US2988657A - Ion pump - Google Patents

Description

June 13, 1961 A. M. KLOPFER ETAL 2,988,657

ION PUMP 3 Sheets-Sheet 1 Filea July 14, 1959 jlllllIHdl FIG. 2

INVENTORS ANTON MARTIN KLOPFER WIN FRIQYGEORG ERM RICE AGEN June 13, 1961 KLOPFER ETAL 2,988,657

ION PUMP Filed July 14, 1959 3 Sheets-Sheet 2 INVENTORS ANTON MARTIN KLOPFER WINFRIED GEORG EP-MRICH AGEN June 13, 1961 A. M. KLOPFER ET AL ION PUMP Filed July 14, 1959 s Sheets-Sheet s INVENTORS ANTON MARTIN KLoPFER WINFRIEO GEoRG ER R H A) z & AGET Unedsm Patent I ION PUMP Anton Martln Klopfer and Winfried Georg Ermrich, Aachen, German assignors to North American Philips Company, Inc., New York, N.Y., a corporation of .Delaware Filed July '14, 1959, Ser. No. 826,961 Claims priority, application Germany Aug. 2, 1958 Claims. (Cl. 313-7) The present invention relates to ion pumps, in which the discharge path extends between a substantially ringshaped anode and cathode parts situated at both sides of the ring plane, provision being made of a magnetic field, the lines of force of which connect the two cathode parts without these lines of force reaching the anode, While during operation a gas-binding metal is constantly precipitated in the proximity of the discharge path. The invention further comprises a discharge system for use in such ion pumps. Moreover, the invention concerns a method of operating such pumps.

Ion pumps of the aforesaid type are known per se. The gas-binding metal precipitating in the proximity of the discharge path originates from two cathode plates which are disintegrated by the discharge. However, the

disintegration declines when the pressure drops, so that extremely low pressures can be reached only by taking special steps.

This getter disintegration suffers from a further disadvantage in that, in the case of an excessive supply of gas, the quantity oiprecipitated getter is insufiicient, so that the pressure increases, due to getter saturation. The known device is rather bulky and suitable only for stationary installations.

Furthermore, ion pumps are known in which, in contrast to the aforesaid pump, no disintegration is to occur, but in which the produced ions are collected by the cathode plates or by an other electrode. Besides the cathode plates provision is made of a particular incandescent cathode, presumably for maintaining the discharge at low pressures, when no further discharge occurs with a cold cathode. Since the gas is collected by the electrodes, the latter may sometimes readily give oil gases such as is in the case of known similarly constructed gasdischarge manometers (Penning).

Furthermore, it is known to evaporate a metal, such as titanium in ion pumps comprising incandescent cathodes, in order permanently to form fresh collecting layers for the ion in the proximity of the discharge path. Thus, for example, a titanium wire is evaporated by unwinding it in contact with a graphite block heated by the discharge. The device used is very complicated and suitable only for large and stationary installations.

The present invention has for its object to provide an ion pump combining the advantages of conventional ion pumps and, moreover, having a simple construction so as to permit, without prohibitive cost, any appropriate electron discharge tube to be equipped with such a dis charge system which constitutes the main part of such ion pumps.

In ion pumps, in which the discharge path extends between a substantially ring-shaped anode and cathode parts situated at both sides of the ring plane, and in which provision is made of a magnetic field, the lines of force which connect the two cathode parts without reaching the anode, while during operation a gas-binding metal is permanently precipitated in the proximity of the discharge path, at least one of the two cathode parts is, according to the invention, an incandescent cathode pvith a supply of gas-binding metal which is evaporated :during operation of the cathode.

Patented June 13, 1961 h re The construction according to the invention has the. following advantages. The gas-binding metal evaporating from the incandescent cathode combines with existing or supplied gas already during evaporation. At very low pressures the electrons emitted by the incandescent cathode permit a heavy discharge which would otherwise not be obtainable and, moreover, the metal evaporating from the cathode may contribute to the discharge. The precipitated layer of the metal may be conductively connected to the cathode or a voltage which is negative relatively to the cathode, may be applied to said layer. The precipitated getter-layer constitutes at the same time a collecting surface for the ions.

The ion pump according to the invention may be used for evacuating an electron tube, which has been exhausted to a preliminary vacuum of approximately 0.1 mm. Hg and sealed oii, further evacuation being taken over by the ion pump. For expediting the binding of gas at pressures higher than 10 mm. of Hg the cathode may be temporarily heated to a slightly higher temperaturein order to accelerate evaporation of the gas-binding metal.

In an ion pump according to the invention, one cathode or both cathodes preferably consist of a tungsten wire spun with a wire of titanium or other metal. It is advantageous to provide the two cathode parts with barium and titanium respectively for evaporation.

