US2880342A

US2880342A - Electron beam for a cathode ray tube

Info

Publication number: US2880342A
Application number: US618316A
Authority: US
Inventors: Frenkel Lothar
Original assignee: General Dynamics Corp
Current assignee: General Dynamics Corp
Priority date: 1956-10-25
Filing date: 1956-10-25
Publication date: 1959-03-31
Anticipated expiration: 1976-03-31

Description

March 31, 1959 FRENKEL ELECTRON BEAM FOR A CATHODE RAY TUBE Filed Oct. 25, 1956 FIE'J INVENTOR LOTHAQ FQENKEL. BY WM ATTORMY.

ELECTRON BEAM FOR A. CATHODE RAY TUBE Lothar Frenltel, San Diego, Calif, assignor to General Dynamics Corporation, Rochester, N.Y., a corporation of Delaware Application October 25, 1956, Serial No. 618,316

6 Claims. (Cl. 313-82) This invention relates generally to cathode ray tubes and more particularly to the formation of a desired elec tron beam for use in the cathode ray tube.

In the art of cathode ray tubes, as for example in shaped beam tubes as shown in U.S. 2,735,956 and 2,761,988, an important consideration is the proper generation and utilization of an electron beam. That is, it is important to effect a desired spot size, or beam cross-section, to adequately utilize the beam emissive surface most efiiciently, and to form the emitted electrons into a beam of electrons of a rather uniform density cross section. It may also be desirable in order to obtain the desired shape and consistency of the electron beam, to do as much controlling and forming of the beam at as close a position to the electron emissive surface as is physically possible. In this manner beam formation is effected upon rather low velocity electrons which respond with considerable case to control and projecting devices. Desired beam formation may also be accomplished by electrodes positioned along the beam path.

The usual electron beam upon formation has a cross section of rather non-uniform electron density. The beam has an inner core of non-uniform high density electrons surrounded by a more uniform lesser density annulus of electrons. Even though the normal beam is controlled at its low velocity stage, the uniformity defects of the beam give rise to additional troubles, such as lensing aberrations, unevenness in exciting electron responsive targets. Or, if the beam is shaped into an information symbol, a poor quality symbol results lacking uniformity in brightness and resolution. While the entire cause of beam non-uniformity is not clearly understood, it is believed generally, that the usual electron beam is affected not only by the spherical aberrations in the beam forming lenses, but by space charge effects Within the beam itself.

In the art of shaped beam tubes the problem of electron beam non-uniformity has caused considerable study and concern. The ultimate or optimum condition desired in the illumination of a beamshaping member within the shaped beam tube is the imaging of the minimal beam cross section at the opening to be illuminated. At present, due to the non-uniformity of the high density electron core of the electron beam, 2. so called hot core condition prevails in minimal beam cross section, The hot core of the beam may be injurious to the member and may also result in poor illumination quality of the desired shaped opening in the member. Therefore, at present, the minimal beam cross-section is formed beyond the beam shaping member. The member being positioned between the hot core and the beam source.

The present invention attempts to overcome these difficulties by shaping the cross-section of the electron beam through elimination of the inner high electron density core. Elimination of the core or center portion of the beam permits utilization then of the annular portion of the remaining beam. Using only the more uniform .elec-. t ty annular p es :rem ts better electron States Patent Pa t' ented Mar. 31, 1 959 response of the beam to lensing in the subsequent elec', tron optics. Further, by eliminating the core of the beam at or near its origin it results in smaller variation in cathode current density or distribution at zero bias conditions. When the core-less beam is then imaged at its minimal beam cross-section it results in a beam cross section of uniform density devoid of any hot corexz is therefore possible to position the beam shaping member directlyat the point of minimal beam cross-section.

It is an object of the present invention to provide a new and improved electron beam for a cathode raytube.

It is another object of the invention to form an elec; tron beam for a cathode ray tube providing higher beam resolution.

It is another object of the present invention to increase the response of the electron beam to lensing operations within a cathode ray tube by improving the beam CI '0S S-, section to permit convergence of the beam at higher than normal convergence angles.

It is another object of the invention to eliminate the normal and non-uniform intense electron density central core of a cathode ray electron beam.

It is another object of the invention to effect a simple structure for eliminating the core of the electron beam.

It is another object of the invention to provide an electron beam which reduced to its minimal cross-section may be used at that point to illuminate a beam shaping member.

Objects and advantages other than those set forth above will be apparent when read in connection with the accompanying description and drawings, in which:

Figure 1 shows diagrammatically a cathode ray tube embodying the present invention;

Figure 2 shows a partial diagrammatic portion of a cathode ray tube embodying another embodiment of the invention;

Figure 3 shows a plan View and a cross sectional view of a grid electrode embodying the invention;

Figure 4 shows a plan view and a cross sectional view of an electrode embodying the present invention;

Figure 5 shows a diagrammatic view of a usual position of a shaping member with respect to the beam cross over point;

Figure 6 shows a diagrammatic view of the beam shaping member when the beam is imaged thereat as taught in the invention.

