US3233404A

US3233404A - Ion gun with capillary emitter fed with ionizable metal vapor

Info

Publication number: US3233404A
Application number: US265292A
Authority: US
Inventors: Huber Harry; Bihan Raymond Le
Original assignee: CSF Compagnie Generale de Telegraphie sans Fil SA
Current assignee: Thales SA
Priority date: 1962-04-02
Filing date: 1963-03-14
Publication date: 1966-02-08
Anticipated expiration: 1983-02-08
Also published as: DE1248820B; FR1327124A; GB982671A

Description

Feb. 8, 1966 H. HUBER ETAL 3,233,404

ION GUN WITH CAPILLARY EMITTER FED WITH IONIZABLE METAL VAPOR Filed March 14, 1963 4 Sheets-Sheet 1 CPQLLQ ATTORNEY Feb. 8, 1966 H. HUBER ETAL 3,233,404

ION GUN WITH CAPILLARY EMITTER FED WITH IONIZABLE METAL VAPOR Filed March 14, 1963 4 Sheets-Sheet 2 FIG. 2

INVENTORS: H-IIUBER cl R-lEBl/MN Feb. 8, 1966 HUBER L 3,233,404

ION GUN WITH GAPILLARY EMITTER FED WITH IONIZABLE METAL VAPOR Filed March 14, 1963 4 Sheets-Sheet 3 15 1S OOOOOOOQOAOOMOOQOOQ Ge (0 '1 E6 E0 INVENTORS:

/E I H- HUBER R-ZE'BIHAIV ATTORNE Feb. 8, 1966 H. HUBER ETAL 3 3,233,404

ION GUN WITH .CAPILLARY EMITTER FED WITH IONIZABLE METAL VAPOR Filed March 14, 1963 4 Sheets-Sheet 4 INVENTORSZ H-HUBER cl R-lEB/HIN ATIORNEY United States Patent 3,233,404 ION GUN WITH CAPILLARY EMITTER FED WITH IONIZABLE METAL VAPOR Harry Huber and Raymond Le Bihan, Paris, France, as-

signors to CSF-Compagnie Geuerale de Telegraphic Sans Fil, Paris, France Filed Mar. 14, 1963, Ser. No. 265,292 Claims priority, application France, Apr. 2,

893,001; June 26, 1962, 901,949 15 Claims. (Cl. 60-355) The present invention relates to an ion gun, and more particularly to an ion gun utilizing a capillary body of refractory metal having at least one straight capillary duct by means of which a relatively high-density ion current can be obtained.

In the copending application Serial No. 108,062, filed on May 5, 1961, in the name of H. Huber and I. Bensimon, and assigned to the assignee of the present application there is described a thermoelectric energy converter, characterized particularly by a capillary emitter fed with metal vapor, such as cesium, rubidium or potassium, carried at an electron emission temperature and supplied by a separate reservoir, this body being a formation with straight capillary channels of tungsten, molybdenum, tantalum, nickel or analogous material.

An experimental study of this emitter, particularly with capillary ducts of tantalum of 0.4 mm. in diameter and of mm. in length, heated to 2100 K. and fed with cesium vapor derived from a reservoir heated to 650 K., has demonstrated that such a body is an abundant source of cesium ions with a surprising ion current density of the order of 1 a./cm. On the basis of this study, the present invention proposes the application of such a body to ion guns, which may, in particular, be intended for ion propulsion.

The present invention, therefore, consists in an ion gun, characterized by the fact that its ion source is constituted by a body having at least one straight capillary channel or duct, made of tungsten, molybdenum, tantalum, nickel or analogous material, this body being fed with a metal vapor such as cesium, rubidium or potassium furnished by a separate reservoir.

According to one realization of the present invention the capillary ducts or channels have a circular transverse cross section.

According to a further feature of the present invention, the capillary ducts or channels have the form of slots, that is, present a rectangular, annular or substantially tri angular transverse cross section.

The usual technique of cesium or analogous ion sources provides for the utilization of porous bodies. However, most frequently these bodies are realized by sintering refractory powders such as is known in the manufacture of cathodes with a barium reservoir. Tests and experiments have shown that the ion current density obtained with the bodies of this nature does not exceed 30 ma./cm. in the most favorable case. This difference With respect to the subject matter of the present invention may be explained by the fact that the straight capillary body used with the present invention possesses a transparency and a pore size greater than a sintered body from which follow transport mechanisms of the cesium and-ion formation mechanisms which are completely different.

