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Publication numberUS3796917 A
Publication typeGrant
Publication dateMar 12, 1974
Filing dateAug 21, 1972
Priority dateAug 21, 1972
Publication numberUS 3796917 A, US 3796917A, US-A-3796917, US3796917 A, US3796917A
InventorsHiller D
Original AssigneeNat Electrostatics Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Devices for ionizing residual gases in vacuum systems
US 3796917 A
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Description  (OCR text may contain errors)

United States Patent [1 1 Hiller Mar. 12, 1974 DEVICES FOR IONIZING RESIDUAL GASES 1N VACUUM SYSTEMS Donald Hillel, Deforest, Wis.

[73] Assignee: National Electrostatics Corp.,

Middleton, Wis.

22 Filed: Aug. 21,1972

21 Appl. No.: 282,329

[75] Inventor:

Primary ExaminerL. T. l-Iix [5 7] ABSTRACT The disclosed ionizers are of the orbitron type utilizing a high voltage anode in the form of a wire or rod extending axially within an outer generally cylindrical electrode which may be in the form of a cylindrical conductive screen connected to the negative terminal of the power supply. One or more of the ionizers are mounted Within a vacuum space containing residual gas molecules to be ionized. The resulting ions may be propelled by electrostatic field forces to the cylindrical screen and also to the walls of the vacuum cham ber where the ions may be absorbed or gettered by freshly deposited titanium or some other gettering material. By this mechanism of ion getter pumping, gas molecules are effectively removed from the vacuum space so as to improve the vacuum. in accordance with the present invention, electrons are injected into I the space between the axial anode and the outer cylindrical electrode by an electron-emitting electrode which is typically in the form of a generally circular loop or ring encircling the axial anode and spaced inwardly from the cylindrical outer electrode in the radial electric field beween the inner and outer electrodes. The electron-emitting electrode is preferably energized with a direct current which causes heating of the electron-emitting electrode so that electrons are emitted therrnionically therefrom. The current also produces an axial magnetic field in the space between the electron-emitting electrode and the anode. The combination of the radial electric field and the axial magnetic field causes a high percentage of the emitted electrons to go into orbits around the anode so that the electrons have extremely long mean-free paths before finally being attracted to the anode. In this way, the orbiting electrons produce a high degree of ionization of the residual gas molecules in the vacuum space. The axial magnetic field may be enhanced by an electromagnet or a permanent magnet disposed near the circular electron-emitting electrode and preferably aligned axially therewith. The electromagnet may take the form of a loop having one or more turns disposed near the electron-emitting electrode or a coil having a multiplicity of turns and preferably having a core of magnetic material. The permanent magnet may be generally cylindrical in shape and disposed axially. The ionizer may also be used to provide an ion gage in which the ion current to the cylindrical electrode is measured.

4 Claims, 18 Drawing Figures PATENIEDMAR 1 2 1974 SHEET 1 OF 4 6 SUPPLY PATENTEUHAR 12 I974 SHEET 2 BF 4 *BIAS LA 0 POWER SUPPLY PATENTEWRZW 3.796.917

SHEET 3 BF 4 POWER SUPPLY 0 Powea 3 SUPPLY 3e PATENTEUMR 12 1974 sum u or 4 EXPECTED FILAMENT LIFE (espoouns) (12,000HRs) v p 4 a D 0 3 2 efo DEVICES FOR IONIZING RESIDUAL GASES IN VACUUM SYSTEMS This invention relates to ionizers for producing ionization of residual gas molecules in a vacuum system. Such ionizers are used to produce ion pumping so as to improve the vacuum. In such ion pumping, the ionized gas molecules are propelled to an electrode or surface where they are absorbed and are preferably also buried by depositing titanium or some other gettering material on the surface. Such ion getter pumping is especially valuable for pumping the noble or inert gases such as helium, argon, neon and the like from the vacuum system.

Such ionizers are also valuable to produce ion gages in which the ionized gas molecules are propelled to an electrode so that the ion current can be measured. The ion current decreases as a function of the decreasing pressure of the residual gases in the vacuum system.

