JP2010177677A - Cooling device for superconducting member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent reduction in cooling efficiency of a cooling apparatus by preventing heat conduction from the cylinder of a refrigerator to liquid nitrogen and prevent fluctuations in the liquid level of the liquid nitrogen, when the cooling head of the refrigerator is immersed directly in liquid nitrogen, to obtain supercooling liquid nitrogen in the apparatus for cooling a high-temperature superconducting member with the liquid nitrogen at a supercooling temperature. <P>SOLUTION: A heat insulating part is provided around the outer surface of the cylinder of the refrigerator. The heat-insulating part has a vacuum heat-insulated structure or the cylinder is surrounded by a heat-insulating material. Furthermore, the heat-insulating part around the outer surface of the cylinder of the refrigerator is extended to the middle position in the vertical direction of the outer surface of the cooling head. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a superconducting member cooling apparatus for cooling and holding a superconducting member such as a superconducting transformer, a superconducting magnet, various other superconducting coils, or a superconducting cable, particularly a high-temperature superconducting member at a low temperature with liquid nitrogen.

In cooling a superconducting member such as a superconducting coil, particularly a superconducting member using high-temperature superconductivity, a relatively inexpensive liquid nitrogen (LN ₂ ) is often used as a cooling medium. In this case, saturated liquid nitrogen at atmospheric pressure, that is, liquid nitrogen of about 77K is generally used. That is, a superconducting member is accommodated in a cooling container substantially open to the atmosphere called a cryostat that is thermally insulated from a vacuum, and about 77 K of atmospheric pressure saturated liquid nitrogen is injected into the cooling container. Usually, the superconducting member is immersed therein, and cooled and held.

  By the way, in a high-temperature superconducting member, it is known that the superconducting characteristics will be greatly improved if the temperature is slightly lowered. For example, it is known that the critical current increases several times even if it falls from 77K to 70K.

  Therefore, it is conceivable to cool the superconducting member to a temperature lower than 77K by immersing the superconducting member in liquid nitrogen whose pressure is reduced to about 65K by reducing the pressure of liquid nitrogen at atmospheric pressure. In that case, in a container for immersing the superconducting member in liquid nitrogen, it is necessary to maintain the reduced pressure state of liquid nitrogen. On the other hand, since a cryostat that is generally used is assumed to be used in a state where it is substantially open to the atmosphere, if this type of general-purpose cryostat is applied to liquid nitrogen that has been depressurized, a lid or a current introduction Sealing at locations such as terminals is inadequate, atmospheric air containing moisture from outside is sucked into the inside, clogging due to moisture freezing in the vent hole of the current introduction terminal, and ice on the surface of the superconducting member May occur, and operation may become impossible in practice. Therefore, for the above-mentioned purpose, a special container must be newly designed and manufactured. In this case, there is a problem that causes a significant increase in cost, so that practical use is hesitant. .

  On the other hand, when the superconducting member is operated by immersing the superconducting member in saturated liquid nitrogen at atmospheric pressure, the saturated liquid nitrogen is immediately vaporized by the heat generated by the superconducting member and gas bubbles are generated. Although there is a problem that the insulating property is lowered or the cooling efficiency is lowered, as described above, even when the superconducting member is immersed in liquid nitrogen whose temperature has been lowered to about 65K by depressurization as described above, Then, since the liquid nitrogen is immediately vaporized and bubbles are generated by the heat generation of the superconducting member, it is not a fundamental solution for the bubble generation. Therefore, this is also one of the reasons why hesitated to use liquid nitrogen with reduced pressure.

  Therefore, the present inventors have already disclosed in Japanese Patent Application Laid-Open No. 10-54637 a superconducting general-purpose cryostat that is open to the atmosphere without performing special vacuum sealing or the like when cooling a high-temperature superconducting member with liquid nitrogen. While being used as a member cooling container, it is possible to improve the superconducting performance by cooling the high-temperature superconducting member at a lower temperature, and the generation of gas bubbles from liquid nitrogen due to the heat generation of the high-temperature superconducting member during operation of the high-temperature superconducting member A superconducting member cooling device is proposed which is suppressed.

