JP6523779B2 - Cryogenic refrigeration system and cryogenic refrigeration method - Google Patents

Description

  Embodiments of the present invention relate to cooling techniques for cooling an object to cryogenic temperatures as high as the superconducting transition temperature.

A superconducting magnet using a superconducting coil can easily generate a high magnetic field because of its remarkable low electrical resistance, and is therefore used in MRI, single crystal pulling apparatus and the like.
In order to maintain the superconducting magnet in the superconducting state, it is necessary to cool it to a cryogenic temperature equal to or lower than the liquid nitrogen temperature using a cryogenic refrigerator (hereinafter, simply referred to as a "refrigerator") or the like.

A high magnetic field superconducting magnet that generates a particularly strong magnetic field by using a plurality of superconducting coils has a large thermal load at the time of cooling, so a plurality of refrigerators are provided.
By cooling one cooling stage with a plurality of cooling systems having the plurality of refrigerators, the superconducting coil is cooled to an optimum temperature.

  By the way, the superconducting coil is a low temperature superconducting coil (hereinafter referred to as "LTS coil") which becomes superconducting at a low temperature of about 4 K and a high temperature superconducting coil (hereinafter referred to as "HTS") which is in a superconducting state at a relatively high temperature of about 20 K It is called "coil".

The HTS coil is characterized by high resistance to a magnetic field, in addition to being able to be used in a temperature range of about 20K.
On the other hand, the LTS coil is more advantageous in terms of production cost or ease of handling.
Therefore, high field superconducting magnets used in physical property research and the like often have an HTS coil combined with an LTS coil.
Even in the case where the HTS coil and the LTS coil are combined, a plurality of cooling systems are provided to optimize the temperature of each superconducting coil having different steady operation temperatures.

The cooling process of the high magnetic field superconducting magnet can be roughly divided into a stage of precooling for cooling the superconducting coil to near the transition temperature and a stage of steady operation for maintaining the temperature of the superconducting coil in a superconducting state. .
When the superconducting transition temperature to cool the low LTS coils, G M / JT refrigerator is used.
However, since the GM / JT refrigerator has a low refrigeration capacity at about 80 K or more, the refrigeration capacity of another refrigerator having a different cooling limit temperature is utilized in order to cool efficiently at the time of precooling.
In other words, the refrigerant circulation path is changed using the precooling piping, and cooling is performed while switching the cooling heat source.
On the other hand, at the time of steady operation, the superconducting state of the superconducting coil is maintained by continuing the cooling of the refrigerant with a specific cold heat source.

JP, 2015-012193, A JP, 2009-243837, A

However, in the above-described conventional technology, there is a problem in that the superconducting coil may be deteriorated due to the thermal stress generated by uneven cooling of the superconducting coil.
In particular, since the high magnetic field superconducting magnet cools the superconducting coil with a plurality of refrigerators having different cooling characteristics, the temperature of the superconducting coil may be uneven.
For example, if the cooling capacities of two refrigerators cooling one cooling stage are different, the cooling stages have an uneven temperature distribution.
In addition, even in the case of two GM / JT refrigerators having the same refrigeration capacity, if only one is assisted by another cooling source, uneven temperature distribution occurs in the cooling stage.

Also, the HTS coil has a smaller heat capacity than the LTS coil.
Therefore, the HTS coils may be cooled first to generate a large temperature difference with the LTS coils, which may generate thermal stress.
Problem thus may deteriorate the superconducting coil by the temperature difference between the plurality of cooling system which occur during the pre-cooling, the configuration of the cooling system regardless of whether homologous or heterologous, which is a problem common to.

  The present invention has been made in consideration of such circumstances, and it is possible to suppress the generation of thermal stress in an object to be cooled by a plurality of cooling systems, as well as a cryogenic cooling device and pole capable of efficiently precooling. The purpose is to provide a low temperature cooling method.

  The cryogenic cooling device according to the present embodiment includes a cooling pipe forming a circulation path of a refrigerant supplied to an object to be cooled disposed in a vacuum vessel to form a cooling system, and a cold heat source for cooling the refrigerant. A cooling pipe connected in an annular manner, and a pre-cooling pipe that constitutes a part of at least one of the plurality of cooling systems and branches the cooling pipe annularly to bypass a specific cold heat source; A bypass valve that is provided in the precooling piping to switch a cold heat source of the refrigerant supplied to the object to be cooled, and a section of the cooling piping from the branch point of the precooling piping to the object to be cooled And a heat exchanger connected to different cooling pipes.

