JP6655487B2 - Superconducting magnet device - Google Patents

Description

  The present invention relates to a superconducting magnet device.

  The superconducting magnet device is composed of a superconducting coil and a permanent current switch installed in parallel with the superconducting coil. The superconducting coil is heated by heating the above permanent current switch to a normal conduction state to generate electric resistance (hereinafter referred to as an open state). ), The current is supplied from the excitation power supply to the superconducting coil, and then the supply current from the excitation power supply is reduced to zero in a state in which the permanent current switch is cooled and brought into the superconducting state (hereinafter, closed state), so that the superconducting coil and The operation is a permanent current operation in which the current continues to flow in the superconducting closed circuit including the permanent current switch with almost no attenuation. Thereby, the superconducting magnet device can hold the magnetic field for a long time.

  Conventional superconducting magnet device, in order to maintain the superconducting coil and the components represented by the persistent current switch in a superconducting state, immersion cooling method used by immersing in a refrigerant represented by liquid helium or liquid nitrogen, and 2. Description of the Related Art A conduction cooling system in which a refrigerator and constituent elements are thermally connected to each other with a metal having good thermal conductivity to cool the refrigerator is often employed. However, in the above cooling method, when the size of the apparatus is increased, a large amount of refrigerant is required in the immersion method, and the temperature gradient in the object to be cooled becomes large in the conduction cooling method, and the desired temperature cannot be maintained. For this reason, a cooling system of a refrigerant circulation type has been studied, and in a large-sized apparatus represented by a nuclear fusion apparatus, a forced cooling system in which a refrigerant flow path is provided inside the apparatus and forcibly circulated by a pump is employed (for example, see Patent Reference 1). In a medium-sized apparatus typified by a magnetic resonance tomography apparatus (MRI), the refrigerant flows in the flow path by utilizing buoyancy caused by a density difference between a refrigerant vaporized by a heat source such as a superconducting coil and a refrigerant liquefied by a refrigerator. A loop-type thermosiphon system in which natural circulation is performed has been proposed (for example, Patent Documents 2 and 3).

  The refrigerant circulation type cooling system is expected to reduce the time required to open and close the permanent current switch as compared with the conduction cooling system. On the other hand, when the permanent current switch is heated to be changed from the closed state to the open state, it is difficult to actively control the circulation of the refrigerant and immediately stop the cooling. It is necessary to continue heating the heater with an output higher than the cooling capacity.

JP-A-07-121421 JP-A-06-342721 International Publication No. 2014/155476

  However, the refrigerant vaporized by the heating of the heater needs to be discharged to the outside of the device in order to avoid an increase in the pressure of the device. there were. Accordingly, an object of the present invention is to provide a superconducting magnet device that employs a refrigerant circulation type cooling method and that can reduce the amount of refrigerant vaporized by heating a heater.

  The present invention may take various embodiments in order to solve the above-described problems, and as one example, `` a superconducting coil, a permanent current switch connected to the superconducting coil, and cooling the superconducting coil and the permanent current switch. A superconducting magnet device having at least a refrigerant circulation type cooling means for circulating a refrigerant in a flow path, wherein the cooling means is at least a refrigerant container for storing a liquefied refrigerant, and a refrigerant circulation flow for circulating the refrigerant. And a heat transfer member for thermally contacting the refrigerant circulation flow path with the superconducting coil and the permanent current switch, and an arrangement location of the heat transfer member in contact with the permanent current switch from the refrigerant container In the section up to, there is a stopping means for stopping the circulation of the refrigerant flowing through the refrigerant circulation channel. "

  According to the present invention, there is provided a superconducting magnet device that employs a refrigerant circulation type cooling method and that can reduce the amount of refrigerant vaporized by heating a heater.

It is a figure showing typically a section of superconducting magnet device 1 concerning a 1st embodiment. FIG. 2 is a diagram schematically showing a superconducting magnet device 1 according to the first embodiment as a circuit. FIG. 2 is a bird's-eye view of the superconducting magnet device 1 illustrated in FIG. 1, in which only a refrigerant circulation channel 6 and a refrigerant container 8 are extracted and illustrated. FIG. 4 shows a cross-sectional view of a superconducting magnet device 1 according to a second embodiment. FIG. 5 is a bird's-eye view of the superconducting magnet device 1 shown in FIG. 4, in which only the refrigerant circulation channel 6 and the refrigerant container 8 are taken out and shown. FIG. 9 is a cross-sectional view of a superconducting magnet device 1 according to a fourth embodiment, particularly regarding a superconducting coil 4 and a coil bobbin 5. FIG. 7 is a cross-sectional view of the superconducting magnet device 1 shown in FIG. FIG. 7 is a BB cross-sectional view of the superconducting magnet device 1 shown in FIG. 6. FIG. 7 is a bird's-eye view of the superconducting magnet device 1 shown in FIG. 6, in which only the refrigerant circulation channel 6, the refrigerant container 8, and the permanent current switch 9 are taken out. FIG. 9 shows a cross-sectional view of a superconducting magnet device according to a fifth embodiment. It is a schematic diagram of a magnetic resonance imaging apparatus.

