US2983433A

US2983433A - Getter ion vacuum pump apparatus

Info

Publication number: US2983433A
Application number: US752591A
Authority: US
Inventors: William A Lloyd; Glen A Huffman
Original assignee: Varian Associates Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1958-08-01
Filing date: 1958-08-01
Publication date: 1961-05-09
Anticipated expiration: 1978-05-09
Also published as: DE1096539B; NL111716C; GB910607A; GB910608A; NL302901A; CH382364A; FR1230921A

Description

} y 1961 w. A. LLOYD El'AL 2,983,433

GETTER ION VACUUM PUMP APPARATUS Filed Aug. 1, 1958 2 Sheets-Sheet 1 INVENTORS' William A. Lloyd Glen A. Huffman Wi /V0522 Attorney May 9, 1961 w. A. LLOYD EI'AL 2,983,433

GETTER ION VACUUM PUMP APPARATUS Filed Aug. 1, 1958 2 Sheets-Sheet 2 j 7 INVENTORS William A. Lloyd y Glen A. Huffman [*T M Attorney William A. Lloyd Los Altos, and Glen A. Huffman, Palo Alto, Calif., assignors to Varian Associates, San Carlos, Calif., a corporation of California Filed Aug. 1, 1958, Ser. No. 752,591 12 Claims. Cl. 230-69) The present invention relates in general to getter ion vacuum pump apparatus and'more specifically, to a novel getter ion vacuum pump configuration in which the pumping speed has been greatly enhanced and which facilitates the use of permanent magnets for supplying the magnetic field. Such high speed vacuum pumps are extremely useful for providing uncontaminated high vacuum as required in many devices such as,-fr example, vacuum tubes, linear accelerators, electron microscopes, ammonia masersand the like.

Heretofore getter ion vacuum pumps have been built in which a plurality of cellular anode members interleaved with a plurality of planar cathode plates were suspended within the interior of a gas tight envelope communicating with a structure it was desired to evacuate.

"The stack of interleaved members was immersed in a. :magnetic field of approximately 1,000 gausses directed substantially perpendicularly to the cathode plates. In :such a pump the pumping speed was enhanced over that previously obtained by the use of unitary cellular anode sandwiched between two cathode plates. One of the difficulties encountered with this prior art vacuum pump has been that the pumping speed is not a linear function of the number of interleaved cathode and anode members. It has been found thatthe impedance that the pump itself offers to the flow of gases into the pump is greatly increased with the length of the stack of interleaved anode and cathode members. This is because the gas must diffuse through a substantial number of the preceding members to get to the pumping members lower down in the stack.

In addition, ithas been-found that the prior art pump configuration is not' well suited to the use of permanent magnets for providing the magnetic field. Electrical solenoids have been utilized, as well as' permanent magnets carried externally of the envelope, but the gap length of the magnets was fairly substantial thereby serving to increase the sizeof the solenoid or the size of the permanent magnets as the case may be.

The present invention provides a getter ion vacuum pump conaining an enlarged central evacuated chamber having a plurality of cellular anode members extending outwardly therefrom as, for example, like the spokes of a wheel. Planar cathode plates are disposed on each side of the individual cellular anode members and the pump envelope is contoured with a plurality of outward protrusions containing therewithin the outwardly extending anode and cathode members. Permanent magnets are carried externally of the pump envelope and between the spoke-like outward protrusions thereof for providing the magnetic field. V W

In the present novel getter ion vacuum pump the internal impedance of the pump to the flow of gases is greatly reduced thereby allowing a vacuum pump, to be constructed of almost indefinite length with a pumping speed proportional toits length. In addition, the novel ni Sta e M) construction of thepresent vacuum pump greatly facilitates the utilization of-reasonably sized permanent magnets carried externally of the vacuum envelope for providing the magneticfield.

The principal object of the present invention is to provide a novel improved high speed, high vacuum, getter ion pump which is useful in providing uncontaminated high vacuums as required in vacuum tubes, linear accelerators, electron microscopes, ammonia masers and the like.

One feature of the present invention is the provision of a novel pump construction having the cathode and anode elements extending outwardly of the pump apparatus as, for example, like the spokes of a wheel whereby the impedance that the pump itself presents to the flow of gases therein is greatly reduced and the utilization of permanent magnets for providing the magnetic field facilitated.