  In the cryogenic cooling method according to the present embodiment, a step of supplying a refrigerant to cooling objects disposed in a vacuum vessel with cooling pipes of two or more cooling systems, and a step of cooling a refrigerant circulating along the cooling pipe And switching the circulation path of the refrigerant supplied to the object to switch the cold heat source, and equalizing the temperatures of the refrigerants of the two or more cooling systems supplied to the object by heat exchange. It is included.

  The present invention provides a cryogenic cooling device and a cryogenic cooling method capable of suppressing the generation of thermal stress in an object to be cooled by a plurality of cooling systems and efficiently precooling.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram of the cryogenic cryogenic refrigeration apparatus concerning 1st Embodiment. Schematic which shows the relationship between the temperature of a single stage GM refrigerator, a 2-stage GM refrigerator, and a JT cooling part, and a freezing capacity. BRIEF DESCRIPTION OF THE DRAWINGS Sectional drawing of the supply heat exchanger of the cryogenic cooling apparatus concerning 1st Embodiment. The figure which shows the heat conductivity in 300 K and 4 K of the constituent material of a supply heat exchanger. Sectional drawing of the modification of the supply heat exchanger of the cryogenic cooling apparatus concerning 1st Embodiment. Sectional drawing which shows a supply heat exchanger when it is put at cryogenic temperature and it deform | transforms. The schematic block diagram of the cryogenic cooling apparatus concerning 2nd Embodiment. The schematic block diagram of the cryogenic cooling apparatus concerning 3rd Embodiment. The schematic block diagram which shows the modification of the cryogenic cooling apparatus concerning 2nd Embodiment. The figure which shows the other modification of the cryogenic cooling apparatus concerning 3rd Embodiment. 3 is a flowchart of a cooling method according to the first embodiment.

  Hereinafter, embodiments of the present invention will be described based on the attached drawings.

First Embodiment
FIG. 1 is a schematic configuration diagram of a cryogenic cooling device 10 (hereinafter simply referred to as “cooling device 10”) according to a first embodiment.

In the cooling device 10 according to the first embodiment, as shown in FIG. 1, a plurality of GM / JT refrigerators 15 are provided in a vacuum vessel 13 in which an object to be cooled (superconducting coil) 11 is disposed. .
In the first embodiment, the object to be cooled 11 is described as one type of LTS coil 11 a (11) which is cooled to about 4 K and generates a high-intensity magnetic field in the internal space 24.

A cooling stage 18 for supporting a LTS coils 11a and the plurality of GM / JT refrigerator 15 (1 5 a, 1 5 b), are connected annularly cooling piping 19 (19A, 19B).
The GM / JT refrigerator 15 annularly connected by the cooling pipe 19 and the cooling pipe 19 form one cooling system.
That is, one cooling system is provided in one or more GM / JT refrigerators 15 in the system, and the refrigerant is circulated to the GM / JT refrigerator 15 and the cooling stage 18 by the cooling pipe 19.
The plurality of cooling systems configured in this way can be independently controlled.

The GM / JT refrigerator 15 cools a refrigerant such as gaseous helium circulating in a cooling system.
For example, as shown in FIG. 1, the GM / JT refrigerator 15 includes one single-stage GM refrigerator 12 (single-stage Gifford-McMahon refrigerator: hereinafter simply referred to as “single-stage refrigerator 12”) and two units. GM / JT refrigerator 15 (15a, 15b) .

The single-stage refrigerator 12 cools the shield plate 21 that shields heat radiation from the outside to about 60K.
In a temperature range of about 80 K or more, the single-stage refrigerator 12 exerts a high refrigeration capacity of five times or more compared to other refrigerators.
Therefore, the single-stage refrigerator 12 is used as a main cold heat source up to about 80 K near the cooling limit of the single-stage refrigerator 12 at the time of precooling.

In addition, a GM / JT refrigerator 15 is a refrigerator in which a two-stage GM refrigerator 16 (hereinafter simply referred to as "GM refrigerator 16") and JT (Joule-Thomson) cooling unit 17 (17a, 17b) are combined. It is.
JT cooling unit 17, JT valve 31 (31a, 31b) and via, liquefying helium is a refrigerant by adiabatic expansion.
The GM / JT refrigerator 15 can be cooled to about 4 K by utilizing the latent heat of the liquefied helium.

