US3076112A

US3076112A - Ion source

Info

Publication number: US3076112A
Application number: US2877A
Authority: US
Inventors: Wasserman Marien
Original assignee: CSF Compagnie Generale de Telegraphie sans Fil SA
Current assignee: Thales SA
Priority date: 1959-02-02
Filing date: 1960-01-18
Publication date: 1963-01-29
Anticipated expiration: 1980-01-29
Also published as: DE1204754B; FR1224888A

Description

,Jan. 29, 1963 M. WASSERMAN ION SOURCE 2 Sheets-Sheet 1 Filed Jan. 18, 1960 ATTORNEYS Jan. 29, 1963 M. WASSERMAN ,112

ION SOURCE Filed Jan. 18, 1960 2 Sheets-Sheet 2 IMVENTOR M. WAJ'SERMA/V ATTO NEY M 4 $5 +r 2 72% T..

aired tee l stens 3,076,112 N SQURCE Marian Wasserznan, Paris, France, assignor to (Iompaguie Generals do Telegraphic liens Fil, Paris, France Filed Jan. 13, 19st), tier. No. 2,877 Claims priority, application France Feb. 2, 1.959 iliainis. (Cl. 313-63) The present invention relates to an apparatus constituting an ion source, and more particularly relates to an ion source apparatus producing a hollow ion beam for use in connection with utilization devices in which a magnetic field having a circular symmetry is used.

Utilization devices for ionized gases are known in the prior art in which the ions have to be placed into a magnetic field with circular symmetry which may be produced, as known, by the flow of an intense current through an axial metallic rod or conductor. When an injection of the ions in the sense of this sleeve or conductor is desired with simultaneous preservation of the conditions of symmetry thereof, it is necessary that the ion source produces a hollow beam having as its axis the metallic rod or conductor in question. While ion guns are known in the prior art which produce ion beams of either full cylindrical configuration or plane configuration, none of the prior art ion sources is suitable for the injection of ions into a utilization device or" a type described hereinabove, which requires a hollow ion beam of circular symmetry.

The present invention has for its principal object to provide a source furnishing a hollow ion beam which is injected into the utilization vessel or enclosure both axially and symmetrically about the central rod or conductor of this vessel, whereby the rod or conductor is traversed by a current generating the magnetic field having lines of force with circular symmetry.

The ion source according to the present invention belongs generally to the type in which the ionizing electrons move in mutually crossed electric and ma netic fields, as described for example in the United States Patent 2,935,- 634, filed on lune 13, 1957, in the name of A. Lerbs and assigned to the assignee of the present invention which patent describes a source providing a plane ion beam.

Accordingly, it is an object of the present invention to provide an ion source for use with load or utilization devices of the type described hereinabove which obviates the disadvantages and shortcomings of the prior art devices.

It is another object of the present invention to provide an ion source which produces a fully satisfactory, hollow ion beam by relatively simple means.

Another object of the present invention resides in the provision of an ion source producing a hollow circular ion beam which may be used within a utilization enclosure or vessel in which a magnetic field with circular symmetry is established.

T ese and other objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing, which shows, for purposes of illustration only, two embodiments in accordance wit the present invntion and wherein:

FEGURE l is an axial, longitudinal cross-sectional view of a first embodiment of an ion source in accordance with the present invention, and

FIGURE 2 is an axial, longitudinal cross-sectional view through a modified embodiment of an ion source in accordance with the present invention.

The present invention is characterized by the fact that the ion source comprises an electron-optical and ionic system of electrodes with symmetry of revolution about the magnetic-field-producing axial rod or conductor, and that not only the ionizing electrons but also the was leaving the ionization space move within crossed electric and magnetic fields, established within a cylindrical space comprised between the electrode for the extraction of the ions and the axial rod or conductor in such a manner that the ions are concentrated or focused into a hollow beam within this space.

Referring now to the drawing, wherein like reference numerals are used throughout the two views to designate corresponding parts, and more particularly to FIGURE 1, reference numeral 1 designates therein an ion stabilization vessel or enclosure which is defined or limited by the walls 2 and includes within the axis thereof a metallic rod or conductor A source of current supply 4, which is connected between the ends of the rod 3, sends current therethrough in the direction indicated in PEGURE l by the arrow, that is, from the right to the left as viewed in FIGURE 1, which establishes a magnetic field with the circular lines of force about the axis, this field being directed toward the plane of the drawing in the upper part of the cross-sectional view of FIGURE 1 and toward the observer or viewer in the lower part thereof, as indicated also by the encircled small cross and dot, respectively, and designated by reference character B.

