JP2020076519A - Dilution - Google Patents

Abstract

To provide a piston cylinder type dilution refrigerator capable of shortening precooling time.SOLUTION: A dilution refrigerator 1 is a piston cylinder type one equipped with an outer layer pipe 3 closed at a tip end, and a plunger 5 inserted in the outer layer pipe 3. The plunger 5 is made from a core material having plural stages of large diameter portions 5a and small diameter portions 5b toward the tip end. The large diameter portion 5a is formed with a spiral multiple thread screw groove 25, and a main piping 19 used at normal operation and a precooling piping 21 used at precooling can be respectively arranged in the screw grooves.SELECTED DRAWING: Figure 1

Description

The present invention relates to a dilution refrigerator for obtaining a cryogenic temperature of 0.1 K or less by utilizing the physical properties of isotopes ( ³ He and ⁴ He) of helium gas.

The mixed liquid of the liquid phase of ³ He and the liquid phase of ⁴ He undergoes two-phase separation at 0.8 K or less, and a dilute phase containing 6.4% of ³ He at a low temperature and a concentrated phase containing 100% of ³ He. Coexist. Then, when ³ He of the rich phase is dissolved (diluted) in the dilute phase, heat is absorbed from the outside, and as a result, an ultralow temperature of 1 to 10 ⁻³ K can be obtained. A refrigerator utilizing such a phenomenon is a dilution refrigerator.

As an example of the dilution refrigerator, a compact piston-cylinder type dilution refrigerator in which a plunger is inserted into an outer layer pipe has been developed.
As such a dilution refrigerator, for example, there is the one illustrated in FIG. 4 as a conventional technique in Patent Document 1.

  As shown in FIG. 4, a dilution refrigerator 101 of a conventional example has an outer layer pipe 102, a plunger 103, a mixing chamber 104, a pipe 106, a fractionating chamber 107, and a heat exchange chamber 108. It is roughly configured.

The mixing chamber 104 and the fractionating chamber 107 communicate with each other, and in the space between the mixing chamber 104 and the fractionating chamber 107, a mixed liquid of ³ He dissolved in ⁴ He (hereinafter, referred to as “ ³ He- ⁴ He” "Mixed liquid"). The liquid ³ He is supplied to the mixing chamber 104 via the pipe 106.
In the mixing chamber 104, and the dense phase of ^100% 3 ^He, 3 He has two phases separated into a dilute phase of ^{4 He-6.4%} 3 He which melted into ⁴ the He, lower lean phase by density difference ( ⁴ He-6.4% ³ He), and the upper layer becomes a concentrated phase ( ³ He phase). Then, when ³ He sent into the rich phase melts into the dilute phase, the above-mentioned heat absorption occurs, and it is cooled to an ultralow temperature of the order of 10 mK. That is, since this mixing chamber 104 serves as a cold head as a refrigerator, if the object to be cooled (sample) is held in this portion, the sample can be cooled to the order of 10 mK.

JP, 2016-188737, A JP, 2009-74774, A

When the dilution refrigerator is started, it is at room temperature, and from there it is gradually pre-cooled and each part is cooled to an appropriate temperature.
The fractionating chamber, heat exchanger, and mixing chamber are each insulated, and the ³ He- ⁴ He gas refrigerant and the circulation piping are optimized for operation at a low temperature of 0.1 K, so the refrigeration capacity at a high temperature is extremely high. It is very small, and it takes a very long time to precool to 4.2K only by circulating the refrigerant gas.

In particular, the dilution refrigerator, which is not shown in FIG. 4, employs a configuration for liquefying ³ He by utilizing the Joule-Thomson effect, so that in the flow path of ³ He , The flow rate must be reduced. That is, a flow path having an extremely high impedance that can liquefy ³ He is required. For this reason, during pre-cooling, the flow rate of the ³ He- ⁴ He gas refrigerant that can pass becomes extremely small, and thus it takes a long time to reach the low temperature.

