US2548283A

US2548283A - Ion gauge

Info

Publication number: US2548283A
Application number: US75043A
Authority: US
Inventors: Bashkin Stanley
Original assignee: Individual
Current assignee: Individual
Priority date: 1949-02-07
Filing date: 1949-02-07
Publication date: 1951-04-10
Anticipated expiration: 1968-04-10

Description

s. BASHKIN April 10, 1951 ION GAUGE Filed Feb. '7, 1949 Fi g.l.

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INVENTOR. STANLEY BASHKIN /mM/flw Patented Apr. 10, 19 51 c UNITED STATES PATENT OFFICE ION GAUGE Stanley Bashkin, Madison, Wis., assignor to the United States of America as represented by the United States Atomic Energy Commission Application February 7, 1949, Serial No. 75,043

2 Claims. (01. 313-293) I The present invention relates to an improved ion gauge. Conventional ion gauges consist of an air-excluding jacket enclosing three concentrically arranged electrodes, the filament being the innermost electrode, the grid being a cylindrical electrode surrounding the filament electrode and the ion collector electrode being a cylindrical electrode surrounding the previous two. The filament electrode is electron emissive. It is surrounded by the positively charged grid electrode, and this in turn is surrounded by the ion collector electrode which is negatively charged with respect to the grid electrode and the filament electrode. from the electron emissive filament electrode are accelerated by the positive charge on the grid electrode and those which do not strike the grid electrode directly are caused to oscillate around the strands of which it is composed, until they are captured by the grid electrode or ions are formed when the electrons strike gas molecules. The ions formed by the rapidly moving electrons are, for the most part, positively charged ions. One of the difiiculties arising from the arrangement of electrodes in such previously known ion gauges is the trapping of positively chargedions in the volume defined within the grid electrode. Because of the relatively high potential on the grid electrode the positive ions, formed in the volume defined within said grid electrode, are repulsed from the grid electrode and alarge number thereof are caused to strike the filament electrode to which they are attracted. This action results in two deleterious efiects on the conventional ion gauge. One of these is the reduction in sensitivity which follows 'from the reduced In operation, electrons emitted number of positive ions reaching the ion collector plate. The second is the reduced life of the filament electrode resulting from the bombardment thereof by the positively charged ions enclosed within the volume defined by the grid electrode. The second efiect is usually evidenced by the formation of a carbonaceous deposit on the filament electrode or of the wearing through and breaking of said electrode either of which necessitates frequent replacement thereof.

It is accordingly an object of the present invention to provide an ion gauge having a greater sensitivity than previously known ion gauges.

It is another object of the present invention to provide an ion gauge which retains its sensitivity over a longer period of time.

It is a further object of the present invention 7 to provide an ion gauge which minimizes the bombardment of the filament and the formation thereon oi a carbonaceous deposit.

means adaptable to be connected with a vessel which may contain gas at very low pressure, an electrode assembly including a grid electrode, an ion collector electrode and a filament electrode within said ,means, said filament electrode being positioned-between at least a portion of said grid. electrode and at least a portion of said collector electrode so thatcharged particles passing from said filament to said portion of said collector electrode do not pass through a grid electrode, and means for measuring the current flowing to said collector electrode. V

' Two embodiments of the present invention are illustrated in the accompanying drawing and the manner of achievement of the objects of the present invention may be explained more clearly with reference to the drawing wherein:

Figure 1 is an elevation of a tube assembly with the jacket broken away along broken line l| of Figure 2 and with a part of the collector electrode broken away.