Shown in Figure 1 is an evacuated envelope 1i), preferably shaped as a cathode ray tube 11. Tube 11 maybe of any desired type but is preferably shown as a shaped beam tube as exemplified in the patents to Joseph T. McNaney, U.S. 2,735,956 and 2,761,988.

Positioned at one end of the tube ill is an electron beam source 12, such as a thermionic or photo responsive cathode (as shown in U.S. 2,738,499), preferably shown in this invention as a thermionic cathode.

Source 12 is capable of generating and projecting an electron beam 15 along the tube 11 toward an electron responsive target 17, such as phosphor screen, at the other end of the tube.

Electron beam 15, which has a substantially circular cross section as generated and projected, has a center portion or core of a high electron density that is generally non-uniform and of a high electron density. Surrounding the center portion or core is an annular portion or annulus of electrons of a substantially uniform and predetermined density distribution. In certain applications such as the shaped beam tube, the electron beam desired is one of uniform, predetermined electron density and intensity. This permits imaging of the minimal beam cross section at a beamshaping member 16. A nor; mal electron beam exhibits non-uniform beam density and intensity and has a hot core" at the cross over,

imaging or point of minimal beam cross section. This necessitates placement of the shaping member 16 at a point prior to imaging of the beam cross section as shown in Figure 5. Through utilization of the instant invention, by;removing the core of the beam 15, it is possible to image the beam cross section at the shaping member 16 as shown in Figure 6.

Removal of the core or central portion of beam 15 may be accomplished by. employing a limiting means interposed in the path of the beam and permitting only the annular portion of the beam to pass therethrough by preventing passage of the center portion beyond the limiting means. The limiting means, which may take the form of an annular opening or aperture 18 (or 30), in either a control grid or electrode 19 or an electrode 29,101 various other type openings may be employed to obtain a beam corrective device which is capable of eliminating the core of the beam and passing a substantial portion of the annular portion of the beam thereby forming the desired electron beam 15.

The control grid or electrode 19 may be positioned adjacent the source 12. Grid 19 may further have an indented cup 20 which is lens shaped as well as provided with the aperture 18. The lens-shaped cup 20 may extend inwardly toward the source 12 and effect the coreless beam cross section at substantially its source or origin. If desired, a complementing shape may be imparted to source 12 to complement the lens-shaped cup 20. The cup then would also aid in lensing and imaging of the beam cross section. .v g

The beam 15, as shown in Fig. 1, has its core removed by; control grid 19, and is accelerated and lensed by electrode elements 21, and deflected by first deflection means, such as electrostatic deflection plates 22, to a desired opening or information symbol in beam shaping member 16.

.Means capable of lensing and focusing the beam may provide an area of influence upon the beam, such means may be electrostatic or electromagnetic and may employ an electromagnetic convergence coil 23 disposed about and adjacent tube 11. The area of magnetic influence of coil 23 is exerted through the envelope 11 upon beam 15.

The beam cross section, shaped in accordance with the information symbol illuminated in the beam shaping member 16, is lensed and focused by the coil 23, and, is thereafter deflected to a desired position on the target 17 by a second deflection means. The second deflection means, which may be electromagnetic or electrostatic, is shown as electrostatic deflection plates 25. The various parts within and the coil without the enevelope may be energized and controlled by a circuitry 28.

Figure 2 shows an embodiment of the instant invention wherein the central portion or core of the beam may be removed by electrode 29 (shown in detail in Figure 4) which is provided with a substantially annular aperture or opening 30 of a configuration similar to opening 18. Of course, electrode 29 may, by application thereto of appropriate voltage, not only remove the core of beam 15 but also act to accelerate the beam.

The particular embodiments of the invention illustrated and described herein are illustrative only and the invention includes such other modifications and equivalents as may readily appear to those skilled in the art and in the scope of the appended claims.

I claim:

1. In a cathode ray tube the combination comprising an electron beam source positioned at one end of the tube for generating and projecting an electron beam of a predetermined density toward the other end of said tube, an electron responsive target positioned at the other end of the tube being responsive to said electron beam, said electron beam initially having substantially a circular cross section, said cross section having a center portion of greater electron density than said predetermined electron density and an annular portion surrounding said center portion having said predetermined electron density, limiting means interposed in the path of said electron beam and being adapted to cause a substantial portion of said annular portion to pass therethrough and preventing passage of said center portion, beam shaping means for shaping said electron beam into predetermined information symbols, and means for positioning said symbols on said screen.