The ionizers of the present invention are of the orbitron type An ionizer of the orbitron type comprises an axial anode, typically in the form of a wire or rod, extending within an outer electrode, typically in the form of a coaxial cylinder. A positive voltage is applied to the anode relative to the outer electrode so as to produce a radial electric field therebetween. Electrons are injected into the space between the inner and outer electrodes in such a manner that at least some of them will go into orbits around the anode. The orbiting electrons will traverse long paths before finally being attracted to the central anode. The orbitron arrangement makes it possible to increase the mean-free path of the electrons to a great extent so that the residual gas molecules in the vacuum space will be ionized to a much greater extent than would be the case if the electrons were not caused to travel in orbits.

One important object of the present invention is to provide an ionizer of the orbitron type having new and improved means for injecting the electrons into orbits around the anode so that electrons are injected into orbits with significantly greater efficiency, with the result that much greater ionization of the residual gas molecules is produced by the ionizer.

Another object is to provide a new and improved ionizer of the foregoing character in which the device for emitting and injecting the electrons is exceptionally rugged and capable of giving extremely long life so that the useful life of the ionizer will be extended.

A further object is to provide a new ionizer which achieves greatly improved freedom from operating instability due to oscillations or the like.

In accordance with the present invention, the ionizer preferably comprises a generally cylindrical outer electrode, adapted to be connected to the negative terminal of the power supply, and an inner electrode or anode disposed axially within the outer electrode and adapted to be connected to the positive terminal of the power supply so that a positive potential will be provided be tween the anode and the outer electrode. The ionizer is adapted to be mounted in a vacuum space containing residual gas molecules which are to be ionized. The voltage on the anode produces a radial electric field in the annular space between the anode and the outer electrode. To inject electrons into orbits around the anode, an electron-emitting electrode is mounted between the outer electrode and the anode so as to extend at least partially around a circular path encircling the anode and spaced inwardly from the outer electrode.

Typically, the electron-emitting electrode may be in the form ofa loop or ring encircling the anode and disposed in a plane perpendicular thereto. The electronemitting electrode is in the radial electric field between the anode and the outer electrode. A small positive biasing voltage may be provided between the electronemitting electrode and the negatively charged outer electrode.

The ionizer also includes means for producing a general axial magnetic field at the location of the electronemitting electrode. Such magnetic field preferably extends axially in the space between the anode and the electron-emitting electrode. To produce such axial magnetic field, means may be employed to cause an electrical current to flow along the electron-emitting electrode. Such current may be employed not only to produce the axial magnetic field, but also to heat the electron-emitting electrode to such an extent that thermionic emission of electrons will be produced from the electrode.

A direct current is preferably employed so that the axial magnetic field will be unidirectional and of a steady intensity.

The electrons emitted by the generally circular electrode tend to travel inwardly toward the anode due to the radial electric field. However, the axial magnetic field imparts curvature to the paths of the electrons so that a high percentage of the electrons miss the anode and are injected into orbits around the anode. The orbiting electrons tend to spiral axially with a relatively slow axial velocity due to the Coulomb repulsion of the electrons in the space charge produced by the continu ous injection of electrons into orbits.

The axial magnetic field may also be produced or enhanced by an electromagnet or a permanent magnet positioned in the vicinity of the electron-emitting electrode. The electromagnet may take the form of a single loop or turn adapted to carry a magnetizing current and preferably coaxial and coplanar with the electron emitting electrode. Alternatively, the electro-magnet may comprise a multi-turn coil, aligned axially with the electron-emitting electrode and preferably provided wih a core made of a magnetic material.

The axial magnetic field may be produced by a generally cylindrical permanent magnet axially aligned with the electron-emitting electrode. If an electromagnet or a permanent magnet of sufficient strength is employed, the electron-emitting electrode may be heated by the use of alternating current.

The circular electron-emitting electrode may be rugged and may be operated at a relatively low tempera ture so that it will provide extremely long operating life.

Further objects, advantages and features of the present invention will appear from the following description, taken with the accompanying drawings, in which:

FIG. 1 is a diagrammatic elevational view of an ionizer to be described as an illustrative embodiment of the present invention.