Another feature of the present invention is the pro vision of permanent magnets positioned between the outward protrusions of the pump envelope for providing a magnetic field in a plane substantially at right angles to the longitudinal axis of the pump.

Another feature of the present invention is the provision of a novel easily replaceable pumping element canister including a cellular anode member sandwiched between two planar cathode members extending lengthwise of the canister, whereby replacement of used elements is facilitated.

Another feature of the present invention is the pro.- vision of a spacer member disposed between the cathode plates of the canister assembly for properly spacing apart the cathode plates and preventing undesired buckling of the cathode plates in use.

Other and further features of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein, a

Fig. 1 is a perspective view partially cut away and partially exploded showing the novel vacuum pump of the present invention,

Fig. 2 is an enlarged cross-sectional shortened view of a portion of the structure of Fig. 1 taken along line 22 in the direction of the arrows,

Fig. 3 is a reduced cross-sectional view of a portion of the structure of Fig. 1 taken along line 3-3 in the direction of the arrows,

Fig. 4 is a fragmentary view of the broken away portion of the structure of Fig. 1,

Fig. 5 is an enlarged perspective view of a portion of the structure of Fig. 2 delineated by line 55,

Fig. 6 is an enlarged cross-sectional viewof a portion of the structure of Fig. 5 taken along line 66 in the direction of the arrows,

Fig.- 7 is a cross-sectional view of a portion of the structure of Fig. 6 taken along line 77 in the direction of the arrows, and

Fig. 8 is a cross-sectional view of a sputter ion vacuum pump apparatus of the present invention.

. Referring now to the drawings, Figs. 1-4, there is shown the novel getter ion vacuum pump apparaus of the present invention. More specifically, a tubular envelope 1 is provided with a central rectangular-shaped chamber 2 having a plurality of lesser rectangular chambers 3 outwardly extending therefrom and communicating therewith through longitudinal openings in the side [walls of thecentral rectangular chamber 2. The envelope 1 is made, for example, of a plurality of inch stainless steel plate members which are each suitably bent inan identical. generally stair-step configuration. Four such members are suitably fixed together at adjoining edges spot-welded together.

as by, for example, heliarc welding to form the side Walls of the tubular envelope 1.

The bottom end of the envelope 1 is closed off via an end wall 4 suitably sealed to the side walls of the envelope 1 as by, for example, heliarc Welding. The other end of the envelope 1 is close dolf via a centrally apertured end closing wall 5 as of, for example, stainless steel which is heliarc welded to the side walls of the envelope.

A cylindrical adaptor tubing 6 as of, for example, stainless steel is carried from the apertured end closing Wall 5 and communicates with the central chamber 2 via the central opening in the end closing wall 5. An annular flange 7 as of, for example, stainless steel is suitably grooved and carried from the end of the adaptor tubing 6 in a vacuum tight manner as by, for example, heliarc welding. An exhaust tubing 8 has 'aiiixed thereto a suitably grooved flange 9 and is adapted for communication with the pump envelope 1 for evacuating structures connected thereto, as desired.

Flanges

7 and 9 are pulled together via a plurality of bolts 10 extending through a plurality of apertures provided in the peripheral edge of the flanges. When the

flanges

7 and 9 are pulled tightly against each other they serve to compress therebetween a suitable gasket 11 as of, for example, copper sheet, thereby forming a vacuum tight seal.

A plurality of pumping element canisters 12 are carried within the lesser rectangular chambers 3 communicating with the central chamber 2. The canisters 12 are shown in greater detail in Figs. 5-7 and include rectangular end blocks 13 as of, for example, stainless steel. Cathode plates 14 as of, for example, A; inch reactive material as of, for example, titanium or Zirconium are fixedly secured to the bottom rectangular end block 13 via a plurality of screws 15 extending through apertures in the cathod plates 14 and mating with tapped holes in the end block 13. Other suitable reactive materials are molybdenum, tungsten, tantalum, niobium, iron, chromium, nickel, barium, thorium, magnesium, calcium, strontium, plus other transition elements of the fourth, fifth and sixth groups of the periodic table, including the rare earths. At the upper end block 13 the cathode plates 14 are provided with longitudinal slots therein which slidably receive therewithin pins 16 which are carried from the end block 13. In this manner the plates 14 are made freely slidable with respect to the upper rectangular end block 13 to allow for thermal expansions of the plate 14 but are restrained from moving lengthwise of the block 13 by the pins 16.

