US3240421A

US3240421A - Ion transport pump

Info

Publication number: US3240421A
Application number: US253640A
Authority: US
Inventors: Philo T Farnsworth
Original assignee: Deutsche ITT Industries GmbH
Current assignee: TDK Micronas GmbH; International Telephone and Telegraph Corp
Priority date: 1963-01-24
Filing date: 1963-01-24
Publication date: 1966-03-15
Anticipated expiration: 1983-03-15
Also published as: BE642926A; CH428073A; NL6400494A; GB1045721A

Description

March l5, 1966 P T. FARNswoRTH 3,'40,41

ION TRANSPORT PUMP Filed Jan. 24, 1963 WN..... m n wm..

United States Patent O 3,240,421 ION TRANSPORT PUMP Philo T. Farnsworth, Fort Wayne, Ind., assignor to International Telephone and Telegraph Corporation, Nutley, NJ., a corporation of Maryland Filed Jan. 24, 1963, Ser. No. 253,640 22 Claims. (Cl. 230-69) The present invention relates to an ion transport pump, and more particularly to an electron discharge device for use in evacuating closed vessels.

In transport pumping, ions are rst formed from neutral atoms and then transported by electric field and space charge forces to a region remote from the point of formation, where the ions are neutralized and then scavenged by means of a conventional vacuum pump. As the pressure in the vessel being evacuated reduces, the number of neutral gas atoms for ionization correspondingly reduces. Since the rate of ionization is directly related to the number of neutral atoms to be ionized, it is important in obtaining an ecient evacuating operation that the capability of ionization be relatively high at all times. Additionally, it is important that once the ions are formed, they be transported to a region from which the probability of escape retrogressively is minimal. Furthermore, when such ions are transported to this region, it is necessary that they be neutralized and scavenged continuously such that the processes mentioned in the foregoing can continue without interruption, thus reducing the pressure in the vessel being evacuated to an extremely low level.

It is, therefore, an object of this invention to provide a transport pump wherein the combined forces of an electrical field and an electron discharge serve in propelling ions in a common direction from a region or regions of ionization.

It is another object of this invention to provide a transport pump which utilizes field and charge forces for transporting ions in one direction and mechanical means for restricting ow of neutral gas atoms in the opposite direction.

It is yet another object of this invention to provide a transport pump which is arranged in stages functionally interconnected by means of flow-limiting apertures and electron concentrations which assist in guiding ions developed in the stages through said apertures and eventually to a deionizing chamber.

In the accomplishment of this invention, there is provided a transport pump comprising an envelope divided into first and second tandem pump sections. In the first section, there is provided rst and second spaced-apart electron-repelling electrodes which define the opposite ends, respectively, of a space current region. An anode electrode is interposed between said rst and second electrodes and surrounds said space current region. The envelope is provided with an inlet port which directly communicates with this space current region. The second electrode is provided witha beam-receiving aperture which serves as the only means of gaseous communication between the aforesaid rst and second pump sections.

The second pump section is provided with a third electron-repelling electrode which is spaced from the second electrode for defining the opposite ends, respectively, of a second space current region. A second anode electrode is interposed between the second and third electrodes and surrounds the second space current region. Also, the third electrode is provided with a second aperture which may be aligned with the aperture in the second electrode.

A fourth electron-repelling electrode is spaced from the third electrode and may be aligned with both of the aforesaid apertures. An exhaust port in the envelope directly ice communicates with the space between the third and fourth electrodes.

In the operation of the foregoing described structure, some electrons are directed from said fourth electrode through the closer of said apertures and into the second pump section. A first electric field is established within the second pump section between said second and third electrodes for oscillating an ionizing cloud of electrons therebetween. Similar means establish another field within the first pump section between the rst and second electrodes for oscillating another ionizing cloud of electrons therebetween. These elds are arranged to have an overall potential distribution which generally progresses from a maximum positive value within the first pump section to a minimum negative value in the second pump section. Therefore, ions developed in both pump sections are propelled through the aforesaid apertures toward the fourth electrode at which they become neutralized. Once neutralized, the atoms can be pumped from the envelope via the exhaust port.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. l is a longitudinal sectional illustration of one embodiment of this invention;

l FIG. 2 is a graph of the potential distribution along the axis of the pump; and

FIG. 3 is -a fragmentary sectional view of another embodiment of this invention.

Referring to the drawings, a glass envelope 1 which is generally cylindrical in shape is hermetically sealed with the exception of an inlet port 2 at one end and an exhaust port 3 at the opposite end. The envelope 1 is of two different diameter sections, the larger diameter section being indicated by the numeral 4 and the smaller diameter section by the numeral 5. The larger diameter section 4 has fixedly mounted therein two facing concave cathodes and electron-repelling electrodes 6.and 7, respectively, which are segments of spheres and which preferably are formed of some suitable secondary emitting material such as beryllium copper, stainless steel and the like. These electrodes are spaced apart as shown and are arranged coaxially with the tube axis which passes through the centers thereof.

While any suitable means may be employed for securing the electrodes 6 and 7 within the envelops, it is important that the means supporting the electrode 6 be substantially open to provide for the free flow of gas within the envelope. For this purpose, a metallic disc 8 which is secured to the periphery of the electrode 6 and also to the wall of the envelope 1 is provided with a multiplicity of apertures throughout the entire circumference thereof.

