JP6432087B2 - Dilution refrigerator - Google Patents

Description

  The present invention relates to a dilution refrigerator.

Many methods are employed in which the detector is cooled to a very low temperature to use the analyzer with higher sensitivity and higher resolution. For cooling the detector of the analyzer, a dilution refrigerator using helium and a circulation type ³ He refrigerator are often used.

Here, in the dilution refrigerator and the circulation type ³ He refrigerator, first, the ³ He gas is cooled by a mechanical refrigerator or liquid helium that can obtain a cold heat of 4.2 K or less, and is liquefied by the Joule-Thomson effect. Next, the liquefied ³ He is depressurized with a pump to cool to a temperature of 1K or lower. Since ³ He gas is expensive, it is used after being exhausted by a pump and circulated by a compressor.

Further, in order to obtain the Joule-Thomson effect, a high impedance of 10 ¹⁰ cm ⁻³ or more (for example, a pipe having an inner diameter of 0.05) is attached to such a helium circulation line. Since this high impedance portion is at a low temperature of 4K or less, if only a slight amount of impurity gas such as air or hydrogen is present in addition to helium, the high impedance portion is easily clogged.

  In the first place, for pumps and compressors, leak-tight and oil-free products should not allow impurities from the outside to enter the helium circulation line. However, it is known that impurities (air, moisture, hydrogen, etc.) that are originally adsorbed in the pipes and pumps are gradually released to cause clogging.

  Therefore, for the purpose of removing impure gas, a low-temperature purifier (liquid nitrogen trap type) in which a container filled with activated carbon is cooled with liquid nitrogen is used (see Patent Document 1). Specifically, as shown in FIG. 4, the conventional dilution refrigerator 110 includes a compressor 131, a low-temperature purifier (purifier) 150 using liquid nitrogen, a heat exchanger 133, an impedance 135, and a fractionator 136. The heat exchanger 137 and the mixing chamber 138 are provided in this order, the helium gas circulation path 130, the refrigerator 120 having the cold generator 121 that generates cold by supplying liquid helium, and the vacuum-insulated inner part The heat exchanger 133, the mixing chamber 138, and the cold insulation outer tank 140 that stores the cold generation unit 121 described above are schematically configured in the space.

  In the conventional dilution refrigerator 110, when operating to cool the detector of the analyzer or the like, the liquid level is supplied by supplying liquid nitrogen to the low-temperature purifier 150 and periodically adding liquid nitrogen. Since it is necessary to manage, it was common to install it outside the cold insulation outer tub 140 together with the compressor 131.

JP 2008-232455 A

  By the way, with the recent development of research and development, there is an increasing demand to apply low-temperature devices such as dilution refrigerators to instruments such as analyzers, and to cope with long-term continuous operation for dilution refrigerators. Is required. Therefore, in the dilution refrigerator, a refrigerator using a liquid helium-free type mechanical refrigerator is the mainstream as a cold generation source for generating cold in the cold insulation outer tank. An analyzer that can detect a signal with high sensitivity and high resolution by cooling a low-temperature detector using such a liquid helium-free type dilution refrigerator has been developed. These analyzers are required to operate continuously for a long period of time once activated, and during that time, maintenance of the apparatus is not required.

  However, in the conventional dilution refrigerator, liquid nitrogen is periodically supplied to the low-temperature purifier (liquid nitrogen trap) 150 even if the operation is automated as a liquid helium-free type refrigerator and maintenance is not required. There is a problem that it is difficult to operate stably for a long time because it is necessary.

  This invention is made | formed in view of the said situation, and makes it a subject to provide the dilution refrigerator which automates operation and can operate continuously for a long period of time without requiring a manual labor for a maintenance.

In order to solve this problem, the present invention has the following configuration.
That is, the invention according to claim 1 is a mechanical refrigerator having a cold generator,
It has at least a compressor for compressing helium gas, a purifier for removing impurities in the helium gas, a heat exchanger for exchanging heat with the cold generator, and a mixing chamber for low temperature output, which are provided in this order. Helium gas circulation path,
In the space insulated by vacuum, the cold generator, the purifier, the heat exchanger, and a cold storage outer tank for storing the mixing chamber,
The purifier has a heater for keeping the purifier at 60-77K;
The cold generator and the purifier are in thermal contact with each other through a member made of a first metal and a member made of a second metal having a lower thermal conductivity than the first metal ,
It is a dilution refrigerator which the said heater is provided in the position spaced apart from the contact part of the said refiner | purifier and the said cold generation part.

