconducting transition temperature of the superconducting coil 11 (for example, room temperature). In other words, in this embodiment, due to the difference in thermal contraction rates between the heat capacity portion 41 and the contacted portion 70, the state in which the heat capacity portion 41 and the contacted portion 70 are in thermal contact to a first degree and the state in which the heat capacity portion 41 and the contacted portion 70 are not in contact switch depending on the temperature.

[0042] If, after the superconducting magnet 1 has been cooled to an extremely low temperature, the power supply for driving the cooling unit 60 is lost due to a power outage or for other reasons, and the cooling unit 60 ceases to function properly, the temperature of the internal space 12s of the helium container 12 may rise. In this case, evaporation of liquid helium and a rise in the temperature of gaseous helium will occur, causing a temperature rise in the cryogenic section 10 and the heat shield 20.

[0043] To suppress such a temperature rise, the heat capacity portion 41 makes contact (thermal contact to a first degree) with the heat shield 20, which is the contacted portion 70, at a temperature below the first temperature. That is, by the heat capacity portion 41 making contact with the heat shield 20, the heat capacity of the heat shield 20 increases, and the temperature rise of the heat shield 20 and the cryogenic portion 10 housed therein is suppressed. Note that, as long as thermal contact to a first degree based on the difference in thermal shrinkage rates between the heat capacity portion 41 and the contacted portion 70 can be achieved, the specific shape of the heat capacity portion 41, the thermal shrinkage rate, and the components constituting the heat capacity portion 41 can be appropriately changed.

[0044] On the other hand, if the cryogenic section 10 and the heat shield 20 have large heat capacities, they become difficult to cool, increasing the time required to cool the superconducting magnet 1 to cryogenic temperatures. To solve this problem, in the superconducting magnet 1, heat transfer between the heat capacity section 41 and the contacted section 70 (heat shield 20) is mediated by the thermal resistance section 30, which has high thermal resistance.

[0045] When cooling by the cooling unit 60 begins, the temperature of the contacted portion 70 (heat shield 20) starts to decrease. The contacted portion 70 absorbs heat from the heat capacity portion 41 via the thermal resistance portion 30, thus cooling the heat capacity portion 41 as well. Here, since the thermal resistance of the thermal resistance portion 30 is greater than that of the connection portion 71, heat transfer from the heat capacity portion 41 to the contacted portion 70 is suppressed by the thermal resistance portion 30. Therefore, the heat capacity portion 41 cools more slowly than the contacted portion 70. More specifically, the rate at which the temperature of the heat capacity portion 41 decreases is slower compared to the case where the heat capacity portion 41 is directly connected to the contacted portion 70. As a result, for a while after the start of cooling, the heat capacity portion 41 is maintained at a higher temperature than the contacted portion 70. Therefore, for a while after the start of cooling, the heat capacity portion 41 does not reach the first temperature, and the heat capacity portion 41 does not come into contact with the contacted portion 70. This keeps the heat capacity of the heat shield 20, which is the contacted part 70, low, and ensures the cooling efficiency of the cooling unit 60.

[0046] After a sufficient amount of time has elapsed since the start of cooling, the heat contained in the heat capacity section 41 is absorbed by the contacted section 70, and a thermal equilibrium state is reached where the heat capacity section 41 and the contacted section 70 are at approximately the same temperature. In the thermal equilibrium state, the heat capacity section 41 becomes below the first temperature, and the heat capacity section 41 and the contacted section 70 come into contact. As a result, the heat capacity section 41 increases the heat capacity of the contacted section 70 (heat shield 20), and the above-mentioned temperature rise suppression effect is obtained.

[0047] Here, an expandable portion 42 may be provided in the region AR1 (see Figure 3) where the heat capacity portion 41 and the contacted portion 70 (heat shield 20) are in contact. Figure 4 is an enlarged view of region AR1 when the superconducting magnet 1 is equipped with an expandable portion 42.

[0048] As shown in Figure 4, the expandable portion 42 is positioned between the heat-capacitating portion 41 and the contacted portion 70 (heat shield 20). The expandable portion 42 expands and contracts in the opposing direction between the heat-capacitating portion 41 and the contacted portion 70. In the illustrated example, the opposing direction is the radial direction R. In the example in Figure 4, the expandable portion 42 is a disc spring.

[0049] The expandable portion 42 exerts a biasing force in opposing directions such that the heat-capacitating portion 41 and the contacted portion 70 move away from each other. The expandable portion 42 makes contact with both the heat-capacitating portion 41 and the contacted portion 70, thereby causing thermal contact between the heat-capacitating portion 41 and the contacted portion 70.

