US2410822A - High frequency electron discharge apparatus - Google Patents

Description

NOV 12, w46 D. E. KENYON ZAQZZ HIGH FREQUENCY ELECTRON DISCHARGE APPARATUS Filed Jan. 3, 1942 2 Sheets-Sheet 1 DAVE D E. KENYON AQPLNEY Nav. 12, 1945. D. E. KENYON 2,419,822

HIGH FREQUENCYELECTRON DISCHARGE APPARATUS Filed Jan. 3, 1942 Y 2 Sheets-Sheet 2 .a 3 as ze' 2|' s' m34 l l z 'H" i M 25' f l x la i 5 "1 i I INVENTOR DAVID E. KENYON Y i vf ma AT'ORNEY.

Patented Nov. 12, 1946 HIGH FREQUENCY ELECTRON DISCHARGE APPARATUS David E. Kenyon, Smithtown, N. Y., assigner to Sperry Gyroscope Company, Inc., a corporation of New York Application January 3, 1942, Serial No. 425,491

13 Claims. l

This invention relates, generally, to vacuum tube structures and the invention has reference, more particularly, to a cathode structure designed for the production of high current density electron beams. In prior art cathodes for such purposes, great difficulty has been experienced in producing heater coils having very low magnetic fields, Said magnetic fields having an undesirable tendency to modulate the electron beam unless special shielding precautions are resorted to. It has also generally been necessary to use oxidecoated emitting surfaces in order to produce usa-ble emission currents, the temperature of the emitting surface being usually limited by the maximum temperature at which the cathode heater element can be operated and still give the device a reasonable life of operation. The present invention discloses a cathode structure relatively free of magnetic fields and whose emitting surface may be operated at elevated temperatures.

The principal object of the present invention is to provide a cathode having an emitting surface p portion that is heated by electron bombardment, the electrons for effecting such bombardment being supplied from a second surface.

Another object is to provide means for heating said second surface to a predetermined initial temperature, and switching mechanism for then stopping said heater means and causing the rst and second emitter surfaces to heat each other by means of a high voltage alternating current acting from electrons emitted on the adjacent surfaces of the two emitters.

An object is to provide a cathode emission surfacerelatively free of warping due to thermal effects.

Yet another object is to provide such a cathode structure for the production of cylindrical electron beams.

Still another object is the provision of such a cathode structure for the production of radially projected electron beams.

Yet another object is to provide such a cathode in which all elements in use in other than starting operations are heated by means of high voltage, low current electron beams, thus minimizing undesirable effects due to magnetic elds.

An object is to provide a cathode structure in which heating laments are operated only in starting emission, thus allowing said emitting surfaces to be operated at very elevated temperatures.

A further object of the invention is the provision f a cylindrical, radial or other beam producing cathode in which the heating filament (Cl. Z50-27.5)

used in starting emission does so in only a limited area of the emitter surface, the emission being spread from the original hot spot after the current through said heater element is turned oil.

Other objects and advantages will become apparent from the specication, taken in connection with the accompanying drawings wherein the invention is embodied in concrete form.

In the drawings:

Fig. 1 is a fragmentary perspective longitudinal cross-sectional view and wiring diagram of a form of the invention.

Fig. 2 is a longitudinal cross-sectional view, partly in elevation, showing an application of the cathode disclosed in Fig. 1.

Fig. 3 is a cross-sectional view of a modified form of a portion of Fig. 1.

Fig. 4 is a fragmentary longitudinal cross-sectional view of another modied form of the present invention.

Fig. 5 is a plan view on a reduced scale of the structure shown in Fig. 4, taken along the line 5 5 of Fig. 4.

Fig. 6 is a fragmentary longitudinal cross-sectional view of a further modification of the present invention.

' which may pass through the conventional type glass press (not shown) usually used in vacuum tube structures to provide current lead and support means, is positioned preferably centrally within a heat shield inner wall 4, leads 2 and 3 passing through holes 5 and 6 in end wall 1 of the heat shield.- 'Ihis heat shield has a folded back portion in the form of a cylindrical Wall 8 spaced outwardly from and concentric to wall 4, to provide more effective heat shielding by the well vknown double-wall eiect. Wall 8 extends below end wall 7 of said heat shield, and pressed into the inner diameter of wall 8 is a second end wall 9 for the heat shield, leads 2 and 3 passing through holes I 0 and II in wall II.