Figure 2 is a horizontal section taken on the line 22 of Figure l. Figure 3 is' an elevation of another tube assembly with the jacket broken away along broken line 3 -3 of. Figure 4 and with a part of its collector electrode broken away. j

Figure 4 is a horizontal section taken on line 4-4 of Figure 3. g g j I Referring toFigures 1 and 2, gas is excluded from. an electrode assembly by a glass jacket I00. The jacket is preferably made of glasses such as those generally designated as Pyrex and Nonex. The jacket is essentially Pyrex glass with Nonex glass sealed thereto atthe portions of the jacket I00 through which electrical contacts are sealed for connecting the electrode assembly with the tube exterior. The seal through the Nonex

portions

90, 92; 94- and 96 was made by means of 10 mil tungsten wires H5, H1, I09 and ll'll. The chamber enclosed by the glass jacket I00 may be connected to a system which may contain gas at a very low pressure by means of the tapered ground glass joint 88. As in conventional ion gauges, electrons areemitted from a heated filament I06 which is supported on the nickel rods I 13 and Ill which are'in turn connected respecr 3 tively to the tungsten leads II! and H5, said leads being sealed through the jacket I at the Nonex

portions

90 and 92 respectively. The emitted electrons bombard the gas present within the jacket Ito and cause ionization of said gas. An ionic current therefore flows between the filament I00 and .a collector plate I02 which collects the ions formed by the electrodes. The current in tensity bears such a relation to the pressure or gas present in the jacket I00 that the pressure may be measured by measuring the current flowing to the collector plate I02.- Electrical connection is made between the filament I06 and the collector plate I02 through an external current measuring device (not shown The positioning of the collector plate I02 in the jacket I00 and the electrical connection to the jacket exterior is effected by the nickel rod I05 and the tungsten tioned within the volume defined by the generally cylindrically shaped collector plate I02 in relatively closeproximity to the filament I06. Such a grid may be in the form of a conductive strand crimpd in a zigzag configuration to define a generally rectangular shape.

\ As an example of the tube dimensions in one tube such as that illustrated in Figure l, which tube was found to operate with higher efficiency than the conventional tubes, the following dimens'ion were found satisfactory. were approximately 2 inches in height. whole assembly was enclosed in a jacket of about 2 inches in diameter, the collector being spaced about A; .of an inch. from the jacket wall. The

H4 by causing a suitable high voltage to be placed on a grid IIE which is disposed between the filament I I8'and the outer collector plate I I4. Such a grid may have, for example, a helical shape. Electrical connection to the tube exterior from the grid I I6, the filament H0 and the collector plate I20 and II 4 is made by means of the nickel rods I30, I32 and I34 respectively and the tungsten leads I35, I38 and I40 respectively, said leads being sealed through the Nonex portions I42, I44 and I40 of the jacket IIO. Conventional electrical supply and measuring apparatus (not shown) is employed in the external circuit.

The following is offered as an explanation of the more efiicient operation of ion gauges pro- 'vided by the present invention over those provided by prior ion gauges although it will be understood that the concept of the present invention is not limited by the accuracy of this explanatioh. Referring to Figure 2; electrons are emitted from filament I06. Those electrons which are emitted toward the portion of the ion collect'or I92 on the filament side of broken line A'A will be repulsed by the low potential on the ion collector 102 toward the grid I04. The high potential on the grid I04 'will attract the elec trons repulsed from the aforementioned portion ,7 of the ion collector 92 past the filament I00 and The electrodes 7 The filament wasspace'dabout of an inch from the ja'jkt wan alld th grid, which had a Width 0f about of an inch. was spaced about of an inch from the same point on the jacket wall from which the filament was spaced of an inch. Electrical connection was made from the v grid I04 to an external voltage control means (not shown) through the nickel rod IOI and the tungsten l'ead I09 which was sealed through the jacket I00 at the Nonex portion 94 thereof. A bent tungsten wire having a thickness of about 10 mil was found suitable for the filament I06 and the grid I04 and a nickel foil of approximately 5 mil in thickness, formed into a generally cylindrical shape, was found suitable asa collector plate "I02. All metal tometal connections were made by spot welding. Conventional external electrical supply and 'detectioh means were used in conjunction with the tube. Q 7

Many alternatives of the electrode arrangement whereby at least a portion of the filament electrode is disposed between at least a portion of the collector electrode and a portion of the, grid electrode such that electrons may pass between the portions of the filament and collector electrodes without passing through a grid will be apparent to one familiar with the art. One such arrangement is illustrated in Figures 3 and 4 wherein gas is excluded from an electrode assembly by a glass jacket IIO which may be connected to a system which maycontain gas at very low pressure by means of the tapered ground glass joint 80. Electrons are emitted within said jacket IIO from a filament H8 and cause ions to form, which ions pass to either an inner collector plate I20 or an outer collector plate H4.

