US3075115A

US3075115A - Ion source with space charge neutralization

Info

Publication number: US3075115A
Application number: US98726A
Authority: US
Inventors: John W Flowers; John S Luce; William L Stirling
Original assignee: Individual
Current assignee: Individual
Priority date: 1961-03-27
Filing date: 1961-03-27
Publication date: 1963-01-22
Anticipated expiration: 1980-01-22
Also published as: GB936137A; DE1222589B; FR1316804A

Description

.J. W. FLOWERS ETAL ION SOURCE WITH SPACE CHARGE NEUTRALIZATION Jan. 22', 1953- 2 Sheets-Sheet 1 Filed March 27, 1961 20 NEUTRAL gums/Tons. John W. Flowers. John S. Luce r William 1.. Stirling ATTQRNEY SOURCE W GAS,

C Jan. 22, 1963' J. w. FLOWERS ETAL 3,975,115

ION sow-10s WITH SPACE CHARGE NEUTRALIZATION- Filed March 27, 1961 2 Sheets-Sheet 2 Fig. 2.

INVENTOBS. John W, Flowers BY John S. Luce William L. Stir/mg 0v 7 Maw ATTORNB United States Fascias Q 3,975,115 ION SOURCE WHTH SPACE (Il-IARGE NEUTRALlZATlON John W. Flowers, Gainesville, Fla, .lohn S. Luce, Danville, Calif., and William L. Stirling, Gait Ridge, Tend, assignors to the United States of America as represented by the United States Atomic Energy (Zommission.

Filed Mar. 27, 196i, Ser. No. 98,726

. 9 Claims. (Cl. 3l3-63) This invention relates to an ion source and more particularly to an ion source in'which means are provided to insure space charge neutralization to thus provide an ion beam which is neutralized at all times.

Space charge, neutralization is normally obtained in the prior art by providing a source of. electrons near the exit of the ion source or by means of a neutralvapor to provide a cloud of electrons around the ions. However, it is indeed dllficult to provide the proper amount and spacial distribution of electrons at all times because of changes in the ion density. in addition, plasma oscillations will occur due to non-uniform electron distribution across the ion exit beam. Also, by providing space-charge neutrali zation at the exit end of the ion source and only after acceleration, complete neutralization does not occur throughout the machine. Thus, space charge forces will exist in the machine before acceleration so as to limit the ion current and thus the thrust unless electrons are provided. The thrust of the neutralized beam is an important aspect of the ion source of this invention when such a source is used in the field of ion propulsion of space vehicles. Unless the space charge effect is completely new tralized, there 'will bea definite limit on the thrust ob- I as a result of the space-charge effect, when intense ion beams are ejected from an ion .source. This difiiculty includes a limitation of the output as predicted by Lang- .7 muir-Childs law andprevcnts the formation of a well-' defined beamdue to the well known ion beam blow up. In the field of plasma physics, there are many applications where a-high current, well-defined ion source is desirable. In addition to the use of such a source in the ion propulsion of space vehicles as mentioned above, one other specific field for such usage is-the ion injection into machines for producing high density plasmas for neutron production. Another use for such an ion source is for the'ion injection into experimental machines to study the feasibility of controlled thermonuclear reactions.

With a knowledge of the limitations of prior art ion sources, as discussed above, it is a primary object of this invention to provide. an ion beam that is neutralized at all times so that space charge forces cannot develop.

it is a further object of this invention to provide'an ion source with means for ejecting a high energy neutralized beam therefrom.

It is another object of this invention to provide an ion source with means for ejectinga high density neutral plasma therefrom. I

' It is an additional object of this invention to provide a high. specific impulse arc-ion system for the propulsion of space vehicles.

These and other objects and'advantages of this invention will become apparent upon consideration of the following detailed specification and the accompanying drawings, wherein:

FIG. 1 is a schematic drawing of a neutralized electron-- ion source;

FIG. 2 is a sectional view of an injector device employing the ion source and electron gun of FIG. 1 for producing an energetic neutralized beam of electrons and ions; I

e t smalls 35g Patented'dan. 22, secs FIG. 3 is a sectional view of an injectordevice em- I ploying the ion source oi,-FlG. l for producing high may be used as a variable specific impulse system for.

propulsion of space vehicles; and,

FIG. 5 is a schematic drawing of another embodiment of a variable specific impulse system for the propulsion of space vehicles. p