  The proposed superconducting member cooling device basically has a configuration in which a superconducting member is accommodated and a cooling container for cooling the superconducting member is substantially opened to atmospheric pressure, and the superconducting member is in a supercooled state at atmospheric pressure. For example, liquid nitrogen of about 67K is disposed in the cooling container, and the superconducting member is cooled by liquid nitrogen in a supercooled state at the atmospheric pressure. In the proposed superconducting member cooling apparatus, liquid nitrogen in an overcooled state at atmospheric pressure that functions as a cooling medium for the superconducting member is obtained as follows. In other words, a decompression vessel is provided separately from the above-described cooling vessel, and a heat exchanger is disposed in the decompression vessel, and the heat exchange liquid nitrogen (for example, an atmospheric pressure of about 77 K) is provided in the decompression vessel. Saturated liquid nitrogen) is supplied, and the pressure in the decompression vessel is reduced by a vacuum pump, and the liquid nitrogen in the decompression vessel is reduced from atmospheric pressure to lower the temperature to a low temperature of, for example, 65K. On the other hand, separately from the liquid nitrogen for heat exchange, liquid nitrogen for cooling at atmospheric pressure (for example, saturated liquid nitrogen of about 77K) is led to the heat exchanger, and 65K in the decompression vessel is depressurized in the heat exchanger. Heat exchange with the liquid nitrogen for heat exchange is performed, for example, cooling to about 67K with atmospheric pressure, and a supercooled state is obtained at atmospheric pressure. Then, for example, the cooling liquid nitrogen of 67K in a supercooled state at this atmospheric pressure is led to the above-mentioned cooling container, and the superconducting member is cooled to a low temperature close to 67K (for example, 70K).

  In such a superconducting member cooling apparatus proposed in Japanese Patent Laid-Open No. 10-54637, the superconducting member can be reliably cooled to a lower temperature than when saturated liquid nitrogen at atmospheric pressure of about 77 K is used as a cooling medium. Therefore, the performance of the superconducting member can be improved, and in this case, the space above the liquid surface of the cooling liquid nitrogen in the supercooled state in the cooling vessel is an atmospheric nitrogen gas evaporated from the cooling liquid nitrogen. Therefore, there is little possibility of atmospheric air containing moisture from the outside being sucked into the inside, and therefore the sealing of the lid of the cooling container and the current introduction terminal is not particularly required, and further Since the cooling liquid nitrogen in which the superconducting member is immersed is in a supercooled state as described above, even if the superconducting member generates heat during operation of the superconducting member, the liquid nitrogen is vaporized around the heat generating portion. To reach the temperature is a temperature margin, therefore immediately have advantages such as fear less not generated gas bubbles, thus the cooling efficiency lowered insulating property by gas bubbles or drops.

  However, the proposed superconducting member cooling device still has the following problems.

  That is, in the proposed superconducting member cooling device, heat exchange liquid nitrogen is supplied into the decompression container separately from the cooling liquid nitrogen, and the inside of the decompression container is decompressed by a vacuum pump, and the heat exchange liquid is supplied. The temperature of the nitrogen is lowered, and the liquid nitrogen for cooling and the liquid nitrogen for cooling are subjected to heat exchange to obtain liquid nitrogen for cooling in an overcooled state at atmospheric pressure. The liquid nitrogen for heat exchange in the container is gradually evaporated and evaporated by decompression, and the vaporized gas is exhausted by the pump, so the liquid nitrogen liquid level in the decompression container is rapidly lowered and finally decompressed. The heat exchanger in the container will be exposed. If the heat exchanger is exposed from the liquid surface in this way, sufficient heat exchange efficiency cannot be obtained, and it becomes difficult to cool the cooling liquid nitrogen so as to be in a sufficiently subcooled state. In practice, before the heat exchanger is exposed from the liquid level, liquid nitrogen must be replenished into the decompression vessel, and the operation must be temporarily stopped when the liquid nitrogen is replenished.

  As described above, the proposed superconducting member cooling device has a problem that it cannot be operated continuously for a long time since it needs to be stopped for replenishment of liquid nitrogen in the decompression vessel. There is a problem that the trouble of replenishing nitrogen and stopping the operation and resuming the operation becomes complicated. Of course, there is no particular problem in the case of short-time operation, but it is often required to operate continuously for a long period of time in experiments, research, measurements, etc. for practical application of superconducting members. The fact is that the supply of liquid nitrogen to the vessel for heat exchange has become a major bottleneck for the spread of the proposed apparatus.

  Accordingly, the present inventors follow the above proposal and use liquid nitrogen that has been supercooled at atmospheric pressure or higher than atmospheric pressure as a cooling medium for the superconducting member, but liquid nitrogen is used by the refrigerator to achieve atmospheric pressure. Then, the liquid is cooled to a temperature at which it is supercooled below, and the obtained supercooled low-temperature liquid nitrogen is directly used as a cooling medium for cooling the superconducting member as it is. Long-term continuous operation is possible by avoiding the use of a decompression vessel or heat exchanger and avoiding the need to shut down the supply of liquid nitrogen for heat exchange in the decompression vessel. Japanese Patent No. 2859250 proposes a superconducting member cooling device.

