JP5017640B2 - Cryogenic refrigeration method and cryogenic refrigeration system - Google Patents

Description

The present invention relates to a high-temperature superconductor, a device to which the high-temperature superconductor is applied, a cryogenic refrigerant used for cooling an infrared detector in an infrared telescope, a cryogenic refrigerating method and a cryogenic refrigerating system using the cryogen.

Conventionally, there are some which are used after being cooled to a very low temperature, such as a superconductor used in a magnetic resonance tomography (MRI) apparatus or a nuclear magnetic resonance (NMR) analyzer, or an infrared detector in an infrared telescope.

For example, a superconductor used in an MRI apparatus or the like has conventionally been composed of a low temperature superconducting (LTS) wire, and has been brought into a superconducting state by an immersion cooling method using liquid helium. This immersion cooling method using liquid helium is expensive in liquid helium and requires skill in handling, and the running cost is very high.

In contrast, in recent years, bismuth-based and yttrium-based high-temperature superconducting (High Tc Superconductor: HTS) wires, which are cheaper than liquid helium and can be cooled by liquid nitrogen, have been vigorously developed. It is approaching practical use. However, even the immersion cooling method using liquid nitrogen still lacks simplicity and has a high running cost.

On the other hand, the performance of cryogenic refrigerators such as GM (Gifford-McMahon) refrigerators and pulse tube refrigerators has improved dramatically in recent years, and superconductors can be directly used with such cryogenic refrigerators. In other words, a so-called conduction cooling method for conducting cooling is proposed. According to this conduction cooling method, it is not necessary to handle liquid helium or liquid nitrogen, and the superconducting state can be maintained only by electric power, so that the system can be very simple and low in running cost. Furthermore, if a cryogenic refrigerator is used, not only high-temperature oxide superconductors but also MgB ₂ superconductors can be cooled.

However, since the conduction cooling method is insulative except for the cooling surface by the cryogenic refrigerator, it lacks thermal stability, and when it is temporarily stopped due to trouble or when the superconductor is disturbed during operation, The temperature rose in a short time, and in the worst case, it could burn out.

Therefore, in the conduction cooling system, a method of improving the thermal instability by enclosing a superconductor with solid nitrogen as a refrigerant storage body to increase the heat capacity has been proposed (for example, see Non-Patent Document 1).

This conduction cooling method using solid nitrogen as a refrigerant storage body not only improves thermal instability, but also has the following features.
1. A high cold storage effect enables intermittent operation of the refrigerator.
2. Nitrogen is inert and environmentally friendly.
3. The superconductor can be prevented from being deformed by electromagnetic force generated during operation.

However, when solid nitrogen is used as a refrigerant storage body, nitrogen gas is introduced and liquefied in the cryostat, or liquid nitrogen is introduced and then solidified to form solid nitrogen so as to surround the superconductor while being in contact therewith. However, when solidifying, the volume shrinks by about 6%, and generally it is difficult to make solids closely contact each other. Therefore, as shown in the conceptual diagram of FIG. As a result, there was a problem of poor thermal contact.
Further, when the superconductor generates heat due to disturbance generated during operation, the contact portion of the solid nitrogen with the superconductor sublimates, and so-called dryout occurs in which the thermal contact completely disappears (see the conceptual diagram shown in FIG. 11B). In some cases, only the convective heat transfer by the nitrogen gas was performed and the cooling characteristics were extremely deteriorated.

Therefore, as shown in the conceptual diagram of FIG. 12, the applicant of the present invention introduces a small amount of liquid neon LN into the solid nitrogen SN so that the liquid neon LNe fills the gap portion between the solid nitrogen SN and the superconductor 2. Thus, the cryogenic regenerator R that improves thermal contact and avoids dryout has been proposed (see Non-Patent Documents 2 and 3).
Y. Iwasa, "A 'Permanent' HTS Magnet System: Key Design & Operational Issues", Advances in Superconductivity X [Proc. ISS '97] (Springer-Verlag, Tokyo), 1998-05 Takemura Nakamura and three others, "Improvement of heat loss and liquid neon characteristics of high-temperature superconducting wire impregnated with solid nitrogen," IEEJ Superconducting Applied Power Equipment and Linear Drive Joint Study Group, January 2004, P55-60 T. Nakamura, K. Higashikawa, I. Muta and T. Hoshino “Performance of Conduction-Cooled HTS Tape with the Aid of Solid, Nitrogen-Liquid Neon Mixture”, Physica C, vol. 412-414 (2004), pp. 1221-1224.

