JPH01147175A - Coating method for cryopanel - Google Patents

Abstract

PURPOSE:To form such coating that is uniform in film thickness in a short time by coating aluminum on the surface of a cryopanel by means of a sputtering process. CONSTITUTION:A vacuum tank 31 is deevacuated by a vacuum pump from an evaculating port 35, and afterward, argon gas is sealed into this vacuum tank 31 from a gas inlet port 34, whereby DC glow discharge is generated there. With this discharge, ionization energy has targets 32A, 32B set up in outer cylinders 31A, 31B inside the vacuum tank subjected to sputtering, whereby aluminum is scattered. The scattered aluminum floats in the vacuum tank 31, and it is stuck and stored up on a cryopanel 30, and thus such an aluminum coating film that is high in stable adhesion is formed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to a neutron injection device (Neutral Beam I).
Regarding the cryopanel, which is a main component of the cryopump (hereinafter referred to as NBI), we form an aluminum coating to reduce the thermal load on the cryopump caused by the penetration of electromagnetic waves due to cyclotron radiation during plasma test equipment operation. Relating to a coating method.

[Conventional technology]

NBI, which is one of the two-stage plasma heating devices, is composed of the equipment shown in FIG. That is, an ion source that supplies hydrogen gas to generate plasma-like high-speed ions 1. A neutralization cell that neutralizes this and converts it into neutral particles, and a magnet that deflects high-speed ion particles.

A beam dump that converts deflected ion particles into heat, a calorimeter that measures the energy of neutralized particles, and a cryopump with 7 and 8 degree partitions that increases the pressure inside the main tank to an ultra-high vacuum state. Beamline equipment including plate 9 etc. 2. The beam line equipment 2 and this beam line equipment 2 are used to introduce neutral particles into the plasma vacuum vessel 5.
A drift tube 3 connects the plasma vessel 5 and the plasma vessel 5, a gate valve 4 separates the plasma vessel 5 from the beam line equipment 2, and prevents the ion source 1 from being influenced by the magnetic fields of various coils provided to confine the plasma. It is composed of a magnetic shield 6 and the like.

The cryopump 7.8 usually consists of the equipment shown in Fig. 56, namely, the cryopanel 11, which consists of two thin plates superimposed in a quilted structure, through which helium He flows to condense and exhaust a large amount of hydrogen gas. ．． A chevron baffle 10 has the largest conductance for hydrogen gas and minimizes radiation transmission from room temperature to the cryopanel, and a shield plate 12 prevents radiation transmission from the tank side plate. Of these, the chevron baffle 10 and the shield plate 12 are cooled with liquid nitrogen LNz and shield the cryopanel 11. In addition, a cryo frame 13 that mutually assembles and connects the cryo panel 11, chevron baffle 10, and shield plate 12, a support insulator 14 that supports and fixes the cryo panel 11 to this cryo frame 13, a chevron baffle 10, and a LN2 There is a manifold 15°LN2 piping that supplies .

The cryopanel 11 has a structure shown in FIG. 6, in which two thin plates are overlapped in a quilted structure, a portion 19 is spot welded, and the end face is closed with TiG welding all around. Supply port 16 and discharge port 1 for liquid helium Llle at the upper and lower ends of the panel
7, and hanging hinges 18 are attached at two locations in the longitudinal direction of the panel. Cryopanels are usually made of stainless steel (SUS316L) in order to encapsulate LHe, but when operating the main body's plasma test equipment, the panel absorbs large electromagnetic waves from the plasma's cyclotron radiation, and the pumping action is affected by the heat load caused by this. It may drop and become impossible to pump. Therefore, it is necessary to apply an aluminum coating on the surface of the cryopanel with a skin thickness several times that of the electromagnetic waves of cyclotron radiation to reduce the heat load. On the other hand, if the aluminum coating is made thicker than necessary, eddy currents will be generated in the cryopanel due to the influence of the magnetic field around the plasma body, and the loss caused by this will conversely increase the heat load on the cryopanel. The upper limit of the thickness is set to be 1.2 times or less the conductivity of the original cryopanel.