  The superconducting member cooling apparatus according to the above-mentioned patent basically includes a cooling container that contains the superconducting member and is substantially open to the atmosphere for cooling the superconducting member, and liquid nitrogen to be supplied to the cooling container. A supply-side container that is substantially open to atmospheric pressure for containing; liquid nitrogen supply means for supplying liquid nitrogen to the supply-side container; and liquid nitrogen in the supply-side container under atmospheric pressure. A refrigerating machine for cooling to the supercooling temperature, and a transfer means for transferring the liquid nitrogen cooled to the supercooling temperature under atmospheric pressure in the supply side container to the cooling container. The space on the liquid level of the supply side container and the cooling container is set to atmospheric pressure or higher than atmospheric pressure, and the liquid nitrogen in the supercooled state supplied into the cooling container by the transfer means Soaked superconducting member And characterized in that it has a so that shows a specific example in FIG.

In FIG. 4, the superconducting member 1 to be cooled is disposed at the bottom of the cooling container 3. The cooling container 3 is composed of a general-purpose cryostat that is substantially open to the atmosphere. The outer peripheral wall and the bottom wall of the cooling container 3 have a vacuum heat insulating structure 5 and can be opened and closed at the upper end. A lid 7 is provided. The lid portion 7 is not vacuum-sealed with respect to the container body, and the lid portion 7 is provided with a current introduction terminal similar to a general-purpose cryostat. The interior of the cooling container 3 is substantially open to the atmosphere through a gap between the container main body part and a current introduction terminal. The lid portion 7 is provided with a safety valve 19, which is opened when the internal pressure exceeds, for example, +0.1 kgf / cm ² with respect to the external atmospheric pressure to increase the internal pressure. It functions to maintain the pressure within the range of atmospheric pressure to atmospheric pressure + 0.1 kgf / cm ² , that is, atmospheric pressure or slightly higher than atmospheric pressure. The superconducting member 1 is suspended from the lid portion 7 by support members 9A and 9B. As will be described later, supercooled liquid nitrogen (cooling liquid nitrogen) 11 at atmospheric pressure is supplied to the bottom of the cooling container 3 via a transfer tube 45 as described later, and the superconducting member 1 is supplied to the liquid nitrogen 11. Soaked. Further, the outer shape of the horizontal cross section is substantially similar to the inner peripheral shape of the horizontal cross section of the cooling container 3 at a position slightly below the liquid surface 11A of the liquid nitrogen 11 in the cooling container 3. And the heat insulation member 13 which has predetermined | prescribed thickness in the up-down direction is arrange | positioned. The heat insulating member 13 may be formed of a material having a low thermal conductivity, such as FRP, or hollow, as long as the heat conduction in the vertical direction as a whole is much less than that of liquid nitrogen. What is necessary is just to make the hollow part into a vacuum heat insulation structure as a structure. The heat insulating member 13 is suspended from the lid portion 7 by the support members 9A and 9B described above, and the space around the heat insulating member 13 keeps a slight gap 14 with respect to the inner peripheral wall surface of the cooling container 3. Is made. On the other hand, a space (space between the lid 7 and the liquid surface 11A) 15 left above the liquid surface 11A of the cooling liquid nitrogen 11 in the cooling container 3 is supplied from an external first nitrogen gas supply source 16. Atmospheric pressure nitrogen gas is supplied through the nitrogen gas supply pipe 18. Further, at the position on the lower surface side of the heat insulating member 13 in the cooling container 3, a proximal end side opening end of a reflux pipe 17 described later is opened.

  Further, a supply side container 21 is provided separately from the cooling container 3 that is substantially open to the atmosphere as described above.

  The supply side container 21 is substantially open to the atmosphere like the cooling container 3 described above, and the outer peripheral wall part and the bottom wall part thereof are the vacuum heat insulating structure 23, and the upper end can be opened and closed. A lid portion 25 is provided. The lid portion 25 is not vacuum-sealed with respect to the container body, and the inside of the supply-side container 21 is substantially opened to the atmosphere through such a gap between the lid portion 25 and the container body portion. It is in the state. The supply side container 21 is supplied with liquid nitrogen 33 from an external liquid nitrogen supply source 27 through a control valve 29 and a supply pipe 31. The outer shape of the horizontal cross section is substantially similar to the horizontal cross sectional shape of the supply side container 21 at a position slightly below the liquid level 33A of the liquid nitrogen 33 in the supply side container 21 and A heat insulating member 35 having a predetermined thickness in the vertical direction is disposed in a state of being suspended from the lid portion 25 by support members 37A and 37B. The heat insulating member 35 is also required to have a heat transfer in the vertical direction that is significantly less than that of liquid nitrogen as in the same manner as the heat insulating member 13 in the cooling vessel 3, and has a thermal conductivity such as FRP. It may be made of a small material or a hollow vacuum heat insulating structure. Further, as with the heat insulating member 13 in the cooling container 3, the periphery of the heat insulating member 35 holds a slight gap 39 with respect to the inner peripheral wall surface of the supply side container 21.