FIG. 2 is a longitudinal section taken generally along the line 22 in FIG. 1.

FIG. 3 is a transverse section taken generally along the line 33 in FIG. 2.

FIG. 4 is an elevational view similar to FIG. 1 but showing a modified ionizer.

FIG. 5 is a transverse section taken generally along the line 55 in FIG. 4.

FIG. 6 is an enlarged diagrammatic longitudinal section through the ionizer of FIGS. 4 and 5 and showing the electric and magnetic fields around the electronemitting electrode.

FIG. 7 is a diagrammatic transverse section through the ionizer of FIG. 6 and illustrating the manner in which the electrons are injected into orbits.

FIG. 8 is a fragmentary elevation, similar to FIG. I, but showing another modified construction utilizing a singleturn loop to enhance the axial magnetic field.

FIG. 9 is a fragmentary longitudinal section taken generally along the line 99 in FIG. 8.

FIG. 10 is a diagrammatic transverse section taken generally along the line ll010 in FIG. 9.

FIG. 11 is a fragmentary elevation, similar to FIG. 8, but illustrating another modified construction utilizing an electromagnet to produce or enhance the axial magnetic field.

FIG. 12 is a fragmentary longitudinal section taken generally along the line l.212 in FIG. 11.

FIG. 13 is a transverse section taken generally along the line 1313 in FIG. 12.

FIG. 14 is a fragmentary elevation similar to FIG. 1, but showing another modified construction utilizing a permanent magnet to produce or enhance the axial magnetic field.

FIG. 15 is a fragmentary longitudinal section taken generally along the line l5l5 in FIG. 14.

FIG. 16 is a transverse section taken generally along the line l616 in FIG. 15.

FIG. 17 is a diagrammatic perspective view showing a getter-ion vacuum pump utilizing the ionizers of the present invention.

FIG. 18 is a graph illustrating the pumping characteristics of a getter-ion pump utilizing one of the ionizers of the present invention.

More detailed consideration will now be given to FIGS. l3 which illustrate an ionizer 20 adapted to be employed to ionize residual gas molecules in a vacuum space. One possible application of the ionizer 20 is shown in FIG. 17 which illustrates a getter-ion vacuum pump 22 for pumping residual gas molecules from a vacuum space 24 within a casing 26.

The getter-ion pump 22 comprises a plurality of the ionizers 20, although a single ionizer could be employed. The use of a plurality of ionizers increases the pumping rate which can be achieved by the pump 22. As shown, the pump 22 utilizes eight of the ionizers 20.

The getter-ion pump 22 of FIG. 17 also employs one or more devices 28 for evaporating or subliming titanium or some other gettering material, which is condensed or deposited upon the inside of the casing 26 and is effective to absorb gas molecules so that they are effectively removed from the vacuum space 24. The ionizers 20 are employed to ionize the gas molecules so that they will be propelled by electrostatic forces to the inside of the casing 26 where the ions are neutralized and absorbed by the getter material. The neutral gas molecules are buried by the progressive deposition of the getter material.

Each of the getter-subliming devices 28 may comprise a body 30 of titanium or some other getter material, together with means for heating the body 30 so that the getter material will be sublimed or evaporated.

As shown, the body 30 of getter material is adapted to be heated by an electrical heating element 32 mounted within or adjacent the body 30. As shown, the titanium body 30 is in the form ofa hollow cylinder within which the electrical heating element 32 is mounted.

While a single titanium sublimer 28 would produce a pumping action, it is preferred to employ a plurality of sublimers within the casing 26 to provide a greater pumping capacity and to prolong the life of the pump by providing a larger quantity of titanium which can be sublimed to maintain the pumping action. It is preferred to bring a plurality of leads 34 out of the casing 26 to an external power supply 36 so that each of the heating elements 32 can be energized individually. In this way, one or more of the sublimers 28 can be energized according to the desired pumping capacity. Either direct or alternating current may be employed to energize the heating elements 32 of the sublimers 28, but alternating current is generally preferred because it can be supplied more easily and economically.