Conventionally, the coating film thickness set under these conditions was 0.
Vacuum deposition has been a common method for forming a thickness of about 5 to 2.0 microns. FIG. 7 shows the working status of the aluminum coating method for cryopanels using the vacuum evaporation method. To deposit aluminum on the cryopanel 11 (stainless steel plate), first wash the cryopanel 11 with a neutral detergent, Triflene.

It is thoroughly cleaned using ultrasonic freon vapor, etc., and placed horizontally in the vacuum chamber 20. After that, I
X 10-I! After evacuation to about Torr, the substrate preheating heater 24 and substrate preheating power supply 25 installed near the substrate 28 are heated to 300° C. for about 2 hours to remove dust and organic substances attached to the surface of the cryopanel. , keeping the substrate 28 in an active state. Generally, stainless steel and aluminum cannot be bonded together unless this condition is met. Next, when the evaporation source power source 23 is turned on to the evaporation source heater 22 and the evaporation source 26 placed at a predetermined position is heated and evaporated, aluminum is scattered and deposited on the surface of the cryopanel 11. In addition, an aluminum foil 27 is pasted all around the inner surface of the vacuum chamber 20 to cover the inside of the vacuum chamber so that the heat from the plate heater and the evaporation source heater does not escape, and the inside of the vacuum chamber is not contaminated with scattered objects from the evaporation source. are doing. Incidentally, cryopanels are disclosed in Japanese Patent Application Laid-open No. 142067/1983.

[Problem that the invention seeks to solve]

The adhesion force of aluminum usually depends on the thermal energy of the heating evaporation source 22 and the pretreatment conditions of the cryopanel 11 (mainly the heating temperature and time), but when the area of the cryopanel is 0.5 r! (approximately 550mm x 900m), and the thickness that can be deposited with one heating evaporation is 1000mm~
Since the number of participants was limited to 3,000, there was a drawback that the desired film thickness could not be obtained without replacing the evaporation source 26 many times and repeating evacuation and heating. Furthermore, even when the cryopanel 11 is heated using the preheater 24, the heater can only heat from one side. However, there is an air layer in the middle of the cryopanel, which is made of two laminated plates, and there is a temperature difference between the deposition surface and the heating surface, resulting in a product with poor reliability in terms of adhesion. In addition, aluminum coating films deposited by vacuum evaporation are generally porous and have poor uniformity in film thickness, and if the aluminum coating film is deposited by changing the evaporation source many times, the final coating film may It had the disadvantage of requiring heat treatment such as annealing.

An object of the present invention is to provide a cryopanel coating method that can economically form a cryopanel coating with uniform thickness and high reliability in a short time.

[Means for solving problems]

The present invention utilizes a cathode sputtering method as a method for inexpensively forming an aluminum coating film with a more uniform coating thickness and stronger adhesion than the vacuum evaporation method.
Moreover, both sides of the cryopanel are sputtered at the same time.

[Effect]

If cathode sputtering is used as in the present invention, argon gas particles ionized by the energy generated when ionizing argon gas collide with the target aluminum, and the emitted sputtered aluminum can be deposited on the cryopanel. The energy is 10 to 100 times larger than vacuum evaporation energy,
Formation of an aluminum coating film with stable and high adhesion will be explained with reference to FIGS. 1 to 3.

The general configuration of the vacuum system of the sputtering apparatus in this embodiment is approximately the same as that of the vacuum evaporation apparatus.

In the figure, the pipe supply ports and discharge ports at the upper and lower ends are blocked, the panel surface is polished with a designated paper or material, and then washed with a neutral detergent and soaked in Triclean.

The cryopanel 30, which has undergone pre-treatments such as acetone wiping and ultrasonic freon vapor cleaning, is arranged vertically using a hinge set on the side of the panel and installed in a sputtering fixture. A lead wire is drawn out from this cryopanel 3o, and a high voltage terminal 33 is insulated from the vacuum chamber 31.
and is connected to the positive side of a DC power source 37 via a lead wire 36.

Further, pure aluminum target materials 32A and 32B are embedded in the vacuum chamber outer cylinder 31A and inner cylinder 31B shown in FIG. One side is grounded. In this state, the inside of the vacuum chamber 31 is pumped through the vacuum exhaust port 35 by a vacuum pump.
The vacuum chamber 31 is evacuated to approximately x10'' fiTorr, and then argon (Ar) gas is filled in from the gas inlets 34 provided at several locations in the vacuum chamber 31 to generate a direct current glow discharge.