  Further, in the supply side container 21, the liquid nitrogen 33 in the supply side container 21 is brought to a supercooling temperature (a temperature lower than about 77K, for example, 65 to 70K) lower than the temperature of the saturated liquid nitrogen under atmospheric pressure. A refrigerator 41 for cooling is disposed. This refrigerator 41 has a compression unit (compressor) 41A for compressing a refrigeration medium gas (usually helium gas), expands the compressed high-pressure refrigeration medium gas to obtain a low temperature, and cools the low temperature ( A cooling head 41B for exchanging heat with liquid nitrogen), a switching unit 41C such as a motor valve for switching the flow of the high-pressure medium gas from the compression unit 41A and the expanded low-pressure medium gas returning from the cooling head 41B; The cylinder portion 41D is formed with a passage for reciprocating the refrigeration medium gas between the switching portion 41C and the cooling head 41B. The switching portion 41C is disposed on the lid portion 25 of the supply side container 21. The cylinder portion 41D passes through the lid portion 25 downward from the switching portion 41C, passes through the space 47 on the liquid nitrogen liquid surface 33A in the supply side container 21, and below it. There are immersed in liquid nitrogen, the cooling head 41B is provided in the immersion portion in its portion or in liquid nitrogen. Here, the cylinder portion 41D is generally made of stainless steel. The cooling head 41B has a configuration in which a heat transfer block made of a good heat transfer material such as copper is provided on the outer surface thereof. Note that the compression unit 41A is normally disposed at a position away from the supply side container 21, and the compression unit 41A and the switching unit 41C are connected by a high-pressure gas pipeline 41E and a low-pressure gas pipeline 41F.

  In addition, a liquid feed pump 43 is disposed in the supply side container 21 while being suspended from the lid portion 25. The liquid feed pump 43 is disposed such that its intake (pump outlet) is located below the heat insulating member 35 in the supply side container 21 (usually near the bottom of the supply side container 21). The outlet side of the liquid feed pump 43 is connected to a transfer tube 45, and the transfer tube 45 is guided into the cooling container 3 as described above. Further, the reflux pipe 17 from the cooling container 3 is led into the supply side container 21, and the opening end of the reflux pipe 17 is at the bottom of the supply side container (lower than the cooling head 41 </ b> B of the refrigerator 41). Position).

  Further, in the space 47 (the space between the lid portion 25 and the liquid surface 33A) 47 left above the liquid surface 33A of the liquid nitrogen 33 in the supply side container 21, nitrogen is supplied from the external second nitrogen gas supply source 49. Nitrogen gas having a pressure equal to or higher than atmospheric pressure is supplied through the gas supply pipe 51.

  Here, the liquid nitrogen supply source 27, the control valve 29, and the supply pipe 31 constitute liquid nitrogen supply means 63 for supplying liquid nitrogen to the supply side container 21. Further, the liquid feed pump 43 and the transfer tube 45 constitute transfer means 65 for transferring the liquid nitrogen cooled to the supercooled state at atmospheric pressure in the supply side vessel 21 to the cooling vessel 3. On the other hand, the first nitrogen gas supply source 16 and the nitrogen gas supply pipe 18 are a first nitrogen gas supply for supplying nitrogen gas having a pressure equal to or higher than atmospheric pressure to the space 15 above the liquid level in the cooling container 3. The second nitrogen gas supply source 49 and the nitrogen gas supply pipe 51 constitute means 67 and supply nitrogen gas having a pressure equal to or higher than atmospheric pressure to the space 47 on the liquid level in the supply side vessel 21. The second nitrogen gas supply means 69 for this purpose is configured.

  The overall function of the superconducting member cooling device of the embodiment shown in FIG. 4 as described above will be described below.

  The liquid nitrogen supplied from the liquid nitrogen supply source 27 of the liquid nitrogen supply means 63 to the supply side container 21 is about 77K, and the liquid nitrogen is supplied to the cooling head 41B of the refrigerator 41 in the supply side container 21. Is cooled under atmospheric pressure or a pressure higher than atmospheric pressure, and the temperature is lowered to a temperature lower than the saturated liquid nitrogen temperature (about 77 K) under atmospheric pressure, for example, about 65 to 70 K. Then, the liquid nitrogen 33 that is supercooled to about 65 to 70 K or at a pressure higher than atmospheric pressure is pumped from the vicinity of the bottom of the supply side container 21 by the liquid feed pump 43, and is returned to the atmosphere via the transfer tube 45. It is led into the cooling vessel 3 which is substantially open. The supercooled liquid nitrogen introduced into the cooling container 3 is indicated by reference numeral 11 in FIG. 4 and corresponds to the cooling liquid nitrogen.

