US2445404A

US2445404A - Electron discharge device and associated circuit

Info

Publication number: US2445404A
Application number: US526181A
Authority: US
Inventors: Mayo Bernard Joseph
Original assignee: EMI Ltd
Current assignee: EMI Ltd; Electrical and Musical Industries Ltd
Priority date: 1941-08-08
Filing date: 1944-03-13
Publication date: 1948-07-20
Anticipated expiration: 1965-07-20
Also published as: NL79204C; CH252440A; DE934065C; FR919073A; GB576126A

Description

July 20, 1948. B. J. MAYO 4 2,445,404

ELECTRON DISCHARGE DEVICE AND ASSOCIATED GIRCUIT Filed March 13, 1944 INVETOR Behm-J "are Amer Patented July 20, 1948 ELECTRON DISCHARGE DEVICE AND ASSOCIATED CIRCUIT Bernard Joseph Mayo, Hayes, England, assignor to Electric & Musical Industries Limited, Hayes, England, a company of Great Britain Application March 13, 1944, Serial No.

In Great Britain August 8, 1941 Section 1, Public Law 690, August s, 1946 Patent expires August 8, 1961 This invention relates to electron discharge devices employing hollow resonators constructed for use as generators of oscillations. The invention is concerned with such devices of the kind in which reflecting means are provided capable, if suitably charged, of setting up a reflecting field to cause the electrons in the electron beam of the device after having passed through the gap in the resonator where they become velocity modulated to be reflected back through the gap. The resonator in such devices may be of toroidal form and is tuned in known manner to the frequency of the oscillations that it is desired to generate.

It is necessary for efficient operation that the electric field which is set up in operation between the resonator and the reflecting electrode should firstly be such as to cause a reasonable degree of bunching. Secondly, the field should be such as to ensure that as much as possible of the electron beam is reflected back through the gap and thirdly the field should be such that the drift time of the axial and marginal electrons is substantially the same so that substantially all such electrons after reflection reach the gap in phase.

It has been proposed in known forms of devices of the kind referred to, to employ a reflecting electrode in the form of a flat disc or in the form of a, portion of a sphere with the concavity facing the resonator. In the former case the electric field which is set up between the resonator and the reflecting electrode is composed of equipotential surfaces which, adjacent the resonator, follow the contour of the latter and facing the resonator are convex at the aperture in the resonator, but which, as they recede from the resonator, rapidly become flatter and thereafter remain flat throughout the remaining distance. Where the reflecting electrode comprises a portion of a sphere as aforesaid, here again the equipotential surfaces adjacent the resonator follow the contour of the resonator and are convex at the aperture but subsequently the equipotential surfaces become flat and then become concave facing the resonator with increasing curvature as they recede from the resonator, the equipotential surface having the maximum curvature being the one closest to the reflecting electrode, the curvature of such surface being the same as the curvature of the reflecting electrode. Since the reflecting electrode is maintained at a negative potential with respect to the potential of the cathode, the 'zero equipotential surface, i. e., the surface having the 4 Claims. (01. 250-275) potential of the cathode, is situated between the resonator and the reflecting electrode. Where the reflecting electrode is in the form of a flat disc the equipotential surfaces between the zero equipotential surface and the reflecting electrode are all flat, whilst where the reflecting electrode is of partially spherical form as aforesaid, the equipotential surfaces between the zero equipotential surface and the reflecting electrode are of increasing curvature.

A flat reflecting electrode is satisfactory in that it affords efficient bunching, but where, as is usually the case, the electron beam is divergent as it passes towards the reflecting electrode, very few of the marginal electrons will be reflected back through the aperture inthe resonator. Hence the device will lack efliciency.

A system of concave equipotential surfaces as set up by a concave reflecting electrode is eflicient in its ability to reflect both the axial and marginal electrons back through the resonator, but is ineflicient in that only a small degree of bunching of the electrons occurs.

It will be appreciated therefore that devices embodying either a flat or concave reflecting electrode do not satisfy the aforementioned requirements for efl'icient operation.

I have found that these requirements can be more completely satisfied compared with known constructions of devices of the kind referred to if the equipotential surfaces which are set up in operation transversely to the path of the electron beam are of concave form facing the resonator, the curvature of said surfaces as they recede from the resonator increasing as they approach the zero equipotential surface and in the region of the central part of the beam decreasing as they recede from the zero equipotential surface.

According therefore to one feature of the invention, an electron discharge device of the kind referred to is provided in which said reflecting means is so constructed as to be capable, if suitably charged, of setting up equipotential surfaces to cause reflection of the beam, which surfaces transversely to the path of the beam, are of concave form facing the resonator, the curvature of said surfaces as they recede from the resonator increasing as they approach the zero equipotential surface and in the region of the central part of the beam decreasing as they recede from the zero equipotential surface so as to improve the eiflciency of the device. As stated above, the equipotential surfaces immediately adjacent the resonator will be convex owing to those surfaces which lie between the point where the surfaces change to concave form and the reflecting means. beam is, for the purpose of the specificat n,.,1d e fined as that part of the beam lying along the centre of the space occupiedl fby. theb mland.

which has a cross-section approximatelyfequaij to half the area of the aperture from whichthe beam emerges from the resonator.