The above objects have been accomplished in the present invention by providing an ion source in which a refluxing type of gas-fed arc discharge is used to provide ions, and providing an electron gun'for directing a controlled, monoenergetic electron beam through thedischarge. There will be an intimate mixing of the fiCCCIe erated ions and electrons within the ion source and beyond the ion source for more efi'ective space charge ncutralization. I The space charge neutralization in the ion source and accelerating gap is effected by oscillating, low energy electrons, and the space charge neutralization of the exit beam from the ion source is effected by the monoenergetic it obviates the possibility of'a net charge developing in the space vehicle. When a conventional ion source is used in the vehicle, ions may be attracted back to the vehicle and thus limit or prevent the ions from theconventional ion source from being ejected from the source, andv render such a propulsion system ineffective.

FIG. 1 illustrates one embodiment of an electron-ion source in. which the principles of this invention may be carried out. The energetic electrons for this source are provided by an electron gun now to be described.

A filament cathode 1, which may be either directly or indirectly heated, is axially and magnetically-aligned with 'a hollow anode 2. Gas, argon for example, is fed from a source 4 and through tubing 3 to the hollow area of the anode 2. A volt 11C. source 5 is connected between cathode 1 andanode 2 by leads 7 and 6, respectively. A gas arc is struck between the cathode 1 and anode 2. This 150 'volt DC. potential is actually applied across the narrow plasma sheath formed by theme plasma at the filament surface. Thus, the electrons see a very strong electric field gradient. This arrangement permits 1 tential. The electron gun is positioned in a strong, that is,

about 6000 gauss, axial magnetic field provided byelec tromagnets, not shown, so, that the electron stream 11 is well collimated. The direction of the magnetic field is shown by the arrow H. A high-potential shield 8 surrounds the electron gun. The shield increases the gas efiiciency of the gun and reduces electrical breakdown problems at high accelerating potentials. Anaccelcration electrode 19 is provided-just beyond the shield 8, and is electrically connected to the shield 8 by a lead 9. The shield 8 and electrode 10 are connected to a source of high potential of about 39 to 43 kv., negative, with respect to the ion source, to be described below. v

This electron gun will produce a 1 ampere, non- I divergent, 5 kv. electron beam of inch diameter- This mounted within a tubular member 14. The member 14 is provided with flanges on each end. An annular insulating member 13 is mounted between end plate 12 and the flange portion at one end of member 14. An annular shield is mounted to and within the annular insulator 13 and closely encompasses the hollow cathode 16. The member 14 is provided with an internal, enlarged portion which closely encompasses the hollow cathode 16, as shown, for preventing ions from the arc discharge entering the area occupied by the shield 15. The cathode 16 and anode 17 are axially and magnetically aligned with the electrodes of the electron gun.

An. annular end plate 20 with a tungsten insert 21 is affixed to the flange portion on the other end of member 14. The

plates

12 and 20 are connected to D.C.

' sources of 99.85-kv. and 100 kv., respectively, not shown.

An annular electrode 22. is positioned beyond the end plate 22. This electrode 22 is insulated'and is thus electrically floating. Gas which may be deuterium, for ex-.

ample, is fed from a source 19 and through a tube 18 to the interior of'the hollow anode 17. A refluxing gas arc discharge 23 is initiated between the cathode 16 and anode 17 in the same manner as set forth in the US. patent to John S. Luce, No. 2,927,232, issued March 1, 1960, with the exception that gas is not fed to the cathode.

The axial magnetic field of 6000 gauss provided for the electron gun is also used for the ion source. The electron gun and the ion source are both enclosed within a chamber, not shown, which is evacuated to a pressure of about 3X 10- mm. Hg. The ion source will produce a /2 ampere, 6 kv. ion beam using deuterium as the feed gas.

The energetic electron stream 11 from the electron gun is directed through the center of the refluxing arc discharge 23. There is an intimate mixing of the accelerated ions and electrons within the ion source and accelerating gap due to the oscillating electrons within the source and an intimate mixing of the accelerated ions and electrons beyond the exit end'of the ion source due to the energetic electrons emerging with'the exit ion beam. Thus, there is effective space charge neutralization within and beyond the ion source. An acceleration electrode 24 at ground potential is provided for withdrawing the ions from the source through end plate 20 and electrode 22. Some of the electrons from the energetic stream 11 of electrons will arrive at the acceleration electrode 24 and have sufiicient energy to pass through this electrode along with the ions from the ion source to thus provide a neutralized beam 25 of electrons and ions.v By providing space charge neutralization within the arc gap, the current output of the beam 25 is substantially increased above that which is obtained from a conventional ion source because the emission from the conventional ion source is limited by space charge forces.