In FIGS. 13, the casing which forms the walls of the vacuum system is not shown, but it will be understood that the ionizer 20 is adapted to be operated in a vacuum space.

As previously indicated, the ionizer 20 is of the orbitron type having a central anode 4t), typically in the form of a wire or rod which extends axially within an outer electrode 42, typically in the form of a hollow conductive cylinder. However, the outer electrode 42 need not be cylindrical in shape just so long as the outer electrode extends around the inner electrode or anode 40 so that an approximately radial field is produced between the anode 40 and the outer electrode 42 when a positive voltage is applied between the anode and the outer electrode.

As shown in FIG. 1, the positive voltage is provided by an external high votlage supply 44. Leads 46 and 48 are brought out of the vacuum space to the positive and negative terminals of the high voltage supply from the anode 40 and the outer electrode 42. A meter 50 may be connected in series with the outer electrode lead 48 to measure the ion current to the outer electrode 42. Such ion current provides an indication of the residual gas pressure in the vacuum space. Thus, the ionize may be utilized as an ion gage.

Forion pumping applications, the anode voltage provided by the high voltage supply 44 is typically quite high, up to about 10 kilovolts, for example. However, the voltage may be varied widely according to the desired pumping capacity. For small pumps, the anode voltage may be only a few kilovolts, for example. When the ionizer is used as an ion gage, the anode voltage is typically quite low, amounting to only a few hundred volts, for example.

The outer cylindrical electrode 42 may be in the form of a solid conductive wall made of sheet metal or the like, but is preferably in the form of a cylindrical screen or mesh as illustrated in FIG. 1. The cylindrical mesh permits most of the positively charged gas ions to travel outwardly through the mesh without being intercepted so that the ions will continue to travel outwardly to the outer walls of the casing 26 where the ions will be ab sorbed and buried by the getter material as explained above in connection with FIG. 7.

The illustrated anode 40 is in the form of a wire stretched between two springs or resilient supports 52 mounted on insulators 54. The anode wire 40 extends through axial openings 56 in a pair of end plates 58 at the opposite ends of the outer cylindrical electrode 42. As shown, the cylindrical electrode 42 is connected to the end plates 58 so that the end plates are at the same electrical potential as the outer electrode 42. However, the end plates 58 could be insulated from the outer electrode 42 and maintained at a somewhat different potential, if desired.

The ionizer is provided with means for injecting electrons into the radial electric field between the anode 40 and the outer electrode 42 in such a manner that many of the electrons will go into orbits around the anode. In accordance with the present invention, such means may take the form of an electron-emitting electrode 60 disposed between the anode 40 and the outer electrode 42. The electron-emitting electrode 60 preferably extends at least part way around a generally circular path encircling the anode 40 and spaced inwardly from the outer electrode 42.

FIG. 3 illustrates on typical form of the electronemitting electrode 60. It will be seen that the electrode 60 is in the form of a generally circular loop or ring constituting a one-turn coil and having its ends connected to supporting leads 62 and 64. One or more insulators 66 are provided to mount the leads 62 and 64 on one of the end plates 58. The loop electrode 60 is in a plane perpendicular to the central anode 40 which extends axially through the loop 60. The electron emittng electrode 60 may be mounted anywhere along the length of the anode 40 between the end plates 58, but preferably not 'too close to the end plates so that the electrode 60 will be in a substantially radial electric field.

The ionizer 20 is also provided with means for producing an axial magnetic field in the vicinity of the electron-emitting electrode 60. Preferably, the magnetic field extends in a generally axial direction through the plane of the electrode 60. In the ionizer 20 of FIG. 1, the axial magnetic field is produced by causing an electrical current to flow around the loop electrode 60 which acts as a single'turn coil. FIG. 2 includes a diagrammatic illustration of the magnetic lines of force 68 produced by the current flowing along the circular electrode 60.

The electrons emitted by the generally circular electron-emitting electrode 60 are attracted inwardly toward the positively charged anode 40.. Due to the axial magnetic field produced by the current in the electrode 60, the inward paths of the electrons are given a curvature which causes them to miss the anode 40 so that many of the electrons are injected into orbits around the anode.

