US3134919A

US3134919A - Stabilized electron gun

Info

Publication number: US3134919A
Application number: US80635A
Authority: US
Inventors: Schlesinger Kurt
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1961-01-04
Filing date: 1961-01-04
Publication date: 1964-05-26
Anticipated expiration: 1981-05-26

Description

y 26, 1954 K. SCHLESINGER 3,134,919

STABILIZED ELECTRON GUN Filed Jan. 4, 1961 2 Sheets-Sheet 2 H65. FIG.3.

1 i l I I I I06 132 W I I 114 I34 i' I i i 5 ,5 was INVENTOR: KURT SCH ESINGER,

HIS TTORNEY United States Patent 016 ice 3,134,919 Patented May 26, 1964 3,134,919 STABILIZED ELECTRON GUN Kurt Schlesinger, Fayetteville, N.Y., assignor to General Electric Company, a corporation of New York Filed Jan. 4, 1961, Ser. No. 80,635 13 Claims. (Cl. 313-78) The present invention relates to improvements in electron guns for electron discharge devices such as cathode ray tubes.

The present invention is an improvement over that disclosed and claimed in my copending application Serial No. 16,523, filed March 21, 1960, now Patent No. 2,995,676, and commonly assigned herewith. That copending application describes and claims an electron gun in which a narrow and intense electron beam is generated from a relatively large area and relatively low emission density source by focused and intensity modulated transmission through a defining aperture which forms a virtual cathode. The electron supply to the defining aperture is in the form of a collimated beam of electrons derived from a cathode having an emission area substantially larger than the defining aperture. Between the source of the collimated relatively large-area beam and the defining aperture is provided means for both focusing the beam at the aperture and modulating its intensity. The focusing and modulating means is basically a hyperbolic electrostatic lens which focuses by deceleration, the degree of deceleration being at times sufiicient to bring the electrons to a standstill. The lens is so constituted as to project the beam crossover through an annular intensitycontrol or gate electrode into the defining aperture. Further according to the invention, this focusing of the beam crossover at the defining aperture is made to occur at substantially the same modulation-voltage as that providing maximum current transfer through the intensity control or gate electrode. As a result of such coincidence, smooth intensity modulation of the beam at the output side of the defining aperture, from a high intensity to substantially complete cut-off, is obtainable from small magnitude modulating signals of the order of a few volts, and with desirably high transconductance.

Under certain conditions of operation of such an electron gun, the electrons not passing through the defining aperture are reflected back toward the emission source. The reflected electrons interfere with emitted electrons in such a way as to produce space charge accumulations, which in a symmetrical electrode system causes an effective potential depression by space charge confronting the cathode. This interaction produces radio frequency oscillations of the Barkhausen-Kurz type, such as to give rise to objectionable radio frequency interference. To preclude such objectionable interference it is a feature of the electron gun of the present invention that means is provided to prevent objectionable collision and interaction between the emitted electrons and those reflected from or not transmitted through the defining aperture.

Accordingly, a principal object of the invention is to provide an electron gun particularly adaptable for use with electron beam intensity modulation signals of the order of a few volts, such as are conveniently obtainable from transistorized circuitry,

Another object of the present invention is to provide an electron gun having a high transconductance such as to provide control of currents in the range of to 1500 microamperes with drive signals in the range of 15 volts and less, and with a conventional oxide cathode.

Another object is to provide an improved electron gun of the foregoing character which requires a minimum number of dilferent values of bias voltage for its various electrodes and hence requires a minimum number of separate connections to external potential sources.

Another object is to provide an electron gun in which the control signal serves to control transmission of the electron beam through, and focusing of the electron beam at, an exit aperture.

Another object is to provide an electron gun capable of delivering a modulated electron beam which can be readily focused to provide high resolution, and with little change of resolution with beam current.

Another object is to provide an electron gun capable of delivering an electron beam of high intensity through an opening of very small size with controlled small exitdivergence and smoothly modulatable in intensity to virtually complete cut-off by control signals of relatively small magnitude.

Another object is to provide improved means for efficiently intensity modulating an electron beam emanating from a cathode of relatively large area and focused on an aperture of relatively small area.

Another object is to provide improved means for efficiently generating an electron beam of relatively high local intensity over a small cross-section, from an emission source operated at no more than a moderate level of emission density, such as 0.3 to 0.5 amp./cm.

Another object is to provide electron beam generating means particularly suitable for use in cathode ray tubes and exhibiting minimum variation in luminescent screen spot size with beam intensity.

