US3536418A - Cryogenic turbo-molecular vacuum pump - Google Patents

Description

Oct. 27, 1970 o. P. BREAUX 3,536,418

CRYOGENIC TURBO-MOLECULAR VACUUM PUMP Filed Feb. 13, 1969 2 sheets-sheet 1 70 j 477Mo SPWM( lol/NP cfm/v e Le ra A @f INVENTOR.

0162/06 l. l 0x BY n/y 0t- 27, 1970 o. P. BREAUX 3,536,418

CRYOGENIC TURBO-MOLECULAR VACUUM PUMP Filed Feb. 15, 1969 `2.snetS14-she@t z g; frz/e Paw/P u Q mw# sw U M5 u u.

IN VEN TOR. a/vz /nf 0. Mtnl WJM" 3,536,418 Patented Oct. 27, 1970 3,536,418 CRYOGENIC TURBO-MOLECULAR VACUUM PUMP Onezime I. Breaux, 104 E. 3rd St., Dayton, Ohio 45402 Filed Feb. 13, 1969, Ser. No. 799,003 Int. Cl. F04b 19/16, 19/22; F17c 7/02 U.S. Cl. 417-49 7 Claims ABSTRACT OF THE DISCLOSURE A turbo-molecular pump is cooled to cryogenic ternperature with liquid helium so that the particles being pumped have very low thermal energy. The outlet pressure of the turbo-molecular pump is reduced to about l-12 torr so that the reduced outlet pressure in combination with the low thermal energy of the particles substantially eliminates backstreaming through the turbomolecular pump thus providing much higher vacuum in the chamber to be evacuated.

BACKGROUND OF THE INVENTION This invention relates to vacuum pumps for obtaining ultrahigh vacuum.

In simulating outer space conditions there is a continuing effort to obtain ultrahigh vacuum. Prior art systems which are used to obtain ultrahigh vacuum are the cryogenic vacuum pump, which is based on the condensation of gases and vapors on metal surfaces which have been cooled by substances at a very low temperature, such as, liquid helium, and the molecular pump wherein the molecules strike a moving surface which gives the molecules a resultant velocity in the direction of motion of the surface. Channels cut in a stator adjacent the moving surface direct the movement of the molecules such that a pumping action is produced. Cryogenio pumps will not effectively pump neon, helium or hydrogen, and molecular pumps suffer from backstreaming. Since these gases are always present in air, a vacuum of about -12 torr has been the limit of prior art pumping systems.

SUMMARY OF THE INVENTION According to this invention, a vacuum pump is provided which gives improved results in obtaining very high vacuums. In the device of the invention, a conventional turbo-molecular pump is cooled with liquid helium. The outlet pressure on the pump is reduced to about 10-12 torr, or lower, by conventional pumping. By reducing the outlet pressure and by cooling theturbo-molecular pump, such that the particles have very low thermal energy, backstreaming through the molecular pump is substantially eliminated. This backstreaming through the molecular pump will be reduced even when neon, helium, and hydrogen are the materials being pumped. Thus the device of the invention may be used to obtain higher vacuum than prior art devices.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a partially schematic block diagram of a high vacuum pumping system according to the invention; and

FIG. 2 is a partially schematic block diagram of another embodiment of the device of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIG. l of the drawing, reference character 10 shows a conventional turbo-molecular pump with a rotor 11 having a shaft 12 and a plurality of radial blades 13 and a stator 15 having a plurality of blades 16 interleaved between blades 13. Such a pump can be found on page 200 of High Vacuum Pumping Equipment, by Powers, Reinhold Publishing Corporation, New York, 1966.

