JPH0742671A - Cryopump with louver blind type baffle - Google Patents

Abstract

PURPOSE:To improve exhaust speed without enlarging a pump. CONSTITUTION:Plural rows of cryopanels 12 are disposed vertically in an 80K shield, and the cryopanels 12 are surrounded by vertical louver type baffles 13 so that the cryopanels 12 are invisible from an intake port (gas inflow port) B. Inside a back face shielding plate 21 opposed to the intake port B, a cryopanel 22 provided with 80K baffles 23 is disposed parallel with the back face shielding plate 21. Hydrogen can be thereby exhausted even at the shield bottom part positioned inside the back face shielding plate 21, so that the exhaust speed can be increased, and in association with this, the size of a cryopump can be made small in comparison to a conventional system in the case of the same exhaust speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryopump having a large pumping speed for hydrogen, which is used in a neutral particle injection device (NBI) for a nuclear fusion experimental device and a plasma science experimental device.

[0002]

2. Description of the Related Art In a cryopump having a large pumping speed of hundreds of thousands / s to several millions / s for hydrogen for a neutral particle injecting apparatus, a large cryopanel is used to increase the pumping speed. is necessary. The cryopanel is usually covered with an outer shield plate so as not to be heated by radiant heat (heat rays) radiated from the outside, and a plurality of louvers having a structure capable of passing gas molecules but blocking radiant heat incident from a gas inlet. It is equipped with a blind type baffle.

Conventionally, in order to obtain a high pumping speed, hydrogen has been exhausted by condensing hydrogen with a cryopanel having a large area. Liquid helium has been used to cool large area cryopanels because of the low temperatures required for hydrogen to condense. Liquid nitrogen is used for cooling the radiation shield of the cryopanel and the baffle.

A louver blind type baffle, which has a high probability of passing hydrogen, is known as a means for increasing the exhaust rate of hydrogen. (As one example, JP-A-61
No. 169682).

FIG. 3 is a schematic structural diagram of a louver blind type cryopump, in which (a) is a front view,
(B) is a cross-sectional view and (c) is a perspective view of a main part. This cryopump has a cryopanel 1 normally arranged in a plurality of rows in the vertical direction in an 80K shield 11 cooled by liquid nitrogen.
2 are arranged, and the periphery thereof is surrounded by a vertical louver type baffle 13 cooled by liquid nitrogen. The cryopanel 12 is hollow, and liquid helium 14 is filled or circulated therein, and is cooled to about 3.2 to 4.2K by the liquid helium 14.

There are various shapes of the cryopanel 12, and the cryopanel 12 is composed of a vertically arranged hollow pipe and a panel made of a material having a high thermal conductivity such as copper or aluminum. There is also known a system in which liquid helium is filled or circulated in the inside to cool it.

FIG. 4 is an explanatory view showing a process in which a louver blind type cryopump exhausts hydrogen. In the figure, the same reference numerals as those shown in FIG. 3 indicate the same or similar parts. In FIG. 4, hydrogen introduced into the vacuum device passes through the vacuum container 1 and is injected into another vacuum device (for example, a torus-type fusion plasma experimental device).
The hydrogen scattered while passing through the vacuum container 1 enters the cryopump 2 as shown in the figure, collides with the shield 11 and the baffle 13, and is condensed and exhausted by the cryopanel 12 cooled with liquid helium. However, the cryopump 2
The total amount of hydrogen that has entered is not captured by the cryopanel 11 and exhausted.

[0008]

The above-mentioned conventional louver blind type cryopump has the following problems.

(I) Since the pumping speed is high and the pumping efficiency is high, the size of the cryopump can be made smaller than that of other cryopumps having the same pumping speed. One factor that determines the exhaust efficiency of this cryopump is the shape of the cryopump. In the process in which the cryopump exhausts hydrogen, first, the light enters the portion B (corresponding to the intake port) in FIG.
Then, after passing through the louver blind type baffles 13 on both sides, only hydrogen that has entered the cryopanel 12 (in the case of liquid He) or the cryosorption panel (in the case of using a helium refrigerator) is exhausted. But,
Since the bottom portion 11a of the 80K shield 11 does not contribute to the exhaust of hydrogen, the hydrogen that reaches the bottom portion 11a is reflected there, and a part of the hydrogen enters the baffle 13, and the molecules that reach the cryopanel 12 are exhausted. However, the rest returns to the inlet (intake port) B again.