In effect, in the case of the prior art porous bodies realized by sintering refractory powders, one' obtains very fine pores, of the order of some microns in diameter which isthe reason that the transport of the cesium across one has capillary'ducts of the order of some tenths of a millimeter of transverse dimension (of the order of 100 times larger than the preceding case), which amounts for the fact that the transport of the cesium across the capillary ducts takes place essentially by Knudsen flux or' still by a typeof flux comprised between that of Knudsen flux and that of so-called viscous flux. As a result of the multiple impact of cesium atoms, there. takes place a formation of cesium ions by the eifect of surface lOl'llZ8";

tion; also there occurs electron emission on the inside of the pore in such a manner that there takes place a formation of a strongly ionized gas (in a particular case the positive and negative charges are equal) which leaves the capillary ducts by eilusionabout as the molecules of a non-ionized gas leave a tubulure. This ionized and almost neutral gas which effuses from the capillary duct and of which the ions may be extracted by an electrode having a relatively very low voltage, forms in front of the collect-or electrode for the ions a closed screen whereas in the known guns, the corresponding space is filled with the positive space charge which limits the ion current.

Accordingly, it is an object of the present invention to provide an improved ion gun which provides a higher ioncurrent density than has been realizable heretofore.

Another object of the present invention resides in theprovision of an ion gun with high ion current densities which is simple in construction and requires only rel' atively low voltages for proper operation thereof.

Still a further object of the present invention resides in the provision of an ion gun utilizing straight capillary ducts which permits of high ion current densities without problem of positive space charges limiting the ion current.

These 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, several embodiments in accordance with the present invention, and wherein: 1

FIGURE 1 is a cross sectional view through an ion gun in accordance with the present invention utilizing,

as ion emitter, a single straight capillary duct of circular cross section.

FIGURE 2 is a partial perspective view, partially in cross section, of an ion gun utilizing, as ion emitters, an

array of the capillary ducts shown in FIGURE 1,

FIGURE 3 is a longitudinal cross sectional view through a modified embodiment of an ion gun in accord- ;ance with the present invention utilizing straight capillary ducts in the form of rectangular slots,

FIGURE 4 is a perspective view, partially in cross sec-f tion and on an enlarged scale, of the ion gun of FIG- URE 3,

FIGURE 5 is a partial perspective view, partially in cross section, of a modified embodiment of an ion gun .cross section, of a still further modified embodiment of Patented Feb.'8, 1966 an ion gun in accordance with the present invention utlizing triangular slots.

Referring now to the drawing wherein like reference numerals are used throughout the various views to designate like parts, and more particularly to FIGURE 1, reference numeral 1 designates therein a straight capillary duct utilized in the gun according to the present invention, this capillary duct 1 being heated by means of a filament 2 of any conventional construction. The material and the dimensions of the capillary duct 1 may be, for example, those utilized in the experimental study mentioned hereinabove.

The. capillary duct 1 is fed with cesium vapor from the reservoir 3 in which the cesium 4 is carried at the evaporation temperature thereof by any suitable means not illustrated herein. Reference numeral 5 designates a focusing electrode carried at the potential of the capillary duct 1 and reference numeral 6 designates an accelerating electrode carried at a negative potential of some kv. with respect to the capillary duct 1. It will be noted that owing to the case with which the ions are extracted,

the orifice of the passage 7 of the electrode 6 may be relatively far from the discharge aperture 8 of the capillary duct 1. The

electrodes

5 and 6 comprise cavities 9 to receive a cooling fluid. The ion beam obtained from the ion gun in accordance with the present invention is designated in FIGURE 1 by reference. numeral 10.

FIGURE 2, in which the same reference numerals as in FIGURE 1 have been utilized to designate analogous elements, differs'from FIGURE l-by the fact that in lieu of a single capillary duct a battery of

capillary ducts

1, 1,, 1", 1" is used which are disposed, for example, in a linear array. It is obvious that the capillary ducts could also be disposed in any other arbitrary formation, for example, along a circle. It is also possible to form bidimensional groups of these capillary ducts.

