JPH08222429A - Device for cooling to extremely low temperature - Google Patents

Abstract

PURPOSE: To provide a device which has a simple structure since it does not necessitate a liquid helium tank and almost uniformly cools even a relatively large magnet. CONSTITUTION: An expander 1 is used for a cooling device and low temperature helium gas, which is generated by a refrigerator provided with at least one expansion valve, is permitted to flow in cooling piping 16c. A superconducting magnet is cooled by bringing the cooling piping 16c into thermal contact with the magnetic frame 25 of the superconducting magnet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryogenic device, and more particularly, to a direct cooling type cryogenic device in which a cooling portion of a cooling means and an object to be cooled are in thermal contact with each other.

[0002]

2. Description of the Related Art Nuclear magnetic resonance diagnostic equipment using superconducting magnets, thermophysical property measuring equipment, various electronic equipment such as Josephson elements and various sensors, cryopumps of high vacuum and high pumping speed, and electronic equipment using superconducting magnets. Cryogenic liquid helium is used as the coolant for the accelerator, the synchrotron radiation generator, and the magnetic separator using a superconducting magnet.

Generally, these devices to be cooled are equipped with a liquid helium tank for storing liquid helium as a refrigerant, and the liquid helium evaporates with a slight amount of heat, and
Since it is expensive, a refrigeration unit that condenses the evaporated helium gas is installed.

However, the cooling method using liquid helium requires a person with special skill in handling, and since the liquid helium tank is installed, the apparatus becomes complicated and large-scale.

Then, Gifford McMahon (G.
An example of a direct cooling type superconducting magnet system in which a M) type reciprocating refrigerator is thermally connected to a superconducting magnet to cool the superconducting magnet by conduction is shown in, for example, Japanese Patent Laid-Open No. 6-132567. There is.

This apparatus uses a two-stage G / M refrigerator,
It has a structure in which a current lead composed of a superconducting magnet and a high temperature superconducting material is brought into thermal contact with a cooling stage of a refrigerator to cool it.

[0007]

In the above-mentioned conventional example, the liquid helium tank for cooling the superconducting magnet is unnecessary, so that the apparatus is simple, but the nuclear magnetic resonance apparatus, the magnetic separation apparatus, etc. Bore diameter is close to 1m or 1
In the case of cooling a magnet having a length of m or more, there are the following problems, and it has been difficult to put it into practical use. When the magnet becomes large, the thermal resistance between the cooling part to which the refrigerator is connected and the tip of the magnet becomes large, and the temperature difference inside the magnet causes the temperature to rise at a position distant from the cooling part.
There is a risk that the superconducting state will be destroyed. Further, in order to reduce the temperature difference, it is necessary to install a cooling plate made of copper or aluminum having a good thermal conductivity and having a large cross-sectional area around the superconducting magnet, resulting in an increase in weight and size. In addition, the inflow of heat from the support and the current leads, which must be increased with the size of the magnet, increases, so that the G / M refrigerator that can generate only a relatively small refrigerating capacity has insufficient refrigerating capacity, resulting in a superconducting state. In order to keep it, it is necessary to install a plurality of refrigerators, the weight and size increase, and the initial cost and running costs such as power consumption increase. Therefore, the direct cooling type superconducting magnet using the G / M refrigerator is limited to a relatively small size, and liquid helium must be used to cool a larger magnet.

[0008]

[Means for Solving the Problems] A GM refrigerator is used in a cold generation circuit for precooling, and a heat exchanger, a Joule-Thomson (JT) liquefaction circuit composed of a throttle valve and piping are combined. (GM + JT) A low-temperature helium gas is generated by adding one heat exchanger and one throttle valve to the refrigeration cycle of the liquefier, and the pipe through which the low-temperature helium gas flows is thermally connected to the superconducting magnet. By doing so, the above problems can be solved.