However, in Non-Patent Documents 2 and 3, quantitative analysis on the amount of neon introduced is not in time, and the techniques described in Non-Patent Documents 2 and 3 have not reached the practical range. In Non-Patent Documents 2 and 3, only liquid neon is mentioned, and solid neon was not considered.

The present invention is a further development of the above-described research. The object of the present invention is to provide a cryogenic regenerator that has good thermal contact and is suitable for avoiding dryout, and further uses it. An object is to provide a cryogenic refrigeration method and a cryogenic refrigeration system that are simple and low in running cost.

In order to solve the above-mentioned problems, the present invention is (1) a cryogenic storage medium that cools in contact with an object to be cooled, and is 0.1 to 50% by weight based on solid nitrogen and the solid nitrogen. Provided is a cryogenic refrigerant storage body comprising a complex with neon, wherein at least a part of the neon is inserted in a solid or liquid state between the cooled object and the solid nitrogen To do.
Here, solid or liquid means that the cryogenic refrigerant is in a solid or liquid state in an environment where the object to be cooled is cooled.

Moreover, this invention provides the cryogenic refrigerant | coolant thermal storage body characterized by further including the reinforcement member which surrounds the said to-be-cooled body in non-contact or a contact state in the said structure (1).

In order to solve the above problems, the present invention is (3) a cryogenic refrigeration method for cooling an object to be cooled, and (A) forms solid nitrogen in contact with the object to be cooled contained in a cryostat. And (B) impregnating liquid neon into the solid nitrogen and inserting at least a part thereof between the cooled object and the solid nitrogen; and (C) solidifying the liquid neon to form a solid Forming a complex comprising nitrogen and solid neon; (D) cooling the cooled object only by cooling the complex; and (E) in step (D), the solid neon is liquid. The present invention provides a cryogenic refrigeration method including the step of performing the steps after step (C) again after the state is reached.

In the configuration (3), the present invention provides (4) the step (A) includes (A1) a step of cooling the cryostat to a temperature at which nitrogen is maintained in a liquid state by a cryogenic refrigerator, and (A2) ) Introducing nitrogen gas into the cryostat cooled to a temperature at which nitrogen is maintained in a liquid state, liquefying, or introducing liquid nitrogen so that the cooled object is immersed in the liquid nitrogen; (A3) The step of further cooling the cryostat to a temperature at which the liquid nitrogen solidifies by the cryogenic refrigerator, and the step (B) is performed by (B1) the cryogenic refrigerator, Further cooling the inside of the cryostat formed with solid nitrogen to a temperature at which neon maintains a liquid state; and (B2) neon maintains the liquid state. Introducing neon gas into the cryostat cooled to a temperature at least until it liquefies or introducing liquid neon, the step (C) is performed by the cryostat using the cryostat. The inside of the cryostat is further cooled to a first temperature lower than the temperature at which neon solidifies, and the temperature in the cryostat is equal to or higher than the temperature at which neon liquefies in step (D). When the temperature reaches the second temperature, the cryogenic refrigeration method is characterized in that the steps after the step (C) are executed again.

In order to solve the above problems, the present invention provides (5) a cryogenic refrigeration system for cooling a cooled object, and a cryostat for housing the cooled object, and for cooling the cooled object. A cryogenic refrigerator, a nitrogen introducing means for introducing nitrogen gas or liquid nitrogen into the cryostat, a neon introducing means for introducing neon gas or liquid neon into the cryostat, and a temperature related to the inside of the cryostat. A temperature measuring device for measuring, a pressure measuring device for measuring a pressure related to the inside of the cryostat, a temperature measured by the temperature measuring device and a pressure measured by the pressure measuring device, and the cryogenic refrigerator And a controller for controlling the nitrogen introduction means and the neon introduction means. There is provided a temperature refrigeration systems.