The insulated electrode 22 is employed as a defining electrode and it has been found that the use of this electrode also increases the current output of the neutralized beam 25. The relatively cold electrons of the arc dis charge 23 and those of'the energetic beam 11 which are slowed down by collision processes do not have sufficient energy to pass through the electrode 24 since this electrode will repel such low energy electrons which will then oscillate between the electrode 24 and the cathode 16. These oscillating electrons will provide for space charge neutralization within the ion source and accelerating gap as discussed above. It should be noted thatthe electrons and ions in the ion source are subjected to the same magnetic and electrostatic fields. By controlling the density of all of the electrons, the resultant beam would be neutralized at all times. Space charge neutralization will take place within the ion source in the accelerating gap, and beyond the accelerating electrode.

The neutralized beam of FIG. 1 may be used in an injector for injecting the beam into a neutron producing plasma machine. In order to provide a high density plasma in such machines, the density of the injected ions should be as great as possible, for example, about l0 /cc. at 600 k.e.v. By using the principles of FIG. 1 in such an injector, it is possible to achieve such density which would not otherwise be possible with conventional ion source because the electrostatic force resulting from space charge would blow up the beam. FIG. 2 illustrates how the ion. source of FIG; 1 may be used in a neutralized beam injector. An electron source tube 27 supports an indirectly heated filament 28 which is spaced from a hollow anode 29. The electron stream 50 from the electron source is directcd through a plurality of annular

electromagnetic coils

52, 53, 54, 55, and 56, then through the ion source to be described below, then through a. plurality of

electromagnetic coils

58, 59, 60, and 61, and then through a shielded injection tube 49. The ion source is encompassed by an electromagnetic coil 57. The coils 52-61 provide a collimating magnetic field whose strength is about 6000 gauss at the coil centers and about 2000 gauss in the gaps between the coils and whose direction is indicated by the arrow H. The device of FIG. 2 is enclosed within a vacuum chamber 30. This chamber 30 is formed by the member 31, an annular plate 32, a tubular insulating wall 33, an annular plate 33, a tubular plate 63, an annular plate 40, a tubular insulating wall 41, an annular plate 46, and a vacuum manifold 47. The member 31 is connected to two vaccum pumps 26 and 26; The manifold 47 is connected to two

vacuum pumps

48 and 48. The chamber 30 is evacuated by these

pumps

26, 26', 48, 48 to a pressure of about 3X10 mm. Hg.

The coils 52-56 and 53-61 are enclosed within metallic housings. The housings around coils 52 and 53 are connected to zero potential by electrical leads, not shown. The housings around coils 54, 55 and 56 are connected through

members

34 and 35 and electrical leads, not shown, to sources of DC. potential of kv., 300 ltv., and 450 kv., respectively. The upper and lower plates of the ion source are connected through members 38 and 40, and electrical leads, not shown, respectively, to D.C. sources of 599.85 kv. and 600 kv., respectively. The housings around coils 58, 59 and 60 are connected through

members

42 and 43. and electrical leads, not shown, to sources of DC. potential of 450 kv., 300 kv., and 150 kv., respectively. The housing around coils 61 is connected to zero potential by electrical leads, not shown. A shield member 62 is positioned at the exit end of coil 61 to insure that the electron-ion beam 51 will enter the injector tube 49.

The potential gradients between the housings of the coils 53-56 will first accelerate the electrons from the electron source and the potential gradients between the housings of coils 58-61 will then decelerate the electrons after they pass through the ion source. The potentialgradicnts between the housings of coils 58-61 will in turn accelerate the ions from the ion source in such a manner that the ham 51 of electrons and ions being ejected from the tube 49 will have substantially the same velocity and the beam 51 will be substantially spacecharged neutralized. In order to prevent these potential gradients between the coil housings from breaking down the insulating

members

33 and 41, shield members 36 are provided above the ion source to protect the member 33, and shield members 44 are provided below the ion source to protect the member 41.

The ion source of FIG. 2 includes a hollow cathode 65, a hollow anode 66. and an accelerating electrode 64. Gas is fed to the interior of anode 66 through a feed tube 67. The accelerating electrode 64 is connected to a source of accelerating potential, not shown, of about 560 kv. The

electrodes

28, 29, 65, 66, and 64, the coils 52- 56, the coils 58-61, and the tube 49 are all in axial alignment on a common axis and this axis is parallel to the direction of the magnetic field H.