  Next, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

(First embodiment)
Hereinafter, a superconducting magnet device 1 according to a first embodiment of the present invention will be described with reference to FIGS. 1, 2, and 3. FIG. FIG. 1 schematically shows a cross section of a superconducting magnet device 1 according to the first embodiment.

  The superconducting magnet device 1 includes a vacuum vessel 2, a radiation shield 3 contained in the vacuum vessel 2, a plurality of superconducting coils 4 contained in the radiation shield, a coil bobbin 5 to which the superconducting coil 4 is fixed, a refrigerant circulation channel 6, a refrigerant The refrigerant 7 contained in the circulation channel 6, a refrigerant container 8 for storing the refrigerant 7, a permanent current switch 9, and a refrigerator 12 attached to the refrigerant container 8 have a basic configuration. As the refrigerant 7, for example, liquid helium or liquid nitrogen can be used. Further, the shape of the vacuum vessel 2 and the radiation shield 3 shown in FIG. 1 can take any shape as long as the support structure and the components constituting the superconducting magnet device 1 are allowed.

  Note that the central axis 21 of the superconducting coil 4 of the present embodiment is oriented in the vertical direction. The central axis 21 is a winding central axis of the superconducting coil 4 and coincides with the direction of a magnetic field generated when the superconducting coil 4 is energized. Further, the refrigerant circulation channel 6 has a structure in which the superconducting coil 4 and the coil bobbin 5 are brought into thermal contact with the coil bobbin 5 via a heat conduction path 11 which is a heat transfer member, and are cooled. Therefore, the heat conduction path 11 is made of a good conductor having a high thermal conductivity, and specifically, a copper mesh wire or the like is used. Further, the permanent current switch 9 is also cooled by the refrigerant circulation flow path 6 like the superconducting coil 4. The cooling means of the present embodiment is mainly constituted by the refrigerant circulation passage 6 and the heat conduction path 11.

  FIG. 2 schematically shows the superconducting magnet device 1 as a circuit. As shown in this figure, the same number of protection resistors 10 as the number of superconducting coils 4 are provided, and each protection resistor 10 is installed in parallel with each superconducting coil 4. A DC power supply 13 and a current breaker 14, which are current sources for exciting the superconducting coil 4, are installed outside the vacuum vessel 2. Inside the vacuum vessel 2, a superconducting coil 4 and a permanent current switch 9 are provided, and the superconducting state is maintained below the critical temperature.

  The procedure for generating a permanent current in the circuit as shown in FIG. 2 is, for example, as follows. First, a current is supplied from the DC power supply 13 to the superconducting coil 4 with the permanent current switch 9 opened. Thereafter, the current supplied from the DC power supply 13 is reduced to zero while the permanent current switch 9 is closed, and the current breaker 14 is opened. As a result, a permanent current operation in which a current continues to flow in the superconducting closed circuit including the superconducting coil 4 and the permanent current switch 9 with little attenuation is provided. Thereby, the superconducting magnet device 1 can hold the magnetic field for a long period of time. When the permanent current switch 9 is opened, it means that the permanent current switch 9 is shifted to a normal conduction state to generate electric resistance. Further, the permanent current switch 9 is shifted to the superconducting state to make the electric resistance extremely low, thereby closing the permanent current switch 9.

  FIG. 3 is a bird's-eye view of the superconducting magnet device 1 shown in FIG. 1 in which only the refrigerant circulation flow path 6 and the refrigerant container 8 are extracted, and the refrigerant flow path in the superconducting magnet device 1 is shown. The refrigerant circulation path and the mechanism by which the refrigerant 7 circulates through the path will be described as follows.

  The refrigerant circulation path 6 is a refrigerant circulation part 6 d that is in thermal contact with the permanent current switch 9, a refrigerant circulation part 6 e that is in thermal contact with the superconducting coil 4, a refrigerant circulation part that connects the refrigerant circulation part 6 d and the refrigerant container 8. 6c (6a and 6b).

  The refrigerant 7 flowing through the refrigerant circulation units 6d and 6e has a smaller density per unit volume than the refrigerant 7 in the refrigerant container 8 and the refrigerant circulation unit 6c. Due to this density difference, buoyancy is generated, and the refrigerant 7 has a vertical upward force and moves along the refrigerant circulation channel 6. The reason that the density of the refrigerant 7 flowing through the refrigerant circulating portions 6d and 6e is reduced is that the refrigerant 7 that has absorbed heat from these heat sources is vaporized or heated because it is thermally connected to the permanent current switch 9 and the superconducting coil 4. This is because the volume per unit mass increases due to the rise. After moving along the refrigerant circulation channel 6, the refrigerant 7 moving by buoyancy returns to the refrigerant container 8, is cooled and condensed or cooled by the refrigerator 12, and is supplied to the refrigerant circulation channel 6 again. Reference numeral 20 in the figure indicates the circulation direction of the refrigerant 7 described above.

  As described above, since the loop-type circulphon is a refrigerant circulation system utilizing a difference in density of the refrigerant 7 generated in the refrigerant circulating section, there is an advantage that a pump or the like for circulating the refrigerant 7 becomes unnecessary. Also, since the amount of the refrigerant 7 used is sufficient to create a flow circulating through the refrigerant container 8 and the refrigerant circulation channel 6, even if the amount of the refrigerant 7 used is small compared to the immersion cooling method, the cooling state Can be held.