The invention will be more fully understood from the following description and the accompanying drawings, wherein:

FIGURE 1 is a fragmentary axial sectional view of a cathode ray tube having an electron gun constructed according to the invention; and

FIGURE 2 is an enlarged fragmentary sectional view of a portion of the structure shown in FIGURE 1; and

FIGURE 3 is a fragmentary axial sectional view of another embodiment of an electron gun constructed according to the present invention; and

FIGURE 4 is a view similar to FIGURE 2 of an alternative embodiment of my invention; and

FIGURE 5 is a view similar to FIGURE 4 of an additional embodiment of my invention; and

FIGURE 6 is a view similar to FIGURE 4 of another alternative embodiment; and

FIGURE 7,is a view similar to FIGURE 4 of still another alternative embodiment of my invention.

Turning to FIGURE 1, an electron gun constructed according to the present invention is shown mounted in the neck 1 of an envelope of a cathode ray tube having a luminescent screen provided with a conductive coating 7 which extends into the forward end of the neck of the tube. The electron gun includes a disk cathode 2, which may be planar or of outwardly concave parti-spherical profile, and which faces along an emission axis 3 extending longitudinally inthe tube neck. Spaced along emis sion axis 3 in the direction of flow of the electron beam is an annular anode 8 having a central passage 9 coaxial with the emission axis 3. The forward face of the anode 8, i.e. that facing the direction of flow of the electron beam, has a forwardly convex parti-spherical central portion 11, concentric with axis 3, surrounded by a radially extending flange substantially normal to the emission axis 3. The passage 9 is of sufficient size to accommodate a collimated electron beam from the cathode 2, and the beam of electrons emitted from cathode 2 is collimated for passage through the opening 9 by a centrally apertured planar collimating electrode 4 spaced between cathode 2 and electrode 8, and coaxial with emission axis 3. By a suitable dimensioning of such factors as the spacing of collimator 4 from cathode 2 and the size of the central opening in collimator 4, the collimator can if desired be operated at cathode potential, and hence may be directly electrically connected to the cathode so as to eliminate a need for one external lead through the tube envelope. Although cathode 2, collimator 4, and anode 8 are spaced coaxially along the emission axis 3, the remaining electrodes of the gun of FIGURE 1, hereinafter to be described, are spaced coaxially along a transmission axis 6 which is parallel with axis 3 but transversely spaced a distance of the order of 5 to 20 mils from axis 3. Transmission axis 6 may be substantially coaxial with the 'neck of the tube envelope.

Next in sequence along the electron beam path in FIG- URE 1 is an annular gate electrode having, concentric with transmission axis 6, a rearwardly facing concave surface 12 centrally apertured .at 13 to form an axial cylindrical throat as best shown in FIGURE 2. The gate electrode 10 is shaped and spaced relative to the anode 8 to enable formation therebetween of a particular type of electrostatic field whose radial force component is independent of displacement along the axis 6, butproportional to radial distance from the axis 6. The equipotentials of such field are coasymptotic hyperboloids of revolution substantially coaxial with the transmission axis 6, and whose asymptote is a cone coaxial with the transmission axis and having an apex angle of 109 and an apex substantially coincident with aperture 13. To this end the rearwardly facing concave surface 12 of gate electrode 10 and the confronting convex surface 11 of electrode 8 conform substantially to such coasymptotic hyperboloids. However surfaces 11 and 12 may be conveniently manufacturable approximations of such hyperboloidal surfaces, and thus surface 11 may be partispherical, as shown, having a radius equal to about twice the axial spacing of the anode 8 from aperture 13, and surface 12 may comprise a cone coaxial with the transmission axis 6 and having an apex angle of about 109.

Closely spaced'from the gate electrode, and next in' sequence along transmission axis6 in FIGURE 1, is a meniscus electrode 14 of annular shape having a'central aperture 20 coaxial with transmission axis 6, a rearward face transverse to axis 6, and a forwardly concave profile which may preferably be formed by a conical forward face 16 'ofapproximately 109 apex angle. The central 4 collision and interaction with electrons being emitted from the cathode.

With respect to biasing of the electrodes of the gun of FIGURE 1, the cathode 2 is biased at relative ground I potentiaL'and the collimator 4. may receive from a suitable bias supply 54 a potential, preferably adjustable,

equal to or within a few volts above or below that of the cathode so as to provide good collimation of the electron beam through passage 9. a a

The anode 8 is biased positive relative to the cathode an'amount'which may be of the orderof 500 volts, while gate ltl has a direct current potential at or near ground 7 so as to'prov'ide 'a decelerating hyperbolic focusing field between anode 8 andgate IO. Beam current modulating voltage is supplied to gate 1 0 from a suitable source 56 of modulating signals such as television video signals.