[0050] Before cryogenic cooling (i.e., at a temperature of the second temperature or higher), the expandable portion 42 is in an extended state. At this time, the expandable portion 42 makes line contact with the heat capacity portion 41 and the contacted portion 70 along the upper edge 42a and lower edge 42b of the expandable portion 42, which is a disc spring. On the other hand, after cryogenic cooling (i.e., at a temperature of the first temperature or lower), the heat capacity portion 41 contracts more than the contacted portion 70, reducing the gap between the heat capacity portion 41 and the contacted portion 70 in the opposing direction. As a result, the expandable portion 42 becomes contracted. At this time, the expandable portion 42 makes surface contact with the heat capacity portion 41 and the contacted portion 70 along the surface 42c of the expandable portion 42 (the surface constituting the outer surface of the cone and the surface constituting the inner surface of the cone), which is a disc spring.

[0051] In other words, the expandable portion 42 expands and contracts in accordance with the temperature, and this changes the contact area between the expandable portion 42 and the heat capacity portion 41 and the contacted portion 70. Specifically, after cryogenic cooling (i.e., at temperatures below the first temperature), the expandable portion 42 and the heat capacity portion 41 and the contacted portion 70 are in contact with a first contact area S1. The first contact area S1 is the area where the surface 42c of the expandable portion 42, which is a disc spring, is in contact (surface contact) with the heat capacity portion 41 and the contacted portion 70. On the other hand, before cryogenic cooling (i.e., at temperatures above the second temperature), the expandable portion 42 and the heat capacity portion 41 and the contacted portion 70 are in contact with a second contact area S2 which is smaller than the first contact area S1. The second contact area S2 is the area where the upper edge 42a and lower edge 42b of the expandable portion 42, which is a disc spring, are in contact (line contact) with the heat capacity portion 41 and the contacted portion 70.

[0052] As the contact area changes in this way, the degree of thermal contact between the heat capacity portion 41 and the contacted portion 70 changes. That is, after cryogenic cooling (i.e., at a temperature below the first temperature), the expandable portion 42 brings the heat capacity portion 41 and the contacted portion 70 into thermal contact to a first degree based on the first contact area S1. On the other hand, after cryogenic cooling (i.e., at a temperature above the second temperature), the expandable portion 42 brings the heat capacity portion 41 and the contacted portion 70 into thermal contact to a second degree, which is smaller than the first degree, based on the second contact area S2. The second contact area S2 is smaller than the first contact area S1, and the smaller the contact area, the smaller the thermal contact (heat flow) between the heat capacity portion 41 and the contacted portion 70, so the second degree is smaller than the first degree.

[0053] In the superconducting magnet 1 equipped with the expandable portion 42 described above, the difference in thermal contraction rates between the heat capacity portion 41 and the contacted portion 70, and the expansion and contraction of the expandable portion 42, cause the heat capacity portion 41 and the contacted portion 70 to switch between a state of thermal contact to a first degree and a state of thermal contact to a second degree, depending on the temperature. Even with this configuration, the same effects as a configuration without the expandable portion 42 can be obtained, namely, an increase in the heat capacity of the contacted portion 70 after cryogenic cooling and ensuring cooling efficiency immediately after the start of cryogenic cooling. Furthermore, the expandable portion 42 maintains a distance between the heat capacity portion 41 and the contacted portion 70, reducing the possibility of unintentional contact between the heat capacity portion 41 and the contacted portion 70.

[0054] Furthermore, the expandable portion 42 does not have to be a disc spring, as long as the degree of thermal contact between the heat-capacitating portion 41 and the contacted portion 70 can be changed by expansion and contraction. For example, the expandable portion 42 may be a coil spring. In the case of a coil spring, for example, the degree of thermal contact between the heat-capacitating portion 41 and the contacted portion 70 can be changed by switching between contact and non-contact between the windings contained in the coil spring as the coil spring expands and contracts.

[0055] <Second Embodiment> Next, a second embodiment will be described, but its basic configuration is the same as that of the first embodiment. Therefore, the same reference numerals are used for similar components, and their descriptions are omitted; only the differences will be described.

[0056] Figure 5 is a cross-sectional view showing the superconducting magnet 2 according to the second embodiment. Note that Figure 5 is a cross-sectional view showing the superconducting magnet 2 before cryogenic cooling. Figure 6 is a cross-sectional view showing the superconducting magnet 2 after cryogenic cooling. As shown in Figures 2, 3, 5, and 6, the superconducting magnet 2 according to the second embodiment differs from the superconducting magnet 1 according to the first embodiment in the configuration of the thermal resistance section 30 and the heat capacity section 41.

[0057] In this embodiment, the thermal resistance section 30 and the heat capacity section 41 are arranged between the heat shield 20 and the cryogenic section 10 (helium container 12). Specifically, the thermal resistance section 30 and the heat capacity section 41 are located inward in the radial direction R from the outer wall 20b of the heat shield 20. The thermal resistance section 30 and the heat capacity section 41 are located outward in the radial direction R from the outer wall 12b of the helium container 12.

