US 3795833 A
The accel electrode in a Kaufman-type of electron bombardment ion thrustor is created by interengaging panels of insulative material. These panels are angularly related to each other to define the openings of the accel electrode. Conductive blades are installed in each opening for electrostatic deflection of the beamlet issuing therethrough.
Description (OCR text may contain errors)
United states Patent [191 King et al. 1 Mar. 5, 1974  ION BEAM DEFLECTION SYSTEM 3,071,154 1/1963 Cargill et al. 60/202 X  Inventors: Harry King woodland Hills; 3,552,125 1/1971 Banks et a1. 313/63 X David E. Schnelker, Northridge, both of Calif. Primary ExaminerPalmer C. Demeo 1 Asslgneer fl s Aircraft p y Culver Attorney, Agent, or FirmW. H. MacAllister; Allen A.
Callf- Dicke, Jr.
 Filed: May 25, 1972  Appl. No.: 256,987
Related US. Application Data 57 ABSTRACT  Continuation of Ser. No. 9,774, Feb. 9, 1970,
The accel electrode in a Kaufman-type of electron 52 US. Cl 313/63, 60/202, 60/230 bombardment thrust is created by interengaging 313/257, 313/348 panels of insulative material. These panels are angu- 511 1111.01 F0311 5/00, HOSh 5/00 larly related to each other to define the openings of 5 i l of Search. 257 4 0/202 230 the accel electrode. Conductive blades are installed in 7 each opening for electrostatie deflection of the beam-  References Cited let issuing therethrough.
UNITED STATES PATENTS 2,500,929 3/1950 Chilowsky 315/169 TV 15'Claims, 3 Drawing Figures ION BEAM DEFLECTION SYSTEM CROSS REFERENCE This application is a continuation of patent application Ser. No. 9,774, filed Feb. 9, 1970, and now abandoned.
BACKGROUND This invention is directed to an improved ion beam deflection system, particularly arranged for the deflection of all of the beamlets issuing from a Kaufman-type electron bombardment ion thrustor, particularly when the accel electrode thereof is a'perforated electrode.
The original electron bombardment ion thrustor, as disclosed in H. R. Kaufman U.S. Pat. No. 3,156,090, produces an ion beam which is of such nature that the thrustor can be employed to produce thrust. The thrust is produced on the ground, as well as in space applications, although the thrust produced finds its particularly important utility in space devices because of its high specific thrust. This same high specific thrust is obtainable on theground and, thus, the thrustor is useful in vacuum chamber work where such thrusts are desired, although it is usually more economic to employ other types of thrust-producing devices in earth-bound vacuum chambers. Anothersuch thrustor is illustrated in Dryden U.S. Pat. No. 3,345,820. In this latter patent, the beamlets are accelerated through perforations in the accel electrode, so that the large plurality of small circular beamlets are produced. This ion optical structure is of greater efficiency than the plurality of parallel rod ion optics of the Kaufman patent.
Another patent showing means for ion beam deflection for the directing of thrust from such a thrustor is George R. Brewer and George A. Work, U.S. Pat.- No. 3,535,880 granted Oct. 27, 1970. The Brewer and Work patent is limited to deflecting beam in a single plane, to thus provide mere steering in a single plane. Additionally, Harry J. King and James W. Ward U.S. PaLNo. 3,604,209 granted Sept. 14, 1971 shows the deflection of a small part of the total beam. It deflects only a row of beamlets as issuing from a'perforated accel electrode. These patents show net electrostatic deflection of the ion beam issuing from the accel electrode, with the result of net thrust which is not axial of the engine. However, they are limited in direction and net amount of deflection,.as discussed above.
SUMMARY conductive blades are interengaged with the interengaging insulative panels to be retained in position.
