JPS63183279A - Cryopump - Google Patents

Abstract

PURPOSE:To ensure always stable exhaust speed by forming a condensed gas layer of nitrogen in the exhaust exhausted by the cryotrapping action or adsorbing action of the adsorbing medium formed of the condensed gas layer condensed on the exhaust surface having extremely low temperature. CONSTITUTION:When an exhausted vacuum container 19 connected to an intake port flange 18 in a cryopump is evacuated, nitrogen introduced from a nitrogen introducing device 14 through a nitrogen introducing pipe 13 into a nitrogen jetting pipe 12 is sprayed from a nitrogen jet 11 to an exhaust surface 1. Since this exhaust surface 1 is cooled by liquid helium accumulated in a liquid helium reservoir 2 and circulated through a liquid helium inlet 4, gas/liquid separator 3 and liquid helium outlet 5, the sprayed nitrogen is condensed on the exhaust surface 1 to form a condensed layer. Helium in a vacuum container 19 is exhausted through a spepron type baffle 6 by a cryotrapping action of forming the condensed nitrogen layer or adsorbing action of condensed nitrogen layer.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a cryopump having an adsorption medium cooled to an extremely low humidity that exhausts gas by an adsorption action or a cryodrapping action. The adsorption medium is a nitrogen condensation layer condensed on a cryogenic surface.

(Prior Art) A cryopump is a vacuum pump that evacuates gas by condensing or adsorbing it on a surface cooled to an extremely low temperature in a vacuum. Due to its advantages of being able to obtain a relatively high pumping speed and a clean vacuum, it is used in everything from laboratory-scale vacuum vessels to vacuum vessels of large-scale nuclear fusion test equipment.

A cryopump that condenses gas onto a surface that has been cooled to an extremely low temperature and then exhausts it is called a cryocondensation pump. This cryocondensation pump uses liquid helium as a refrigerant, and generally cools the exhaust surface to 4.2K, which is the boiling point of liquid helium. In this case, it is theoretically impossible to exhaust helium.

Hydrogen can only be pumped down to the medium vacuum region. This is because the vapor pressure of hydrogen is higher than other gases even at 4.2 K, and the vapor pressure of helium is even higher than that of hydrogen.

Cryocooling is a method in which a porous material such as activated carbon is cooled using a refrigerant such as liquid helium or a cooling device such as a helium refrigerator to act as an adsorption medium, and the adsorption action of this adsorption medium adsorbs gas and exhausts it. The pump is called a cryosorption pump. By utilizing an adsorption function such as this cryosorption pump, it is possible to pump to a much lower pressure than when using a condensation function at the same cooling temperature. Therefore, by using a cryosorption pump, it is possible to evacuate hydrogen, which is difficult to exhaust with a cryocondensation pump, and helium, which cannot be evacuated. Cryosorption pumps are also widely used because even gases that can be sufficiently exhausted by cryocondensation pumps can be exhausted at a cooling temperature higher than the cooling temperature required for condensation.

It has been reported that gas condensed on the surface of an object cooled to an extremely low temperature acts as an adsorption medium that has an adsorption effect on other gases, and may function as a cryopump. An example of this report is (Hen@evoss and E
, A. TrendelenburgContinuou
sCryotrappiB of ) Iydrogen
and l(elium byArgon at
4.2Ke Vacuum, vol, 17.
p495. 1967). The conclusion of the above literature is that the argon condensation layer that is continuously condensed on the metal surface cooled to 4.2K by liquid helium has a pumping velocity relative to hydrogen and helium.

A cryo-trapping pump is a cryopump that continuously condenses gas on a cryogenic cooling surface to form a condensed layer, thereby trapping and exhausting other gases such as hydrogen and helium.

The trapping effect is called cryotrapping effect.

In particular, when a gas condensation layer that acts as an adsorption medium is not continuously formed, it is called a cryosorption pump that uses the gas condensation layer as an adsorption medium to exhaust gas by adsorption action.

Regarding the cryotrapping effect, see the literature (John F.
・Written by O'Hanlon, translated by Tamotsu Noda and Yasushi Saito, Tsuyoshi Okutani, Vacuum Technology Manual, 1st edition, 2nd printing, page 214, lines 4 to 2 from the bottom, Sangyo Tosho Co., Ltd., first edition published July 30, 1988. ), there is a theory that one gas is simply adsorbed onto the surface or inside of a porous condensation layer of another gas.

