JPH0432957B2 - - 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 vacuum pump.

[Technical background of the invention and its problems]

As shown in FIG. 1, this type of cryopump includes a cryopanel 2 provided in a vacuum chamber 1, surrounded by a radiation shield 4 having an opening 3 on the front side, and a Chevron Bumpful 5 installed in the opening 3. The chevron buff full 5 is subjected to a blackening process so that its emissivity is approximately 1.

Generally, the pumping speed per unit area of the cryopanel excluding the buff of the cryopump has a value approximately equal to the amount of incident gas V expressed by the following equation in the molecular flow region.

V=1/4... (1) Here, V: Volume of gas incident per unit area [cm ³ /
sec・cm ² ]: Arithmetic mean velocity of gas in vacuum [cm/sec] M: Molecular weight of gas R: Gas constant 8.314×10 ⁷ [erg/Kmol] T: Temperature of gas [K] π: Pi According to the above relational expression, the pumping speed of the bare cryopanel for hydrogen gas at a temperature of 293°K is 44.0 [l/sec·cm ² ]. (The following explanation uses hydrogen gas at room temperature as an example.) However, when actually applying a cryopump, it is necessary to provide a radiation shield and a buffer that are cooled with liquid nitrogen in order to reduce the heat load on the cryopanel. This is essential, so that the pumping speed is considerably reduced compared to the pumping speed of the bare cryopanel.

In other words, in the cryopump shown in FIG.
0.23, the pumping speed per unit area of the cryopump is V=1/4η=10.1 [l/sec·cm ² ]. This is because the pumping efficiency of the entire cryopump is equal to the passage probability of the Chevron Batsuful.

However, in the cryopump shown in FIG. 1, the exhaust efficiency of the cryopump as a whole decreases to 0.23 due to the passage probability of the Chevron buffle of 0.23.

As described above, in order to have a cryopump structure with a high pumping speed, it is necessary to configure the cryopanel, radiation shield, and buffle so as not to reduce the pumping efficiency of the entire cryopump.

Therefore, as shown in Figure 2, a modular cryopump using a louver blind buttful was developed.

The above-mentioned modular cryopump has a cooling pipe 8 in a shield plate 7 having an opening 6 on the front surface.
The cryopanel 9 integrated with the shield side plate 7
It is constructed by arranging a plurality of rows parallel to the cryopanels 9a and 7b, and there are louver blind-type buttful plates 1 on both sides of each cryopanel 9.
0 and 10 are also provided with front shield plates 11 of the module adjacent to each other on the front side.
Gas entering from the front opening 6 of the space between adjacent modules is repeatedly reflected inside, reaches the cryopanel 9 or the cooling pipe 8, and is exhausted.

In the above modular cryopump, the width of the front opening 6 is set to a, as shown in FIG.
The width of one module other than the part included in a is b, the number of modules that make up the entire cryopump is n, and the gas particles incident on the front opening 6 reach the cryopanel 9 or the cooling tube 8. Let ηa be the passage probability of exhausting the cryopump, the pumping efficiency η per unit area of the entire cryopump is η=(n-1)a・ηa/{(n-1)a+nb}
...(3) becomes.

The above passage probability ηa varies depending on the shape of the louver blind buttful, the width of the front opening, etc., but in consideration of maximizing the exhaust efficiency η as a practical shape, it is assumed that a = 15 cm and b = 5 cm. ,
It was found that the passage probability ηa was about 0.40.

However, when the entire cryopump is composed of four modules, η = 0.277 from equation (3),
Considering the pumping efficiency only at the front opening, 40% of the incident gas particles are pumped out, and the pumping speed per unit area in this part reaches 17.6 [l/sec cm ² ], but the pumping efficiency as a whole of the cryopump is Considering this, only 27.7% of the incident gas particles are exhausted, and the exhaust velocity per unit area is about 12.2 [l/sec·cm ² ].

In other words, the exhaust efficiency of the cryopump equipped with the louver blind type baffle shown in Figure 2 is 0.40 at the front opening, which is considerably larger than the exhaust efficiency of 0.23 of the cryopump shown in Figure 1, but the exhaust efficiency of the cryopump as a whole is 0.40. Considering the effective area of , the pumping efficiency is greatly reduced from 0.4 to 0.277, and compared to the cryopump shown in FIG. 1, despite having a more complicated structure, the pumping speed is not much different.

On the other hand, in order to increase the pumping efficiency of the cryopump as a whole, a technical measure has been proposed in which the width b is reduced in order to reduce the area of the cryopump that does not contribute to the pumping speed. In order to prevent direct contact between the part and the liquid helium cooling part, the liquid helium cooling pipe 8
If the diameter of the cooling pipe 8 is made small, the vapor lock phenomenon tends to occur in the liquid helium inside, and in this case, the cooling effect of the cryopanel and the cooling pipe is reduced, and the pumping speed is significantly reduced. The problem is that it decreases.

[Purpose of the invention]

The present invention has been made in view of the above points, and
It is an object of the present invention to provide a cryopump that significantly increases pumping efficiency and pumping speed per effective unit area.

