JPS59119076A - Cryopump - Google Patents

Abstract

PURPOSE:To facilitate assembling, disassembling and repairing of a cryopump, by covering the outside of a liquid helium reservoir and an upper liquid helium reservoir by partition plates, and suspending them from a cap of a vacuum vessel. CONSTITUTION:An upper liquid helium reservoir 31 is disposed above a liquid helium reservoir 2, and the outside of the upper liquid helium reservoir 31 and the liquid helium reservoir 2 excluding the outer surface 2a of the bottom of the reservoir 2 is covered completely by partition plates 210a, 210b. These two reservoirs 2, 31 are suspended from a cap 103 of a vacuum vessel. With such an arrangement, assembling and disassembling of a cryopump can be facilitated. Further, even if the inner liquid helium reservoir 2 or the upper liquid helium reservoir 31 is damaged after assembling of the cryopump is completed, they can be repaired with ease by taking out the reservoirs to the outside of the vacuum vessel 101, 102 together with the cap 103 and cutting and removing the partition plate 210a or 210b.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a cryopump used in ultra-high vacuum devices, nuclear fusion devices, and the like.

[Technical background of the invention and its problems]

Cryopumps (cryo pumps include type A, such as "cryocondensation pumps, cryosorption pumps, and taliotrapping," but here we will use "cryocondensation pumps" as an example.) A metal surface placed on a metal surface is heated with liquid helium (
The temperature of liquid helium at atmospheric pressure is 4.20. The metal surface (this is called the "cryo surface") is cooled with a refrigerant such as
This is a vacuum pump that lowers the pressure inside a vacuum container by condensing and depositing the Since liquid helium is usually expensive, the area around the part to be cooled with multi-liquid helium containing liquid helium should be cooled with liquid nitrogen (liquid nitrogen temperature at atmospheric pressure is 77°). It is common to surround it with a shield plate (referred to as a "shield plate") and vacuum insulate it to reduce the consumption (evaporation amount) of liquid helium.

However, since it is necessary to condense and adhere the exhaust gas molecules to the cryo surface, the chevron baffle (usually made of aluminum or The structure is such that it is not possible to see directly from one side to the other, but the gas molecules to be exhausted can pass through the gaps between the plates. ).Hereinafter, the name "cryo pump" will refer to these generic terms.

FIG. 1 shows the configuration of a conventional cryopump. In the figure, 1 is a vacuum container, 2 is a liquid helium reservoir, 20 is liquid helium stored inside the liquid helium reservoir 2, and 20a is the liquid level. 21 is the liquid helium reservoir 2, excluding the bottom outer surface 2a of the liquid helium reservoir 2.
The space 23 inside is a partition plate that covers the periphery of the exhaust pipe 2.
2, the vacuum can be evacuated by an auxiliary vacuum pump 5" installed outside the vacuum container 1. 3 is a liquid nitrogen reservoir installed to surround the liquid helium reservoir 2, and 30 is a liquid helium reservoir 2. Liquid nitrogen is stored inside the nitrogen reservoir 3, and 30a is its liquid level. 4 is a chevron baffle, and the molecules of the gas to be exhausted pass through the gap between the plates on the @ side of the "<" shape. Bottom outer surface 2a of liquid helium reservoir 2
(Since exhaust gas molecules are most likely to condense and adhere to the surface 2sL closest to the chevron baffle 4, this surface is referred to as the "cryo surface."). chevron baffle 4
is fixed around its periphery by a frame 4a, and by connecting the frame 4a to the lower part of the liquid ME reservoir 3 by bolts or welding (not shown), it is cooled to the liquid nitrogen temperature by heat conduction. Reference numeral 5 denotes an auxiliary vacuum pump for reducing the pressure inside the liquid helium reservoir 2 to below atmospheric pressure, and is usually installed outside the vacuum container 1. 5' is for pre-evacuating the inside of the vacuum container 1 before supplying the refrigerant (general term for liquid helium, liquid nitrogen, etc.) (in order to reduce the consumption (evaporation amount) of the refrigerant, it is necessary to perform vacuum insulation. .) Another auxiliary vacuum pump installed outside the energized vacuum container 1.

