US3614264A

US3614264A - Ionization getter pump

Info

Publication number: US3614264A
Application number: US818322A
Authority: US
Inventors: Kart-Georg Gunther
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1958-06-06
Filing date: 1959-06-05
Publication date: 1971-10-19
Anticipated expiration: 1988-10-19
Also published as: NL239135A; NL132318C; DE1075272B; FR1226838A; GB915748A; CH366625A

Abstract

A pair of electrically conducting collector electrodes are disposed in a housing on either side of an anode. A cathode is disposed between the anode and each collector electrode and insulated from each. Each of the cathodes comprises a getter substance. The space between the anode and each of the cathodes defines a discharge space. Cathode-sputtering voltage is applied between the anode and the cathodes. A magnetic field is impressed upon the discharge space and has field lines extending from one collector electrode toward the other. Each of the cathodes defines at least one aperture therein having an axis parallel to the magnetic field lines and through which ions from the discharge space and material sputtered from the cathodes pass to the collector electrodes.

Description

United States Patent [72] Inventor Karl-Georg Gunther Nurnberg, Germany [21] Appl No. 818,322 [22] Filed June 5, 1959 [45] Patented Oct. 19, 1971 [7 3] Assignee Siemens Aktiengesellschaft Erlangen, Germany [32] Priority June 6, 1958 [3 3] Germany [31] S 58505 l /27d [54] IONIZATION GETTER PUMP 5 Claims, 4 Drawing Figs.

[52] U.S. Cl [51] Int. Cl [50] Field of Search [5 6] References Cited UNITED STATES PATENTS 2,197,079 4/1940 Penning Primary Examiner-William L. Freeh Attorney-Curt M. Avery ABSTRACT: A pair of electrically conducting collector electrodes are disposed in a housing on either side of an anode. A cathode is disposed between the anode and each collector electrode and insulated from each. Each of the cathodes comprises a getter substance. The space between the anode and each of the cathodes defines a discharge space. Cathode-sputtering voltage is applied between the anode and the cathodes. A magnetic field is impressed upon the discharge space and has field lines extending from one collector electrode toward the other. Each of the cathodes defines at least one aperture therein having an axis parallel to the magnetic field lines and through which ions from the discharge space and material sputtered from the cathodes pass to the collector electrodes.

PAIENTEUnm 19 IBII VIIIIIIIIII IVA I /A IVA I/1 IONIZATION GETTER PUMP DESCRIPTION OF THE INVENTION My invention relates to evacuating pumps operating on the ionization getter principle according to which the gases to be removed from the pump chamber are permanently bonded to absorptive substances, called getters", while anelectric discharge is effective within that chamber. Pumps of this type are applicable, for example, continuously maintaining a vacuum within the evacuated envelope of a vacuum switch, an electronic transmitter tube, a corpuscle accelerator and the like devices.

There is known ionization getter pump whose pumping action is predicated upon continuous formation of fresh absorption layers by cathode sputtering and simultaneous ionization and excitation of the gas molecules, and in which-seen from the viewpoints gained by the present invention and more fully explained below-two different area groups are used for sputtering or spattering the getter substance on the one hand and for receiving the resulting absorption layers on the other hand.

It is an object of my invention to improve such ionization getter pumps as regards effectiveness and reliability.

To this end, and in accordance with a feature of my invention, the area group for receiving the absorption layers of getter substance enclose or border the electric discharge space at least on those sides that extend at a right angle to the electric and magnetic field lines that control the electric discharge in the space subjected to pumping action.

In the above-mentioned known ionization getter pump, it is necessary to apply a particular suction voltage for the purpose of causing the resulting ions and excited gas molecules to pass onto the surfaces that are being continuously coated with absorption layers. Only part of the ions and excited molecules are pulled out of the discharge space in this manner. In the absorption pump according to the invention, in contrast, virtually all ions and excited molecules reach the absorption surfaces. This is due to the fact that the drifting motion imparted to the ions by the field strength of the discharge gap is directed onto the surface groups coated with the getter substance. The improved effectiveness is further due to the fact that, by virtue of the above-mentioned spatial disposition of the coated surface group, the diffusion travel of the excited gas molecules to the absorptive surface group is reduced to a very slight distance, namely virtually down to the minimum, and that the excited molecules do not have any other possibility of escaping from the discharge space. For the same reasons, an ionization getter pump according to the invention is to a large extent free of maintenance requirements, possesses a long useful life, and exhibits a very high evacuating action relative to any given size of the pump.