The individual pairs of end blocks 13 are fixedly connected together via the intermediaries of rectangular cellular anode 17 as of, for example, titanium sheet metal The cellular anodes 17 are carried within a rectangular frame member 18 as of, for example, stainless steel straps spot-welded to the cellular anodes 17 at a plurality of points lengthwise of the frame member 18. Four studs 19 extend longitudinally from the ends of the frame member 18 and carry therefrom four frusto-conical high voltage insulators 21 as of, for example, ceramic. The insulators 21 are carried at their other'end within cylindrical recesses 22 in end blocks 13 via screws 23.

The cathodev plates 14 of the pumping element canister 12 are slidably mounted with respect to the end block 13 to prevent building up of excessive stresses within the canister 12 occasioned by unequal thermal expansions of the anode member 17, frame 18, and the cathode plates 1 which becomes very hot in use.

An enlarged opening is provided in the cellular anode 17 substantially midway of its length to accommodate two cylindrical cathode spacers 24 as of, for example,

titanium interconnecting the two planar cathode plates 14. The cathode spacers 24 serve to preserve the correct spacing between the cathode plates and to prevent excessive bucklingthereof which'rnight otherwise disturb the correct spacing between the cellular anode 17 and cathode plates 14 in use. The cathode spacers 24 are further made of a reactive material, as of titanium. It has been found that considerable pumping action is attributable to the disintegration of the reactive cathode spacers 24 by ion bombardment.

Rectangular guide tabs 25 as of, for example, stainless steel are fixedly secured substantially at the innermost ends of the guide blocks 13 as by, for example, heliarc welding. Guide retainers 26 are fixedly carried from the inside of the pump envelope 1 as'by, for example, heliarc welding and serve to receive therewithin the guide tabs 25 thereby assuring proper positioning of the pumping element canister 12 within the lesser chambers 3. When in position the pumping element canister 12 bears at the lower most end, at block 13, upon the end closing wall 4.

The upper guide retainers 26 are slotted at 27 to slidably receive therewithin retainer screws 28 which are carried within suitably tapped holes in the guide tab 25 and are bottomed therein to prevent a bearing engagement between the retainers screws 28 and the slotted guide retainer 26. The retainer screws 28 serve to prevent the pumping element canister 12 from falling out of the guide retainers 26 when the-getter ion vacuum pump is inverted.

A plurality of high voltage insultors 29 extend radially from the tubular adaptor 6 and-serve to insulate a plurality of center high voltage leads 31 from the otherwise grounded pump envelope 1. A' plurality of metal straps 32 as of, for example, copper are clamped tothe center conductors 31 via clamps 33. The other ends of the conducting straps 32 are secured by screws to the anode frames 18. In this manner the high positive voltage with respect to the cathode plates 14 is applied via leads 31 and straps 32 to the cellular anodes 17.

The cathode plates 14 are electrically insulated from the anodes 17 via the ceramic insulators 21. The cathode plates 14 are electrically connected via the end blocks 13 and guide tabs 25 to the grounded pump envelope 1. Thus in use a high positive potential as of, for example, 3,000 volts is applied to the anodes 17 with respect to the cathode plates 14 for initiating the glow discharge therebetween.

A magnetic field of LOGO-1,800 gausses is applied perpendicularly to the cathode plates 14 -(see Fig. 1) and is supplied via a plurality of rectangular permanent magnets 35 as of, for example, nickel aluminum steel. The permanent magnets 35 are centrally bored longitudinally thereof to receive therewithin bolts 36. The bolts pass through the permanent magnets 35 and anchor in tapped holes in rectangular pole pieces 37 as of, for example, iron. The permanent magnets 35 are stacked in a plurality of columns, the plane of adjacenttcolumns is disposed substantially at right angles to each other. At the intersection of the columns the permanent magnets are rigidly connected together via a square rod 38 made of a magneticallypermeable material as of, for example, iron and is suitably apertured to receive the bolts 36 therethrough. I

An alternative permanent magnet configuration is shown in Fig. 3A, wherein the magnetic field strength is increased by increasing the length of thepermanent magnets 35' and disposing them at the outermost extremity of the pole pieces 37.