Forward of the meniscus electrode 14 in FIGURE 1 is an electron beam accelerating, reconverging and focusing electrode lens system including an einzel lens formed between the spaced

elements

62, 64 and 66 all of which are coaxial with the'trans mission axis 6. The

elements

62 and 66 are cylinders provided with reduced diameter con vexly

opposing end walls

68 and 70 which are theoretically' biparted hyperboloids coaxial ;with the transmission axis but in practice may be approximations to such theoretical surfaces, such as parti-spherical surfaces. The radius of end walls 68 and 70' is preferably aboutequal to their axial spacing, and the end walls have axial apertures 69, 71, of preferably minimum size to pass the electron beam. The element 64 is a cylinder partially overlapping inside the tube envelope, or outside as shown, so as'to opening 20 in the meniscus electrode 14 is substantially closed by aiconductive diaphragm 19 carried by the meniscus electrode and having a minute defining aperture 18 coaxial with'transmission axis 6 and substantially coinciding with the apex of surface 16. This aperture'18 actually defines the spot size, and hence the revolution of the gun.

To optimize formed between' electrodes 8 and 10' and to minimize undesired field aberrations, the conical surface of electrode 10 is preferably extended outwardly and rearwardly so that its peripheral edge is as close to the marginal portion of anode 8 as voltage breakdown considerations will permit. 'Thus the lens field between anode'8' andfgate 10 a theinfluence of the electrostatic lens have a common accelerating potential which is substantially higher than that of meniscus electrode 14, and which preferably may equal or approximate the luminescent screen potential. Electrode 64 has a lesser potential which by a suitable choice of diameter for cylinder 64 and axial spacing of

elements

62 and 66 may bermade equal to ground or to one of the available 'bias potentials supplied to another electrode such as anodes, thus minimizing the number of connectionsthrough the tube envelope, and minimizing the numberof separate bias poten V tials. I V In' the operation of the electron gun of FIGURE l, modulating signal voltage supplied to the gate electrode 10. controls'the amount'of current in the output beam emerging fromaperture 18 in two ways.

latlng voltage'determines whatportion of the current entering the lens will beforwarded'through the gate elec-@ trode 10,'the remainder of the current supplied to the lens being reflected'back toward the anodeS for collecis effectively substantially. wholly enclosed, minimizing field discontinuities and aberrations,

Similarly theconical surface 16 of electrode 14 is ex- 7 ,tended forwardly and outwardly as far'as the transverse dimensions'of the tube neck and electrode supporting rods 7 '50 will practically permit, so as to maximize the influence of the field between electrodes '14and 20 on the electron beam emerging from aperture 18. I

To deflect the electron beam passing through-electrode -8 ontojthe axis 6 in alignment with the central aperture 13 of.g'ate electrode 10, a weak magnetic field, perpendicular to the electron beam and 'to the direction of displacement of the two relatively displaced electrode axes 3, i6, is applied to theregion of anode 8.1 The magnetic field maybe formed by suitable magnetic pole pieces 52 which may be situated within or 'without'the tubeenye Since the virtual cathode at trons froma'cathode2 which is very much larger than aperture 18, 'it will beappre'ciated that the virtualcathode 1 lope. Thissame field also directs reflected electronsaway l from the axis 3, so that their return path avoids the emission area 'of' cathode 2 and henceprecludes objectionable tion thereby. Second, the 'modulation-signal voltage.

varies thefocal length of the lens between" anode 8 and gate '1(l, and hence varies the'position' ofits'focal point relative to the aperture 18. Thus when the gate'ele'ctrode' 10. is supplied with beam intensity modulating signals, an

' intensity modulated virtual cathode is'formed' adjacent;

aperture 18, and the electron beamemerging fromaperture 18 can be smoothly varied from maximum intensity to virtually cut-off with a desirablylarge transconductanc'e" characteristic, averaging about microamperes per volt. The electrons reflectedfrom gate 10 toward anode 8 are deflected by the magnetic field of poles 52 out of the path of the electrons traveling toward gate'1 0, thus avoiding potential'depression; by space charge, and objectionable. ra diofrequency oscillations. i

has a potential'peak'emission density many times' that of a cathode 2, Land peak emission densities: corresponding to approximately '10 'arnperes per square centimeter, onthe equivalent spherical diodebasis, have been obtained in aperture draws elec: 7

After going through aperture 18, the beam is reconverged to a desirably narrow divergence angle by the lens actions of the accelerating field between the meniscus electrode 14 and the adjacent portion of electrode 62. The focusing action of

electrode lens system

62, 64, 66 then serves to focus the beam with desirably small spot size on the luminescent screen, such spot size and shape being determined by the object aperture 18.