A liquid helium supply pipe 6 supplies liquid helium 20 to the aircraft helium reservoir 2, and is connected via a stop valve 7 to a supply pipe 8 from a liquid helium container installed outside (the inside of the container is normally at atmospheric pressure). 9 is a helium gas discharge pipe for discharging evaporated helium gas to the outside. 9 is a helium gas discharge pipe for discharging evaporated helium gas to the outside. 6k is connected to the auxiliary wall pump 5 via a helium gas control valve 10 and an exhaust pipe 11. .

12 is a liquid nitrogen supply pipe for supplying liquid nitrogen 30 to the liquid nitrogen reservoir 3, and 13 is a nitrogen gas discharge pipe for releasing nitrogen gas evaporated in the liquid nitrogen reservoir 3 to the outside. Reference numeral 14 designates another vacuum container (for example, a vacuum container for an ultra-high vacuum space or a nuclear fusion device) that is evacuated by this cryopump, and the vacuum container 1 and the vacuum sealing gasket 15 are sandwiched between them. 16 and nut 17. Reference numeral 18 indicates a vacuum space (referred to as "ultra-high vacuum space") which is coagulated and evacuated by the cryo surface 2a.

The liquid helium 20 stored in the liquid helium reservoir 2 is normally at atmospheric pressure, and the liquid temperature (saturated vapor temperature of liquid helium) at that time is 4.20.

However, the exhausted gas (strictly speaking, it is condensed and layered) in the Ri-2 Iop/P is mostly hydrogen gas, and the gas that is condensed and deposited is When the temperature of the surface (surface) is 4.2°, the saturated vapor pressure of hydrogen is 10
In other words, when using a cryopump with a cryo surface temperature of 4.2°, the pressure inside the vacuum vessel will not fall below 10-7 Torr. , the pressure inside the vacuum container is 10
If it is desired to lower the temperature to below the Torr level, the simplest method is to reduce the pressure inside the liquid helium reservoir 2 to below atmospheric pressure and to lower the saturated vapor temperature of the liquid helium 20 to 4.2° or less.

The table below exemplifies the relationship between the saturated vapor pressure and saturated vapor temperature of liquid helium, and the relationship between the saturated vapor pressure of hydrogen when the cryo surface is set equal to the saturated vapor temperature of liquid helium.

〔table〕

In the case of the cryopump shown in Figure 1, the liquid helium reservoir 2
When supplying liquid helium 20, the internal pressure of the liquid helium retainer 2 must be atmospheric pressure, and after the supply is completed, the stop valve 2 of the adult hem/cum supply pipe 6 is closed, and the helium gas regulating valve 10 is closed. It is necessary to open the liquid helium reservoir 2 to an appropriate opening degree and then operate the auxiliary wall pump 5 to reduce the pressure inside the liquid helium reservoir 2 to a predetermined pressure below atmospheric pressure.

When supplying the liquid helium 20, the helium gas control valve is closed and the stop valve 7 is opened to supply the liquid helium 20. At this time, the internal pressure of the liquid helium reservoir 2 becomes atmospheric pressure again.

As mentioned above, the periphery of the liquid helium reservoir 2 is the bottom outer surface 2.
A vacuum space 18 (referred to as an "ultra-high vacuum space") is covered with a partition plate 21 except for a, and the internal space 23 is evacuated by an auxiliary vacuum bonder 5", and is evacuated by a cryoplane 2thK (referred to as "ultra-high vacuum space"). A separate vacuum space 23 (referred to as "auxiliary vacuum space") is formed. This means that when the pressure inside the liquid helium reservoir 2 is reduced to 38 Torr,
The temperature of liquid helium 20 is 2.18°), and liquid helium 20 is in a "superfluid state" (in superfluidity, viscosity disappears,
This is a state in which there is no pressure gradient even though there is a flow. ). At this time, if the constituent materials of the liquid helium reservoir 2 have welds or minute defects that penetrate through the wall thickness, the liquid helium reservoir 2
° is significantly more likely to leak than the normal state (0, which is referred to as the "normal flow state"). Therefore, if you want to lower the pressure inside the vacuum container 1 as low as possible, there is a strong possibility that the liquid helium 20 in the liquid helium reservoir 2 will be in a superfluid state, so the space 20 around the liquid helium reservoir 2 By forming this as a vacuum space separate from the ultra-high vacuum space 18, even if liquid helium 20 in a superfluid state leaks into the auxiliary vacuum space 23, an adverse effect on the ultra-high vacuum space 18 can be prevented. It can be prevented.