  However, in the above-described method, when the permanent current switch 9 is heated by a heater or the like to make a transition to the normal conduction state (when it is opened), it is difficult to actively control the natural circulation of the refrigerant 7 and stop the cooling. is there. Because, even if a part of the permanent current switch 9 changes to the normal conduction state due to the heating of the heater, when the heating of the heater is stopped, part of the temperature immediately drops due to the action of the circulating refrigerant 7 and the superconducting state is changed. Will return to. Therefore, it was necessary to continue heating to keep the permanent current switch 9 open. In addition, it is necessary to discharge the refrigerant 7 to the outside of the superconducting magnet device 1 in order to avoid an increase in the internal pressure of the superconducting magnet device 1 due to the refrigerant 7 vaporized by the heating of the heater. The use of conduction cooling to avoid increased emissions is also considered. However, when the permanent current switch 9 is cooled to be in the closed state, the cooling time tends to be longer than that of the loop-type thermosiphon system that can use the latent heat or sensible heat of the refrigerant.

  Further, even if the cooling means is not of a loop type thermosiphon type but of a forced circulation type, a time lag occurs even if a pump or the like used for circulation is stopped until the circulation of the refrigerant is stopped. Therefore, similarly to the loop-type thermosiphon type cooling, it is necessary to keep heating the heater for a certain time so that the permanent current switch 9 maintains the critical temperature or higher.

  Thus, the superconducting magnet device 1 of the present embodiment discharges or shields the refrigerant 7 flowing through the refrigerant circulation flow path 6 in a section from the refrigerant container 8 to the location of the heat conduction path 11 in contact with the permanent current switch 9, A stop means for stopping the circulation of the refrigerant 7 is provided. The specific concept of the stopping means will be described below. In the following description, a case where a loop-type thermosiphon type is adopted will be described as an example, but a forced circulation type can be similarly applied.

  The superconducting magnet device 1 of the present embodiment has a structure shown in FIGS. 1 and 3 as a stopping means for stopping the circulation of the refrigerant 7. These structures mainly include a refrigerant circulating section 6c, a heater 52 serving as a circulation suppressing means, a branch pipe 6f, and a means for opening and closing the branch pipe 6f. Further, the refrigerant storage unit 15 may be added to the basic structure.

  The refrigerant circulation part 6c is a meandering part provided in a part of the refrigerant circulation flow path 6 in the vertical direction. As shown in FIG. 3, it is composed of a refrigerant circulation part 6a and a refrigerant circulation part 6b. The refrigerant circulation part 6 a is a pipe connected to the vicinity of the bottom of the refrigerant container 8 and extending vertically from the vicinity of the bottom of the refrigerant container 8. The refrigerant circulating portion 6b is a pipe extending downward from the upper end of the refrigerant circulating portion 6a. In the connection structure between the refrigerant circulating unit 6a and the refrigerant circulating unit 6b, the refrigerant storing unit 15 is provided at each end, and the upper end of the refrigerant circulating unit 6a and the upper end of the refrigerant circulating unit 6b are connected to the refrigerant storing unit 15. Structure. Specifically, as shown in FIG. 1, the refrigerant circulating portion 6c has a structure in which the refrigerant storing portion 15 is provided at a vertically folded position. In addition, the refrigerant | coolant storage part 15 may use a container different from piping as the refrigerant | coolant storage part 15, and without providing another member as the refrigerant | coolant storage part 15, near the edge part of the refrigerant | coolant circulation part 6a and the refrigerant | coolant circulation part 6b. It may be formed by expanding the diameter and connecting the expanded portions.

  When the refrigerant storage unit 15 is made of a material different from that of the refrigerant circulation unit, it is desirable that the refrigerant storage unit 15 be made of a material having better heat conductivity than the refrigerant circulation unit. When the permanent current switch 9 is opened, the refrigerant reservoir 15 is heated by the heater 51, and the internal refrigerant 7 needs to be quickly evaporated. Therefore, it is desirable to be made of copper or aluminum. The refrigerant circulation section 6c and the refrigerant container 8 connected to the refrigerant storage section 15 are made of a material having low thermal conductivity, for example, stainless steel. By using a material having a low thermal conductivity, even when the refrigerant storage unit 15 is heated, heat transfer to the superconducting coil 4 can be reduced, and the temperature of the superconducting coil 4 can be efficiently maintained with the refrigerant saved. it can.

  The refrigerant storage section 15 is installed so as to be at a position lower than the liquid level of the refrigerant 7 accommodated in the refrigerant container 8 in the vertical direction. This is because the refrigerant 7 filled in the refrigerant storage unit 15 rises and flows into the refrigerant circulation unit 6a against gravity due to the own weight of the refrigerant 7 accommodated in the refrigerant container 8.

  The heater 51 is provided at least in the vicinity of the meandering portion, and prevents the refrigerant 7 from circulating by evaporating the refrigerant 7 flowing through the refrigerant circulating portion 6c. The mounting position of the heater 51 is the refrigerant storage section 15 or the refrigerant circulation section 6a or 6b as shown in FIG. Even if the heater 51 is provided in the refrigerant circulating portions 6a and 6b, bubbles generated by the heating work toward the branch pipe 6f to stop the circulation of the refrigerant 7.