Generally, the JT refrigerator is superior to the GM refrigerator in refrigeration efficiency in the temperature range of about 4 K, but the refrigeration efficiency in the temperature range higher than this temperature zone is inferior to the GM refrigerator.
Therefore, at the time of precooling, the refrigeration capacity of the combined GM refrigerator 16 is switched at about 20 K or less at which it is reduced, and becomes a main cold heat source.
That is, the GM / JT refrigerator 15 internally has two cold heat sources of the GM refrigerator 16 and the JT cooling unit 17.
The refrigerant is circulated in the cooling system by the circulation compressor 35 (35a, 35b) provided in the JT cooling unit 17.
In place of the GM / JT refrigerator 15, a Stirling / JT refrigerator (not shown) may be used.

The cooling pipe 19 includes: supply pipes 22A and 22B for supplying the cooling stage 18 with a refrigerant cooled by a cold heat source such as the JT cooling unit 17 provided inside the GM / JT refrigerator 15; And a return pipe 23 (23A, 23B) for returning the heat source to a cold heat source.

GM / JT refrigerator 15 supply pipe 22 ₁ internal of (22A _1, 22B ₁₎ is a integrally connected outside of the supply pipe 22 A, the 22B.
Refrigerant is cooled JT supply pipe 22 ₁ of the tube that is thermally connected to each stage of the GM refrigerator 16 hot-side stage 26a, stepwise to cryogenic flow in the order of the low temperature-side stage 26b.
The JT supply pipe 22 _1, the internal return tube 23 (23A, 23B) of the refrigerator 16 before and after each stage 26 (26a, 26b), is thermally connected by JT heat exchanger 28.

The two GM / JT refrigerators 15 (15a, 15b) are provided with precooling pipes 22a, 22b branched from the JT supply pipes 22 ₁ (22A ₁ , 22B ₁ ), respectively.
The precooling pipes 22a and 22b are provided with bypass valves 29 (29a and 29b) for controlling ON / OFF of the flow of the refrigerant, respectively.
The first pre-cooling pipe 22 a connected to the high temperature side stage 26 a of the first GM / JT refrigerator 15 a is connected to the first supply pipe 22 A via the single-stage refrigerator 12.
The JT valve 31a connected downstream of the low temperature side stage 26b is bypassed by the first precooling pipe 22a.

At the initial stage of precooling, the refrigerant cooled by the single-stage refrigerator 12 having a high refrigeration capacity bypasses the JT cooling unit 17a by the first precooling pipe 22a and cools the cooling stage 18.
That is, the first cooling system including the first GM / JT refrigerator 15 a is strongly assisted by the single-stage refrigerator 12 outside the system to cool the cooling stage 18 at the initial stage of pre-cooling.

Here, FIG. 2 is a schematic view showing the relationship between the temperatures of the single-stage refrigerator 12, the GM refrigerator 16 and the JT cooling unit 17 and the refrigeration capacity.
As can be seen from FIG. 2, the single-stage refrigerator 12 has a high refrigeration capacity compared to the GM / JT refrigerator 15 at about 80 K or more.
That is, at the time of precooling, the LTS coil 11a can be efficiently cooled by utilizing the refrigeration capacity of the single-stage refrigerator 12, and the precooling time can be significantly shortened.

However, at about 50 K or less, the remaining refrigeration capacity of the single-stage refrigerator 12 in consideration of heat penetration to the shield plate 21 is rapidly reduced.
Therefore, when the cooling stage 18 is equal to or less than about 50K, the bypass valve 29a and sealed closed, it switches the cold heat source in the JT cooling unit 17a.

On the other hand, the second pre-cooling pipe 22b branched from the first 2JT supply pipe 22B ₁ is connected directly to the second supply pipe 22B to bypass the JT valve 31b without passing through the other cold source.
The refrigerant cooled by the low temperature side stage 26b of the GM refrigerator 16 bypasses the JT cooling unit 17 and is supplied directly to the cooling stage 18 by the second precooling pipe 22b.
The refrigeration capacity of the GM refrigerator 16 is larger than that of the JT cooling unit 17 at a high temperature of about 20 K or more.
Therefore, the second cooling system including the second GM / JT refrigerator 15 b can efficiently cool the cooling stage 18 using the refrigeration capacity of the GM refrigerator 16.

However, as shown in FIG. 2, these refrigeration capacities reverse at about 10K to 20K.
Therefore, switching the cold heat source in the JT cooling portion 17b of the bypass valve 29b Upon cooling to a temperature at which the refrigerating capacity is reversed sealed closed.
In this manner, the LTS coil 11a is efficiently cooled by the precooling pipes 22a and 22b to cryogenic temperatures by appropriately utilizing the refrigeration capacities of the single-stage refrigerator 12 and the GM refrigerator 16 at the time of precooling.