Therefore, in order to reduce the pre-cooling time, in a general dilution refrigerator, a fractionating chamber, a heat exchanger, a mixing chamber, etc. are usually separated inside a vacuum heat insulating container (external vacuum container) by a 4.2K stage anchor. The vacuum container (internal vacuum container) of (1) is often provided and the structure is stored therein. At the time of precooling, a method is used in which the heat exchange gas is put into the internal vacuum container to cool the whole to around 4.2K, and then the heat exchange gas is exhausted.
However, although the above-described method shortens the precooling time, it has many disadvantages such as the complexity of exhausting the heat exchange gas after the precooling, the complicated structure, and the large-sized apparatus.

The piston-cylinder dilution refrigerator targeted by the present invention has a small overall heat capacity because of its compactness, and can be pre-cooled in a short time if the circulation amount of the ³ He- ⁴ He gas refrigerant becomes large to some extent. Becomes
For that purpose, it is necessary to bypass the impedance in the flow path of the ³ He- ⁴ He mixed gas refrigerant, and in order to introduce the bypass piping for the impedance, a branch should be provided on the downstream side of the impedance and the piping should be connected there. I have to.

  In this respect, for example, in a dilution refrigerator that can secure a sufficient space as disclosed in Patent Document 2, a joint having a size that is easy to connect can be used. Since the machine is compact, it is not possible to secure a space for installing the joint downstream of the impedance.

  In addition, it is necessary to minimize the heat leak by making the gap between the plunger and the outer layer pipe extremely narrow (tolerance control on the order of 10 microns), and it is not possible to dispose a precooling pipe through this gap. Can not.

  As described above, since the piston-cylinder type dilution refrigerator is compact, it has a unique problem of how to dispose the precooling pipe.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a piston-cylinder-type dilution refrigerator that can shorten the precooling time.

The inventor, as a result of extensive studies to solve the above problems, as a method of arranging the precooling pipe, a large diameter portion and a small diameter portion are provided in the plunger, and a thermal buffer portion is formed by the large diameter portion, We got the idea that the spiral groove provided in the large diameter part should be a multiple thread groove.
The present invention is based on this idea, and specifically has the following configuration.

(1) A dilution refrigerator according to the present invention is of a piston cylinder type including an outer layer pipe with a closed tip and a plunger inserted into the outer layer pipe,
The plunger is composed of a core material having a plurality of steps of a large diameter portion and a small diameter portion toward the tip, and a spiral multi-thread screw groove is formed in the large diameter portion, which is used in normal operation. Each of the pipe and the precooling pipe used during the precooling operation can be arranged in each thread groove.

(2) Moreover, in the thing described in said (1), the said multiple thread groove is a 3 thread groove, one thread groove is this piping, another one thread groove is a precooling piping, A wiring is provided in each of the remaining one thread grooves.

According to the present invention, by providing the multiple thread groove in the large diameter portion of the plunger, the precooling pipe can be arranged up to the mixing chamber without passing through the impedance while maintaining the thermal buffer portion of the plunger. You can As a result, during the pre-cooling operation, the ³ He- ⁴ He refrigerant gas can be circulated through the pre-cooling pipe, and the heat exchange gas is exhausted after the pre-cooling as in the method of providing the vacuum container (internal vacuum container). The pre-cooling operation time can be shortened without the disadvantages such as complication, increase in size of the apparatus, and increase in labor of work.

It is explanatory drawing explaining the structure of the dilution refrigerator which concerns on embodiment of this invention. It is explanatory drawing explaining the winding state of the plunger of this dilution refrigerator shown in FIG. 1, main piping, and pre-cooling piping, (a) is the state which wound only this piping, (b) is in addition to this piping The state where the pre-cooling pipe is wound is shown. It is explanatory drawing of the other aspect of a plunger. It is explanatory drawing of a prior art example.

As shown in FIG. 1, the dilution refrigerator 1 according to the present embodiment is a piston-cylinder-type dilution refrigerator having an outer layer pipe 3 having a closed tip and a plunger 5 inserted into the outer layer pipe 3. 1, and the mixing chamber 7, the distiller 9, the condenser 15, the refiner 17, the main pipe 19, the precooling pipe 21, and the circulation pump 23 are used as schematic components.
Note that, in the drawings used in the following description, in order to make the features easy to understand, there are cases in which features that are the features are enlarged for convenience, and the dimensional ratios of the components are not necessarily the same as the actual ones. Absent.
Hereinafter, each component will be described in detail.