[0009]

Operation: Cooling is performed by bringing a pipe through which low-temperature helium gas generated in a refrigerator flows into thermal contact with an object to be cooled such as a superconducting magnet. Thereby, cooling can be performed without using the liquid helium tank. When the helium gas flowing through the cooling section is supercritical helium,
Due to the forced cooling, in the range where the Reynolds number is large, the cooling capacity is superior to that of the immersion cooling with the conventional structure of liquid helium. Further, since the low temperature helium gas pipe can be brought into thermal contact with the periphery of the object to be cooled, it is possible to uniformly cool the object to be cooled. It is also easy to increase the refrigerating capacity by increasing the flow rate of helium gas.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. The cold generator 1 arranged in the cold generating circuit for precooling is composed of, for example, a Gifford-McMahon expander. The high-pressure gas of the helium compressor unit 2 flows into the cold generator 1 and undergoes adiabatic expansion inside to generate cold at temperatures of about 40K and 15K at the first stage 3 and the second stage 4, respectively. The expanded gas returns to the compressor unit 2 again.

On the other hand, J separated from the cold generation circuit for pre-cooling
The high-pressure helium gas pressurized to about 1.6 MPa in the compressor unit 5 of the T circuit passes through the high-pressure pipe 16a and the first heat exchanger 6, the second heat exchanger 7, the first adsorber 8, the It enters the three heat exchanger 9, the fourth heat exchanger 10, the second adsorber 11, the fifth heat exchanger 12, and the third adsorber 13. There is a first JT valve 14 in the high pressure passage after the outlet of the third adsorber 13, and the pressure is expanded to about 0.8 MPa here. Further, it passes through the sixth heat exchanger 15 and becomes low temperature helium gas having a temperature of about 5K, which is expanded to about 0.12MPa by the second JT valve 17 and partly liquefied, and the temperature of about 4.4K is increased. It becomes a two-phase flow of helium and flows into the cooling section pipe 16c.

In the superconducting magnet, as shown in FIG. 2, a magnet frame 25 serving as a cooling plate is provided around the superconducting coil 24.
The magnet frame 25 and the cooling part pipe 16c of the cooling means are in thermal contact with each other by welding or the like.
Between the magnet frame 25 made of metal such as copper, aluminum or stainless steel and the superconducting coil 24, Kapton,
Insulation is performed by sandwiching a thin insulating film such as FRP or Bakelite. The cooling section pipe 16c is connected to the superconducting magnet in a circumferential direction substantially once, and has a structure in which there is not much temperature difference in the circumferential direction.

The helium gas which has flowed through the cooling section pipe 16c and has been subjected to a heat load due to heat intrusion from the outside and evaporated has flowed into the low pressure pipe 16b as it is, and the sixth heat exchanger 15,
The fourth adsorber 18, the fifth heat exchanger 12, the fifth adsorber 19,
After passing through the third heat exchanger 9, the sixth adsorber 20, the second heat exchanger 6 and the seventh adsorber 21, the temperature becomes almost room temperature, and the low pressure pipe 16
Return to compressor unit 5 from b.

The inside of the cryostat 22 is vacuum-insulated,
The cryogenic part shields radiant heat from the outside by a liquid nitrogen tank or a heat shield plate 23 cooled by the first stage 3 of the cold generation circuit. Each adsorber removes impurities in the helium gas.

In this embodiment, the structure of the refrigerator having two J / T valves is shown. However, even if the structure does not have the first J / T valve 14 and the sixth heat exchanger 15, the efficiency may be reduced depending on the operating conditions. A little worse, but the effect is similar.

In this embodiment, the cooling method of the magnet as shown in FIG. 2 is shown, but another cooling method is shown in FIGS. 3, 4 and 5.

FIG. 3 shows a structure in which the cooling pipes 16c are installed at both ends of the superconducting magnet, and this structure suppresses a temperature difference in the axial direction of the magnet.

FIG. 4 shows a structure in which the cooling pipe 16c is wound around the superconducting magnet and brought into thermal contact with the superconducting magnet so that even a larger magnet can be cooled well. In the case of a nuclear magnetic resonance apparatus or a magnetic separation apparatus, a bore at room temperature is required inside the superconducting coil, and the larger the bore diameter, the more desirable the apparatus. Therefore, in this structure, the cooling pipe 16c is installed outside the superconducting magnet. In a device that does not require a large bore in the superconducting coil, the same effect can be obtained by installing the cooling pipe 16c inside the coil.