By the way, when the LTS coil 11a is cooled with the configuration as described above, a refrigerant whose temperature is lower by several tens K flows in the first pre-cooling pipe 22a in the temperature range of about 50 K or more compared to the second pre-cooling pipe 22b.
In the temperature range of about 50K to 20K, a refrigerant having a temperature lower than that of the first precooling pipe 22a flows to the second precooling pipe 22b.
When these refrigerants having a temperature difference are supplied to the cooling stage 18, a temperature difference occurs between the portion cooled by the GM / JT refrigerator 15a and the portion cooled by the GM / JT refrigerator 15b.
Due to this temperature difference, a temperature difference is also generated inside the LTS coil 11a, and the characteristics of the LTS coil 11a may be degraded by thermal stress.

Therefore, using the supply heat exchanger 33, heat exchange is performed between the supply pipes 22A and 22B through which the refrigerant that has flowed through the precooling pipes 22a and 22b flows, at the front stage of the cooling stage 18.
By heat exchange with the supply heat exchanger 33, the temperature difference between the refrigerants in the supply pipes 22A and 22B can be reduced to several K or less, and this thermal stress can be reduced to a level at which the LTS coil 11a does not deteriorate.

Here, constituent materials and a configuration of the supply heat exchanger 33 will be described.
During steady operation , helium mist is produced inside the GM / JT refrigerator 15 by adiabatic expansion of helium (refrigerant) in the JT cooling unit 17.
The refrigeration capacity of the GM / JT refrigerator 15 is determined by the amount of generated helium mist.

On the other hand, the cooling limit temperature of the GM / JT refrigerator 15 is determined by the saturated vapor pressure temperature irrespective of the amount of generation.
Therefore, when the heat load is equal to or less than the refrigeration capacity, the temperature of the helium mist in the refrigerator becomes constant.
On the other hand, when the heat load exceeds the refrigeration capacity, the temperature of the helium mist evaporates at once, and the temperature in the refrigerator rises.

Here, FIG. 3 is a cross-sectional view of the supplied heat exchanger 33 of the cooling device 10 according to the first embodiment.
For example, as shown in FIG. 3, the supply heat exchanger 33 is in close contact with and fixed to two tubes 34 arranged in parallel and the two tubes 34. And a metal block 37 for thermally connecting 34.

Now, it is assumed that the saturated vapor pressure of two GM / JT refrigerators 15 deviates and the temperature in the refrigerator is different.
In this state, if the heat transfer of the metal block 37 and the tube 34 is good, heat is transferred from the high temperature side to the helium mist flowing through the low temperature side supply pipes 22A and 22B .
This moving heat causes the freezing function of the GM / JT refrigerator 15 to malfunction when all the helium mist on the low temperature side evaporates as described above.
In this case, the cooling stage 18 cooled by only one of the two cooling systems generates thermal stress in the LTS coil 11a.

In consideration of the cooling principle of such a GM / JT refrigerator 15, the metal block 37 is desirably made of a material whose thermal conductivity decreases at low temperature.
More specifically, the heat transfer at a temperature difference of 0.1 K is preferably 0.5 W or less, and at a high temperature of about 300 K, the heat transfer at a temperature difference of 10 K is preferably about 500 W.
That is, it is desirable that the thermal conductivity in the cryogenic temperature band of about 4 K is 1/10 or less of the thermal conductivity in the room temperature band of about 300 K.

As a material suitable as a constituent material of the metal block 37 which satisfies such conditions, JIS standard SUS316 or SUS304 stainless steel, copper alloy, aluminum alloy such as JIS standard A5083 or A2024, carbon reinforced plastic (CFRP), etc. may be mentioned.
By using these materials, the heat transfer between the two tubes 34 is good at high temperatures, but hardly transfers at low temperatures.

Here, FIG. 4 is a figure which shows the heat conductivity in 300 K and 4 K of the material mentioned above.
As shown in FIG. 4, the thermal conductivity of the materials shown in FIG. 4 including stainless steel is different by 10 times or more between 300 K and 4 K, and thus the above requirements are satisfied.
The two pipes 34 may not be specially prepared as the supply heat exchanger 33, but may be the supply pipes 22A and 22B .