Accordingly, it is an object of this invention to provide an ion beam deflection system, particularly for electron bombardment ion thrustors, where each of the beamlets issuing through the openings in a perforated accel electrode is electrostatically deflectable in more than one plane through the axis to direct the thrust of the thrustor. It is another object to provide-an integrated structure comprised of an accel electrode and electrostatic deflection plates whereby the potential difference between individual conductive blades in the accel electrode causes deflection in selected conically defined direction, and the overall voltage of the blades in the accel electrode with respect to the screen electrode of the thrustor causes ion beam acceleration. It is still another object to provide an accel electrode which is comprised of a plurality of inter-engaging insulative panels which define accel electrode openings, together with conductive blades positioned around the openings so that the blades are retained in position by the panels, and the blades serve as the electrical portion of the electrode. It is still another object to provide effective ion beam deflection by providing electrostatic deflection in selected conically defined direction at all of the beamlet openings in an electron bombardment ion thrustor having a perforated accel electrode. Other objects and advantages of this invention will become apparent from a study of the following portion of the specification, the claims and the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION FIG. 1 fairly schematically illustrates a Kaufman-type electron bombardment ion thrustor at 10. Thrustor 10 comprises a cylindricalv body 12 in which is positioned a cathode 14. The cathode 14 produces electrons which move toward anode 16. The electron path is lengthened by provision of a suitable magnetic field so that the electrons move in a spirally lengthened path toward anode 16. A material to be ionized, such as, a gas, is introduced into the interior space of the anode so that, by electron bombardment, the ionizable material is ionized. For example, pipe 18 is connected to supply ionizable vapor or gas through the cathode into the interior space. i I
The outlet of the chamber defined by body 12 is covered by screen electrode 20, which is at the potential of body 12. Screen electrode 20 preferably has a plurality of perforations therethrough to permit the ions to drift out of the interior body of the thrustor. Accelerator electrode 22 is positioned downstream of screen electrode 20. Accel electrode 22 also has a plurality of openings therethrough, and the accel electrode is maintained at a suitable potential to accelerate the ions passing through the screen electrode, to produce thrust. In order to prevent the buildup of a space charge, neutralizer 24 is positioned downstream of the accel electrode 22 to inject electrons into the ion beam to provide a zero electrical charge. This prevents buildup of a charge on the body 12 of the thrustor or the structure upon which it is mounted. Neutralizer 24 also prevents a buildup of ionized material around the thrustor.
Power supply 26 performs as discharge supply between anode 16 and cathode 14; beam supply between cathode l4 and ground; and accel supply between ground and accel 22. Power supply 26 is connected to pipe 18, which is electrically connected to cathode 14, in order to provide the cathode power. Anode 16 is also connected to the beam power supply. A cathode heater may also be required, and this would also be connected to power supply 26. Furthermore, body 12 is connected to the power supply to provide potential reference for screen 20. Neutralizer 24 is supplied with power from the power supply in order to provide its electron beam.
Accel electrode 22 conventionally has an overall average negative voltage of about 1.0 KV with respect to ground, and this voltage is supplied by line 28. The differential voltage power supply 32 has output lines 34, 36 and 38, 40. The differential voltage power supply is able to provide a potential difference between these pairs up to 500 volts, above and below the potential in line 28, for total electrostatic differential deflection voltage therebetween of 1,000 volts. This voltage differential can either be selectable from any value from zero up to full voltage. or the differential voltage power supplies can provide either zero differential voltage or the illustrative 1,000 volts differential voltage. The difference is only in the complexity of the differential power supply.
The accel electrode 22 is shown in detail in FIGS. 2 and 3. It comprises ring 42 with which circular boss 44 is integrally formed. Ring 42 and boss 44 have a central hole 46 therethrough with the ring and boss comprising the'supporting structure for the balance of the accel electrode. It is made of electrically-insulative material, having high temperature strength, such as ceramic.
Boss 44 has a plurality of slots 48, 50, 52 and 54 therein extending down to the top surface of ring 42. These slots are in the upright direction across the circular boss, both above and below hole 46. Similarly, it has slots 56, 58, 60 and 62 through the circular boss positioned substantially at right angles with respect to slots 48 through 54. The slots define the size of the openings in the accel electrode, and define the number of the openings. In the present instance, nine openings are defined through which beamlets pass, and in which electrostatic deflection takes place. The use of nine openings in which electrostatic beamlet deflection control is accomplished is merely an exemplary number, and any convenient number of openings can be defined by the appropriate number of slots and associated equipment.