In one exemplary embodiment of an electron gun constructed as shown in FIGURE 1, the diameter of the emissive surface of the cathode 2, was about .030 inch; and outer diameter of

surface

12 and 16 was about /2 inch; the radius of surface 11 was about /2 inch; the diameter of passage 9 was about .040 inch; the throat had a diameter of about .040 inch and an axial length of about .020 inch; electrode 10 and diaphragm 19 were axially spaced about .007 inch; aperture 18 had a diameter of about .007 inch; the axial spacing of surface 11 from aperture 13 was about .140 inch; the periphery of gate 10 was spaced about .023 inch from electrode 8; and collimator 4 was spaced from electrode 8 about .050 inch and had a central opening about .062 inch in diameter. With such a gun excellent operating results were obtained with bias voltages relative to the cathode of +i-10 volts for electrode 4, +500 volts for electrode 8, +500 volts for electrode 14, +16,000 volts for

electrodes

62 and 66, +300i300 volts for electrode 64, and a modulating signal at gate electrode 10 varying from about volts to 10 volts. Under such operating conditions beam currents emerging from aperture 18 could be varied from about 1500 microamperes down to complete cutoff with subtended beam angles of about 3 degrees at emergence from aperture 18. Excellent resolution of television pictures exceeding 500 lines, with brightness levels of the order of 300 foot lamberts and beyond Was achieved, and the spot size increase with current was much less than in conventional television picture tubes, by a factor of about three.

The alternative embodiment of the electron gun shown in FIGURE 3 is functionally similar in all respects to the one in FIGURE 1, but certain of the parts of FIG- URE 3 are more specifically adapted for fabrication from sheet metal stock. The plane-convex anode 108 is .formed from a centrally apertured parti-spherical sheet member 109 joined to a centrally apertured disk 105, and the gate electrode 110 includes a cylindrical peripheral portion 130 and a reentrant conical portion 112 terminating at its apex in an axial cylindrical throat 115. The meniscus electrode 114 is of cylindrical cup shape having cylindrical side walls 132 with a rolled upper edge, and a flat transverse bottom wall 134 provided with an enlarged central opening closed by a diaphragm 110 having a small central aperture 118. As in the structur of FIGURE 1, the emission axis 103 defined by the openings .in anode 108, collimator 104 and by cathode 102 is transvversely displaced from the transmission axis 106 defined .by the openings in gate electrode 108, meniscus electrode 114 and the focusing

lens system

162, 164, 166.

In the alternative embodiment of FIGURE 4 collision of the electrons emitted from the cathode with those which may be reflected back from the gate 10 is prevented by tilting the common axis 3a of the cathode 2a, .collimator 4a, and anode 8a relative to the transmission .axis 6 of the throat 15 of the gate 10. The degree of .angular tilt of axis 3a relative to axis 6 is shown in exaggerated fashion in FIGURE 4 and need be only suflicient -so that any electrons reflected from the gate 10 follow a path, such as that shown at 57, which avoids the emission area of the cathode 2a. Optionally, as shown in .FIGURE 5, a transverse magnetic field 52a similar to that provided at 52 in FIGURE 1 may be employed with .a'structure similar to that of FIGURE 4 to minimize the required amount of tilt of axis 3a. In the structure of FIGURE 5 the path of electrons emitted from cathode 2a isbent by the magnetic field into optimum coincidence with axis 6 upon arrival at throat'15, as shown schemath cally by line 53, reflected electrons are further deflected away from the axis 3a so as to miss the passage 9a in anode 8:1, as shown schematically by line 55.

