Ion Pump

This invention relates to improvements in ion pumps.

Ion pumps, including a vacuum housing, a magnet system providing a magnetic field, an anode positioned in the magnetic field and a reactive metal cathode positioned between the anode and the magnet system for reacting with gaseous ions impinging thereon for their collection, are well known in the art. Such known pumps, however, are subject to a number of deficiencies.

For example, the reactive metal cathode, because of its reaction with the gaseous ions, in time has its efficiency reduced to the extent that it must be replaced, as determined by the measurement of pressure-related current, that is, the ion current flowing between anode and cathode. This requires a substantial disassembly and reconstruction of the pump.

Another problem arises because the deposition of sputter products on the ceramic high voltage anode insulator in time increases the leakage current to the extent that the insulation must be replaced or the sputter products removed. Again, this requires a substantial disassembly and reconstruction of the pump.

Another problem with known ion pumps involves the difficulty of measurement of their leakage current independently of their pressure-related current, so that their operating efficiency cannot readily be determined.

Still another problem arises because of the necessity of providing known ion pumps with separate high voltage power supply and current metering systems.

In addition, the construction of known ion pumps is both unduly complicated and expensive.

Accordingly, it is a major object of the invention to provide a novel ion pump not subject to any of the above mentioned problems and one which provides a simpler and more economical construction.

These objects are accomplished according to the present invention by providing a novel ion pump having a number of unique features.

In one aspect, the present invention provides novel cathode mounting means for removably mounting the cathode for removal and replacement without the necessity for dissassembly and reassembly of the ion pump.

In another aspect, the present invention provides novel sputter shielding for preventing deposition of sputter products on the outer surface of the anode insulator.

In still another aspect, the present invention provides a novel magnet system which makes it possible to measure leakage current alone simply by removing the system from the pump. The system, furthermore, is not only so simple as to be readily removable and replaceable, but also provides a closed magnetic loop for improved efficiency.

In a further aspect, the invention provides both power supply and current metering means which may be mounted on and directly connected to the ion pump of the invention.

For the purpose of fully describing the above and further objects and features of the invention, reference is now made to the following detailed description of a preferred embodiment thereof, taken together with the accompanying drawings, wherein:

FIG. 1 is a side sectional view of the ion pump of the invention;

FIG. 2 is a sectional view of the ion pump of FIG. 1 taken on line 2--2 thereof;

FIG. 3 is a sectional view of the ion pump of FIG. 1 taken on lines 3--3 of FIGS. 1 and 2;

FIG. 4 is a sectional view of the ion pump of FIG. 1 taken on line 4--4 thereof; and

FIG. 5 is a disassembled perspective view of the ion pump of FIG. 1.

Referring to the drawings, the ion pump of the present invention includes a generally circular, tubular housing 12 having a central axis C with a gas input opening 16 at one end and an axially extending high voltage power input terminal 44 at its opposite end. A sealing flange 14 and associated mounting ring 18 is provided on the end of housing 12 around its gas input opening 16. Other known mounting arrangements may also be used. A filter screen 20 is removably mounted by a press fit within gas input opening 16.

Externally on housing 12 is mounted a readily assembled magnet system, including a pair of identical, opposed removable ferrous metal magnet yokes 23, 33, each extending around about one half the periphery of housing 12 to together surround housing 12, and a pair of identical, opposed cylindrical magnets 22, 32, each positioned and removably retained between one of yokes 23, 33 and the exterior surface of housing 12, with their axes located on transverse axis A perpendicular to and passing through housing central axis C, to provide the necessary magnetic field therebetween. Housing 12 includes a pair of opposed recesses 21, 31 and yokes 23, 33 each include a recess 24, 34, respectively, for positioning and retaining magnets 22, 32, respectively, therebetween. Yokes 23, 33 are identical and extend around housing 12 for slightly in excess of 180 degrees, yokes 23, 33 each having a concentric outwardly offset end 25, 35, respectively, which overlies their other ends 26, 36, respectively, to provide a closed magnetic loop around housing 12. Although magnets 22, 32 and their yokes 23, 33 are normally retained in position by magnetic forces, they may be positively secured by a temporary securing wire 38 passing therearound through slots 27, 37 in the exterior surface of yoke recesses 24, 34. By removing securing wire 38, yokes 23, 33 and magnets 22, 32 may be readily removed from housing 12, since they are not positively secured thereon except by temporary securing wire 38, in order to make possible the measurement of leakage current independently of pressure-related current, since removal of the magnets 22, 32 eliminates pressure-related current flow, as is well known in the ion pump art.