This glow discharge is influenced by the applied voltage, the pressure inside the vacuum chamber 31, and the gap between the cryopanel 30 and the inner and outer cylinders of the vacuum chamber 31. The ionization energy of Ar due to the discharge sputters the targets 32A and 32B installed in the inner and outer cylinders 31A and 31B of the vacuum chamber, scattering aluminum. These scattered aluminum are inside the vacuum chamber 3.
1 is suspended and deposited on the cryopanel 30 which is rotated within the vacuum chamber by a rotating mechanism as shown in FIG. 3, and a direct current flows through the lead wire 36 outside the vacuum chamber. Does cathode sputtering use Ar gas? I.J.
The ionized Ar gas particles are caused to collide with the target aluminum by the ionization energy of the ionizing energy, and the emitted sputtering aluminum is deposited on the cryopanel 30.The energy is 10~10% compared to the energy of vacuum evaporation. An aluminum coating film that is 100 times larger and has a stable and highly adhesive strength is formed.

When the quality of the film formed in this way is observed using a scanning electron microscope, it is found that the sputtering method is denser and has fewer pinholes than the vapor deposition method.

In addition, unlike in the case of vacuum evaporation, once the material is placed in the vacuum chamber, it can be controlled by simply controlling the voltage, current, and degree of vacuum for 9 hours, and unlike in the case of vacuum evaporation, the evaporation source can be There is no need to replace or heat it. In particular, since there is no need for heating, as shown in Figure 2,
Aluminum coatings can be formed on both sides of the cryopanel simultaneously. The present inventors conducted a heat cycle test 100 times in which an aluminum-coated cryopanel was immersed in an LNz tank and then pulled out and left in the air, but the cathode sputtering method of the present invention did not show any peeling. There wasn't. On the other hand, with vacuum evaporation methods, peeling occurs if the heating method is not successful.

〔Effect of the invention〕

According to the present invention, compared to conventional methods, an aluminum coating film with a uniform thickness and strong adhesion can be produced in a short time and at a low cost, and also can coat both sides of a cryopanel at the same time. provided.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle of the cryopanel aluminum coating method using the cathode sputtering method of the present invention.
Fig. 2 is a longitudinal cross-sectional view of the double-sided coating method, Fig. 3 is a cross-sectional view thereof, Fig. 4 is a diagram showing the general system of NBI,
FIG. 5 is a diagram showing the structure of a cryopump, FIG. 6 is a diagram showing the structure of a cryopanel, and FIG. 7 is a diagram showing a cryopanel aluminum coating method using a vacuum evaporation method. 1...Ion source, 2...Beam line equipment, 3...
・Drift tube, 4... Gate valve, 5... Plasma vacuum vessel, 6... Magnetic shield, 7, 8... Cryopump, 10... Chevron baffle, 11... Cryopanel, 12 ... Shield plate, 15... Manifold, 16... Supply port, 17... Discharge port, 2o
... Vacuum chamber, 21... Vacuum exhaust port, 22... Evaporation source heater, 23... Evaporation source power source, 24... Substrate preheating heater, 25... Substrate preheating power source, 26... evaporation source,
30... Cryopanel, 31... Vacuum chamber, 31A
...Vacuum chamber outer cylinder, 31B...Vacuum chamber inner cylinder, 32.3
2A, 32B...Target, 33...High voltage terminal,
34... Gas inlet, 35... Vacuum exhaust port, 36.
...Lead wire, 37...DC power supply.

Claims (1)

[Claims] 1. The surface of a cryopanel used in a cryopump for condensing and exhausting a large amount of hydrogen gas by stacking two thin plates in a quilted structure and flowing liquid helium therein to condense and exhaust a large amount of hydrogen gas is coated with aluminum. In the method,
Coating is carried out by a cathode sputtering method in which an inert gas is ionized, inert gas particles ionized by the ionization energy collide with the target aluminum, and the sputtering aluminum released thereby is deposited on the cryopanel. Characteristic cryopanel coating method. 2. A cryopanel coating method according to claim 1, characterized in that the cryopanel is arranged vertically and both surfaces of the cryopanel are sputtered simultaneously.