US2401777A - Electron discharge apparatus - Google Patents

Description

Eme M, A w. G. sx-liEPHER/D I2,4%,777

ELECTRON DISCHARGE APPARATUS Filed Sept. 5, 1941 -P MAGNET/C FIELD 1 /NVENTOR By WGSHEPHE'RD @am @M A 7` TORNE V Patented June 11, 1946 UNITED STATES PATENT` OFFICE (Cl. Z50-,174)

8 Claims.

This invention relates to electron discharge apparatus and more particularly to electron discharge devices especially suitable for use ashigh frequency or feedback amplifiers and including a secondary electron emissive target or electrode in cooperative relation with the output electrode.

The luse of a secondary electron emissive electrode in cooperative relation with the output electrode of an electron discharge device enables the realization of relatively high transconductances. The attainment of stable operating characteristics and long life for such a device entails shielding of the secondary electron emissive surface to prevent contamination thereof by material evaporated from the primary cathode. This, in turn, has entailed heretofore the direction of the primary electrons; along relatively long curved paths in flowing to the secondary electron emissive surface. It has been found that, as a result, in such devices the electron transit time is higher than in more conventional devices not utilizing secondary emission and: as a consequence the amount of feedback obtainable Was less than with more conventional de- Vices.

One object of this invention is. to increase the feedbackk obtainable. inelectron discharge, devices includinga secondary electronY emissive target or electrode. More specically, one object of this invention is to obtainboth effective shielding of the, secondary electron emissivev target or electrode and a low electron transit time in such devices,

In` one illustrative embodiment of this invention, an electron discharge device comprises a primary cathode and control and accelerating electrodes for producing an electron stream, a target electrode having a secondary electron emissive surface against which the primary electron stream is directed, and a collector or output electrode in cooperative relation with the secondary electron emissive surface.

In accordance with one feature of this invention, the secondary electron. emissive electrode is an apertured member the emissive surface of which extends generally in the direction of projection of the primary electron stream, the electrode being mounted adjacent the path of the projected primary electron Stream andv having its emissive surface remote therefrom, and means are provided for producing cooperating electric and magnetic fields adjacent this electrode such that the Primary electrons are directed along paths passing through the. aperture, in the ele@- trode and terminating atv the secondary electron emissive surface.

The invention and the abovernoted andother features thereof will be understood more clearly and fully from the following detailed descriptionY with reference to the accompanying drawing in which: v

Fig. 1 is a perspective View of electron discharge apparatus illustrative of one embodimentv of this invention, a portion of the field coil and of the enclosing vessel of the discharge device. being broken away to show the electrodes ofthe device more clearly;

Fig. 2 is a diagrammatic side view of the apfparatus illustrated in Fig. 1 showing the relation of the electrodes andv indicating the electron paths; and

Fig. 3 is a perspective Viewof electron discharge apparatus, portions of which are broken away for the sake of clarity, illustrativey ofl another embodiment of this invention wherein` the electrodes of the device aremounted in coaxial-relation.

Referring now to the drawing, the. elect/ron discharge apparatus` illustrated in. Figs. 1V and. 2 comprises an evacuated enclosing vessel l, for example of glass, adjacent one end;k of which there lis mounted a cathode Il, forv example of the equipotential indirectly heated type, having a rectangular electron emissive surface i2, extending normal to the 'longitudinal axis of the enclosing vessel I6. 'I'he cathode may be supported by.l a leading-in` conductor i3. sealed to one end Wall of thev enclosing vessel, in which wall the leading-in conductors YHl for. the cathode heater element, not shown, also arev sealed.

Mounted Opposite; the cathodeemissive surface I2 and parallel thereto are a controlelectrode I5 and an accelerating electrode l5. The control and accelerating electrodes may be grids or may be plates having aligned, parallel slots or apertures Il and I3, respectively, the. control elec-y trode being supported by a leadingfin` conductor I9. Extending normal toV the accelerating electrode I5 from adjacent the aperture i8 is a metallic plate member 25, which may be secured to the electrode E6 as shown and is supported by a leading-in conductor 2l.