For convenience of explanation, cryotrapping is a special case of adsorption using a gas condensation layer as an adsorption medium, and is a case in which a gas condensation layer is continuously formed as an adsorption medium that exhibits adsorption. We will explain this on the assumption that there is no difference in the pumping principle from the adsorption action that uses a discontinuous gas condensation layer as the adsorption medium. The name and function are used to emphasize the continuous formation of a gas condensation layer in a cryosorption pump.

Currently, in order to pump out helium with a cryopump, there are several methods available in the literature (T, 11. Batzer, R, E, Patri).
ck, and V,R.

Ca11. ^TSTA compound cryopu
+mp+ J, Vac, Sci.

Technol,, VOl, 189 No. 3. p
There is an example of an argon trapping cryopump using an argon condensation layer as an adsorption medium, as shown in Fig. H25, April 1981).

We have manufactured a cryopump that pumps out helium by adsorption or cryotrapping using an argon condensation layer as an adsorption medium. When helium was pumped out using this fabricated cryopump, the relationship between pumping speed and helium accumulation amount shown in FIG. 8 was obtained. In FIG. 8, the horizontal axis represents the accumulated amount of helium adsorbed or trapped on or within the argon condensation layer, which increases as helium continues to be pumped out. The vertical axis represents the magnitude of the pumping speed for helium produced by adsorption or cryotrapping using the argon condensation layer as an adsorption medium.

(Problems to be Solved by the Invention) As a result of actual tests conducted at our company, a cryopump that exhausts helium using the adsorption action or cryotrapping action of an argon condensation layer manufactured using the above-mentioned conventional technology is shown in Figure 8. The pumping speed shown in As is clear from FIG. 8, the pumping speed for helium showed rapid fluctuations, such as a sudden decrease as the amount of helium accumulated increased. It has been discovered that this sudden change in pumping speed for helium causes a serious drawback in that the pressure of helium in the vacuum vessel being pumped rises rapidly, making it impossible to maintain the intended pressure. .

In view of the above-mentioned circumstances, the present invention provides a cryosorption pump that uses a gas condensation layer condensed on a cryogenic surface to act as an adsorption medium, and exhausts a gas other than the adsorption medium through the adsorption action or cryotrapping action of the adsorption medium. In,
It is an object of the present invention to provide a lyopump capable of eliminating sudden fluctuations in pumping speed and obtaining a stable pumping speed for gas to be pumped even when the accumulated amount of gas to be pumped is increased.

[Configuration of the invention]

(Means for Solving the Problems) Describe the features of the present invention achieved to achieve the above object. The present invention is to form a gas condensation layer using nitrogen on an extremely low temperature exhaust surface, which acts as an adsorption medium. It is also characterized by being equipped with a nitrogen introduction device for this purpose.

(Created by Jll) According to the present invention, gases such as helium that cannot be evacuated by cryocondensation pumps and hydrogen that is difficult to evacuate are removed by the adsorption or cryotrapping effect of the nitrogen condensation layer formed on the cryogenic surface. Experiments have shown that it is possible to easily pump the air at a stable pumping speed.

(Examples) Example 1 A first example of the present invention will be described below with reference to FIGS. 1 and 2.

In Figures 1 and 2, (1) is the exhaust surface where nitrogen condenses and forms a nitrogen condensation layer that acts as an adsorption medium;
2) is a liquid helium reservoir for cooling the exhaust surface (1);
(3) is a gas-liquid separator for a liquid helium reservoir, (4) is a liquid helium inlet, and (5) is an outlet for evaporated gaseous helium. (6) is a chevron-shaped baffle that has been blackened and cooled with liquid nitrogen; (7) is a radiation shield to reduce heat radiation from parts cooled with liquid helium, such as the exhaust surface (1); (8) is a liquid nitrogen reservoir, (9) is a liquid nitrogen inlet,
(lO) is the outlet for evaporated gaseous nitrogen. (11) is a nitrogen blow-off hole for blowing nitrogen directionally onto the exhaust surface (1), which is provided in a nitrogen blow-off pipe (12) placed in front of the exhaust surface (1).

(13) is from the nitrogen introduction device (14) to the nitrogen blowing pipe (12).
) is a nitrogen introduction pipe that introduces nitrogen to (15) is an auxiliary evacuation device for evacuating the cryopump container (16), (17) is the lid of the cryopump container (16) that supports the entire cryopump, and (18) is the cryopump that is evacuated. Suction i (low flange,
(19) is a vacuum vessel to be evacuated by a cryopump.