The high evacuating action of the novel pump can be explained as follows. For achieving the desired evacuation by getter action it is necessary that the ionized or excited gas molecules impinge upon surfaces of substances that are freshly formed and are particularly absorptive because of their chemical composition. The absorptive action depends upon the rate of formation of these layers on the one hand, and upon the impinging density of the gas ions and excited gas molecules on the other hand. However, there is the possibility that the already absorbed gas molecules may again be knocked out by impinging new particles of high velocity, and may then return into the gas space. It is an essential concept of my invention to exclude such possibility; and this is achieved by the above-described separation and spatial disposition of the active surfaces in two groups of which the group from which getter substance is being sputtered or spattered is given a higher electric potential relative to the anode of the discharge space than the surface group serving for receiving the spattered getter substance and hence for absorbing the gas ions and excited molecules.

The invention will be further explained with reference to the embodiments illustrated on the accompanying drawing by way of example. On the drawing:

FIG. I shows in longitudinal section a first embodiment;

FIG. 2 illustrates, also in section, a somewhat modified embodiment;

FIG. 3 illustrates a third embodiment likewise in longitudinal section; and

FIG. 4 illustrates a longitudinal section of another embodiment of the invention.

In FIG. I the pump housing is denoted by I and the appertaining suction conduit by 2. Mounted in the pump housing and insulated therefrom is the anode 3 of the electric discharge gap. The anode has the shape of a helix and consists of a metal having a high-melting point, for example tungsten or molybdenum. The anode 3 is connected through a lead 4 to a positive potential U An electrically insulating seal 5 serves for passing the lead 4 through the wall of the pump housing I.

The pump housing may be grounded. as shown in FIG. I. it consists of nonmagnetic metal such as copper or stainless steel. Two

metallic plates

6 and 7 are mounted in coaxial relation to the helical anode 3. The plates may be attached to the wall of pump housing 1, for example by soldering or welding. In this manner or by any other suitable :means the

plates

6 and 7 are both in electrically conducting connection with the pump housing I and thus are kept at zero (ground) potential. If desired, however, the two plates may be insulated from the housing 1 and can then be connected by a separate lead to any desired potential, for example different from zero. In any event, the plate potential must considerably differ from the potential U, of the anode 3, because the

plates

6 and 7 constitute the main cathode of the discharge gap. The

cathode plates

6 and 7 consist of getter substance, for example of pure, vacuum-degassed titanium or zirconium. Since the cathode plates have no extraneous source of heat they are generally termed cold cathodes.

The surfaces for receiving the absorptive layers are arranged about the

plates

6 and 7. In the illustrated embodiment, these surfaces are formed by two

ringshaped discs

8 and 9 preferably of a high-melting material such as molybdenum, tungsten or stainless steel. The

discs

8 and 9 are in electrically conducting connection with each other and are connected by a lead 10 to a potential U An electrically insulating seal 11 serves to pass the lead 10 through the wall of the pump housing 1.

The magnetic field required for the operation of the pump is preferably produced by means of a permanent magnet as shown at 12. The pump housing 1 is mounted, in the position apparent from the drawing, between the pole shoes N, S of the permanent magnet R2. The magnet serves, as known, for extending the effective travel path of the electrons thus expanding the working range of the pump toward small pressures.

For operating the pump, a potential difference U,, for example of 2,000 to 4,000 volts, is applied by leads 4 and I0 between the anode 3 and the pump housing 1 with the

plates

6 and 7; and a potential difference U of about 400 to 800 volts is applied between the anode 3 and the mutually-intercom nected

annular discs

8, 9.

The performance is as follows. Under the effect of the high voltage U between the

plates

6, 7 and the anode 3, some of the getter substance of which the plates are made is atomized by cathode spattering. The spattered particles continuously precipitate in form of absorptive coatings mainly upon the

plates

8 and 9 which constitute the second surface group in the sense of the foregoing explanations. The particles coming from plate 6 reach particularly the top side of plate 9, relative to the position shown in FIG. ll, whereas the particles spattered from plate 7 mainly reach the bottom side of plate 8. Those particles that pass from plate 6 onto plate 7, and from plate 7 to plate 6, contribute little or nothing to the suction effect because they are again subjected "to spattering. The spattered particles that precipitate upon the anode 3 do contribute to the pumping action, but their share is slight since the anode surface is relatively small.