[0058] Furthermore, the thermal resistance section 30 according to this embodiment is connected to the helium container 12 (cryogenic section 10) rather than the heat shield 20. That is, the thermal resistance section 30 is in contact with the helium container 12 and is fixed to the helium container 12. In other words, in this embodiment, the contacted section 70 is the helium container 12 (cryogenic section 10). The thermal resistance section 30 has a greater thermal resistance than the connection section 71 of the helium container 12 (cryogenic section 10).

[0059] The heat capacity portion 41 according to this embodiment has a greater thermal contraction rate than the helium container 12 (cryogenic portion 10), which is the contacted portion 70. That is, the heat capacity portion 41 according to this embodiment contracts more than the helium container 12 when cooled.

[0060] As shown in Figure 6, after cryogenic cooling (i.e., at a temperature below the first temperature), the heat capacity portion 41 shrinks more than the helium container 12 (cryogenic portion 10), which is the contacted portion 70, so that the heat capacity portion 41 makes thermal contact with the contacted portion 70 to a first degree. As a result, similar to the first embodiment, the heat capacity of the contacted portion 70 is increased by the heat capacity portion 41 after cryogenic cooling, and the temperature rise of the cryogenic portion 10 can be suppressed. In addition, the thermal resistance portion 30 ensures cooling efficiency immediately after the start of cryogenic cooling, similar to the first embodiment. Although detailed illustrations are omitted, in the superconducting magnet 2 according to this embodiment, as with the superconducting magnet 1 according to the first embodiment, an expandable portion 42 may be provided in the region AR2 where the heat capacity portion 41 and the contacted portion 70 (helium container 12) are in contact.

[0061] <Third Embodiment> Next, a third embodiment will be described, but its basic configuration is the same as that of the second embodiment. Therefore, the same reference numerals are used for similar components, and their descriptions are omitted; only the differences will be described.

[0062] Figure 7 is a cross-sectional view showing the superconducting magnet 3 according to the third embodiment. Note that Figure 7 is a cross-sectional view showing the superconducting magnet 3 before cryogenic cooling. Figure 8 is a cross-sectional view showing the superconducting magnet 3 after cryogenic cooling. As shown in Figures 5, 6, 7, and 8, the superconducting magnet 3 according to the third embodiment differs from the superconducting magnet 2 according to the second embodiment in the configuration of the cryogenic section 10.

[0063] In this embodiment, the cryogenic section 10 does not include a helium container 12. In other words, there is no helium container 12 between the superconducting coil 11 and the heat shield 20. The superconducting coil 11 is directly housed in the heat shield 20 and is positioned in the internal space 20s of the heat shield 20. As a result, the superconducting coil 11 is positioned in a vacuum provided by the vacuum container 50, rather than in helium. The position in which the superconducting coil 11 is positioned in the internal space 20s is not particularly limited, but for example, the superconducting coil 11 may be positioned along the inner wall 20a of the heat shield 20.

[0064] In this embodiment, the cooling unit 60 and the superconducting coil 11 are mechanically connected by a heat transfer member 61. The heat transfer member 61 mediates heat transfer between the cooling unit 60 and the superconducting coil 11. In this embodiment, the superconducting coil 11 is cooled to an extremely low temperature by heat being transferred to the cooling unit 60 via the heat transfer member 61. In other words, the superconducting coil 11 in this embodiment is cooled (conductive cooling) not by contact with helium, but by contact with the heat transfer member 61 connected to the cooling unit 60. The heat transfer member 61 may be included in the cryogenic unit 10. In other words, the cryogenic unit 10 in this embodiment can be interpreted as including the heat transfer member 61 instead of the helium container 12.

[0065] Furthermore, the thermal resistance portion 30 according to this embodiment is connected to the superconducting coil 11. That is, the thermal resistance portion 30 is in contact with the superconducting coil 11 and is fixed to the superconducting coil 11. In other words, in this embodiment, the contacted portion 70 is the superconducting coil 11. The thermal resistance portion 30 has a greater thermal resistance than the connection portion 71 of the superconducting coil 11.

[0066] The heat capacity portion 41 in this embodiment has a greater thermal contraction rate than the superconducting coil 11, which is the contacted portion 70. That is, the heat capacity portion 41 in this embodiment contracts more than the superconducting coil 11 when cooled.

