JP2017117980A - Superconducting magnet and superconducting magnet device for MRI - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a superconducting magnet and superconducting magnet device for MRI, capable of suppressing a sudden change in the intensity of a magnetic field even when a superconducting coil is quenched.SOLUTION: A superconducting magnet 1 includes: a cooling coil body 63; a conductive guide plate 64 disposed, being spaced from the cooling coil body 63; and a heat insulation spacer 65 interposed between the cooling coil body 63 and the guide plate 64. The cooling coil body 63 has a superconducting coil 66 and a cooling plate 67 overlapped on the superconducting coil 66.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a superconducting magnet having a superconducting coil and a superconducting magnet device for MRI.

  2. Description of the Related Art Conventionally, a superconducting coil device is known in which a cooling plate is brought into contact with a superconducting coil formed by winding a high-temperature superconducting wire in a ring shape, and the cooling plate is cooled by a refrigerator to cool the superconducting coil (for example, Patent Document 1).

JP 2012-182176 A

  However, in the conventional superconducting coil device disclosed in Patent Document 1, when a part of the superconducting coil changes from the superconducting state to the normal conducting state, that is, quenches, an induced current flows through the cooling plate due to a change in the magnetic field, and the cooling plate Heats up. In the conventional superconducting coil device, since the superconducting coil is in contact with the cooling plate, when the cooling plate is heated and heated, other parts of the superconducting coil in the superconducting state are easily quenched, and the quenching chain of the superconducting coil is It tends to occur. Thereby, in the conventional superconducting coil device, the change in the strength of the magnetic field of the superconducting coil device tends to increase. Therefore, for example, when the conventional superconducting coil device shown in Patent Document 1 is applied to a medical superconducting magnet device for MRI (Magnetic Resonance Imaging), if a part of the superconducting coil is quenched, the subject The change in the strength of the magnetic field received by the human body is likely to increase, and there is a risk that the human body will be adversely affected.

  The present invention has been made to solve the above-described problems. A superconducting magnet and an MRI superconducting magnet apparatus capable of suppressing a rapid change in magnetic field intensity even when the superconducting coil is quenched. The purpose is to obtain.

  A superconducting magnet according to the present invention includes a cooling coil body having a flat superconducting coil and a cooling plate overlapping the superconducting coil, a conductive induction plate disposed away from the cooling coil body, and a cooling coil body. A heat insulating spacer is provided between the induction plate and the guide plate.

  According to the superconducting magnet and the MRI superconducting magnet apparatus according to the present invention, when the superconducting coil is quenched, an induced current can be generated in the induction plate in a direction to suppress the change of the magnetic field, and the change of the magnetic field of the superconducting magnet can be achieved. Can be relaxed. Thereby, even if the superconducting coil is quenched, a sudden change in the strength of the magnetic field can be suppressed.

1 is a partially broken perspective view showing a superconducting magnet device for MRI according to Embodiment 1 of the present invention. FIG. It is sectional drawing which shows the superconducting magnet of FIG. It is a graph which shows the relationship between the center magnetic field B0 (T) and elapsed time t (sec) about the superconducting magnet by each of Example 1, Comparative Example 1, and Comparative Example 2. It is a graph which shows the relationship between the change dB / dT (T / sec) of magnetic field about the superconducting magnet by each of Example 1, Comparative Example 1, and Comparative Example 2 and elapsed time t (sec). It is a disassembled perspective view which shows the unit lamination | stacking part of the superconducting magnet by Embodiment 3 of this invention. It is an expanded sectional view which shows the unit lamination | stacking part of the superconducting magnet by Embodiment 4 of this invention.

Embodiments of the present invention will be described below with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a partially broken perspective view showing an MRI superconducting magnet apparatus according to Embodiment 1 of the present invention. The superconducting magnet device for MRI has a cylindrical superconducting magnet 1, a vacuum heat insulating container 2 that houses the superconducting magnet 1, and a refrigerator 3 that is a cooling device that cools the superconducting magnet 1. The MRI superconducting magnet device is used for medical purposes, for example.