The vessel or enclosure 1 is supplied with ions from the left thereof by means of an ion source constructed in accordance with the present invention. This ion source cornprises an electrode system including a cathode electrode in the form of two cylinders 5- and 6, separated by a gap 7; an ion extraction electrode in the form of two cylinders S and separated by a gap lb and disposed between the cylinders 57 and 6 and axial rod 3; an annular cathode 11, supported on the cylinder 5; an electron-optical or focusing anode in the form of a cylinder 12, facing the cathode ll; and an anode electrode in the form of a cylinder 13, surrounding the cylinders 5 and 6. All of these electrodes have a symmetry of revolution about rod 3.

The

electrodes

12 and 13, for example, are incorporated into the walls 14 of the glass vessel or enclosure which contains the gun and which belongs to the enclosure or vessel 1. This vessel is closed by an annular member 15 made of Kovar, secured to the ring member 16 which is adapted to slide along the rod- 3. The ring member 36 is connected by means of bellows 1'7 made of tombac to a boss 13 provided on the rod 3. in that manner, the rod 3 may expand freely without damaging the glass structure M.

The electrodes 5 and a are interconnected with each other in any suitable manner and are also connected to a positive potential with respect to the rod 3. The cathode ll, supplied from a source not illustrated, is also connected to the potential of electrode 5. The anodes l2 and 13 are carried at suitable positive potentials with respect to electrodes 5 and 6 by means of source 19. The

electrodes

8 and 9 are interconnected in any suitable manner and are also carried at a potential suitably chosen intermediate that of the rod 3 and that of electrodes 5 and 6 by means of the same source 19.

A tubular channel 2%? discharges through electrode 13 to permit the admission of a gas under slight pressure to be ionized. A tubular member 21, connected to a suitable vacuum pump (not illustrated herein) terminates through wall 14 to permit evacuation and therewith the establishment of a vacuum within a portion of the gun enclosure or vessel. This intercornrnunication between the portion in which prevails the slight gaseous pressure and the portion in which the vacuum prevails is essentia ly precluded almost completely, on the one hand, by an end cover 22 formed by cylinder 5 and provided in the center thereof with an aperture just sufficiently Ii large to permit passage therethrough of rod 3 and, on the other, by an end cover 23 formed by cylinder 13 and provided in the center thereof with an aperture suificient to permit the passage therethrough of the cathode cylinder 5 and including additionally an annular gap 24 intended for the passage of the electrons. Another end cover of the same cylinder 13 serves as collector for the electrons.

Operation The operation of the device illustrated in FIGURE 1 is as follows:

When the particular voltages are applied to the various electrodes and current flows through rod 3, the electrons emitted from the cathode 11, under the effect of the radial electric field established between the electrode 12 and the electrode 5, and of the transverse magneti: field caused by the how of current through rod 3, follow urved paths or trajectories 26. These paths or trajectories 20' enter through the gap 24 into the space comprised between electrodes 13 and 5, 6 in which electrons move from the left to the right, as viewed in FIGURE 1, and parallelly to the rod 3 by the action of the same magnetic field or" which the direction is indicated by the circles B, crossed with the radial electric field directed from the interior toward the exterior thereof, and established between electrodes 13 and 5 or 6. The parallel electron paths define a cylindrical pattern of the ionizing beam which is coaxial with the rod 3. The electron paths pass through what are in efiect a plurality of ionizing areas located at difierent angularly spaced points around the rod 3, these ionizing areas combining with each other to form an ionizing chamber completely encircling the rod 3. At the end of the electron fiow, the electrons are captured by collector 2.5.

The gas emitted into the same space through tubular member 2% is ionized by these electrons. The positive ions are attracted by the

negative extraction electrode

8, 9 and leave the ionization space through successive gaps 7 and 16.

According to the particular feature of the present invention, the ions which leave through gap 10 find themselves anew within the mutual crossed electric and magnetic fields, these fields being established between the cylindrical space between the

extraction electrode

8, 9 and the rod 3. The transverse magnetic field and the radial electric field have here the same direction as in the ionization space. The electric field, in effect, is directed from the interior toward the exterior, thanks to the difference of potential between

electrodes

3 and 8 or 9. It is known that when neither the direction of the magnetic field nor that of the electric field changes, the ions move in the same axial direction as the electrons of the beam 26. Consequently, the ions eventually move in parallel paths and are concentrated into a hollow beam 27 directed from the left to the right as viewed in the drawing and are thereupon injected into the enclosure 1. The parallel paths of the ions define a cylindrical pattern of the ion beam which is also coaxial with the rod 3.

The embodiment illustrated in FIGURE 2 in which the same parts are designated by identical reference numerals as in FIGURE 1 discloses an arrangement in which the current in rod 3 has been reversed with respect to that of FIGURE 1.