With a cryopump configured in this way, it is necessary to assemble the inner parts sequentially during manufacture), and defects may occur in the partition plate 21 or liquid helium reservoir 2 when the cryopump is used after assembly is completed. If leakage into the ultra-high vacuum space 18 occurs, repair is extremely difficult and virtually impossible. (It is necessary to temporarily cut the outer liquid nitrogen reservoir 3 and reassemble it after repairing the inside.) Therefore, when assembling the cryopump, detailed leakage tests and non-destructive inspections are carried out for each process, and the constituent materials are It is necessary to confirm that there are no defects, which is very time-consuming and requires careful attention.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to provide a highly reliable cryopump that is easy to assemble and disassemble, and can be repaired.

[Summary of the invention]

In order to achieve the above object, the present invention provides a liquid helium reservoir that is disposed in a vacuum container consisting of an upper vacuum container and a lower vacuum container, and stores liquid helium at a liquid temperature of 4.2°K or 4.20°C. In the apparatus in which gas molecules to be exhausted are deposited on the outer surface of the bottom and exhausted, an upper liquid nitrogen reservoir for storing liquid nitrogen at a liquid temperature of 77° is provided in the vacuum vessel and above the liquid helium reservoir, and the liquid helium reservoir The surrounding area excluding the bottom outer surface of the liquid nitrogen reservoir and the upper liquid nitrogen reservoir are completely covered with a partition plate, and these are suspended from the lid of the vacuum container, and the partition plate is removed by an auxiliary vacuum pump installed outside the vacuum container. A space between the plate and the liquid helium reservoir and the upper liquid nitrogen reservoir is evacuated to form another vacuum space separated from the vacuum space created by the evacuation of the cryosurface, and An outer liquid nitrogen reservoir for storing liquid nitrogen at a liquid temperature of 770°C is provided on the outside of the partition plate, and a chevron baffle cooled by the liquid nitrogen is attached to the outer surface of the bottom of the reservoir, and these are suspended from the lower vacuum container. , the upper vacuum container is connected to the bottom of the vacuum container and the lower vacuum container.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 shows a cross-sectional view of the structure of the cryopump according to the present invention, and the same parts as in FIG. In FIGS. 2 and 3, 31 is an upper liquid nitrogen reservoir installed above the liquid helium reservoir 2, 30 is liquid nitrogen stored inside the upper liquid nitrogen reservoir 31, and 30a is its liquid level. The surroundings of the liquid helium reservoir 2 and the upper liquid nitrogen reservoir 31 are the bottom outer surface of the liquid helium reservoir 2, ? Except for af, the partition plate 210a,
210b. One end of the partition plate 110a is attached near the bottom of the liquid helium reservoir 2, and the other end is attached by welding or the like to the lower part of the partition plate 210b.