' In FIGURES 3 and 4 the body having capillary channels or ducts is formed by a stack of plates such as

plates

11 and 12 made of tungsten, molybdenum, tantalum or analogous material. plates, 12 and 11 is provided an interval 13 which is maintained by any desired number of spacers 14 which separate the interval 13 into a certain number of aligned slots 15. These slots constitute the straight capillary channels or ducts. Between the

plates

11 and 12 in contact with each other are inserted the strands or wires 16 of the heating filaments with interposition of insulating sheaths or layers 17. The extremities of the plates 11 arid 12 are profiled r shaped to define grooves 18 parallel to which are disposed a network of tubes 19 carried at a negative potential with. respect to the body having the capillary ducts and operatingas accelerating electrode analogous to the electrode 6 of FIGURES 1 and 2, The focusing electrodes analogous to the electrode of FIG- URES l and 2 have not been illustrated in this embodiment. If there be, need of such electrodes, the form and disposition thereof along the channels 18 may take any suitable conventional aspect as known to a person skilled in the art.

The assembly of the capillary body is fixed on a support 20, provided with a tube 21 leading to a reservoir of cesium or analogous material.

In operation, when the capillary body is heated by the filaments 16, and when the cesium vapor arrives through the tube 21 toward the bottom of the capillary channels 15, there is produced from the top of these channels an ion discharge by the mechanism explained hereinabove, These ions are extracted by the electrode 19 and are concentrated into a beam for ultimate utilization purposes.

Experiments have shown that with the improvement according to FIGURES 3 and 4 which considerably increases the utilization coeflicient of the gross surface of the gun by the apertures of the capillary channels, one increases considerably the output in ions and one reduces the ratio Between each pair of consecutive 4, between the heating power of the source and the power transmitted to the jet.

As illustration, by taking a total surface of the capillary body of 5 x 5 cm., a width of the slots 15 of 0.8 mm, a spacing of the slots 15 of 3.2 mm., a heating temperature of the capillary body of 1800 K. with a temperature of the reservoir of cesium of 573 K., a distance between the electrodes 19 and the capillary body of 0.8 mm. and a voltage of these electrodes of 4 kv. with respect to the body, one obtains a total intensity of ion current of about 1.25 a., that is an electric power in the jet of corresponding to a total thrust of 13.4 grams. The power consumption for the heating of the capillary body is then established at about 1-kw., that is at about 20% of the power in the jet. These figures show to a person skilled in the art the genuine and veritable progress realized with the means of FIGURES 3 and 4.

The invention, of course, is not limited to the examples described so far but encompasses all variations susceptible to be imagined by one skilled in the art without requiring any inventiveness. For example, instead of being formed by a stack of plates, the capillary body could also be constituted by an assembly of coaxial cylinders spaced slightly from each other; in that case, the slots would have an annular transverse cross section. Or, in the alternative, one could also dispose a system of plates diverging radially in a star-shaped manner from a common center and surrounded by a cylindrical envelope; in that case the cross section of the slots would 'be substantially triangular. These two variations are represented schematically in FIG-

URES

5 and 6, respectively, where the reference numeral 22 designates the metallic parts and the reference numeral 23 the slots.

Additionally, the present invention does not depend on any particular manner of heating the capillary channels or ducts which may take place by conduction or thermal radiation, by electron bombardments, by direct passage of current, or any other known means.

Thus, while we have shown and described several embodiments in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications within the spirit and scope of a person skilled in the art, and we, 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.

We claim:

1. An ion gun, comprising:

a capillary body of a refractory metal having at least one straight capillary duct,

means for feeding said duct with a vaporized metal chosen from the group consisting of cesium, rubidium and potassium,

means for heating said duct to thereby ionize said vaporized metal,

and means including negatively biased accelerating electrode means for extracting ions of said metal from said duct.