  The heater 51 operates at the same timing as the heater 52 that heats the permanent current switch 9. Therefore, by sharing the power supply and the conductor with the heater 52, the heating timing can be easily synchronized, and the structure can be simplified. The heater 51 is a general electric heater, for example, a nichrome wire heater can be used.

  The branch pipe 6f is a pipe that reaches the outside of the vacuum vessel 2, and is a pipe that discharges the refrigerant 7 evaporated by the operation of the heater 51. Further, a pressure sensor or a temperature sensor may be attached to the branch pipe 6f as means for detecting the liquid level of the refrigerant 7. Under the permanent current operation, the liquid level position of the refrigerant 7 (the liquid level position in the rated state) is substantially the same between the refrigerant container 8 and the branch pipe 6f. Detecting the liquid level of the refrigerant 7 in the branch pipe 6f has the following advantages.

  The superconducting magnet device 1 of the present embodiment employs a loop-type thermosiphon cooling system. Therefore, if air bubbles accumulate in the refrigerant circulation flow path 6 or the refrigerant storage section 15, the buoyancy derived from the density difference, which is the source of the conveyance force of the refrigerant 7, is not efficiently transmitted, and the circulation of the refrigerant 7 stops or the efficiency decreases. Could be In particular, the meandering section composed of the refrigerant circulation section 6c and the refrigerant storage section 15 of this embodiment has no heat source under the permanent current operation. The refrigerant 7 is conveyed by pressure generated by a difference between the density of the refrigerant 7 in the refrigerant container 8 and the density of the refrigerant 7 in the refrigerant circulation part 6d. Therefore, in order to circulate the refrigerant 7 efficiently, it is desirable to suppress a decrease in the circulation efficiency of the refrigerant 7 in the meandering portion and to detect a decrease in the efficiency as soon as possible. Therefore, a means for detecting the liquid level position of the refrigerant 7 and a means for estimating the storage state of the refrigerant 7 may be provided in the branch pipe 6f.

  The temperature sensor, which is one of the specific means candidates, is mounted in the liquid at a position lower than the liquid level position in the rated state, for example, in the liquid in the rated state, so that the temperature detected by the temperature sensor becomes higher than the rated state. In this case, it can be understood that the liquid level has dropped. In addition, the pressure sensor obtains information on the gas pressure in the rated state in advance, so that when the gas pressure is higher than the rated state regardless of the rated state, excessive evaporation of the refrigerant 7 occurs. Can be detected. When the refrigerant 7 in the refrigerant storage section 15 is depleted, the stored gas is discharged from the branch pipe 6f and the liquefied refrigerant 7 is supplied to return the amount of the refrigerant 7 to an appropriate state. it can.

  The means for controlling the opening and closing of the branch pipe 6f is, for example, a valve 61 as shown in FIG. The valve 61 is provided outside the vacuum vessel 2 and may be operated manually or automatically. When the circulation of the refrigerant 7 is stopped, the heater 51 is operated to evaporate the refrigerant 7. When the valve 61 is opened after the permanent current switch 9 is opened by an operation described later, the vaporized refrigerant 7 is discharged to the outside. This discharge can prevent excessive pressure from being applied to the meandering portion and stop the circulation of the refrigerant 7. Further, as shown in FIG. 1, a configuration may be adopted in which a flow path returning from the branch pipe 6f to the refrigerant container 8 is provided, and the refrigerant gas generated in the branch pipe 6f is liquefied again and used. By providing the flow path returning to the refrigerant container 8, the consumption of the refrigerant 7 can be further reduced.

  In the superconducting magnet device 1 of the present embodiment described above, the opening and closing of the permanent current switch 9 is executed as follows.

  When the permanent current switch 9 is switched from the closed state to the open state, the heater 51 is energized with the valves 61 and 62 closed. The refrigerant 7 circulating through the meandering portion is vaporized by the heater 51. The vaporized refrigerant 7 or the refrigerant 7 whose density has decreased due to the temperature rise obtains buoyancy and stays in the refrigerant storage unit 15. The staying refrigerant 7 hinders the circulation of the refrigerant 7 in the meandering portion, and the circulation of the refrigerant 7 toward the permanent current switch 9 is stopped. The energization of the heater 52 is performed in conjunction with the energization of the heater 51, and the refrigerant 7 in the refrigerant circulating portion 6d that is in thermal contact with the permanent current switch 9 evaporates or rises in temperature. Returns to the refrigerant container 8.

  When the heater 52 is energized, the permanent current switch 9 and the refrigerant 7 present in the refrigerant circulating portion 6d evaporate, and the liquid level quickly decreases. When the liquid level becomes lower than the permanent current switch 9, in other words, the position where the liquid level of the liquefied refrigerant 7 at the liquid level is in direct or indirect thermal contact with the permanent current switch 9. When the temperature becomes lower than the above, the power supply to the heater 51 and the heater 52 may be stopped. At such a stop time, the cooling speed of the permanent current switch 9 via the refrigerant circulation unit 6d is lower than the rated state, and the cooling of the permanent current switch by the liquefied refrigerant 7 is suppressed. This is because the permanent current switch 9 is kept in the open state even if the heating is not continued.