The invention according to claim 2, member made of the first metal is a flange shape, a dilution refrigerator according to claim 1.

The invention according to claim 3 is the dilution refrigerator according to claim 1 or 2 , wherein the member made of the second metal is a fixture.

The invention according to claim 4 is the dilution refrigerator according to any one of claims 1 to 3 , wherein the purifier is a cylindrical container formed of a member having thermal conductivity.

The invention according to claim 5, wherein the cold generating portion has a first cold generating portion, and a second cold generating section for generating a low temperature refrigeration than the first cold generating unit, according to claim 1 to 4 It is a dilution refrigerator as described in any one of these.

The invention according to claim 6 is the dilution refrigerator according to claim 5 , wherein the purifier is in contact with the first cold generator.

  The dilution refrigerator of the present invention stores the cold generator of the mechanical refrigerator and the purifier provided in the circulation path of the helium gas in the space inside the vacuum-insulated cold storage outer tank, and the cold generator And the purifier are in thermal contact with each other, and part of the cold heat generated in the cold generator can be used as a cooling heat source for the purifier. Is no longer necessary, and long-term continuous operation is possible.

It is a distribution diagram showing an example of the composition of the dilution refrigerator which is one embodiment to which the present invention is applied. It is a cross-sectional schematic diagram of the refiner | purifier which comprises the dilution refrigerator which is one Embodiment to which this invention is applied. It is a figure which shows the temperature change of each component in the cooling experiment of a dilution refrigerator. It is a systematic diagram which shows an example of a structure of the conventional dilution refrigerator.

  Hereinafter, a dilution refrigerator which is an embodiment to which the present invention is applied will be described in detail with reference to the drawings. In addition, in the drawings used in the following description, in order to make the features easy to understand, there are cases where the portions that become the features are enlarged for the sake of convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. Absent.

  First, an example of the configuration of a dilution refrigerator that is an embodiment to which the present invention is applied will be described. FIG. 1 is a schematic diagram showing an example of the configuration of a dilution refrigerator 10 that is an embodiment to which the present invention is applied. As shown in FIG. 1, the dilution refrigerator 10 of the present embodiment is schematically configured to include a mechanical refrigerator 20, a helium circulation path 30, and a cold insulation outer tub 40. The dilution refrigerator 10 can be used in an analyzer that can detect a signal with high sensitivity and high resolution by cooling the detector.

  The mechanical refrigerator 20 includes a first cooling stage (first cold generating unit) 21 that cools the helium circulating in the circulation path 30 to about 50K, and a second that further cools the helium to about 4.2K. A cooling stage (second cold generating part) 22 and a two-stage cold generating part are provided. Further, the first and second cooling stages 21 and 22 are respectively stored in spaces inside the cold insulation outer tub 40.

The circulation path 30 is a flow path made of piping or the like through which helium gas and liquid can flow. The circulation path 30 includes a compressor 31 that compresses helium gas, a first heat exchanger (inlet side) 32, a purifier 50, and a second heat exchanger (heat exchanger) that exchanges heat with the first cooling stage 21. 33, condenser 34 for exchanging heat with the second cooling stage 22, impedance 35 for reducing the pressure of helium gas, fractionator (incoming side) 36, third heat exchanger (incoming side) 37, c-phase 38A and d-phase 38B So that the mixing chamber 38, the third heat exchanger (return side) 37, the fractionator (return side) 36, and the first heat exchanger (return side) 32 are in this order. The ³ He helium gas can be circulated from the first heat exchanger (return side) 32 to the compressor 31 again.

  The cold insulation outer tub 40 includes first and second cooling stages (cold generators) 21 and 22 and a first heat exchanger 32. A part of the circulation path 30 provided with the purifier 50, the second heat exchanger (heat exchanger) 33, the impedance 35, the fractionator 36, the third heat exchanger 37, and the mixing chamber 38 is stored. Thereby, contact with these apparatuses and external air is interrupted | blocked, and it can be set as a vacuum heat insulation state. On the other hand, the compressor 31 provided in the circulation path 30 is provided outside the cold insulation outer tub 40.

