JPH0326878A - Complex cryopump - Google Patents

Abstract

PURPOSE:To obtain a cryopump which can be used as helium gas exhaust pump for a nuclear reactor and possesses a large exhaust quantity and the superior safety for activation by previously forming an SF6 gas condensed layer on the cryopanel before exhaust gas adsorption medium for helium gas. CONSTITUTION:A complex cryopump is equipped with a 80K chevron 1, 4K chevron 2, cryopanel 3, SF6 gas introducing pipe 6 and a heat shield 7. When the complex cryopump is operated, the temperature of the 80K chevron 1 is cooled to 80 deg.K, and each temperature of the 4K chevron 2 and the cryopanel 3 is cooled to 4 deg.K, and the temperature of the heat shield 7 is cooled to about 80 deg.K. SF6 gas is introduced into between the 4K chevron 2 and the cryopanel 3 through a gas introducing pipe 6, and condensed onto the cryopanel 3, and an SF6 gas condensed layer 5 is formed. After the SF6 gas condensed layer 5 is formed to a prescribed thickness, exhaust is started.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to a composite cryopump.
More specifically, the present invention relates to a composite cryopump useful as a pump for exhausting helium gas in a nuclear fusion reactor. (Prior art and its problems) Cryopumps have been known as high-speed vacuum pumps for obtaining ultra-high vacuums of 10-2 to 10-'Torr or more, but in recent years, cryopumps have been known as It is also being considered to use this as a pump for exhausting helium gas generated by the reaction between deuterium and tritium in a reactor. Usually, in this cryopump, the surface of the pump's internal container is cooled to a temperature of liquid hydrogen or liquid helium, and the gas to be evacuated is ammed onto the surface. Figures 2 and 3 show an example of a proposal to use such a cross-sectional structure near the surface of a vessel as a helium pump for a nuclear fusion reactor. For example, the cryopump shown in Figure 2 has an 80K chevron (1) to reduce radiation from the atmosphere, a 4K chevron (2) to exhaust deuterium and tritium, and helium gas exhausted from the fusion reactor. It has a composite structure in which a cryopanel (3) is installed, which serves as the exhaust surface. The cryopanel (3) is used after being cooled to approximately 4K with liquid helium in order to capture the helium gas exhausted from the fusion reactor, but it is also coated with a porous solid material (4) such as activated carbon or molecular sieve on its surface. It is attached with adhesive, which allows it to adsorb helium gas from the fusion reactor. Like the cryopump shown in FIG. 2 above, the cryopump illustrated in FIG. Inside, a new gas condensation layer (5) of argon gas, etc. is constantly formed on the surface of the cryovanel (3).This allows the helium gas exhausted from the fusion reactor to entrain and condense. For example, according to the cryopumps that have been proposed so far, as illustrated in Figures 2 and 3, it is theoretically possible to exhaust helium gas from a nuclear fusion reactor. An exhaust pump used in a fusion reactor must not only have the function of simply exhausting helium gas from the fusion reactor, but must also have a large displacement capacity and ensure safety against activation. However, in the example of the cryobump shown in Figure 2, there is a drawback that the adhesive that adheres the porous solid material (4) to the cryopanel (3) becomes radioactive, and due to fatigue of the adhesive, the porous solid material ( 4) is peeled off.Also, in the cryopump example shown in Figure 3, there is a problem that the gas that entrains and condenses helium gas itself becomes radioactive; about 50 of
Since it is necessary to introduce more than double the amount of gas, there is a problem that the gas flows into the plasma of the fusion reactor, causing an increase in the impurity concentration in the plasma. All of these problems remain unresolved issues.This invention was made based on the above circumstances, and can also be used as a helium gas pump for fusion reactors. The aim is to provide a cryopump with a large displacement and excellent safety against activation. (Measures for Solving the Problems Vi) This invention solves the above problems by forming an SF & gas condensation layer in advance on the cryopanel as an adsorption medium for helium gas before evacuation. We provide a composite cryopump featuring the following. The composite cryopump of the present invention can have a composite structure using chevrons cooled to a predetermined temperature as appropriate, like conventional composite cryopumps, but in order to make it possible to exhaust helium gas, Before evacuation, a layer of SF6 gas condensation is formed on the flannel using a cryono,
After that, exhaust gas is started and the exhaust gas is adsorbed into this gas condensation layer. In forming the SF6 gas autsm, the cryopanel is cooled and the SF6 gas autsm is formed to form a condensation layer there.
6 gases should be introduced. In this case, for example, the gas W is cooled to the temperature of liquid helium. The formed SF 4 gas condensation layer becomes a porous layer and has very good contact with the cryopanel, making it an excellent exhaust gas adsorption medium. If this gas condensation layer sufficiently adsorbs exhaust gas and the adsorption function decreases, the exhaust is temporarily interrupted, the temperature of the cryopanel is raised to vaporize the gas condensation layer, and then the cryopanel is cooled down. All you have to do is form a new gas condensation layer and restart the exhaust. When re-forming the gas condensation layer in this way, for example, as in the conventional entrainment condensation method shown in Figure 3, a large amount of gas such as argon used to condense the exhaust gas is introduced. do not have to. When the cryopump of this invention is used as a helium gas exhaust pump in a fusion reactor, there are no problems with activation of the gas itself or flow into the plasma. The SF4 (sulfur hexafluoride) gas that forms the gas condensation layer is thermally and chemically stable and has condensation and vaporization properties.
A gas condensation layer suitable as a helium adsorption medium can be formed. Hereinafter, the composite cryopump of the present invention will be specifically explained based on examples. FIG. 1 is a partial sectional view showing an example of the present invention.
Note that the same reference numerals are given to the same components as those of the conventional cryopump.

