US2409499A - Beam deflection electron discharge device - Google Patents

Description

Oct. 15,1946. G, R; KILGORE 2,409,499

BEAM DEELECTION ELECTRON DISCHARGE DEVICE Filed March 6, 1942 2 Sheets-Sheet l Ourpur -57 I INPUT 1 PUT INVENTOR.

George Eff/[gore Oct. 15,1946. G. R. MLGQRE 9,49

BEAM DEFLECTION ELECTRON DISC HARGE DEVICE 1 Filed, March 6, 1942 2 Sheets-Sheet 2 INVENTOR Georige R. K 1' 1 01's.

ATTURNEY Patented Oct. 15, 1946 BEAM DEFLECTION ELECTRON DISCHARGE VICE George Ross Kilgore, Verona, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application March 6, 1942, Serial No. 433,579

9 Claims.

My invention relates to electron discharge devices, more particularly such devices utilizing a beam of electrons which is deflected during operation.

In tubes of the type under consideration a beam of electrons is directed between a pair of deflecting electrodes toward an apertured electrode behind which is usually placed a collector. Alternating voltages are applied to the deflecting electrodes to cause the electron beam to be deflected across the aperture to thus control the amount of current flowing toward the collector or output electrode. In such types of tubes the deflection sensitivity drops off rapidly as the frequency at which the tube is operated is increased. Efforts have been made to increase the sensitivity or the transcond-uctance of the tube by increasing the separation between the end of the deflecting plates and the apertured electrode. Such efforts, however, have not resulted in the expected improvement of the transconductance of the tube since the current density at the aperture in this case falls ofi in proportion to the increase in any deflection sensitivity which may have resulted by spacing the deflection plates farther from the apertured electrode.

The principal object of my invention is to increase the transconductance of electron discharge devices employing beam deflection and to provide for improved operation of devices of this kind.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawings in which Figure 1 is a schematic diagram showing the conventional deflecting electrode and apertured electrode arrangements utilized in an electron beam deflection device, Figure 2 is a schematic diagram showing the electrode arrangement in a device made according to my invention, Figure 3 is a longitudinal schematic section of an electron discharge device embodying my invention and its associated circuit, and Figures 4 and 5 show modifications of an electron discharge device and its associated circuits made according to my invention.

Figure 1 shows schematically the conventional deflecting electrode system comprising deflecting electrodes II and I2, apertured electrode l4 and collector [3, the means for applying rj voltages being indicated at [5.

From an analysis of beam deflection devices it 2 can be shown that the current density at an aperture depends upon the angle of convergence of the beam, the cathode current density, the velocity of emission, and the velocity at the aperture,

[1 sin (1 Where I1=current density at aperture in amps/sq. cm. Io=cathode current density amps/sq. cm. V=potential of deflecting electrodes in volts. Vo=initial kinetic energy of electrons in volts. :half angle of converging beam.

Now in a simple deflection device such as shown in Figure 1, is approximately equal to so that the current density at the aperture is Where Z=length of deflecting plates in cm. d=separation of deflecting plates D1 and D2 in cm. and the deflection sensitivity for the parallel deflecting plates is given by therefore,

g gsl w 4 b mhos.

g %0.75% b.1' 10 mhos. (5) where b=length of beam measured parallel to cathode. =transit time through deflecting plates These expressions show that pm in the case of Figure 1 is independent of the separation (12) seconds and is directly proportional to transit time (1-).

In accordance with my invention I propose to increase the transconductance by shaping the deflecting electrode in conformity with the converging beam so as to increase the deflection sensitivity without decreasing current density. This has the further advantage of bringing the electrodes closer to the electron beam and thus decreasing space charge eifects.