  The vacuum heat insulating container 2 is a cylindrical container having an inner peripheral wall located on the radially inner side of the superconducting magnet 1 and an outer peripheral wall located on the radially outer side of the superconducting magnet 1. Thereby, a columnar space surrounded by the inner peripheral wall of the vacuum heat insulating container 2 is formed inside the vacuum heat insulating container 2. In a space surrounded by the inner peripheral wall of the vacuum heat insulating container 2, a support base 11 on which the subject 10 is placed is disposed. Examples of the subject 10 include a human body. The degree of vacuum in the space in which the superconducting magnet 1 is accommodated in the vacuum heat insulating container 2 is kept below a preset degree of vacuum.

  The refrigerator 3 is connected to the superconducting magnet 1 via a plurality of heat conducting members. The superconducting magnet 1 is conductively cooled by the refrigerator 3 through each heat conducting member. The temperature of the superconducting magnet 1 becomes an extremely low temperature below the set temperature by cooling the superconducting magnet 1 by the refrigerator 3. The set temperature is, for example, 30K.

  FIG. 2 is a cross-sectional view showing the superconducting magnet 1 of FIG. The superconducting magnet 1 has a cylindrical inner frame 5 and a cylindrical laminated coil 6 provided on the outer periphery of the inner frame 5. The inner frame 5 is disposed coaxially with the axis of the superconducting magnet 1.

  The laminated coil 6 includes a plurality of unit laminated portions 61 arranged in the axial direction of the superconducting magnet 1 and a plurality of heat insulating spacers 62 interposed between the unit laminated portions 61. Accordingly, in the laminated coil 6, the unit laminated portions 61 and the heat insulating spacers 62 are alternately overlapped in the axial direction of the superconducting magnet 1. The heat transfer between the unit laminated portions 61 is suppressed by the heat insulating spacers 62.

  Each unit laminated portion 61 includes a cooling coil body 63, an induction plate 64 that is a conductive metal plate disposed away from the cooling coil body 63 in the axial direction of the superconducting magnet 1, and the cooling coil body 63 and the induction plate. And a heat insulating spacer 65 interposed therebetween. The heat transfer between the cooling coil body 63 and the induction plate 64 is suppressed by the heat insulating spacer 65. The heat insulating spacers 62 and 65 are annular flat plates having electrical insulating properties and thermal insulating properties. In this example, the sizes of the heat insulating spacers 62 and 65 are the same.

  The cooling coil body 63 includes an annular flat superconducting coil 66 and a cooling plate 67 that is an annular metal flat plate overlapping the side surface of the superconducting coil 66 in the axial direction of the superconducting magnet 1.

  The superconducting coil 66 has a tape-like coil wire wound in an annular shape with a predetermined number of turns. The superconducting coil 66 is a pancake coil in which the coil wire 7 is formed so as to overlap in the radial direction of the superconducting coil 66. The coil wire constituting the superconducting coil 66 is a superconducting wire.

  The cooling plate 67 is thermally connected to the superconducting coil 66. The cooling plate 67 is provided with a connecting portion 67 a that protrudes radially outward of the cooling plate 67. The refrigerator 3 is connected to the connection portion 67a of the cooling plate 67 via a heat conducting member. The superconducting coil 66 is cooled by the refrigerator 3 via the heat conducting member and the cooling plate 67. The state of the superconducting coil 66 becomes superconducting when the superconducting coil 66 is cooled by the refrigerator 3. In the space surrounded by the inner peripheral wall of the vacuum heat insulating container 2, the magnetic field of the superconducting magnet 1 is formed by exciting each superconducting coil 66.

  The guide plate 64 is an annular flat plate. In this example, the induction plate 64 overlaps the surface of the superconducting coil 66 opposite to the cooling plate 67 side via a heat insulating spacer 65. Further, in this example, the outer diameters of the induction plate 64, the superconducting coil 66, and the cooling plate 67 are the same. Further, in this example, the outer diameters of the heat insulating spacers 62 and 65 are larger than the outer diameters of the induction plate 64 and the superconducting coil 66, respectively.

  Next, the operation will be described. When each superconducting coil 66 is excited by supplying power to the laminated coil 6, the magnetic field of the superconducting magnet 1 is formed in the space surrounded by the inner peripheral wall of the vacuum heat insulating container 2.