As the spattered particles mainly precipitate upon the

annular discs

8 and 9, the absorption coatings thus being formed continuously are impinged upon the ionized and excited gas molecules due to the effect of the voltage U, These two molecule groups are permanently captured by the absorption coatings as no spattering or sputtering takes place at these cations. This is because the impinging velocity is too low for appreciable spattering due to the relatively small voltage U,, for example 400 to 800 volts, obtaining between the anode 3 and the

annular discs

8, 9.

The second surface group upon which the absorption coatings are formed can readily be enlarged by joining, according to FIG. 2, the

annular discs

8 and 9 with a metallic cylinder 13, the embodiment of FIG. 2 being otherwise in accordance with that of FIG. 1. The

annular discs

8 and 9 form together with the cylinder 13 a unit of the same potential. Hence the entire inner surface of this unit constitutes the second surface group for receiving the absorption layers, thus greatly increasing the area of the second surface group. The unit formed of

parts

8, 9 and 13 is mounted in the pump housing 1 in insulated relation thereto and is connected to the potential U, by the lead 10. The anode 3 is mounted within the

unit

8, 9, 13 and is insulated therefrom.

According to FIG. 3, the anode 21 mounted in the pump housing 1 is ring-shaped. If the anode is to be connected to the same potential as the housing 1, namely preferably to ground potential, then the anode can be directly attached to the housing 1, in which case the seal shown at 28 need not be electrically insulative. Such an arrangement is shown in FIG. 4, otherwise corresponding to FIG. 3. Mounted (in FIG. 3) on both sides of the anode 21 and in coaxial relation thereto are

respective screen plates

22 and 23. These perforated plates constitute the cathode and thus one of the two surface groups. They are in electrically conducting connection with each other and are connected to the potential U through a common lead 24 which passes through the wall of the pump housing 1 by means of an insulating seal 25. The

plates

22 and 23 consist of getter substance. The anode 21 may consist of highmelting metal, for example tungsten or molybdenum. The pump housing is located between the pole shoes N and S of a permanent magnet 26 serving the same purposes as the magnet 1 in the embodiment of FIG. 1. When, in FIG. 3, the housing 1 and the anode 21 are connected to zero potential (see FIG. 4), then the potential U is to be so chosen that a potential difference of about 2,000 to 4,000 volt obtains between the anode 21 and the two

screen plates

22, 23 jointly forming the cathode of the discharge gap.

The performance of the pump according to FIG. 3 is as follows. Getter substance is spattered from the

plates

22 and 23 under the effect of the high voltage U,. The getter substance precipitates upon the entire inner wall of the housing 1, but collects predominantly at the surface areas located behind the openings of the

screen plates

22 and 23. The ionized and excited gas molecules impinge upon the continuously precipitating absorption coatings. Since in the operation of the embodiment of FIG. 3 described above these coatings have the same potential as the anode, the ions arrive with zero velocity so that no spatter-ing of the absorption surfaces can occur. However, the embodiment of FIG. 3 may be modified by insulating the anode 21 from the housing 1 and maintaining a potential difference U, of approximately 400 to 800 volts between the anode and the housing with the aid of the lead 27 passing through an insulating seal 28 in the housing wall. In the latter case the amount of ion capture by the absorptive coating is increased because these coatings are also impinged upon these molecules that are ionized only at some distance from the anode. However, since the arriving velocity is small, there cannot occur any appreciable spattering of the ion layers being formed.

I claim:

1. An ionization getter pump for pumping action by continuous formation of cathode-sputtered getter layers and simultaneous ionization of the gas molecules being evacuated, comprising a pump housing having an intake opening for gas to be pumped, an anode and a first group of surface members mounted in said housing, said first group of members being interconnected to form a cathode and being located on opposite sides respectively of said anode to define together therewith a discharge axis directed from anode to cathode, said members having respective surfaces formed by getter substance, magnetic field means having between said anode and cathode a field parallel to said discharge axis, electric connecting means extending out of said housing for applying cathode-sputtering voltage between said anode and cathode, a second group of surface members surrounding said axis between said anode and said first-group members respectively, said second-group members having respective surface areas extending transverse to the magnetic and electric field lines for receiving getter substance from said first-group members, and mutually insulated electric conductor means extending from said anode and said second-group members out of said housing for applying a lower voltage therebetween than said cathode-sputtering voltage.

