JP2905799B2 - Cryopump - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryopump which has a cryogenic cooling surface, condenses and captures gas molecules incident from a gas phase on the cooling surface, and exhausts the inside of a vacuum vessel.

In an accelerator for elementary particles, a nuclear fusion device, a semiconductor manufacturing device, etc., it is extremely important to obtain an ultra-high vacuum environment, and a cryopump is used as a device for realizing such an ultra-high vacuum.

[0003]

2. Description of the Related Art Conventionally, in a liquid storage type cryopump, liquid helium and liquid nitrogen are used as cryogens (since liquid helium is expensive, its surroundings are covered with a liquid nitrogen temperature region so as to suppress the amount of evaporation. ), The gas molecules in the vacuum vessel were evacuated by condensing the gas molecules on the low-temperature cooling surfaces at the temperatures of 4.2K and 78K, thereby realizing an ultra-high vacuum.

In such a cryopump, a chevron baffle provided at a connection portion between the cryopump and a vacuum vessel below the cryopump reflects heat radiation from the wall surface of the vacuum vessel at normal temperature on the baffle surface and transmits through the baffle. In order to prevent the liquid helium from reaching the cooling surface of the liquid helium container, it is entirely blackened.

[0005]

However, in the conventional cryopump, the chevron baffle, as described above, prevents the heat radiation from the wall of the vacuum vessel from being reflected by the baffle and transmitted to the liquid helium vessel. Since it is blackened for the purpose of prevention, there is a problem that the heat absorbed by the baffle inevitably increases, and the consumption of liquid nitrogen used to cool the baffle increases.

SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to reduce the amount of liquid nitrogen used for cooling a chevron baffle by minimizing heat radiation from a vacuum vessel wall. It is an object of the present invention to provide a cryopump capable of performing the following.

[0007]

SUMMARY OF THE INVENTION A cryopump according to the present invention has been devised to achieve the above object, and includes a liquid helium container, a liquid nitrogen container disposed on the liquid helium container, and a liquid nitrogen container. In the cryopump provided with a cylindrical screen shield plate provided to surround the liquid helium container at the lower peripheral edge of the cryopump, and a chevron baffle provided in the lower end of the screen shield plate, An angle-type vacuum vessel is provided in a communicating manner, and a screen coated with a low-emissivity metal thin film is provided on the inner surface of the vacuum vessel .
Electronic refrigeration element clean the outer surface is characterized in that is eclipsed set.

In the above cryopump, the screen
Is cooled by the electronic refrigeration element.

The low-emissivity metal thin film may be coated directly on the inner surface of the vacuum vessel. in this case,
There is no screen, and the electronic refrigeration element is provided on the outer surface of the vacuum vessel.

[0010] The chevron baffle is blackened as a whole and absorbs heat radiation from the vacuum vessel wall to prevent it from penetrating into the liquid helium vessel.

[0011]

EXAMPLES Next, examples of the present invention will be described in order to specifically explain the present invention.

Embodiment 1 In FIGS. 1 and 2, the basic structure of a cryopump (8) is a liquid helium container (1) and a liquid helium container (1).
Liquid nitrogen container (2) and liquid nitrogen container (2)
A cylindrical screen shield plate (3) provided around the lower edge of the liquid helium container (1), and a chevron baffle (4) provided in the lower end of the screen shield plate (3). It is.

The chevron baffle (4) is designed to prevent heat radiation from the vacuum vessel wall at room temperature from being reflected by the baffle face, transmitting through the baffle, and reaching the cooling face of the liquid helium vessel (1). The screen shield plate (3) has a function of absorbing radiation, and functions to block heat radiation incident from the outside.The liquid nitrogen container (2) has a screen shield plate.
(3) and serves to cool the chevron baffle (4). The chevron baffle (4) is entirely blackened.

An angle type vacuum vessel (5) is provided in communication with the lower end opening of the cryopump (8). Vacuum container
(5) On the inner surface, a screen coated with an aluminum thin film with low emissivity (ε = 0.02) by vapor deposition
(6) is provided. The installation range of the screen (6) is
It is a visual field range on the vacuum vessel side of the chevron baffle (4). The vacuum vessel (5) and the screen (6) are thermally insulated. Further, a plurality of electronic refrigeration elements (7) are provided on the outer lower surface of the horizontal bottom of the screen (6), whereby the screen (6) is cooled to a temperature of about 250K.