Moreover, FIG. 5 is sectional drawing of the modification of the supply heat exchanger 33 of the cooling device 10 concerning 1st Embodiment.
And FIG. 6 is a cross-sectional view showing the supplied heat exchanger 33 of FIG. 5 when it is placed at a cryogenic temperature and deformed.
As the feed heat exchanger 33 is shown by FIG. 5, the two pipe bodies 34 are arrange | positioned in parallel with the housing | casing 38, and are comprised.
The two pipes 34 are provided with stainless steel blocks of good conductivity at the same position.

Each stainless steel block is bonded to the inner wall surface of the housing 38 with a heat shrinkable material 39.
The heat-shrinkable material 39 is, for example, a resin-based adhesive such as an epoxy resin which shrinks by 2% or more at room temperature by 80 K or less.
The stainless steel blocks are fixed by the heat shrinkable material 39 in close contact at room temperature.
As precooling progresses and the heat-shrinkable material 39 which has been cooled to 80 K or less, it is thermally shrunk to separate the two tubes 34 as shown in FIG.

These tubes 34 are pulled apart in vacuum and insulated to stop heat exchange.
The supply heat exchanger 33 allows the cooling device 10 to supply the refrigerant supplied from different cooling systems to one cooling stage 18 at a uniform temperature.
The structure of the feed heat exchanger 33 as described above is due to the characteristics of the JT cooling unit 17 utilizing the latent heat of helium and mist.
Therefore, for a refrigerator configured without combining the JT cooling unit 17, a normal heat exchanger without any device for stopping heat exchange at a cryogenic temperature may be used.

  Next, the cooling method according to the first embodiment will be described using the flowchart of FIG. 11 (see FIG. 1 as needed).

For the vacuum vessel 13 at room temperature, the installed GM / JT refrigerator 15 is activated to start precooling (S11).
First, the bypass valves 29 of both the first cooling system and the second cooling system are opened to flow the refrigerant through the precooling pipes 22a and 22b .
The LTS coil 11a is cooled by the single-stage refrigerator 12 and the GM refrigerator 16 (S12).

At around room temperature, the heat exchange between the two supply pipes 22A and 22B is performed well by the supply heat exchanger 33, so the temperature of the refrigerant supplied to the LTS coil 11a becomes uniform (S13).
By cooling the cooling stage 18 with the refrigerant thus homogenized, the generation of thermal stress in the LTS coil 11 a is suppressed.
Cooling is continued in this state until the temperature inside the vacuum vessel 13 becomes about 50 K or less (S14: NO: to S12).

When the temperature becomes lower than about 50K, the cooling closes the bypass valve 29 while continuing the, induces precooled pipe 22 a, the refrigerant flowing through 22b to JT supply pipe _{22 1 (S14: YES: S15} , S16).
By this switching, the cold heat source is switched from the single-stage refrigerator 12 to the JT cooling unit 17.
Then, the GM refrigerator 16 and the switched JT cooling unit 17 are used as a cold heat source, and cooling is continued until the temperature becomes about 20 K or less (S17: NO: to S15).
At this time, equalization of the refrigerant by the supply heat exchanger 33 is also continued.

When the internal temperature of the vacuum vessel 13 is below about 20K, it closes the bypass valve 29, to induce pre-cooling pipe 22 a, the refrigerant flowing through 22b to JT supply pipe _{22 1 (S17: YES: S18} ).
As a result of this switching, the cold heat source switches from the GM refrigerator 16 to the JT cooling unit 17 to complete precooling (S18).
At this time, since the temperature of the supply heat exchanger 33 is about 20 K, the thermal conductivity of the supply heat exchanger 33 becomes almost zero, and almost no heat exchange is performed (S19).

Since heat exchange is not performed between the two supply pipes 22A and 22B , even if the cooling temperatures of the two JT cooling units 17 (17a and 17b) deviate, the refrigeration function fails due to evaporation of the refrigerant due to heat transfer. It will never be.
In this state, the cooling is further continued, and the temperature of the LTS coil 11a is set to 4 K which can maintain the superconducting state of the LTS coil 11a (S20).
The two JT cooling units 17 maintain 4 K, which is the steady-state operating temperature of the LTS coil 11a (S21).

  As described above, according to the cooling device 10 according to the first embodiment, even when the object to be cooled 11 is cooled by a plurality of cooling systems, the generation of thermal stress in the LTS coil 11 a can be suppressed and the precooling can be performed. it can.

Second Embodiment
FIG. 7 is a schematic block diagram of the cooling device 10 according to the second embodiment.