FIGURE 6 shows another alternative embodiment in which the emission axis 3 and transmission axis 6 are coincident, rather than transversely displaced as in FIG- URE 1, but wherein collision of the electrons reflected from gate 10 with those electrons emitted from cathode 2b is prevented by making cathode 2b hollow. An opening 31 is provided in the center of the emission surface of cathode 2b so that the emission surface itself, shown at 71, is of annular shape, and the emission surface is suitably dimensioned to permit the reflected electrons, which as shown at 73 follow paths closely adjacent the axis 3, through the opening 31 and out of interacting relationship with electrons emitted from the emission surface. The electrons passing through the opening 31 may be collected by any suitable means such as for example heater 41, whose potential may if desired be adjusted slightly positive relative to the cathode as by means of bias source 72, to enhance its effectiveness as a collector. With this arrangement only a small loss of emission from the cathode 2b is incurred as compared with an emission surface of the same diameter not having a central opening, since the portion of the emissive surface removed by the central opening is only a very small fraction of the annular emissive surface remaining.

FIGURE 7 shows another embodiment of the invention wherein collision of reflected electrons, or electrons not transmitted through the aperture 18, with electrons emitted from the cathode 2, is avoided by collection of the reflected electrons in the vicinity of the throat 15. This is accomplished by dividing the gate electrode into two axially spaced elements, namely the element 10a having the conical rearwardly facing surface 12 coaxial with axis 6 and to which the modulation signal may be applied, and an apertured disk or washer 10b spaced forwardly of element 10a and having a coaxial central opening providing a throat 15b. In this embodiment the emission axis 3 may be coincident with the transmission axis 6 as shown. As with the structure of FIGURE 1 the modulation signals may be provided to the element 10a through a lead 47. No modulation is su lied to element 101;, and effective collection of reflected electrons by element 10b is afforded by provision to element 10b of a suitable positive bias, for example through lead 39. Such bias may be made adjustable to asuitable value in the range of, for example, +50 to +500 volts, which will afford optimum collection of electrons which would otherwise interact with the emission from the cathode.

It will be appreciated by those skilled in the art that the invention may be carried out in various ways and may take various forms and embodiments other than those illustrative embodiments heretofore described. It is to be understood that the scope of the invention is not limited by the details of the foregoing description, but

will be defined in the following claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

.1. An electron optical system comprising means for genera-ting an electrostatic field in which the equipo-tential surfaces correspond substantially to hyperboloids of revolution asymptotic to a cone of apex angle 109 and coaxial with a reference transmission axis, said field generating means including an annular anode having a central opening through which an electron beam may be admitted to said field and an annular gate electrode coaxial with said transmission axis, said anode and said gate electrode having confronting surfaces conforming substantially to equipotential surfaces of said field, said gate electrode having a central aperture coaxial with said transmission axis and substantially coincident with the apex of said asymptotic cone, said gate electrode and said anode being adapted to have applied, therebetween a potential difference decelerating flow of electrons from said anode toward said gate electrode, said gate electrode being adapted to have applied thereto modulation signals for controlling the flow through said central aperture of electrons in a beam admitted to said electrostatic field through said anode, whereby electrons in said beam not passing through said central aperture are subject to repulsion toward said anode, and means for directing electrons in said beam approaching said central aperture along paths different from those of electrons repolled by said gate electrode to minimize interaction 7 between said approaching andrepelled electrons.

2. An electron optical system comprising means for generating an electrostatic field in which the equipotential surfaces correspond substantially to hyperboloids 'of revolution asymptotic to a cone of apex angle 109 and said anode being adapted to have applied therebetween a potential difference decelerating flow of electrons from said anode toward said gate electrode, said gate'electrode being adapted to have applied thereto modulation signals for controlling the flow through said central aperture of electrons in a beam admitted to said electrostatic field through said anode, whereby electrons in said beam not passing through said central aperture are subject to repulsion toward said anode, an electron beam-reconverging meniscus electrode forward of said gate electrode and having a central electron beam passage, and means for sorting rejected electrons not passing through the a central passage of said meniscus electrode from elec-" trons approaching said central aperture to minimize interaction between said approaching and said rejected electrons.

' electrons of said electron beam comprising means sup- 7 3. An electron optical system comprising means for generating an electron beam coaxial with a reference emission axis, an anode forward of said beam generating means along said emission axis and having a central open 7 ing coaxial with said emission axis for passage of said electron beam, said anode having a forward convex for- 'ward surface coaxial with said emission axis, a gate electrode forward of said anode having a rearwardly concave rearward surface centrally apertured for passage of said electron beam, said anode and gate electrode being adapted to have applied therebetween a potential differ-Q ence for decelerating flow of electrons from said anode forwardly toward said gate electrode, said gate electrode being adapted to have applied thereto modulation signals for varying the flow of electrons in said beam forwardly through said central aperture, whereby electrons not flowing through said central aperture are repelled toward said anode, and means for direct-ing rearwardly traveling electrons repelled from said gate electrode along paths different from forwardly traveling electrons of said electron beam to inhibit interaction between said repelled and said forwardly travel-ing electrons.

