JPH0468581A - Cryostat - Google Patents

Abstract

PURPOSE:To effectively suppress the heat penetrating a cryogenic refrigerant vessel through a pipe by inversely proportioning the emissivity at the inner face of a pipe, which is offered for the injection of a cryogenic refrigerant, the withdrawal of evaporated gas, the guide of a current lead, etc., to the temperature of the inner face of the pipe, that is, making the emissivity smaller, the higher the temperature at the inner face of the pipe is, and making it larger, the lower the temperature at the inner face of the pipe is. CONSTITUTION:The emissivity at the inner face of a pipe 7, which is offered to the injection of a cryogenic refrigerant 2, the withdrawal of evaporated gas, the guide of a current lead, etc., is controlled by applying several kinds of coating different in emissivity (different in color), or charging the surface roughness inside the pipe. According to this constitution, the radiation from or to the normal temperature side of the pipe 7 can be decreased, and reversely the low temperature side can absorb much entering radiation, and as a result, the heat penetrating a cryogenic refrigerant vessel 3 can be reduced.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to a cryostat used in superconducting equipment and the like.

(Prior Art) Conventionally, a cryostat for maintaining a superconducting magnet or the like at a cryogenic temperature has the following configuration in order to minimize evaporation of a cryogenic refrigerant. That is, a refrigerant container containing cryogenic refrigerant.

a vacuum container that covers the refrigerant container and forms a vacuum insulation layer between it and the refrigerant container; a heat shield provided within the insulation layer; one end communicates with the refrigerant container; It is installed so that it penetrates the vacuum insulation layer, heat shield and wall of the vacuum container and is located in the normal humidity area.
It consists of piping used for injection of cryogenic refrigerant, collection of evaporated gas, guidance of current leads, etc.

In a cryostat configured as above,
The heat entering the refrigerant container other than the piping can be suppressed to several mW by installing a small refrigerator or the like. but,
The intrusion heat related to the piping is generally several tens of milliwatts, which poses a big problem in reducing the amount of evaporation of the refrigerant. The main causes of the heat intrusion into the piping are the convection of evaporated gas within the piping and the radiant heat through the piping. Among these, the convection of the evaporated gas can be suppressed by providing a convection prevention plate, etc., but the problem is how to suppress the intrusion heat related to radiation. For this reason, conventional cryostats have inserted baffle plates made of materials such as aluminum with low emissivity.

However, even if a baffle plate was provided inside the pipe as described above, it was not actually very effective.

This can be explained as follows.

The piping is made of a material with low thermal conductivity, such as stainless steel, in order to suppress heat intrusion due to conduction.

Usually used stainless steel has an emissivity of 0.01 to 0.
It is small, about 05. In other words, a low emissivity means a high reflectance, and electromagnetic waves that enter the pipe at room temperature are repeatedly reflected, with most of them reaching the cryogenic refrigerant container.

Therefore, even if a baffle plate or the like is inserted, it is not very effective.

(Problem to be solved by the invention) As mentioned above, simply providing a baffle plate inside the piping will not solve the problem.
It is not possible to suppress intrusion heat due to radiation.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a cryostat that can effectively suppress the intrusion heat that enters the cryogenic refrigerant container through the inside of the pipe.

[Structure of the invention]

(Means for Solving the Problems) The cryostat of the present invention makes the emissivity of the inner surface of the pipe, which is used for injection of cryogenic refrigerant, recovery of evaporated gas, guidance of current leads, etc., in inverse proportion to the temperature of the inner surface of the pipe. In other words, the emissivity is made smaller where the pipe inner surface temperature is higher, and the emissivity is larger where the pipe inner surface temperature is lower.

(Function) As mentioned above, by making the emissivity of the inner surface of the pipe smaller on the normal temperature side and larger on the low temperature side, the radiation entering or exiting from the normal temperature side of the pipe can be reduced, and conversely,
A large amount of incident radiation can be absorbed on the low temperature side. Naturally, on the low-temperature side, where the emissivity is high, the radiation is greater than that of pipes with conventional configurations, but this radiation is proportional to the fourth power of the absolute temperature, so in the low-temperature area, the radiation is very small and almost No impact. Furthermore, the radiant heat absorbed by the low temperature portion of the pipe is removed from the evaporated gas and the thermal anchor. As a result, heat intrusion due to radiation through the piping is suppressed.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

The basic structure is the same as the conventional cryostand, but there is one difference between this embodiment and the conventional cryostand.

This is because the emissivity of the inner surface of the pipe 7 is actively changed.