The action of the axial magnetic field may also be explained by noting that the magnetic field applies a lateral force to the electrons as they travel inwardly toward the axial anode. Such lateral force is perpendicular to both the radial and axial directions. Thus, the lateral force imparts angular momentum to the electrons. Such angular momentum is conserved as the electrons travel in the radial electric field which exists between the coaxial electrodes 40 and 42. Thus, the electrons tend to travel through many orbits around the axial anode 40 before they eventually are attracted to the axial anode. Some of the orbiting electrons collide with gas molecules or encounter them in such a manner as to cause ionization of the gas molecules. Due to the orbiting of the electrons, they have an extremely long mean-free path so that the probability of a particular electron causing ionization of a gas molecule is greatly increased. Thus, the orbiting of the electrons greatly increases the total ionization of the gas molecules.

The magnetizing current in the circular electrode 60 also causes heating of the electrode. While the electrode 60 may be heated by other means, it is preferred to regulate the current through the electrode so that it is heated sufficiently to produce copious thermionic emission of electrons. Thus, the circular electrode 60 preferably comprises both a thermionic filament for emitting electrons and a single-tum coil for producing an axial magnetic field.

As shown in FIG. 3, leads 70 and 72 are preferably brought out of the vacuum space from the supports 62 and 64 for the circular filament 60 to an energizing circuit comprising a power supply 74. As shown, a vari' able resistor 76 and an ammeter 78 are connected in series with the power supply 74 and the filament 60, so that the filament current can be adjusted to any desired value. The power supply 74 preferably supplies direct current so that the axial magnetic field will be unidirectional and constant in intensity.

The electron-emitting electrode 60 may be operated at the potential of the outer electrode 42, which is usually at ground potential. However, it is preferred to bias the electrode 60 to a potential which is greater than the potential of the outer electrode 42, but much less than the positive potential on the anode 40. Thus, for example, for an anode potential of l0 kilovolts, the electronemitting electrode 60 may be biased to a positive potential of a few hundred volts.

As shown in FIG. 1, the biasing potential for the electron-emitting electrode 60 is provided by a bias voltage supply 80 having its negative output terminal connected to the negative terminal of the high voltage supply 44. To provide for adjustment of the biasing potential, a potentiometer 82 is connected between the positive and negative output terminals of the bias voltage supply 80. The potentiometer 82 has a movable contact 84 which is connected by means of a lead 86 to one side of the electron-emitting electrode 60.

In operation, the electron-emitting electrode 66 is heated by energizing the filament power supply 74 so that a direct current will flow along the electrode 60. In this way, the electrode 60 is heated to a sufficiently high temperature to cause the thermionic emission of electrons. The high voltage supply 44 is energized so that a positive potential ranging up to about 10 kilovolts is applied to the anode 40 relative to the outer electrode 42, which usually is at ground potential. The bias voltage supply 80 is also energized so that a much smaller positive biasing voltage is applied to the electron-emitting electrode 60. The potentiometer 82 may be adjusted to vary the biasing voltage.

The direct current which flows around the circular electrode 60 produces an axial magnetic field in the vicinity of the electrode and particularly between the electrode 60 and the anode 40. The thermionicallyemitted electrons are attracted inwardly toward the anode 4G by the radial electric field due to the positive anode potential. However, the axial magnetic field imparts curvature to the paths of the electrons so that many of them miss the anode 40 and go into orbits around the anode. Thus, the electrons pick up angular momentum due to the force exerted on the electrons by the magnetic field.

FIG. 6 constitutes a diagrammatic illustration of the radial electric field between the anode 40 and the outer electrode 42. FIG. 6 also illustrates the magnetic lines of force 68 produced by the direct current flowing around the loop-shaped electrode 60. It will be seen that the magnetic lines of force 68 extend axially in the plane of the electrode 60.