(Ii) Therefore, as a method (means) for increasing the exhaust speed of the louver blind type cryopump, a method for optimizing the shape of the baffle is taken, but the exhaust speed is only improved by improving the shape of the baffle. There is a limit to the improvement.

(Iii) Another method (means) for increasing the exhaust speed is to increase the length D of the baffle 13 to increase the portion that contributes to the exhaust, thereby improving the exhaust speed. The cryopump itself becomes large.

The present invention solves the above-mentioned problems of the prior art, and an object of the present invention is to provide a cryopump having a louver blind type baffle capable of improving the exhaust speed without increasing the size of the pump. I am trying.

[0013]

In order to achieve the above object, the present invention provides a cryopanel equipped with a louver blind type baffle which allows gas molecules to pass therethrough but blocks radiant heat incident from a gas inlet. In a cryopump configured to condense or adsorb the hydrogen molecules, a means for adsorbing the inflowing hydrogen molecules consisting of a baffle and a cryopanel inside the rear shield plate facing the gas inlet of the cryopanels arranged in parallel. As a means for adsorbing the hydrogen molecule,
Inside the rear shield plate facing the gas inlet of the cryopanels arranged side by side, in parallel with the rear shield plate,
It features a cryopanel equipped with a K-baffle.

It is also possible to use a cryosorption panel in which an adsorbent is adhered to the surface of the cryopanel.

[0015]

According to the present invention, as described above, the hydrogen comprising the baffle and the cryopanel is provided inside the rear shield plate facing the gas inlet of the cryopanels arranged in parallel, which does not conventionally contribute to the exhaust of hydrogen. Since the means for adsorbing the molecules is provided, the exhaust surface for exhausting hydrogen becomes large and the exhaust speed becomes high.

[0016]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a cross-sectional view of a main part of a cryopump showing an embodiment of the present invention, in which the same reference numerals as those shown in FIGS. 3 to 5 indicate the same or similar parts. .

In the figure, a part of the cryopump (2 in FIG. 4) installed in the vacuum container (1 in FIG. 4) is shown. As shown in FIG. The cryopanels 12 arranged in a plurality of rows (two rows in FIG. 1) in the vertical direction have a louver-type baffle 13 in the vertical direction.
The conventional example (Fig. 3) is that it is surrounded by
However, in the present embodiment (the present invention), the inside of the rear shield plate 21 facing the intake port B corresponding to the gas inlet of the cryopanel 12 arranged in parallel is parallel to the rear shield plate 21. In addition, a cryopanel 22 having an 80K baffle 23 is newly arranged. The above 80K
The baffle 23 is designed so that the cryopanel 22 cannot be seen from the intake port B.

Next, the operation will be described. Intake port B
The hydrogen molecules incident on reach either the baffle 13 or the baffle 23, are scattered here, a part reaches the cryopanel 22 and is exhausted, and the rest is reflected by the baffle 23. It is reflected in the opposite direction. Some of the reflected molecules will return to the intake port B,
The rest of the molecules are incident on one of the baffles 13 and 23 again, and a part thereof is exhausted. The hydrogen molecules repeat such a process and are either exhausted or return to the intake port B.
By the baffle 23 and the cryopanel 22 behind it,
The exhaust speed increases because the portion that contributes to the exhaust increases.

For example, in the case of 45 degree louver baffle 13 with equal baffle intervals, the probability that gas molecules can pass through this baffle is about 0.44. In FIG. 1, when the width a of the intake port is equal to the depth d, the exhaust probability (capture coefficient) of the conventional shape is about 0.54, and the hydrogen capture coefficient of the cryopanel 12 is 1.0. In case of
54% of the hydrogen molecules that have entered the intake port B are exhausted.

However, in the case of the present invention in which hydrogen can be exhausted even at the shield bottom (back), the bottom baffle 23 has the same shape (the width a of the intake port B = the depth d).
When the passage probability is 0.44, which is the same as that of the louver blind baffle 13, the trapping rate is calculated to be about 0.70 because the trapping rate increases as the air is exhausted at the bottom of the shield. The pumping speed can be increased by about 30%. On the contrary, if the pumping speed of hydrogen is the same, the size of the cryopump itself can be made smaller in the present invention, so that the NBI device itself can be made smaller and the manufacturing cost of the entire device can be reduced.