  The purifier 50 is a low-temperature purifier provided to remove impurities in the helium gas before the first cooling stage 21 and the second heat exchanger 33, which are cold generating parts, exchange heat. Instead of the liquid nitrogen trap type low-temperature purifier, the circulation path 30 is provided. In the dilution refrigerator 10 of the present embodiment, the purifier 50 is a space inside the cold insulation outer tub 40 and is provided on the primary side of the second heat exchanger 30. The first cooling stage 21 that is the generation unit is in thermal contact. Thereby, a part of the cold generated in the first cooling stage 21 can be used as the cold heat source of the purifier 50.

Here, the configuration of the purifier 50 will be described in detail.
FIG. 2 is a schematic cross-sectional view showing an example of the configuration of the purifier 50 applicable to the dilution refrigerator 10 of the present embodiment. As shown in FIG. 2, the purifier 50 includes a cylindrical main body (body) 51 </ b> A that is open at both ends, a first flange surface 51 </ b> B that closes one open surface, and a first that closes the other open surface. A two-flange surface 51 </ b> C is provided and is schematically configured. The first and second flange surfaces 51B and 51C are fixed to the open surfaces of the main body 51A by brazing, welding, or the like. Thereby, the refiner 50 is a sealed cylindrical container.

  On the inner side of the main body 51A, a plurality of partition plates 52, 52... Are provided at intervals in the axial direction of the main body 51A. Thereby, the inside of the main body 51A is divided into a plurality of spaces. The plurality of divided spaces inside the main body 51A are each filled with activated carbon as an adsorbent. In addition, a seal member 52A is provided in the center of each partition plate 52.

  As the material of the main body 51A, the first flange surface 51B, the second flange surface 51C, and the plurality of partition plates 52, 52,..., Materials having excellent conductivity are preferable. As such a material, a metal is preferable, and among these, copper, silver, gold and the like are more preferable, and copper is particularly preferable from the viewpoint of economy. By using copper having excellent conductivity as the material of the surface 51A, 51B, 51C of the purifier 50 and the partition plate 52 member provided inside, the activated carbon inside the purifier 50 can efficiently cool from the outside. Can be communicated to.

  On the first flange surface 51B, a helium supply pipe 53A and a helium discharge pipe 53B are provided so as to penetrate the first flange surface 51B.

  Here, the base end of the helium supply pipe 53 </ b> A is connected to the entry side 30 </ b> A of the circulation path 30. On the other hand, the tip 53a of the helium supply pipe 53A passes through the seal members 52 provided in the plurality of partition plates 52, 52... And opens into a space facing the second flange surface 51C. That is, the helium supply pipe 53A also functions as a support for the partition plates 52, 52.

  Further, the base end of the helium exhaust pipe 53B is connected to the return side 30B of the circulation path 30. On the other hand, the tip 53b of the helium discharge pipe 53B opens into a space facing the first flange surface 51B.

  Thus, by providing the tip of the helium supply pipe 53A and the tip of the helium discharge pipe 53B at both ends of the space inside the main body 51A, the contact area with the activated carbon is increased by the siphon effect, so Impurities can be removed efficiently.

  Gasket type filters 54 and 54 are provided at the base end sides of the helium supply pipe 53A and the helium discharge pipe 53B, respectively, so that the activated carbon filled in the main body 53A does not flow out into the circulation path 30. Is provided.

  As described above, the base end sides of the helium supply pipe 53A and the helium discharge pipe 53B are provided on the first flange surface 51B side, so that the second flange surface 51C is heated with the first cooling stage 21 serving as a cold generation part. It can be set as the attachment surface of the connection member 60 (it mentions later) for making it contact.

  In the dilution refrigerator 10 of the present embodiment, the first cooling stage (first cold generating unit) 21 and the purifier 50 are in thermal contact. As shown in FIGS. 1 and 2, this thermal contact is performed through a connection member 60 having thermal conductivity. Specifically, the first cooling stage 21 and the purifier 50 are in thermal contact with each other by being connected (fixed) by a connection member 60 having thermal conductivity.

  The connecting member 60 may be composed of a single member, but may be composed of two or more members. In the present embodiment, the connection member 60 is a flange-shaped first member 61 attached so as to be in contact with the first cooling stage 21, and a fixture for fixing the purifier 50 to the first member 61. And a second member 62 for adjusting heat transfer from the first cooling stage 21 to the purifier 50.