  When any part of each superconducting coil 66 is quenched for some reason and a large resistance is generated in a part of the superconducting coil 66, the current of the laminated coil 6 is rapidly reduced, and the superconducting coil 66 is generated. The magnetic field changes greatly. At this time, an induction current flows through the induction plate 64 in a direction in which the change of the magnetic field by the superconducting coil 66 is suppressed. Thereby, the change of the magnetic field of the superconducting magnet 1 becomes gentle. Therefore, when the subject 10 is in the space surrounded by the inner peripheral wall of the vacuum heat insulating container 2, the change in the magnetic field received by the subject 10 becomes moderate, and the adverse effect of the subject 10 due to the change in the magnetic field is suppressed. At this time, Joule heat is generated by the induction current flowing in the induction plate 64, but the heat transfer from the induction plate 64 to the superconducting coil 66 is suppressed by the heat insulating spacers 62 and 65, and the superconducting coil 66 Induction and promotion of quenching is suppressed.

  In such a superconducting magnet device for MRI and the superconducting magnet 1, the cooling coil body 63 has a superconducting coil 66 and a cooling plate 67 overlapping the superconducting coil 66, and the conductive induction plate 64 is a cooling coil body. Since the heat insulating spacer 65 is interposed between the cooling coil body 63 and the induction plate 64, the magnetic field generated by the superconducting coil 66 is generated when at least a part of the superconducting coil 66 is quenched. An induction current can be generated in the induction plate 64 in a direction to suppress the change, and the change in the central magnetic field of the superconducting magnet 1 can be moderated. Thereby, even if the superconducting coil 66 is quenched, a rapid change in the strength of the magnetic field received by the subject 10 can be suppressed. Further, the heat generated in the induction plate 64 can be made difficult to be transmitted to the superconducting coil 66 by the heat insulating spacer 65. Thereby, the temperature rise of the superconducting coil 66 can be suppressed, and induction and promotion of quenching of the superconducting coil 66 can be suppressed.

  Here, a case where the induction plate 64 is not present in the superconducting magnet 1 is considered. In the absence of the induction plate 64, if any of the superconducting coils 66 is quenched and the magnetic field generated by the superconducting coil 66 changes greatly, there is no effect of suppressing the change of the magnetic field by the induction plate 64. The magnetic field of the superconducting magnet 1 formed in the space surrounded by the inner peripheral wall also greatly changes. Since the decay time constant of the magnetic field is determined by the inductance Lc of the laminated coil 6 and the generated resistance Rc of the laminated coil 6, considering that the generated resistance Rc of the laminated coil 6 increases with time, for example, Lc is 20H and Rc is In the case of 20Ω, the decay time constant of the magnetic field is 1 second. Therefore, in this case, when the central magnetic field of the superconducting magnet 1 is 3T, a large magnetic field change of several T / sec occurs. When the subject 10 is a human body, if the change in the magnetic field received by the subject 10 is 1 T / sec or more, for example, a flash phenomenon may occur as an adverse effect on the subject 10.

  On the other hand, in the present embodiment, since the change of the magnetic field is suppressed by the magnetic field generated by the induced current flowing through the induction plate 64, the apparent resistance Rc of the laminated coil 6 is smaller than that without the induction plate 64. The value can be suppressed to, for example, 1Ω or less, and the decay time constant of the magnetic field can be set to 10 seconds or more. Thereby, the bad influence with respect to the subject 10 can be eliminated. Further, the thermal time constant between the induction plate 64 and the superconducting coil 66 can be set to a predetermined value or more by the heat insulating spacer 65 interposed between the induction plate 64 and the superconducting coil 66. Thereby, induction and promotion of quenching of the superconducting coil 66 can be suppressed, and rapid attenuation of the magnetic field can be suppressed.

  In addition, in order to confirm the effect of suppressing the change in the magnetic field in the superconducting magnet 1 according to the present embodiment, a part of the superconducting coil 66 is quenched for the superconducting magnets of Example 1, Comparative Example 1, and Comparative Example 2. Relationship between the central magnetic field B0 (T) and the elapsed time t (sec), and the change in magnetic field dB / dT (T / sec) and the elapsed time t (sec) when a part of the superconducting coil 6 is quenched. And the analysis results of Example 1, Comparative Example 1, and Comparative Example 2 were compared.