  In the cooling container 3, the superconducting member 1 is cooled and held at about 67 to 72K, for example, by the supercooled liquid nitrogen 11 of 65 to 70K as described above. Also, the liquid nitrogen whose temperature has risen to, for example, about 70 K or more due to heat from the superconducting member 1 in the cooling container 3 returns to the supply side container 21 through the reflux pipe 17. The fluid nitrogen refluxed to the supply-side container 21 in this manner is cooled again to about 65 to 70K by the cooling head 41B of the refrigerator 41 under atmospheric pressure or a pressure higher than atmospheric pressure, and sent as described above. It is sent again to the cooling container 3 by the liquid pump 43.

  Here, nitrogen gas having a pressure equal to or higher than atmospheric pressure is introduced into the space 15 above the liquid surface 11 </ b> A of the cooling liquid nitrogen 11 in the cooling vessel 3 through the nitrogen gas supply pipe 18. Therefore, the space 15 on the liquid surface of the cooling container 3 is filled with nitrogen gas having a pressure equal to or higher than the atmospheric pressure. Therefore, the pressure in the cooling container 3 is reliably maintained at atmospheric pressure or a pressure higher than atmospheric pressure, and it is ensured that air is drawn from the outside through the sealing portion of the lid portion 7 or the current introduction terminal portion. To be prevented.

  Further, since the heat insulating member 13 is disposed under the liquid level of the cooling liquid nitrogen 11 in the cooling vessel 3, the liquid level of the cooling liquid nitrogen 11 (about 77K because it is a gas-liquid interface) and its heat insulating member. A thermal gradient can be reliably applied to the lower side than 13, particularly to the cooling vessel bottom where the superconducting member 1 is located. Further, the presence of the heat insulating member 13 prevents convective stirring between the bottom surface near the liquid surface 11A. As a result, the cooling liquid nitrogen 11 at the bottom where the superconducting member 1 is located can be reliably maintained in a low-temperature supercooled state of about 65K. Thus, since the superconducting member 1 is surrounded by the low-temperature liquid nitrogen 11 in a supercooled state of, for example, 65 to 70K, even if the superconducting member 1 generates heat during operation of the superconducting member 1, the surrounding liquid nitrogen remains. There is a margin of about 10K before the vaporization temperature under atmospheric pressure (about 77K) or higher, so that the heat generation of the superconducting member 1 immediately vaporizes the surrounding liquid nitrogen and generates gas bubbles. It can be effectively prevented.

  Note that nitrogen gas having a pressure equal to or higher than the atmospheric pressure is introduced into the space 47 above the liquid surface 33A of the liquid nitrogen 33 in the supply side container 21 via the nitrogen gas supply pipe 51, and the atmospheric pressure or It will be filled with nitrogen gas at a pressure higher than atmospheric pressure. Therefore, the pressure in the supply-side container 21 is reliably maintained at atmospheric pressure or a pressure higher than atmospheric pressure, and air can be reliably prevented from entering through the sealing portion of the lid portion 25 and the like. .

  Further, similarly to the cooling container 3, a heat insulating member 35 is also disposed below the liquid nitrogen 33 level in the supply side container 21, so that the liquid level of the liquid nitrogen 33 (about 77K because it is a gas-liquid interface). A thermal gradient can be surely provided below the heat insulating member 35 and particularly near the intake port of the liquid feed pump 43. Further, the presence of the heat insulating member 35 prevents convective stirring between the vicinity of the liquid surface 33 </ b> A and a portion below the heat insulating member 35. As a result, the liquid nitrogen 33 in the vicinity of the inlet of the liquid feed pump 43 is reliably maintained in a low-temperature supercooled state of about 65 to 70K, and the low-temperature supercooled liquid nitrogen of about 65 to 70K. Can be fed into the cooling container 3.

  In the apparatus shown in FIG. 4, the compression unit 41A of the refrigerator 41 compresses a medium gas (usually helium gas) at room temperature (about 300K), and the compressed high-pressure gas of about 300K is supplied to the high-pressure gas line 41E, It reaches the cooling head 41B through the switching part 41C and the cylinder part 41D, and is expanded in the cooling head 41B to obtain a required low temperature. The low-pressure medium gas after expansion returns from the cooling head 41B to the compression unit 41A through the cylinder part 41D, the switching part 41C, and the low-pressure gas pipe 41F. Here, the liquid surface 33A in the supply-side container 21, that is, the interface between the liquid phase and the gas phase is at atmospheric pressure or a saturation temperature (approximately 77K or higher) under a pressure slightly higher than atmospheric pressure as described above. In order to obtain liquid nitrogen having a supercooling temperature (for example, 65 to 70K), the temperature of the cooling head 41B of the refrigerator 41 is set to a temperature of, for example, about 65K, which is lower than the saturation temperature, and the cooling head 41B. Must be immersed in the liquid at a position somewhat lower than the liquid level 33A (for example, a position 15 to 20 mm lower than the liquid level). If the cooling head 41B of the refrigerator 41 is arranged in this way, the cylinder part 41D necessarily passes through the liquid surface position, and the lower part thereof is immersed in liquid nitrogen.