4. An electron ,opticalsystem' comprising means for generating an electron beam coaxial with a reference emission axis,an anode forward of said beam generating means along said emission axis and having a central open,-

ling coaxial with saidem-ission axis for passage of said electron beam, said anode having a forwardly convex forward surface coaxial with said emission axis, a gate electrode forward of said'anode having a rearwardly con: cave rearward surface centrally apertured for passage tially to hyperboloids of revolution coasyrnptotic to a cone having an apex angle of 109 and an apex substantially coincident with the central aperture'in said gate electrode, said anode and gate electrode being, adapted to have'applied therebetween a potential difference de celerat-ing flow of electrons from said anode forwardly toward said gate electrode, said gate electrode being adapted to have applied thereto modulation signals for varying the flow of electrons in said beam through said central aperture, whereby electrons not flowing through said central aperture are repelled toward said anode, and means for directing rearwardly traveling electrons repelled from said gate electrode and forwardly traveling electrons of said electron beam along different paths..

5.,An electron optical system comprising means for generating an electron beam coaxial with a reference emission axis, an anode forward of said beam generating means along said emissionaxis and having a central opening coaxial with said emission axis for passage of said electron beam, said anode having a forwardly facing forwardly convex surface coaxial with said emission axis,

an annular gate electrode forward of said anode having a rearwardly facing rearwardly concave surface coaxial with a reference transmission axis and a central a'per- I tore coaxial with said transmission axis for passage of said electron beam, said anode and gate electrode being adapted to have applied therebetween a potential dif ference for decelerating flow of electrons from said anode forwardly toward said gate electrode, said gate electrode being adapted to have applied thereto modulation signals for varying the flow of electrons in said beam forwardly through said central aperture, whereby electrons not flowing through said central aperture are repelled toward said anode, and means for preventing oscillation-generating interaction between rearwardly travelingrelectrons repelled from said gate electrode and forwardly traveling porting said anode and beam generating means withiits emission axis parallel to and transversely displaced from said transmission axis, and means providing a magnetic electron beam deflecting field orthogonal to theelectron beam path and to the direction of relative displacement of said emission axis and said transmission axis.

6. An electron optical system comprising means eluding an emitterand a collimator for generating an electron beam coaxial with a reference emission axis, an anode forward of said beam" generating meansalongsaid emission axis and havingacentral opening coaxial with said emission axis for passage of'said electron beam,

said anode having a forwardly convex forward surface coaxial with said emission axis, an annular gate electrode forward of-said anode having a rearwardly concave -rear- 'ward surface coaxial with a reference transmission axis and a centralaperture coaxial with said' transmission axis forpassage of said electron beam, said emission and trans mission axes beingcoincidenhlsaid' anode and gate electrode being adapted to have applied therebetween a po-- tential difference for decelerating flow of electrons from said anode forwardly toward said gate electrode, "said gate electrode being adapted to have applied ithereto modulation signals for varyingthe flow of electronsih said beams forwardly through said, central aperture} whereby electrons not flowing through saidtcentral aperof said electron beam, the confronting surfaces of said gate electrode and anode electrode conformingsubstanture are repelled toward said; anode, and means for'pre venting interaction between rearwardly traveling "elecf trons repelled from said gate electrode and forwardly traveling electronsfof said electron beam comprisingt means forming an openingin the central portion of the emitter through which electrons repelled from said gate electrodemay pass out of'interacting relation with for wardlytraveling electrons of said electron beam,

7. 'An electron optical'system comprising meansfin-l-t eluding an'emitter and a collimatorfor generating an' electronbearn coaxial with a reference emission axis, an

anode forward of said beam generating means alongsaid is emission axis and having a central opening coaxial with said emission axis for passage of said electron beam, said anode having a forwardly convex forward surface co axial with said emission axis, an annular gate electrode forward of said anode having a rearwardly concave rearward surface coaxial with a reference transmission axis and a central aperture coaxial with said transmission axis for passage of said electron beam, said emission and transmission axes being coincident said anode and gate electrode being adapted to have applied therebetween a potential difference for decelerating flow of electrons from said anode forwardly toward said gate electrode, said gate electrode being adapted to have applied thereto modulation signals for varying the flow of electrons in said beam forwardly through said central aperture, whereby electrons not flowing through said central aperture are repelled toward said anode, and means for preventing interaction between rearwardly traveling electrons repelled from said gate electrode and forwardly traveling electrons of said electron beam comprising means forming an opening in the central portion of the emitter through which electrons repelled from said gate electrode may pass out of interacting relation with forwardly traveling electrons of said electron beam, and means rearwardly of said emitter opening for collecting electrons which have passed through said emitter opening.