In distinct contrast, the electrode 7 should be impervious (with the exception of an aperture) to the flow of gas such that it corresponds to a Wall or partition within the envelope 1. Since the electrode 7 as shown is somewhat smaller in diameter than the envelope 1, an annular metal disc 9 is welded around its inner perimeter to the electrode 7 and is similarly welded or fused around the entire outer perimeter thereof to the envelope 1. The importance of this feature will be explained more fully hereinafter.

The central portion of the electrode 7 is provided with the aforesaid aperture 10 which coincides with the tube axis.

As shown, the two electrodes 61and 7 are spaced relatively widely apart. In this space is an anode assembly which consists of two cylindrical `

sleeves

11 and 12 of conductive material which are coaxial with respect to the tube axis and axially spaced apart as shown. These sleeves may be in the form of metallic tubes or conductive coatings on the inner wall of the lenvelope 1, but in any event they are insulated from each other. Otherwise, these sleeves should be made of non-magnetic material.

Between the sleeve 11 and the electrode 6 is a frusto- 4conical element 13 made of a conductive material which is nonmagnetic. This element 13 is coaxially mounted with its smaller diameter end 14 being adjacent to the electrode 6 andthe larger diameter end 15 adjacent to the sleeve 11. This larger diameter end 15 approximates in size the diameter of the sleeve 11. A mounting 16 for the element 13 for securing the latter in place may -be substantially identical to the apertured disc 8 which is -used to support the electrode 6. Alternatively, if it iS desired for the supporting ring 16 to be solid, the element,13 may be formed of metal mesh which permits the free flow of gas therethrough and into the space inside the two

anode sleeves

11 and 12.

Between the sleeve 12 and the electrode 7 is positioned a metallic tubular element 17 which -is held in its illustrated coaxial position by means of a radial flange 18 suitably secured to the wall of the envelope 1. As clearly shown in the drawing, the diameter of this element 17 is approximately the same as that of the electrode 7. The sleeve 11 and the frusto-conical element 13 are electrically connected together by means of a wire 20 or the like. Similarly, the sleeve 12 and the tubular element 17 are electrically connected together by means of a suitable wire 21 or the like.

A 'solenoid 22 surrounds the larger envelope section 4 and is supplied with direct current from a source 23 for establishing a longitudinal magnetic field in the space between the electrodes 6 and 7.

The smaller envelope section 5 is cylindrical and coaxial with respect to the larger section 4, and in effect constitutes an extension thereof. In the envelope section 5 about midway between the ends thereof is mounted another cathode or electron-repelling electrode 24 which is spherically concave facing the electrode 7. Both the concave and convex surfaces of this electrode 24 are coaxial and symmetrical with respect to the majo-r axis of the entire tube.

This electrode 24, like the electrode 7, serves as a partiltion or wall in the envelope section 5. An annular flange portion 25 serves to mount the outer perimeter of the electrode 24 to the wall of the envelope, this flange v25 being made of a Asuitable metal which is nonrnagnetic.

A coaxially positioned aperture 26 is provided in electrode 24 as shown.

Interposed between the two electrodes 7 and 24 is a frusto-conically shaped anode sleeve 27 which is held in its illustrated coaxial position by means ofa suitable annular disc or support 28. The :smaller diameter end 29 of this anode is positioned adjacent to the convex surface of the electrode 7 while the larger diameter end 30 is located opposite the electrode 24.

Suitably and conductively secured by welding or the like to the convex side of the electrode 7 is a 'concave focusing cup 31 which faces :the anode 27 and has a diameter which is substantially the same size as that of the anode end 29. This cup 31 is coaxially positioned and carries on its surface 32 a material which is secondary emissive. The emission ratio of this material is preferably greater than unity. Also, this cup has an aperture which is coextensive with the aperture 10 in the electrode 7. The cup 31 may be fabricated of beryllium copper or the like.

In the right-hand end of the envelope section 5 and axially opposite the electrode 24 is a cathode cup 33 which is coaxial and spherically concave facing the electrode 24. This cathode 33, unlike the electrode 24, is supported in the envelope section 5 by means of three or more angularly spaced wires or supports 34 having substantial spacing therebetween such that the chamber or space between the cathode 33 and the electrode 24 is in direct communication with the exhaust port 3. It is desirable for the cathode 33 to be electron emissive under ion as well as electron bombardment, .and a suitable material for this cathode may be Iberyllium copper.

In a working embodiment of the invention, the center of curvature of the cathode 33 is located within the aperture 26 of the electrode 24. The center of curvature of the electrode 24 is located on the tube axis about midway between the ends -of the anode cone 27. The center of curvature of the electrode 7 is on thetube axis and adjacent to the right-hand end ofthe anode sleeve 12. Similarly, the radius of curvature of the electrode 6 is also located on the tube axis at a point adjacent to the left-hand end of the sleeve 11.

Another solenoid 35 surrounds the envelope section 5 and extends for a distance which approximates that between electrode 7 and cathode 33. A battery 36 supplies the solenoid with direct current whereby a longitudinally extending magnetic field between the

electrodes

7, 24 and 33 may be established.

The operating circuitry for the pump grounds the two electrodes 6 and 7 as shown and interconnects the anode sleeves 11 andlZ by means of a battery 37, the positive terminal being connected to the sleeve 11 and the negative terminal to the sleeve 12.v In an operating embodiment K. of this invention, the battery 37 delivers approximately 90 volts. The midpoint of the battery 37 is connected to the positive terminal of a high voltage supply 38, the negative terminal of the latter being grounded as shown. This supply 38 in a working embodiment of this invention provides approximately 1,000-volts.

A battery 39 has its positive terminal connected to the anode cone 27 and its negative terminal to the electrode 24. A variable tap 40 on the battery 39 connects approximately the midpoint thereof to ground as shown. This battery 39 should deliver a voltage of from 500 to 1,000 volts.

