US2308800A - Electron discharge device - Google Patents

Description

Jan. 19, 1943. A. E. ANDERSON 2,308,800

ELECTRON DISCHARGE DEVI-CE Filed Feb. 15, 1941 lNVENTOR :1. E. ANDERSON A T TORNEY mediate vicinity of the axis are Patented Jan. 19, 1943 ELECTRON DISCHARGE DEVICE St. George, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application February 15, 1941, Serial No. 379,103

Alva Eugene Anderson,

9 Claims.

This invention relates to electron discharge devices and more particularly to electrode systems, commonly designated as electron guns, for producing a beam of electrons in such devices.

In general, electron beam discharge devices comprise an electron gun for producing an electron beam, an electron receiving electrode, such as a target or anode, upon which the beam is directed, and one or more auxiliary electrodes between the electron gun and the electron receiving electrode for affecting or controlling the direction, intensity or velocity of the beam or withdrawing energy therefrom. The electron gun usually comprises a cathode and two or more electrodes in cooperative relation therewith for concentrating the electrons emanating therefrom into a beam, one of the electrodes being main tained at a positive potential with respect to the cathode and commonly referred to as the accelerating anode.

Two of the factors of considerable import in determining the operating characteristics of such devices and affecting the merit thereof are the magnitude of the current which can be obtained in the beam from a cathode'of a particular rating and the degree to and uniformity with which the electrons in the beam can be affected or controlled at any particular region in the path traversed by the beam. In known devices, usually the attainment of a beam current fairly large in comparison to the total emission obtainable from the cathode necessitates the use of relatively high potentials upon the accelerating anode. Consequently, such devices have a relatively low perveance, the perveance being expressed by the relation I being the total beam current and V the voltage of the accelerating anode.

It has been found also that in electron beam devices wherein the electrodes are constructed and arranged to constitute an axially symmetrical system, the fields extant in the major portion of the path traversed by the beam are of considerably less intensity along and in the vicinity of the axis of the system than at points removed from the axis. Hence, those electrons in the beam which traverse paths on and in the imafiected less by potentials on the auxiliary electrodes, or conversely have less effect upon the auxiliary .electrodes, than those which traverse paths .somewhat removed from the axis, whereby .both the efficiency and the frequency range of operation of the device are limited and non-uniform interchange of energy between the beam and these electrodes results.

One general object of this invention is to improve the operating characteristics of electron beam discharge devices.

More specifically objects of this invention are to" beam distion, an electron gun comprises a cathode having a relatively large area emissive surface and a plurality of electrode members in cooperative relation with the cathode emissive surface for concentrating the electrons emanating therefrom into a beam of annular cross-section throughout the major portion of its length.

In a specific construction, the emissive surface conforms to an annular section of a toroid and the concentrating system includes inner and outer electrode members extending from the boundaries of the emissive surface and a pair of coaxial electrodes having juxtaposed portions defining an annular passageway converging away from'the emissive surface and coaxial therewith.

The invention and the various features thereof will be understoodmore clearly and fully from the following detailed description with reference to the accompanying drawing, in which:

Fig. l is an elevational view partly in section of an electron discharge device including an'electron gun illustrative of one embodiment of this invention, a portion of the electron gun being broken away toshow details thereof;

Fig. 2 is an enlarged view in section, along plane 2-2 of Fig. 1 of the electron gun; and

Fig. 3 is an enlarged outline view showing the configuration and relation of surfaces of the electrodes in the electron gun illustrated in Fig. 2.

Referring now to'the drawing the electron dis- Attain a high perveance in electron beam disenclosing vessel members 23 and disc 24, it will be apparent, serve charge device shown in Fig. 1 comprises an elongated evacuated enclosing vessel I0, for example of vitreous material, having at one end thereof an inwardly extending stem II' from which an anode I2, of metal or carbon, is supported by rigid leading-in conductors I3. The anode I2 is j generally cup-shaped asshownto minimize secondary electron emissive effects. An electron gun, described in detail hereinafter, is mounted adjacent the other end of the enclosing vessel III,

in coaxial relation with the anode I2 and sup:

ported by leading-in conductors sealed in the end wall of the enclosing vessel I0.

