JPH04187945A - Small-sized helium refrigerator - Google Patents

Abstract

PURPOSE:To develop a particular vacuum degree inside a cryostat by a method wherein absorbent is attached on parts where the temperature drops below a specified temperature, especially on cold heads. CONSTITUTION:Absorbent 11 is attached on parts where the temperature drops below 100K such as cold heads of two-stage refrigerating machine 6 (1st stage 7 and second stage 8) and the external wall of a helium gas flow path, for example. Activated carbon, molecular sieve (made by BLD Co.Ltd.), etc., are used as absorbent. Air, hydrogen gas, helium gas, etc., are absorbed by the absorbent attached on the parts where the temperature drops below 100K, and the vacuum degree inside a cryostat can be maintained below about 10<-6>Torr for a long term.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a refrigerator for cooling to an extremely low temperature (4.2K).

(Prior Art) A small helium refrigerator for cooling to an extremely low temperature (4.2K) generally has a configuration as shown in FIG.

After the high-pressure gas from the compressor 1 passes through the heat exchanger 2, it is cooled by the precooler 3, and is blown out from the Joule-Thomson valve 4 to the low-pressure section, where the temperature is further lowered by the Joule-Thomson effect and reaches a cryogenic temperature (e.g. 4.2K) and enters the condenser 9 to cool the object to be cooled 10. The gas leaving the condenser 9 passes through the low-pressure circuit and enters the compressor again while cooling the high-pressure side by the heat exchanger 2. This cycle is repeated to achieve cryogenic conditions. These devices, except for the compressor, are housed in a cryostat 5 whose interior is evacuated and thermally insulated.

(Problems to be Solved by the Invention) Incidentally, in the above-mentioned small helium refrigerator, in order to maintain the refrigerating capacity, it is necessary to reduce the degree of vacuum in the cryostand to about 10-' Torr or less.

However, with conventional technology, hydrogen gas, air, etc. can be exhausted by the cryo effect, or even if the temperature reaches 4.2 K, helium gas cannot be exhausted, so the degree of vacuum must be reduced to about 10-' Torr or less. I couldn't. Additionally, outgas (mainly hydrogen gas) from the metals that make up the equipment, as well as air and helium gas leaking into the cryostat, deteriorated the vacuum level, resulting in poor insulation and reduced refrigeration capacity. . In particular, if this equipment is stopped due to a power outage or other reasons and the temperature of each part increases, the gas that has adhered to the cryostat will be released into the cryostat due to the cryo effect described above, and the degree of vacuum will become extremely poor. The insulation deteriorated, and even after restarting the plant, it could not reach its initial capacity. .

The present invention provides a high degree of vacuum inside the cryostat (approximately 10-
The objective is to prevent the degree of vacuum inside the cryostat from deteriorating and to prevent the refrigerating capacity from deteriorating over a long period of time.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention provides
A small helium refrigerator is constructed by attaching an adsorbent to the part where the temperature is below K, especially the cold head part of the precooler.

(Function) With this configuration, helium gas can be exhausted by the adsorbent, so the degree of vacuum inside the cryostat can be reduced to approximately 10
−' Torr or less. Furthermore, the adsorbent attached to the following parts of 100 adsorbs outgases such as air and helium, so that the degree of vacuum inside the cryostat can be maintained for a long period of time.

(Example) (Configuration of Example) An embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, a portion where the temperature is below 100°C, for example, a cold head portion of a two-stage refrigerator 6 (1st stag
The adsorbent 11 is attached to the outer wall of the helium gas channel (e7 and 2nd stage 8) and the helium gas flow path. Although the adsorbent is attached at a plurality of locations in the embodiment, it may be installed at at least one location as shown. Activated carbon, molecular sieve (manufactured by BDL), etc. are used as the adsorbent.

(Effects of the Embodiment) In such a configuration, air, hydrogen gas, helium gas, etc. are adsorbed by the adsorbent attached to the part where the temperature becomes 100℃ or less, and the degree of vacuum in the cryostat can be maintained for a long period of time.

(Effects of Examples) As explained above, in the present invention, helium gas can be exhausted by attaching an adsorbent to the part where the temperature is below 100°C, so the degree of vacuum inside the cryostat can be reduced to about 10-' Torr or below. can. Furthermore, it is possible to adsorb outgas from metals constituting the device and gas leaking into the cryostat, thereby preventing deterioration of the degree of vacuum within the cryostat and preventing deterioration of refrigerating capacity over a long period of time.

(Other Examples) Only the 2nd stage adsorbent may be attached to the cold head part of the 2-stage refrigerator, which is a precooler).

〔Effect of the invention〕

According to the present invention, the helium gas inside the device can be evacuated, so the degree of vacuum inside the cryostat is high (approximately 1O-6To
rr or less) and increase the refrigeration capacity.

Furthermore, deterioration of the degree of vacuum inside the cryostat due to outgas from the metal constituting the device and leakage of air, helium gas, etc. into the inside of the cryostat is prevented, and the refrigerating capacity of the small helium refrigerator can be maintained for a long period of time.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, and FIG. 2 is a diagram showing a conventional example. 1...Compressor 2...Heat exchanger 3...
Precooler 4... Joule-Thomson valve 5
...Cryostat 6...Two-stage refrigerator 7°゛1st stage 8-2nd stag
e9... Condenser 10... Cooled object 1
1... Adsorbent agent Patent attorney Noriyuki Chika Figure 1

Claims (1)

[Claims] 1) A compressor that compresses helium gas, a precooler that precools high pressure gas from the compressor, a heat exchanger that exchanges heat between high pressure gas and low pressure gas, and a high pressure section and a low pressure section. In a small helium refrigerator, the precooler, heat exchanger, and Joule-Thomson valve are housed in a cryostat whose inside is evacuated. A small helium refrigerator characterized by having an adsorbent attached to the part where it becomes. 2) The small helium refrigerator according to claim 1, wherein the portion where the temperature becomes 100 K or less is a cold head of the precooler. 3) The small helium refrigerator according to claim 1) or 2), wherein the precooler is a two-stage refrigerator using a Gifford-McMahon cycle.