  The configuration of the superconducting magnet according to the first embodiment is the same as that of the superconducting magnet 1 shown in FIG. The superconducting magnet according to Comparative Example 1 is a superconducting magnet in which the induction plate 64, the heat insulating spacers 62 and 65, and the cooling plate 67 are eliminated from the configuration of Example 1 and the remaining superconducting coils 66 are thermally short-circuited. The superconducting magnet according to the comparative example 2 is a superconducting magnet in which the induction plate 64 and the heat insulating spacers 62 and 65 are eliminated from the configuration of the first embodiment, and the remaining cooling coil body 63, that is, the superconducting coil 66 and the cooling plate 67 are thermally short-circuited. . The superconducting magnet used for the analysis is a simple model using a small superconducting coil having an inductance of about 20H in order to qualitatively compare the effects of the present invention. Further, in the analysis, the thermal time constant between the induction plate 64 and the superconducting coil 66 in Example 1 is calculated at 20 (sec), and temperature dependence is not considered.

  FIG. 3 is a graph showing the relationship between the central magnetic field B0 (T) and the elapsed time t (sec) for the superconducting magnets according to Example 1, Comparative Example 1, and Comparative Example 2. FIG. 4 is a graph showing the relationship between the magnetic field change dB / dT (T / sec) and the elapsed time t (sec) for the superconducting magnets according to Example 1, Comparative Example 1, and Comparative Example 2. .

  As shown in FIG. 3, in the superconducting magnet of Comparative Example 1 having only the superconducting coil 66, the magnetic field disappears about 7 seconds after the superconducting coil 66 is quenched, whereas the induction plate 64, the heat insulating spacer 65, and the superconducting magnet. In the superconducting magnet of Example 1 having the coil 66 and the cooling plate 67, it can be seen that the magnetic field disappears about 18 seconds after the superconducting coil 66 is quenched. Further, in the superconducting magnet of Comparative Example 2 in which the induction plate 64 is not present and the cooling plate 67 is present, an induction current flows through the cooling plate 67 due to a change in the magnetic field of the superconducting coil 66, and therefore about 2 seconds after the superconducting coil 66 is quenched. Until then, the attenuation of the magnetic field is suppressed. However, since the superconducting coil 66 is heated by the heat generated by the induced current of the cooling plate 67 and the resistance of the superconducting coil 66 is increased, the magnetic field is rapidly attenuated. It can be seen that the magnetic field disappears about 5 seconds after the superconducting coil 66 is quenched. Thus, it can be seen that the superconducting magnet of Example 1 has a longer magnetic field decay time than the superconducting magnets of Comparative Examples 1 and 2.

  Further, as shown in FIG. 4, in the superconducting magnet of the comparative example 2 in which the induction plate 64 is not provided and the cooling plate 67 is present, the maximum change of the magnetic field is larger than that of the superconducting magnet of the comparative example 1 having only the superconducting coil 66. ing. In the superconducting magnet of Comparative Example 2, the maximum change in the magnetic field is 1.2 T / sec, which is greater than or equal to a value that adversely affects when the subject 10 is a human body. On the other hand, in the superconducting magnet of Example 1, the maximum change in the magnetic field is 0.3 T / sec, which is found to be suppressed to less than half that of the superconducting magnet of Comparative Example 1. Thus, it can be seen that in the superconducting magnet of Example 1, the change in the magnetic field is more gradual than in the superconducting magnets of Comparative Examples 1 and 2.

  In addition, when the large-sized superconducting magnet 1 used in the MRI superconducting magnet apparatus is used, the stored energy is more than 10 times that of the simple model used for the analysis, so the magnetic field change characteristics are different from the above analysis. However, it is considered that the effect of suppressing the change of the magnetic field by the superconducting magnet 1 used in the MRI superconducting magnet device becomes more remarkable than the above analysis.