2. An ionization getter pump for pumping action by continuous formation of cathode-sputtered getter layers and simultaneous ionization of the gas molecules being evacuated, comprising a pump housing having an intake opening for gas to be pumped, a generally ring-shaped anode and two cathode plates of getter substance mounted in said housing in coaxial relation to said anode and on opposite sides respectively thereof, so as to jointly define a discharge axis directed from cathode to anode, magnetic field means having between said anode and cathode a field parallel to said discharge axis, a surface structure having two getter-receiving areas around said axis between said anode and said two cathode plates respectively, said areas extending transverse to said axis and to the magnetic and electric field lines, and mutually insulated electric conductor means extending from said anode and said cathode plates out of said housing for applying a cathode-sputtering potential between the cathode and anode.

3. In a pump according to claim 2, said surface structure comprising two ring-shaped discs having respective ring surfaces extending about said discharge axis and at a right angle thereto.

4. An ionization getter pump, wherein ionization of gas takes place in a cold cathode discharge, and whose pumping action is based upon continuous cathode sputtering and simultaneous ionization and excitation of the gas molecules being pumped, comprising a pump housing having an intake opening for gas to be pumped, an anode and a cathode insulated from each other in the housing, the cathode comprising getter substance, the space between the said anode and cathode defining a discharge space, magnetic field means for impressing a magnetic field upon the discharge space, means providing a surface inside said housing upon which getter substance removed from the said cathode is received, said means comprising an electroconductive vessel having a wall, the anode being within the vessel, the vessel having apertures in its wall, the cathode comprising plates of getter substance mounted upon the inner walls of the housing opposite said apertures, the housing being electroconductive and being grounded, said vessel bordering the discharge space at least at those sides that extend perpendicular to the electric and magnetic field lines, the magnetic field lines extending longitudinally of the electric field lines, electric connections for passing cathode-sputtering voltage between said anode and said cathode and for passing ionizing voltage between said anode and said surface.

5. An ionization getter pump, wherein ionization of gas takes place in a cold cathode discharge, and whose pumping action is based upon continuous cathode sputtering and simultaneous ionization and excitation of the gas molecules being pumped, comprising a pump housing having an intake opening for gas to be pumped, an anode and a cathode insulated from each other in the housing, the cathode comprising getter substance, the space between the said anode and cathode defining a discharge space, magnetic field means for impressing a magnetic field upon the discharge space, means providing surface area inside said housing upon which getter substance removed from the said cathode is received, said means comprising muand magnetic field lines, the magnetic field lines being longitudinal of the electric field lines, electric connections for passing cathode-sputtering voltage between said anode and said cathode and for passing a voltage between said anode and said surface which is less than that between the anode and cathode.

Claims

1. An ionization getter pump for pumping action by continuous formation of cathode-sputtered getter layers and simultaneous ionization of the gas molecules being evacuated, comprising a pump housing having an intake opening for gas to be pumped, an anode and a first group of surface members mounted in said housing, said first group of members being interconnected to form a cathode and being located on opposite sides respectively of said anode to define together therewith a discharge axis directed from anode to cathode, said members having respective surfaces formed by getter substance, magnetic field means having between said anode and cathode a field parallel to said discharge axis, electric connecting means extending out of said housing for applying cathode-sputtering voltage between said anode and cathode, a second group of surface members surrounding said axis between said anode and said first-group members respectively, said second-group members having respective surface areas extending transverse to the magnetic and electric field lines for receiving getter substance from said first-group members, and mutually insulated electric conductor means extending from said anode and said second-group members out of said housing for applying a lower voltage therebetween than said cathodesputtering voltage.

5. An ionization getter pump, wherein ionization of gas takes place in a cold cathode discharge, and whose pumping action is based upon continuous cathode sputtering and simultaneous ionization and excitation of the gas molecules being pumped, comprising a pump housing having an intake opening for gas to be pumped, an anode and a cathode insulated from each other in the housing, the cathode comprising getter substance, the space between the said anode and cathode defining a discharge space, magnetic field means for impressing a magnetic field upon the discharge space, means providing surface area inside said housing upon which getter substance removed from the said cathode is received, said means comprising mutually opposed apertured plates, the cathode comprising plates of getter substance mounted upon the inner walls of the housing apertured plates, the cathode comprising plates of getter substance mounted upon the inner walls of the housing opposite said apertures, the housing being electroconductive and being grounded, said plates bordering the discharge space at least at those sides that extend perpendicular to the electric and magnetic field lines, the magnetic field lines being longitudinal of the electric field lines, electric connections for passing cathode-sputtering voltage between said anode and said cathode and for passing a voltage between said anode and said surface which is less than that between the anode and cathode.