  It should be noted that energization of the heater 52 may be continued even after the liquid level of the refrigerant 7 has sufficiently decreased. As the energization is continued, the temperature of the permanent current switch 9 also rises quickly and can be shifted to the open state. In addition, according to FIG. 1, the portions of the permanent current switch 9 and the refrigerant circulating portion 6d to be heated are disposed so as to be substantially at the same position in the vertical direction. With such an arrangement relationship, both structures can be heated together by one heater 52, and the configuration is simplified. In addition, when the permanent current switch 9 and the refrigerant circulating unit 6d are connected by the heat conduction path 11 and the mounting positions of the heat conduction paths 11 are different from each other in the vertical direction, a heater is provided at each mounting position. Is also good.

  In the case of the loop-type thermosiphon system, the position where the permanent current switch 9 is thermally connected to the refrigerant circulation portion 6d and the position where the refrigerant storage portion 15 is installed are lower than the liquid level of the refrigerant container 8 and the liquid level. It is desirable to be near. Under permanent current operation, the liquid level of the refrigerant container 8, the branch pipe 6f, and the refrigerant circulating portion 6d are substantially the same, and are present in the branch pipe 6f and the refrigerant circulating portion 6d when the circulation of the refrigerant 7 is stopped. It is necessary to evaporate and remove the refrigerant 7. Therefore, by providing the above-described connection position and installation position at a position close to the liquid level of the refrigerant container 8, the amount of the refrigerant 7 to be evaporated is reduced, and the liquid level of the refrigerant 7 is quickly reduced to circulate the refrigerant 7. Can be stopped.

  In addition, the connection portion between the branch pipe 6f and the refrigerant container 8 is located at a position higher than the liquid level of the refrigerant 7 in the refrigerant container 8. At this position, it is possible to prevent the refrigerant 7 from flowing back into the branch pipe 6f due to gravity. Further, the branch pipe 6f is made of a material having a low thermal conductivity such as stainless steel, thereby suppressing heat conduction through the branch pipe 6f other than the heated part, whereby the permanent current switch 9 is cooled and closed. Can be avoided. In order to quickly adjust the liquid level in the refrigerant circulation unit 6d, the refrigerant circulation unit 6d may be made of two materials. For example, a portion where the heater 52 is installed is made of a high heat conductive member such as aluminum, and the other portions are made of stainless steel, and are joined to each other by a dissimilar joint.

  In the above-described example, the case where the cooling method of the loop thermosiphon type is adopted has been described. When a system in which the refrigerant 7 is forcibly circulated by using a pump or the like is employed, the permanent current switch 9 is shifted from the closed state to the open state according to the same procedure as described above after the pump or the like is stopped. When the pump or the like is stopped, the circulation of the refrigerant 7 to the superconducting coil 4 is stopped. Therefore, the cooling of the superconducting coil 4 may be continued by using cooling utilizing heat storage of the solid refrigerant or conduction cooling. Alternatively, a plurality of independent refrigerant containers 8 may be provided to separate the circulation of the refrigerant 7 for cooling the superconducting coil 4 and the circulation of the refrigerant 7 for cooling the permanent current switch 9.

  The case where the permanent current switch 9 shifts from the closed state to the open state has been described above. When cooling the permanent current switch 9 from the open state to the closed state, the following procedure is executed. First, the valve 61 shown in FIG. 1 is opened to discharge the low-density refrigerant 7 remaining in the refrigerant storage unit 15 out of the superconducting magnet device 1. A check valve 71 is provided between the discharge-side end of the branch pipe 6f and the valve 61 so that the air does not flow through the branch pipe 6f.

  When the internal pressure of the refrigerant storage section 15 is reduced by the discharge of the refrigerant 7 and the pressure generated by the own weight of the refrigerant 7 stored in the refrigerant container 8 exceeds the internal pressure, the refrigerant 7 passes from the refrigerant container 8 through the refrigerant circulation section 6a. It flows into the refrigerant storage unit 15. When the refrigerant storage unit 15 is sufficiently cooled by the flowing refrigerant 7, the refrigerant circulating unit 6c basically has no heat source, so that the refrigerant 7 maintains the same density as the state stored in the refrigerant container 8. As it flows into the refrigerant circulation part 6d.

  Since the permanent current switch 9 serves as a heat source for the refrigerant circulating unit 6d, a difference in the density of the refrigerant 7 occurs, and the circulation of the refrigerant 7 resumes. The permanent current switch 9 starts to be cooled because the refrigerant liquid level inside the refrigerant circulating unit 6d rises and is held at a position higher than the position where the refrigerant is in thermal contact with the permanent current switch 9. When the closed state of the permanent current switch 9 is maintained, the refrigerant circulating portion 6c basically has no heat source, but it is difficult to completely exclude the influence of radiant heat or the like. The refrigerant 7 that has been vaporized by the heat that enters the refrigerant circulating units 6a and 6b without being shielded stays in the refrigerant storing unit 15 to hinder the refrigerant circulation. In order to prevent such a state from occurring, the valve 61 may be closed, the valve 62 may be opened, and the vaporized refrigerant 7 may return to the refrigerant container 8 through the refrigerant circulation part 6g. The refrigerant circulating unit 6g can be used as a flow path for supplying the refrigerant 7 to the refrigerant container 8 in a preparation stage for operating the superconducting magnet device 1. In addition, a check valve 72 is provided to prevent air from flowing into the air, similarly to the end of the branch pipe 6f on the air side.