Theindiv-idual permanent magnet assemblies including permanent magnets 35, pole pieces 37 and a-rod 38 form an integral rigid unit which 'is carried externally of the pump envelope 1 via a plurality of rectangular spacer plates 39 as of, for example, stainless steel fixedly secured to the pump envelope 1 substantially at the ends thereof as by, for example, heliarc welding. The spacer plates 39 are provided-with tappedholes at 41.

The magnet pole pieces 37 fit between "the spacer plates 39 provided at thetopand bottom 'of the-envelope 1 and are retained in'positionvia'rectangular -pole piece retainer-blocks. 42 as of, for example, stainless steel.

Pole piece retainer blocks42aresuitably apertured in,

alignement with the tappad holes 41 in the spacer blocks 39 and receives therewithin screws 43 for tightly pulling the pole piece retainer blocks 42 against the spacer plates 39 for capturing the magnet assemblies and thereby restrain them from falling away from the pump envelope 1.

anodes 17 and the cathode plates 14. The glow dischargeis subdivided into a plurality of closely grouped discharge columns defined by the openings or cells forming the glow dischargepassageways through the anode 17.

In the glow discharge, positive ions are created which bombard the negative cathode plates 14 thereby disintegrating portions of the reactive plates 14. v The disintegrated reactive material sputters from the plates 14 and the largest percentage thereof is collected on the large area of the cellular anodes 17. Molecules in the gaseous state coming in contact with the freshly deposited reactive cathode material are entrapped thereon and eflectively removed from the gaseous state thereby evacuating the envelope 1 and other chambers communicating therewith through the exhaust tubulation 8.

Due to the enlarged central chamber 2 of the vacuum pump, gas which diifuses into the pump from other structures, which are being evacuated, encounters little impedance to its flow, and the pumping speed is accordingly enhanced.

The provision of the pumping element canisters 12 facilitates replacement of used pumping elements. To replace the canister 12 the strap conductor 32 is disconnected from the high voltage lead 31 by removing clamp 33. Removal of retainer screws 28 allows the pumping element canister 12 to be lifted out of the adaptor tubulation 6 and replaced by a new or renovated pumping element canister 12.

Another embodiment of the present invention is shown in Fig. 8. The view depicted by Fig. 8 is like the view as depicted by Fig. 3 of an alternative pump structure. In the embodiment of Fig. 8 a larger number of rectangular lesser chambers 3 are provided communicating with a large central cylindrical chamber 41. The rectangular lesser chambers 3 extend outwardly of the cylindrical central chamber 41 like the spokes of a wheel.

The outside walls of the

chambers

3 and 41 define the pumpenvelope 42. Each of the lesser rectangular chambers 3 contains therewithin a pumping element canister 12. The canisters 12 are supported in the same manner as previously shown with regard to Figs. 5, 6 and 7. The magnetic field is provided by a plurality of sector-shaped permanent magnets 43 which are radially bored to receive studs 44 therethrough. The studs 44 are fixedly secured as by, for example, spot-welding to the envelope 42 and extending radially therefrom. The studs 44 are threaded at their outermost end portions to receive nuts to firmly hold the permanent magnets 43 in posit-ion between adjoining lesser rectangular chambers 3.

The pumping speed of a pump constructed according to the teachings of Fig. 8 and having a central chamber diameter of 30", a pump length of approximately 5, is 3,500 liters per second at 10- millimeters of mercury.

