US2509254A - Line focusing cathode-ray tube - Google Patents

Description

May 3Q, 1959 P. J. SELGIN 2,509,254

LINE FOCUSING CATHODE-RAY TUBE Filed Nov. 27, 1946 B g 1, w

INVENTOR PAUL J. SELGIN ATTORNEY Patented May 30, 1950 LINE FOCUSING CATHODE-RAY, TUBE Paul J. Selg-in, Fort Wayne, Ind, assignor by mesne assignments, to Farnsworth .Research Corporation-a: corporation .oflndiana- ApplieationNovember 2'7, 1946, Serial No. 712,567

This invention relates tocathode-ray tubesand particularly to the focusing facilitiesfor the electron beams of such tubes.

For certain purposes cathode ray tubes, wherein an electron beam or beams are deflected over a target electrode system for the purpose ofsignal generation. and/or amplification, have been used with a considerable measure of success in preference to vacuum'tubes'wherein the-electron current is controlled by grids or similar structures. A deflection type of cathode ray tube has certain advantages over, grid-controlled tubes. For example, it is possible to achieve a higher ratio of mutual conductance to average input current. Such a characteristic is particularly advantageous at low signal levels for the reason that the electron current in. the grid-controlled device must be maintainedat a' relatively low level for weak signals, thereby permitting the introduction into the output circuit of the tube of the relatively small uncontrollable variations in the electron. emission from the cathode, This produces spurious signal effects. In the deflection type of cathode ray tube, on the other hand, the magnitude of the electron current is not varied in accordance with the signals, but instead ismaintained at a relatively high'intensity.

Nevertheless, it is well known that, in conventionally operated, cathode ray tubesof the deflection type, wherein a relatively small pencillike' electron beamisemployed, it is possible to produce at thetarget electrode, a beam which has a limited maximum current densityythat is, thebeam has only a relatively low intensity per unit area. Where a beam of, this. character is formed to have a relatively small cross-sectional area, it is evident that the total beam current is limited to a relatively small magnitude. In order to' increase the current magnitude of a beam of pencil-like form, it is necessary to form it in such a manner that it has a relatively large cross-sectional area. However, a beam of this size isnot practical for use in a deflection type of cathode ray tube, wherein the signal which is to be reproduced is developed by deflecting the beam over an aperture or similar surface discontinuity. Such' devices do not have the required sensitivity to reproduce relatively high frequency signals with the'desired fidelity. A deflection type of cathode ray tube for faithful signal reproduction requires a beam having a dimension in the direction of deflection which is relatively small. In order to meetthis requirement and, at the same time, to meet the requirement of relatively large cross-sectional area, it is seenthat it is desirable 3 Claims. (CL 250-J-160) 2- to spread the electron beam overthe targetelectrodeto a muchgreater extent in one dimens ion than in theother.

It is an obj ect' of the present invention, therefore,- to provide a noyel cathode ray'tube having facilities for producing an electron beam-which, in the plane-ofa target electrodais of'relatively small intensity per unit; area, but-yet is of relatively great total intensity.

-Another object of the invention isto provide, in a deflection type cathode ray -tube, a novel focusing system whereby to convert a relatively high intensity electron beam of pencil-likeform, into an electron stream of sheet-likeform wherein one dimension is great relative to the other.

In accordance with this invention, there-is provided a cathode ray tubehaving means such as anelectron gun for producing a; pencil-like electron beam having arelatively large electron current. The tube-also is provided with a focusing system which is located adjacent to the .:path of the beam and preferably extends longitudinally thereof. Inasmuch as any.bearn.-has..an inherent tendencyto expand in all. dimensions thereof, the simplest form of focusing: system needed consists of a means for compressingthe beam in one of its dimensions. .Wherearelatively great expansion-of the beam .is desired, however, the focusing system comprises-a meanslsuch as an electrode structurefor producing a field of such a character to either .increase-.. or decrease one dimension of the beam. Also,.incl=ud'ed-,;in the focusing system are twooppos-ite electrodes located adjacent to the .path of the beam and energized in: suitable. polarity relative tOUtheqfilStnamed field producing means to. eitherld'ecrease orincrease the otherndimension.of. the: beam. More specifically, where the first-named fieldproducingmeans is effective to compress, the beam in one dimension. thetwo opposite electrodes arejeffective to. expand. thebeam .in its-other dimension. Oloviously; it iswithin the sc0pe ,0f;the;present invention .to. so energize-the ,compcnentsof the focusing system to. produce. opposite effects upon the beam. 1 By this means the-peneiL-like beam of electrons. is converted into.. an electron stream having asheet-like form which-impinges upon. thetarget electrode substantially in a linear manner.

More specifically, in accordance with. an illustrative embodiment. ofv the invention-disclosed herein, the focusing system comprises-fomrelon gated electrodes mounted at:9. degrees, .-to .Qne another and extendinglongitudinally-of the path of the electron beam. Diametrically opposite ones of these electrodes are connected in pairs to a source of energizing voltage in such a manher that the two pairs of electrodes are charged positively and negatively with respect to one :another. The two negatively charged electrodes efiect a compression of the pencil-like beam in one dimension and the two positivel charged electrodes effect an expansion of the beam in the other dimension. The target electrode is located in the focal plane of the system wherein the maximum beam compression occurs.