A refluxing arc discharge is established in the ion source of FIG. 2 in the same manner as set forth for FIG. 1 above. The density of the electron stream 50 is so cong 79 is affixed to the. plate 91.

' vehicles.

' the electron gun portion of FIG. 4,

trolled as to provide substantially complete space charge neutralization of the exit beam 51. It should thus be seen that the device of FIG. 2 will provide an energetic, neutralized beam of electrons and ions. The injector of FIG. 2 is particularly suited for the injection of two or more molecular ion species into plasma, neutron producing devices. Since the beam of HG. 2 is straight throughout the length of the injector, both diatomic and triatomic ions produced in the ion source can be injected simultaneously into such devices.

It may be desirable to provide a higher density neutralized plasma beam injector. This may be accomplished by eliminating some of the accelerating and decelerating stages of FIG. 2 and by using low'er accelerating and decelerating voltages. Such a device is illustrated in FIG. 3. An electron source tube 85 which supports an indirectly heated filament 86 is mounted in an end plate 72. A hollow anode 87 is spaced from the filament 36 and is axially aligned therewith. The electron gun provides an electron beam 74.

The ion source of FIG. 3 includes an annular end plate 91 in which a hollow cathode 82 is supported, a hollow anode 83 to which is fed a source of gas through a feed tube 84, an annular end plate 92, an accelerating electrode 71, and an electromagnetic coil 89 surrounding the cathode 82 and anode 83. An electromagnetic coil 38 is mounted to the plate 72 and encompasses the filament cathode 86 and anode 87 of the electron gun. The space be ween the coil 88 and end plate 91 is encompassed by an annular shield member 77. An electromagnetic coil 90 is spaced from the accelerating electrode 71 and is mounted on an end plate 73. The space between the coil 90-and the plate 92 is encompassed by an annular shield member 76.

The

coils

88, 89 and 90 provide a collimating magnetic field whose direction is indicated by the arrow Hand whose strength is about 6000 gauss at coil centers and about 2000 gauss in the gaps between the coils. The

electrodes

86, 37, 82, 33, and 71, and the

coils

88, 39, and 90 are axially aligned on a common axis and this axis is parallel to the direction of the magnetic field H.

A member 78 is afiixed to the plate 72 and a member These

members

78 and 79 are provided with tlange portions, as shown, to provide openings which are connected to vacuum pumps, not shown. A member 80 is connected to plate 92, and a member 81 is connected to plate 73. These

members

80 and 31 are provided with flange portions, as shown, to provide openings which are connected to vacuum pumps, not shown. The area within the device of FIG. 3 is evacuated by these pumps to apressure of about 3X10- mm. Hg. The

plates

72 and 73 are connected to zero volts by means, not shown. The

plates

91 and 92 are connected to sources of about 99.85 kv. and 100 kv., respectively, by means, not shown, and the accelerating electrode 71 is connected to a source of about 50 kv. by means, not shown.

The device of FIG. 3 operates in the same manner as the device of FIG. Z'with the exception that much lower accelerating and deceleration potentials are used. The resultant beam 75 of electrons and ions is substantially completely spaced charged neutralized and has a substantially higher density than that produced by the device of FIG. 2. By providing a high density neutral plasma, it will be possible to inject such a plasma across magnetic field lines into devices for producing high density plasmas for neutron production.

A neutralized electron-ion beam may be used in a variable specific impulse system for the propulsion of space Such an arrangement is illustrated in FIG. 4. The device of FIG. 4 issimilar to that of FIG. 1 with the exception that a different electron gun is employed. In a hollow cathode 98 is mounted in a basemember 97. Gas is fed from a source 95, through a tube 96 and through a passageway in member 97 to the interior of the cathode 98. A hollow anode 99 is spaced from and in axial alignment with the cathode 98. A DC. source 100 of about 150 volts is connected between the cathode 98 and anode 99 by leads 101 and 102, respectively. An axial, collimating magnetic field is provided for the device of FIG. 4 by coils, not shown, and the direction of this magnetiofield is shown by the arrow 1-1. A hollow rcllux arc is 'estab lished between the cathode 98 and anode 99. The ion gun of FIG. 4 will produce an electron beam 103 of about 3 amperes at 2.5 kv. accelerating potential. The acceleration of the electrons from the electron gun is provided by an accelerating electrode, not shown, in a manner similar to that set forth for FlG. 1.