Embodiment 2. FIG.
In the second embodiment, the guide plate 64 is made of an alloy. Examples of the alloy constituting the guide plate 64 include white copper, brass, stainless steel, and duralumin. The temperature dependence of the electrical resistivity of the alloy constituting the induction plate 64 is lower than the temperature dependence of the electrical resistivity of a pure metal (for example, pure copper or pure aluminum). That is, in the second embodiment, an alloy having a temperature dependency of electrical resistivity lower than that of pure metal is used as a material constituting the induction plate 64. Thereby, even if the temperature of the induction | guidance | derivation board 64 changes, the change of the electrical resistivity of the induction | guidance | derivation board 64 becomes small, and the rapid change of the attenuation | damping time constant of the magnetic field of the superconducting magnet 1 is suppressed.

For example, when the material constituting the induction plate 64 is 90Cu-10Ni white copper, even if the temperature of the white copper changes from 20 K to room temperature, the electrical resistivity of the white copper is 1.5 × 10 ⁻⁷ Ωm to 1. It only changes to 7 × 10 ⁻⁷ Ωm and changes only 10%. On the other hand, when the material constituting the induction plate 64 is pure copper, when the temperature of the pure copper changes from 20K to room temperature, the electrical resistivity of the pure copper changes from 1.8 × 10 ⁻¹⁰ Ωm to 1.8 × 10. It changes to ^-8 Ωm and increases 100 times. Thus, the temperature dependence of the electrical resistivity of white copper is lower than the temperature dependence of the electrical resistivity of pure copper. The temperature dependence of the electrical resistivity of brass, stainless steel and duralumin is also lower than the temperature dependence of the electrical resistivity of pure copper, as is the case with white copper. Other configurations are the same as those in the first embodiment.

  In such a superconducting magnet device for MRI and the superconducting magnet 1, the induction plate 64 is made of white copper, brass, stainless steel or duralumin, so that a part of the superconducting coil 66 is quenched and the temperature of the induction plate 64 changes. However, the change in the electrical resistivity of the guide plate 64 can be made smaller than when the guide plate 64 is made of pure metal. Thereby, the rapid change of the magnetic field of the superconducting magnet 1 can be further suppressed.

Embodiment 3 FIG.
FIG. 5 is an exploded perspective view showing a unit laminated portion 61 of a superconducting magnet according to Embodiment 3 of the present invention. In each unit laminated portion 61, a cooling plate 67 that is an annular flat plate is provided with a slit 67 b that is a cutting portion that reaches the outer peripheral portion of the cooling plate 67 from the inner peripheral portion of the cooling plate 67. The slit 67 b is opened at each of the inner peripheral portion and the outer peripheral portion of the cooling plate 67. In this example, the slit 67 b is provided along the radial direction of the cooling plate 67. The two facing portions facing each other through the slit 67b of the cooling plate 67 are separated from each other. Thereby, the cooling plate 67 is electrically insulated at the position of the slit 67 b in the circumferential direction of the cooling plate 67. Moreover, the slit 67b is provided in the cooling plate 67 in the position farthest from the connection part 67a connected to the refrigerator 3 (FIG. 1). Other configurations are the same as those in the first embodiment.

  In such a superconducting magnet device for MRI and the superconducting magnet 1, the cooling plate 67 is provided with slits 67b reaching from the inner periphery to the outer periphery of the cooling plate 67, so that even if the magnetic field received by the cooling plate 67 changes. The generation of the induced current in the cooling plate 67 can be prevented by the slit 67b, and the generation of large Joule heat in the cooling plate 67 can be prevented. As a result, a metal material having a high thermal conductivity, such as pure copper or pure aluminum, can be used for the cooling plate 67, and the cooling performance for the superconducting coil 66 can be enhanced. Further, even when excitation and demagnetization of the superconducting coil 66 are performed by normal power supply control, a temperature rise of the superconducting coil 66 can be prevented, and excitation and demagnetization of the superconducting coil 66 can be performed stably.

  Further, since the slit 67b is provided in the cooling plate 67 at the position farthest from the connecting portion 67a connected to the refrigerator 3, even if the slit 67b is provided in the cooling plate 67, superconductivity by the cooling plate 67 is achieved. The cooling performance of the coil 66 can be made difficult to deteriorate.