A pair of plate electrodes 22 and 2 3. are mounted parallel to the plate` member 2Q, as by leading-in conductors` g4, and respectively, the electrode 22 having an elongated aperture or slot 26 therein and having the surf-ace 2J thereof remote from the plate member 2.0, coated with a material having, goed secondary electron. emissive properties. Mounted between the electrodes 22 and 23 is a collector or output electrode 28 which may be supported by a leading-in conductor 29.

The enclosing vessel is encompassed by a coil 30 capable of producing a strong magnetic field having its lines of force parallel to the longitudinal axis ofthe enclosing vessel Ill.

During operation of the device, the accelerating electrode I6 is maintained at a positive potential with respect to the cathode H so that an i electron stream, which is concentrated by the magnetic eldproduced by the coil 30, is projected through the aperture I8 intc the regio-n between the plate members 22 and 22. The intensity of the stream may be controlled or modulated by suitable potentials applied between the control electrode l and cathode Il. The electrode 22 is maintained at a positive potential with respectto the plate member 2l). The electrons issuing from the aperture I8, then, are projected into a region wherein crossed magnetic and electric fields, that is, the magnetic field parallel to the direction of projection of the electron stream, i. e., parallel to the longitudinal axis of the vessel Ill, and an electric field normal to this direction, i. e., normal to the planes of the electrode 22 and plate member 20, exists. Consequently, the electrons are directed along paths, the projection of which on a plane normal to the direction of projection of the primary electron stream is a cycloid or trochoid, passing through the aperture 2t and enter into the space between the electrodes 22 and 23. The electrode 23 may be operated at the same potential as the electrode 22 so that the electrons flowing through the aperture 26 are projected into an electrostatically eld free space. Because of the magnetic field which is present between the electrodes V22 and 23 and the velocity normal to this field which the electrons have acquired, however, these electrons will be directed along curved paths and caused to impinge upon the surface 21 cf the electrode 22 whereby secondary electrons greater in number than the electrons impinging upon the surface 21 are released. These secondary electrons flow to the collector electrode .28, which is at a higher positive potential than the electrode 22, and constitute the output current. The electron paths are indicated by the broken lines inFig. 2^.

In another mode of operation, the electrode 23 is maintained at a higher positive potential than the electrode 22, most favorably at a potentialV corresponding to a linear variation of potential from the'plate member 20 to the electrode 23, so that the secondary electrons emanating from the surface 21 are drawn to and collected by the electrode 23. In this case, the electrode 23 serves as the output electrode and the collector electrode 28 may be omitted.

It will be noted that, inasmuch as the magnetic field is in the direction of projection of the primary electron stream into the region between the plate member 20 and the target electrode 22, it will have no material effect upon either the electron transit time between the cathode i i and this region, or the transconductance of the device. Furthermore, it will be apparent that the electron paths between the aperture I8 and the secondary electron emissive surface 21 may be made short so that the electron transit time between this aperture and surface is small. Hence, the total electron transit time in the device will be small. Finally, it Will be noted that the secondary electron emissive surface 21V is 'highly shielded from the emissive Vsurface l2 of the cathode Il so that contamination of the surface 21 by material evaporated from the surface I2 is prevented.

`In the case described above where the electrodes 22 and 23 are operated at the same potential and the collector electrode 28 is employed as the output electrode, the primary electrons passing'through the aperture 23 and flowing to the surface 21 are traveling in electrostatically field free space so that their transit time in flowthe coaxial electrodes 22B, 220, and 230, the latter of which has a frusto-conical portion 23! and the electrode 220 having its outer surface 212 treated or coated so that copious secondary electron emission is obtainable therefrom.

The electrode 233 is maintained at a positive potential with respect to the central electrode Z and the collector electrode 280 is maintained at a positive potential with respect to the secondary electron emissive electrode 22D. The cylindrical electron beam enters into a region between the electrodes 230 and 230 and thus comes under the influence of the radial electric field between these electrodes, which field is substantially normal tc the magnetic field due to the coil 330. Consequently, the primary electrons constituting the beam are directed along curved paths and impinge upon the emissive surface 21E! to cause the release of secondary electrons therefrom. The secondaryV electrons thus produced ilow to the collector electrode 283 and constitute the output current of the device.