  However, as described above, high-pressure medium gas passes from the switching unit 41C to the cooling head 41B in the cylinder unit 41D, but the temperature is around room temperature, which is much higher than the temperature of liquid nitrogen. Therefore, a large amount of heat flows from the medium gas into the liquid nitrogen at the portion immersed in the liquid nitrogen in the cylinder portion 41D, and a large heat intrusion into the liquid nitrogen occurs. As a result, there is a problem that the cooling efficiency in the superconducting member cooling device is lowered, and the heat intrusion from the cylinder part 41D as described above causes the evaporation of liquid nitrogen from the liquid surface, but the amount of heat intrusion is constant. In general, the level of the liquid surface 33A of the supply-side container 21 becomes unstable due to fluctuations in the amount of heat penetration, and as a result, there is a problem that the operating state of the system as a whole becomes unstable.

  On the other hand, in order to improve the cooling efficiency of the entire system, the infiltration heat from the liquid surface 33A of the supercooled liquid nitrogen in the supply side vessel 21, that is, the gas-liquid interface (for example, 77K) to the cooling head 41B (for example, 65K). It is desirable to reduce Since the intrusion heat from the gas-liquid interface 33A to the cooling head 41B is determined by the distance between the gas-liquid interface 33A and the cooling head 41B, in order to reduce the intrusion heat, the cooling head 41B Although the position should be lowered as much as possible, in general, in commercially available refrigerators, the length of the cylinder portion 41D is set to a specific length in advance, so that the position of the cooling head 41B can be arbitrarily lowered. Therefore, there is a limit to reducing the heat of penetration from the gas-liquid interface to the cooling head.

  This invention has been made against the background as described above. The cooling head of the refrigerator is immersed in liquid nitrogen in a supply-side container pressurized to atmospheric pressure or a pressure higher than atmospheric pressure, and the atmospheric pressure When liquid nitrogen is cooled to the supercooling temperature below, and the liquid nitrogen at the supercooling temperature is led to the superconducting member to cool the superconducting member, heat intrusion into the liquid nitrogen from the cylinder part of the refrigerator is possible. Therefore, the basic purpose is to prevent the cooling efficiency of the refrigerator from being lowered, and to prevent the liquid nitrogen liquid level from changing as much as possible.

  Another object of the present invention is to reduce the heat intrusion from the gas-liquid interface in the supply side container to the cooling head as much as possible, thereby improving the cooling efficiency of the entire system.

  In order to solve the problems as described above, in the superconducting member cooling device of the present invention, basically, heat insulation is applied to the cylinder portion of the refrigerator, and further, the heat insulation is provided in the vertical direction of the cooling head of the refrigerator. It was decided to extend to an intermediate position.

  Specifically, the superconducting member cooling device according to the first aspect of the present invention supplies liquid nitrogen while leaving a space on the liquid surface, and supplies the space on the liquid surface to atmospheric pressure or a pressure higher than atmospheric pressure. And a refrigerator for cooling the liquid nitrogen in the supply side container to the supercooling temperature under atmospheric pressure, and the liquid nitrogen at the supercooling temperature in the supply side container is supplied to the superconducting member to be cooled In the superconducting member cooling apparatus configured to guide and cool the superconducting member, the refrigerator includes a compression unit for compressing the medium gas, and expands the compressed high-pressure medium gas to obtain a low temperature. A cooling head for exchanging heat of the low temperature with liquid nitrogen in the supply side container, a switching unit for switching the flow of the high-pressure medium gas from the compression unit and the low-pressure medium gas from the cooling head, and Switching section and cooling head And a cylinder portion for reciprocating the medium gas between them, and the switching portion is disposed above the outside of the supply side container, and the upper end of the cooling head is above the liquid surface of the liquid nitrogen in the supply side container Is arranged so as to be lower by 15 mm or more, and the cylinder part extends across the space above the liquid level of liquid nitrogen in the supply side container and extends below the liquid level of liquid nitrogen. The heat insulation part is provided in the outer peripheral surface of this.

  In the superconducting member cooling device according to the first aspect of the present invention, since the heat insulating portion is provided on the outer peripheral surface of the cylinder portion of the refrigerator, the cylinder portion is also immersed in the liquid nitrogen in the cylinder portion. The amount of heat intrusion into the liquid nitrogen is small, so that the cooling efficiency of the refrigerator is prevented from being lowered, and the evaporation of liquid nitrogen due to heat intrusion from the cylinder part is also reduced. Fluctuation is also reduced.