Panels 64, 66, 68 and 70 are respectively positioned within slots 48,-50, 52 and 54. Similarly, panels 72, 74, 76 and 78 are respectively positioned in slots 56, 58, 60 and 62. These panels are made of electrically-insulative material which is capable of withstanding high temperatures, such as ceramic. As is seen in FIG. 3, each of the panels 64 through 70 have upwardly-directed notches therein, while panels 74 through 78 have downwardly-directed notches therein. These notches inter engage so that each of the panels is continuous, but they are interlocked and interengaged and lie in the same plane to define openings therethrough. This construction is commonly called egg crate." By means of this egg crate construction, openings 80 are defined.
Conductive blades are associated with each of the openings, with an electrically separate blade on each side of the openings so that beamlets passing through the openings can be electrostatically deflected by application of appropriate electrostatic deflection voltages to the blades. Blades 82, 84 and 86 are respectively positioned on the lower side of panels 72, 74 and 76, as seen in FIG. 2, which is the upper side of their respective openings. Similarly, blades 88, 90 and 92 are positioned against the upper sides of panels 74, 76 and 78,-
so that they define the lower side of their respective openings. Thus, the application of differential electrostatic deflection voltages between the blades on the upper and the blades in the lower sides of the openings, causes upper and lower deflection, as compared to the central axis ofn the thrustor, which is normal to the drawing at the center of FIG. 2.
Blades 94, 96 and 98 are respectively on the right sides of panels 64, 66 and 68 to occupy the left sides of the openings while blades 100, 102 and 104 occupy the right sides of the openings. Each of these blades is cut out in the manner of the inter-related slots of the panels, but with larger slots, as illustrated at 106 in FIG. 3, so that the blades are electrically separated from each other where they 'cross each other.
The blades may either be flat stock so that they lie directly against the panels, in which case rectangular openings are defined, or they may be formed as illustrated in FIG. 2 to maintain circular beamlet cross sections which are more easily controlled. The formed characteristic is preferred, becausecircular openings 80 are, thus, defined within the blades. Each of the blades s formed so that it forms nearly a segment of a cylindrical tube. The adjacent segments of the other blades which define a particular opening are formed in such a manner that these tube segments are slightly separated so that there is electrical separation, as illustrated. Where the blades need cross each other in the lateral direction, there is axial spacing between the blades, as illustrated in FIG. 3. The conductive blades are attached to the insulative panels by brazing with copper filler material in an atmospheric furnace at approximately l,l20 C. The blade-panel assembly is likewise attached to the circular support ring.
In order to control the deflection of the beam as it passes through the openings, the several blades are connected to the sources of accel and deflection voltage. For example, blades 82, 84 and 86 are connected to line 38, while blades 88, 90 and 92 are connected to line 40. Thus, up-and-down deflection is controlled. Similarly, blades 94, 96 and 98 are connected to line 34, while blades 100, 102 and 104 are connected to line 36 to control the lateral or left-to-right beamlet deflection. The advantage of the present construction is that all the beamlet openings can be controlled for the most desirable or maximum control of the ion beam. If
deflection in only one plane is desired, of course, the blades need not be connected to deflection potential. Furthermore, it may be'desirable in an unusual circumstance to deflect only a portion of the beamlets. In such a circumstance, only those portions of blades necessary for the desired direction of deflection in the desired openings is provided. However, as presently understood, it is more desirable to deflect all of the beamlets a small amount to obtain a certain amount of net angular deflection, rather than deflect only a few of them a larger angular amount to obtain the same net deflection. Accordingly, in the structure illustrated, all of the beamlet openings are provided with deflection blades. Of course, the blades are electrically conductive in order that the deflection voltage can be transmitted therethrough, and in view of the fact that the accel electrode is positioned in an high temperature region of the ion thrustor, the preferred material has a high melting point, such as molybdenum.