Positioned centrally above spiral heater element I is disk I2 which may be somewhat dished, in which case the convex side of disk I2 faces heater I. Somewhat spaced from disk I2 on the side thereof away from heater I is a second disk I3 which may also be dished similarly to disk I2. Heater I may be of tungsten and disks I2 and I3 of tantalum, columbium, nickel, or other metal f low electron work function; or heater I and disks vI2 and ,I3may be oxide-coated with any of the well' known barium, strontium, etc., emission materials. On the side of disk |3 away from disk I2 is a focussing element with a central aperture nearly as large in diameter as the diameter of disk I3 and consisting of an inclined annular portion I4, a flat annular surface I5 `substantially perpendicular to the axis of symmetry of the structure, l and aV cylindrical y-wall surface |6 extending fromsurface I5 vconcentric to heat shield wall 8 and of somewhat greater diameter.

tuated relay 43 has been set to open its associated circuits, and time delay relay 4I closes, thus placing a moderately high alternating current voltage between disks I2 and I3. By energizing the disks I2 and I3 through symmetrically disposed leads 26 and 24 respectively, the magnetic fields i produced by the flow of alternating current into Focussing shield I4, I5, I6 may be supported by( three leads I1, I8, -I'S spaced 120apartand exftending into the glass press of the vacuum kenvelope surrounding the cathode. Focussing shield I4, I5, I6, supports, in turn, disk I3 by means of angularly spaced wires 20, preferably-symmetrically disposed about the axis of the disk, e. g., at 120 intervals in the manner shown in Fig. 3 spot welded to the inner surfaces of shield portion I4 and disk I3. Heat shield 4, 8 may be` supported by three angularly spaced leads 2|, also extending into the aforementioned glass press.y f l Disk I2 may be supported by three angularly spaced leads 24 projecting radially'through holes 29 and 30 in Walls 4 and 8 of the heat shield. Leads 24 ,are supported by and are equally spaced about a current distributor such as a ring vprojected through aperture 33.

In use, there is preferably applied to spiral heater I aI relatively low alternating voltage by means of leads 2, 3 from the connected secondary 34 of transformer 35. A moderate alternating voltage isv also applied between lead 2 and diskr|2 from the secondary 36 of transformer 35 via lead 26, ring 25 and lead 24. Preferably a relatively high alternating voltage is applied between disks I2 and I3 from a transformer 31 by way of lead I1, focussing shield I6, I5, I4, and wires 20 on theone side and lead 26,' ring 25 and lead 24` on` the other. A moderately high direct current voltage is applied between emitter I3 and electrode 3| from power supply 39 via lead I1, focussing shield |6,'|5, I4, and wires 20 on the one si'de and wire 38 on the other. Transformer 35l is shownsupplied through a time actuated relay43, transformer 31 through a time delay relay 4I, and powervsupply39 through a time delay relay 42, all fromany; suitable alternating current supply to which connection is made by leads 40, 4t.y

W'hen it is desired to put the cathode into operation, the following procedure is used. Switch v 44 is closed, time delay relays IIIA` and 42 being open so that no current flows to transformer 31 or power supply 39. Time actuated relay 43 is of the well known commercial type which closes its circuit immediately when switch 44. is closed, being, set toppenl such circuit after any desired predetermined time interval. With .-switchf44 closed, currentfromtransform'er secondary 34 heats lament- I, and! the alternating 'current voltagevappearing between heater Iand disk'I2 ther disks neutralize one another and inhibit a1- ternating current modulation of the electron stream. Electrons being emitted from disk I2 .are accelerated toward disk I3 during alternate half cycles and impinge upon said disk I3 with high velocity, thus heating it to incandescence.

LAt the time disk I3 is raised to a sufilcient temperature, it begins to emit electrons from both surfaces.` Those emitted from its under surface are accelerated toward disk I 2 striking the latter. The alternating current voltage between disks I2 and I3 thus maintains both at a proper temperature.

Time delay relay 42 is set to close `its associated circuit at the time when the upper surface of disk I3 has reached a sufficient temperature to emit electrons. Relay 42 then applies a high direct accelerating voltage between emission surface I3 and electrode 3|.

Electrode 3| and its contained aperture 33 and grids 32, and focussing shield I4, I5, I6 are so designed that there is projected an electron beam of uniform round cross-section into the space on the side of electrode 3| away from emitter I3. Thus, it is seen that when the cathode is in its final state of operation the heating and accelerating currents involved are high voltage, low current ones, and that the only alternating heating voltage involved is well shielded inside of members 4, 8, I2, I3, I4, I5, I6. Further, the final temperatures of emission sources I2 and I3 are not determined by a resistance heater unit -such as the spiral heater I, and since this spiral heater lI is in use only in starting the cathode, its life time is greatly increased. In fact, disks I2 and I3 may even be operated at temperatures much higher than those at which oxide-coated emitters are usable, so that pure metal emitters of tantalum, columbium and similar metals may be used. It is evident to one skilled in the art that a variety of starting devices are usable to give the desired starting cycle, so that the system of .relays shown is intended to lbe purely illustrative.