The supply heat exchanger 33 of the cooling device 10 concerning 2nd Embodiment is provided in two precooling piping 22a, 22b shown by 1st Embodiment, as FIG. 7 shows.
Since the precooling pipes 22a and 22b also constitute a part of the supply pipes 22A and 22B, the heat exchanger 33 arranged in this manner has the thermal stress of the superconducting coil 11 in the same principle as the first embodiment. Suppress the occurrence of
However, since the supply heat exchanger 33 is provided in the precooling pipes 22a and 22b , when the bypass valve 29a is closed, the heat exchange is also stopped simultaneously.

After the bypass valve 29a is closed and the cooling by the single-stage refrigerator 12 is finished, there is no extreme difference between the temperatures of the refrigerants of the two cooling systems (14a, 14b), so a large thermal stress may be generated. Low.
That is, after the bypass valve 29a is closed, the need for heat exchange is reduced compared to the stage before the closing.

Therefore, the heat exchange ON / OFF is interlocked with the ON / OFF of the bypass valve 29a, and the heat exchange for equalization of the refrigerant is completed when the bypass valve 29a is closed.
Thus, by providing the supply heat exchanger 33 in the precooling pipes 22a and 22b , heat exchange between the two supply pipes 22A and 22B can be reliably shut off when the bypass valve 29a is closed.

The second embodiment has the same structure and operation procedure as the first embodiment except that the installation position of the supply heat exchanger 33 is set to the pre-cooling pipings 22a and 22b , and thus the redundant description will be omitted.
Also in the drawings, portions having common configurations or functions are denoted by the same reference numerals, and redundant description will be omitted.

  As described above, according to the cooling device 10 according to the second embodiment, in addition to the effects of the first embodiment, the heat exchange can be stopped interlockingly with the switching of the bypass valve 29a. It can be surely limited at the time of precooling where heat exchange is required.

Third Embodiment
FIG. 8 is a schematic block diagram of the cooling device 10 according to the third embodiment.
As the feed heat exchanger 33 of the cooling device 10 concerning 3rd Embodiment is shown by FIG. 8, the to-be-cooled object 11 cools the HTS coil 11b (11) cooled in the temperature zone different from the LTS coil 11a. Including.
The LTS coil 11a is cooled by an LTS system constituted by two cooling systems including two GM / JT refrigerators 15 (15a, 15b) as in the first embodiment.

On the other hand, unlike the LTS system, the HTS coil 11b is cooled by the HTS system which is a cooling system having a steady operation temperature of about 20 K that is lower than the transition temperature of the HTS coil 11b.
For example, as shown in FIG. 8, the HTS system is configured by annularly connecting a third cooling pipe 19C (19) provided with a heat exchanger 41 and a circulation compressor 42 to a two-stage GM refrigerator 32. Ru.

In the third embodiment, the supply heat exchanger 33 is provided between the supply pipes 22a, 22b, 22C of the cooling systems (LTS system, HTS system) having different steady operation temperatures.
In particular, in the LTS systems, the supply heat exchanger 33 is pre-cooled pipe 22a of the supply pipe 22 A, 22B, provided in 22b, is linked to the timing of the heat exchanger to the switching of the bypass valve 31 (31a, 31b) .
The temperature of the refrigerant supplied to the LTS coil 11 a and the temperature of the refrigerant supplied to the HTS coil 11 b are equalized by the supply heat exchanger 33.

The HTS coil 11b has a low heat capacity compared to the LTS coil 11a.
Therefore, the HTS coil 11b is cooled earlier than the LTS coil 11a and generates a large temperature difference with the LTS coil 11a.
This temperature difference causes thermal radiation to cause thermal stress in the superconducting coils 11 (11a, 11b).

Therefore, the supply heat exchanger 33 connects the LTS supply pipes 22A and 22B and the HTS supply pipe 22C.
By heat exchange between the HTS system supply pipe 22C and the LTS system supply pipes 22A and 22B , the precooling time of the HTS system becomes longer, and the temperature difference between the HTS coil 11b and the LTS coil 11a is alleviated to generate thermal stress. Is suppressed.

Further, as described above, the single-stage refrigerator 12 has high refrigeration capacity in the temperature range of about 80 K or more.
Then, in the temperature range of about 50 K where the refrigeration capacity of the single-stage refrigerator 12 decreases, surplus occurs in the refrigeration capacity of the two-stage GM refrigerator 32 from the heat capacity of the HTS coil 11b as described above.
The precooling time can also be shortened by mutually assisting the surplus capacity of the HTS system and the LTS system.
Therefore, the feed heat exchanger 33 of the third embodiment makes the temperature of the refrigerant flowing through the pre-cooling pipes 22a and 22b uniform, and utilizes the refrigeration capacity of the single-stage refrigerator 12 in another cooling system.