  When the forced circulation is adopted as the method of circulating the refrigerant 7, the pump or the like may be restarted after discharging the gaseous refrigerant 7 retained in the refrigerant storage unit 15 as described above.

  As described above, the superconducting magnet device 1 of the present embodiment can quickly open and close the permanent current switch 9 by partially stopping the circulation of the refrigerant in the superconducting magnet device of the refrigerant circulation type. In addition, it has a refrigerant circulating section 6c having a refrigerant storing section 15 and a meandering section, and a partial circulation stop can be performed by selective heating of this section. Can be made in small quantities. Further, the heating time of the heater of the permanent current switch 9 can be reduced as compared with the related art, and the waiting time in demagnetization of the superconducting magnet device can be reduced. Particularly, in the loop-type thermosiphon, since the circulation of the refrigerant can be actively controlled, a remarkable effect that the time required for opening and closing the permanent current switch 9 is equivalent to that of the immersion cooling can be obtained.

(Second embodiment)
FIG. 4 shows a cross-sectional view of the superconducting magnet device 1 according to the second embodiment. FIG. 5 is a bird's-eye view showing only the refrigerant circulation channel 6 and the refrigerant container 8. The second embodiment is different from the first embodiment shown in FIG. 1 in that a branch is further provided in a branch pipe 6f for guiding the refrigerant 7 to the outside of the superconducting magnet device 1, and a gas cylinder 81 serving as a gas refrigerant introduction unit is provided. The difference is that the gas refrigerant 81 can be supplied from the gas cylinder 81 to the refrigerant reservoir 15. The stopping means for stopping the circulation of the refrigerant 7 in this embodiment is mainly composed of the refrigerant circulating section 6c, the gas cylinder 81 as the circulation suppressing means, and the branch pipe 6f. Further, a refrigerant storage unit 15 may be added to this. By adopting this structure, a heater for heating the refrigerant storage section 15 can be omitted, the number of components housed inside the vacuum vessel 2 is reduced, and the structure is simplified.

  In the superconducting magnet device 1 according to the second embodiment, the operation of shifting the permanent current switch 9 from the closed state to the open state is executed as follows. First, the valve 61 and the valve 62 are closed, and then the valve 63 is opened. After the valve 63 is opened, the gaseous refrigerant 7 is introduced from the gas cylinder 81 into the branch pipe 6f. Since the valve 61 and the valve 62 are closed, the introduced gaseous refrigerant 7 generates a pressure that pushes down the liquid level of the refrigerant 7 below the branch pipe 6f. When the pressure is controlled by the introduced amount and the gaseous refrigerant 7 is introduced to the extent that the liquid refrigerant 7 is exhausted from the refrigerant storage unit 15, the circulation of the refrigerant 7 in the refrigerant circulation unit 6c is stopped. Thereafter, as in the first embodiment, a current is supplied to the heater 52, and the refrigerant circulating unit 6d is heated, whereby the permanent current switch 9 quickly shifts to the open state.

  When the permanent current switch 9 is shifted from the open state to the closed state, the following procedure is executed. First, the valve 63 is closed, and then the valve 61 is opened. Thus, the gaseous refrigerant 7 stored in the branch pipe 6f and the refrigerant storage unit 15 is discharged through the valve 61. The discharge of the refrigerant 7 continues until the liquid level in the branch pipe 6f and the liquid level in the refrigerant container 8 become substantially the same. When the discharge pressure of the refrigerant 7 decreases and the refrigerant reservoir 15 is filled with the liquefied refrigerant 7, the valve 61 is retightened. Thereafter, when the refrigerant circulating unit 6c and the refrigerant storing unit 15 are sufficiently cooled and have a density substantially equal to the density of the refrigerant 7 in the refrigerant container 8, the circulation of the refrigerant 7 starts again using the permanent current switch 9 as a heat source.

  After closing the valve 63, the valve 62 may be open or closed. While the gaseous refrigerant 7 is discharged through the valve 61, a part of the refrigerant 7 released into the atmosphere by being kept open can be collected and returned to the refrigerant container 8. on the other hand. When the valve 62 is closed, the gaseous refrigerant 7 does not flow into the refrigerant container 8. As a result, since the output of the refrigerator 12 over the period in which circulation is maintained is not required, the superconducting magnet device 1 can be stably operated even with a small refrigerator.

  With the superconducting magnet device 1 according to the second embodiment described above, not only the same effects as in the first embodiment can be obtained, but also the time required for stopping the circulation of the Since the phase change time is not required, it is further reduced as compared with the first embodiment. In addition, since it is not necessary to use heat to stop the circulation of the refrigerant 7, the refrigerant circulating unit 6 c and the refrigerant storing unit 15 are all formed of members having low thermal conductivity, and the heat input from the outside of the vacuum vessel 2. Can be designed by focusing only on reducing the size, and the design constraints can be relaxed.

