JPH0432956B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a large-capacity cryopump used as a pump for evacuation.

[Technical background of the invention and its problems]

The outline of the structure of a cryopump used as a vacuum evacuation pump is shown in FIG. In Figure 1, 1 is the cryopanel.
It is cooled with liquid helium at a temperature of 4.2K or below. The cryopanel 1 is surrounded by a shield plate 2 cooled with liquid nitrogen at approximately 80K, except for the exhaust opening, and the opening is covered with a corrugated chevron buttful or louver blind 3 (lined in the figure). Although it is shown in , it actually has a thin plate, and the same is true for other figures). The evacuation action of the cryopump directs residual gas molecules in the vacuum container 4 through an opening such as a chevron buttful or a louver blind 3,
This is caused by condensation and adsorption on the surface of the cryopanel 1 that has been cooled to a temperature of 4.2K or lower.

The cryopump is characterized by several l/sec per unit opening area in a vacuum of about 10 ^-6 Torr.
cm ² and has a large pumping speed. Important factors that determine this pumping speed include the shape of the opening, ie, the opening angle of the chevron buttle or louver blind, the mounting pitch, etc.

Recently, as shown in Figure 2, cryopanel 1
A unit type cryopump in which a plurality of cryopump units 6 using a louver blind 3 and a cryopump unit 6 are arranged substantially in parallel has been devised. The louver blind 3 is characterized in that the gas molecule passage probability η is approximately twice as large as the passage probability of the chevron buffle. FIG. 3 shows the detailed shape of a part of it.

As shown in FIG. 3, the cryopanel 1 is arranged parallel to the gas molecule entry direction 5, and θ ₁
Louvers 3 with an opening angle of are provided at a constant pitch. When the distance between each unit 6 is a and the width of each unit 6 is b, the passage probability η of gas molecules per unit 6 is determined by the following equation.

η=η _a ·a/(a+b) Here, η _a represents the probability of passage between the units 6. The probability of passage η _a between the units 6 is determined by the shape of the baffle plate or louver blind 3 and the shape of the shield plate 2.

By the way, in the shape of the opening 7 as shown in FIG. 3, gas molecules entering from the front surface of the opening 7 in the entrance direction 5 travel straight and hit the shield plate 2 on the back surface.
Some things are reflected and fly out from the opening 7. The flying gas molecules restrict the probability of passage η _a between the units 6. Therefore, in order to increase the pumping speed, if the gas molecules that entered the opening 7 are prevented from jumping out, the probability of passage η _a between the units 6 increases, and the pumping speed becomes faster. It gets faster.

[Purpose of the invention]

An object of the present invention is to provide a cryopump having a large capacity and a high pumping speed.

[Summary of the invention]

In the present invention, a plurality of cryopump units each including a cryopanel cooled by liquid helium and a louver blind cooled by liquid nitrogen are arranged on both sides of the cryopump unit, and a liquid In a cryopump configured with a shield plate cooled by nitrogen, a mountain-shaped reflective part is provided on the side of the opening between each cryopump unit of the shield plate, so that light enters the shield plate from the opening and The gas molecules reflected by the plate are actively made to reach the cryopump unit, reducing the number of gas molecules that jump out of the opening, increasing the probability of gas molecules passing through the opening, and increasing the pumping speed of the cryopump. It is something.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. Incidentally, the overall schematic structure is as shown in FIG. 2, and since this embodiment is the shield plate 2 of FIG. 2 as shown in FIG. 4, please also refer to FIG. In FIG. 4, parts that are the same as those in FIG. 3 are given the same reference numerals, and explanations will be added although some overlap.

A plurality of cryopanels 1 cooled by liquid helium are arranged substantially parallel to the traveling direction 5 of gas molecules, and louver blinds 3 cooled by liquid nitrogen are arranged on both sides of each, each forming a cryopump unit 6. are doing. The surface of the louver blind 3 is blackened to have an emissivity close to 1. Further, on the back side, a shield plate 2 is arranged which is bent by press working and has a reflective part 8 projecting in the shape of a mountain toward the opening 7 side. This shield plate 2 is cooled with liquid nitrogen, and the surface on the cryopump unit 6 side is blackened to have an emissivity close to 1.

Next, the effect will be explained.

Gas molecules traveling straight toward the shield plate 2 from the opening 7 side are reflected toward the cryopump unit 6 by the mountain-shaped reflecting portion 8, so that they easily reach the cryopanel 1 surface. Therefore, the number of gas molecules flying out from the opening 7 is reduced. This increases the probability of gas molecules passing through the opening 7,
Increase pumping speed as a cryopump.

In another embodiment shown in FIG. 5, a separately manufactured angle-shaped reflector plate 9 is attached to the shield plate 2 as the reflector 8 by bolts, nuts, or welding (not shown). The rest is the same as the embodiment shown in FIG.

In this way, an existing cryopump can be easily modified, and other effects are the same as those of the embodiment shown in FIG.

〔Effect of the invention〕

As explained above, according to the present invention, gas molecules traveling straight from the opening are reflected toward the cryopump unit by the mountain-shaped reflecting portion provided on the shield plate. A cryopump can be obtained in which the passage probability of gas molecules is increased, and therefore the pumping speed is increased.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a cryopump, FIG. 2 is a cross-sectional view showing the main parts of a conventional cryopump, and FIG. 3 is a cross-sectional view showing two units in FIG. 2 enlarged. FIGS. 4 and 5 are sectional views showing essential parts of different embodiments of the cryopump of the present invention. 1... Cryopanel, 2... Shield plate, 3
... Louver blind, 5 ... Gas molecule traveling direction, 6 ... Unit, 7 ... Opening, 8 ... Reflection section, 9 ... Chevron-shaped reflection plate.

Claims (1)

[Claims] 1. A plurality of cryopump units each including a cryopanel cooled by liquid helium and a louver blind cooled by liquid nitrogen arranged on both sides of the cryopump unit are arranged approximately in parallel, and a cryopump unit is arranged on the back side of this group of cryopump units. A cryopump configured with a shield plate cooled by liquid nitrogen, characterized in that a reflective part protruding in the shape of a mountain is provided on the side of the opening between each cryopump unit of the shield plate. 2. The cryopump according to claim 1, wherein the reflecting portion is formed by bending a shield plate. 3. Claim 1, characterized in that the reflecting portion is a chevron-shaped reflecting plate formed separately from the shield plate.
Cryopump described in section.