The composite cryopump shown in this example includes an 80K chevron (1), a 4K chevron (2), and a cryopanel (3).
), S.F. It has a gas inlet pipe (6) and a heat shield (7). To operate this compound cryopump, first
Cool the temperature of the K chevron (1) to 80K, the temperature of the 4K chevron (2) and cryopanel (3) to about 4K, and the temperature of the heat shield (7) to about 80K. And SF. Gas is introduced between the 4K chevron (2) and the cryopanel (3) through the gas introduction pipe (6), and is condensed on the cryopanel (3) to form a gas condensation layer (5) of S Fa. , SF* gas condensation layer (5) to a predetermined thickness, evacuation is started.

When used as an exhaust pump for a fusion reactor, helium, deuterium, and tritium are exhausted from the plasma side of the fusion reactor when exhaust begins, but deuterium and tritium are 4K chevrons. (2) allows all condensation to be exhausted. The helium gas that was not condensed and exhausted by the 4K chevron (2) is stored in the S on the cryopanel (3).
The F & gas reaches the ms layer (5) where it is adsorbed and exhausted. In this way, according to the composite cryopump of the present invention, helium gas discharged from a fusion reactor can be exhausted with high efficiency. SF. Gas “Ii condensed layer (5
), the helium gas adsorption capacity of the SF.
Gas 'Ii condensation layer (5) is vaporized, then the cryopanel (3) is cooled again, SF.gas is introduced and a new S
F. A gas condensation layer (5) is formed. In this way, evacuation can be resumed after the SF gas condensation layer (5) is re-formed. When used as a helium gas exhaust pump in a fusion reactor, it has a large displacement, is safe against activation, and has excellent functionality and ultra-high performance without unnecessary gas flowing into the fusion reactor. Becomes a vacuum bong,

[Brief explanation of drawings]

FIG. 1 is a partial sectional view showing the vicinity of the cryopanel of the composite cryopump of the present invention. Figures 2 and 3
The figure is a cross-sectional view showing the vicinity of the cryopanel of a conventional cryopump. 1...80K Chevron 2...4K Chevron 3...Cryopanel 4...Porous solid material 5...Gas condensation layer 6...SF6 gas introduction tube 7...Heat shield Fig. 1

Claims (2)

[Claims] (1) A composite cryopump characterized in that an SF_6 gas condensation layer is previously formed on the cryopanel as an adsorption medium for helium gas before evacuation. (2) The composite cryopump according to claim (1), wherein the cryopanel is cooled to liquid helium temperature and helium gas is exhausted.