  In the above example, the slit 67 b is provided only at one location in the circumferential direction of the cooling plate 67, but the slit 67 b may be provided at multiple locations in the circumferential direction of the cooling plate 67.

  In the above example, the configuration in which the slit 67b is provided in the cooling plate 67 is applied to the superconducting magnet 1 of the first embodiment. However, the configuration in which the slit 67b is provided in the cooling plate 67 is the superconductivity in the second embodiment. You may apply to the magnet 1. FIG.

Embodiment 4 FIG.
FIG. 6 is an enlarged cross-sectional view showing a unit laminate portion 61 of a superconducting magnet according to Embodiment 4 of the present invention. In the first to third embodiments, the guide plate 64 of the unit laminate portion 61 overlaps the superconducting coil 66 of the cooling coil body 63 via the heat insulating spacer 65. However, in this embodiment, the guide of the unit laminate portion 61 is guided. The plate 64 overlaps the cooling plate 67 of the cooling coil body 63 via the heat insulating spacer 65. The cooling plate 67 overlaps the side surface of the superconducting coil 66.

  The superconducting coil 66 has a tape-like coil wire 7 wound with a predetermined number of turns. The superconducting coil 66 is a pancake coil in which the coil wire 7 is formed so as to overlap in the radial direction of the superconducting coil 66. The aspect ratio of the length and width of the cross section of the coil wire 7 is 5 or more.

  The coil wire 7 is a high-temperature superconducting wire. The coil wire 7 includes a tape-shaped metal substrate 71, a high-temperature superconducting film 72 that is generated and overlapped with the metal substrate 71, and a protective material 73 made of metal (such as copper) that is superimposed on the high-temperature superconducting film 72. And an electrical insulating material 74 that collectively covers the metal substrate 71, the high-temperature superconducting film 72, and the protective material 73. That is, in the coil wire 7, a laminated body in which the metal substrate 71, the high-temperature superconducting film 72 and the protective material 73 are laminated in this order is covered with the electrical insulating material 74.

  The high temperature superconducting film 72 is made of a generally known high temperature superconducting material. As the high-temperature superconducting material constituting the high-temperature superconducting film 72, for example, a rare earth (RE) -based superconducting material (for example, REBCO or the like) or an yttrium (Y) -based superconducting material (for example, YBCO or the like) is used. Further, the protective material 73 is fixed to the high temperature superconducting film 72 by, for example, solder.

  The cooling plate 67 overlaps the end of the tape-shaped coil wire 7 in the width direction with an adhesive 8 that is a heat conductive paste. Thereby, the movement of heat between the superconducting coil 66 and the cooling plate 67 is performed via the adhesive 8. As the adhesive 8, for example, an epoxy adhesive is used.

  Since the laminated coil 6 is placed in a high vacuum environment in the vacuum heat insulating container 2, a high vacuum space is interposed between the superconducting coil 66 and the cooling plate 67. Therefore, when the adhesive 8 is not interposed between the superconducting coil 66 and the cooling plate 67, a high vacuum space is interposed between the superconducting coil 66 and the cooling plate 67, and the superconducting coil 66 and the cooling plate 67 are cooled. The thermal conductivity with the plate 67 becomes extremely small. In the present embodiment, since the adhesive 8 that is a heat conductive paste is interposed between the superconducting coil 66 and the cooling plate 67, the adhesive 8 is interposed between the superconducting coil 66 and the cooling plate 67. The thermal conductivity between the superconducting coil 66 and the cooling plate 67 is higher than in the case where there is not. In the present embodiment, the cooling plate 67 is arranged as close as possible to the superconducting coil 66 in order to improve the cooling efficiency for the superconducting coil 66. Other configurations are the same as those in the first embodiment.

  In this way, even if the induction plate 64 overlaps the cooling plate 67 of the cooling coil body 63 via the heat insulating spacer 65, an induction current is generated in the induction plate 64 in a direction that suppresses the change in the magnetic field of the superconducting coil 66. And the change in the magnetic field of the superconducting magnet 1 can be moderated.