<Outer layer pipe>
The outer layer pipe 3 is a cylindrical body with a closed tip, and is made of a material that can withstand low temperatures and has low thermal conductivity. Specifically, for example, austenitic stainless steel (SUS304, SUS316), white copper or the like can be used.

<Plunger>
The plunger 5 is inserted into the outer layer pipe 3, and forms a mixing chamber 7, a heat exchanger 11, and a fractionator 9 in that order from the tip side thereof.
As shown in FIG. 2, the plunger 5 is a hollow pipe having a plurality of large diameter portions 5a and small diameter portions 5b toward the tip (mixing chamber 7), and the large diameter portion 5a has a spiral multi-thread screw. The groove 25 is formed. The plunger 5 functions as a core material around which the main pipe 19 and the precooling pipe 21 are wound.

  The example shown in FIG. 2 is an example in which a double thread groove is formed in the large-diameter portion 5a, and FIG. 2 (a) shows a state in which only the main pipe 19 used during normal operation is wound around the plunger 5. 2B shows a state in which the precooling pipe 21 (indicated by a solid black line and a broken line in the drawing) used during the precooling operation is further wound. Note that the pre-cooling pipe 21 does not need to be tightly wound around the small-diameter portion 5b, so that the pre-cooling pipe 21 passes diagonally through the small-diameter portion 5b as indicated by the broken line in FIG. 2 (b) where the pre-cooling pipe 21 cannot be seen. It just needs to be wound.

The main pipe 19 is tightly wound around the small-diameter portion 5b, and is arranged and wound within one screw groove of the multiple thread groove 25 around the large-diameter portion 5a.
Further, the pre-cooling pipe 21 is obliquely arranged so as to pass over the main pipe 19 in the small diameter portion 5b, and within the single thread groove of the multiple thread groove 25 in the large diameter portion 5a like the main pipe 19. Is arranged and wound.

By inserting the plunger 5 in which the main pipe 19 and the pre-cooling pipe 21 are wound into the outer layer pipe 3 as described above, the gap between the outer layer pipe 3 and the small diameter portion 5b is transferred from the mixing chamber 7 to the fractionator 9. The low-temperature ³ He gas passing therethrough and the liquid ³ He flowing in the main pipe 19 constitute a heat exchanger 11 that exchanges heat. In the large-diameter portion 5a, the gap between the large-diameter portion 5a and the outer-layer pipe 3 becomes small, so that the large-diameter portion 5a serves as a thermal buffer portion and can maintain the cryogenic temperature of the mixing chamber 7.

  Further, since the multiple thread groove 25 is formed in the large diameter portion 5a so that the precooling pipe 21 can be arranged from the fractionator 9 side to the mixing chamber 7, the precooling operation time can be shortened as described later. Has been realized.

  The material of the plunger 5 is not particularly limited as long as it can withstand a low temperature, and for example, austenitic stainless steel (SUS304, SUS316), white copper, or the like can be used.

<Mixing room>
The mixing chamber 7 is a space provided between the inner peripheral surface of the tip of the outer layer pipe 3 and the tip of the plunger 5.
In the mixing chamber 7, as described above, the dense phase of ^100% 3 ^He, 3 He has two phases separated into a dilute phase of ^{4 He-6.4%} 3 He which melted into ⁴ the He, density difference Thus, the lower layer is a dilute phase ( ⁴ He-6.4% ³ He) and the upper layer is a rich phase ( ³ He phase).

<Heat exchanger>
As described above, the heat exchanger 11 is configured by the space between the small diameter portion 5b of the plunger 5 and the outer layer pipe 3.
The ³ He gas that has passed through the heat exchanger 11 is sucked into the main pipe 19 by the circulation pump 23 and circulates in the dilution refrigerator 1.