That is, in the cryostat of this embodiment, the emissivity of the inner surface of the pipe 7, which is used for injecting the cryogenic refrigerant 2, recovering evaporated gas, guiding the current lead, etc.

The emissivity is inversely proportional to the temperature of the inner surface of the pipe, that is, the higher the inner temperature of the pipe, the lower the emissivity, and the lower the inner temperature of the pipe, the higher the emissivity. Examples of this method include applying paints with different emissivities (different colors) and changing the surface roughness of the inner surface of the pipe.

With this configuration, it is possible to reduce the amount of radiation that enters or exits from the normal temperature side of the pipe 7, and conversely, absorbs a large amount of radiation that enters the low temperature side, and as a result, the cryogenic refrigerant Heat entering the container 3 can be reduced.

Generally, the radioactivity of an object is determined by the following formula.

E=t・4.88・(T/100)' where ε is the emissivity and T is the absolute temperature.

As mentioned above, the radiation activity of an object is proportional to the fourth power of its absolute temperature, so in a normal temperature area (300K) and a low temperature area (30K) where a thermal anchor is installed, for example,
There is a difference of about 0,000 times. On the other hand, the emissivity is generally about 0.01 to 0.9, which is a difference of about 100 times.

In the conventional cryostat, the emissivity of the inner surface of the pipe 7 is considered to be approximately constant, and its value is as small as about 0.05 to 0.1, in other words, the reflectance is large.

For this reason, the electromagnetic waves that enter or are emitted into the pipe 7 at room temperature are repeatedly reflected and most of them are reflected in the cryogenic refrigerant container 3.
reach. According to this embodiment, since the low-temperature part side has a high emissivity (high absorption rate), most of the electromagnetic waves that enter or are emitted into the pipe 7 in the normal-temperature part are absorbed in the low-temperature part, and the temperature becomes extremely low. It does not reach the refrigerant container 3. Conversely, on the low-temperature side where the emissivity is high, the radiation is greater than that of piping with a conventional configuration, but since this radiation is proportional to the fourth power of temperature, the radiation is very small in the low-temperature area and has almost no effect. do not have. In addition, the radiant heat absorbed by the low temperature part of the pipe 7 is taken away by the evaporated gas and the circle anchor 8, and as a result,
Intrusion heat due to radiation through the pipe 7 is suppressed.

Note that the present invention is not limited to the embodiments described above, and various modifications can be made.

That is, in addition to the above-described embodiment in which the emissivity of the inner surface of the pipe 7 is inversely proportional to the temperature of the inner surface, the emissivity of the portion where the thermal anchor 8 is provided is made larger than that of the normal temperature section, and When there are a plurality of anchors, this naturally includes the case where the emissivity is made smaller as the temperature of the portion where the anchor is provided is higher.

Furthermore, it is desirable that the emissivity at room temperature be as low as possible, and it is also within the scope of the present invention to reduce the emissivity of the head 10 of the pipe 7 by applying a mirror finish or the like. .

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide a cryostand in which the amount of heat that enters by radiation is extremely small through the piping used for injection of cryogenic refrigerant, collection of evaporated gas, guidance of current leads, etc. .

[Brief explanation of the drawing]

The figure is a schematic cross-sectional view of a cryostat according to an embodiment of the present invention. 1. Superconducting coil, 2. Cryogenic refrigerant, 3.
...Cryogenic refrigerant container, 4.Vacuum insulation layer, 5.Vacuum container, 6.Heat shield. 7...Piping, 8...Thermal anchor, 9...Small refrigerator agent Patent attorney Noriyuki Chika

Claims (3)

[Claims] (1) A refrigerant container that accommodates a cryogenic refrigerant, a vacuum container that covers the refrigerant container and forms a vacuum insulation layer between the refrigerant container, and a heat shield provided within the insulation layer; In a cryostat, the emissivity of the inner surface of the piping is determined depending on the location of the cryostat, the piping having one end communicating with the refrigerant container and the other end penetrating the vacuum insulation layer, the heat shield, and the wall of the vacuum container and located in the room temperature part. A cryostat characterized by changes. (2) The emissivity of the inner surface of the pipe is inversely proportional to the temperature of the inner surface of the pipe, that is, the higher the inner temperature of the pipe, the lower the emissivity, and the lower the inner temperature of the pipe, the higher the emissivity. The cryostat according to claim (1). (3) When a thermal anchor is present in the piping, the emissivity of the portion of the piping where the thermal anchor is provided is made higher than that of the normal temperature part, and when there are multiple anchors, The cryostat according to claim 1, characterized in that the higher the temperature of the portion where the anchor is provided, the lower the emissivity is.