Another battery 41 has its positive terminal connected to the electrode 24 and its negative terminal to cathode 33. The value of this battery 41 as well as the other 'batteries in the total circuit are so selected or adjusted that the cathode 33 operates at a voltage of about 2,000- volts negative with respect to ground.

In the following is given a simplified statement of operation. After applying the potentials just described to the various pump elements, a conventional vacuum pump,

capable of reducing pressures to a value of 10-3 millimeters of mercury, is connected to the exhaust iittting 3 and a vessel to be evacuated is coupled to the inlet port 2. The vacuum pump 'coupled to the exhaust fitting 3 is operated to reduce the pressure inside the envelope 1 and also inside the vessel to be evacuated to a pressure of from 10-2 to 10-3 millimeters of mercury.

Since the gases in the vessel being evacuated flow into the envelope 1 when the pump of this invention reduces the pressure, it will only be necessary in the following to consider what happens inside the envelope 1.

Generally speaking, by reason of the longitudinal arrangement of the various pump parts and the voltages applied thereto, an electric field is set up which roughly extends between the inlet port 2 and the exhaust port 3. The potential distribution of this field as shown in FIG. 2 has a maxima at the

anodes

11, 12, 27 and minima at the

cathodes

6, 7, 24, 33, and it will be noted that there is a general trend of the potential to diminish progressively from the inlet to the exhaust ports.

Therefore, any ionized gas atoms in the larger envelope section 4 within the region surrounded by the

anode sleeves

11 and 12 will tend to fall down field toward the potential minimum at the cathode 33. Obviously,

l these ions would have to flow through the apertures 10 riving at the cathode '33. Now recapitulating, the objective of this invention is accomplished by the ionization of neutral gas atoms in the left-hand portion of the pump and the transporting or pumping of these ionized atoms toward the right-hand end of the tube from which they may be scavenged by means of the conventional vacuum pump attached to the exhaust port 3.

This pumping action is achieved as follows. After the pressure in the envelope 1 has been reduced to a value of about l0"3 millimeters of mercury by means of the conventional vacuum pump attached to the exhaust port 3, a gaseous discharge occurs inside the tube which results in the development of free electrons and ions which llow in directions corresponding to the forces acting thereon. For example, any ions formed in the chamber between the two electrodes 7 and 24 or between the electrode 24 and cathode 33 will be propelled toward the cathode 33. Some of these ions will strike the cathode 33 and liberate electrons which will be propelled toward the electrode 24 `and more particularly, by reason of the cathode curvature as well as the curvature of the electrode 24, will tend to concentrate onto and pass through the aperture 26. By reason of the various electrode sizes and curvatures, and the accelerating effect of the voltage applied to the anode cone 27, the electrons which are directed through the aperture 26 will be formed `into a pencil-like beam which will pass axially through the pump, through the electrode aperture 10, and onwardly through the

anode assembly

11, 12 and the cone element 13 to the electrode 6. Since this electrode 6 has ground potential applied thereto and since the cathode 33 is operated at approximately -2000 volts with respect to ground, the electron beam sees the electrode 6 as an anode and bombards the same with sutlicient force to liberate secondaries. Hence, there is developed an electron space current or concentration in the central portion of the pump section 4 in a longitudinal direction between the electrodes 6 and 7.

The space current or electron concentration developed in the axial or longitudinal region of the ypump section 4 between the electrodes 6 and 7 is of pencil-like shape but in cross-section is substantially larger in size than the aperture in the electrode 7. As a matter of fact, the crosssectional size of the space current region will correspond to the size of the opening 14 in the anode element 13.

Considering only the secondary electron emission from the electrode or dynode 6, these Aelectrons initially will be attracted toward and through the

anode assembly

11, 12, 13, 17 and consequently will accelerate toward the electrode 7 and will be prevented from striking the anode assembly by the magnetic eld generated by the solenoid 22. As these electrons approach the electrode 7, they encounter the repelling field thereof. The potential of this field is suicient to prevent the electrons from striking the electrode 7 and returns them rearwardly along about the same path they initially traveled. The net result is that the electrons which are emitted by the dynode -6 oscillate back and forth between the electrodes 6 and 7 for a relatively large number of times before they are lost by collection on the anode assembly. As a matter of fact, the oscillating space current between the two electrodes 6 and 7 will increase until the number of electrons released at the dynode 6 by the initial beam is equal to the number of electrons collected by the anode assembly, or until the process is stopped by changing the anode potential or the like.

Two other factors serve to limit the available multiplication. The first of these is the space charge which develops in the space current when the number of released electrons becomes very large. This charge tends to drive the peripheral electrons, i.e., the electrons more remote from the axial center of the tube, toward the anode, making the collection thereby more probable. The second factor is the transverse component of the electrostatic field within the tube. Such a component exists due to the curvature of the lines of force at the ends of the tubular anode elements.

Now having explained the development of the space current in the tube section 4, operation with respect to the formation of ions and the scavenging thereof may be further examined.

Electrons liberated from the dynode 6 are accelerated toward the electrode 7 but fail to reach it. They are retarded and brought to rest just before arrival, after which they are accelerated in the opposite direction. This continues'until, probably after several traversals of the chamber between the two electrodes 6 and 7, the liberated electrous, or some of them, encounter and ionize gas molecules. The positive ions thus released are exposed to a combination of field and charge forces which cause movement thereof in a direction which is the result of such forces; however, before examining in detail the motion of these ions, the action of the oscillating electrons will be further considered. The electrons liberated from the ionized gas molecules join the original electrons in oscillating back and forth between the electrodes 6 and 7; however, the ion-derived electrons oscillate through a shorter traversal. Thus, after a period of operation, the space current region between the two electrodes 6 and 7 will be lilled with oscillating electrons traveling over path lengths which vary, some being longer than others.