Further, in the cooling structure example of the superconducting magnet shown in FIGS. 2 to 4, the magnet frame 25 serving as a cooling plate is installed all around the superconducting coil 24, but the effect is obtained even if it is installed only partially. It is the same.

FIG. 5 shows a connecting portion between the cooling pipe 16c and the magnet frame 25 which is a cooling plate.

The cooling pipe 16c is welded to the pipe connecting portion 27 made of a high thermal conductivity member such as copper or aluminum. The pipe connecting portion 27 and the magnet frame 25 are fixed by screws 29 via indium 28. With this structure, it is not necessary to directly weld the cooling pipe 16c to the magnet frame 25 of the superconducting magnet, and there is no risk of abnormal heat or stress being applied to the superconducting coil 24 by the heat transferred to the superconducting coil 24 during welding.

FIG. 6 shows the structure of a superconducting magnet with a refrigerator according to a second embodiment of the present invention. This structure is almost the same as the structure of the device shown in FIG. 1, but the structure of the cryogenic part of the liquefaction circuit of the refrigerator is different. That is, the structure up to the first J · T valve of the high-pressure pipe 16a of the refrigerator has the same structure, but thereafter, it is cooled by exchanging heat with the liquid helium in the liquid helium tank 26 instead of the heat exchanger, so that the temperature is low. Helium gas of the above flows into the cooling pipe 16c.
After the superconducting magnet is cooled by the cooling pipe 16c through which the supercritical helium gas flows, the superconducting magnet is expanded again by the second JT valve 17. That is, the helium gas, which has been slightly heated due to the heat load from the superconducting magnet, is about 0.12MP in the second JT valve 17.
It expands to a and liquefies and collects in the liquid helium tank 26. Helium gas that has not been liquefied and helium gas that has evaporated due to the amount of heat obtained by exchanging heat with the high-pressure pipes flow to the low-pressure pipes 16b, and thereafter, as in the embodiment shown in FIG. And the heat exchanger 12,
It passes through 9 and 6 and returns to the compressor unit 5. In this structure, the low-temperature helium gas flowing through the cooling pipe 16c is supercritical helium with a pressure of about 0.5 MPa and a temperature of about 4.5 K, and under a condition of high Reynolds number, the temperature is 4.2 K under atmospheric pressure. It has a higher heat transfer rate than the case of cooling with liquid helium and has excellent cooling capacity.

FIG. 7 shows a third embodiment of the present invention. This embodiment is also almost the same as the structure shown in FIG. 1, but the structure of the cryogenic part of the liquefaction circuit of the refrigerator is different. In this structure, after the high pressure helium gas was expanded by the first JT valve 14, it was cooled by the sixth heat exchanger 15 at about 0.5 MPa, about 5 MPa.
A low-temperature supercritical helium gas of K is caused to flow through the cooling pipe 16c for cooling. The second J · T valve 17 expands the helium gas, which has been slightly heated due to the heat load, to about 0.15 MPa to further reduce the temperature, and in some cases, becomes a two-phase flow to form the sixth heat exchanger. It flows into the low-pressure channel side of 15. Hereinafter, the low-pressure flow path 16b is similar to that of the embodiment shown in FIG. With this structure, since a liquid helium tank is not necessary, a cooling system using supercritical helium gas can be made with a simpler structure than the structure shown in FIG.

In the embodiment shown in FIGS. 6 and 7, the effect is the same when the high-pressure discharge pressure of the compressor unit 5 is smaller than 1.6 MPa, for example, about 1.0 MPa. Even if the valve or the structure in which the first J / T valve and the sixth heat exchanger are omitted, the efficiency is deteriorated but the same effect can be obtained.

In the embodiment shown in FIGS. 6 and 7, the cooling pipe 16 is attached to the magnet frame 25 installed around the superconducting coil 24.
Although the example in which c is brought into thermal contact is shown, for example, the supercritical helium gas generated by the refrigerating device flows in the superconducting coil which is composed of an internal cooling conductor such as a bundle conductor and is provided with an inlet and an outlet into which supercritical helium enters. Even if the cooling pipe 16c is connected, the effect is the same. In this case, the structure of the apparatus becomes complicated as compared with the case of the above embodiment, but the cooling capacity is remarkably improved.