For a better understanding of the invention, together with other and further objects thereof, reference is made to the following description, taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing, the single figure is a perspective view of a cathode ray tube embodying one form of the invention.

Referring now to the drawing, the tube is shown as having an evacuated envelope I. The left-hand end of the tube envelope is provided with a press portion 2 which serves as a mounting support for the tube electrodes and also as the means for sealing in lead-in conductors to the electrodes. The electron gun, by means of which the pencil-like electron beam is formed, comprises a cathode 3 which preferably is capable of producing a substantial emission of electrons when heated. The heating facilities for the cathode have not been shown in order not to unnecessarily complicate the drawing, since they may be entirely conventional. Cathode heating may be either direct or indirect as de- :t.;

sired. The electron gun further includes a cylindrical cathode shield 4 and an accelerating anode 5. The anode is provided with a small centrally located aperture 6 in substantial alignment with the cathode.

The tube also is provided with four slender elongated focusing electrodes 1, 8, 9 and 10. These electrodes are provided with glass or ceramic insulating sleeves ll, I2, l3 and I4. These sleeves are inserted through the anode disk and extend on either side thereof substantially as shown. The rearwardly extending ends of the vertical electrodes 1 and 8 are connected together and to a lead-in conductor l5 which is extended through the press 2 to the outside of the tube envelope. Similarly, the rearwardly extending ends of the horizontal focusing electrodes 9 and all] are connected together and to a lead-in conductor 16 which is extended through the press :2 to the outside of the tube. In addition, the -;cathode 3 and the shielding cylinder 4 are con- ;nected together and to a lead-in conductor I! which is extended through the tube envelope. Finally, the anode disk 5 has electrically connected thereto a lead-in conductor IS.

The tube also is provided with a target electrode H! which is located in the path of the electron beam. This electrode is shown diagrammatically as a flat disk. The particular form of target electrode used in a device of this character, will depend uponthe specific purpose for which the tube is intended. Generally, the target electrode of a deflection type cathode ray tube is provided with one or more surface discontinuities with respect to which the beam is deflected. In some cases the electrodes may be shaped so that the beam may be deflected over one or more edges thereof. Such target electrodes frequently are provided with one or more apertures of particular shape over which the beam is deflected.

, such as a battery 20.

Such structures are well known in the art and since they form no part of the instant invention, only a diagrammatic form of target electrode has been shown herein.

The various electrodes of the type which function to develop the primary electron beam and to focus it into the desired shape, are shown connected to sources of potential of a character to accomplish the desired result. The cathode 3 and the shielding cylinder 4 are connected by lead-in conductor [1 to the grounded negative terminal of a source of unidirectional voltage, The positive terminal of this battery is connected by lead-in conductor l8 to the anode 5. The vertical deflecting electrodes 1 and 8 are connected by lead-in conductor E5 to the left-hand terminal of a resistor 21. The right-hand terminal of this resistor is connected by lead-in conductor 16 to the horizontal focusing electrodes 8 and iii. The vertical and horizontal focusing electrodes are maintained at suitable potentials relative to each other by the connection of a source of unidirectional voltage, such as a battery 22, to the resistor 2|. In the case shown, wherein a horizontal sheet of electrons is desired, the negative terminal of battery 22 is connected to the left-hand terminal of this resistor and the positive batttery terminal, to the right-hand resistor terminal. In order to maintain the focusing electrode structure as a whole, at the proper potential relative to the other electrodes, the center point of the resistor 25 is connected to the positive terminal of the battery 28.

Referring now to the operation of the described device embodying this invention, it will be assumed that the cathode 3 is properly conditioned, such as by heating, for the emission of a copious quantity of electrons. These electrons are drawn through the anode aperture 6 from which they emerge in a beam having a substantially circular cross-section. In order to obtain a relatively large total electron current for deflection over the target electrode the cross-sectional area of this beam may be relatively large. By reason of the described connection of the focusing electrodes, it is seen that negative potentials are impressed upon the vertical electrodes 1 and 8 relative to the positive potentials impressed upon the horizontal electrodes 9 and Ill. The electric field which is produced within the space encompassed by these electrodes, is of such a character that the electron beam, emerging from the anode aperture 6, is subjected to a converging action vertically, and a diverging action horizontally. Without considering these actions in detail, it may be seen in general that the negatively charged vertical electrodes 'l' and 8 repel the negatively charged electrons, forcing those in the upper half of the beam downwardly and those in the lower half of the beam upwardly. At the same time, the positively charged electrodes 9 and I0 draw the electrons in the left-hand half of the beam farther toward the leftand those in the right-hand half of the beam farther toward the right.