  Further, in such a superconducting magnet device for MRI and the superconducting magnet 1, the coil wire 7 constituting the superconducting coil 66 is a high-temperature superconducting wire, so that it does not have to be cooled to an extremely low temperature such as the temperature of liquid helium. The superconducting coil 66 can be brought into a superconducting state, and the cooling equipment for the superconducting coil 66 can be simplified.

  On the other hand, when the coil wire 7 constituting the superconducting coil 66 is a high-temperature superconducting wire, the critical temperature for transition from the superconducting state to the normal conducting state is higher than that of the normal superconducting wire. To be late. For this reason, it is known that when the coil wire 7 is a high-temperature superconducting wire, a hot spot in which the temperature rise is concentrated is generated in the superconducting coil 66 and the superconducting coil 66 is locally burned. When local burning occurs in the superconducting coil 66, the resistance of the superconducting coil 66 increases abruptly, and the attenuation of the magnetic field by the superconducting coil 66 becomes severe. In the present embodiment, even when local burning occurs in the superconducting coil 66, an induced current can be generated in the induction plate 64 in a direction to suppress the change in the magnetic field of the superconducting coil 66, and the superconducting magnet 1 The change in the magnetic field can be moderated.

  In the present embodiment, since the cooling plate 67 overlaps the coil wire 7 with the adhesive 8, the thermal time constant between the superconducting coil 66 and the cooling plate 67 has no adhesive 8. The sensitivity of the superconducting coil 66 is sensitive to the heat generated by the cooling plate 67. Therefore, in the present embodiment, as in the third embodiment, by providing the cooling plate 67 with the slit 67b, the induction of quenching of the superconducting coil 66 due to the Joule heat generation of the cooling plate 67 can be prevented, and the superconducting magnet. 1 can be further suppressed.

  In the above example, the configuration in which the coil wire 7 constituting the superconducting coil 66 is a high-temperature superconducting wire is applied to the superconducting magnet 1 of Embodiment 1, but the coil wire 7 constituting the superconducting coil 66 is heated to a high temperature. You may apply the structure made into the superconducting wire to the superconducting magnet 1 of Embodiment 2 or 3.

Embodiment 5. FIG.
In the fifth embodiment, the resistance value of the induction plate 64 is set so that the attenuation time constant of the magnetic field of the superconducting magnet 1 is equal to or greater than a target set attenuation time constant (for example, 10 seconds). It is specified based on the mutual inductance L. That is, if the target set decay time constant is 10 seconds, the resistance value of the guide plate 64 is L / 10. In addition, the total amount of induction heat generated by the induction plate 64 when the superconducting coil 66 is excited by normal power supply control is 1/10 or less of the cooling capacity of the refrigerator 3 that cools the cooling coil body 63. Thereby, when the normal excitation time and the normal demagnetization time for the superconducting coil 66 are 1000 seconds or more, the Joule heat generation of the induction plate 64 becomes sufficiently smaller than the cooling capacity of the refrigerator 3, and the temperature rise range of the induction plate 64 is superconducting. It remains in a range where there is no problem in the attenuation of the magnetic field of the coil 66.

In this example, a 1-turn flat plate made of brass is used as the induction plate 64, and a 1000-turn coil wound with a coil wire is used as the superconducting coil 66. Therefore, in this example, the winding ratio between the induction plate 64 and the superconducting coil 66 is 1: 1000. Thereby, when the resistance value of the guide plate 64 is 1 × 10 ⁻³ Ω and the circumferential length of the guide plate 64 is 3 m, the thickness of the guide plate 64 is about 5 mm. In addition, the thickness of the induction | guidance | derivation board 64 is adjusted, adjusting the whole resistance value of the induction | guidance | derivation board 64, by providing the induction | guidance | derivation board 64 by providing the copper plate with a resistance value lower than that of brass by plating or the like. Can be made even thinner.