According to the present invention, in the configuration (5), (6) the controller controls the cryogenic refrigerator when the object to be cooled is accommodated in the cryostat so that nitrogen is contained in the cryostat. Cool to a temperature that maintains the liquid state, and then control the nitrogen introduction means to introduce nitrogen gas into the cryostat to be liquefied, or introduce liquid nitrogen, and the object to be cooled is immersed in the liquid nitrogen. And then controlling the cryogenic refrigerator to further cool the inside of the cryostat to a temperature at which the liquid nitrogen solidifies, and then cool the inside of the cryostat to a temperature at which neon maintains a liquid state, The neon introduction means is controlled to introduce neon gas into the cryostat at least until it is liquefied or to introduce liquid neon. Then, the cryogenic refrigerator is controlled to further cool the inside of the cryostat to a first temperature lower than the temperature at which neon solidifies, and the temperature related to the inside of the cryostat is equal to or higher than the temperature at which neon liquefies. When the second temperature is reached, the cryogenic refrigerator is controlled to cool the inside of the cryostat to a first temperature lower than the temperature at which neon solidifies. A cryogenic refrigeration system is provided.

The present invention also provides a cryogenic refrigerant storage unit characterized in that, in the above configurations (1) and (2), (7) the nitrogen is replaced with argon and the neon is replaced with nitrogen.

The present invention also provides a cryogenic refrigeration method characterized in that, in the above configurations (3) and (4), (8) the nitrogen is replaced with argon and the neon is replaced with nitrogen.

The present invention also provides a cryogenic refrigeration system characterized in that, in the above configurations (5) and (6), (9) the nitrogen is replaced with argon and the neon is replaced with nitrogen.

Moreover, this invention provides the cryogenic refrigerant | coolant storage body characterized by the said structure to be cooled being a superconductor in said structure (1) (2) (7).

The present invention also provides the cryogenic refrigeration method characterized in that, in the configurations (3), (4), and (8), (11) the object to be cooled is a superconductor.

Moreover, this invention provides the cryogenic refrigeration system characterized in that in the above configurations (5), (6), and (9), (12) the object to be cooled is a superconductor.

According to the cryogenic regenerator of the present invention, neon can be cooled only by the heat capacity of the cryogenic regenerator in a wide temperature range in which neon is maintained from a solid state to a liquid state, so that the refrigerator can be operated intermittently during that time. Thus, the running cost can be reduced.

In addition, even if the temperature of the cooling target rises due to heat generation or a refrigerator failure, when the temperature of neon exceeds the temperature at which the neon enters a liquid state, the solid neon liquefies first, filling the gap with the cooling target and making thermal contact. Since it becomes very good, it is possible to suppress further temperature rise, and therefore it is possible to continue operation for a while.
Moreover, even if a large disturbance occurs and solid nitrogen is dried out, thermal runaway can be avoided by the temperature rise suppression effect by liquid neon.

Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings.

The cryogenic refrigeration system 1 according to the present embodiment mainly transfers heat to a cryostat 4 that houses a high-temperature superconducting coil 2 used in an MRI apparatus or the like, and a high-temperature superconducting coil 2 as shown in FIG. A cryogenic refrigerator 6 connected through the member 5, a nitrogen introducing means 7 and a neon introducing means 8 for introducing nitrogen and neon into the container 3 in the cryostat 4, and a temperature for measuring the cryostat 4. Based on the temperature measuring device 10, the pressure measuring device 11 for measuring the pressure related to the cryostat 4, the temperature measuring device 10 and the temperature and pressure measured by the pressure measuring device 11, the refrigerator 6, the nitrogen introducing means 7 and And a controller 9 for controlling the neon introduction means 8.

The cryostat 4 is configured so as to be thermally insulated in the same manner as a known cryostat, and has a container 3 for housing the high-temperature superconductor 2 therein.

The high-temperature superconducting coil 2 is made of, for example, a bismuth-based, yttrium-based, or thallium-based oxide high-temperature superconducting wire or a MgB ₂ wire, and is housed in a container 3 in the cryostat 4.

The nitrogen introducing means 7 includes a nitrogen introducing device 7 a composed of a nitrogen storage device and a flow rate controller (both not shown), and a nitrogen introducing tube 7 b extending from the nitrogen introducing device 7 a to the container 3 of the cryostat 4.

Similarly to the nitrogen introduction means 7, the neon introduction means 8 includes a neon introducer 8 a composed of a neon reservoir and a flow rate controller (both not shown), and a neon introduction pipe extending from the neon introducer 8 a to the container 3 of the cryostat 4. 8b.

