JPS61232391A - Cryopump - Google Patents

Abstract

PURPOSE:To set up such a structure of a cryopump as being highly reliable as well as being easily maintain by enabling the cryopump to perform its regenerating operation certainly without provision of any heater or thermocouple located therein but just by heating its surface of extremely low temperature by the use of liquid nitrogen. CONSTITUTION:Two units of cryopumps 1, 2 are driven alternately. In the cryopump to be regenerated in its operation, a valve V2a is closed to stop the supply of liquid helium, and liquid helium is removed from a tank 10a through a vacuum pump 32. Subsequently, only valves V1a, V3a, V4d8a are opened to supply liquid nitrogen from a tank 30 to the liquid helium tank 10a, and a chevron sheet 12 is heated up to 77K to cause regeneration. In addition, only a valve V6a is opened to collect liquid nitrogen into the tank 30 under the pressure of nitrogen gas evaporating within the tank 10a, so that liquid helium may be supplied from a tank 31 to a cryopump 2. Such a regenerating operation is to be performed alternately between the two cryopumps 1, 2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a cryopump, and particularly to a cryopump having a structure suitable for regenerating a cryopump for a nuclear device.

[Background of the invention]

Regarding the regeneration of cryopumps that exhaust and recover deuterium (D2) and tritium (T2) generated in nuclear fusion reactors, Performance of BNL-TSTA
As discussed in Compound CryoPump, a method is adopted in which a cryogenic surface cooled with liquid helium (L Ha ) is heated with a heater to evaporate deuterium D2 and tritium T2 that are condensed on the cryogenic surface. ing.

However, the regeneration method using a heater has the following drawbacks. That is, (1) A thermocouple or a heater for measuring the regeneration temperature of the cryogenic surface is installed on the cryogenic surface, and a lead wire or the like is routed from the cryogenic surface to the outside of the cryopump. The wires are connected to the atmospheric temperature, and heat enters through these wires by conduction, increasing the amount of liquid helium consumed.

(2) The cryogenic surface usually has a chevron shape, and the work of fixing the thermocouple to the chevron plate and guiding it outside the cryopump through a vacuum seal requires skill, and at the same time requires a lot of work to manufacture and assemble the cryopump. time is required.

(3) In cryopumps for nuclear devices, it is necessary to exhaust tritium (T2), which is a radioactive substance.

If a thermocouple or heater breaks, these wires are installed inside the cryopump and cannot be repaired without disassembling the cryopump. However, since the inside of the cryopump is activated by T2, it is not possible to disassemble and repair the cryopump until the radiation dose drops to an acceptable level, and the cryopump will remain broken for a long period of time.

[Purpose of the invention]

An object of the present invention is to provide a cryopump that can perform reliable regeneration without providing a heater or thermocouple inside the cryopump.

[Summary of the invention]

The present invention attempts to perform reliable regeneration without providing a heater or thermocouple within the cryopump by heating the cryogenic surface with liquid nitrogen (LN2).

[Embodiment of the Invention] An embodiment of the cryopump according to the present invention will be described below with reference to FIGS. 1 to 11, using a cryopump for exhausting hydrogen pentatium and tritium as an example.

First, the exhaust system will be explained using FIG.

In the figure, cryopumps 1 and 2 are connected in parallel to the vacuum vessel via a valve 3.5. 7 is a vacuum evacuation unit for rough evacuation and regeneration/recovery, and is connected to the cryopump 1.2 via valves 4 and 6, respectively. The reason why two cryopumps are installed in parallel is to alternately switch between exhaust operation and regeneration operation of the cryopumps.

Next, the schematic structure of the cryopump 1 will be explained using FIG. 3. Cryopump 2 has the same structure as cryopump 1. A radiation shield plate 18 cooled with liquid nitrogen LN is provided in the cryopump chamber, and inside this radiation shield plate 18, two liquid nitrogen LN, tanks B and 15, and one liquid helium L are installed. A He tank 10 is installed. LN, a chevron plate 16.17 is connected to the lower part of the tank 13.15 via a heat transfer pipe,
There is also a chevron plate 12 at the bottom of the L He tank 10.
is connected. The chevron plates 16 and 17 are cooled to about 77K with liquid nitrogen LN2, and are mainly Go2. Condenses and exhausts H, O, etc. Liquid helium LH on the chevron plate
e to about 4.2K, hydrogen (H2), deuterium (
D, tritium (T2) is condensed and exhausted.