A cathode producing such an electron beam has many uses, such as in beam power tubes, cathode ray tubes, in electron beam velocity modulating tubes such as those disclosed in patents, No. 2,242,275 ventitled Electrical translating system and method, issued May 20, 1941, to Russell H. Varian and No. 2,259,690 entitled High frequency radio apparatus," issued October 21, 1941, to John R. Woodyard, William W. Hansen, and Russell H. Varian and in other types of electron tubes.

In Fig. 2, a cathode of the type described in Fig. 1 is shown mounted in a reflex-type electron beam velocity modulating device of the type disclosedin Patent No. 2,250,511 of Russell H. Varian and William W. Hansen. As therein described, an electron beam is projected through aperture 33 offth'eaccelerating grid electrode 3|, passes on through field-free-space tufbe 45, and is velocity modulated by an ultra high frequency alternating electric eld appearing between grids 46 and 41,

andere said alternating ileid being generated by a high frequency electromagnetic field of natural frequency characteristic of resonator 43. The velocity modulated electron beam passes on through grid 41 and is reflected in the region near reflector plate 43, said plate `43 being at or near the potential o1' emitter surface I3. During the time required for the electrons to nrst pass through grid 43, becomerefiected by plate 43, and return through grid 46, the velocity modulation has resulted in density modulation, the electron groups thus produced returning energy to the electric neld between grids 46 and 41, thus maintaining the electromagnetic eid in resonator 43. Ultra high frequency energy may then be removed from resonator 48 by means of well known types of coupling devices (not shown). It is evident to one skilled in the art that beams of various degrees of convergence or ,divergence may be obtained from such a cathode structure, depending chiefiyupon the design of the focussing element I4, I5, I6, or upon the use of cooperating magnetic focussing means.

As shown in Fig. l, emitter elements I2 and I3 are slightly concave. The degree of concavity 6 emitter I 2'. The bombarding trons from spiral I is to heat an approximately circular area of emitter I2' just below and concentric to spiral I. Emission from s, corresponding circular area on the lower surface of emitter I2.' then startaand if a moderately high alternating current voltage is imposed between annular emitters I2' and I3', a corresponding circular area on emitter I3' becomes heated. As time passes, the two heated areas on I2' and I3' spread around these annular members, and the entire surfaces of emitters I2' and'l3' 4become hot enough to emit, the voltages betweenl leads 2 and 3 and between leads 3 and 23 having been removed at the proper time as in the above previously described sequence ofevents. At approximately 'the time when the entire lower surface of cathode emitter I3' has become hot enough to emit electrons, a high direct voltage is placed is such that the percentage distortion of the disk is very much less for a given temperature change than that obtaining in the case of a flat emitter surface. The structure shown in Fig. 3 may ibe used in place of the disks I2 and I3 in Fig. 1. In Fig. ,3, the convex disks :50, 53 have cylindrical walls orskirts 5I, 52 of equal diameter attached to their respective peripherles, extending inwardly so that said walls areseparated lby a small gap.

Such a construction improves freedom from warp- 1 about an axis external thereto, in any'desired manner. Two ofthe possible resultant configurations are disclosed in Figs. 4, 5 and 6.

Referring to Figs. 4 and 5, there is shown a cathode for the production of an annular beam,

-of a. type which may be used in an electron velocity modulating device such as the high power oscillator shown in Fig. 'I of the aforementioned Patent No; 2,259,690. Enclosed in an annular heat shield composed of annular walls 4', 1', 8' and 9" are two coopera-ting annular emitters I2',

. I3. The electron beam from emitter I3'.is improved in form by annular focussing member I 4',

I5', I5",and projected toward electrode 3 I which between cathode I3' and electrode 3l", thus projecting a cylindrical electron beam through annuiar aperture 33' and into the space below acl Concentric toand attached to emitter I3 is a may contain annular grid structure 32' in aperture 33', if desired. Focussing ring I4', I5', I6' and emitter I3' are supported by leads I1', I8', I3', heat shield 4', 8', 1', 9', by leads 2l', and emitter I2' by ring 25' and leads 25', 21', 28' all of said leads being supported in turn from the glass press Vof the vacuum tube envelope or by other suitable well known methods.

Starting filament I and cooperating leads 2 and 3 may be exactly similar to the starting niament shown in Fig. 1, as is seen in Figs. 4 and 5, or may actually be a ngure of revo tion as a ribbona wire, or any other suitable form. In operation, the simple spiral cathode I of Fig. 4 is similar to that of Fig. 1. A proper current is vallowed to ow through lead 2, spiral I, and out lead 3, heating the illament, and a proper alterfocussing element consisting of annular inclined portions I t", cylindrical wall I5", and apertured wall I6". Heater 54 is positioned and has its power-supplied by leads 55 and 58, lead 56 may also support heat shield 53; Heat shield 51' may be supported by lead 2i".