In the ion source portion of FIG. 4, a hollow tungsten cathode 109 is mounted in an annular end plate 105. A hollow carbon anode 110 is mounted to and within a tubular member 108. Member 108 has flange portions at its respective ends. The flange portion at one end of member 108 is supported by an insulating member 106 which in turn is suported by the end plate 105. An annular shield member 107 is mounted to and within memher 106. Shield member 107 closely encompasses the cathode 109. The flange portion at the other end of member 108 is attached to an annular end plate 113. The plate 113 is provided with an annular tungsten insert 114. An insulated, annular electrode 115 is positioned just beyond the plate 113. An accelerating electrode 116 is providedbeyond the electrode 115 and is connected to zero potential. Gas from a source 19' is fed through a tube 112 to the interior of anode 110.

A door 104 is provided for covering the annular opening in plate when the electron gun is not being used. The electron gun and ion source of FIG. 4 are enclosed in any suitable enclosure. When the device of this figure is being used in a space vehicle, the exit end of the enclosure is connected to regions of negligible atmosphere encountered in outer space so that the enclosure is thus evacuated to the prevailing pressure encountered in outer space. if the device of FIG. 4 is to he used for other purposes, the enclosure may be evacuated to a pressure of about 3 X10 mm. Hg by pumps, not shown, in the same manner that FIG. 1 is evacuated.

The

electrodes

98, 99, 109, and are axially aligned on a common axis and this axis is parallel to the direction of the magnetic field H. A refluxing arc discharge 111 is initiated in the ion source in the same manner as set forth in FIG. 1 above. The beam 103 of electrons is directed hrough this are discharge 111 such that substantially complete space charge neutralization takes place at all points within and beyond the ion source, to thus provide a space charge neutralized beam 117 of electrons and ions in the same manner as set forth for FIG. 1

above. I

The amount of thrust provided by the device of FIG. 4 is directly related to the choice of ions which are fed to the interior of the anode 110. With the elimination of space charge efiects by neutralization throughout the entire propulsion system, ions in various mass ranges and energy may be utilized so as to provide a' propulsion engine having a variable specific impulse to provide, in turn, for optimum thrust under various conditions. With conventional ion sources, the choice of the propellant ion is limited and is closely associated with the specific im-.

pulse and space charge equations. By being able to utiobtained by vacuum pumps. Then, by injecting selected ones of these propellant ions into the test facility by use of the device of FIG. 4, the facility is further pumped down by the gettering action of these ions when they condense at room temperature. Thus, it will be possible to conduct a more thorough study in the laboratory of the basic phenomena associated with ion propulsion in space.

Rather than using the ion plasma for direct propulsion, the plasma may be used to heat a separate neutral gas and eject the heated gas through a noule for achieving propulsion. Such a systemis shown in FIG. 5. This would provide an engine in the lower specific impulse range.

in FIG. the

elements

96', 97, 98', and 99 of the electron gun are shown, sincethcy may or may not be used in the device of this figure. When they are not used, the door 104' is positioned over the annular opening in the end plate 105', and this door is removed from such opening when they are used. The flange portion of one end of member 108' is afitxed to an annular insulator 106' which, in turn, is afilxed to end plate 105'. An annular shield 107' is altered to and within insulator 106'. The flange portion of the other end of member 108' is aiiixed to the annular end plate 113' which is provided with an annular insert 14'. A nozzle 118 is provided adjacent to the end plate 113'. A hollow cathode 109' is mounted to end plate 105 and is axially aligned with a hollow anode 120' which is mounted to and within the member 108. The propellant neutral gas is fed from a source 120 and through a tube 112 to the interior of hollow anode 110'.

A magnetic field of about 6000 gauss, average flux density, is provided by coils, not shown. The direction of this field is indicated by the arrow H and is parallel to the'axis of the cathode 109' and anode 110'. The

device of FIG. 5 is enclosed in any suitable enclosure and the enclosure is wnnected to the regionsoi negligible atmosphere in space when the device is used in a space vehicle. A refluxing arc discharge 111' is established between the anode 110' and cathode 109' in the same manner as set forth in FlG. l. The propellant gas fed to the anode is heated by the arc discharge 111' and the heated gas 119 is ejected from the device through the nozzle 118.