Consequently, in the embodiment of FIGURE 2, the magnetic field has changed its direction and is directed toward the observer in the upper portion of the crosssectional View of the drawing, and toward the plane of the paper in the lower portion thereof. Under these conditions, with the electric field within the ionization space remaining directed from the interior toward the exterior, the movement of the electrons which ionize the gas changes its direction, and is directed from right to left as viewed in FIGURE 2. The arrangement of the electrodes within the ionization space is therefore modified in FIGURE 2 by placing the cathode 11 and the focusing anode 12 toward the right, and the cylinder 13 with the collector 25 toward the left thereof. Furthermore, the

electrodes

8, 9 are now carried at a negative potential with respect to rod 3. Consequently, the electric field within the space between these

electrodes

8, 9 and rod 3 is directed from the outside toward the inside, and is, therefore, inverse with respect to the electric field within the ionization space. Thanks to this simultaneous inversion of the magnetic field and of the electric field with respect to the conditions of FIGURE 1, the ion beam 27 moves in FIGURE 2 in the same direction as in FIGURE 1, and in the opposite direction with respect to the flow of electrons in FIGURE 2, that is, from left to right as viewed in FIGURE 2. Otherwise, the operation of the device shown in FIGURE 2 is the same as that of FIGURE 1.

While I have shown and described'two embodiments in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of many changes and modifications within the spirit and scope of the present invention, and I, therefore, do not Wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

I claim:

1. In a rotational symmetry device traversed along its axis by a metal rod and having feeding means for said rod to send an electric current therethrough, thereby gen erating magnetic field having lines of force of circular shape around said rod, an ion source having a cylindrical extraction electrode coaxial with said rod, an evacuated vessel surrounding said electrode, means for feeding gas to be ionized into said vessel, means for emitting a hollow electron beam propagating substantially parallel to said rod through said gas thereby ionizing it including first radial electric field generating means acting together with said circular magnetic field on said electrons to direct the same substantially perpendicularly to both said fields, and means for generating a second radial electric field in the space between said rod and said extraction electrode, said last-mentioned space receiving ions produced by said ionizing electrons and extracted through said extraction electrode, and said circular magnetic field acting on said ions to concentrate said ions into a hollow tubular beam propagating in said space substantailly parallel to said.

rod' and substantially perpendicular to both said lastmentioned fields.

2. An ion source as claimed in claim 1, wherein both said first and second radial electric fields are of the same sense, and both said electron and ion beams are propagating in the same direction.

3. An ion source as claimed in claim 1, wherein both said first and second radial electric fields are of opposed sense, and both said electron and ion beams are propagating in opposed directions.

4. An ion source having an ionization space for producing a hollow ion beam, comprising means for establishing crossed magnetic and electric fields in said space with the magnetic field being generally circular about a predetermined axis and the electric field being radial with respect to said axis, gas supply means for supplying a gaseous medium adapted to be ionized by an electron beam generally encircling said axis within said ionization space, and means including said first-mentioned means for producing said ionizing electron beam and for extracting the ions created by the said ionizing electron beam in the form of a hollow cylindrical ion beam encircling said axis.

5. An ion source having a generally annular ionization space for producing a hollow ion beam, comprising means for establishing crossed magnetic and electric fields in said space including axial conductor means through which current fiows for setting up a circular magnetic field thereabout, gas supply means for supplying a gaseous medium adapted to be ionized by an electron beam Within said ionization space, means including said first-mentioned means for producing said ionizing electron beam, and means including electrode means in combination with said first-mentioned means for directing the ions produced by the said ionizing electron beam in such a manner that the ions move in the form of a hollow cylindrical ion beam encircling said conductor within said crossed electric and magnetic fields.

6. An ion source according to claim 5, wherein said electric field is a radial field.

7. An ion source having an ionization space for producing a hollow ion beam, comprising means for establishing crossed magnetic and electric fields in said space including axial conductor means through which current passes for setting up a circular magnetic field thereabout, gas supply means for supplying a gaseous medium adapted to be ionized by an ionizing electron beam within said ionization space, electron emissive means for emitting an ionizing electron beam guided by said first-mentioned means and encircling said conductor in said space, and means including said first-mentioned means and additional electrode means for establishing a second electric field to focus and guide said ions produced in said space by the said ionizing electron beam in such a manner that the ions move in the form of a hollow cylindrical ion beam encircling said conductor within said crossed electric and magnetic fields.

8. An ion source according to claim 7, wherein both of said electric fields are radial fields.

9. An ion source having an ionization space for producing a hollow ion beam, comprising means for establishing crossed magnetic and electric fields including axial conductor means through which current passes for setting up a circular magnetic field thereabout and electrode means having a symmetry of revolution about said conductor means for establishing at least one electric field, gas supply means for supplying a gaseous medium adapted to be ionized by an ionizing electron beam within said ionization space, and means for producing said electron beam propagating within said fields, the ions produced by said ionizing electron beam also propagating within said fields and being focused thereby into a hollow cylindrical ion beam within said crossed electric and magnetic fields.