6 is exactly similar to .that of Fig. 1, a radially projected electron beam resulting. It is obvious -to one skilled in the art that beams of ringshaped cross-section, diverging or converging, can b e made by placing the axis about which the cross-section of Fig.'1 is rotated at various angles between the two used to produce the structures of Figs.4 and 6, such cathodes being useful in producing beams ofthe type shown in Figs. 13 and 15 of the aforementioned prior Patent No.

As many changes could be made in the above constructionl and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. Electron discharge apparatus comprising a substantially planar iliamentary element adapted to serve as a source of electrons when heated, ay

nating voltage is imposed between niament I and 76 emitters for providing an alternating voltage beaction or the elec# Emitter I3" and` focussing shield I4", I5",` I6" may be supported tween said emitters whereby said emitters heat substantially parallel electron emitter elements,

means in said apparatus supporting said elements in adjacent relation, said supporting means including. leads symmetrically, disposed with respect to and extending from said elements,

means connected to said leads for applying an alternating voltage between said emitter elements so that they heat each other by mutual electron bombardment, said symmetrical disposition of leads tending to neutralize the magnetic effects produced by the flow of current through said leads to said elements, an electron permeable conductive member mounted in alignment with said elements and adjacent the non-bombarded surface of one of said emitter elements, means connected to said one emitter element and said member for applying a substantially unidirectional voltage between said one emitter element and said member for accelerating electrons emitted by said non-bombarded surface, and an electron beam focusing means mounted intermediate said one emitter element and said member.

4. The apparatus dened in claims, including a ilamentary heater member adjacent the other of said emitter elements for initially heating said other emitter element, and time controlled means connected to said heater rendering said heater inoperable when the non-bombarded surface of said one emitter element becomes electron emis-` sive.

5. Electron discharge apparatus comprising two spaced emitter elements, electrical means connected to said elements in a predetermined sym- -metrical arrangement for applying a relatively high alternating voltage between said elements so that they heat each other by mutual electron bombardment of adjacent surfaces, and beamforming electrode means mounted in alignment Withsaid elements for forming the electrons leaving the non-bombarded surface of one of said emitter elements into an electron beam of substantially uniform cross-section, said emitter element electrical arrangement shielding said beam v against undesired magnetic disturbances from heating currents in said emitter elements.

6. Electron discharge apparatus comprising two spaced electron emitters, means in said apparatus adjacent one of said emitters for heating said one of said emitters by electron bombardment, electrical means connected to said emitters for providing an alternating voltage between said emitters such that they heat each other by mutual electron bombardment, time controlled means connected to said heating means and said emitters for rendering said heating means inoperable after a predetermined period ofoperation and for applying said alternating voltage betweensaidy emitters, an electron beam-control electrode mounted in spaced alignment with the non-bombarded electron emission surface of the other of said emitters. and time controlled means for applying a substantially unidirectional electron accelerating voltage between said other emitter and said electrode.

7. Electron discharge apparatus comprising a heater element, a substantially cup-shaped heat shield partially enclosing said heater element, and substantially parallel spaced emitter elements supported substantially across the-open end of said shield, said emitter elements being non-conductively connected with said shield.

8. 'I'he apparatus dened in claim 7, including means conductively interconnecting said heater element and said shield.

9. The apparatus deiined in claim '1, comprising fixed support means electrically separated from said shield, and means on said support means mounting said emitter elements in said spaced relation.

10. Electron discharge apparatus comprising two spaced electron emitter elements, means connecting said elements for producing an oscillating potential between said elements such that they heat each other by mutual elec-tron bombardment, an electron focusing electrode disposed adjacent a non-bombarded surface of one of said emitter elements, and means supporting said one emitter element from said focusing electrode.

11. Electron discharge apparatus comprising a pair of electron emitter members adapted to be energized by a stream of electrons and mounted in closely spaced adjacent relation to be capable of mutual electron bombardment of adjacent surfaces, and skirt-like peripheral walls on each of said members extending toward each other providing a shield about the electron discharge between said surfaces.

12. Electron discharge apparatus comprising a cathode assembly comprising spaced emitters adapted to heat each other by mutual electron Ibombardment,'means connected to said emitters for energizing said emitters, and means aligned with said assembly and operable only after said energization has proceeded to a predetermined condition for accelerating electrons from a nonbombarded surface of one of said emitters.

13. Electron discharge apparatus comprising a heater element, a substantially cup-shaped heat shield partially enclosing said heater element, an emitter element supported substantially across the open end of said shield and non-conductively connected therewith, and electrical means connecting said heater element and said emitter element for supplying a difference of potential between said elements.

DAVID E. KENYON.

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