(Third embodiment)
FIG. 5 shows a cross-sectional view of the superconducting magnet device 1 according to the third embodiment. The third embodiment has a structure in which a refrigerant circulating portion 6 d thermally in contact with the permanent current switch 9 is extended from 6 e in thermal contact with the superconducting coil 4, as compared with the first embodiment. Is different. Note that the present embodiment has a structure having the heater 51 as in the first embodiment, but may have a system in which the gaseous refrigerant 7 is introduced as in the second embodiment. By employing a structure in which the refrigerant circulating unit 6c and the refrigerant circulating unit 6d are branched from the refrigerant circulating unit 6e as in the present embodiment, the permanent current switch 9 is arranged near the superconducting coil 4, and the vacuum vessel 2 The entire storage container can be made compact.

  In the system shown in FIG. 5, when the heater 51 heats the refrigerant storage unit 15, the heat is easily transmitted to the refrigerant circulation unit 6 e through the refrigerant circulation unit 6 c. Therefore, it is desirable that the refrigerant circulating section 6a be made of a stainless steel material having a low thermal conductivity and reduce the amount of heat input to the refrigerant circulating section 6e. Such a configuration reduces the thermal load on the superconducting coil 4 due to the heat generated by the heater 51 and contributes to stabilizing the temperature of the superconducting magnet device 1.

(Fourth embodiment)
FIG. 6 is a cross-sectional view of the superconducting magnet device 1 according to the fourth embodiment, particularly showing a superconducting coil 4 and a coil bobbin 5. FIG. 7 is a sectional view of the superconducting magnet device 1 taken along the line AA shown in FIG. FIG. 8 is a sectional view taken along line BB of the superconducting magnet device 1 shown in FIG. FIG. 9 is a bird's-eye view of the superconducting magnet device 1 shown in FIG. 6, in which only the refrigerant circulation channel 6, the refrigerant container 8, and the permanent current switch 9 are taken out.

  The fourth embodiment is different from the first embodiment in that the center axis 21 of the superconducting coil 4 is oriented in the horizontal direction, and that the refrigerant circulating portion 6e that is in thermal contact with the superconducting coil 4 is a superconducting coil. 4 in that it is configured as a plurality of arc-shaped members that share the central axis 21 with 4. 7 and 8, as shown in the example, when the superconducting magnet device 1 of the present embodiment acquires a cross section perpendicular to the central axis 21, the cross section of the inner peripheral surface has a circular or elliptical shape. The vacuum container 2 is configured so as to form an open space along the direction of the central axis 21. Further, the outer peripheral surfaces of the vacuum vessel 2 and the radiation shield 3 have an arbitrary shape depending on a use form. As shown in FIG. 6, the superconducting magnet device 1 includes a plurality of superconducting coils 4 in the direction of the central axis 21. The diameter of each superconducting coil 4 may be different.

  In the superconducting magnet device 1 according to the fourth embodiment, since the central axis 21 of the superconducting coil 4 is oriented in the horizontal direction, the shape of the refrigerant circulation part 6e is different from the first to third embodiments. 8 and 9 show the refrigerant circulating unit 6e in the present embodiment. The refrigerant circulating portion 6 e mainly includes an arc-shaped pipe formed along the outer peripheral curved surface of the superconducting coil 4 and a horizontal pipe for circulating the refrigerant 7 in the direction of the central axis 21. By providing the arc-shaped pipe along the outer peripheral curved surface, the refrigerant 7 flowing through the refrigerant circulating portion 6e is intensively used for cooling the superconducting coil 4, and the cooling efficiency can be improved.

  Note that the arrangement of the arc-shaped pipe is not limited to the mode along the outer periphery of the superconducting coil. If it is structurally acceptable, it may be configured along the inner peripheral surface. In this case, for example, a heat conduction path 11 penetrating through the coil bobbin 5 is provided to cool the superconducting coil 4. Further, the arc-shaped pipe may be provided at a different position from the superconducting coil 4 in the direction of the central axis 21. For example, an arcuate pipe or a straight pipe may be arranged at the position of line AA in FIG. Also in this case, superconducting coil 4 is cooled by providing heat conduction path 11 so as to penetrate coil bobbin 5. As described above, the piping structure that does not follow the outer peripheral curved surface is useful for suppressing the radial expansion of the internal structure of the vacuum vessel 2 with respect to the center shaft 21 and for miniaturizing the superconducting magnet device 1. is there.

  Further, by adopting such a structure, the same effect as that of the first embodiment can be obtained, and the magnetic resonance tomographic imaging apparatus (FIG. 11A) in which the central axis 21 is oriented in the horizontal direction. The superconducting magnet apparatus 1 can be applied to a horizontal magnetic resonance imaging apparatus and a horizontal MRI apparatus. FIG. 11A is a schematic diagram of a horizontal type MRI apparatus 100.

  An MRI apparatus requires a static and strong magnetic field (static magnetic field) for imaging, and a superconducting magnet apparatus is used as a component for generating the static magnetic field. The superconducting magnet device 1 of the present embodiment can be used as a device for generating the static magnetic field (static magnetic field generating device). Since the static magnetic field generator in the conventional MRI apparatus adopts the immersion cooling method using liquid helium, the consumption of helium accompanying the excitation and demagnetization of the superconducting magnet was enormous. On the other hand, in the MRI apparatus 100 to which the superconducting magnet device 1 of the present embodiment is applied, the amount of the refrigerant 7 used is remarkably small as compared with the immersion cooling, and the consumption is in principle reduced to the volume of the refrigerant storage unit 15. It can also be suppressed.