2. An ion gun, comprising:

a capillary body of a refractory metal having a plurality of straight capillary ducts located side-by-side, means for feeding said ducts with a vaporized r'netal chosen from the group consisting of cesium, rubidi um and potassium,

means for heating said ducts to thereby ionize said vaporized metal, and means including negatively biased accelerating electrode means for extracting ions of said metal from means for feeding said duct with a vaporized metal chosen from the group consisting of cesium, rubidium and potassium,

means for heating said duct to thereby ionize said vaporized metal,

4. An ion gun, comprising:

a capillary body of a refractory metal having at least one straight capillary duct of elongated substantially rectangularly cross section thereby being effectively slot-shaped,

means for heating said duct to thereby ionize said vaporized metal,

5. An ion gun, comprising:

a capillary body of a refractory metal having at least one straight capillary duct of substantially annular cross section,

means for heating said duct to thereby ionize said vaporized metal,

6. An ion gun, comprising:

a capillary body of a refractory metal having at least one straight capillary duct of substantially triangular cross section,

means for heating said duct to thereby ionize said vaand means including negatively biased accelerating porized metal, electrode means for extracting ions of said metal from said duct.

7. A ion gun, comprising:

a capillary body of a refractory metal having a plurality of substantially straight capillary ducts forming a bi-dimensional array,

means for heating said duct to thereby ionize said vaporized metal,

8. An ion gun, comprising:

a capillary body of a refractory metal having at least one straight capillary duct, the cross section of said capillary duct being of the order of several tenths of a millimeter,

means for heating said duct to thereby ionize said vaporized metal,

9. An ion gun, comprising:

a capillary body of a refractory metal having at least one straight capillary duct, said body being composed of a stack of plates of said refractory metal and current, comprising:

capillary body means provided with substantially straight capillary duct means,

means for supplying to said duct means a vaporized metal,

means for producing within said duct means a strongly ionized gas by multiple impact of the atoms of said metal leaving said duct means by effusion,

and means for extracting ions from said duct means.

11. An ion gun capable of producing a high density ion current, comprising:

capillary body means made of a refractory metal provided with substantially straight capillary duct means,

means for supplying to said duct means a vaporized metal,

and means for extracting ions from said duct means.

12. An ion gun capable of producing a high density ion current, comprising:

capillary body means provided with substantially straight capillary duct means,

means for supplying to said duct means a vaporized metal chosen from the group consisting of cesium, rubidium and potassium,

and means for extracting ions from said duct means.

13. An ion gun capable of producing a high density ion current, comprising:

capillary body means provided with substantially straight capillary duct means of transverse dimension of the order of at least one tenth of .a millimeter,

means for supplying to said duct means a vaporized metal,

means for producing within said duct means a strongly ionize-d gas by multiple impact of the atoms of said metal leaving said duct means by effusion,

and means for extracting ions from said duct means.

14. An ion gun capable of producing a high density ion current, comprising:

and means for extracting ions from said duct means.

15. An ion gun capable of producing a high density ion current, comprising:

capillary body means made of a refractory metal provided with substantially straight capillary duct means of transverse dimension of the order of at least one tenth of a millimeter,

means for producing Within said duct means a strongly '7 8 ionized gas by multiple impact of the atoms of said 2,754,442 7/ 195 6 Beutry e't 211. 3-13*-6-3 I metal leaving sa-id duct means by effusion, 3,005,931 10/1961 Dandl 7 313- 63 and means for extracting ions from said duct means. 3 121 816 2/1964 B k t 1, v t 313 63 v 3,122,882 3/1964 Schultz et a1. GIL-35.5 References Cited by the Exam 5 3,137,801 6/1964 Brooks et a1. 3'13 s3 UNITED STATES PATENTS Y k y Primary E-XGITZUIGI.

2,714,166 7/ 195 5 Starr 313-63 SAMUEL LEVINE, Examiner.

Claims

1. AN ION GUN, COMPRISING: A CAPILLARY BODY OF A REFRACTORY METAL HAVING AT LEAST ONE STRAIGHT CAPILIARY DUCT, MEANS FOR FEEDING SAID DUCT WITH A VAPORIZED METAL CHOSEN FROM THE GROUP CONSISTING OF CESIUM, RUBIDIUM AND POTASSIUM, MEANS FOR HEATING SAID DUCT TO THEREBY IONIZE SAID VAPORIZED METAL, AND MEANS INCLUDING NEGATIVELY BIASED ACCELERATING ELECTRODE MEANS FOR EXTRACTING IONS OF SAID METAL FROM SAID DUCT.