US3112864A

US3112864A - Modular electronic ultrahigh vacuum pump

Info

Publication number: US3112864A
Application number: US842294A
Authority: US
Inventors: Lewis D Hall; Sugg John William
Original assignee: Ultek Corp
Current assignee: Ultek Corp
Priority date: 1959-09-25
Filing date: 1959-09-25
Publication date: 1963-12-03
Anticipated expiration: 1980-12-03
Also published as: NL256013A; DE1240619B; GB934415A

Description

1.. D. HALL ETAL 3,112,864

MODULAR ELECTRONIC ULTRAHIGH VACUUM PUMP Filed Sept. 25, 1959 Dec. 3, 1963 E Ea y JOHN W. G

ATTORNEYS United States Patent 3,112,864 MODULAR ELECTRQNIC ULTRAHIGH VAQUUM PUMP Lewis D. Hall, lalo Alto, and John William Sugg, San

Mateo, (lalifi, assignors to Ultelc Corporation, Palo Alto, Calif., a corporation of California Filed Sept. 25, 1959, Ser. No. 842,294 12 Claims. (Cl. 230-69) This invention relates generally to vacuum pumps and more particularly to vacuum pumps of the electronic type.

Electronic pumps employing cold-cathode discharge in in magnetic field are well known in the art. In such pumps an electric field is provided between the cathode and anode. A magnetic field is applied substantially parallel to the anode surface. Electrons travelling from the cathode to the anode are deflected by the magnetic field and traverse a relatively long path. These electrons collide with the gas molecules and form ions, atoms (dissociated molecules) and metastable molecules. The latter two species are captured chiefly upon the reactive surface of the anode. The reactive surface of the anode is continuously replenished from the cathode by sputtering. The term sputtering denotes removal of material from a surface at cathode potential by positive ion bombardment. It is analogous to thermal evaporation or sublimation.

Electronic vacuum pumps of the prior art, although they produce a relatively high vacuum, have been restricted by pump speed. This restriction in volume or in speed of evacuation has been due to two primary causes. The first is the relatively small size of the vacuum pumps which are capable of use with the limited range of voltage and magnetic field available. The second limitation is in the rate at which sputtering action from the cathodes onto other surfaces is possible. The pumping action is dependent upon two primary mechanisms. First, in the creation of chemically active states, such as atoms and metastables, and second, the trapping of these chemically active states by deposits of sputtered cathode material, such as titanium, or other reactive metal or alloy.

in certain instances, it is desirable to increase pumping speeds for short periods of time. Such an instance occurs during the conversion of oxide coated cathodes in the course of processing vacuum tubes. When an oxide coated cathode is converted, large volumes of carbon dioxide gas are evolved in a short time interval. During this short time interval, considerably more pumping speed is required than during the remainder of the tube processing cycle. Since the increased speed is required only for a small fraction of the total processing cycle, it is inelficient to use a cold cathode discharge pump large enough to handle the peak gas load without strain. It is much more eflicient to provide a pump capable of eflicient performance at normal loads and having a higher pumping speed upon demand. Such a pump will be highly beneficial under any condition Where gas bursts may occur.

The electronic vacuum pumps of the prior art are basically constant volumetric speed devices. In the coldcathode discharge pumps, the discharge produces such an abundance of chemically active states (atoms, metastales) that the sputtered deposits are saturated as rapidly as they are laid down. Consequently, the rate at which gas molecules are trapped in the cold-cathode discharge pumps is directly proportional to the rate at which the reactive material is sputtered. Also, the rate of sputtering is directly proportional to the pressure within the pump. Since the volumetric speed of pumping is directly proportional to the rate at which gas molecules are 3,112,864 Patented Dec. 3, 1963 trapped and inversely proportional to the pressure, the cold-cathode discharge pumps provide a constant volu metric speed. In accordance with one embodiment of the invention, an evaporator is used which does not activale gas but merely deposits reactive material. The additional deposit of the reactive material traps additional gas molecules and thereby increases the volumetric speed of the pump. Since the rate of evaporation can readily be controlled, the number of additional molecules trapped and consequently the volumetric pumping speed can be easily controlled within limits.

The evaporators can be and have been used by themselves in the prior art; however, since the deposits from the evaporator trap active particles (atoms, metastables) much more readily than unactivated molecules, they are relatively inefficient in the absence of a discharge.

It is, therefore, a general object of this invention to provide an improvement in electronic vacuum pumps.

It is an object of this invention to provide a vacuum pump assembly which is compact and light in construction and at the same time capable of producing a high pumping rate.

It is another object of the invention to enhance performance of a multiple cold cathode discharge high vacuum pump by combining therewith additional means serving to greatly increase pumping speed.