Mounted between the electron gun and the anode I2 are a pair of centrally apertured electrodes I4 and I5, coaxial with the electron gun. These electrodes, although shown as discs, may

be of various forms and utilized for various pur 1 poses. Several formswhich'they: may take and various functions thereof are disclosed in Patent 2,281,717, granted May 5, 1942 to Arthur L. Samuel. Although but a single pair of electrodes has been shown in Fig. 1, it will be understood that several pairs or an odd number of electrodes may be provided depending upon the intended oper- I allel to the flange H, the electrodes I9 and 23 being insulated from the member I6 by the gaps 'therebetween. The electrode I9 is supported by a leading-in conductor secured to an elongated stem on the electrode I9 extending through the hub I8. The accelerating anode 2i] is supported by rigid conductors 22. aflixed to. the annular portion 2 I and sealed in the end wall of'the vessel II] as shown in Fig. 1.

A plurality of substantially hemispherical metallic members 23 are mounted in spaced relation on the flange H, the outermost member 23 being s'ecured,,as by welding, 'to a metallic disc 24 which is supported from leading-in conductors by rigid tie wires or connectors M. The innermost member 23 defines a chamber with the dished metallic member I5 in which an insulated heater filament 26 is positioned, the ends of the heater filament 26 being 'connectedto leading-in conductors sealed in the end wall of the III as shown. The metallic as shields to reduce the radiation of heat from the heater filament, so that efficient heating of the emissive surface of the member I 6 is realized.

In a particular construction especially advantageous-for use in devices wherein a magnetic field is employed to focus or otherwise affect the electron beam, the accelerating anode 20 and the heat shields 23 are made of magnetic material whereby the member I6 is 'eifectively shielded from the magnetic field.

The configurations and relation of the electrodes of the electron gun are of particular character so that a conical converging electron beam annular in section and focussed at a point on the axis of alignment of the several electrodes of the device is produced. In general, the configurations and relations are determined in accordance with the principles and methoddescribed in Patent 2,268,197, granted December 30, 1941 Moreover, it has been established that a high to John R. Pierce, so that substantially all of the electrons emanating from the emissive portion of the member I6 traverse rectilinear paths in flowing to the'focal point of the beam. The specific configurations and relation will be seen'most clearly from Fig. 3. As shown in thisfigure, the dishedsurface of the. member I6, which is gen-- erally toroidal and symmetrical about the axis of alignment of the electron gun and the anode V I2, includes an arcuate portion I6a, which is coated with a material having good thermionic emission characteristics, and inner and outer non-emissive flanged portions I62) and IE0 respectively, generally L-shaped in section. The angle 0 of the arcuate portion is substantially 126.5 degrees; The electrodes I9 and 20 have juxtaposed frusto-conical surfaces I9a and 20a respectively of equal angles defining an annular passageway converging away from the emissive surface I6a. The angle ,8 of the surfaces I9a and 20a is substantially 60 degrees. The surfaces I9a and 20a, it willbe noted project into the gap between the juxtaposedends of the beam forming elements I 6?) andIGc. a g

During operation of the device, the electrodes I9 and 20 are maintained at'positive potentials with respectto the member I6. They, may be biased atthe same potential or the potential "of theelectrode I9 may be greater or less, forexample of the order of 20 per cent than that of H the electrode to control to some extent the focal point of the'beam;

The portions I61) and I60, same potential as the emissive surface I6a, function as beam forming electrodes and in 'CQODQY', ationwith the accelerating anodes I9 and 20 concentrate substantially all of the electrons emanating from the emissive surface I6a into a hollow conical beam having a focal point F on the axis of the system and in which all: of the electronstraverse substantially rectilinear paths. The boundaries of the beam are indicated by the dotted lines in Fig. 3.;

There is thus obtained an efiicient electron gun inasmuch as the total beam current is commensurate withthe total emission from the surface I6a, and also a concentrated sharply focussed beam. Furthermore, it will be appreciated that substantially uniform fields are realized within;

the beam boundaries, whereby uniform; control of all the electrons in the beam and uniform transfer of energy therebetween and electrodes, such as the electrodes I4 and I5, is enabled.- In

addition, efiicient operation at frequencies; of. the

order of 3,000 to 30,000 megacycles is possible.

beam current can be obtained with relatively low potentials, for example 200 volts, on the accelerating anode 20 so that a perveance of as high as 30 10- isrealized. if

Although in the specific embodiment shown and described the beam formingelectrode members IBb and IE0 are'structurally integral with the emissive portion IBa they may, be physically separate therefrom, for-example spaced from the edges of the emissive portion .I6a of the orderof 10 mils, and electrically connected to the emissive portion. Such construction is especially advantageous if creepage of the emissive coating to the beam-forming portions isfound to be :suf ficient to render the portions IBb'and IGcemissive and thereby'reduce the sharpness of the focussing of the electron beam. Also, althoughin the specific construction shown and described, the

whiclrare a the eratrices composed of straight lines, they may have curved generatrices conforming substantially to those shown. Furthermore, it will be understood that various other modifications may be made in the specific construction shown and described without departing from the scope and spirit of this invention as defined in the append-- ed claims.