[0067] As shown in Figure 8, after cryogenic cooling (i.e., at a temperature below the first temperature), the heat capacity portion 41 shrinks more than the superconducting coil 11, which is the contacted portion 70, so that the heat capacity portion 41 makes thermal contact with the contacted portion 70 to a first degree. As a result, similar to the second embodiment, the heat capacity of the contacted portion 70 is increased by the heat capacity portion 41 after cryogenic cooling, and the temperature rise of the cryogenic portion 10 (superconducting coil 11) can be suppressed. In addition, the thermal resistance portion 30 ensures cooling efficiency immediately after the start of cryogenic cooling, similar to the second embodiment. Although detailed illustrations are omitted, in the superconducting magnet 3 according to this embodiment, as with the superconducting magnet 2 according to the second embodiment, an expandable portion 42 may be provided in the region AR3 where the heat capacity portion 41 and the contacted portion 70 (superconducting coil 11) are in contact.

[0068] <Variation> In the first embodiment described above, the cryogenic section 10 included a helium container 12, but the cryogenic section 10 does not need to include a helium container 12. In this case, similar to the third embodiment, the cryogenic section 10 may include a heat transfer member 61 that mediates heat transfer between the cooling section 60 and the superconducting coil 11 instead of the helium container 12. Furthermore, in the superconducting magnet 3 according to the third embodiment, the thermal resistance section 30 may be connected to the heat transfer member 61 or the like. In other words, the connection portion 71 may be located on the heat transfer member 61 or the like.

[0069] According to at least one embodiment described above, the superconducting coil 11 includes a cryogenic section 10 cooled by a cooling section 60, a heat shield 20 covering the cryogenic section 10, a thermal resistance section 30 connected to the contacted section 70 which is the cryogenic section 10 or the heat shield 20, and a heat capacity section 41 connected to the thermal resistance section 30. The heat capacity section 41 has a different thermal contraction rate than the contacted section 70, the heat capacity section 41 is in thermal contact with the contacted section 70 to a first degree at a first temperature, the heat capacity section 41 is not in contact with the contacted section 70 at a second temperature higher than the first temperature, or is in thermal contact with the contacted section 70 to a second degree less than the first degree, and the thermal resistance section 30 has a greater thermal resistance than the part of the contacted section 70 to which the thermal resistance section 30 is connected (connection section 71). This makes it possible to suppress temperature rise when the cooling section 60 does not operate normally and to ensure cooling efficiency.

[0070] While several embodiments have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of symbols]

[0071] 1, 2, 3…Superconducting magnet 10…Cryogenic section 11…Superconducting coil 20…Heat shield 30…Heat resistance section 41…Heat capacity section 42…Expandable section 60…Cooling section 61…Heat transfer component 70…Contacted section 71…Connection section

Claims

1. A cryogenic section containing a superconducting coil and cooled by a cooling section, A heat shield covering the cryogenic section, A thermal resistance portion connected to the cryogenic portion or the heat shield portion is a thermal resistance portion, It comprises a heat capacity section connected to the thermal resistance section, The heat capacity portion has a different thermal contraction rate than the contacted portion. The heat capacity portion is in thermal contact with the contacted portion to a first degree at a first temperature. The heat capacity portion does not contact the contacted portion at a second temperature higher than the first temperature, or it is in thermal contact with the contacted portion to a second degree less than the first degree. The thermal resistance portion has a greater thermal resistance than the portion of the contacted portion to which the thermal resistance portion is connected. Superconducting magnet.

2. The heat-capacitating portion and the contacted portion are further provided with an expandable portion that is disposed between them, brings the heat-capacitating portion and the contacted portion into thermal contact, and expands and contracts in a direction opposite to the heat-capacitating portion and the contacted portion. At the first temperature, the expandable portion contracts, causing the expandable portion to bring the heat-capacitating portion and the contacted portion into thermal contact to a first degree. At the second temperature, the expandable portion expands, causing the expandable portion to bring the heat-capacitating portion and the contacted portion into thermal contact to the second degree. The superconducting magnet according to claim 1.

3. The aforementioned expandable part is a disc spring. The superconducting magnet according to claim 2.

4. The contacted portion is the heat shield, The heat capacity section is positioned on the opposite side of the heat shield from the cryogenic section. The heat capacity portion has a greater thermal contraction rate than the heat shield. A superconducting magnet according to any one of claims 1 to 3.

5. The contacted portion is the cryogenic portion, The heat capacity section is disposed between the heat shield and the cryogenic section. The heat capacity portion has a greater thermal contraction rate than the cryogenic portion. A superconducting magnet according to any one of claims 1 to 3.

6. The contacted portion is the superconducting coil, The heat capacity section is disposed between the heat shield and the superconducting coil. The heat capacity portion has a greater thermal contraction rate than the superconducting coil. The superconducting magnet according to claim 5.

7. The superconducting coil is cooled by heat being transferred to the cooling unit via a heat transfer member connecting the cooling unit and the superconducting coil. The superconducting magnet according to claim 6.

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