By reason of the differential in voltage applied to the two

anode sleeves

11 and 12 by means of the battery 37, it will be seen that the electrons as they approach the electrode '7 will move somewhat more slowly than is true when the electrons approach dynode 6. This being true, a greater percentage of ionization will occur in the righthand regions of the space between the electrodes 6 and 7, and this is indeed a desirable phenomenon.

Next to be examined are the forces acting on the ions which result from electron collision or gas discharge. A lirst ion developed in the left-hand regions of the

anode assembly

11, 12, 13 experiences two different forces, one being that produced by the ield developed by the particular configuration of the anode assembly and the other being the charge attraction whi-ch the ion has for the axial electron concentration in the aforesaid space current region between the two electrodes 6 and 7. The frusto-conical element 13 is so shaped that the positive potential applied thereto will obviously repel the ion toward the right, or in other words toward the electrode 7. This being true, the ion is prevented from being attracted toward the dynode 6 and thereby neutralized to become once again a neutral atom. In its flight toward the electrode 7, the ion encounters the dropping gradient developed by the two

anode sleeves

11 and 12 and alsois attracted toward the axial center of the tube by the axial electron concentration. Thus, when the ion arrives at the electrode 7, it can be traveling axially through the electron concentration and penetrate the aperture 10. While it is possible for the same ion to continue to fall through the electron concentration because of the potential gradients inside the pump and eventually end up at the cathode 33, this does not necessarily happen as will be explained in more detail hereinafter.

Other ions formed inside the

anode assembly

11, 12 will likewise be projected toward the right and through the aperture 10 in the electrode 7. As this process of ionization and ion-transport continues, it is obvious that the pressure inside the tube section 4 correspondingly reduces.

As will become apparent from a reading of the description to follow, that portion of the pump just described, between the two electrodes 6 and 7, constitutes the first stage of a 2-stage pump, and based upon experimental results is capable of reducing the pressure therein by a factor of l02 to lO-4 of the pressure of the second stage into which it feeds.

The second stage of the pump constitutes those elements in the envelope section 5 which include and lie between the electrodes 7 and 24. The initial beam which emanates from the cathode 33 passes first through the aperture 26 and secondly through the aperture 10. However, some of these electrons do not pass through the aperture 1t) but instead strike the bottom 32 of the focusing cup 31. This results in the liberation of secondary electrons which are accelerated by the anode 27 toward the electrode 24. However, as in the case of the first stage just described, these electrons never quite reach the electroder 24 but are turned rearwardly and accelerate toward the cup 31. Since the cup 31 is slightly more positive than the electrode 24, the electrons will once again impact the bottom of the cup and liberate more secondaries. This electron multiplication continues until a stable space current is developed, this space current being composed of electrons oscillating through the center of the anode 27 between `the two electrodes 7 and 24. Electron multiplication may be enhanced by use of the multipactoring circuits and principles disclosed in my application Serial No. 183,440, led Mar. 29, 1962, now Patent No. 3,181,028, entitled Vacuum Pump.

Any ions which are developed within the space of the anode 27 will be propelled toward the electrode 24 and also toward and through the aperture 26 the same as was true in connection with the first stage described previously. All of the ions which pass through the aperture 26 fall toward and against the cathode 33 at which they are converted into neutral atoms which no longer respond to any electrical fields `or charge forces. Instead, these neutral atoms are scavenged via the exhaust port 3 by means of the conventional vacuum pumping apparatus which is connected thereto. The process of ion transport is continuous and so is the reduction in gas pressure inside the pump.

Some of the ions passing through the aperture from left to right recombine with electrons and become neutral atoms. These atoms randomly travel through the space between the two electrodes 7 and 24 until they become reionized. The newly formed ions travel toward the electrode` 24 through the aperture 26 and are neutralized at the cathode 33.

It an ion is formed so close to the electrode 7 that it is attracted thereagainst, it will become neutralized and once again will randomly travel throughout the space until it is once again ionized. Itis important, of course, that the forces acting on the ions result in their progression in a rightward direction through the aperture 26, and this is facilitated by the particular shape of the anode 27 which tends to repel and direct ions toward the right even though they may be created near the left-hand end thereof.

In order to facilitate the establishment of relatively large spa-ce currents within the two pump sections, the alternative structure of FIG. 3 is preferred. This structure is quite similar to the cathode assembly 7, 31 of FIG. l, but differs inthe separation of the two cups 7 and 31 and the disposition therebetween of an annular thermionic emitter 52 yof tungsten or the like. This emitter is maintained suitably negative with respect to both cups 7 and 31, so as to provide currents of from l0 to 50 milliamperes through both apertures 10 and 10a. T-hese cups 7 and 31 are electrically connected together by means of metallic posts 53 which also serve as supports for securing the cup 31 in position with respect to cup 7. The electrons from this emitter 52, which penetrate the apertures 10 and 10a, serve in establishing initially the axial electron concentrations in the two pump sections.

It is the purpose of the solenoids 22 and 35 to produce focusing magnetic elds which prevent collection of the electrons by the

respective anodes

11, 12 and 27. While solenoids have been shown, it will be understood by a Alternatively electheillustrated'pump which is drawn to scale provides the necessary electrostatic forces for the necessary focusing effects. In a working embodiment of the invention, however, it has been found that the solenoids 22 and 35 improve somewhat the pump operation.