The device of FIG. 5 may be operated in the same manner as is the device of E16. 4. For example, the door 104 is moved to the same position as the door 104 of FIG. 4, the ion gun is then actuated the same as in H6. 4, gas ions are fed to the anode 110' through the tube 112', and the nozzle 118 is connected to a source of accelerating potential the same as in FIG. 4.

This invention has been described by way of illustration rather than limitation and it should be apparent that this invention is equally applicable in fields other than those described.

What is claimed is:

1. A neutralized electron-ion source comprising an elongated enclosure provided with axial openings at its respective ends, means for establishing a body of ions along the axis of said enclosure and to provide space charge neutralization therewithin, an electron gun positioned in spaced relation to one end of said enclosure, said electron gun including a cathode, an anode, means for feeding gas to the interior or said anode, a high voltage shield encompassing said anode and cathode and provided with an opening in axial alignment with said cathode and anode, a source of operating potential connected between said anode and cathode, an electron accelerating electrode spaced from and in axial alignment with the opening in said shield and with said anode and said cathode, and a source of acceleration potential connected to said shield and said accelerating electrode, said cathode, anode and accelerating electrode being axially aligned with the axis of said enclosure, means for cstablishing a strong magnetic held having a direction parallel to the axis of said enclosure, said enclosure and electron gun being enclosed within an evacuated chamher, said electron gun providing an energetic stream of electrons which is directed through said body of ions within said enclosure, and an ion accelerating electrode provided with an axial opening along the axis of said enclosure and being positioned beyond the other end of said enclosure, said electron stream having sufilcient density and energy to provide complete space charge neutralization beyond said accelerating electrode to thus provide an energetic, neutralized beam of electrons and ions beyond said accelerating electrode.

2. A neutralized electron-ion source comprising an elongated enclosure provided with axial openings at its respective ends, an elongated, hollow, open-ended cathode mounted in the axial opening in one end of said enclosure, an elongated, hollow, open-ended anode mounted within said enclosure and being spaced from and in axial alignment with said cathode, a source of feed gas, means for feeding gas from said source to the interior of said anode, means for establishing and sustaining a space charge neutralized, refluxing arc discharge within said enclosure between and within said cathode and said anode, means for providing a collimating magnetic field having a direction parallel to the axis of said cathode and anode, an electron gun positioned beyond and in axial aligment with the axial opening in said one end of said enclosure, said electron gun providing an energetic stream of electrons, means disposed between said gun and said cathode for accelerating said stream of electrons through said refluxing are discharge, said enclosure and electron gun being enclosed within an evacuated chamber, and an ion accelerating electrode provided with an axial opening and being positioned beyond and in axial alignment with the axial opening in the other end of said enclosure, said accelerating electrode withdrawing ions from said enclosure, said energetic stream of electrons having sumeient density and energy to provide an energetic, neutralized beam of electrons and ions beyond said accelerating electrode.

e 3. A neutralized electron-ion source comprising an elongated enclosure provided with axial openings in each of its ends, means for establishing a body of space charged neutralized ions along the axis of said enclosure, an electron gun positioned beyond one end of said enclosure and in axial alignment with the axis of said enclosure, said electron gun providing a stream of electrons, means disposed between said gun and said enclosure for accelerating said stream of electrons through said body of ions within said enclosure, means for providing a uniform collimating magnetic field along the axis of said enclosure and said electron gun, said enclosure and electron gun being enclosed within an evacuated chamber, and an ion accelerating electrode disposed beyond the other end of said enclosure for withdrawing and accelerating ions from said enclosure, said electron stream having sufficient energy to pass through said ion acceleration electrode to thus provide an energetic, neutralized beam of electrons and ions beyond said accelerating electrode.

4. The electron-ion source set forth in claim 3 and further including additional means positioned beyond said accelerating electrode for further accelerating the ions withdrawn from said enclosure, said additional means decelerating the energetic electrons in said electron stream such that the emerging electron-ion beam is neutralized and is provided with electrons and ions having substantially the same relative velocity.

5. The electron-ion source set forth in claim 4, wherein the accelerating means disposed between said electron gun and said enclosure includes first several stages of accleration, and said additional means beyond said accelerating electrode includes second several stages of accleration for the ions withdrawn from said enclosure, said acceleration electrode and said second several stages also providing deceleration for the electrons in said stream of electrons after they leave said enclosure.