The electrons emitted from the filamentl I8 are accelerated outwardly toward the collector pate some of those electrons which do not strike the grid I0 4 "will oscillate around the strands thereof until they have struck a molecule and formed an ion, or until they strike the grid I04. Some of the electrons emitted from filament I05 toward the grid side of the collector plate I02 will proceed directly toward the grid I04, and will spiral around said grid I04 as hereinabove described. Whatever positive ions are formed along'any of these electrons paths will be in such a position with respect to the ion collector plate I02 that they will not have to pass through the grid I04 to'rea'ch said collector plate I 02 and thus substantially all positivejions formed will be collected on collector plate I02.

H A similar phenomenon occurs in the apparatus illustrated in Figures 3 and 4; Positive ions ;-'-mee between the filament I I8 and the collector lfiiil will be attracted to the collector I20 since the semester potential is below that of the filament potential. Similarly. ions formed between the grid electrodel I6 and th'e'filame'nt electrode H8 collected without any interference on the "outer collector I I4.

The materials and potentials which may be used in the present invention are "substantially the sameas those used'i'n a conventional ion gauge. For example, the grid potential may be kept'a't about volts above the filamentpotential and the" collector maybe kept at a potential approximately 20 volts below theiilament'p'otential. The substitution of other materials for the nickel and tungsten employed in the disclosedembodimnts is not 'a departure from the scope of the present "htion. It is desirable to keep the volume of the'i'on gauge relatively small, thus, for example, thespace between the collector electrode and, the envelope serves ho useful purpose and should be minimized.

1 foam to operate with higherefiiciency and with greater sensitivity thanpreviaany rmbwngauges.

The useful life of the filament is greatly extended and relatively small deposits of carbonaceous material form within comparable time to that in which filaments of previously known ion gauges were coated so as to materially reduce the efficiency of the gauge. In addition, the filament of such a gauge was not Worn away after continued use to the extent that could be expected for previously used gauges.

It is apparent from the foregoing that the present invention provides a very highly efficient gauge. It will be understood that the scope of the present invention is not limited to the two illustrative embodiments set forth and represented in the figures but that other variations may be employed without departing from the substance of the present concept. Thus, for example, filaments might be disposed on both sides of the grid I04 rather than on the one side only as indicated by the broken line I05 in Figure 2. Similarly, a filament and grid and collector plate might be incorporated in that order outside the collector plate of either of the illustrative embodiments set forth thus making a series of collector, filament, grid, collector, filament, etc, Other variations which provide free access of ions formed in the ion gauge to the collector plate will be apparent to those familiar with the art.

Since many embodiments might be made in the above-described invention and since many changes might be made in the embodiment illustratively disclosed herein, it is to be understood that all matter hereinabove set forth is to be interpreted as illustrative only and not in a l m g sense,

comprises gas-excluding means adapted to be connected with a vessel which contains gas at very low pressure, said means having a generally cylindrical shape and enveloping a collector electrode which closely conforms to the shape of the cylindrical portion of said means, a grid electrode consisting of a conductive strand crimped in a zigzag configuration to define a generally rec-v tangular shape, a filament electrode consisting of a conductive strand crimped to form an inverted V, said grid electrode and filament electrode being juxtaposed in and enveloped by said cylindrical collector electrode.

STANLEY BASHKIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,372,798 Buckley 1 Mar. 29, 1921 1,723,869

Langmuir Aug. 6, 1929