  The superconducting member cooling device according to claim 2 is the superconducting member cooling device according to claim 1, characterized in that the heat insulating portion is extended to an intermediate position in the vertical direction of the outer peripheral surface of the cooling head. To do.

  In the superconducting member cooling device according to the second aspect of the present invention, the heat insulating portion is extended to the middle position in the vertical direction of the outer peripheral surface of the cooling head of the refrigerator, and the upper portion of the outer peripheral surface of the cooling head is thermally insulated. Therefore, the heat intrusion from the gas-liquid interface in the supply side container to the cooling head is reduced, so that the cooling efficiency of the entire system can be improved.

  The effect of the invention of claim 2 is particularly effective when the lower end of the cooling head is extended to the vicinity of the bottom surface of the supply side container as defined in claim 3.

  Here, as the heat insulating portion extending to the intermediate position in the vertical direction of the outer peripheral surface of the cylinder portion or the cooling head outer peripheral surface, a vacuum heat insulating structure as defined in claim 4 or claim 5 is provided. It may be formed by a heat insulating material as defined in.

  In the superconducting member cooling device according to the present invention, the cooling head of the refrigerator is immersed in the liquid nitrogen in the supply-side container so that the liquid nitrogen is directly cooled by the cooling head. The lower part of the part is also immersed in liquid nitrogen, but since a heat insulating part is provided on the outer peripheral surface of the cylinder part, heat penetration from the cylinder part into liquid nitrogen can be reduced, and therefore It is possible to prevent the cooling efficiency of the superconducting member cooling device from being lowered, and since the evaporation from the liquid nitrogen liquid surface due to the heat intrusion into the liquid nitrogen from the cylinder portion is reduced, the liquid surface level also varies. As a result, the operating state of the system can be stabilized. In addition, in the superconducting member cooling device of the invention of claim 2, in addition to the above-mentioned effect, the heat insulating portion of the outer peripheral surface of the cylinder portion of the refrigerator is extended to the middle position in the vertical direction of the cooling head. The heat penetration from the gas-liquid interface to the cooling head is reduced, so that the cooling effect of the entire system can be stably improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. It is an expanded front sectional view of the principal part in the superconducting member cooling device in FIG. It is an expanded front sectional view which shows the other example of the part of the supply side container in the superconducting member cooling device of this invention. It is an approximate solution figure showing the whole superconducting member cooling device composition.

  FIG. 1 shows an example of a superconducting member cooling device according to an embodiment of the present invention, and FIG. 2 shows an enlarged view of the main part thereof, that is, a part near a refrigerator in a supply side container. In FIG. 1 and FIG. 2, the same elements as those in the prior art shown in FIG. 4 are denoted by the same reference numerals as those in FIG.

  In FIG. 1 and FIG. 2, the refrigerator 41, as already described, compresses the refrigeration medium gas (usually helium gas) 41A and expands the compressed high-pressure refrigeration medium gas to lower the temperature. A cooling head 41B for exchanging the low temperature with the object to be cooled, a switching unit 41C for switching the flow of the high-pressure medium gas from the compression unit 41A and the low-pressure medium gas from the cooling head 41B, and the switching unit 41C And a cylinder portion 41D formed therein with a passage for reciprocating the refrigeration medium gas between the cooling head 41B and the switching portion 41C is disposed on the lid portion 25 of the supply side container 21, and the cylinder portion 41D passes through the lid portion 25 downward from the switching portion 41C, passes through the space 47 on the liquid nitrogen liquid level 33A in the supply side container 21, and its lower end is immersed in liquid nitrogen. Cooling head 41B is provided to the portion or dipped portions in liquid nitrogen. Here, the cylinder portion 41D is generally made of stainless steel. The cooling head 41B has a configuration in which a heat transfer block made of a good heat transfer material such as copper is provided on the outer surface thereof. Furthermore, the compression part 41A is arranged separately from the supply side container 21, and the compression part 41A and the switching part 41C are connected by a high-pressure gas pipe 41E and a low-pressure gas pipe 41F.

  And the heat insulation part 71 is provided in the outer peripheral surface of cylinder part 41D of the refrigerator 41. FIG. As shown in detail in FIG. 2, the heat insulating portion 71 has a vacuum heat insulating structure, and has a double wall structure including an inner wall 71A and an outer peripheral wall 71B, and a space between the inner wall 71A and the outer wall 71B is formed. It is a vacuum heat insulating space 71C, and further, a vacuum exhaust pipe 71D is connected to one end side of the vacuum heat insulating space, and is configured to be evacuated by a vacuum pump (not shown).