In a typical pumping operation, the pressure at the inlet port (hence in the evacuated vessel) can be lowered to values from 10-6 to 10-lo millimeters -of mercury, while the pressure at the exhaust port 3 (hence in the space between the electrodes 7 and 24) is at a value somewhere between 10-2 to 10-3 millimeters of mercury.

In the following is given a brief explanation of how t0 design a pump for a given desired performance. As an example, vassume that it is desired to operate the second stage (the stage on the right-hand side of electrode 7 in FIG. l, hereinafter identified as stage D) at a pressure ybut to pump down the rst stage (the stage on the lefthand side of electrode 7 in FIG. 1, hereinafter referred to as stage C) to a pressure If the aperture in electrode 7, between the two stages, has an area A (in sq. cm.), the number of neutral gas molecules streaming per second from stage D to stage C through this aperture is a=35 1020 Ap,

where it is assumed that the gas is air at room temperature and p2 is measured in mm. of Hg.

There is also back streaming of neutral molecules through the same aperture in the opposite direction, but

this can be ignored inasmuch as the pressure in stage C is so much smaller.

At operating equilibrium, that is when the terminal vacuum has been reached, the number of positive ions moving from stage C to stage D must equal the value (1, and the ion current must be where e=l.6 10-19 Coulomb as the charge per ion. For p2=103 mm. Hg

and

A=0.05 sq. cm. z'=2.8 milliamperes These ions must be generated by the electron discharge in stage C. Let it be assumed that these electrons have an average energy of 1,000 volts, corresponding to a velocity of An electron of this energy generates about 4p1 ions/cm. or

4p1 v ions/sec.

lf the n is the number of electrons per cubic centimeter, and if the effective part of the discharge (that is, the part which is capable of directing ions through aperture 10) is a cylinder of length L and cross-section A1 there will thus be l'generated per second which constitute the ion current passing through' the aperture.

At equilibrium,

Using the figures given above, an estimating A1=5 sq. cm.

L23() cm.

it follows that to obtain B2: 1 03 171 there will be required a discharge of n=1.5 1010 electrons per cm.3

This density n is equivalent to an electron current density nve, or a current Ie=nveA1 which in our example would be 22.5 amperes. While this would seem to be a high value of current, it must be realized that this is not the current which an ammeter in series with the external pump circuitry would indicate. In an electron discharge of this character, the electrons oscillate many times in opposite directions before they are collected by the anode, and during these oscillations, they are available to generate ions. If an electron makes, on an average, of N=100 trips before being collected, the current measured by the aforesaid ammeter would be only T= 225 milliarnperes The number N will increase as the pressure p1 becomes smaller; it will also increase with the efiiciency with which the focusing or concentrating means prevent -the electrons from reaching the anode.

As already explained, the electrodes 7 and 24 correspond to walls or partitions which are almost completely impervious to gas flow. However, by reason of the apertures 10 and 26, the axial electron beam, and the various electrode arrangements, during pumping operation, ion fiow through the apertures in the direction from the inlet port 2 to the exhaust port 3 is encouraged and is at a greater rate than How in the opposite direction of neutral gas molecules. The mechanism which includes the particular electrodes 7 and 24 thereupon constitutes differential flow means whereby the ion flow in one direction exceeds neutral gas fiow in t-he opposite direction.

In a working embodiment of this invention, the various parts and co'rnponents have dimensions as given in the following; however, it will be understood that these dimensions are given by way of example only and are not to be considered as limitations.

Reference numerals: Dimensions Dimension 43 inches 1.250 Radius 44 do 2.125

Dimension 45 do 8 Dimension 46 do 1% Radius 47 do 2.125 Dimension 48 do 2.75 Dimension 49 inch 1 Dimension 50 inches 1.295 Radius 51 do 1.295 Diameter of cathode 33 inch 11A@ Diameters of apertures 10 and 26 do 1/16 to 1/s inasmuch as FIG. 1 is to scale, any remaining dimension not listed hereinabove may be taken therefrom by determining the scale from the dimensions already given.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention. y

What is claimed is:

1. A transport pump comprising an envelope having spaced apart inlet and exhaust ports, means establishing an electric field between said inlet and exhaust ports having a potential which progressively increases from a low value in a region adjacent to said exhaust port to a higher value in a region adjacent to said inlet port, means for forming within said field an electron cloud having electrons which oscillate at ionizing velocities within the confines of said field, ions resulting therefrom thereby being propelled into the region of low potential from which they may be scavenged in the form of neutral atoms.

2. A transport pump comprising an envelope having spaced apart inlet and exhaust ports, means establishing an electric field between said inlet and exhaust ports having a potential which progressively increases from a low value in a region adjacent to said exhaust port to a higher value in a region adjacent to said inlet port, a wall member in said envelope extending across said field in between said regions, said wall having a flowrestricting orifice, means for forming a cloud of oscillating electrons within said field for ionizing a gas, ions resulting therefrom thereby being propelled into the region of low poten-tial from which they may be scavenged in the form of neutral atoms.

3. A transport pump comprising an envelope having spaced apart inlet and exhaust ports, means establishing an electric field between said inlet and exhaust ports having a potential which progressively increases from a low value in a region adjacent to said exhaust port to a higher value in a region adjacent to said inlet port, means for developing an electron space current in said field for ionizing a gas therein, ions resulting therefrom thereby being propelled into the region of low potential, means interposed in said field between said exhaust and inlet ports for restricting gas fiow in a direction from said exhaust port toward said inlet port, and means for neutralizing ions in the region of said low potential.