Next, the detailed structure of the refrigerant tank and the chevron plate will be explained using FIG. 4. FIG. 4 is a sectional view taken along the line xx in FIG. 3.

At the top of the liquid helium LHe tank 10 is a liquid helium LHe supply pipe 26.

A pipe 25 for discharging evaporated helium (He) gas is provided, and a heat transfer pipe 20°21.23 is provided at the bottom.
, 24 are connected. 22 is also a heat transfer pipe and communicates with other heat transfer pipes 20, 21, 23° 24 at the lower part.

Only the heat transfer pipe 20 is not in contact with the chevron plate 12, and the heat transfer pipes 21, 22, 23, and 24 are welded to the chevron plate 12. Therefore, since the heat load on the heat transfer pipe 20 is small, a flow of liquid helium (L He ) as shown by the arrow in FIG. Chevron plate 12 is cooled to about 4.2K.

As shown in FIG. 4, only the heat transfer pipe 22 is guided outside the cryopump 1 without being directly connected to the liquid helium LHe tank 10, and is used as a recovery pipe for liquid helium LHe as described later.

Next, an embodiment of the present invention will be described in more detail using FIG.

FIG. 1 shows two cryopumps 1 and 1 shown in FIG.
2 shows the hydrogen H2, deuterium D2, and tritium exhaust gas sections, liquid helium (LHe) circuit, and liquid nitrogen (LN2) circuit. Subscripts a and b of number h correspond to cryopumps 1 and 2, respectively. Cryopump 1 L
A pipe 26a provided at the top of the He tank 10a is connected to the L He main tank 31 via a valve V2a and a valve V3a.
It is connected to the LNe main tank 30 via a valve V4b, and further to the pipe 22b of the cryopump 2 via a valve V4b.

The pipe 25a also communicates with the atmosphere via a valve Vla. The pipe 22a is connected to the pipe 25b of the Talaiobompu 2 through the valve V4a, and to the LN2 main tank 30 through the valve V6a.
to the atmosphere via valve V 8 a.

It is connected to the vacuum pump 32 via valve V7a.

The pipes and valves on the cryopump 2 side are also arranged in the same way.

Next, the operation of this embodiment will be explained using FIGS. 5 to 10.

In Figures 5 to 10, arrows indicate L He, L N,
.

The flow of He gas and N2 gas is shown, with filled valves showing open states and white valves showing closed states.

Figure 5 shows cryopump 2 in exhaust operation, cryopump 1 in regeneration operation, and liquid nitrogen (LN2) tank 1.
Liquid nitrogen LN, 14 is supplied to 0a through the valve V 3 a, and the chevron plate 12a is heated to about 77K, and the hydrogen (Ht), deuterium (D,), Evaporate tritium (T2).

That is, the chevron board 12a is being regenerated. The liquid helium (LHe) tank 10b contains liquid helium L.
Hall is supplied via valve V2b to cool the chevron plate 12b to about 4.2 K and condense hydrogen (H,'), deuterium (D2), )-lithium (T2).

In other words, exhaust is being performed. Valves Vla and V8a discharge nitrogen N2 gas, and valves Vlb and V8b discharge helium He gas. in this way.

Since cryopump 1 is regenerated using liquid nitrogen LN, there are no heaters or thermocouples necessary for controlling the regeneration temperature inside the cryopump, and the structure is simple and highly reliable. There are only three pipes 22°25.26 that communicate with the tank, and the amount of liquid helium LHe consumed can be reduced because there is less heat intrusion from the outside. Furthermore, even if the 10,000-valve breaks down, it can be easily and safely repaired because the valve is located outside the talion valve.

Figure 6 shows the regeneration of cryopump 1 completed and liquid nitrogen
This shows the case where N.14 is recovered.

Cryopump 2 is in the same situation as in FIG. Since all the valves connected to the liquid nitrogen (LNs) tank 10a are closed, the pressure of the evaporated nitrogen (N2) gas causes
The liquid nitrogen LN is recovered to the liquid nitrogen LN2 main tank 30 via the valve V6a.

In order to speed up the recovery time of liquid nitrogen LN2, nitrogen N2 gas may be supplied from valve V 1 a.

FIG. 7 shows a state in which the N2 gas remaining in the liquid nitrogen tank 10a and pipes of the cryopump 1 is exhausted by the vacuum pump 32 via the valve V7a.