Embodiment 2 In FIG. 3, the inner surface of the vacuum vessel (5) has a low emissivity (ε
= 0.02) is directly coated by evaporation. The upper end of the vertical part of the vacuum vessel (5) is connected to the lower end opening of the cryopump (8) through a stainless steel bellows-like connecting member (9), and the tip of the horizontal part of the vacuum vessel (5) is also made of stainless steel. Is connected to the conduit (10) through the bellows-like connecting member (9). The connection member may be made of a titanium alloy, plastic, or the like.

In this embodiment, there is no screen,
The electronic refrigeration element (7) is provided on the outer surface of the vacuum vessel (5), and the plurality of vacuum vessels (5) are covered with a heat insulating material (11).

The other structure is the same as that of the first embodiment.

[0018]

[Function] The heat flux transmitted to the blackening chevron baffle (4) by thermal radiation is expressed by the following equation.

[0019] _{Q = ε eff σA 1 (T} 2 4 -T 1 4) Here, the effective thermal _{emissivity, ε eff = ε 1 ε 2} / [ε 2 + (1-ε 2) ε 1 A 1 / A ₂ ] A ₁ : Area of black body chevron baffle A ₂ : Area of vacuum vessel surface T ₁ : Temperature of black body chevron baffle T ₂ : Temperature of vacuum vessel surface σ: Stefan-Boltzmann constant, 5.67 × 10
^-8 [Wm ^-2 K ^-1 ].

Since the chevron baffle is blackened, assuming that ε _{1 is} almost equal to 1, ε _eff = ε ₂ / [ε ₂ + (1−ε ₂ ) A ₁ / A ₂ ].

In order to suppress the above heat flux, T ₂ , ε
_What is necessary is just to make both ₂ small. Suppose that T ₂ = 300K
However, when T ₂ = 250K, Q becomes １ ／. Also, assuming that A ₁ / A ₂ = 1, ε ₂ = 0.1 becomes ε ₂ =
If 0.02, ε _eff = 0.1 becomes ε _eff = 0.0
It becomes 2.

[0022]

Since the cryopump according to the present invention is constructed as described above, the heat radiation from the vacuum vessel wall is reduced as much as possible to reduce the amount of liquid nitrogen used for cooling the chevron baffle. The consumption can be reduced.

[Brief description of the drawings]

FIG. 1 is a vertical vertical sectional view showing a basic configuration of a cryopump.

FIG. 2 is a vertical longitudinal sectional view showing a cryopump provided with a vacuum vessel.

FIG. 3 is a vertical longitudinal sectional view showing a cryopump provided with a vacuum vessel.

[Explanation of symbols]

 1: liquid helium container 2: liquid nitrogen container 3: screen shield plate 4: chevron baffle 5: vacuum container 6: screen 7: electronic refrigeration element 8: cryopump 9: connection member 10: conduit 11: heat insulating material

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masaharu Miki 1-3-5 Oiwa Building 1-3-5 Makuhari Hongo, Hanamigawa-ku, Chiba (72) Inventor Masaharu Furuji 5-3-28 Nishikujo, Konohana-ku, Osaka Inside Shipbuilding Co., Ltd. (72) Inventor Yoshio Kawahito 5-3-28 Nishikujo, Konohana-ku, Osaka-shi Inside Nippon Shipbuilding Co., Ltd. -144085 (JP, U)

Claims (2)

(57) [Claims] 1. A liquid helium container, a liquid nitrogen container disposed on the liquid helium container, a cylindrical screen shield plate provided on a peripheral edge of a lower end of the liquid nitrogen container so as to surround the liquid helium container, In a cryopump provided with a chevron baffle provided in a lower end of a screen shield plate, an angle type vacuum vessel is provided in communication with a lower end opening of the cryopump, and a low-emissivity metal thin film is provided on an inner surface of the vacuum vessel. Is provided , and an electronic refrigeration element is provided on the outer surface of the screen.
A cryopump characterized by being used . 2. A liquid helium container, and a liquid helium container.
Liquid nitrogen container and the lower edge of the liquid nitrogen container
Cylindrical shape provided around the edge of the liquid helium container
Screen shield plate and below the screen shield plate
Client with a chevron baffle provided in the end
Communication with the lower end opening of the cryopump
Angle type vacuum vessel is provided in the shape of
A low-emissivity metal thin film is coated outside the vacuum vessel.
Characterized in that an electronic refrigeration element is provided on the surface.
Rio pump.