A high voltage conductor 42 extends along housing central axis C from external high voltage terminal 44 and has mounted on its free end, by eyelet 43, a conventional hollow cylindrical anode 40 having its axis coincident with magnet axis A and with its ends spaced from the interior surfaces of housing magnet recesses 21, 31, in the magnetic field between magnets 22, 32, for ionizing gaseous atoms in the usual manner. Conductor 42 has a surrounding ceramic insulating sleeve 46 having its free end 54 spaced from anode 40 and having its terminal end 50 sealingly connected, at its input terminal 44 by mounting ring 48 to sleeve 46. Sleeve 46 is itself sealingly mounted at its terminal end 50 adjacent the input terminal end of housing 12 by an outer mounting cup 56 mounted within in housing 12 and an inner mounting cup 58 mounted on outer mounting cup 56 and insulating sleeve 46. Inner mounting cup 58 has a retroverted portion 60, concentric with the outer surface of sleeve 46, which cooperates with surrounding sleeve protuberance 52, from which it is slightly spaced outwardly, to prevent passage of sputter products onto the outer surface of insulating sleeve 46 in its portion between protuberance 52 and the edge of inner mounting cup 58 mounted on insulating sleeve 46.

For preventing the deposition of sputter products on the outer peripheral surface of insulating sleeve 46 between its free end 54 and protuberance 52, a novel circular sputter shield 62 is provided. Sputter shield 62 has its outer edge mounted on outer cup 56 and its inner inner edge 64 closely spaced, about 0.025 inches, from and extending outwardly from the free end 54 of insulating sleeve 46 spaced from and adjacent to anode 40. The novel tandem configuration of the two sputter shielding gaps provides exponential sputter shielding attenuation.

A novel reactive metal cathode, preferably of high purity titanium and generally designated 65, is removably mounted within housing 12 between and spaced from the ends of anode 40 and in contact with the inner surface of housing magnet recesses 21, 31 for reacting with gasous ions impinging thereon to collect said ions by chemical reaction, as is well known in the ion pump art. More specifically, the novel removable cathode 65 according to the present invention comprises a "U" shaped sheet metal member having a base portion 70 and leg portions 66,68, with its base portion 70 frictionally retained between spring clip 72, which has its inner end secured within housing 12 and its free end 76 generally parallel to the inner surface of housing 12 and facing opening 16, and the inner surface of housing 12, so that leg portions 66, 68 are located between each of magnets 22, 32 and anode 40. With this arrangement, cathode 65 is securely retained within housing 12 in proper low resistance electrical contact therewith, yet may be easily removed, after first removing filter screen 20, and replaced through opening 16, after which filter screen 20 may be replaced.

Further in accordance with the present invention, a high voltage power supply unit 78, including a conventional solid state high voltage power supply 80, having low voltage input terminals 84, 85 on one end and a high voltage output terminal 82 on its opposite end may be mounted by surrounding mounting sleeve 98 on the power input terminal end of housing 12 with its high voltage output terminal 82 connected directly to high voltage input terminal 44 and its ground terminal 83 connected directly to housing ground terminal 13 of the ion pump.

There may also be provided a current metering unit 88 having low voltage input terminals 84, 85 and low voltage output terminals 94, 95 with a conventional microammeter 90 connected therebetween, current metering unit 88 being mounted by mounting sleeve 98 on the low voltage input terminal end of power supply unit 78, with its low voltage output terminals 94, 95 connected directly to low voltage input terminals 84, 85 of power unit 78. Microammeter 90 may be provided with a logarithmic scale to provide a direct pressure reading, as is well known in the ion pump art.

In operation, with metering unit 88 connected to a suitable low voltage power source and with power unit providing a suitable high voltage to anode 40, gaseous atoms passing into housing opening 16 are removed in the usual manner by converting or implanting them into reactive metal solid products on the surface of cathode 65. As is well known, such conversion degrades the cathode surface, so that cathode 65 must be replaced in time. However, the novel replaceable cathode 65 of the invention makes it possible to do this in the field, without significant disassembly of the ion pump, as has been explained above.

The ion conversion also produces sputter products, which, if deposited on the surface of ceramic insulating sleeve 46, provide a current leakage path and a resulting resistive leakage current which in time reduces the efficiency of the pump to a sufficient degree that it must be replaced or repaired. The narrow gap between the free end of the ceramic insulating sleeve 46 and the inner edge 64 of sputter shield 62 of the present invention, particularly in tandem arrangement with the narrow gap between insulating sleeve protuberance 52 and the surrounding retroverted portion 60 of inner sleeve mounting cup 58, as explained above, essentially prevents significant deposition of sputter products on the surface of insulating sleeve 46, so that the resistive leakage current is insignificant.

In this regard the novel removable magnet system of the invention makes it possible to directly measure any resistive leakage current in the field, by simply removing the magnet system, also as explained above. The true pressure-related current can then be determined by subtracting the measured leakage current from the measured total current.

Finally, the pump mounted high voltage and current measuring units of the invention provide not only a simplified, but also a safer arrangement, as well as one which can be readily operated by an emergency power supply, such as a battery.

Various modifications of the inventions herein described, within the spirit thereof and the scope of the appended claims, will occur to those skilled in the ion pump art.