At about 10 K to 20 K near the superconducting transition temperature of the HTS coil 11b, the precooling by the precooling pipes 22a and 22b ends, so the HTS system independently maintains the steady operation temperature.
As shown in the first embodiment, the LTS coil 11a is further cooled to about 4 K using the JT cooling unit 17 as a cold heat source even after the precooling by the precooling pipes 22a and 22b is finished.

Such shortening of the pre-cooling time has a favorable effect even when a quench occurs.
When the LTS coil 11a which has been quenched and raised to about 60 K is recooled, it is necessary to recool as short as possible.
At the time of recooling, the superconducting coil 11 can be brought into a superconducting state in a short time by assisting the JT cooling unit 17 with low refrigeration capacity with the cooling capacity of the two-stage GM refrigerator 32 by the supply heat exchanger 33.

Moreover, FIG. 9 is a schematic block diagram which shows the modification of the cooling device 10 concerning 3rd Embodiment.
The cooling of the LTS coil 11a may be provided by one cooling system.
For example, as shown in FIG. 9, pre-cooling pipes 22a and 22b are provided on the high temperature side stage 26a and the low temperature side stage 26b of one GM refrigerator 16 for cooling the LTS coil 11a.

The first precooling pipe 22a connected to the high temperature side stage 26a passes through the single-stage refrigerator 12 and bypasses the JT cooling unit 17 and is connected to the supply pipe 22A as in the first embodiment.
On the other hand, the second precooling pipe 22b connected to the low temperature side stage 26b bypasses the JT cooling unit 17 and is directly connected to the supply pipe 22B to which the first precooling pipe 22a is connected.
Then, the first precooling pipe 22a, the second precooling pipe 22b, and the supply pipe 22C are thermally connected by the supply heat exchanger 33.
Even with such a structure, the cooling of the HTS coil 11 b can be assisted by the single-stage refrigerator 12 by the supply heat exchanger 33.

Moreover, FIG. 10 is a figure which shows the other modification of the cooling device 10 concerning 3rd Embodiment of FIG.
As shown in FIG. 10, the second precooling pipe 22b is joined to the first precooling pipe 22a, and the supply heat exchanger 33 is provided downstream of the junction point of the second precooling pipe 22b.
Also when the feed heat exchanger 33 is connected to the precooling pipes 22a and 22b joined in this manner, the generation of thermal stress and the reduction of the precooling time can be performed as in the cooling device 10 described above.
Further, by providing the supply heat exchanger 33 downstream of the junction of the pre-cooling pipes 22a and 22b , the configuration of the supply heat exchanger 33 can be simplified, and the frequency of failure etc. can be suppressed.

The third embodiment is the same as the first embodiment except that the temperatures of the refrigerant supplied to different objects to be cooled 11 (11a, 11b) are made uniform by exchanging heat between different cooling systems. Since the structure and the operation procedure will be described, the redundant description will be omitted.
Also in the drawings, portions having common configurations or functions are denoted by the same reference numerals, and redundant description will be omitted.

As described above, according to the cooling device 10 according to the third embodiment, even when there are superconducting coils 11 having different heat capacities and cooling temperatures, the occurrence of thermal stress in one of the superconducting coils 11 is suppressed and cooled. Can.
In addition, the precooling time can be shortened by assisting other cooling systems with the refrigeration capacity of the cooling system that has sufficient refrigeration capacity.
Further, by using the feed heat exchanger 33 having the configuration shown in the first embodiment, it is possible to shut off heat exchange at the steady operation temperatures of the HTS system and the LTS system having different steady operation temperatures.

In FIGS. 8 and 9, heat exchange is performed with all the precooling pipes 22a and 22b , but heat exchange is performed between only a part of the plurality of first precooling pipes 22a of the LTS system and the supply pipe 22C of the HTS system. If you do, you can expect the effect.

According to the cooling device 10 of at least one embodiment described above, even when the object to be cooled 11 is cooled by a plurality of cooling systems, the generation of thermal stress in the object to be cooled 11 is suppressed and the precooling time is shortened . It becomes possible.

While certain embodiments of the present invention have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention.
These embodiments can be implemented in other various forms, and various omissions, substitutions, changes, and combinations can be made without departing from the scope of the invention.
These embodiments and modifications thereof are included in the invention described in the claims and the equivalents thereof as well as included in the scope and the gist of the invention.