FIG. 7 illustrates a sample orbit 88 of one of the electrons emitted into the radial electric field and the axial magnetic field by the electrode 60. Generally, the orbits are approximately eliptical rather than circular in shape.

Due to the continuous emission of electrons by the circular electrode 60, a space charge of electrons is developed in the vicinity of the electrode 60. By Coulomb repulsion, the space charge causes the orbiting electrons to spiral or drift slowly along the length of the anode 40 so that gradually the orbiting electrons occupy the entire space between the anode 40 and the outer electrode 42. The spiraling electrons tend to be reflected axially by the end plates 58 so that the electrons are caused to drift in the opposite axial direction along the anode 40.

Some of the orbiting electrons collide with residual gas molecules or come into close enough proximity to the gas molecules to cause ionization thereof. The positive gas ions are attracted outwardly toward the outer electrode 42 by the electric field between the electrodes 40 and 42. Some of the positive gas ions impinge upon the outer electrode 42 whereupon the electric charges of the ions are neutralized. The resulting ion current is measured by the meter 50. Some of the gas ions are absorbed by the outer electrode 42, which may be made of or coated with a gettering material, such as titanium, for example.

In the vacuum pump 22 of FIG. 17, the getter material is condensed or deposited upon the outer electrode 42 so that some of the gas molecules tend to be buried by the freshly deposited getter material.

Due to the open mesh construction of the outer electrode 42, most of the positive gas ions travel outwardly through the openings in the screen electrode 42 and continue to travel outwardly until the gas ions impinge upon the outer wall of the casing 26. Generally, the easing 26 and the outer electrode 42 are at the same potential. Typically, both are at ground potential. The ions which strike the inner wall of the casing 26 are absorbed and buried by the titanium or other getter material, which is condensed or deposited on the inside of the casing 26 after being vaporized by one or more of the subliming devices 28.

The circular electron-emitting electrode or filament 60 is rugged in construction so that it gives a long operating life.

FIGS. 4 and illustrate a modified ionizer 90 which is similar to the ionizer of FIG. 1, except that the electron-emitting electrode or filament 60 is located centrally between the end plates 58 rather than being disposed relatively close to one of the end plates as in FIG. 1. Actually, the electrode 60 may be located any where along the axis of the ionizer 90. The electrode 60 produces its own axial magnetic field due to the current which is employed to energize the electrode. Thus, the magnetic field is present regardless of the position of the electrode 60.

Due to the central position of the electrode 60 in FIG. 4, the electrode has relatively long supports 92 and 94 in the form of stiff conductive wires or rods. It will be seen that the supports 92 and 94 extend into the space within the outer electrode 42 through an opening 96 therein. The ionizer may be supplied with energizing voltages in the same manner as illustrated in FIGS. l-3.

In the operation of the ionizer 90, electrons are injected into orbits in the same manner as described in connection with FIGS. 1-3. The orbiting electrons produce a space charge in the vicinity of the electrode 60. By Coulumb repulsion, the space charge causes the orbiting electrons to spiral or drift gradually along the axis of the ionizer 90 in both directions from the electrode 60. At the end plates 58, the axial movement of the orbiting electrons is reversed so that the electsons can continue to travel in orbits around the anode 40.

In FIG. 6, the electron-emitting electrode is shown in a central location along the axial anode 40, but the diagrammatic illustration of the electric and magnetic fields is applicable to FIGS. l-3 as well as FIGS. 4 and 5 In both FIGS. 6 and 7, the distribution of the electric field is represented by a series of cylindrical equipotential surfaces designa ted )1 1 V0, 0.2 V015 V where V0 is the anode voltage. Several of the magnetic lines of force 68 are also shown in FIG. 6 as previously indicated.

FIGS. 8l(l illustrate another modified ionizer 100, which is similar to the ionizer of FIG. 1, except that the magnetic field produced by the circular electronemitting electrode 60 is enhanced by an elementary electromagnet in the form of a Single conductive loop or turn 102 disposed in the vicinity of the electronemitting electrode 60. As shown, the loop 102 is coaxial and coplanar with the electrode 60. Preferably, the loop 102 is spaced outwardly from the electronemitting electrode 60. The loop 102 may be made of wire which is heavy enough to be rigid and selfsupporting, Inasmuch as the loop 102 does not need to be heated, there is no particular advantage in making it out of fine wire.