The pump 10 is located within a chamber 17 which is hermetically sealed except at the inlet and outlet and has its rotor 11 supported by conventional magnetic bearing 18 and 19. The magnetic bearings reducing the frictional heat added to the system. The rotor 11 is driven by a `conventional induction motor shown schematically at 20. The rotor 21 and the stator 22 of motor 20 are located within the jacket 23 to reduce the heating effect of the motor by reducing the resistance in the motor windings. Leads L for the stator 22 are brought out through a liquid seal S. The fluid-tight jacket 23 is positioned around chamber 17 and has liquid helium supplied to it from supply 24. A valve 25 controls the flow of helium to jacket 23. The inlet end 26 of pump 10 is connected to the chamber 27 to be evacuated. The outlet ends 28 of pump 10 are connected to a cryo pump 29, a diffusion pump 31 and a roughing pump 33. Valves 34, 35, and 36 are provided to bypass the diffusion pump during initial pump down. Cryogenic pumps can be found in chapter 7 of the text High Vacuum Pumping Equipment reference above. The diffusion pump is described in chapter 2 of the same text. A Roots pump described in chapter 5 or an oil seal pump described in chapter 1 of the same text may be used for the roughing pump.

In the operation of the device, valves 34 and 35 are closed and valve 36 is opened and roughing pump 33 is started to bring the system to approximately 10H3 to 10-5 torr. The pump 10 is then started, the cryo pump 29 is supplied with coolant, valves 34 and 35 are opened and valve 36 is closed. The diffusion pump 31 is then started and the system is pumped to provide a pressure of about 10-12 torr at the outlet of the turbo-molecular pump. The `cryogenic pump 29 reduces backstreaming from the diffusion pump 31. Valve 25 is then opened to admit liquid helium to the jacket 23. With the outlet pressure at the outlets 28 of pump 10, at 10-12 torr, and with the cooling effect of the liquid helium on the turbo-molecular pump, much higher vacuums are attainable in chamber 27.

While one system is shown in FIG. l for attaining a vacuum of 10-12 torr at the outlets 28- of pump 10, other systems may be used, for example, as shown in FIG. 2, a Getter Ion Pump 37, as described in chapter 9 of High Vacuum Pumping Equipment, may be used together with cryogenic pump 29.

The parts within the pumping system are preferably made of stainless steel or other material which will not outgas and contaminate the system. Those parts that cannot be made of stainless steel such as the magnetic bearing, can be covered with stainless steel.

There has thus been provided a vacuum pumping system for obtaining higher vacuum than prior art systems.

I claim:

1. A system for providing very high vacuum in a chamber to be evacuated, comprising: a turbo-molecular pump having an inlet and an outlet: said turbomolecular pump being located within a housing which is hermetically sealed except for said inlet and said outlet; said inlet being connected to said chamber to be evacuated; means for reducing the pressure at the outlet of said turbo-molecular pump to at least 10-12 torr and means for cooling said turbo-molecular pump to approximately the temperature of liquid helium.

2. The device as recited in claim 1 wherein said means for reducing the pressure at the outlet of said turbomolecular pump includes a roughing pump for initial pump down, a diffusion pump for further reducing the pressure to approximately 10-12 torr and a cryogenic pump to impede backflow from the diffusion pump.

3. The device as recited in claim 2 wherein said turbomolecular purnpV has a rotor having means, connected thereto, for inductively driving the rotor through the wall 0f said housing.

4. The device as recited in claim 1 wherein the means for reducing the pressure at the outlet of said turbomolecular pump includes a getter ion pump and a cryogenie pump.

5. The device as recited in claim 4 wherein said turbomolecular pump has a rotor having means, connected thereto, for inductively driving the rotor through the wall of said housing.

6. The device as recited in claim 1 wherein said turbomolecular pump has a rotor having means, connected thereto, for inductively driving the rotor through the wall of said housing.

4 7. The device as recited in claim 6 wherein the turbomolecular pump rotor is supported by magnetic bearings.

References Cited UNITED STATES PATENTS 3,066,849 12/1962 Beams.

3,137,551 6/1964 Mark 62-55.5 XR 3,189,264 6/1965 Becker 230-118 X 3,226,012 12/1965 Trask 230-118 X 3,399,827 9/1968 Schwartzman 230-118 X 3,443,390 5/1969 Webb 62-55.5 3,485,054 12/1969 Hogan G12-55.5

r MARK M. NEWMAN, Primary Examiner 0 W. I. KRAUSS, Assistant Examiner U.S. Cl. X.R.

Images