[Summary of the invention]

In the present invention, a chevron-type buffle is provided on the front side of a module in which louver blind-type buffles are provided on both sides of a cryopanel, thereby increasing the exhaust efficiency of the cryopump as a whole.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 5, the same members as in FIG. 4 are given the same reference numerals.

In FIG. 5, reference numeral 20 is a Chevron-type buffle, and the surface of the Chevron-type buffle 20 is blackened so that the emissivity is close to 1. The Chevron-type baffle 20 has a width corresponding to the width b, and is arranged in line with the cryopanel 9 so as to maintain the width a of the front opening 6. That is, the longitudinal direction of the chevron-shaped fins is located in the longitudinal direction of the module. The Chevron type baffle 20 has a structure in which it is cooled by liquid nitrogen introduced from a cooling pipe (not shown).

Therefore, if the passage probability of the Chevron-type Batsuful 20 is ηb, the pumping efficiency η of the cryopump is η={(n-1)aη _a +nbη _b }/{(n-1)a+nb
}...(4) becomes.

Here, when calculating with a = 15 cm and b = 5 cm, the passage probability at the front opening 6 is ηa = 0.40.

Note that since the passage probability of the Chevron-type buffful is ηb=0.23, if the entire cryopump is configured with four modules, the pumping efficiency η of the entire cryopump will be 0.348.

That is, the pumping speed per unit area of the entire cryopump is approximately 15.3 [l/sec·cm ² ]. This is about 26% more efficient than the conventional model.

Next, the action will be explained.

Gas particles that have entered the Chevron type baffle 20 on the front side of the module enter the inside of the module depending on the probability of passing through the Chevron type baffle, reach the cryopanel 9 and the cooling pipe 8, and are exhausted. In addition, gas particles entering the cryopump from the front opening 6 of the gap between the modules are
It is reflected by the radiation shield plate 7 and the louver blind baffle 10 on the back, and reaches the cryopanel 9 and the cooling pipe 8 at a certain rate and is exhausted. FIG. 6 shows the pumping efficiency of the cryopump according to the present invention, where the horizontal axis shows the number of cryopump modules that make up the whole cryopump, and the vertical axis shows the pumping efficiency of the whole cryopump. is the present invention, and symbol B is the conventional example.

7 to 10 show other embodiments of the present invention, and in the embodiment shown in FIG. 7, the chevron-shaped buttful 30 is arranged such that the longitudinal direction of the fin is located in the lateral direction of the module. has been done. If the Chevron-type baffle installed on the front of the module has a probability of passage of gas particles exceeding a certain value and prevents heat radiation from the room temperature part to the cryopanel, the structure is suitable for the cooling of the Chevron-type buffle itself. It is determined by considering the method and overall cryopump configuration.

In the embodiment shown in FIG. 8, the cryopanel 40
has a quilted structure, which is effective when the cryopanel is large and the temperature distribution on the cryopanel becomes so large that it cannot be ignored.

In the embodiment shown in FIG. 9, the cryopanel 50
A fin 51 is provided on the front end surface of the module so as to correspond to the front surface of the module, thereby increasing the exhaust efficiency for gas particles passing through the Chevron type buffle 20.

In the embodiment shown in FIG. 10, the frontmost fin 10a of the louver blind buttful 10 is integrally connected to the fins 20a and 20b of the chevron-type buttful 20 provided at the front of the module, and the chevron-type buttful 20 and the louver blind are connected together. Heat radiation from the room temperature section is prevented from directly entering the cryopanel 9 inside the module through the gap in the baffle 10.

〔Effect of the invention〕

As described above, according to the present invention, the pumping efficiency and pumping speed per effective unit area are significantly increased compared to conventional ones, and therefore it is possible to manufacture cryopumps with large capacity and high pumping speed. This has the effect of making it possible.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a cryopump, Figure 2 is a schematic diagram of a modular cryopump using a louver blind buttful, Figure 3 is a cross-sectional view taken along the - line in Figure 2, and Figure 4 is a schematic diagram of a modular cryopump using a louver blind buttful. FIG. 2 is an enlarged view of the main parts of the cryopump, FIG. 5 is an explanatory diagram showing the module configuration of the cryopump according to the present invention,
FIG. 6 is a diagram showing the pumping efficiency of the cryopump, and FIGS. 7 to 10 are diagrams showing other embodiments of the present invention. 6... Opening, 7... Shield plate, 8... Cooling pipe, 9... Cryopanel, 10... Louver blind type buttful plate, 20... Chevron type buttful.

Claims (1)

[Scope of Claims] 1. A module consisting of a cryopanel cooled by liquid helium and louver blind type baffles cooled by liquid nitrogen on both sides of the cryopanel cooled by liquid nitrogen is arranged at a predetermined interval in a vacuum container, and the front opening is A cryopump configured to exhaust gas that has entered a gap between modules, characterized in that a chevron-type buttful is disposed in front of the module. 2. The cryopump according to claim 1, wherein the longitudinal direction of the fins of the chevron-type buttful is located in the longitudinal direction of the module.