In Figures 2 and 3 I show the electrode arrangement of the electron discharge device employing beam deflection and its incorporation in tubes and its associated circuit. Briefly the fundamental electrode structure shown in Figure 2 comprises a concave surface cathode 20 for providing a converging beam of electrons 25 directed through the apertured electrode 23 to collector 24. The beam deflecting plates 2i and 22 extend between the concave electrode 20' and apertured electrode 23, converging toward the aperture in the apertured electrode 23. A slight inward curvature of these deflecting plates might increase the ultimate gain but for practical purposes the flat plates will serve just as well.

As shown in Figure 3 the envelope 30 Contains at one end a concave surface cathode 3| heated by the heater 32. The converging beam from this cathode is directed through the aperture 34' in the apertured electrode 34 to the collector 33, the

beam passing between the converging deflecting plates 35 and 36. If desired, electrode 33 .could be coated with secondary emitting material and the secondary emission captured by electrode 34, electrode 34 in this case serving as the output electrode. The input signal is introduced between the deflecting plates 35 and 33 by means of the input 37 and the output is taken from the output transformer 48. Voltage sources 39 and 38 provide the necessary potentials for the various electrodes, the collector electrode 33 in this case being maintained at a higher potential than the apertured electrode 34. From an analysis of the effects of space charge on focusing I have found the best radius of curvature of the cathode is approximately one-half the deflecting plate length, a

In Figure 4 I show the longitudinal schematic section of a modification of an electron discharge device made according to my invention which, due to its construction, maintains the beam better focused than the arrangement shown in Figure 3 because of the lens action effect taking place between vthe portions of the deflecting electrode structure.

The envelope 4!! contains the cathode 4!, heater 42, apertured electrode 44, collector 43 and the modified deflecting plate construction. In this case the deflecting electrodes 45 and 46 have .positioned on the beam side the sections 4l49 and 48 and 50 insulatingly separated from the plates 45 and 46 by means of insulating elements and 52 for example of mica. It is thus possible to apply to the plates 41 and 48 a lower positive potential than the plates 39 and 56 thus having an increasing accelerating field in moving from the the structure shown the electrode 43 may be coated with secondary emitting material so that electrode 44 serves as the output electrode. Voltage source 54 for the cathode heater is provided as well as the voltage source 53 for the various other electrodes. In order to prevent R. F. currents from flowing in the leads for providing D. C.

potentials, chokes 55, 56, 51 and 58 are provided. These serve well for all but the very high frequencies.

In the arrangement shown in- Figure 5, which is intended for operation at the higher frequencies, the input voltage is supplied to the deflecting electrodes by means of a Lecher wire system comprising tubular elements 60 and 6! shorted by the movable shorting bar 62." 'The leads for carrying the D. C. potential to the defleeting electrodes pass through the tubular members and are capacity coupled thereto by means of condenser 64 and 65 so that the R. F. potential may be applied to the deflecting electrodes when the input signal is introduced into the Lecher wire system by means of coupling loop 63. The other numerals designate the same elements as those in Figure 4.

In Figures 4 and 5, due to the large capacity coupling between the outer plate members 45 and 46 and their associated sections 41, 49 and 48, 53, deflecting plate 45 and plates 41 and 49 in the one case are at one R. F. potential and plate 46 and the sections 48 and 50 in the other case are at the same different R. F. potential. Elements 45' and 46' are D. C. connectors.

While I have indicated the preferred embodiments of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my invention is by no .means limited to the exact forms illustrated or the use indicated,- but that many variations may be made in the particular structure used and the purpose for which it is employed without departing'from the scope of my invention as set forth in the appended claims.

What I claim as new is: p 7

1. An electron discharge device having means for supplying a converging beam of electrons, an apertured electrode through which'said beam of electrons .is directed, and a collector all in the order named, and a single pair of oppositely disposed deflecting electrodes positioned closely adjacent saidbeam and between said beam supplying means and-said aperturcd; electrode and having surfaces continuously approaching'each other inthe direction of movement of the beam, said beam supplying means and said output electrode being next adjacent said deflecting electrodes. V V a 2. An electron discharge device having a cathode having a concave emitting surface for supplying a converging beam of electrons; an aper tured electrode through which said beam of electrons is-directed, and a collector allin the order named, and asingle pair of oppositely disposed deflecting electrodes positioned closely adjacent said beam-andbetween said cathode and said apertured electrode and having surfaces continuously approaching each other in the direction of the movement of the electron beam; said cathode and-said apertured. electrode being next adjacent said deflecting electrodes.