DESCRIPTION OF SYMBOLS 10 ... Cryogenic cooling device (cooling device), 11 ... object to be cooled (superconducting coil), 11a (11) ... low temperature superconducting coil (LTS coil), 11b (11) ... high temperature superconducting coil (HTS coil), 12 ... single Stage GM refrigerator (single stage refrigerator), 13 ... vacuum vessel, 15 (15a, 15b) ... GM / JT refrigerator, 16 ... 2 stage GM refrigerator (GM refrigerator), 17 (17a, 17b) ... JT Cooling part, 18 ... cooling stage, 19 (19C) ... cooling pipe, 21 ... shield plate, 22A, 22B, 22C ... supply pipe , 22a, 22b ... precooling pipe (supply pipe) , 22 ₁ (22a ₁ , 22b ₁ ) ... JT supply pipe (supply pipe) , 23 ... return pipe, 24 ... internal space, 26 (26a, 26b) ... stage (high temperature side stage, low temperature side stage) 28 ... JT heat exchanger, 29 (29a, 29b) …by Valves, 31 (31a, 31b) ... JT valves, 33 ... Supply heat exchangers, 34 ... Tubes, 35, 42 ... Compressors for circulation, 37 ... Metal blocks, 38 ... Housings, 39 ... Heat-shrinkable materials, 41 ... heat exchanger.

Claims (13)

A cooling pipe forming a circulation path of a refrigerant supplied to an object to be cooled disposed in a vacuum vessel to form a cooling system;
A refrigerator having a cold heat source for cooling the refrigerant, and the cooling pipe being annularly connected;
Pre-cooling piping which constitutes a part of at least one of the plurality of cooling systems and which branches the cooling piping annularly to bypass a specific cold heat source;
A bypass valve provided in the pre-cooling pipe to switch a heat source of the refrigerant supplied to the object to be cooled;
A heat exchanger provided in a section from the branch point of the precooling piping to the object to be cooled among the cooling piping, and the cooling piping is connected to a cooling piping having a different cooling system. Cryogenic cooler. The cryogenic cooling apparatus according to claim 1, wherein the heat exchanger is provided in the precooling pipe. Another precooling pipe joins the precooling pipe,
The cryogenic cooling device according to claim 2, wherein the heat exchanger is provided downstream of a junction point where the other precooling pipes are joined among the precooling pipes. The cryogenic cooling device according to claim 1 or 2, wherein at least one of the precooling pipes passes through a cold heat source other than the bypassed cold heat source. The cryogenic cooling device according to any one of claims 1 to 4, wherein the object to be cooled is a superconducting coil. The cryogenic cooling apparatus according to claim 5, wherein the object to be cooled is a combination of a high temperature superconducting coil and a low temperature superconducting coil. The cooling system is
A first cooling system for cooling the first object to be cooled;
A second cooling system for cooling a second object to be cooled,
The cryogenic cooling device according to any one of claims 1 to 6, wherein the heat exchanger connects a cooling pipe of the first cooling system and a cooling pipe of the second cooling system. The cryogenic temperature according to any one of claims 1 to 7, wherein the heat exchanger is made of a material whose thermal conductivity at steady-state operating temperature is 1/10 or less of thermal conductivity at 300 K. Cooling system. The cryogenic cooling device according to claim 8, wherein a constituent material of the heat exchanger is any one of stainless steel, copper alloy, aluminum alloy and CFRP. The heat exchanger is
Two or more tubes arranged parallel to the housing and in close contact with one another at room temperature;
A heat-shrinkable material which adheres each of the two or more tubes to the inner wall surface of the housing and thermally shrinks by at least 1% from room temperature at 20 K or less to separate the two tubes. 9. A cryogenic cooling system according to any one of the preceding claims. 11. The cryogenic cooling apparatus according to any one of claims 1 to 10, wherein at least one of the plurality of refrigerators is any one of a GM / JT refrigerator and a Stirling JT refrigerator. The cryogenic refrigeration system according to any one of claims 1 to 11, wherein at least one of the plurality of refrigerators is a combination of a GM refrigerator and a refrigerant circulation path. Supplying a refrigerant to the object to be cooled disposed in the vacuum vessel with cooling pipes of two or more cooling systems;
Cooling the refrigerant circulating along the cooling pipe;
Switching the circulation path of the refrigerant supplied to the object to switch the cold heat source;
And D. equalizing the temperatures of the refrigerants of the two or more cooling systems supplied to the object to be cooled by heat exchange.

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