The refrigerator 6 is a cryogenic refrigerator composed of a compressor, an expander, and a heat exchanger (all not shown), and is composed of, for example, a two-stage expansion refrigerator using a GM cycle or a Solvay cycle. ing.
Further, the cooling stage 6a of the refrigerator 6 is connected to the high-temperature superconducting coil 2 in the cryostat 4 via the heat transfer member 5, and directly cools the high-temperature superconducting coil 2 and indirectly uses the container 3 Cool inside.

The controller 9 is connected to the refrigerator 6, the nitrogen introducing means 7, the neon introducing means 8, the temperature measuring instrument 10 and the pressure measuring instrument 11, and the temperature and pressure measuring instrument 11 measured by the temperature measuring instrument 10 are measured. Based on the pressure, it is possible to control the introduction amount and introduction timing of nitrogen and neon, ON / OFF of the refrigerator 6, the cooling temperature, and the like.

Next, a cryogenic refrigeration method using the cryogenic refrigeration system 1 according to the present embodiment will be described with reference to FIG.

First, the container 6 in the cryostat 4 is cooled by the refrigerator 6 to a temperature at which nitrogen is kept in a liquid state (for example, 63.2K to 77.3K) (S1).

Next, nitrogen gas is introduced into the container 3 of the cryostat 4 to be liquefied by the nitrogen introduction means 7 or liquid nitrogen is introduced so that the high temperature superconducting coil 2 is immersed in the liquid nitrogen (S2). .

Next, the refrigerator 6 cools the container 3 to a temperature at which nitrogen solidifies, for example, around 25K, and solidifies the liquid nitrogen (S3).
25K is also a temperature at which neon maintains a liquid state.

Next, neon gas is introduced into the container 3 by the neon introduction means 8 until it is liquefied, or liquid neon is introduced and infiltrated into solid nitrogen (S4).
At this time, as shown in the conceptual diagram of FIG. 12, the liquid neon LNe hardly chemically bonds with nitrogen, easily penetrates into the solid nitrogen SN, and enters between the solid nitrogen SN and the high-temperature superconducting coil 2. .
In addition, about the introduction amount in the case of introduce | transducing neon gas, the pressure in the container 3 should be measured with the pressure measuring device 11, and it should introduce | transduce until it reaches the saturated vapor pressure of neon.
Here, the amount of neon introduced may be 0.1 to 50% by weight with respect to nitrogen, but neon is expensive, so it is not necessary to introduce more than necessary. According to an example (see Experiment 1 or 2 described later), the amount of neon introduced is preferably 1 to 5% by weight, and more preferably about 3% by weight.

Next, the refrigerator 6 cools the inside of the container 3 to a temperature at which neon solidifies, for example, around 20 K, and solidifies liquid neon to form a cryogenic refrigerant that is a composite of solid nitrogen and solid neon. (S5).

Next, the operation of the refrigerator 6 is stopped (S6), and the high-temperature superconducting coil 2 is cooled only by the cooling of the cryogenic storage medium (S7).

In step S7, when the temperature in the container 3 rises and reaches or exceeds the temperature at which neon liquefies, for example, reaches 25K, the operation of the refrigerator 6 is resumed when the operation is continued (S9). ), The steps after step S5 are executed again (S8).

Thereafter, the cryogenic refrigeration system 1 repeats the cycle in which the above steps S5 to S9 are executed, and the high temperature superconducting coil 2 is continuously cooled.

According to the cryogenic refrigeration method using the cryogenic refrigeration system 1 configured as described above, the following effects can be obtained.

That is, solid neon has a specific heat approximately twice as high as that of solid nitrogen at a temperature of 20 K (solid neon: 1.4 J / (cm ³ · K), solid nitrogen: 0.73 J / (cm ³ · K). )), The cooling performance can be enhanced as compared with the case of solid nitrogen alone.

Furthermore, even if the temperature of the object to be cooled rises due to heat generation or a failure of the refrigerator, the solid neon liquefies when the temperature of neon exceeds the liquid state, and the gap between the object to be cooled is filled and the thermal contact is extremely good. Therefore, further temperature rise can be suppressed. Therefore, even if a large disturbance occurs and solid nitrogen is dried out, thermal runaway can be avoided by the temperature rise suppression effect by liquid neon.

Further, since the cryogenic refrigerant can be cooled only until the neon changes from a solid state to a liquid state, the refrigerator can be operated intermittently, and the running cost can be reduced.

Further, by surrounding the object to be cooled while being in contact with the solid refrigerant storage body, a mechanical reinforcement effect can be obtained, and the superconductor can be prevented from being deformed by electromagnetic force generated during operation.