Next, the operation of this embodiment will be explained.

Nitrogen introduced from the nitrogen introduction device (14) to the nitrogen blow-off pipe (12) through the nitrogen introduction pipe (13) is passed through the nitrogen blow-off hole (1
Spray from 1) towards the exhaust surface (1). The blown nitrogen condenses on the exhaust surface (1) and forms a condensation layer. The helium in the vacuum vessel (19) is exhausted through the chevron-shaped baffle (6) due to the cryotrapping effect when forming the nitrogen condensation layer or the adsorption effect of the nitrogen condensation layer.

A cryopump that pumps out helium by the cryotrapping action or adsorption action of the nitrogen condensation layer of the first embodiment shown in Figs. 1 and 2 was fabricated and tested, and the experimental results shown in Fig. 3 were obtained. Ta. In FIG. 3, as in FIG. 8, the horizontal axis is the accumulated amount of helium adsorbed or cryotrapped on or within the nitrogen condensation layer.
This amount increases as helium continues to be pumped out.

The vertical axis represents the pumping speed for helium produced by adsorption or cryotrapping using the nitrogen condensation layer as an adsorption medium. According to the experimental results shown in Figure 3, even if the helium accumulation amount shown on the horizontal axis increases, the pumping speed shown on the vertical axis changes gradually. Compared to cryopumps that pump out helium as an adsorption medium, it has become clear that the pumping speed does not suddenly decrease and a much more stable pumping speed can be obtained.

Example 2 Next, a second embodiment shown in FIG. 4 will be described.

FIG. 4 is a longitudinal cross-sectional view of an example of a composite cryopump equipped with an exhaust surface for exhausting helium using a nitrogen condensation layer as an adsorption medium. In Figure 4, (21) is a chevron-shaped auxiliary baffle placed in front of the exhaust surface (1), (22) is a cooling pipe for cooling the auxiliary baffle (21) to liquid helium temperature, and (23) is a cooling pipe. pipe (22)
The auxiliary gas-liquid separator (24) is the auxiliary gas-liquid separator (22)
(25) is the outlet for the evaporated gaseous helium. The rest is as in Example 1.

According to the second embodiment shown in FIG. 4, in addition to the effects of the first embodiment, when a mixed gas containing helium in the vacuum container (19) is exhausted, almost all gases other than helium are at the liquid helium temperature. Only helium reaches and is exhausted from the exhaust surface (1), where a nitrogen condensation layer is formed as an adsorption medium. There is an advantage that the capacity is fully exhibited without being hindered by other gases.

Enemy 3 Next, a third embodiment shown in FIG. 5 will be described.

FIG. 5 is a longitudinal sectional view showing the case where nitrogen is not introduced into a vacuum in front of the exhaust surface (1). In Figure 5, (26) is the cryopump container (
16) This is a nitrogen introduction hole to be introduced into the inside. In order to form the nitrogen condensation layer of the present invention according to the example shown in FIG. 5, the vacuum container (19) to be evacuated and the cryopump container (16) are shut off with a valve (27), and then the nitrogen inlet (26) is opened. This is carried out by introducing nitrogen into the cryopump container (16) using a nitrogen introduction device (14). The introduced nitrogen is on the exhaust surface (1)
It condenses to form a condensation layer.

Thereafter, the valve (27) is opened and the helium in the vacuum container (19) is exhausted by the adsorption action of the nitrogen condensation layer. The rest is as in Example 1. According to this method, there is no need to pipe the nitrogen introduction pipe to the front of the exhaust surface (1), so there is an advantage that the structure in front of the exhaust surface is simplified.

Other effects are as in Example 1.

Example 4 Next, a fourth embodiment shown in FIG. 6 will be described.