What is claimed is:

1. An electron gun comprising a cathode having an annular electron emissive surface, and means for concentrating electrons emanating from said surface into a hollow conical beam, said means comprising a pair of electrode members extending inwardly from the inner and outer boundaries of said emissive surface and forming an annular gap symmetrical with respect to and inclined toward the longitudinal axis of said cathode and a pair of spaced electrodes opposite said surface and defining an annular passageway coaxial therewith.

2. An electron gun comprising a cathode having a circular electron emissive surface arcuate in section, a pair of electrode members extending from the inner and outer boundaries of said emissive surface inclined toward one another and defining an annular gap, and a pair of electrodes opposite said surface and having juxtaposed surfaces defining an annular passageway coaxial with said gap and converging away therefrom.

3. An electron gun comprising a cathode having a dished annular electron emissive surface, a pair of electrode members extending inwardly from the boundaries of said emissive surface and defining an annular gap, and a pair of electrodes coaxial with said emissive surface, said electrodes having juxtaposed conical surfaces extending into said gap and defining an annular passageway ooaxial with said emissive surface and converging away therefrom.

4. An electron gun comprising an electrode having a dished annular surface the inner and outer edge portions of which are non-emissive and the intermediate portion of which is coated with an electron emissive material, and means including said edge portions for concentrating electrons emanating from said emissive surface into a hollow electron beam, said means including also a pair of spaced electrodes opposite said annular surface and forming an annular passageway coaxial therewith.

5. An electron gun comprising a cathode having a dished annular surface the intermediate portion of which is arcuate in section and electron emissive and the inner and outer portions of which are non-emissive and inclined toward each other, an annular electrode opposite said outer portion and having a frusto-conical inner surface, and a second electrode opposite said inner portion and having an outer frusto-conical surface opposite said first frusto-conical surface and defining therewith an annular passageway converging away from said annular surface.

6. An electron gun comprising a cathode having a dished annular electron emissive surface inclined toward and symmetrical with respect to the longitudinal axis of said cathode, and a pair of electrodes opposite said surface and coaxial therewith, one of said electrodes being annular and having a frusto-conical inner wall, and the other of said electrodes having a frusto-conical portion opposite said frusto-conical wall and defining therewith an annular passageway converging away from said emissive surface.

'7. An electron gun comprising a cathode having an annular surface conforming to an oblique section of a toroidal surface, a portion of said annular surface being electron emissive, an electrode opposite said. annular surface, coaxial therewith and adjacent the inner edge thereof, and a second electrode having an outer portion adjacent the outer edge of said annular surface and having also an annular inner portion encompassing said first electrode and defining therewith an annular passageway coaxial with said annular surface.

8. An electron gun comprising a cathode having an annular substantially toroidal surface, an electron emissive coating on the central portion of said surface, an electrode within the boundary of said surface, adjacent the inner edge thereof and having an outer surface tapering away therefrom, and a second electrode having an outer portion adjacent the outer edge of said first surface and an inner frusto-conical wall opposite and of substantially the same form as said tapering outer surface and defining therewith an annular passageway coaxial with said first surface and converging away therefrom.

9. An electron gun comprising a cathode having a dished annular surface the edge portions of which extend toward one another, an electron emissive coating on the central portion of said surface, and a pair of electrodes in juxtaposition to said surface to concentrate the electrons emanating therefrom into a hollow conical beam converging away from said surface, one of said electrodes including an outer portion overlying the outer edge of said surface and an inner frusto-conical wall extending within the boundaries of said surface and coaxial therewith, the larger end of said wall being toward said surface, and the other of said electrodes overlying the inner edge of said surface and having a frustoconical wall extending into the space bounded by said first wall and tapering in the same direction as said first wall.

ALVA EUGENE ANDERSON.

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