4. A transport pump comprising an envelope having spaced apart inlet and exhaust ports, means establishing an electric field between said inlet and exhaust ports having a potential which progressively increases from a low value in a region adjacent to said exhaust port to a higher value in a region adjacent to said inlet port, means producing an electron beam which flows through said field from the region of low value to the region of higher value, means for developing an electron space current in a region surrounding said electron beam for ionizing a gas which permeates said fields, means disposed adjacent to said region of higher value and also said inlet port for directing'ions in a direction from said inlet port toward said exhaust port, means interposed in said eld between said exhaust and inlet ports for restricting gas liow in a direction from said exhaust port toward said inlet port, said beam-producing means including means for neutralizing ions in the region of said low value.

5. A transport pump comprising an envelope, first and second electron-repelling electrodes mounted in said envelope in spaced-apart relation for defining a space current region therebetween, an anode electrode mounted -in said envelope between said first and second electrodes and surrounding said space current region, a third electronrepelling electrode mounted in said envelope and spaced from said second electrode, said first, second and third electrodes lbeing, tandemly arranged 4with said second electrode being between said first and third electrodes, said second electrode having a lbeam-receiving aperture therein, inlet and exhaust ports in said envelope, said inlet port directly communicating with 4the space between said first and second electrodes, said exhaust port communicating with the space between said second and third electrodes, and means including said first, second and anode electrodes establishing an electric field between said first and second electrodes to cause electrons to oscillate repeatedly therebetween in said space current region.

6.- The transport pump of claim wherein said second electrode constitutes a partition which divides said envelope into two gas chambers with the only communication therebetween being by way of said aperture, and means including said anode electrode which directs a majority of ions formed in said space current region in a direction from said first electrode toward said second electrode, whereby said ions fiow through said aperture and onwardly to said third electrode where they become neutralized.

7. The transport pump of claim 5 wherein said second electrode constitutes a Ipartition which divides said envelope into two gas cham-bers with the only communication therebetween being by way of sa-id aperture, and said anode electrode is of frusto-conical sleeve shape with the Ismaller end thereof being adjacent to said first electrode and the larger end thereof being adjacent to said second electrode.

8.' The transport pump of claim 5 wherein said second electrode constitutes a partition which divides said envelope into two gas chambers with the only communication therebetween being by way of said aperture, and said anode electrode is of frusto-conical sleeve shape with the smaller end thereof being adjacent to said first electrode and the larger end thereof being adjacent to said second electrode, and means for retaining electrons within said space current region for a period of time sufiicent to produce ionization.

9. A transport pu-mp comprising an envelope, first and second electron-repelling electrodes mounted in said envelope -in spaced-apart relation for defining a space current region therebetween, an anode electrode mounted in said envelope between said first and second electrodes and surrounding said space current region, a third electron-repelling electrode mounted in said envelope and spaced from said second electrode, said first, second and third electrodes being tandemly arranged with said second electrode lbeing between said first and third electrodes, said second electrode having a beam-receiving aperture therein, inlet and exhaust ports in said envelope, said inlet port communicating with the space between said first and second electrodes, said exhaust lport communicating with the space between said second and third electrodes, and means for directing electrons from said third electrode through said aperture and against said first electrode at velocities which produce secondary e-mission from the latter, and means for applying an electric field -between said first and second electrodes which causes electrons to oscillate repeatedly therebetween in said space current region.

10. A transport pump comprising an envelope having spaced-apart inlet and exhaust ports, first and second tandem pump sections in said envelope; said first section including first and second spaced-apart electron-repelling electrodes which define the opposite ends respectively of a space current region, a first anode electrode interposed between said first and second electrodes and surrounding said space current region, said space current `region directly communicating with said inlet port, said second electrode having a first beam-receiving aperture therein; said second section having a third electron-repelling electrode spaced from said second electrode for defining the opposite ends respectively of a second space current region, a second anode electrode interposed between said second and third electrodes and surrounding said second space current region, said third electrode having a second ,beam-receiving aperture which is aligned with said first beam-receiving aperture; a fourth electron-repelling electrode spaced from said third electrode and being aligned with both said first and second apertures, said exhaust port directly communicating with the space between said third and fourth electrodes; means for establlshing a field within said second pump section between said second and thind electrodes for oscillating an ionizing cloud of electrons therebetween, means for establishing a field within said first pump section between said first and second electrodes for oscillating an ionizing cloud of electrons therebetween, said fields having a potential distribution which generally progresses from a given high value within said first pump section to a given lower value in said second pump section at said fourth electrode, where-by ions developed in both said pump sections are propelled through said apertures toward said rfourth electrode at which they become neutralized and can thereafter be scavenged through said exhaust port.

11. A transport pump comprising an envelope having spaced-apart inlet and exhaust ports, first and second tandem pump sections in said envelope; said first section including first and second spaced-apart electron-repelling electrodes which define the .opposite ends respectively of a space current region, a first anode electrode interposed between said first and second electrodes and surrounding said space current region, said space current region directly communicating with said inlet port, said second electrode having a first beam-receiving aperture therein; said second section having a third electron-repelling electrode spaced from said second electrode for defining the opposite ends respectively of a second space current region, a second anode electrode interposed between said second and third electrodes and surrounding said second space current region, said third electrode having a second beam-receiving aperture which is aligned with said first beam-receiving aperture; a fourth electron-repelling electrode spaced from said third electrode and being aligned with both said first and second apertures, said exhaust port directly communicating with the space between said third and fourth electrodes; said second electrode being a wall within said envelope which separates two gas chambers, said third electrode -being a wall within said envelope which separates two -gas chambers.