Figure 3 shows how the partition plate 210a is attached to the liquid helium reservoir 2 by welding. The lower end of the partition plate 210h is welded 210W near the outer surface of the bottom of the liquid helium reservoir 2. Of course, the cryo surface 2a cannot be memorized in the auxiliary vacuum space 23, so the cryo surface 2a should not be provided with a bath contact part, and the material constituting this surface should be subjected to non-destructive testing, etc. Care must be taken to use materials free of defects. On the other hand, in FIG. 2, one end of the partition plate 210b is near the bottom of the upper liquid nitrogen reservoir 31, and the other end M is near the bottom of the lid 103 of the vacuum container. It is attached by melting to -#: etc. Therefore, the liquid helium reservoir 2, the upper liquid nitrogen reservoir 31, the partition plates 210a, 210b, etc. are suspended from the lid 103 of the vacuum container. Several small holes 211 are provided at one end of the lower part of the partition plate 210b, and the space 23m formed by the liquid helium reservoir 2, the upper liquid nitrogen reservoir 31, and the partition plate 210a is divided into three holes of the upper liquid nitrogen reservoir. The space 23b formed by the lid 103 of the vacuum container and the partition plate 210bK is connected to the auxiliary vacuum bonder 5'' installed outside via an exhaust pipe 220 provided through the lid 103.
The auxiliary JLC research laboratory 23 is evacuated by the cryo surface 2a and separated from the ultra-high vacuum space 18 by evacuation of the coagulation on the cryo surface 2a.
m, forming 23b. The lower end of the partition plate 21θb is attached near the bottom of the upper liquid nitrogen reservoir 31.
This is to set the temperature of the lower part of the lid 10b and the upper part of the partition plate 210a to liquid nitrogen temperature, and to remove the heat that enters from the room temperature lid 103 through the partition plate 210b by thermal conduction.

32 is an outer liquid nitrogen reservoir provided outside the partition plates 210a and 210b, 30' is liquid nitrogen stored inside, 30a' is the liquid level, and 012' is the liquid nitrogen 3
13' is a liquid nitrogen supply pipe that supplies 0' from the outside, and 13' is a nitrogen gas discharge pipe that discharges the evaporated lid purple gas to the outside.A pipe 13' is a nitrogen gas discharge pipe that discharges the evaporated lid purple gas to the outside. The chevron baffle 4 is joined via the frame 4a by bolts or bath welding (not shown),
The liquid is cooled down to room temperature by heat conduction. These outer liquid nitrogen reservoir 32, chevron baffle 4, etc. are connected to the upper vacuum container 102 by attaching the lower end of the outer partition plate 33 to the outer liquid nitrogen reservoir 32 and the upper end to the upper vacuum container 102 by bath welding or the like. It has a suspended structure.

The lower flange of the upper vacuum container 102 is connected to the upper flange of the lower S-valley vessel 101 with a vacuum sealing gasket 1.
The upper vacuum container 102 is connected to the lid 103 of the vacuum container by a bolt 16" and a nut 17" with a vacuum sealing gasket 15" in between. The cryopump is constructed by connecting the cryopump with the above structure.
In addition to making disassembly easier, even if a defect occurs in the internal liquid helium reservoir 2 or upper liquid nitrogen reservoir 31 after the assembly of the cryopump is completed, the bolts 1 of the lid 103 of the vacuum vessel can be removed.
6", remove the nut 12" and remove the vacuum container 1 together with the lid 103.
By taking out the liquid helium reservoir 2 and the upper liquid nitrogen reservoir 31 to the outside and cutting and removing the partition plate 210a or 210b, the internal liquid helium reservoir 2 and upper liquid nitrogen reservoir 31 can be easily repaired. After repair, only the partition plate 2108 or the partition plate 210b needs to be reattached. In addition, partition plate 2
Reinstalling 10a and 210b also makes it easy to test for leaks at bath contact parts, etc. Furthermore, auxiliary vacuum spaces 23a, 2
3'l) and the ultra-high wall space 18 created by exhausting the cryoplane 2IL are completely separated, so the auxiliary vacuum space 23m
, 23b, even if there is a small amount of dirt or a small leak, it will not cause any problem in the operation of the cryopump as long as it can be evacuated by the auxiliary vacuum pump 5''.

Figure G4 shows another embodiment of the invention, in which bellows fittings 212a and 212b with connecting fittings at both ends are provided in place of the partition plates 210m and 210b in Figure WJ2. By using these thin-walled metal (usually stainless steel) paze tubes 212m and 212b,
The amount of heat intrusion due to heat conduction from the lid 103 of the vacuum container at room temperature can be reduced, and therefore the amount of heat intrusion due to heat conduction into the liquid helium reservoir 2 can be reduced, so the amount of consumption (amount of evaporation) of expensive liquid helium can be reduced. can be reduced.