  Further, for example, when the normal excitation time of the laminated coil 6 is 1000 seconds, the superconducting magnet 1 has a magnetic field decay time constant of 10 seconds, so that a delay of 1/100 magnetic field generation occurs. In this case, the heat generation amount of the induction plate 64 is about 1 mW per one superconducting coil 66. Therefore, when the number of superconducting coils 66 included in the laminated coil 6 is 1000, the total amount of induction heat generated by the induction plate 64 is about 1 W, and induction relative to the cooling capacity of the refrigerator 3 at an operating temperature of 20 K is about 20 W. The temperature rise range of the plate 64 is 1K or less. The temperature rise of 1 K or less of the induction plate 64 is a temperature rise range that does not hinder the excitation of the superconducting coil 66. If the total amount of induction heat generated by the induction plate 64 when exciting the superconducting coil 66 by normal power supply control is 1/10 or less of the cooling capacity of the refrigerator 3, the induction plate is within a range that does not hinder the excitation of the superconducting coil 66. The temperature rise of 64 can be stopped. Other configurations are the same as those in the first embodiment.

  In such a superconducting magnet device for MRI and the superconducting magnet 1, induction is performed based on the mutual inductance L between the superconducting coil 66 and the induction plate 64 so that the attenuation time constant of the magnetic field of the superconducting magnet 1 is equal to or greater than the set attenuation time constant. Since the resistance value of the plate 64 is specified and the total amount of induction heat generated by the induction plate 64 when exciting the superconducting coil 66 is 1/10 or less of the cooling capacity of the refrigerator 3, the induction heat generation of the induction plate 64 The occurrence of quenching of the superconducting coil 66 due to can be more reliably suppressed, and a sudden change in the magnetic field of the superconducting magnet 1 can be further reliably suppressed.

  In the above example, the above-described configuration related to the resistance value of the induction plate 64 and the cooling capacity of the refrigerator 3 is applied to the first embodiment. However, the resistance value of the induction plate 64 and the cooling capacity of the refrigerator 3 are related. You may apply said structure to Embodiment 2-4.

  Further, in each of the above embodiments, the heat insulating spacer 65 in each unit laminated portion 61 is an integrated flat plate, but a plurality of heat insulating spacers 65 are separated from each other between the superconducting coil 66 and the induction plate 64 and dispersed. May be interposed. In this case, since an electromagnetic force is generated between the superconducting coils 66 of each unit laminated portion 61, the strength of the plurality of heat insulating spacers 65 is strong enough to withstand the electromagnetic force generated between the superconducting coils 66. In this way, if a plurality of heat insulating spacers 65 are spaced apart from each other between the superconducting coil 66 and the induction plate 64, a high vacuum space is created between the superconducting coil 66 and the induction plate 64. The thermal time constant between the superconducting coil 66 and the induction plate 64 can be ensured more reliably. Further, the material required for the heat insulating spacer 65 can be reduced, and the cost can be reduced.

  In each of the above embodiments, the superconducting magnet 1 of the present invention is applied to a superconducting magnet device for MRI. However, the superconducting magnet 1 of the present invention is applied to, for example, a superconducting magnet device for NMR (nuclear magnetic resonance). May be.

  1 superconducting magnet, 7 coil wire (high temperature superconducting wire), 63 cooling coil body, 64 induction plate, 65 heat insulation spacer, 66 superconducting coil, 67 cooling plate.

Claims (6)

A cooling coil body having a flat superconducting coil and a cooling plate overlying the superconducting coil;
A superconducting magnet comprising: a conductive induction plate disposed away from the cooling coil body; and a heat insulating spacer interposed between the cooling coil body and the induction plate.   The superconducting magnet according to claim 1, wherein the induction plate is made of white copper, brass, stainless steel, or duralumin. The cooling plate is an annular flat plate,
The superconducting magnet according to claim 1 or 2, wherein the cooling plate is provided with a cutting portion that reaches from the inner periphery of the cooling plate to the outer periphery of the cooling plate.   The superconducting magnet according to any one of claims 1 to 3, wherein the coil wire constituting the superconducting coil is a high-temperature superconducting wire. The resistance value of the induction plate is specified based on the mutual inductance of the superconducting coil and the induction plate so that the attenuation time constant of the magnetic field is equal to or greater than a set attenuation time constant,
5. The total amount of induction heat generated by the induction plate when the superconducting coil is excited is 1/10 or less of the cooling capacity of a cooling device that cools the cooling coil body. The superconducting magnet described in 1.   A superconducting magnet device for MRI, comprising the superconducting magnet according to any one of claims 1 to 5.

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