This invention having been described in its preferred embodiment, it is clear that it is susceptible to numerous modifications and embodiments within the ability of those skilled in the art and without the exercise of the inventive faculty. What is claimed is: 1. An ion beam device, said ion beam device having a housing having an axis, an accelerator electrode positioned downstream with respect to said housing on said axis, means for supplying a negative potential to said accelerator electrode as an ion beam accelerating voltage for accelerating the ions generally along said axis, the improvement comprising:
said accelerator electrode being comprised of a plurality of intersecting insulative panel members positioned so that openings through said electrode are formed by the intersection of said panel members intersecting in groups of at least three;
conductive blades lying against said panel members so that said accelerator electrode openings are defined between said' blades, there being at least three blades in each of said openings, each of said openings being bounded on all sides by blades, each of said blades bounding a particular opening being electrically separate so that, upon application of differential voltage between blades in said openings, the ion beam can be electrostatically deflected in a selected direction.
2. The ion beam device of claim 1 wherein a plurality of first insulative panels extend in a first direction, and a plurality of second insulative panels extend in a second direction, said first insulative panels having notches therein for engagement on said second insulative panels, and said second insulative panels having notches therein for engagement on said first insulative panels so that said panels intersect to define the plurality of. openings.
3. The ion beam device of claim 2 wherein said conductive blades comprise first blades lying adjacent said first panels and second blades lying adjacent said second panels, said blades being notched so that none of said first blades electrically contact said second blades.
4. The ion beam device of claim 3 wherein said blades are formed as a segment of a cylindrical tube in each of said openings.
5. The ion beam device of claim 4 wherein said cylindrical tube segments in one of said openings between said panels have substantially coaxial axes.
6. Theion beam device of claim 1 wherein a plurality of first conductive blades extend in a first direction, and a plurality of second conductive blades extend in a second direction, said first conductive blades having notches therein for engagement around said second conductive blades, and said second conductive blades having notches therein for engagement around said second panels and to define openings between said first and second panels;
accelerator and deflection blades positioned against said panels and lying next to said openings, said blades in each opening being electrically separate so that an electric field can be provided therebetween so as to act upon an ion beam passing through said accelerator electrode, there being a sufficient number of blades to selectively deflect the beam within a conically defined direction. 10. An accelerator electrode for an ion beam device, said accelerator electrode comprising a plurality of first panels and a plurality of second panels arranged so that said panels intersect each other, said first panels being recessed to receive said second panels to retain said second panels and to define openings between said first and second panels;
conductive accelerator and deflection blades positioned against said panels and lying next to said openings, said conductive blades comprising first blades lying adjacent said first panels and second blades lying adjacent said second panels, said blades being notched so that none of said first blades electrically contact said second blades, said blades being connectable to a source of electrical potential so as to act upon an ion beam passing through said accelerator electrode, there being a sufficient number of blades to selectively deflect the beam within a conically defined direction.
11. The ion beam device of claim 10 wherein said blades are formed as a segment of a cylindrical tube in each of said openings.
12. The ion beam device of claim 1 1 wherein each of said cylindrical tube segments in one of said openings between said panels has substantially coaxial axes.
13. An ion beam device, said ion beam device having a housing having an axis, an accelerator electrode positioned downstream with respect to said housing on said axis, means for supplying a negative potential to said accelerator electrode as an ion beam accelerating voltage for accelerating the ions generally along said axis, the improvement comprising:
said accelerator electrode being comprised of a plurality of intersecting interengaged conductive blades, so that said accelerator electrode openings are defined between said blades, there being at least three blades defining each of said openings, each of said openings being bounded on all sides by blades, each of said blades bounding a particular opening being electrically separate, so that, upon application of differential voltage between said blades defining an opening, the ion beam can be electrostatically deflected in a selected direction. 14. An accelerator electrode for an ion beam device, said accelerator electrode comprising a first plurality of at least three electrically separate conductive acceleraelectrically separate from each other.
15. The accelerator electrode of claim 14-wherein each of said first and second adjacent beamlet openings is defined by four intersecting electrode blades, said blades between said adjacent openings being electrically separate, and said blades intersecting with said adjacent electrically separate blades being the same blades extending to define sides of said first and second beamlet openings.