FIG. 8 shows a state in which the regeneration of the cryopump 1 has been completely completed and the chevron plate 12a is being cooled with liquid helium L Hell before starting the pumping operation. Cryopump 2 is in exhaust operation, but once cooling of cryopump 1 is completed, it will shift to regeneration operation, so liquid helium (L) is used.
He) There is no need to store a large amount of liquid helium (LHe) 11 in the tank fob. Therefore, the cryopump 1 includes a valve V2b for supplying liquid helium (LHe) 11 from the liquid helium LHe main tank 31 and a valve V2b for discharging He gas.
16. Close valve V8b, and conversely open valve V4b to supply part of the liquid helium (LHe) 11 in cryopump 2 to cryopump 1. , t & body helium (LHa) 1
The supply of 1 is He evaporated in the liquid helium tank 10b.
This is done automatically by gas pressure. Liquid helium (L
To speed up the transfer of He) 11, He gas can be supplied from the valve Vlb. When cooling of the cryopump 1 is completed in this state, the cryopump 1 is shifted to exhaust operation and the cryopump 2 is shifted to regeneration operation. In this case, all the liquid helium (LHe) 11 in the tank 10b is transferred to the tank 1.
Move to 0a.

As will be described later, while performing the evacuation operation of the cryopump 2 in this way, the liquid helium (LHe) inside the cryopump 2 is
) 11 to cool the cryopump 1, the regeneration time is shortened, and at the same time, the cryopump 1 is cooled using liquid helium (L He
) consumption decreases. Conventionally, LHe was evaporated by a heater and discharged from the system without being recovered.

Figure 9 shows the liquid helium tank 10b of the cryopump 2.
This shows a state in which the He gas remaining in the pipe is being exhausted by the vacuum pump 32 via the valve V7b. Cryopump 1 is performing exhaust operation and is in the same situation as cryopump 2 in FIG. 5.

In Figure 10, the cryopump 2 is used with liquid nitrogen LN.

14, and the cryopump 1 is performing exhaust operation, and the operation mode is reversed from that in FIG. 5.

FIG. 11 shows the characteristics (broken line A) when the cryopump is regenerated using the embodiments shown in FIGS. 1 to 10 in comparison with the conventional regeneration characteristics (actual MB). Conventionally, the liquid nitrogen L He stored in a tank or pipe was first evaporated using a heater, and then heated to the regeneration temperature T2, so the temperature of the chevron plate varied from T, (approximately 4.2K) to T, (approximately 77K) as shown in FIG. 11B.

- In the strength tree embodiment, after recovering liquid helium LHe, liquid nitrogen LN2 is supplied to heat the chevron plate;
The time required for heating can be shortened, and as shown in FIG.
It can be reduced by 0%. Furthermore, the amount of liquid helium L He consumed can be reduced by about 30% compared to the conventional method.

In this example, liquid helium LHe was transferred between two cryopumps during regeneration, but liquid helium LHs may also be transferred to the liquid helium (LHe) main tank. Although described above, a louver or planar shape may be used.

In addition to cryopumps that condense gas on a cryogenic surface and exhaust the gas, it can also be applied to cryopumps that use adsorbents such as activated carbon at extremely low temperatures to exhaust gas using their low-temperature adsorption properties. can.

(Effects of the Invention) According to the present invention, the cryopump can be regenerated by simply supplying LN from the outside without installing a heater or the like inside the cryopump, making maintenance and inspection of the cryopump easy and reliable. This has the effect of creating a highly functional structure.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of the present invention, Fig. 2 is a diagram of the exhaust system of the cryopump for the device, Fig. 3 is a diagram of the internal structure of the cryopump, and Fig. 4 is taken from the line X-X in Fig. 3. Cross-sectional views, Figures 5 to 10 are diagrams showing the operation of the embodiment shown in Figure 1;
Figure 1 is a diagram showing the regeneration characteristics of a cryopump. 1.2... Cryopump, 11... Liquid helium, 12... Chevron liquid, 14... Liquid nitrogen, ■1
~v8...Valve, 22...Liquid helium recovery pipe,
25... Helium gas discharge pipe, 26... Liquid helium supply pipe.

Claims (1)

[Claims] 1. In a cryopump that exhausts gas by adsorbing or condensing gas on a cryogenic surface cooled by liquid helium, the liquid helium stored in the refrigerant tank and heat transfer pipe in the cryopump is used as a cryopump. A cryopump comprising: a device for transferring liquid nitrogen to the outside; and a device for supplying and discharging liquid nitrogen to the refrigerant tank.