FIG. 8 shows a fourth embodiment of the present invention. This structure is almost the same as the structure shown in FIG.
Superfluid helium is produced by expanding it to about 0.002 MPa with the T valve. The superfluid helium is the low-pressure pipe 16 as it is.
Although it enters b and returns to the compressor unit 5, the helium in the cooling pipe 16c branched at the cryogenic portion becomes superfluid helium. Therefore, the superconducting magnet is cooled by superfluid helium, which has a large thermal conductivity, and has a structure suitable for preventing a temperature difference between the magnets. By branching the pipe in the cryogenic part and making the cooling pipe 16c independent, the pressure in the cooling pipe 16c is constant regardless of the position, and the heat load received from the outside is of high thermal conductivity of superfluid helium. Because it is transmitted to the whole, cooling pipe 16c
The temperature of superfluid helium inside is constant regardless of position.
Therefore, there is almost no temperature difference in the magnet cooled by this structure. Further, since the superconducting magnet is cooled with superfluid helium of about 1.8 K, the temperature of the superconducting magnet is low, and the critical magnetic field and the critical temperature can be increased. Therefore, a strong magnetic field of the magnet is possible and cooling stability is improved.

FIG. 9 shows a fifth embodiment of the present invention. The superconducting magnet is provided with a current lead 30 for supplying an electric current when exciting the magnet. The current lead 30 is brought into thermal contact with the first stage 3 and the second stage 4 of the cold generator for pre-cooling in order to suppress conduction heat transfer from room temperature, and further, in order to suppress Joule heat generation as much as possible, the current lead 30 is kept in contact with the room temperature. The space between the stages 3 is made of copper, and the cryogenic temperature side of the first stage is an oxide superconductor. Insulation is performed by inserting an insulator such as sapphire, Kapton, or aluminum nitride between the current lead 30 and the cold generation circuit. Conducting heat transfer from the current lead 30 to the superconducting coil 24 is further reduced by taking a thermal anchor by thermally contacting the cryogenic portion of the current lead 30 with the magnet frame 25 or the cooling pipe 16c installed on the outer circumference of the magnet. It is possible to In this case as well, insulation is provided by sandwiching an insulating material between the thermal anchor portions. Although the refrigerator of this embodiment has the structure shown in FIG. 6, the same effects are obtained in the refrigerators shown in FIGS. 1, 7, and 8.

FIG. 10 shows a sixth embodiment of the present invention.
In this embodiment also, the refrigerator has the same structure as that shown in FIG. 6, but the same effects can be obtained with the refrigerators shown in FIGS. 1, 7, and 8. In the present embodiment, in addition to the first heat shield plate 23 of about 50K cooled by the first stage of the cold generation circuit 1 for precooling, about 13 by the second stage 4.
A second heat shield plate 32 that is cooled to K is installed.
With this structure, it is possible to reduce the radiant heat that enters the superconducting magnet. Further, when the superconducting magnet is large, a support for supporting the superconducting magnet from the room temperature portion of the cryostat 22 is required. However, if the thermal anchor is taken by the first and second heat shield plates in the middle of the support, the support can be Therefore, it is possible to reduce the conduction heat transfer that enters the superconducting magnet. The present embodiment has the same effect even when the current lead is installed as shown in FIG.

FIG. 11 shows a seventh embodiment of the present invention. In this embodiment, the heat shield plate is cooled by bringing the heat shield plate and the high-pressure pipe of the refrigerator into thermal contact with each other. In this embodiment, the pre-cooling cold generation circuit and the upstream side pipe for heat exchange and the heat shield plate 23 are in thermal contact with each other.
The effect is the same even when the downstream side pipes are brought into contact with each other. With this structure, even if the size of the heat shield plate 23 is large and thin, there is almost no temperature difference inside the heat shield plate 23, and it is possible to suppress radiant heat and conductive heat that enter the superconducting magnet.