It is another object of this invention to provide an improved electronic vacuum pump wherein the volumetric pumping speed is variable.

These and other objects of the invention will become more clearly apparent from the following description when taken in conjunction with the accompanying draw- Referring to the drawing:

FiGURE 1 is a perspective view of a stacked unit of vacuum pumps in accordance with the invention;

FIGURE 2 is a sectional view taken along the line 2-2 of FIGURE 1;

FIGURE 3 is a perspective view of a cathode structure in accordance with the invention;

FEGURE 4 is a perspective view of a cartridge employin several units of vacuum pumps in accordance with the invention;

FIGURE 5 is an elevational view of the envelope utilizing an evaporator in accordance with the invention;

FIGURE 6 is a cross-sectional view taken of the completed unit including cartridge and envelope.

Referring to FIGURES 1, 2 and 3, eight anodes 11 are rigidly joined together with support elements 13 by welding or some other convenient method. The anode elements form an anode module. Rather than the exemplary eight anodes, any number can be joined together to form anode modules. In the center of the anode module is a cathode shaft 15 upon which are rigidly attached a series of cathodes 17. The cathodes 17 are suitably placed within the anode module so as to provide insulation from the anodes. As shown in the drawings of the insulator 19 provides this function. The complete assembly forms a pump module which includes a plurality of individual pump units, each pump unit including an anode and cooperating cathode.

Referring to FIGURE 4, a plurality of these pump modules are joined together to form a cartridge. In cartridge form it is convenient to join the cathode shafts 15 by a plate 21 at top and at bottom. Such an arrangement provides an overall rigid structure wherein the cathode and the anodes are insulated from each other.

The outside case or envelope as shown in FIGURE 5 includes a body portion 23 and a cover plate 25. Sections of tubing such as 27 may be attached to the case for connection to the apparatus wtih which the pump is associated. The evaporator in accordance with the invention is attached to the case by welding at 29 or by some other convenient means. The evaporator, as can be seen more clearly in FIGURE 6, comprises a tubing section 31 and a plate 33 upon which the internal evaporator element 35 is carried.

In the construction of the evaporator, it is advantageous to provide a maximum amount of refractory material and a maximum thermal conductivity between the refractory supporting element and the reactive material. In one embodiment of the invention, the aforementioned characteristics are accomplished by winding a wire or strip of reactive material around a length of refractory filament with no space between turns, and spot welding the reactive material to the filament at each turn. Welding at each turn improves the heat transfer characteristics which results in lower filament temperature, decreased power input and increased filament life.

The cartridge such as that shown in FIGURE 4 is mounted within the envelope and insulated therefrom with

insulators

19 and 37. At the top and bottom of the case are mounted the pole pieces 3% of the magnet 41.

In the operation of the pump, the cathodes and anodes 17 and 11 are connected to a source of potential. The evaporator element 35 having the titanium wire welded thereto is connected to a source of heating current. As the electrons are drawn from the cathode towards the anodes, the magnetic field produced by the magnet 41 causes a relatively long spiral path. While traveling the path from the cathode to the anode, the electrons activate numerous gas molecules. Positive ions are drawn to the cathode and sputter titanium from the cathode onto the other surfaces. Neutral activated molecules impinge on these other surfaces and are captured by the sputtered titanium. The heater element 35 causes additional titanium to be evaporated, consequently producing an additional amount of trapping material for the gas molecules. The additional evaporated titanium increases the efiiciency of the overall pump so as to provide an increased speed of evacuation. Likewise, the increased number of anodes and each of the individual cathodes produces an additional amount of titanium to be sputtered and consequently gas molecules are trapped at a high rate.

The evaporating element is arranged such that upon evaporation of all titanium upon the heating element a new element can be readily installed.

Vacuum pumps in accordance with the above description have been built and tested. The addition of the evaporator has increased the evacuating efficiency of the pump to such an extent that the pressure was reduced to approximately A; of the value which was attained by the use of cold-cathode discharge sections alone.

We claim:

1. An electronic vacuum pump comprising a module of independent pump units, each unit including a cylindrical anode and a cathode transverse thereto, a casing about said module, magnetic means associated wtih said module wherein a magnetic field is applied parallel to the axis of said cylindrical anodes, and an evaporator unit within said casing, said evaporator unit including a source of reactive material and a heating element associated therewith, and an inlet to said casing.

2. An electronic vacuum pump in accordance with claim 1 wherein said module includes at least two of said independent pump units in a horizontal direction and at least two of said units in a vertical direction.

3. An electronic vacuum pump comprising a cartridge of independent pump modules, each module including at least two coaxial cylindrical anodes and cathodes trans verse thereto, an envelope about said cartridge, magnetic means associated with said cartridge for applying a magnetic field parallel to the axis of said cylindrical anodes, and an inlet formed in said envelope.