Upon emerging from the field produced by the focusing electrodes, the electrons comprising the beam are directed in such a manner that, as the beam moves toward the target electrode 19, it is continuously converging in a vertical sense and diverging in a horizontal sense. The target electrode is located in the focal plane of the system. In this plane there is a cross-over in the vertical convergence of the electron movement. As is well known in electron optics, beyond this plane the beam begins to diverge in a vertical sense. It is seen, therefore, that in the focal plane the cross-section of the beam has a relatively large horizontal dimension and a relatively small vertical dimension. With suitable construction of such a tube, the vertical dimension of the beam can be made extremely small, such as 1 millimeter or less, for example, so that it is substantially a one-dimensional beam.

By reversing the potentials impressed upon the focusing electrodes, a vertical electron sheet may be formed. In some oases also it is possible to superimpcse alternating deflecting voltages upon the electrodes 7, 3, 9 and E8, in which case a beam may be formed in the manner described, and at the same time this beam may be deflected over the target electrode. In most cases, however, it is preferable to employ a separate deflecting system located between the focusing electrodes and the target electrode so that the deflectin electrodes may be more closely spaced and thereby achieve greater deflecting efliciencies. Either electrostatic or electromagnetic deflecting systems may be used, as desired. The beam deflection plane should correspond with the small dimension of the beam. In the illustrative embodiment of the invention disclosed herein, deflection should be efiected in the vertical plane. It should be apparent that the principles under1ying the present invention may be embodied in other forms specifically different from that illustrated and described herein. Broadly, what is required to practice the invention is a means for producing a field of such a character to either expand or compress the pencil-like beam in at least one dimension and an additional field-producing facility for producing an opposite efiect upon the beam in another dimension. It may be more advantageous to employ a single electrode having a suitable configuration to effect either an expansion or a compression of the beam in al1 dimensions and, in conjunction with such an electrode, a pair of oppositely disposed electrodes of the form disclosed herein, for example, for producing an opposite effect upon the .beam in one dimension. In some cases the inherent tendency for an electron beam to spread out may produce a sufficient beam expansion to obviate the necessity of providing a focusing facility for this purpose. The focusing system would then include only a name for compressing the beam.

In the particular electrode arrangement illustrated in the described embodiment of the invention, it was more convenient to extend the electrodes rearwardly toward the base of the tube to a point beyond the cathode. These extensions of the electrodes also produce an electric field from which it is preferable to shield the cathode. This is one of the main functions of the cylindrical shield 4 surrounding the cathode.

While there has been described what, at present, is considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications maybe made therein without departing from the invention, and therefore, it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a cathode ray tube, means including a cathode and an accelerating anode spaced from said cathode for producing a compact electron beam of relatively high intensity, and four wire focusing electrodes spaced at degree angles around, and extending longitudinally of, the path of said beam on the side of said anode remote from said cathode, two opposite ones of said eiectrodes being positively charged and the other two opposite ones of said electrodes being negatively charged, whereby to compress said beam in one coordinate direction and to expand said beam in another coordinate direction so as to produce, in a focal plane, an electron beam having substantially linear cross section.

2. In a cathode ray deflection tube, an electron gun includin a cathode and an accelerating anode spaced from said cathode and having a small aperture of symmetrical cross-section for producing a relatively small pencil-like electron beam of relatively high intensity, and four elongated Wire focusing electrodes spaced at .90 degree angles around, and extending longitudinally of, the path of said beam on the opposite side of said anode from said cathode, two diametri cally opposite ones of said electrodes being negatively charged and located in the deflection plane of said beam and the other two diametrically opposite ones of said electrodes being positively charged and located in a plane perpendicular to said beam deflection plane, whereby to compress said beam in said beam deflection plane and to expand said beam in said perpendicular plane so as to produce, in a third plane at right angles to said beam deflection and said perpendicular planes, an electron beam having a cross-section of a relatively large dimension in said perpendicular plane and a relatively small dimension in said beam deflection plane.

3. In a cathode ray tube, an electron gun including a cathode and an accelerating anode spaced from said cathode and having a small circular aperture for producing an electron beam of relatively high intensity and having a substantially circular cross-section, a hollow cylindrical shield surrounding the space between said cathode and said anode, and four slender elongated focusing electrodes spaced at 90 degree angles around, and extending longitudinally of, the path of said beam through, and insulated from, said anode, two diametrically opposite ones of said electrodes being negatively charged and located in a vertical plane and the other two diametrically opposite ones of said electrodes being positively charged and located in a horizontal plane, whereby to compress said beam vertically and to expand said beam horizontally so as to produce, in a focal plane at right angles to said vertical and horizontal planes and spaced longitudinally from said electrodes, an electron beam having a substantially rectangular cross-section of relatively large horizontal and small vertical dimensions.

PAUL J. SELGIN.

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

UNITED STATES PATENTS- Number Name Date 2,075,717 Hehlgans Mar. 30, 1937 2,183,398 Hehlgans Dec. 12, 1939 2,212,640 Hogan Aug. 27, 1940 2,305,617 Hansel] Dec. 22, 1942 2,383,855 Hansell Aug. 28, 1945

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