  The material of the connection member 60 is not particularly limited as long as it has thermal conductivity. Examples of the material having excellent thermal conductivity include metals. The connection member 60 may be made of a single material, but may be made of two or more materials. Specifically, the connecting member 60 includes a first member (member made of a first metal) 61 made of a metal (for example, copper) having excellent thermal conductivity, and a metal (for example, stainless steel) having a lower thermal conductivity than copper. And a second member 62 (member made of a second metal).

Here, when the temperature in the purifier is high (above 77K), the adsorption ability of the impurity gas of the activated carbon also decreases. On the other hand, if it is cooled to less than 60K, the circulating ³ He gas also begins to be adsorbed by the activated carbon. Therefore, it is necessary to keep the purifier at an appropriate temperature (60 to 77 K).

  By the way, according to the conventional low-temperature purifier, since liquid nitrogen at atmospheric pressure is used as a cold heat source, there was a lower limit value of the operating temperature of the purifier 50 (the boiling point of nitrogen under atmospheric pressure: about 77 K). Therefore, in the conventional low-temperature purifier, removal may be difficult depending on the type of impurities. Moreover, in order to continue cooling a refiner, there existed a subject that liquid nitrogen had to be regularly added.

  On the other hand, according to the purifier 50 that constitutes the dilution refrigerator 10 of the present embodiment, the first cooling stage 21 is used as a cooling heat source, so that the temperature can be set freely as compared with the conventional purifier. Is possible. Further, as long as the mechanical refrigerator 20 is operating, it is not necessary to add liquid nitrogen. However, since the temperature of the first cooling stage 21 is approximately 40 to 50K, it is necessary to prevent the temperature of the purifier 50 from being excessively lowered.

Therefore, the first member 61 connected to the first cooling stage 21 is made of a material having excellent heat conductivity, and the fixture made of a material having poor heat conductivity between the purifier 50 and the first cooling stage 21. A temperature difference is provided by sandwiching the second member 62 as a spacer, and the temperature of the purifier 50 is adjusted so as not to decrease too much. Note that the heat transfer amount of the second member 62 serving as the spacer can be determined from the heat input amount due to the circulation of ³ He and the temperature difference due to the spacer. At this time, the material, thickness, and the like of the second member 62 serving as a spacer are determined so that the maximum circulation flow rate of helium is 77K or less and the minimum circulation flow rate is 60K or more.

  The second member 62 constituting the connecting member 60 is preferably made of a material having a low thermal conductivity in order to suppress heat transfer. That is, the second member 62 adjusts the cold heat transmitted from the first cooling stage 21 via the first member 61 and transmits it to the purifier 50, while the first cooling stage 21 from the purifier 50. It is necessary to suppress the transfer of intrusion heat to the water. Specifically, normal temperature compressed helium is introduced into the purifier 50 from the inlet side 30A of the circulation path 30 via the helium supply pipe 53A, and the purified low-temperature helium gas passes through the helium discharge pipe 53B from the purifier 50. To the return side 30B of the circulation path 30. The amount of heat becomes heat entering the first cooling stage 21 from the purifier 50 through the second member 62. Therefore, from the viewpoint of heat transfer, it is desired that the second member 62 be made of a material that does not easily transfer heat and that the heat transfer area is reduced.

  In the dilution refrigerator 10 of the present embodiment, a bolt is used as the second member 62 serving as a spacer and fixture, and the flange-shaped first member 61 connected to the first cooling stage 21 and the second flange of the purifier 50 are used. It is connected and fixed to the surface 51C. In this case, when the mechanical refrigerator 20 is operated from a normal temperature state to a low temperature state, these need to be fixed so that no backlash occurs due to contraction / expansion due to temperature change. That is, from the viewpoint of temperature change, it is desirable that the thermal expansion coefficients of the materials of the first member 61, the second member 62, and the purifier 50 are relatively close.

  If these are judged comprehensively, it is preferable that the first member 61 and the purifier 50 are made of copper, and the second member serving as a fixture is made of stainless steel (see Table 1 below).