According to another feature of theinvention.

there is provided a circuit arrangement ,e

bodying an electron discharge devicelof the referred to in which said reflecting means is so constructed and is maintained at suchapotem tial with respect to the potential of the resonator nd atn ss of eaidw e i ei t et u he derer tentia sur-ie esr fe dzt abov so .t ammate e f e en r ,th euce P ef bl aid refle ti -m ans qmr s e e e in ectr de und b a Short Qq dnc n ur ageh h;rem ra es h eam.

h en ion imar a appl dect 0 dishar e de is s m ler ns :31? rqn b am. ha msa u stan ia y i ula or-m rbss..-se i9 in which case the.reflectingelectrode is of'cirler form h v n r hera dense and also to ele tm i e a edeyicesi wh ch t a e t beam -;is of ribbon-shape in which. ca e thereflecting electrode will be of elongatedform to it hebb n-s a ed beam- 11 ord ha h aidin ent on ma be clearly understoodand-readily carried into effect, it will now bemore fully-- described with reference to the m any n d win in whi Figure-1 illustratesdiagrammatically an elec-i tron discharge device according to the; pref erred for of the -invention, ,and

Fi ure 2 is a diaeramen n enlareefiz al the equipotential surfaces which are-set up. in pe ation etween the. e ona r a d, h r flec ing electrodeof thedevice, shown in Figure 1, Figure 3 is a sectiontakenalongTthe line ,3,.. -3 of Figure; 1; Figure 4 is, a section taken along a similar line as Fi ure 3'; but showing a modification of "the apertures and reflecting electrode.

As ,shown-in Figure 1, a cathode is provided for generatinga beam of electrons, the, cathode being surrounded-by apathodeshield 2'. A focussing electrode "3 isprovided in the form of an apertured diaphragm which serves, in conjunction with-the cathodeshield 2, to generate, when the electrodes are maintained at suitable potentials, a. focussing field. The ,hollowresonator isindicated by the reference numeral 6; and is of toroidal shape andprovidedwith a pair of oppositely-disposed apertures 5 and .B-providing a gap through which the; electronbeam is caused to pass. The field, which serves to reflect the electron beam back through the aperture 6- in the resonator for thepurpose of maintaining the. generation ofoscillations in the resonator, is :set up by the provision of. a reflecting electrode 1 which, in operation, is suitably chargedby maintaining it at a negative potential-with respect to the cathode l.

The device shown in the drawing employs a beam ofcircular form incross-section and it is desirable that the electronstream should form a cross-over at the gap. Consequently, the electron;beam, when itemerges from the, resonator,

Also the ntral rest f, 11s.-

4 will be of divergent form. The reflecting electrode I, since the electron beam has a circular cross-section, is of circular form and in order to improve the field in the path of the beam so that the requirements aforesaid are more completel satisfied, the electrode I is substantially flat and is provided with a short conducting surfacee nbracing the beam, said conducting surface being in the form of a peripheral flange m as show j-Fig'ui'efZ of the drawings illustrates some of the equipotential surfaces which are set up between the resonator t and the reflecting electrode =I whenthelatter is maintained at a negative potential-withzrespect to the cathode l and when the resonator 4 is maintained at a positive potential with respect to the cathode I. As shown,

' the e'quipotential surfaces at and b are of convex form inthe vicinity of the aperture 6 in the resonator whilst between the equipotential surface b and the surface c shown in the figure the equipotential surfaces change from the convexform,

to the concave form, as shown. The curvature of the equipotential surfaces as exemplified .by the surface d increases as they approach the zero equipotential surface which may be the surface e and said surfaces in the region of the central part of the beam as they recede from the zero equipotential surface decrease in curvature as will b seen from the shape of the surface 1. The divergence of the beam in its passage between the resonator i and the reflecting electrode 1 may be as indicated by the dotted lines shown in Figure 2 and it will be observed that whilst the decreas ing curvature mentioned above holds for the central part of the beam the curvature in the region of the marginal electrons of the beam is greater compared with the curvature of the said surfaces in the region of the centralpart of the beam. The equipotential surfaces which lie between the surfaces ;f and the reflecting electrode l, as exemplified by the surface g further decrease in curvature and those surfaces which lie close. to the reflecting electrode .will follow the contour of said electrode. The electrons will however be reflected before they reach the reflecting electrode. Thus, by providing the reflecting electrode with ashort conducting surface which embraces the beam, a field can be set up between the resonator and-the reflecting electrode which is effectively a compromise of'the fields which would be produced when using a flat reflecting electrode without a conducting surface embracing the beam and when employing a reflecting electrode of concave form. The equipotential-surfaces will of course extend beyond the limits shown in Figure 2 and the portions beyond the limits shown will, where the surfaces are close to the reflecting electrode, tend to lie substantially parallel to the flange la. These portions, however, play substantially no part in the re,- flecting operation since they do not lie in the path of the beam.