3. An electron discharge device having means for supplying a converging beamof electrons,.an apertured electrode through which said beam of electrons is directed, and a collector all in the order named, and a single pair of oppositely disposed deflecting electrodes positioned closely adjacent said beam and between said beam supplying means and said apertured electrode and having flat converging surfaces approaching each other in the direction of the movement of the electron beam, said beam supplying means and said apertured electrode being next adjacent said deflecting electrodes.

4. An electron discharge device having means for supplying a converging beam of electrons, an apertured electrode through which said beam of electrons is directed, and a collector all in the order named, and a single pair of oppositely disposed deflecting electrodes positioned closely adjacent said beam and between said beam supplying means and said apertured electrode and having surfaces continuously approaching each other in the direction of the electron movement, said collector electrode having a secondary electron emitting surface for releasing secondary electrons which are received by said apertured electrode during operation of said electron discharge device, said beam supplying means and said apertured electrode being next adjacent said deflecting electrodes.

5. An electron discharge device having means for providing a converging beam of electrons, an apertured electrode toward which said electrons are directed, and a collector all in the order named, a pair of deflecting electrodes positioned between the cathode and the apertured electrode, and including conducting elements converging toward the apertured electrode, a plurality of conducting sections positioned closely adjacent the converging inducting elements and between said elements and the beam, and insulatingly separated from said elements whereby different direct potentials may be applied to said elements and said sections.

6. An electron discharge device having means for providing a converging beam of electrons, an apertured electrode toward which said electrons are directed, and a collector all in the order named, a pair of deflecting electrodes positioned between the cathode and the apertured electrode, and including conducting elements converging toward the apertured electrode, a plurality of conducting sections insulatingly supported by said converging conducting elements and adapted to have increasingly positive direct potentials applied to successive conducting sections for providing a lens action during operation of said electron discharge device for maintaining said beam of electrons focused.

7. An electron discharge device having means for providing a converging beam of electrons, an apertured electrode toward which said electrons are directed, and a collector all in the order named, a pair of deflecting electrodes positioned between the cathode and the apertured electrode, and including conducting elements converging toward the apertured electrode, a plurality of conducting sections insulatingly supported by said convergin conducting elements and adapted to have increasingly positive direct potentials applied to successive conducting sections for providing a lens action during operation of said electron discharge device for maintaining said beams of electrons focused, and an electrical connection between each conducting section adjacent the apertured electrode and its supporting converging conducting element.

8. An electron discharge device having a cathode provided with a concave emitting surface for supplying a converging beam of electrons, an apertured electrode through which said beam of electrons is directed, and a collector all in the order named, and deflecting electrodes positioned adjacent said beam and between said cathode and said apertured electrode and having surfaces approaching each other in the direction of the movement of the beam, the radius of curvature of the concave surface of said cathode being equal to one-half the length of the deflecting electrode.

9. An electron discharge device having a cathode provided with a concave emitting surface for supplying a converging beam of electrons, an apertured electrode toward which said electrons are directed, and a collector all in the order named, a pair of deflecting electrodes positioned between the cathode and the apertured electrode, and including conducting elements converging toward the apertured electrode, a plurality of conducting sections positioned closely adjacent the converging conductin elements and between said elements and the beam, and insulatingly separated from said elements whereby different direct potentials may be applied to said elements and said sections, the radius of curvature of the concave surface of said cathode being equal to one-half the length of the deflecting electrode.

GEORGE ROSS KILGORE.

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