12. The transport pump lof claim 11 wherein the anode electrode of said first pump section includes means for directing ion flow in a direction from said first electrode toward said second electrode, and the anode electrode of said second pum-p section includes means for directing ion liow in a direction from said second electrode toward said third electrode.

13. A transport pump comprising an envelope having inlet and exhaust ports, first and second spaced-apart electrodes having electron-repelling surfaces, respectively, which face each other and which extend transversely to the direction of spacing therebetween, annular anode means interposed between said surfaces, said anode means surrounding a space current region between said surfaces, said second electrode'being in the form of a partition which provides a gas chamber within said envelope, said inlet port directly communicating with said chamber, said second electrode having a kcentrally located beam-receiving aperture therein, a third electrode spaced from said second electrode on the side opposite said first electrode, said third electrode being in the form of a partition within said envelope thereby forming with said second electrode a second gas chamber, said third electrode having a centrally located beam-receiving aperture which is longitudinallyaligned with the first-mentioned aperture, said third electrode having an electronrepelling surface facing said second electrode which extends transversely of the direction of spacing between said second and third electrodes, said second electrode having an electron-emitting surface facing said third electrode surface, second annular anode means interposed between the facing surfaces of said second and third electrodes and surrounding a space current region therebetween, and a cathode electrode spaced fr-om said third electrode on the side opposite said second electrode, said cathode electrode having an electron-emitting surface facing said third electrode and extending transversely of the spacing between said third and cathode electrodes, said last-mentioned electron-emitting surface being longitudinally aligned with said beam-receiving apertures, said exhaust port communicating directly with the space between said third and cathode electrodes.

14. The transport of claim 13 including means for providing an electron discharge in said space current regions, means including said second and third electrodes and said second anode means for oscillating electrons in the space current region between said second and third electrodes, means including said first and second electrodes and said first anode means for oscillating electrons in the space current region between said first and second electrodes, and means including the aforesaid electron-directing and electron-oscillating means for providing an electric field which progresses generally from a given high value in the first-mentioned chamber to a given lower value at said cathode electrode, whereby ions created in both said chambers will migrate through said apertures toward said cathode electrode.

15. A transport pump comprising an envelope having inlet and exhaust ports, first and second spaced-apart electrodes having electron-repelling surfaces, respectively, which face other and which extend transversely to the di-rection of spacing therebetween, an annular anode assembly interposed between said surfaces, said anode assembly coaxially surrounding an elongated space current region which extends between said surfaces, said assembly including two axially spaced electrically insulated cylindrical surfaces and a frusto-conically shaped element electrically connected to the one of said cylindrical surfaces which is closest to said first electrode, said element coaxially surrounding said space current region and having a smaller diameter end adjacent to said rst electrode surface; said second electrode 'being in the form of a partition which provides a gas chamber within said envelope, said inlet port directly communicating with sai-d chamber, said second electrode having a centrally located beam-receiving aperture therein, a third electrode spaced from said second electrode on the side opposite said first electrode, said third electrode being in the form of a partition within said envelope thereby forming with said second electrode a second gas chamber, said third electrode having a centrally located beam-receiving apertu-re which is longitudinally aligned with the first-mentioned aperture, said third electrode having an electron-repelling surface facing said second electrode which extends transversely of the direction of spacing between said second and third electrodes, said second electrode having an electron-emitting surface facing said third electrode surface, a frusto-conically shaped anode interposed between the facing surfaces of said second and third electrodes and coaxially surrounding an elognated space current region therebetween, the smaller diameter end of said frusto-conical anode being adjacent to said second electrode and the larger diameter end being adjacent to said third elect-rode, and a cathode electrode spaced from said third electrode on the side opposite said second electrode, said cathode electrode having an electron-emitting surface facing said third electrode and extending transversely of the spacing between said third and cathode electrodes, said last-mentioned electron-emitting surface being longitudinally aligned with said beam-receiving apertures, said exhaust port communicating directly With the space between said third and cathode electrodes.

16. The transport pump of claim 15 including means for directing electrons in a stream-like form from said cathode surface through both beam-receiving apertures and into the space current region between said first and second electrodes, means including said second and third electrodes and said frusto-conical anode for oscillating electrons in the space current region between said second and third electrodes, means including said first and second electrodes and said anode assembly for oscillating electrons in the space current region between said first and second electrodes, and means including the aforesaid electron-directing and electron-oscillating means for providing an electric field which progresses generally from a given high value in the first-mentioned chamber to a given lower value at said cathode electrode, whereby ions created in both said chambers will migrate through said apertures toward said cathode electrode.

17. A transport pump comprising an envelope, first and second electron-repelling electrodes mounted in said envelope, said electrodes being spaced apart along an axis and having surfaces which are spherically concave facing each other, the surface of said rst electrode having a secondary emission ratio greater than unity, the spherical curvature being coaxial with respect to said axis; an annular anode assembly in said envelope interposed between said surfaces and coaxially surrounding asid axis, said assembly including two axially spaced electrically insulated cylindrical surfaces and a frustoconically shaped element disposed adjacent to the surface of said first electrode, said element having its smaller diameter end adjacent to said first electrode surface; said second electrode being in the form of a partition which provides a gas chamber within said envelope, said second electrode having a coaxially located aperture, an inlet port in said envelope which communicates directly with said chamber, a third electron-repelling electrode mounted in said envelope and spaced from said second electrode on the side opposite said first electrode, said third electrode having a surface which is spherically concave toward said second electrode, the curvature of the lastmentioned surafce being coaxial with respect to said axis, said third electrode being in the form of a partition which provides with said second electrode another gas chamber, said third electrode having a coaxially located aperture, a frusto-conically shaped coaxial anode interposed between the facing surfaces of said second and third electrodes, the smaller diameter end of said frusto-conical anode being adjacent to said second electrode, a cathode in said envelope spaced from said third electrode on the side opposite from said second elect-rode, said cathode having a coaxial spherically concave surface which faces said third electrode, and an exhaust port in said envelope in direct communication with the space between said third electrode and said cathode.