8. An electron optical system comprising means for generating an electron beam coaxial with a reference emission axis, an anode forward of said beam generating means along said emission axis and having a central opening coaxial with said emission axis for passage of said electron beam, said anode having a forwardly convex forward surface coaxial with said emission axis, an annular gate electrode forward of said anode having a rearwardly concave rearward surface coaxial with a reference transmission axis and a central aperture coaxial with said transmission axis for passage of said electron beam, said anode and gate electrode being adapted to have applied therebetween a potential difference for decelerating flow of electrons from said anode forwardly toward said gate electrode, said gate electrode being adapted to have applied thereto modulation signals for varying the flow of electrons in said beam forwardly through said central aperture, whereby electrons not flowing through said central aperture are repelled toward said anode, and means for preventing interaction between rearwardly traveling electrons repelled from said gate electrode and forwardly traveling electrons of said electron beam comprising means supporting said gate electrode with the transmission axis thereof tilted relative to said emission axis.

9. An electron optical system comprising means for generating an electron beam coaxial with a reference emission axis, an anode forward of said beam generating means along said emission axis and having a central opening coaxial with said emission axis for passage of said electron beam, said anode having a forwardly convex forward surface coaxial with said emission axis, an annular gate electrode forward of said anode having a rearwardly concave rearward surface coaxial with a reference transmission axis and a central aperture coaxial with said transmission axis for passage of said electron beam, said anode and gate electrode being adapted to have applied therebetween a potential difference for decelerating flow of electrons from said anode forwardly toward said gate electrode, said gate electrode being adapted to have applied thereto modulation signals for varying the flow of electrons in said beam forwardly through said central aperture, whereby electrons not flowing through said central aperture are repelled toward said anode, and means for preventing parasitic oscillation-generating interaction between rearwardly traveling electrons repelled from said gate electrode and forwardly traveling elec trons of said electron beam comprising means supporting said gate electrode with the transmission axis thereof tilted relative to said emission axis, and means providing a magnetic electron beam deflecting field orthogonal to the electron beam path and to the direction of relative tilt of said emission axis and said transmission axis.

10. An electron optical system comprising means for generating an electron beam coaxial with a reference emission axis, an anode forward of said beam generating means along said emission axis and having a central opening coaxial with said emission axis for passage of said electron beam, said anode having a forwardly convex forward surface coaxial with said emission axis, a gate electrode forward of said anode having a rearwardly concave rearward surface and a central aperture for passage of said electron beam, said anode and gate electrode being adapted to have applied therebetween a potential difference for decelerating flow of electrons from said anode forwardly toward said gate electrode, said gate electrode being adapted to have applied thereto modulation signals for varying the flow of electrons in said beam forwardly through said central aperture, whereby electrons not flowing through said central aperture are repelled toward said anode, and means for preventing interaction between rearwardly traveling electrons repelled from said gate electrode and forwardly traveling electrons of said electron beam comprising an electron collector electrode situated adjacent the central aperture in the gate electrode.

11. An electron optical system comprising means for generating an electron beam coaxial with a reference emission axis, an anode forward of said beam generating means along said emission axis and having a central opening coaxial with said emission axis for passage of said electron beam, said anode having a forwardly convex forward surface coaxial with said emission axis, a gate electrode forward of said anode having a rearwardly concave rearward surface and a central aperture for passage of said electron beam, said anode and gate electrode being adapted to have applied therebetween a potential difference for decelerating flow of electrons from said anode forwardly toward said gate electrode, said gate electrode being adapted to have applied thereto modulation signals for varying the flow of electrons in said beam forwardly through said central aperture, whereby electrons not flowing through said central aperture are repelled toward said anode, and means for preventing interaction between rearwardly traveling electrons repelled from said gate electrode and forwardly traveling electrons of said electron beam comprising an electron collector electrode situated adjacent the central aperture in the gate electrode, and means biasing said collector electrode at an (flectron attracting potential relative to said gate electro e.