2. In a cathode ray tube the combination comprising an electron beam source positioned at one end of the tube for generating and projecting an electron beam of a predetermined density toward the other end of said tube, an electron responsive target positioned at the other end of said tube being responsive to said electron beam, said electron beam initially having substantially a circular cross section, said cross section having a center portion of greater electron density than said predetermined electron density and an annular portion surrounding said center portion having said predetermined electron density, limiting means interposed in the path of said electron beam and means adapted to cause a substantial portion of said annular portion alone to pass therethrough, means influencing said beam between said limiting means and said target for lensing said annular portion to a circular electron beam, beam shaping means for shaping said electron beam into predetermined information symbols, and means 1 for positioning said symbols on said screen.

3. In a cathode ray tube the combination comprising an electron beam source positioned at one end of the tube for geri'erating'and projecting an electron beam of a pre determined density toward the other end of said tube, an electron responsive target positioned at the other end of the tube being responsive to said electron beam, said electron beam initially having a cross section, said cross section having a center portion of greater electron density than said predetermined electron density and an annular portion surrounding said center portion having said predetermined electron density, limiting means interposed in the path of said electron beam and being adapted to cause a substantial portion of said annular portion alone to pass therethrough, said limiting means comprising a grid aperture electrode adjacent the beam source having a circular opening therethrough, a lens shaped cup extending inward ly toward the beam source is carried by said electrode at said opening, said cup having formed therethrough a substantially annular aperture for limiting passage of the annular portion therethrough, beam shaping means for shaping said electron beam into predetermined information symbols, and means for positioning said symbols on said screen.

4. In a cathode ray tube the combination comprising an electron beam source positioned at one end of the tube for generating and projecting an electron beam of a predetermined density toward the other end of said tube, an electron responsive target positioned at the other end of the tube being responsive to said electron beam, said electron beam initially having a cross section, said cross section having a center portion of greater electron density than said predetermined electron density and an annular portion surrounding said center portion having said predetermined electron density, limiting means interposed in the path of said electron beam and being adapted to cause a substantial portion of said annular portion alone to pass therethrough, said limiting means comprising an electrode positioned in the path of the electron beam, said electrode being provided with a substantially annular aperture therethrough for limiting passage of the beam to the annular portion therethrough, beam shaping means for shaping said electron beam into predetermined information symbols, and means for positioning said symbols on said screen.

5. In a cathode ray tube the combination comprising an electron beam source positioned at one end of the tube for generating and projecting an electron beam toward the other end of said tube, an electron responsive target positioned at the other end of the tube for responding to said electron beam, said electron beam having substantial- 1y a circular cross section, said cross-section having a center portion of predetermined electron density and an annul-ar portion surrounding said center portion having an electron density of less than said predetermined density, limiting means interposed in the path of said electron beam and being adapted to cause said annular portion alone to pass therethrough, a first deflection means positioned intermediate the limiting means and the target for deflecting the electron beam, a second deflection means positioned intermediate the first deflection means and the target, a beam shaping member positioned intermediate the first and second deflection means for shaping the beam into predetermined information symbols, and means capable of lensing and focusing said beam having its area of influence upon said beam positioned intermediate said first and second deflection means, said area extending on both sides of said beam shaping member, whereby said annular portions of said beam are formed into a circular beam having said electron density prior to illumination of said beam shaping member by :said beam.

6. In a cathode ray tube the combination comprising an electron beam source positioned at one end of the tube for generating and projecting an electron beam toward the other end of said tube, an electron responsive target positioned at the other end of the tube for responding to said electron beam, said electron beam having substantially a circular cross section, said cross-section having a center portion of predetermined electron density and an annular portion surrounding said center portion having an electron density of less than said predetermined density, limiting means interposed in the path of said electron beam and being adapted to cause said annular portion alone to pass therethrough, a first deflection means positioned intermediate the limiting means and the target for deflecting the electron beam, a second deflection means positioned intermediate the first deflection means and the target, a beam shaping member positioned intermediate the first and second deflection means for shaping the beam into predetermined information symbols, and means capable of lensing and focusing said beam having its area of influence upon said beam positioned intermediate said first and second deflection means, said area extending on both sides of said beam shaping member, said annular portion being imaged to minimal cross section at said beam shaping member.

References Cited in the file of this patent UNITED STATES PATENTS 2,189,998 Schenk Feb. 13, 1940 2,573,287 Szegho Oct. 30, 1951 2 2,647,220 Broadway et al. July 28, 1953 0 2,769,116 Koda et al. Oct. 30, 1956 2,784,334 Barnett Mar. 5, 1957 2,802,135 Dodds Aug. 6, 1957 2,844,759 Bryan July 22, 1958 FOREIGN PATENTS 56,838 France July 30, 1952 701,871 Great Britain Jan. 6, 1954 OTHER REFERENCES Anthony: New Apparatus and Techniques of Air Traf fie Control Data Handling and Display, I.R.E. Con. Record, vol, 3, No. 6-10, Part 10, pages 55 to 61.

McNaney: The Type 019K Charactron Tube and its Application to Aircraft Surveillance Systems, 1955,