<Distiller>
Fractionator 9 is a space formed above the heat exchanger ^11, selectively ³ He from ^{3 He-4} He mixture during by utilizing the difference in the saturated vapor pressure of 3 He and ⁴ He It is for discharging to.
The ³ He sent from the condenser 15 is heat-exchanged in the heat exchanger 13 which is in thermal contact with the fractionator 9 to be cooled to about 0.5 to 0.7 K, and further 100 mK in the heat exchanger 11. It is cooled to a certain degree and sent to the mixing chamber 7.

<Condenser>
The condenser 15 is for liquefying the gas ³ He having a temperature of about 300 K sent out by the circulation pump 23.
The ³ He liquefied in the condenser 15 is sent to the heat exchanger 13 in the fractionator 9 via the impedance 29.

<Refiner>
The purifier 17 is provided in the middle of the main pipe 19 for the purpose of removing the impure gas, and a liquid nitrogen trap type in which a container filled with activated carbon is cooled with liquid nitrogen is used.

<Main piping>
The main pipe 19 is a pipe that circulates ³ He and ³ He- ⁴ He gas refrigerant in the dilution refrigerator 1 during normal operation and precooling operation.
From the outlet 27 of the outer layer pipe 3, the main pipe 19 passes through the circulation pump 23, the refiner 17, and passes through the condenser 15, the fractionator 9, and the heat exchangers 11 and 13 in the outer layer pipe 3. It reaches the mixing chamber 7.
As described above, the main pipe 19 is densely wound around the small-diameter portion 5b of the plunger 5 to form the heat exchanger 11, and the large-diameter portion 5a of the plunger 5 is arranged in one thread groove of the multiple thread groove 25. Is installed in.

An impedance 29 is provided between the condenser 15 and the fractionator 9 in the main pipe 19. This impedance 29 provides resistance to the flow of ³ He, maintains the pressure at temperature in the condenser 15 and liquefies ³ He.
The material of the main pipe 19 is not particularly limited as long as it can withstand a low temperature, and for example, austenitic stainless steel (SUS304, SUS316), white copper, or the like can be used.

<Pre-cooling piping>
The pre-cooling pipe 21 is newly applied in the present invention, and is used for circulating the ³ He- ⁴ He gas refrigerant during the pre-cooling operation to cool the equipment to the 4K level.
One end of the pre-cooling pipe 21 is connected to the downstream side of the purifier 17 in the main pipe 19, is inserted into the outer layer pipe 3, passes through the condenser 15, the fractionator 9, and the heat exchangers 11 and 13 and is mixed. Reach room 7.

Since the pre-cooling pipe 21 is used only during the pre-cooling operation, the valve 31 for stopping the flow of the pre-cooling pipe 21 during the normal operation is provided. On the other hand, since the precooling pipe 21 is not provided with the impedance 29 as provided in the main pipe 19, the ³ He- ⁴ He gas refrigerant can be smoothly circulated.
As described above, the pre-cooling pipe 21 obliquely passes over the main pipe 19 in the small diameter portion 5b of the plunger 5, and the main pipe 19 in the multiple thread groove 25 is wound in the large diameter portion 5a of the plunger 5. It is arranged in the non-threaded groove.

<Circulation pump>
The circulation pump 23 is provided on the downstream side of the outlet 27 of the outer layer pipe 3 in the main pipe 19 and circulates the ³ He and ³ He- ⁴ He refrigerant gas.

Next, an outline of the operation of the dilution refrigerator 1 of the present embodiment configured as described above will be described with reference to FIG. 1 separately for precooling operation and normal operation.
<Pre-cooling operation>
The pre-cooling operation is an operation for cooling the entire dilution refrigerator 1 to the vicinity of 4.2 K, and ³ He- ⁴ He refrigerant gas is circulated by the circulation pump 23.
During the precooling operation, the valve 31 provided in the precooling pipe 21 is opened, and the ³ He- ⁴ He refrigerant gas is circulated in both the precooling pipe 21 and the main pipe 19.