FIG. 6 is a longitudinal cross-sectional view of an example in which a refrigerator such as a helium refrigerator is used as a means for cooling the exhaust surface, instead of the means using liquefied gas as a refrigerant as shown in FIG. In Fig. 6, (32), (33) and (34) are respectively about 80K, about 20K and about 20K in the first stage cooling part, second stage cooling part and third stage cooling part of the helium refrigerator (31). Approximately 4
It is cooled to K. The third stage cooling section (34) corresponds to the liquid helium reservoir (2) of the first embodiment. (The heat exchanger, JT valve, and piping for the helium working fluid are not shown.) (1) The cooling plate (36) made of metal or the like with good heat conduction is cooled in the third stage cooling section (34). On the gas exhaust surface, nitrogen released from the nitrogen introducing device (14) through the nitrogen introducing pipe (13) into the vacuum from the nitrogen blowing hole (11) of the nitrogen blowing pipe (12) forms a condensed layer and acts as an adsorption medium. This is the exhaust side. (6) is a chevron-shaped baffle cooled by the first stage cooling section (32) for reducing radiant heat of the exhaust surface (1).

(38) is a radiation shield cooled by the first stage cooling section.

According to the configuration shown in FIG. 6, since liquefied gas is not used as a refrigerant, there is an advantage that the cryopump can be handled only for a limited time.

Example 5 Next, a fifth embodiment shown in FIG. 7 will be described.

FIG. 7 shows, in longitudinal section, another case in which a helium refrigerator is used as means for cooling the exhaust surface. In Figure 7 (21
) is a chevron-shaped auxiliary baffle that is cooled to about 4K by the third stage cooling section (34).

(40) is a radiation shield cooled by the third stage cooling section (34). The exhaust surface (1), which forms a nitrogen condensation layer as adsorption medium by the nitrogen introduction device (14), is located inside the chevron-shaped baffles (6), (22).

The action of the chevron-shaped baffles (6) and (21) is similar to that of the chevron-shaped baffles (6) and (21) in FIG. 4 of Example 2, respectively.
21) is the same as that explained above. According to this method, the composite cryopump that pumps out a mixture of helium and gases other than helium, as shown in Figure 4, can be constructed without using liquefied gas as a refrigerant, which simplifies the handling of the cryopump. There are some advantages.

〔Effect of the invention〕

As explained above, according to the present invention, a gas condensation layer condensed on a cryogenic exhaust surface is used as an adsorption medium.

In a cryopump that exhausts air by the cryotrapping action or adsorption action of this adsorption medium.

Since the gas condensation layer is made of nitrogen, the pumping speed of helium and other gases to be pumped out has a stable pumping speed that does not fluctuate rapidly even when the amount of gas to be pumped out on the exhaust surface increases. It is now possible to provide cryopumps.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing a first embodiment of the cryopump of the present invention. 2 is a sectional view taken along the line A-A in FIG. 1, and FIG. 3 is a curve diagram showing the relationship between the pumping speed of helium and the amount of helium accumulated in the cryopump of the first embodiment. 4 to 7 are longitudinal sectional views showing second to fifth embodiments. FIG. 8 is a curve diagram showing the relationship between the pumping speed of helium and the amount of helium accumulated in a conventional cryopump. (Explanation of symbols) 1... Exhaust surface, 2... Liquid helium reservoir, 3... Gas-liquid separator, 4... Liquid helium inlet, 5... Gaseous helium outlet, 6.
... Baffle, 7... Radiation shield, 8.
...Liquid nitrogen reservoir, 9...Liquid nitrogen inlet, 1
0... Gaseous nitrogen outlet. 11...Nitrogen blow-off hole, 12...Nitrogen blow-off pipe, 13...Nitrogen introduction pipe, 14...Nitrogen introduction device. 15... Auxiliary exhaust device, 16... Cryo, pump container, 17... Lid, 18...
Inlet flange, 19... vacuum container,
21... Auxiliary baffle. 22...Liquid helium cooling pipe, 23...Auxiliary gas-liquid separator, 24...Liquid helium inlet, 25...Liquid helium outlet, 26...Nitrogen introduction hole, 27
···valve. 31... Helium refrigerator, 32... First stage cooling section, 33... Second stage cooling section, 34...
- Third stage cooling section, 36... cooling plate. 38... Radiation shield cooled by the first stage cooling section. 40... Radiation shield cooled by the third stage cooling section.

Claims (3)

[Claims] (1) Nitrogen introduction to form a nitrogen condensation layer by introducing nitrogen into the cryopump container connected to the vacuum container to be evacuated, the exhaust surface housed in the cryopump container and cooled to an extremely low temperature, and the exhaust surface. A cryopump characterized by being equipped with a device. (2) The cryopump according to claim 1, wherein the gas to be exhausted contains helium as one of its main components. (3) The cryopump according to claim 1, wherein the gas to be exhausted contains hydrogen as one of its main components.