It is. found that there is an optimum ratio of diameter of theelectrode I to the width of the flange M for maximum efficiency. This optimum ratio is approximately 3, that is to say, the width of-the flange 1a is one-third of thediameter of the disc. It is also found that there is. an optimum diameter for the reflecting electrode of approximately three to four times the diameter of the aperture 6 in the resonator. The aperture 6, in one example, may be 2 mms, and with such a diameter the diameter of the reflecting elec rod isan qximai fi to 6 .1

The invention can also be applied to electron discharge devices which employ ribbon-shaped beams as aforesaid. In such a case the apertures in the resonator are elongated to accommodate the ribbon-shaped beam and the reflecting electrode is of elongated form suitable for causing reflection of the ribbon-shaped beam. The reflecting electrode in this case will be provided with a short conducting surface embracing the beam, but such surface need not extend around the whole periphery of said electrode but may merely extend along its longer sides. The optimum dimensions referred to above also hold for the elongated form of reflecting electrode, but in this case the ratios referred to are in respect of the minor axes of the reflecting electrode and the elongated aperture.

It is preferred to dispose the reflecting electrode close to the resonator and since, in operation, the resonator will be maintained at a high positive potential and the reflecting electrode at a low or negative potential, there is the danger that, due to the proximity of the reflecting electrode to the resonator, sparking there-between may occur. In order to reduce this possibility the wall of the resonator adjacent the reflecting electrode 1 is provided with an annular depression 8, as shown, in the vicinity of the peripheral flange Ia of the reflecting electrode so that an adequate space is aflorded between the periphery of the flange and the adjacent surface of the resonator to reduce the possibility of sparking.

In operation of the device shown in the drawing the focussing electrode 3 may be maintained at a potential of 300 to +300 volts with the cathode I and the cathode shield 2 at zero potential, the resonator is at a positive potential of 1000 to 2000 volts and the reflecting electrode 1 at a negativ potential of 150 to 500 volts. Figure 3 shows a cross section of Figure 1 taken along the line 33 showing an end view of the device utilizing my invention in which a disc electrode arrangement is used. Figure 4 is a view similar to Figure 3, showing a modification utilizing an elongated slot 60 and elongated reflecting electrode 1c having opposed flanges 1c directed toward the cavity resonator 4.

Figures 3 and 4 show end views of a device utilizing my invention in which Figure 3 shows the disc electrode arrangement 1 and Figure 4 the elongated slot and the elongated reflecting electrode 10.

I claim:

1. An electron discharge device having a cathode for supplying a stream of electrons, and a reflecting electrode in the path of said electrons, a cavity resonator having a pair of oppositely disposed apertures through which said stream path extends, the transverse dimension of the aperture in said resonator adjacent said refiecting electrode being between one-third and onefourth the transverse dimension of said reflecting electrode, said reflecting electrode having a conducting flange parallel to the beam path, said flange having a dimension along the beam path one-third that of the transverse dimension of said reflecting electrode.

2. An electron discharge device having a cathode for supplying a stream of electrons and a reflecting electrode in the path of said electrons, said reflecting electrode comprising a disc, a cavity resonator positioned between said cathode and said reflecting electrode and having oppositely disposed circular apertures in the walls thereof through which the path of said stream of electrons lies, said apertures having a diameter between one-third and one-fourth the diameter of said reflecting electrode, said reflecting electrode having a flange extending toward said resonator and having a dimension along the path of said electrons equal to one-third the diameter of said reflecting electrode.

3. An electron discharge device having a cathode for supplying a stream of electrons, a reflecting electrode in the path of said electrons, a cavity resonator positioned between said cathode and said reflecting electrode, said cavity resonator having oppositely disposed apertures through which the path of the stream of electrons lies, said reflecting electrode being elongated and said apertures being elongated, the shorter transverse axis of the reflecting electrode being between three and four times the shorter transverse axis of said apertures, said reflecting electrode having a flange extendingtoward said resonator and having a dimension parallel to the path of the electron stream equal to onethird the shorter transverse axis of said reflecting electrode.

4. An electron discharge device having a cathode for supplying a stream of electrons and a reflecting electrode in the path of said electrons, and a cavity resonator positioned between said cathode and said reflecting electrode, and hav ing apertures in the walls thereof through which the electron path lies, said reflecting electrode having a flange extending toward said resonator and lying parallel to the path of the electrons, said resonator and said reflecting electrode being closely spaced, said resonator having a depression registering with the flange on said reflecting electrode.

BERNARD JOSEPH MAYO.

REFERENCES CITED The following references are of record in the flle of this patent:

UNITED STATES PATENTS Number Name Date 2,190,511 Cage Feb. 13, 1940 2,190,515 Hahn Feb. 13, 1940 2,190,735 Rust Feb. 20, 1940 2,244,672 Brett June 10, 1941 2,250,511 Varian et al. July 29, 1941 2,259,690 Hansen et a1. Oct. 21, 1941 2,280,026 Brown Apr. 14, 1942 2,293,151 Linder Aug. 18, 1942