6. The electron-ion source of claim 4, wherein said accelerating means disposed between said electron gun and said enclosure accelerate the electrons from said electron gun to an energy of about 99.85 ltv., and said ion accelerating electrode and said additional means accelerating said ions to an energy of about lO0J v., said ion acceleration electrode and said'additional means also serving as a means for decelerating said energetic electrons after they leave said enclosure.

7. The electron-ion source of claim 5, wherein said first several stages of acceleration accelerate said electrons from said ion gun to an energy of about $99.85 kv. before they enter said enclosure, and said ion acceleration electrode and said second several stages of acceleration for said ions accelerate said ions to an energy of about 600 kv.

8. A neutralized electron-ion source device for providing a variable thrust for the propulsion of. a space vehicle comprising an elongated enclosure provided with axial openings in each of its ends, means for establishing a refiuxing; space charge neutralized, gas-fed arc discharge along the axis of and within said enclosure and in alignmen t with said openings, an electron gun positioned beyond one 'end of said enclosure and in axial alignment with the axis of said enclosure, said electron gun providing a stream of electrons, means for providing a collimating magnetic field, said field having a direction parallel to the axis of said gun and enclosure, said gun and said enclosure being enclosed within a chamber which is mounted within said vehicle, said chamber being in communication with regions of negligible atmosphere which is encountered in outer space. means for accelerating electrons from said electron gun through said are discharge, and an ion accelerating electrode positioned beyond the other end of said enclosure for withdrawing and accelerating ions from said enclosure, said electrons having sufficient density and energy to pass through said ion acceleration electrode to thus provide an elected. energetic, neutralized beam of electrons and ions beyond said acceleration electrode, the specific thrust to said vehicleprovided by said ejected beam being directly related to the type of selected gas fed to said are discharge. 1

9. The device set forth in claim 8, wherein said electron gun is disabled, a door being placed over the axial opening in said one end of said enclosure, said accelerating electrode being replaced by a nozzle. and the gas fed to said discharge is a neutral gas, whereby the said discharge heat said neutral gas which is then ejected-through said nozzle to provide a specific thrust to said vehicle as a function of the type of selected neutral gas fed to said discharge.

References Cited in the file of this patent UNITED STATES PATENTS 2,969,308 Bell et al. Jan. 24, 1961

Claims

1. A NEUTRALIZED ELECTRON-ION SOURCE COMPRISING AN ELONGATED ENCLOSURE PROVIDED WITH AXIAL OPENINGS AT ITS RESPECTIVE ENDS, MEANS FOR ESTABLISHING A BODY OF IONS ALONG THE AXIS OF SAID ENCLOSURE AND TO PROVIDE SPACE CHARGE NEUTRALIZATION THEREWITHIN, AN ELECTRON GUN POSITIONED IN SPACED RELATION TO ONE END OF SAID ENCLOSURE, SAID ELECTRON GUN INCLUDING A CATHODE, AN ANODE, MEANS FOR FEEDING GAS TO THE INTERIOR OF SAID ANODE, A HIGH VOLTAGE SHIELD ENCOMPASSING SAID ANODE AND CATHODE AND PROVIDED WITH AN OPENING IN AXIAL ALIGNMENT WITH SAID CATHODE AND ANODE, A SOURCE OF OPERATING POTENTIAL CONNECTED BETWEEN SAID ANODE AND CATHODE, AN ELECTRON ACCELERATING ELECTRODE SPACED FROM AND IN AXIAL ALIGNMENT WITH THE OPENING IN SAID SHIELD AND WITH SAID ANODE AND SAID CATHODE, AND A SOURCE OF ACCELERATION POTENTIAL CONNECTED TO SAID SHIELD AND SAID ACCELERATING ELECTRODE, SAID CATHODE, ANODE AND ACCELERATING ELECTRODE BEING AXIALLY ALIGNED WITH THE AXIS OF SAID ENCLOSURE, MEANS FOR ESTABLISHING A STRONG MAGNETIC FIELD HAVING A DIRECTION PARALLEL TO THE AXIS OF SAID ENCLOSURE, SAID ENCLOSURE AND ELECTRON GUN BEING ENCLOSED WITHIN AN EVACUATED CHAMBER, SAID ELECTRON GUN PROVIDING AN ENERGETIC STREAM OF ELECTRONS WHICH IS DIRECTED THROUGH SAID BODY OF IONS WITHIN SAID ENCLOSURE, AND AN ION ACCELERATING ELECTRODE