18. The transport pump of claim 17 including means for generating and directing electrons through said apertures and into said chambers, means including said second and third electrodes and said frusto-conical anode for oscillating electrons in a direction axially between said second and third electrodes, means including said first and second electrodes and said anode assembly for oscillating electrons in a direction axially -between said first and second electrodes, and means including the aforesaid electron-directing and electron-oscillating means for providing an electric field which progresses generally from a -given high value in the first-mentioned chamber to -a given low value at said cathode electrode, whereby ions created in lboth said chambers will migrate through said apertures toward said cathode electrode.

19. A transport pump comprising an envelope having inlet and exhaust ports, first and second spaced-apart electrodes having electron-repelling surfaces, respectively, which face each other and which extend transversely to the direction of spacing therebetween, annular anode means interposed between said surfaces, said anode means surrounding a space current region between said surfaces, said second electrode lbeing in the form of a partition which provides a gas chamber within said envelope, said inlet port directly communicating `with said chamber, said second electr-ode having a centrally located beam-receiving aperture therein, a third electrode spaced from said second electrode on the side opposite said first electrode, said third electrode being in the form of a partition within said envelope thereby forming with said second electrode a second gas chamber, said third electrode having a centrally located beam-receiving aperture which is longitudinallyA aligned with the first-mentioned aperture, said third electrode having an electron-repelling surface facing said second electrode which extends transversely of the direction of spacing between said second and third electrodes, said second electrode having a dynode element electrically connected thereto and mounted on the side thereof opposite from said rst electrode, said dynode element having an aperture in the central portion thereof which is aligned with the aperture in said second elec* trode, a therrnionic cathode interposed between said second electrode and said dynode element adjacent the apertures thereof whereby electrons may lbe directed through said apertures,tsecond annular anode means interposed between said dynode element and said third electrode and surrounding a space current region therebetween, and a cathode electrode spaced from said third electrode on the side opposite said second electrode, said cathode electrode having an electronemitting surface facing said third electrode and extending transversely of the spacing between said third and cathode electrodes, said last-mentioned electron-emitting surface lbeing longitudinally aligned with said beam-receiving apertures, said exhaust port cornmunicating directly with the space between said third and cathode electrodes.

201A transport pump comprising an envelope having inlet and exhaust ports, rst and second spaced-apart electrodes having electron-.repelling surfaces, respectively, which face each other and which extend transversely to the direction of spacing therebetween, annular anode means interposed lbetween said surfaces, said anode means surrounding a space current region between said surfaces, said second electrode being in the form of a partition which provides a gas chamber within said envelope, said inlet port directly communicating with said chamber, said second electrode having a #centrally located beam-receiving aperture therein, a third electrode spaced from said second electrode `on the side opposite said first electrode, said third electrode being in the form of a partition within said envelope thereby forming with said second electrode a second gas chamber, said third electrode having a centrally located beam-receiving aperture which is longitudinally aligned with the first-mentioned aperture, said third electrode having an electron-repelling surface facing said second electrode which extends transversely of the direction of spacing between said second and third electrodes,

l5. said second electrodey having a dynode element electrically connected thereto and mounted on the side thereof opposite from said first electrode, said dynode element having an aperture in the central portion thereof which is aligned with the aperture in said Isecond electrode, a thermionic cathode interposed between said second electrode and said dynode element adjacent the apertures thereof whereby electrons may be directed through said apertures, second annular anode interposed between said dynode element and said third electrodeV and surrounding a space current region therebetween, and means for neutralizing ions after they pass from said second chamber and through the aperture of said third electrode.

21. A transport pump comprising means for ionizing a gas, means for propelling ions of said ygas in a predetermined direction, spaced apart inlet and exhaust means disposed with said ionizing and propelling means being therebetween, and differential flow means in the path of said ions providing for predetermined flow of ions in said predetermined direction and for a more restricted flow of neutral gas in the opposite direction, said differential flow means including partition means substantially im-v pervious to gas flow positioned between said ionizing means and said exhaust means, said partition means being provided with an ion beam-receiving opening smaller in area than the impervious portion of said partition means.

22. A transport pump comprising an envelope, means dening two spaced apart electron-reversing fields between which electrons oscillate repeatedly, said means also dening a space current region between said fields, means for propelling ions created within said space current region in a predetermined direction, spaced apart inlet and exhaust portions in said envelope, the firstrnentioned means being disposed between said inlet and exhaust portions, and differential flow means interposed between one of said fields and said exhaust portion providing for a predetermined flow of ions in said predetermined direction and a more restricted ow of neutral gas in the opposite direction.

References Cited bythe Examiner UNITED STATES PATENTS 2,636,664 4/1953 Hertzler 230-69 X ROBERT M. WALKER,-Prma1y Examiner.

WARREN E. COLEMAN, LAURENCE V. EFNER,

Examiners.