In addition, neon is currently expensive, but it may be a small amount relative to nitrogen, and once introduced, in principle there is no need for replenishment unless the system fails.

Moreover, the cryostat which accommodates a refrigerator and a cryogenic storage body may be an existing one, and no special device or the like is required.

[Verification]
Next, an experiment was conducted to verify the operation and effect of the present invention. Hereinafter, the experiment will be described with reference to the drawings.

[Experimental device]
First, the experimental apparatus ES used in this experiment will be described.
As shown in FIG. 3, the experimental apparatus ES mainly includes a copper stage CS connected to the 2nd stage S2 of the GM refrigerator, a sample chamber SC formed above the copper stage CS, and nitrogen gas in the sample chamber SC. And gas introduction rods GI and GI for introducing neon gas, a vacuum chamber VC formed so as to surround them, and a gas introduction system GS connected to the gas introduction rod GI.

As shown in FIG. 3, the gas introduction system GS includes dedicated mass flow controllers MC1 and MC2 for nitrogen gas and neon gas, respectively, and can control the flow rate of each, and is also equipped with a vacuum / pressure gauge PS (switching type). Thus, the pressure in the sample chamber SC can be measured in detail.
The gas introduction system GS further includes a nitrogen / neon mixer MX, which was not used in this experiment.
In addition, the experimental apparatus ES can perform PID control of the temperature Tcp of the partial CP in the copper stage CS using a heater (not shown).

[Experimental sample]
Next, the sample S used in this experiment will be described.
The sample S is made of a Bi-2223 / Ag multi-core tape material (100A, 20K, self-field), which is an HTS wire, and both ends thereof are connected to a copper block CB as shown in FIG.
In addition, the sample S is provided with a voltage tap VT and a high response temperature sensor TS for evaluating the heat loss characteristics.

Then, a sample holder SH composed of the sample S, the copper block CB, the voltage tap VT, and the temperature sensor TS was placed on the copper stage CS of the experimental apparatus ES via thermal conductive grease as shown in FIG.

[Experiment 1]
Next, Experiment 1 was conducted in order to verify the presence or absence of the mixed phase of solid nitrogen-liquid neon and the amount of neon introduced necessary for forming the mixed phase in the cryogenic refrigerant of the present invention. Hereinafter, the contents of Experiment 1 will be described.

First, the cryogenic refrigerant body made of solid nitrogen-liquid neon was produced using the experimental apparatus ES. That is, 300 g of nitrogen was first introduced, and the temperature Tcp was changed to liquefy and solidify the nitrogen (the mass was evaluated from the integrated flow rate and the specific gravity of the standard state). At this time, the sample S is in a state immersed in solid nitrogen.

Thereafter, the set cooling temperature by the GM refrigerator was fixed at 25.0 K, and after the temperature was stabilized, neon gas was introduced as shown in conditions 1 to 5 shown in Table 1 (measurement positions of temperatures Tcp, Tc, and Ts are shown in FIG. 3). Note that, although the temperature Tcp is controlled to 25.0 K, Tc and Ts gradually increase with the introduction of neon. This is unfortunately caused by a slight leak in the sample chamber SC. However, as is clear from the following description, it is considered that liquid neon is generated at least in solid nitrogen.

[Result of Experiment 1]
FIG. 5 is a plot of the phase states under conditions 1-5 on the pressure P-temperature T diagram. As is apparent from the figure, when the neon introduction amount reaches about 10.8 g, the phase state reaches the saturation curve. Since the saturated vapor pressure of nitrogen at the same temperature is much smaller than that of neon, it is considered that the pressure reflects the phase state of neon. That is, it is presumed that the liquid was liquefied when the neon amount reached around 10.8 g.
However, as is apparent from the pressure change with respect to the neon introduction time at a temperature of 25 K shown in FIG. 6, the pressure is not yet completely saturated under the condition 3 (Ne: 10.8 g). That is, strictly speaking, it is presumed that complete liquefaction exceeded when the neon amount was introduced a little more than 10.8 g.

[Experiment 2]
Next, Experiment 2 was conducted in order to verify the effect of the mixed phase state on the cryogenic refrigerant of the present invention. Hereinafter, the contents of Experiment 2 will be described.