  In the embodiment shown in FIGS. 1 and 2, the lower part of the cylinder part 41D of the refrigerator 41 is immersed under the liquid surface 33A of the liquid nitrogen 33 in the supply side container 21, but the cylinder part 41D Since the outer peripheral surface is insulated by a vacuum heat insulating structure, even when a high-pressure medium gas near normal temperature flows in the cylinder portion 41D, there is very little possibility that the heat of the medium gas enters liquid nitrogen. Therefore, there is little possibility that the cooling efficiency in the superconducting member cooling device is lowered, and since the amount of heat penetration from the cylinder portion 41D is small, the liquid level of liquid nitrogen may fluctuate even if the amount of heat penetration varies. There are few.

  In the above-described example, the heat insulating portion 71 is configured to cover only the outer peripheral surface of the cylinder portion 41D of the refrigerator 41. However, as shown in FIG. You may extend the heat insulation part 71 to. Here, it is desirable that the lower end position (extension tip position) of the heat insulating portion 71 is at or near the level of the upper end position of the liquid feed pump 43. In this way, heat penetration from the liquid surface 33A of the liquid nitrogen 33 in the supply side container 21, that is, the gas-liquid interface 33A, into the cooling head 41B is reduced, and the cooling efficiency of the entire system can be improved. In the example of FIG. 3, the cooling head 41 </ b> B of the refrigerator 41 is configured such that its lower end extends to the vicinity of the bottom surface of the supply-side container 21. In such a case, the above-described effects can be particularly effectively exhibited. Can do.

  In addition, although the heat insulation part 71 was made into the vacuum heat insulation structure in the above-mentioned example, it does not necessarily need to be made into a vacuum heat insulation structure. Depending on the case, resin-type heat insulation materials with low heat conductivity, such as FRP, other inorganic heat insulation materials, etc. It is good also as a structure which covered the outer peripheral surface to the intermediate position of cylinder part 41D or cooling head 41B with the heat insulating material.

  As shown in FIGS. 1 and 2, the superconducting member cooling device of the present invention applies a thermal gradient in the vertical direction below the liquid surface of the liquid nitrogen 33 in the supply side container 21 and prevents convective stirring. A heat insulating member 35 is provided.

  Further, in the above-described example, the superconducting member 1 to be finally cooled is placed in the cooling container 3, and the superconducting member 1 is cooled by transferring supercooled liquid nitrogen from the supply side container 21 into the cooling container 3. However, the specific configuration for cooling the superconducting member 1 with the supercooled liquid nitrogen is not limited to the above-described example. In short, the supercooled liquid nitrogen is supplied from the supply-side container 21 to the superconducting member. Any configuration can be applied as long as it is a configuration that guides and cools the superconducting member.

DESCRIPTION OF SYMBOLS 1 Superconducting member 21 Supply side container 33 Liquid nitrogen 33A Liquid level 41 Refrigerator 41A Compression part 41B Cooling head 41C Switching part 41D Cylinder part 71 Heat insulation part

Claims (5)

A supply-side container that contains liquid nitrogen leaving a space on the liquid level and the space on the liquid level is set to a pressure equal to or higher than atmospheric pressure;
A refrigerator for cooling the liquid nitrogen in the supply side container to a supercooling temperature under atmospheric pressure,
In the superconducting member cooling device configured to guide the liquid nitrogen at the supercooling temperature in the supply side container to the superconducting member to be cooled and cool the superconducting member,
The refrigerator includes a compression unit for compressing the medium gas, a cooling head for expanding the compressed high-pressure medium gas to obtain a low temperature and exchanging the low temperature with liquid nitrogen in the supply side container. ,
A switching unit for switching the flow of the high-pressure medium gas from the compression unit and the low-pressure medium gas from the cooling head;
A cylinder part for reciprocating the medium gas between the switching part and the cooling head,
The switching unit is disposed on the outside upper side of the supply side container, and the upper end of the cooling head is disposed at a position 15 mm or more lower than the liquid level of the liquid nitrogen in the supply side container,
The cylinder portion extends across the space above the liquid level of liquid nitrogen in the supply side container to below the liquid level of liquid nitrogen, and a heat insulating portion is provided on the outer peripheral surface of the cylinder portion. A superconducting member cooling device.   The superconducting member cooling device according to claim 1, wherein the heat insulating portion is extended to an intermediate position in the vertical direction of the outer peripheral surface of the cooling head.   2. The superconducting member cooling device according to claim 1, wherein the cooling head is extended so that a lower end thereof is positioned near a bottom surface of a supply-side container, and the heat insulating portion is formed in a vertical direction of an outer peripheral surface of the cooling head. A superconducting member cooling device, characterized by being extended to an intermediate position.   The superconducting member cooling device according to any one of claims 1 to 3, wherein the heat insulating portion has a vacuum heat insulating structure. The superconducting member cooling device according to any one of claims 1 to 3, wherein the heat insulating portion is formed of a heat insulating material.