The ionizer 100 is provided with means for causing a current to flow around the loop 102 so that it will produce an axial magnetic field. Direct current is preferably employed so that the field will be constant and unidirectional.

The same current which heats the electrode 60 may be caused to flow around the loop 102 so that the magnetic field produced by the current in the electrode 60 will be enhanced by the additional turn provided by the loop 102. As shown in FIG. 10, the loop 102 is connected in series with the electron-emitting-electrode 60. Leads 104 and 106 are brought out of the vacuum space from the ends of the loop 102 so that the series connection can be made externally.

The electrode 60 and the loop 102 are connected in series across a direct current power supply 108. In order to provide for adjustment of the current, a variable resistor 110 may also be connected in series with the power supply 108. Any other suitable regulating arrangement may be employed.

The circuit of FIG. 10 also includes ammeters 112 and 114 in series with the electrode 60 and the loop 102, as well as variable resistors 116 and 118 connected in parallel with the electrode 60 and the loop 102. The variable resistors 116 and 118 make it possible to regulate the currents through the electrode 60 and the loop 102 separately. In this way, the heating current through the electrode 60 can be adjusted to achieve the desired emission of electrons. The magnetic field can then be adjusted by changing the current through the loop 102. If desired, independent power supplies may be provided for the electrode 60 and the loop 102.

FIGS. 1113 illustrate another modified ionizer 102, which is similar to the ionizer of FIGS. 1-3, except that an electromagnet 122 is provided to enhance the axial magnetic field in the vicinity of the electronemitting electrode 60. In this case, the electromagnet 122 comprises a solenoid or coil 124 having a plurality of turns. Preferably, the electromagnet 122 has a core or pole-piece 126 within the coil 124. The core 126 may be made of iron or some other magnetic material having high permeability.

The illustrated core 126 is in the form ofa hollow cylinder arranged to encircle the anode 40. The coil 124 and the core 126 are preferably coaxial with the anode 40 and are located as close as possible to the electronemitting electrode 60. Much of the axial magnetic field produced by the electro-magnet 122 extends through the loop-shaped electrode 60.

In the arrangement of FIGS. 11-13, the electronemitting electrode 60 and the electromagnet 122 have separate power supplies 128 and 130. The electromagnet 122 is preferably energized with direct current so that the axial magnetic field will be constant and unidirectional. As shown, the potentiometer 132 is provided between the power supply 130 and the electromagnet 122 to regulate the energization of the electromagnet so that the magnetic field can be varied.

The power supply 128 for the electron-emitting electrode or filament 60 may provide either direct or alternating current. The use of direct current will make it possible to enhance the axial magnetic field, but such enhancement is not necessary because the electromagnet 122 is capable of producing an intense magnetic field. The filament power supply 128 may utilize any suitable device for adjusting the filament current.

FIGS. 14-16 illustrate still another modified ionizer 140, which is similar to the ionizer 120 of FIGS. 11-13, except that a permanent magnet 142 is employed rather than the electromagnet 122 to produce or enhance the axial magnetic field. The position of the permanent magnet 142 is similar to that of the magnetic core 126. Thus, the illustrated permanent magnet 142 is in the form of a hollow cylinder coaxial with the anode 40 and positioned on the opposite side of the end plate 58 from the electron-emitting electrode 60. Due to the closeness of the permanent magnet 142 to the electrode 60, much of the magnetic field of the permanent magnet extends through the loop-shaped electrode 60.

The permanent magnet 142 is capable of producing a strong electromagnetic field regardless of the current which may be flowing along the electrode 60. Here again, the electrode 60 may be energized with either alternating or direct current. If direct current is employed, the polarity of the magnetic field produced by the direct current should be the same as the magnetic polarity of the permanent magnet 142.