In a particularly suitable construction according to the invention, one cathode part consists of an incandescent cathode spun with the metal to-be vaporized, whilethe other cathode part is a. solid plate consisting of themetal. tobe vaporized, and the anode likewise consists of a solid ring of the metal to be vaporized. i

This ion pump permits a substantially constant rate of pumping with minimum consumption of energy in a considerable pressure range. For obtaining a pumping rate independent of the pressure the rate of vaporization or the disintegration fraction should be proportional to the pressure.

When using such an ion pump in the pressure range between 0.5 mm. and 0.01 mm. the incandescent cathode is sufiiciently heated to obtain a considerable vaporization fraction of the getter metal. Any hydrocarbons are thermally dissociated at the incandescent cathode. At pressures below 0.01 mm. of Hg the pump, working only by disintegration, can be operated economically for a considerable time only until the pressure decreases to a point such that the discharge, with cold incandescent cathode, is no longer maintained. By heating the incandescent cathode, from which the getter material has already been vaporized, a discharge and consequently disintegration is again obtainable at said lower pressures by electron-emission of the hot incandescent cathode. Further, this electron-emission of the hot incandescent cathode may be used for heating the anode sufficiently by electron bombardment, preferably without a magnetic field, so that evaporation of the anode material and consequently an adequate pumping rate are obtained.

In order that the invention may be readily carried into effect, examples will now be described in detail with reference to the accompanying drawings, in which FIG. 1 shows the discharge system of an ion pump according to the invention,

FIG. 2 shows the circuit arrangement of the discharge system,

FIG. 3 shows an electron-discharge tube sealed to an ion pump, and

FIGS. 4 and 5 represent ion pumps with titanium and barium evaporation.

In FIG. 1, the reference numeral 1 designates the bulb of the discharge system, and 2 denotes a ring-shaped molybdenum wire constituting the anode. Twobent tungsten wires 3 are spun with titanium wire 4 and together constitute the cathode of the discharge path. A contact spring 5 serves for establishing the potential of the layer of titanium 6 precipitated on the wall of the bulb.

In FIG. 2, the reference numeral 7 denotes the battery heating one of the twocathode halves 3. Alternatively, the cathode may be heated by means of alternating current. The anode voltage battery is denoted by 8. The reference numeral 9 designates the source of voltage for establishing the potential of the layer of titanium 6 on the bulb 1. The bulb 1 is situated between two schematically shownpole shoes 10 of a permanent magnet for producing a magnetic field of approximately 500. to 1000 gauss.

FIG. 3 represents schematically a cathode-ray tube 11 having sealed to it a discharge system 1 for use in an ion pump. During operation, the ion pump is connected according to want, in the case of an excessive quantity of gas developing in thetube 11. The ion pump may also be used in manufacturing thetube 11 for completing evacuation of the tube after sealing it off.

In FIG. 4, one of both cathode parts consists of three V-shapedincandescent wires 12 of tungsten spun with barium-nickel sheath wire. The other cathode part consists of two V-shaped parts 13 spun with titanium. Dependent upon the kind of gas to be bound and the pressure, one part of the cathode or both of them are heated. If desired, provision may be made of another ring getter 14 for evaporating barium so as to ensure a particularly strong binding of the gas.

In FIG. 5', in contrast to FIG. 4, the anode consists of two double rings 15 of barium-ring getter.

In FIG. 6, the glass bulb is designated by 10. The electrodes are mounted on a number of lead-through pins. Theheatable part 3 of the cathode consists of 4 three V-shaped' tungsten wires spun with titanium wire. The cold cathode part is asolid titanium plate 30. The.anode 40 is a loop of thick titanium band. A contact spring serves for fixing the potential layer deposited on the wall of the bulb.

What is claimed is:

1. An ion pump comprising an envelope, a ring-shaped anode within said envelope, an incandescible cathode comprising two portions disposed on opposite-sidesof the plane of the anode, at least one of said cathode portions being provided with a supply of gas-binding metal which is evaporated during operation of the cathode which is precipitated on the wall of the envelope, and means to produce a magnetic field the lines of force of which extend between the portions of the cathode without intercepting the anode.

2. An ion pump as claimed in claim 1 in which at least.

one of the cathode portions is a tungsten wire spun with a wire consisting of metal to be evaporated.

3. An ion pump as claimed inclaim 2 in which oneof the cathode portions is spun with titanium wire and the other cathode portion is spun with barium-sheath wire.

4. An ion pump as claimed inclaim 2 in which the other cathode portion is a solid plate of the metal to be evaporated and the anode is a solid ring of the same metal.

References Cited in the file of this patent

Images