(Fifth embodiment)
FIG. 10 is a sectional view of the superconducting magnet device according to the fifth embodiment. The fifth embodiment is different from the first embodiment in that a plurality of refrigerant circulating portions 6e that are in thermal contact with the superconducting coil 4 are provided, and the opening is formed by the vacuum vessel 2 and the radiation shield 3 orthogonal to the central axis 21. 22 is formed.

  By adopting such a structure, the same effect as that of the first embodiment can be obtained, and a magnetic resonance tomographic imaging apparatus (a vertical magnetic resonance imaging apparatus, a vertical MRI ) Can be applied to the superconducting magnet device 1. FIG. 11B is a schematic diagram of a vertical type MRI apparatus 100. Also in this case, the MRI apparatus 100 to which the superconducting magnet apparatus 1 of the present embodiment is applied requires only a remarkably small amount of the refrigerant 7 as compared with the immersion cooling, and in principle, consumes the same amount as the volume of the refrigerant storage unit 15 Can also be suppressed.

  In the above, the present invention has been described with reference to a plurality of embodiments. However, the present invention is not limited to these embodiments, and it goes without saying that the structure and materials may be changed, added, or deleted without departing from the scope of the invention. In the above-described embodiment, liquid helium is used as the refrigerant 7, but liquid nitrogen or the like may be used when the superconducting coil 4 is made of a high-temperature superconducting wire. Further, the cooling system of the refrigerant circulation type and the conduction cooling system may be combined. The cooling system of the superconducting magnet apparatus 1 according to the present embodiment includes fields other than the above-mentioned MRI apparatus, such as a superconducting magnet for an accelerator, a superconducting rotating gantry of a particle beam therapy system, a superconducting flyhole, and a superconducting bulk body. Can be applied to all devices and members required to maintain the superconducting state.

DESCRIPTION OF SYMBOLS 1 Superconducting magnet device 2 Vacuum container 3 Radiation shield 4 Superconducting coil 5 Coil bobbin 6 Refrigerant circulation channel 6a, 6b, 6c, 6d, 6e, 6g Refrigerant circulation part 6f Branch pipe 7 Refrigerant 8 Refrigerant container
Reference Signs List 9 permanent current switch 10 protection resistor 11 heat conduction path 12 refrigerator 13 DC power supply 14 current breaker 15 refrigerant storage unit 20 refrigerant circulation direction 21 central axis 22 opening 51, 52 heating heater 61, 62, 63 valve 71, 72 Check valve 81 Gas cylinder 100 MRI equipment

Claims (9)

A superconducting magnet device having at least a superconducting coil, a permanent current switch connected to the superconducting coil, and a refrigerant circulation type cooling unit that cools the superconducting coil and the permanent current switch and circulates a refrigerant in a flow path. So,
The cooling means includes at least a refrigerant container for storing a liquefied refrigerant, a refrigerant circulation channel for circulating the refrigerant, and heat transfer for thermally contacting the refrigerant circulation channel with the superconducting coil and the permanent current switch. includes a member, in the section from the coolant vessel to arrangement position of the heat transfer member in contact with the permanent current switch, have a stopping means for stopping the circulation of the refrigerant flowing through the refrigerant circulation passage,
The stopping means is at least one meandering part formed in the refrigerant circulation flow passage and meandering vertically in the vertical direction, a circulation suppressing means provided in the meandering part, and the superconducting part branched from the meandering part. A superconducting magnet device , comprising: a branch pipe communicating with the outside of the magnet device.
The superconducting magnet device according to claim 1,
A heating heater functioning as the circulation suppressing means,
The heating heater evaporates the refrigerant flowing through the meandering portion and blocks circulation of the refrigerant.
Superconducting magnet device.
The superconducting magnet device according to claim 1 or 2,
A gas refrigerant introduction unit that introduces the refrigerant in a gaseous state that functions as the circulation suppression unit into the meandering unit,
The gas refrigerant introduction unit introduces the refrigerant in a gaseous state into the meandering part, and blocks circulation of the refrigerant flowing through the meandering part.
Superconducting magnet device.
The superconducting magnet device according to claim 3,
The gas refrigerant introduction unit is connected to the branch pipe and connected to the meandering part.
Superconducting magnet device.
The superconducting magnet device according to any one of claims 1 to 4, wherein
The refrigerant circulation flow path has a refrigerant storage section at a vertical turning position of the meandering section, and the circulation suppressing means and the branch pipe are provided in the refrigerant storage section.
Superconducting magnet device.
The superconducting magnet device according to any one of claims 1 to 5, wherein
A flow path is provided from the branch pipe to the refrigerant container via the outside of the vacuum container housing the superconducting coil.
Superconducting magnet device.
The superconducting magnet device according to any one of claims 1 to 6, wherein
The central axis of the superconducting coil is oriented vertically
Superconducting magnet device.
The superconducting magnet device according to any one of claims 1 to 6, wherein
The central axis of the superconducting coil is oriented horizontally
Superconducting magnet device.
The superconducting magnet device according to any one of claims 1 to 8,
Provide as a static magnetic field generator
Magnetic resonance tomography equipment.

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