FIG. 2 is a sectional view of a principal part similar to FIG. 1 showing another embodiment of the present invention. In the figure, the same reference numerals as those shown in FIG. 1 indicate the same or similar parts. To do. In this embodiment, the rear shield plate 21 facing the intake port B
A sieve baffle 33 is attached to the inside of the cryopanel 22 arranged in parallel with the shield plate 21. This one also has a shape such that the cryopanel 22 cannot be directly seen from the intake port B.

In the above-mentioned two embodiments, the angle θ of the louver blind baffle 13 may be an angle other than 45 degrees, and the angle need not be constant. The baffle 1
The pitch P of 3 does not have to be a constant interval as long as the cryopanel 12 cannot be seen from the intake port B. Further, the ratio of the width a of the intake port to the depth d may be any value.

As a method for cooling the cryopump,
Liquid nitrogen or liquid helium may be used, or it may be cooled by a helium refrigerator capable of cooling to 20K or less. 20
A cryopump of a type in which helium gas of K or less is circulated for cooling may be used.

In the case of a helium refrigerator capable of cooling to 20K or less, adsorption and exhaust are performed by a cryosorption panel having an adsorbent such as activated carbon adhered to the surface of the cryopanel.

Further, if liquid helium is used as a cooling method for the cryopanel and a cryosorption panel having an adsorbent adhered to the surface of the cryopanel is used,
Helium gas can also be exhausted. That is, this cryopump is applied to gases other than hydrogen, such as helium, deuterium, and tritium, which cannot be exhausted by condensation at 20K, by adopting a cooling method and a structure suitable for the structure of the cryopanel. It is also possible to apply it to a gas such as nitrogen, oxygen, or argon that can be exhausted by condensation at 20K.

[0026]

As described above, according to the present invention,
A cryopump equipped with a louver blind type baffle to condense or adsorb inflowing hydrogen molecules. By providing the means for adsorbing hydrogen molecules consisting of, the following effects can be achieved.

(I) Since the hydrogen can be exhausted even at the shield bottom located inside the back shield plate which has not conventionally contributed to the exhausting action of hydrogen, the exhaust speed can be increased.

(Ii) Since the pumping speed is high, when the pumping speed is the same, the size of the cryopump can be made smaller than that of the conventional system.

(Iii) Since the cryopump can be downsized, the vacuum device such as NBI can also be downsized, and the manufacturing cost of the device can be reduced.

Helium gas can also be exhausted by using a cryosorption panel in which an adsorbent is adhered to the surface of the cryopanel.

[Brief description of drawings]

FIG. 1 is a sectional view of a main part of a cryopump showing an embodiment of the present invention.

FIG. 2 is a sectional view of a main part of a cryopump showing another embodiment of the present invention.

3A is a plan view of relevant parts of a conventional louver blind cryopump, FIG. 3B is a cross-sectional view of relevant parts, and FIG. 3C is a perspective view of relevant parts.

FIG. 4 is an explanatory diagram showing a hydrogen exhaust process of a conventional louver blind cryopump.

FIG. 5 is an explanatory diagram of a main part of a conventional example.

[Explanation of symbols]

 1 Vacuum Container 2 Cryopump 11 Shield 12 Baffle 21 Back Shield Plate 22 Cryopanel 23, 33 Baffle B Intake Port (Gas Inlet)

Claims (3)

[Claims] 1. A cryopump configured to condense or adsorb inflowing hydrogen molecules by a cryopanel equipped with a louver blind type baffle that allows gas molecules to pass but shields radiant heat incident from a gas inlet.
A louver blind type baffle characterized in that a means for adsorbing inflowing hydrogen molecules consisting of a baffle and a cryopanel was provided inside the back shield plate facing the gas inlet of the cryopanels arranged in parallel. Cryo pump. 2. A cryopanel equipped with a 80K baffle is arranged inside the rear shield plate facing the gas inlet of the cryopanels arranged in parallel, in parallel with the rear shield plate. A cryopump provided with the louver blind type baffle according to 1. 3. A cryopump equipped with a louver blind type baffle according to claim 1, wherein a cryosorption panel having an adsorbent adhered to the surface of the cryopanel is used.