  In addition, as shown in FIG. 1, in the present embodiment, for the purpose of preventing the temperature of the purifier 50 from dropping too much, a heater (heater) 70 and a thermometer 71 are installed in the purifier 50. It is good also as a structure which controls operating temperature. In this case, from the viewpoint of suppressing heat transfer, the heater 70 is preferably provided at a position separated from the contact portion between the first cooling stage 21 and the first member 61 serving as a cold generating portion. In addition, it is also possible to reproduce | regenerate activated carbon using the heater 70 and the thermometer 71 installed in the refiner | purifier 50, when the dilution refrigerator 10 of this embodiment stops.

Next, an example of the operation method of the dilution refrigerator 10 of this embodiment is demonstrated.
In the dilution refrigerator 10 of the present embodiment, first, the circulating helium in the circulation path 30 is boosted by the compressor 31 to about 400 kPa (hereinafter, absolute pressure is indicated unless otherwise specified). The pressurized circulating helium gas at normal temperature is introduced into the first heat exchanger 31 through the circulation path 30 and is cooled to a temperature suitable for impurity adsorption by heat exchange with a low-temperature return helium gas described later.

  Next, the cooled circulating helium gas is introduced into the purifier 50. In the purifier 50, impurities such as moisture and air in the circulating helium gas are removed and introduced into the second heat exchanger 32 from the circulation path 30. The circulating helium is cooled to about 50 K by the first cooling stage 21 of the mechanical refrigerator 20 through the second heat exchanger 32, and then further 4 by the second cooling stage 22 of the mechanical refrigerator 20 through the condenser 34. .Cooled to about 2K. Thereafter, the circulating helium gas is decompressed by the impedance 35 and is introduced into the fractionator 36, the third heat exchanger (inlet side) 37, and the mixing chamber 38.

Next, the circulating helium is separated in the mixing chamber 38 into two phases: a d phase 38B in which ³ He is dissolved in ⁴ He and a c phase 38A in ³ He. Here, the d phase 38B contains a lot of ⁴ He, and the c phase 38A contains a lot of ³ He. Since helium density of c-phase 38A is smaller than the specific gravity of the helium d-phase ^38B, a state floating on the d-phase 38B which c-phase 38A formed by the 3 He is mainly formed by ⁴ the He. From this state, the ³ He in the c-phase 38A is dissolved in the ⁴ He in the d-phase 38B, thereby further cooling. That is, the mixing chamber 38 is a low temperature output part.

Next, ³ He dissolved in the d-phase 38 </ b> B exchanges heat with the above-described circulating helium through the third heat exchanger (return side) 37 and the fractionator 36. Furthermore, in the first heat exchanger 32, the temperature is raised to room temperature by heat exchange with room temperature circulating helium, and the circulation path 30 is circulated again.

  In addition, when the dilution refrigerator 10 of this embodiment is stopped, unlike the conventional dilution refrigerator, the process of the liquid nitrogen etc. which were used for cooling of a low temperature refiner is unnecessary. Further, after the dilution refrigerator 10 is stopped, the adsorbent (for example, activated carbon) in the purifier 50 can be regenerated by introducing a regeneration gas into the purifier 50 and starting the heater 70.

  As described above, according to the dilution refrigerator 10 of the present embodiment, the first cooling stage 21 serving as the cold generating part of the mechanical refrigerator 20, helium, in the space inside the cold insulated outer tub 40 that is thermally insulated from vacuum. The purifier 50 provided in the gas circulation path 30 is housed, and the first cooling stage 21 and the purifier 50 are brought into contact with each other through a connection member 60 having thermal conductivity. Since a part of the cold generated in the stage 21 can be used as a cold heat source for the purifier 50, manual operation such as replenishment of nitrogen to the purifier 50 becomes unnecessary, and a long-term continuous operation is possible.

  Further, according to the dilution refrigerator 10 of the present embodiment, since the purifier 50 can be set to 77 K or less, which is the saturation temperature of liquid nitrogen, impurities that have been difficult to remove with a conventional low-temperature purifier can be obtained. Removal is possible.

  In addition, the connection member 60 that connects the first cooling stage 21 and the purifier 50 is constituted by a first member 61 made of copper having excellent thermal conductivity and a second member 62 made of stainless steel having low thermal conductivity. Thus, the purifier 50 can be easily maintained at an appropriate temperature (60 to 77 K).