10. An ion source according to claim 9, wherein said electrode means establish two electric fields.

11. An ion source according to claim 10, wherein said electric fields extend essentially radially.

12. An ion source having an ionization space for producing a hollow ion beam by the interaction with a gaseous medium of the electrons in an electron beam propagating within crossed magnetic and electric fields, comprising axial conductor means through which current passes for setting up said magnetic field having a circular configuration thereabout, gas supply means for introducing a gaseous medium to be ionized into said ionization space, and electron-optical electrode means generally encircling said conductor means for establishing said electric field and for extracting the ions produced by the said ionizing electron beam from said ionizing space and pro pagating the same in the form of a hollow cylindrical ion beam within said crossed electric and magnetic fields.

13. An ion source for producing a hollow ion beam comprising means for producing a generally cylindrical ionizing electron beam including means for establishing crossed magnetic and electric fields for guiding said electron beam, said last-rnentioned means including an axial conductor through which current passes for setting up the magnetic field as circular thereabout, gas supply means for introducing a gaseous medium to be ionized into said ionization space, an electrode means for focusing and separately grouping said electrons and ions in such a manner that the ions produced by said ionizing electrons move also Within said crossed electric and magnetic fields in the form of a hollow cylinder.

14. An ion source having an ionization space for producing a hollow ion beam by the interaction with a gaseous medium of the electrons in an electron beam propagating within crossed magnetic and electric fields, comprising axial conductor means through which current passes for setting up said magnetic field having a circular configuration thereabout, electron-optical electrode means for establishing said electric field and for extracting the ions produced by the said ionizing electron beam from said ionizing space and propagating the same in the form of a hollow cylindrical ion beam within said crossed electric and magnetic fields, said electrode means including two concentric electrode systems disposed about said conductor means, and means for establishing a first electric field between said two electrode systems and a second electric field in the space between the inter electrode system and said conductor means.

15. An ion source for producing ions propagating in parallel paths generally defining a cylindrical pattern, comprising means for establishing crossed magnetic and electric fields at ionizing areas located at difierent angularly spaced points around the axis of said cylindrical pattern, said last-mentioned means including a conductor extending coaxially of said cylindrical pattern and means for passing a current through said conductor for establishing said magnetic field as a circular field thereabout, means for supplying an ionizable medium to the ionizing areas in said crossed fields, and means including said crossed field establishing means for producing ionizing electrons moving in said ionizing areas parallel to said conductor to ionize said ionizable medium, and means including electrode means in combination with said firstmentioned crossed field establishing means for separating ions from said ionizing electron for propagating said ions in said parallel paths along said cylindrical pattern.

References Cited in the file of this patent UNITED STATES PATENTS 2,760,101 Reverdin Aug. 21, 1956 2,761,088 Warnecke et a1. Aug. 28, 1956 2,935,634 Lerbs May 3, 1960

Claims

1. IN A ROTATIONAL SYMMETRY DEVICE TRAVERSED ALONG ITS AXIS BY A METAL ROD AND HAVING FEEDING MEANS FOR SAID ROD TO SEND AN ELECTRIC CURRENT THERETHROUGH, THEREBY GENERATING MAGNETIC FIELD HAVING LINES OF FORCE OF CIRCULAR SHAPE AROUND SAID ROD, AN ION SOURCE HAVING A CYLINDRICAL EXTRACTION ELECTRODE COAXIAL WITH SAID ROD, AN EVACUATED VESSEL SURROUNDING SAID ELECTRODE, MEANS FOR FEEDING GAS TO BE IONIZED INTO SAID VESSEL, MEANS FOR EMITTING A HOLLOW ELECTRON BEAM PROPAGATING SUBSTANTIALLY PARALLEL TO SAID ROD THROUGH SAID GAS THEREBY IONIZING IT INCLUDING FIRST RADIAL ELECTRIC FIELD GENERATING MEANS ACTING TOGETHER WITH SAID CIRCULAR MAGNETIC FIELD ON SAID ELECTRONS TO DIRECT THE SAME SUBSTANTIALLY PERPENDICULARLY TO BOTH SAID FIELDS, AND MEANS FOR GENERATING A SECOND RADIAL ELECTRIC FIELD IN THE SPACE BETWEEN SAID ROD AND SAID EXTRACTION ELECTRODE, SAID LAST-MENTIONED SPACE RECEIVING IONS PRODUCED BY SAID