The circular electron-emitting electrode or filament 60 has the advantage of producing high emission of electrons and high injection efficiency so that a high percentage of the emitted electrons are injected into stable orbits around the anode 40. In this way, the electrons have an extremely long mean-free path so that the ionizer produces a high level of ionization. Thus, the ionizer produces a high pumping rate when employed in a getter-ion pump of the general type represented by FIG. 17. Moreover, the circular filament is rugged and is capable of providing long filament life.

FIG. 18 is a graph in which the argon pumping speed, in liters per second, is plotted along the Y axis against filament current, in alternating current amperes, plotted along the X axis. The graph represents the performance of a simple getter-ion pump, similar to that of FIG. 17, but having only a single ionizer and a single tita nium sublimer.

It will be seen that in this particular pump the argon pumping speed increased rapidly with increasing filament current up to algnee or bend inthecurve between 9 and 10 amperes. The pumping speed then increased much less rapidly with increasing filament current. By operating the pump approximately at the knee of the curve, a high pumping speed can be achieved while also providing long filament life. The approximate filament life to be expected for various filament currents is also indicated along the X axis in FIG. 18. It will be seen that the filament can be expected to give a life in excess of 65,000 hours when operated at the knee of the curve where the filament current is about 9.5 amperes,

I claim:

1. An ionizer for ionizing residual gas molecules in a vacuum space,

comprising a hollow generally cylindrical outer electrode,

an inner electrode disposed axially within said outer electrode and adapted to be charged with a positive potential with respect to said outer electrode to produce a radial electric field in the annular space between said inner and outer electrodes,

a generally circular electron-emitting loop electrode extending around said inner electrode and spaced radially inwardly from one end portion of said outer electrode,

said loop electrode being generally coaxial with said inner electrode and being disposed near one end thereof,

and a generally cylindrical permanent magnet substantially coaxial with said loop electrode,

said permanent magnet having an outside diameter less than the diameter of said outer electrode and having one end closely spaced axially from said electron-emitting loop electrode in an end-to-end confronting relationship thereto for producing a generally axial magnetic field adjacent said electron-emitting loop electrode and in the space between said electron-emitting loop electrode and said inner electrode to impart curvature to the paths of the electrons emitted by said electronemitting loop electrode whereby the electrons will be injected with high efficiency into orbits around said inner electrode.

2. An ionizer according to claim 1.,

in which said generally cylindrical permanent magnet is ring-shaped and has an axially disposed generally cylindrical opening through which said inner electrode extends,

said opening being larger in diameter than said inner electrode but smaller in diameter than said electron-emitting loop electrode.

3. An ionizer for ionizing residual gas moleculdes in a vacuum space,

comprising a hollow generally cylindrical outer electrode,

an inner electrode disposed axially within said outer electrode and adapted to be charged with a positive potential with respect to said outer electrode to produce a radial electric field in the annular space between said inner and outer electrodes,

21 generally circular electron-emitting loop electrode extending around said inner electrode and spaced radially inwardly from one end portion of said outer electrode,

said loop electrode being generally coaxial with said inner electrode and being disposed near one end thereof,

and an electromagnet having a coil with a generally cylindrical core substantially coaxial with said loop electrode,

said core having an outside diameter less than the diameter of said outer electrode and having one end closely spaced axially from said electron-emitting loop electrode in an end-to-end confronting relationship thereto for producing a generally axial magnetic field adjacent said electron-emitting loop electrode and in the space between said electronemitting loop electrode and said inner electrode to impart curvature to the paths of the electrons emitted by said electron-emitting loop electrode whereby the electrons will be injected with high efficiency into orbits around said inner electrode.

4. An ionizer according to claim 3,

in which said generally cylindrical core is ring-shaped and has an axially disposed generally cylindrical opening through which said inner electrode extends,

said opening being larger in diameter than said inner electrode but smaller in diameter than said electron-emitting loop electrode.

Referenced by
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Classifications
U.S. Classification361/230, 324/462, 313/562, 324/463, 417/49
International ClassificationH01J41/06, H01J41/16, H01J41/00
Cooperative ClassificationH01J41/06, H01J41/16
European ClassificationH01J41/06, H01J41/16