Under the above conditions 1 to 5, an overcurrent disturbance of 122 A (load factor: 1.22) was passed through the sample S for 10 minutes, and the change (ΔTs) from the initial temperature on the surface of the sample S was measured. The result is shown in FIG.

[Result of Experiment 2]
As is clear from FIG. 7, it can be seen that the temperature rise is suppressed when neon is introduced even in a small amount, compared with the case of solid nitrogen alone (condition 1 (Ne: 0 g)). In particular, under conditions 4 (Ne: 16.2 g) and 5 (Ne: 21.6 g), the temperature does not increase at all after about 5 minutes have passed since the overcurrent disturbance is applied, and the sample S maintains a stable state. is doing.

This is presumed to be due to the liquefaction of neon as obtained from the results shown in FIGS. That is, the cooling mechanism of the cryogenic refrigerant of the present invention was demonstrated in a quantitative manner. At this time, the ratio of the neon gas amount to the nitrogen gas in the standard state is 3.6% when the neon gas is 10.8 g and 5.4% when the neon gas is 16.2 g. As described above, in the present system, since there is a leak in the sample chamber SC, it is predicted that the neon gas introduction ratio can actually be set lower.

[Experiment 3]
Next, Experiment 3 was conducted to verify whether or not the solid nitrogen-solid neon state was realized in the cryogenic refrigerant of the present invention. Hereinafter, the contents of Experiment 3 will be described.

First, nitrogen: 300 g (standard state conversion), neon: 32.4 g (standard state conversion) were introduced, and the sample SH was not installed, and was made of solid nitrogen-solid neon in the same manner as in Experiment 1 above. A cryogenic storage medium was produced.
Next, after the temperature Tc was cooled to 13.0K with the refrigerator, the heater was heated to raise Tc to 25.5K. Pc and Tc measured at this time are plotted on the phase diagram of neon and shown in FIG. Moreover, the time change of Pc and Tc in the range whose Tc is 25.0-25.2K is shown in FIG.

And the heating by a heater was stopped and Tc was lowered | hung from 25.5K with the refrigerator. The time change of Pc and Tc at this time is shown in FIG.
[Result of Experiment 3]
8, 9, and 10, when heating or cooling the cryogenic refrigerant of the present invention, there is a state (L in the figure) in which there is almost no change in temperature and pressure near the triple point of neon. I understand that. This indicates that the latent heat is released or absorbed during this period, and neon is surely undergoing a phase transition from the solid state to the liquid state or from the liquid state to the solid state.
Further, FIG. 8 shows that the measurement data of this experiment is on the neon equilibrium line, and no freezing point depression occurs.
That is, in the cryogenic storage medium of the present invention, it was demonstrated that nitrogen and neon each independently form a phase state, and neon independently transitions to solid or liquid with respect to solid nitrogen.

[Modification]
As mentioned above, although embodiment of this invention was described concretely, this invention is not limited to these.
In the above embodiment, the superconductor is used as the object to be cooled. However, the present invention is not limited to this, and any material can be used as long as it is used at a cryogenic temperature like the superconductor, such as an infrared detector in an infrared telescope.

Moreover, in the said embodiment, although the cryogenic refrigerant body was comprised from solid nitrogen and neon which will be in a solid state or a liquid state, you may comprise from solid argon and nitrogen which will be in a solid state or a liquid state. .

Further, for example, when the object to be cooled is large and the object to be cooled due to electromagnetic force is greatly deformed, and the mechanical reinforcement effect is to be further enhanced, the cryogenic refrigerant storage device of the present invention You may comprise so that the reinforcing member of mesh shape etc. which may be enclosed in a contact or a contact state may be further included.

It is the schematic which shows the cryogenic refrigeration system concerning this embodiment. It is a figure which shows the flow of the cryogenic refrigeration method concerning this embodiment. It is a figure which shows the experimental apparatus used for the experiment regarding this invention. It is a figure which shows the experimental sample used for the experiment regarding this invention. It is a figure which shows the result obtained by the experiment regarding this invention. It is a figure which shows another result obtained by experiment regarding this invention. It is a figure which shows another result obtained by experiment regarding this invention. It is a figure which shows another result obtained by experiment regarding this invention. It is a figure which shows another result obtained by experiment regarding this invention. It is a figure which shows another result obtained by experiment regarding this invention. It is a figure which shows notionally the state of the thermal contact of solid nitrogen and a to-be-cooled body. It is a figure which shows notionally the structure of the cryogenic storage body which consists of solid nitrogen and liquid neon.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cryogenic refrigeration system 2 High temperature superconducting coil 3 Container 4 Cryostat 5 Heat transfer member 6 Refrigerator 6a Cooling stage 7 Nitrogen introducing means 8 Neon introducing means 9 Controller 10 Temperature measuring instrument 11 Pressure measuring instrument