12. An electron optical system comprising means for generating an electron beam coaxial with a reference emission axis, an anode forward of said beam generating means along said emission axis and having a central opening coaxial with said emission axis for passage of said electron beam, said anode having a forwardly convex forward surface coaxial with said emission axis, a gate electrode forward of said anode having a rearwardly concave rearward surface centrally apertured for passage of said electron beam, said anode and gate electrode being adapted to have applied therebetween a potential difference for decelerating flow of electrons from said anode forwardly toward said gate electrode, said gate electrode being adapted to have applied thereto modulation signals for varying the flow of electrons in said beam forwardly through said central aperture, whereby electrons not flowing through said central aperture are repelled toward said anode, a meniscus electrode transverse to said electron beam forward of said gate electrode and having an opening located in the path of said electron beam, said meniscus electrode having a convergence lens surface facing away from said gate electrode and means for inhibiting interaction between rearwardly traveling electrons repelled from said gate electrode and forwardly traveling electrons of said electron beam.

13. An electron optical system comprising means for generating an electron beam coaxial with a reference emission axis, an anode forward of said beam generating means along said emission axis and having a central opening, coaxial with said emission axis for passage of said electron beam, said anode having a forwardly convex forward surface coaxial with said emission axis, a gate electrode forward of said anode having a rearwardly concave rearward surface centrally apertured for passage of said electron beam, said anode and gate electrode being adapted to have applied therebetween a potential difference for decelerating flow of electrons from said anode forwardly'toward said gate electrode, said gate electrode being adapted to have applied thereto modulation signals for varying the flow of electrons in said beam forwardly through said central aperture, whereby electrons not means for inhibiting interaction between rearwardly' traveling electrons repelled from said gate electrode and forwardly traveling electrons of said electron beam.

References Cited in the file of this patent V UNITED'STATES- PATENTS 7 2,472,766 Woodbridge June 7,1949 2,995,676

Schlesinger Aug. 8, 1961

Claims

6. AN ELECTRON OPTICAL SYSTEM COMPRISING MEANS INCLUDING AN EMITTER AND A COLLIMATOR FOR GENERATING AN ELECTRON BEAM COAXIAL WITH A REFERENCE EMISSION AXIS, AN ANODE FORWARD OF SAID BEAM GENERATING MEANS ALONG SAID EMISSION AXIS AND HAVING A CENTRAL OPENING COAXIAL WITH SAID EMISSION AXIS FOR PASSAGE OF SAID ELECTRON BEAM, SAID ANODE HAVING A FORWARDLY CONVEX FORWARD SURFACE COAXIAL WITH SAID EMISSION AXIS, AN ANNULAR GATE ELECTRODE FORWARD OF SAID ANODE HAVING A REARWARDLY CONCAVE REARWARD SURFACE COAXIAL WITH A REFERENCE TRANSMISSION AXIS AND A CENTRAL APERTURE COAXIAL WITH SAID TRANSMISSION AXIS FOR PASSAGE OF SAID ELECTRON BEAM, SAID EMISSION AND TRANSMISSION AXES BEING COINCIDENT, SAID ANODE AND GATE ELECTRODE BEING ADAPTED TO HAVE APPLIED THEREBETWEEN A POTENTIAL DIFFERENCE FOR DECELERATING FLOW OF ELECTRONS FROM SAID ANODE FORWARDLY TOWARD SAID GATE ELECTRODE, SAID GATE ELECTRODE BEING ADAPTED TO HAVE APPLIED THERETO MODULATION SIGNALS FOR VARYING THE FLOW OF ELECTRONS IN SAID BEAMS FORWARDLY THROUGH SAID CENTRAL APERTURE, WHEREBY ELECTRONS NOT FLOWING THROUGH SAID CENTRAL APERTURE ARE REPELLED TOWARD SAID ANODE, AND MEANS FOR PREVENTING INTERACTION BETWEEN REARWARDLY TRAVELING ELECTRONS REPELLED FROM SAID GATE ELECTRODE AND FORWARDLY TRAVELING ELECTRONS OF SAID ELECTRON BEAM COMPRISING MEANS FORMING AN OPENING IN THE CENTRAL PORTION OF THE EMITTER THROUGH WHICH ELECTRONS REPELLED FROM SAID GATE ELECTRODE MAY PASS OUT OF INTERACTING RELATION WITH FORWARDLY TRAVELING ELECTRONS OF SAID ELECTRON BEAM.