Since the precooling pipe 21 is not provided with the impedance 29 and a larger amount of gas can be passed as compared with the main pipe 19, the precooling time can be shortened.
When the temperature has cooled to around 4.2K by the pre-cooling operation, the valve 31 is closed and the normal operation by the main pipe 19 is switched to.

<Normal operation>
In normal operation, the gas ³ He having a temperature of about 300 K sent from the circulation pump 23 is liquefied in the condenser 15 and further sent to the heat exchanger 13 in the fractionator 9 via the impedance 29. In fractionator 9, ³ He is selectively discharged from the ³ by utilizing the difference in the saturated vapor pressure of He and ⁴ He ^{3 He-4} He mixture in as described above.
The ³ He sent from the condenser 15 is heat-exchanged in the heat exchanger 13 which is in thermal contact with the fractionator 9 and cooled to about 0.5 to 0.7 K. Further, ³ He is cooled to about 100 mK in the heat exchanger 11 and sent to the mixing chamber 7.

In the mixing chamber 7, a dense phase of ^100% 3 ^He, 3 He has two phases separated into a dilute phase of ^{4 He-6.4%} 3 He which melted into ⁴ the He, lower lean phase by density difference ( ⁴ He-6.4% ³ He), and the upper layer becomes a concentrated phase ( ³ He phase). Then, when ³ He sent to the rich phase melts into the dilute phase, heat absorption occurs as described above, and it is cooled to an ultralow temperature of the order of 10 mK.
At this time, the large-diameter portion 5a provided on the plunger 5 serves as a buffer to prevent cold heat from being transferred upward from the heat exchanger 11, and the mixing chamber 7 is maintained at an extremely low temperature.

As described above, in the present embodiment, by providing the multiple thread groove 25 in the large diameter portion 5a of the plunger 5, the thermal buffer portion of the plunger 5 is maintained and the impedance 29 does not pass through. The pre-cooling pipe 21 could be installed up to the mixing chamber 7. Thereby, during the pre-cooling operation, the ³ He- ⁴ He refrigerant gas can be circulated through the pre-cooling pipe 21 by the circulation pump 23, and the heat exchange gas is exhausted after the pre-cooling like the method of providing the vacuum container (internal vacuum container). The precooling operation time can be shortened without causing the disadvantages such as complicatedness, complicated structure, upsizing of the apparatus, and increase in labor of work.

In the above embodiment, the example of the double thread groove is shown as an example of the multiple thread groove 25 formed in the large diameter portion 5a of the plunger 5, but the multiple thread groove 25 of the present invention is not limited to this. For example, as shown in FIG. 3, it may be a 3-thread groove. In this case, the main pipe 19 may be arranged in one screw groove, the precooling pipe 21 may be arranged in the other screw groove, and the wiring such as a thermometer may be arranged in the remaining one screw groove. Good.
However, a double thread groove may be formed so that the precooling pipe 21 and the wiring are arranged in the same thread groove.

1 Dilution refrigerator 3 Outer layer pipe 5 Plunger 5a Large diameter part 5b Small diameter part 7 Mixing chamber 9 Fractionator 11 Heat exchanger (plunger)
13 Heat exchanger (fractionator)
15 Condenser 17 Purifier 19 Main pipe 21 Pre-cooling pipe 23 Circulation pump 25 Multi-threaded groove 27 Discharge port 29 Impedance 31 Valve <Conventional example>
101 Dilution refrigerator 102 Outer layer pipe 103 Plunger 104 Mixing chamber 106 Piping 107 Fractionation chamber 108 Heat exchange chamber

Claims (2)

A piston-cylinder-type dilution refrigerator having an outer layer pipe with a closed tip and a plunger inserted into the outer layer pipe,
The plunger is composed of a core material having a plurality of steps of a large diameter portion and a small diameter portion toward the tip, and a spiral multi-thread screw groove is formed in the large diameter portion, which is used in normal operation. A dilution refrigerator in which each of the pipes and the precooling pipes used during the precooling operation can be arranged in each thread groove.   The multi-thread screw groove is a three-thread screw groove. One pipe is provided with the main pipe, another one is provided with precooling pipe, and the other one is provided with wiring. The dilution refrigerator according to claim 1, wherein