In addition to having the advantages of high transconductance, low transit times and shielding of the secondary emissive surface of the device disclosed in Fig. 1, the device illustrated in Fig. 3 is characterized by very small stray capacitances and feasibility of association with coaxial transmission lines. Although in Fig.3 the various electrode leading-in conductors are shown as Wires, they may be coaxial conductors whereby association of the device with external coaxial lines is facilitated and matching of the characteristic impedance of the internal and external elements of the input and output circuits is enabled.

Although the invention has been iuustrated in l single stage devices, it may be embodied also in devices adapted for push-pull operation, in which case the cathode would have both of its surfaces electron emissiveand similar electrode systems, symmetrical with respect to the cathode would be associated with the cathode. Also, although coils have been shown for producing the requisite magnetic field, permanent magnets may be utilized for this purpose. Other modifications may be made, of course, in the specific embodiments shown and described without departing from the scope and spirit of this invention as defined in the appended claims,

What is claimed is: A 1. Electron discharge apparatus comprisingan electrode having an aperture therein and having also an electron emissive surface, a collector electrode in electron receiving relation with said emissive surface, means for projecting an an electron stream adjacent said first electrode substantially parallel to said surface and on the side of said first electrode remote from said emissive surface, and means adjacent said first electrode for directing said electron stream along a curved trajectory passing through said aperture and for directing the stream passing through said aperture against said electron emissive surface.

2. Electron discharge apparatus in accordance with claim 1 wherein said directing means comprises electrode means for producing an electric field substantially normal to said surface and means for producing a magnetic field substantially parallel to said surface.

3. Electron discharge apparatus comprising a pair of plane parallel electrodes, one of said electrodes having an aperture therein and having a secondary electron emissive coating on the surface thereof remote from the other of said electrodes, a collector electrode in electron receiving relation with the coated surface of said one electrode, leads connected to said pair of electrodes for establishing an electric field between said pair of electrodes and substantially normal to the surfaces thereof, means mounted to one side of said pair of electrodes for projecting an electron stream between said pair of electrodes and substantially parallel to the surfaces thereof, and means adjacent said pair of electrodes for producing a magnetic field therebetween and having its lines of force substantially normal to said electric field.

4. An electron discharge device comprising an electrode having an aperture therein, means for projecting a stream of primary electrons through said aperture, a plate electrode extending from adjacent said first electrode, at an angle thereto and to one side of said aperture, said plate electrode having a coating of secondary electron emissive material on the face thereof remote from said aperture and having also an aperture therein, a collector electrode in electron receiving relation with said coating, and means including electrode members adjacent said first electrode for directing electrons emanating from said first aperture, through said second aperture and against said coating.

5. Electron discharge apparatus comprising a cylindrical electrode having its outer surface secondary electron emissive, a collector electrode in cooperative relation with said surface, means for projecting a stream of electrons toward said cylindrical electrode and parallel to the longitudinal axis thereof, and means for directing said electron stream along curved paths adjacent said cylindrical electrode and against said surface, said means including cylindrical field electrodes Within and outside of said cylindrical electrode and coaxial therewith and means for producing a magnetic iield adjacent said cylindrical electrode and having its lines of force substantially parallel to the longitudinal axis of said cylindrical electrode.

6. Electron discharge apparatus comprising an electrode having an aperture therein, secondary electron emissive means on one side of said electrode, a collector electrode in electron receiving relation with said emissive means, means for projecting an electron stream into a region on the opposite side of said electrode and in a direction at an angle to an axis passing through said aperture, and means adjacent said first electrode for directing electrons from said region along curved paths passing through said aperture and terminating at said emissive means.

7. Electron discharge apparatus in accordance with claim 6 wherein said directing means includes means for producing a magnetic field adjacent said iirst electrode and said emissive means and having its lines of force parallel to the direction of projection of said stream and includes also electrode means adapted when energized to produce in said region an electric field substantially normal to said magnetic field.

8. Electron discharge apparatus comprising an electrode having a secondary electron emissive surface, means for projecting an electron stream toward said electrode and along a linear path substantially parallel to said emissive surface, means for producing a magnetic eld along and parallel t0 said path and adjacent said electrode, electrode means adjacent said first electrode and adapted when energized to produce adjacent said electrode t. an electric field substantially normal to said magnetic field whereby, adjacent said electrode, said stream is directed along a curved path terminating at said emissive surface, and a collector electrode in electron receiving relation with said emissive surface.

WILLIAM G. SHEPHERD.

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