Since many changes could be made in the above construction and many apparently widely difierent embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained. in the above description or shown in the ac companying drawings shall be interpreted. as. illustrative andnot in. a limiting sense. i 1

. What is claimed is:.. 7

1. A getter, ion vacuum pump apparatus including,- a central hollow chamber communicating with the structure it is desired to. evacuate, a plurality of lesser chambers communicating with said central chamber, said lesser chambers extending outwardly of said central chamber like the spokes of a wheel and extending lengthwise of said central chamber, a plurality of cellular anodes, a pair of reactive cathode plates disposed on opposite sides' of each cellular anode and slightly spaced apart therefrom, each anode with itspair of cathodes being assembled together as a pumping canister, said pumping canister disposed within said lesser chambers, cathode spacer members disposed transversely of. said pumping canister for assuring the proper spacing of said cathode plates, permanent magnets disposed between the lesser chambers for producing a magnetic field directed sub stantially at right right angles to said cathode plates for enhancing the pumping action of the getter ion vacuum. pump. 1 r I 2. A getter ion vacuum pump apparatus adapted to be connected to hollow structures for evacuation thereof including, a tubular envelope containing a central chamber and a plurality of outwardly extending chambers communicating with saidicentral chamber, anode and cathode members disposed within said outwardly extending chambers, said anode and cathode members adapted when energized to produce a glow discharge therebetween for pumping gaseous matter within said envelope and hollow structures communicating therewith, and means for producing and directing a magnetic field transversely of said outwardly extending chambers for enhancing the glow discharge.

3. The apparatus according to claim 2 wherein said magnetic field producing means include, a permanent magnet disposed between said outwardly extending chambers for providing a magnetic field within said outwardly extending chambers to enhance the pumping speed of the pump.

4. A getter ion replaceable pumping element canister including, a pair of spaced apart reactive cathode members, an anode member disposed between said pair of cathode members, said anode and cathode members being slideably connected together to form a sub-assembly with is readily removed as a unit from the vacuum pump for replacement and repair as desired, and said anode and cathode members adapted to have different potentials applied thereto in use for establishing a glow discharge therebetween.

5. A getter ion pumping element canister including, a pair of spaced apart elongated reactive cathode members, an anode member disposed between said pair of cathode members, said anode member being fixedly connected to said cathode members substantially at one end thereof, and said anode member being slideably connected to said pair of cathode members substantially at the other end thereof, whereby relative movement between said anode and cathode members may be accommodated to allow for unequal thermal expansions and contractions of said anode and cathode members in use.

6. The apparatus according to claim 5 including means interconnecting said pair of reactive cathode members substantially intermediately the ends thereof for maintaining the proper spacing between said cathode members to prevent excessive warping and bending of said cathode members in use.

7. An apparatus as claimed in claim 6 including means forming guide tabs fixedly connected to the pumping element canister, means forming a guide retainer for slideably receiving therewithin said guide tab means, and said guide retainer means being fixedly secured to the inner side wall of the pump to assure the proper positioning of the pumping element canister within the vacuum pump.

8. A getter ion replaceable pumping element canister and said anode and cathode members adapted to have.

different potentials applied thereto in use for establishing a glow discharge therebetween.

9. The apparatus according to claim 8 including means, interconnecting said pair of reactive cathode plates sub-.

stantially intermediate the ends thereof for maintaining the proper spacing between said cathode plates to prevent excessive warping and bending of said cathode plates in use.

10. The apparatus as claimed in claim 9 including, means forming guide tabs fixedly connected to the pumping element canister, means forming a guide retainer for receiving therewithin said guide tab means, and said guide retainer means being fixedly secured to the interior side wall of the pump to assure the proper positioning of the pumping element canister Within the vacuum pump.

11. A getter ion vacuum pump apparatus including, a central hollow chamber which it is desired to evacuate, a plurality of cellular anodes, a plurality of reactive cathode plates, said reactive cathode plates arrangedin pairs disposed on opposite sides of each cellular anode and slightly spaced apart therefrom, each cellular anode with its pair of cathode platesbeing assembled together as a pumping canister, said pumping canisters disposed with the plane of said cathode plates extending outwardly of said central hollow chamber and communicating therewith to readily permit gas access thereto from said central hollow chamber, and means for producing amagnetic field directed substantially at right angles to the plane of said cathode plates for enhancing the pumpingaction of. the getter ion vacuum pump.

12. The apparatus according to claim 2 wherein at least one anode member is provided with a plurality of openings therein the openings being distributed transversely of the direction of the magnetic field when said anode member isdisposed within an outwardly extending chamber, the anode openings extending in the direction of the magnetic field and forming a plurality of glow- References Cited in the file of this patent UNITED STATES PATENTS Hertzler Apr. 28, 1953 Lawrence Dec. 13, 1955