4. An electronic vacuum pump in accordance with claim 3 wherein said cartridge includes at least two of 6%. said independent pump modules in a horizontal direction and at least two of said modules in a vertical direction.

5. An evaporator element comprising a length of refractory fiiarnent and a length of reactive material wound about said refractory filament, said reactive material being welded to said filament at each turn.

6. An electronic vacuum pump comprising an anode, a cathode, a vacuum pump casing enclosed with said anode and cathode, means for causing a multiple cold-cathode discharge between said anode and cathode in said casing, means independent of said last named means for depositing reactive material within said casing, and an inlet to the interior of the casing.

7. An electronic vacuum pump comprising anode means defining a plurality of separated discrete glow discharge regions, a cathode, a vacuum pump casing enclosing said anode means and cathode, means for causing a multiple cold-cathode discharge between the anode means and cathode in said casing, means independent of said anode means and said cathode for depositing reactive material within said casing, and an opening communicating with the interior of the casing.

8. An electronic vacuum pump comprising an anode, a cathode, a vacuum pump casing enclosing said anode and said cathode, means for causing a multiple cold-cathode discharge between said anode and cathode in said casing, means within said casing for independently depositing reactive material within said casing, and an inlet to the interior of the casing, said means for independently depositing reactive material comprising an evaporator including a source of reactive material and a heating element associated therewith.

9. An electronic vacuum pump comprising a module of independent pump units, each unit including an anode structure defining a predetermined volume and including aligned openings leading into same, a cathode disposed transversely to said anode structure, a vacuum tight envelope about said module, magnetic means associated with said module wherein a magnetic field is applied substantially parallel to an axis extending between said openings, an evaporator unit within said envolope, said evaporator unit including a source of reactive material and a heating element associated therewith, and an inlet to said envelope.

10. In an electronic vacuum pump, a module of independent pump units, said module comprising anode means defining a plurality of separated glow discharge regions each extending in substantially the same predetermined direction, cathode means disposed transversely to said direction, a vacuum tight envelope about said module, magnetic means associated with said module wherein a magnetic field is applied substantially parallel to said direction, and an evaporator unit within said envelope, said evaporator unit including a source of reactive material and a heating element associated therewith, and an inlet to said envelope.

1]. In an electronic vacuum pump, anode means defining a plurality of separated glow discharge regions, means for producing and directing a magnetic field along a predetermined axis in said regions, cathode means disposed transversely of said axis, a vacuum-tight envelope containing said anode and cathode means, means for causing a cold cathode discharge in each of said regions between said anode and cathode means, means separate from said discharge means for supplying and depositing reactive material within said envelope, and an inlet to the interior of said envelope for communication with a chamber to be evacuated.

12. In an electronic vacuum pump for operation in a magnetic field established in a predetermined direction, in combination, cathode means disposed in said mag netic field and transversely to said direction, anode means disposed in cooperative relation with respect to said cathode means and constructed to define a plurality of separated glow discharge regions between said cathode and anode means, a vacuum tight envelope containing said anode and cathode means, means for causing a cold cathode discharge in each of said regions between said anode and cathode means, means separate from said discharge means for supplying and depositing reactive material with in said envelope, and an inlet to the interior of said envelope for communication with a chamber to be evacuated.

References Cited in the file of this patent UNITED STATES PATENTS Connor June 18, 1957 Herb Sept. 2, 1958 Gale et al July 28, 1959 Agule May 31, 1960 Hall et a1 July 25, 1961 Notice of Adverse Decision in Interference In Interference No. 95,054 involving Patent No. 3,112,861L, L. D. Hall and J. W. Sugg, MODULAR ELECTRONIC ULTRAHIGH VAGCUM PUMP, final judgment adverse to the putentees was rendered July 29, 1969, as to claims 6, 7, 11 and 12.

[Ofiiez'al Gazette January 13, 1.970.]

Claims

1. AN ELECTRONIC VACUUM PUMP COMPRISING A MODULE OF INDEPENDENT PUMP UNITS, EACH UNIT INCLUDING A CYLINDRICAL ANODE AND A CATHODE TRANSVERSE THERETO, A CASING ABOUT SAID MODULE, MAGNETIC MEANS ASSOCIATED WITH SAID MODULE WHEREIN A MAGNETIC FIELD IS APPLIED PARALLEL TO THE AXIS OF SAID CYLINDRICAL ANODES, AND AN EVAPORATOR UNIT WITHIN SAID CASING, SAID EVAPORATOR UNIT INCLUDING A SOURCE OF REACTIVE MATERIAL AND A HEATING ELEMENT ASSOCIATED THEREWITH, AND AN INLET TO SAID CASING.