Claims (7)

A cryogenic refrigeration method for cooling an object to be cooled,
(A) forming solid nitrogen in contact with an object to be cooled contained in a cryostat;
(B) penetrating liquid neon into the solid nitrogen, and inserting at least a portion thereof between the cooled object and the solid nitrogen;
(C) solidifying the liquid neon to form a complex composed of solid nitrogen and solid neon;
(D) cooling the object to be cooled only by cooling the complex;
(E) In the step (D), after the solid neon is in a liquid state, the step after the step (C) is executed again;
A cryogenic refrigeration method comprising: The step (A)
(A1) using a cryogenic refrigerator to cool the cryostat to a temperature at which nitrogen is kept in a liquid state;
(A2) Nitrogen gas is introduced into the cryostat cooled to a temperature at which nitrogen is maintained in a liquid state to be liquefied, or liquid nitrogen is introduced so that the cooled object is immersed in the liquid nitrogen. Steps,
(A3) further cooling by the cryogenic refrigerator to a temperature at which the liquid nitrogen solidifies in the cryostat,
The step (B)
(B1) further cooling the inside of the cryostat in which solid nitrogen is formed with the cryogenic refrigerator to a temperature at which neon maintains a liquid state;
(B2) introducing neon gas into the cryostat cooled to a temperature at which neon is maintained in a liquid state, at least until it liquefies, or introducing liquid neon,
The step (C)
The cryogenic refrigerator is used to further cool the inside of the cryostat to a first temperature lower than the temperature at which neon solidifies,
In the step (E), when the temperature in the cryostat reaches a second temperature equal to or higher than the temperature at which neon liquefies in the step (D), the steps after the step (C) are executed again.
The cryogenic refrigeration method according to claim 1, wherein A cryogenic refrigeration system for cooling an object to be cooled,
A cryostat for accommodating the cooled object;
A cryogenic refrigerator for cooling the object to be cooled;
Nitrogen introducing means for introducing nitrogen gas or liquid nitrogen into the cryostat;
Neon introduction means for introducing neon gas or liquid neon into the cryostat;
A temperature measuring device for measuring a temperature related to the inside of the cryostat;
A pressure measuring device for measuring pressure related to the inside of the cryostat;
A controller for controlling the cryogenic refrigerator, the nitrogen introducing means and the neon introducing means based on the temperature measured by the temperature measuring instrument and the pressure measured by the pressure measuring instrument;
Including
The controller is
When the object to be cooled is accommodated in the cryostat, the cryogenic refrigerator is controlled to cool the inside of the cryostat to a temperature at which nitrogen is kept in a liquid state,
Next, by controlling the nitrogen introduction means, nitrogen gas is introduced into the cryostat to be liquefied, or liquid nitrogen is introduced so that the cooled object is immersed in the liquid nitrogen,
Next, the cryogenic refrigerator is controlled to further cool the cryostat to a temperature at which the liquid nitrogen solidifies,
Next, the cryostat is cooled to a temperature at which neon maintains a liquid state,
Next, the neon introduction means is controlled to introduce neon gas into the cryostat at least until it liquefies, or introduce liquid neon,
Next, the cryogenic refrigerator is controlled to further cool the cryostat to a first temperature lower than the temperature at which neon solidifies,
Next, when the temperature related to the inside of the cryostat reaches a second temperature that is equal to or higher than the temperature at which neon liquefies, the cryogenic refrigerator is controlled, and the first temperature lower than the temperature at which neon solidifies inside the cryostat. Cool to temperature,
A cryogenic refrigeration system configured as described above. The cryogenic refrigeration method according to claim 1 or 2, wherein the nitrogen is replaced with argon and the neon is replaced with nitrogen. The cryogenic refrigeration system according to claim 3, wherein the nitrogen is replaced with argon and the neon is replaced with nitrogen. The cryogenic refrigeration method according to claim 1, wherein the object to be cooled is a superconductor. The cryogenic refrigeration system according to claim 3 or 5, wherein the object to be cooled is a superconductor.