  Moreover, in the dilution refrigerator 10 of this embodiment, since liquid nitrogen is not used for cooling of the refiner | purifier 50, it becomes possible to reduce running cost rather than the conventional dilution refrigerator.

  The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the embodiment described above, activated carbon is described as an example of the adsorbent, but the adsorbent is not limited to activated carbon, and other adsorbents can be used depending on the state of impurities.

  Further, in the above-described embodiment, the configuration in which the stainless steel bolt is used as the spacer and fixing tool as the second member 62 has been described as an example. However, the stainless steel spacer and the bolt made of FRP having poor thermal conductivity are used. A combined configuration may also be used.

  Furthermore, various changes may be added to the spacer structure. Specifically, for example, for the purpose of making it difficult to transmit heat, the ground contact surface with the first cooling stage 21 may be reduced by chamfering and sharpening. Moreover, it is good also as a structure which opens a horizontal hole (like a polka dot pattern) in the trunk | drum of a spacer, and reduces a cross-sectional area. Alternatively, only the spacer may be inclined to increase the distance.

The effects of the present invention will be described below using specific examples.
First, the purifier shown in FIG. 2 was manufactured and incorporated in a liquid helium free type (mechanical refrigerator type) dilution refrigerator having a liquid nitrogen cooling type purifier. Cooling experiments were conducted using a dilution refrigerator equipped with both the liquid nitrogen cooling type purifier and the liquid nitrogen unnecessary type purifier of the present invention.

  Specifically, in the cooling experiment, first, after starting the operation of the dilution refrigerator, it was operated using a conventional liquid nitrogen cooling type purifier. Next, after 180 hours from the start of the dilution refrigerator, the operation of the liquid nitrogen cooled purifier was stopped and the operation of the mechanical refrigerator type purifier of the present invention was started.

FIG. 3 is a diagram showing a temperature change of each component in the cooling experiment of the dilution refrigerator.
As shown in FIG. 3, as a result of performing a cooling experiment by switching between a conventional purifier and the purifier of the present invention, the same minimum temperature and temperature stability performance are obtained regardless of which purifier is used. I was able to confirm. Moreover, even when the purifier of the present invention which does not require liquid nitrogen was used, it was confirmed that continuous operation for 3 days or more was possible.

10 dilution refrigerator 20 mechanical refrigerator 21 1st cooling stage (1st cold generating part)
22 2nd cooling stage (2nd cold generating part)
30 Circulation path 30A Inlet side 30B Return side 31 Compressor 32 First heat exchanger 33 Second heat exchanger (heat exchanger)
34 Condenser 35 Impedance 36 Divider 37 Third heat exchanger 38 Mixing chamber 38A c phase 38B d phase 40 Cold storage outer tank 50 Purifier 51A Body (body)
51B First flange surface 51C Second flange surface 52 Partition plate 52A Seal member 53A Helium supply pipe 53B Helium discharge pipe 54 Filter 60 Connection member 61 First member 62 Second member 70 Heater 71 Thermometer

Claims (6)

A mechanical refrigerator having a cold generating part;
It has at least a compressor for compressing helium gas, a purifier for removing impurities in the helium gas, a heat exchanger for exchanging heat with the cold generator, and a mixing chamber for low temperature output, which are provided in this order. Helium gas circulation path,
In the space insulated by vacuum, the cold generator, the purifier, the heat exchanger, and a cold storage outer tank for storing the mixing chamber,
The purifier has a heater for keeping the purifier at 60-77K;
The cold generator and the purifier are in thermal contact with each other through a member made of a first metal and a member made of a second metal having a lower thermal conductivity than the first metal ,
A dilution refrigerator, wherein the heater is provided at a position separated from a contact portion between the purifier and the cold generator. The dilution refrigerator according to claim 1 , wherein the member made of the first metal has a flange shape. The dilution refrigerator according to claim 1 or 2 , wherein the member made of the second metal is a fixture. The dilution refrigerator as described in any one of Claims 1 thru | or 3 with which the said refiner is a cylindrical container comprised from the member which has heat conductivity. The cold generating section includes a first cold generating portion, it said has a second cold generating section for generating a low temperature refrigeration than the first cold generating portion, according to any one of claims 1 to 4 Dilution refrigerator. The dilution refrigerator according to claim 5 , wherein the purifier is in contact with the first cold generator.

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