FIG. 5 also shows another embodiment of the present invention, in which a liquid helium reservoir 41 for depressurization is provided separately from the liquid helium reservoir 2, and the cryopump (see %Reference No. 56-214934) has its bottom outer surface 41g as a cryosurface. ). The partition plate 210C has one end near the bottom of the liquid helium reservoir 41 for depressurization, and the other end is attached to the lower part of the partition plate 210a by welding or the like. 41, Liquid helium flow control valve 4
2. Around the connecting pipe 42pso and the heat exchange section 51, etc.,
This can be done using the partition plate 210C. This partition plate 210
The internal space 23c of C is connected to the partition plate 210 through a through pipe 201.degree. Space 23m inside a, 210 b
, 23b, and is evacuated by an externally installed auxiliary vacuum pump 5'' via an exhaust pipe 220, thereby evacuating the auxiliary vacuum spaces 23m, 23b.

23c is formed. Therefore, in the case of this implementation row, small holes (see FIGS. 2 and 4) provided near the lower end of the partition plate 210b are
211) in the figure becomes unnecessary.

As in this embodiment, auxiliary vacuum spaces 23m and 23b.

As the number of parts housed in the cryopump 23c increases and the number of parts becomes more complicated, this structure is especially useful as the cryopump can be easily assembled and disassembled, and the interior can be repaired.

〔Effect of the invention〕

As explained above, according to the present invention, the area around the liquid helium 1 retainer (including the liquid helium reservoir for depressurization) and the upper liquid nitrogen reservoir is supported by a partition plate, and an ultra-high vacuum space is created by exhausting in the cryo direction. Since a separate auxiliary vacuum space is formed and the structure is suspended from the lid of the vacuum container, assembly and disassembly of the cryopump is easy and the partition plate can be cut.

By removing it, the internal parts can be repaired, and a cryopump that is easy to manufacture and reliable can be provided.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing a conventional cryopump, Fig. 2 is a sectional view showing an embodiment of the present invention, Fig. 3 is a detailed view of a part of Fig. 2, and Fig. 4 is an implementation of the song of the present invention. A sectional view showing U;
FIG. 5 is a sectional view showing an implementation row of ponds according to the present invention. 101...Lower vacuum container, 102...Upper vacuum container, 103...Lid of vacuum container, 2...Liquid helium reservoir, 4...Liquid helium reservoir 12a for pressure reduction. 41a... Cryo surface, 31... Upper liquid nitrogen reservoir, 32... Outer liquid nitrogen reservoir, 33... Outer partition plate, 4... Chevron baffle, 5, 5', 5"...・
Auxiliary Makabe pump, 22o-m trachea, 210a, 210b
. ;110cm partition plate, 23m, 23b, 23cm auxiliary vacuum space, 18... super high empty space. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 Figure 2 Figure 4 Figure 8 Figure 5

Claims (2)

[Claims] (1) A device that collects and evacuates gas molecules to be exhausted on the bottom outer surface of the liquid helium reservoir, which is disposed in a vacuum container consisting of an upper vacuum container and a lower vacuum container, and stores liquid helium at a maximum temperature of 4.2°. An upper liquid nitrogen reservoir for storing liquid nitrogen at a liquid temperature of 770 is provided in the vacuum container above the liquid helium reservoir, and the surroundings of the liquid helium reservoir except for the bottom outer surface and the upper liquid nitrogen reservoir are The surroundings are completely covered with a partition plate and suspended from the lid of the vacuum vessel, and an auxiliary vacuum pump installed outside the vacuum vessel is used to connect the partition plate and the liquid helium reservoir and upper liquid nitrogen reservoir. The space is evacuated to form another vacuum space separated from the vacuum space created by the evacuation of the two ion surfaces, and liquid nitrogen at a liquid temperature of 770°C is added inside the vacuum container and outside the partition plate. An outer liquid nitrogen reservoir is provided, and a chevron baffle cooled by liquid nitrogen is attached to the outer surface of the bottom of the reservoir, and these are suspended from an upper vacuum container, and the upper vacuum container and the lid of the vacuum container are connected to each other. A cryopump characterized by being connected to a lower vacuum vessel. (2) The cryopump according to claim (1), wherein the partition plate is constructed of a thin-walled gold MH bellows tube.