In the above embodiment, an example in which the compressor operating at room temperature and the expansion valve J.T valve are used as the circulation driving means for the refrigerant has been shown, but a compressor operating at low temperature and an expansion valve are used. The same effect can be obtained when the above is used or when the refrigerant is circulated by the fan.

FIG. 12 shows an embodiment in which the refrigerant is circulated by a fan operating at a low temperature. The fan 33 operating at a low temperature is inserted into the vacuum heat insulating container (cryostat) 22, and the helium gas sent by the fan 33 is about 4 to 6 in the second stage 4 of the cold generating circuit 1 for precooling.
Cooled to K. The helium gas cooled to an extremely low temperature passes through the inside of the cooling pipe 16c to cool the superconducting magnet. The helium gas, which has been slightly heated by the heat load from the outside, returns to the fan 33 and circulates in the circuit.

As described above, in the embodiments shown in FIGS. 1 to 12, the case where the superconducting magnet is used as the cooled object has been described. However, various electronic devices such as Josephson elements and various sensors, high vacuum, high exhaust The effect is the same even when the cryopanel of speed is used as the cooled object.

In the embodiment, an example in which a G / M cycle expander is applied to a cold generator has been described, but a Solvay cycle, a Stirling cycle, a Villemeier cycle,
The same effect can be obtained in a refrigeration cycle or Brayton cycle using a turbine type or Claude type expander.

[0034]

According to the present invention, since the superconducting magnet can be cooled by the cooling pipe through which the low temperature helium gas flows, there is almost no temperature difference in the magnet, and even in the case of a large superconducting magnet, liquid helium is not required. It becomes possible to perform stable cooling.

[Brief description of drawings]

FIG. 1 is a block diagram of a superconducting magnet with a refrigerator that is an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a superconducting magnet and a cooling pipe according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram of a superconducting magnet and a cooling pipe according to a second embodiment of the present invention.

FIG. 4 is an explanatory diagram of a superconducting magnet and a cooling pipe according to a third embodiment of the present invention.

FIG. 5 is an explanatory diagram of a connecting portion of a superconducting magnet and a cooling pipe according to an embodiment of the present invention.

FIG. 6 is a block diagram of a superconducting magnet with a refrigerator according to a second embodiment of the present invention.

FIG. 7 is a block diagram of a superconducting magnet with a refrigerator according to a third embodiment of the present invention.

FIG. 8 is a block diagram of a superconducting magnet with a refrigerator according to a fourth embodiment of the present invention.

FIG. 9 is a block diagram of a superconducting magnet with a refrigerator according to a fifth embodiment of the present invention.

FIG. 10 is a block diagram of a refrigerator-equipped superconducting magnet according to a sixth embodiment of the present invention.

FIG. 11 is a block diagram of a superconducting magnet with a refrigerator according to a seventh embodiment of the present invention.

FIG. 12 is a block diagram of a superconducting magnet with a refrigerator according to an eighth embodiment of the present invention.

[Explanation of symbols]

1 ... Expander, 2, 5 ... Compressor unit, 6, 7, 9, 1
0, 12, 15 ... Heat exchanger, 13, 17 ... J · T valve, 1
6c ... Cooling piping, 22 ... Vacuum container, 23 ... Heat shield plate, 24 ... Superconducting coil, 25 ... Magnet frame, 26 ... Liquid helium tank.

Claims (1)

[Claims] 1. A body to be cooled, cooling means for cooling the body to be cooled, and an adiabatic vacuum container containing the body to be cooled and the cooling means, the body to be cooled being in the cooling means. In a direct cooling type cryogenic device, which is located outside the refrigerant flow path for circulating the cooling target and the cooling means is in thermal contact with the cooling means, the cooling means circulates with a cold generation circuit for precooling. At least a part of a pipe through which a low-temperature refrigerant flows is composed of the pipe to be a refrigerant flow path, a series of heat exchangers containing the pipe, and a refrigerant circulation drive means for circulating the refrigerant. A cryogenic device characterized by being in thermal contact with.