US3496406A

US3496406A - Cathode ray tubes with electron beam deflection amplification

Info

Publication number: US3496406A
Application number: US739910A
Authority: US
Inventors: Jacques Deschamps
Original assignee: CSF Compagnie Generale de Telegraphie sans Fil SA
Current assignee: Thales SA
Priority date: 1965-09-03
Filing date: 1968-06-17
Publication date: 1970-02-17
Anticipated expiration: 1987-02-17
Also published as: GB1157202A; NL156858B; NL6611954A; FR1455405A; DE1539800B2; DE1539800A1

Description

Feb. 17, 1970 J. DESCHAMPS 354565406 CTHODE RAY TUBES WITH ELECTRO BEAM DEFLECTION MPLIFICATION Original Filed Sept. 2. 1966 +J T.|l

i N v EN ro R.' n Jacque.: BESCIMMPS BY v ATroRNEY Int. ci. Ho1j29/70, 29/74 U.S. Cl. 315-17 6 Claims ABSTRACT 0F THE DISCLOSURE The present invention provides a cathode ray tube having 'a quadrupolar lens for amplifying deflections of the electron beam, wherein a post acceleration device consisting of a dome-shaped electrode placed between the quadrupolar lens, which is utilized for amplifying deflections of the electron beam, and the fluorescent screen so as to surround at least a portion of the lens. The domeshaped electrode is provided with a slot whose center line coincides substantially with the locus of the cross-overs of the electrons that traverse the lens. The internal wall of the tube, extending from the uorescent screen to the dome-shaped electrode, is coated with a conductive coating which is maintained, together with the fluorescent screen, at a high direct-current potential with respect to the dome-shaped electrode.

This is a continuation of U.S. application Ser. No. 577,050, filed Sept. 2, 1966, now abandoned.

The present invention relates in general to cathode ray tubes of the type in which the deection of the electron beam is amplified by electron lenses, and more particularly to a tube of this type having an improved post-acceleration device.

In known cathode ray tubes post-acceleration may be provided to increase the energy of the electrons after the electron beam has been deccted both horizontally and vertically, thereby obtaining on the fluorescent screen an increased brilliance. However, the helical and grid induced arrangements used at present for this purpose possess certain disadvantages in that helical post-acceleration reduces the sensitivity of the tube, and post-acceleration with the aid of a grid, placed in front of the screen, causes a decrease in the resolution and contrast.

It is therefore a principal object of the present invenr tion to provide an improved tube in which post-acceleration is achieved without the above-mentioned disadvantages in a cathode ray tube having a quadrupolar electron lens.

It is an object of the present invention to provide a post-acceleration device for a cathode ray tube having a quadrupolar electron lens, which combination avoids or altogether eliminates the disadvantages inherent in known combinations of a similar nature.

It is another object of the present invention to provide a cathode ray tube of the type described having an irnproved post acceleration device.

It is a further object of the present invention to provide a cathode ray tube of the type described which provides for post acceleration of the electron beam by simple and economical means.

, Quadrupolar electron lenses are known for amplifying the deflection of electron beams produced by conventional beam forming arrangements passing a beam through a known deflection system. These lenses have a divergent action in one plane and a convergent action in a second 3,496,406 Patented Feb. 17, 1970 plane, perpendicular to the first one. In the second plane all the trajectories or paths of the electrons intersect in a common intersection point, called the cross-over.

The present invention consists in providing a cathode ray tube having a quadrupolar lens for amplifying deflection of the electron beam, wherein a post acceleration device is provided which includes a dome-shaped electrode placed between the quadrupolar lens and the fluorescent screen so as to surround at least a portion of the lens, the dome-shaped electrode being provided with a slot whose center line coincides substantially with the locus of the cross-overs of the electrons that traverse the lens when the tube is operating and the geometric center of the domeshaped electrode coinciding substantially with the center of deflection of the nearest deflection system, and wherein the internal wall of the tube, extending from the fluorescent screen to the dome-shaped electrode, is coated with a conductive coating, the conductive coating and the fluorescent screen being arranged to be maintained at a high direct-current potential with respect to the dome-shaped electrode.

With this arrangement, the electrons traverse the aperture of the dome-shaped electrode and continue their trajectory, without changing their direction, toward the screen upon which they impinge with a great energy.

These and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the invention when taken with the accompanying drawings which illustrate one embodiment of the present invention, and wherein:

FIGURE 1 shows schematically and in section, one embodiment of the present invention;

FIGURE 2 shows a quadrupolar electron lens used in the tube of FIGURE l, and

FIGURE 3 is a front view of an electrode used in the tube of FIGURE l.

In carrying the invention into effect according to one convenient mode by way of example, FIGURE 1 shows a cathode ray tube which includes an evacuated envelope 1 composed, for example, of glass, and containing an emissive cathode 2, heated by a filament 3, a Wehnelt electrode 4, focussing and accelerating electrodes S, 6 and 7, vertical deflection plates 8, a first quadrupolar electron lens 9, horizontal deilection plates 10, a second quadrupolar electron lens 11, a dome-shaped electrode 12 provided with a slot 13, and a fluorescent screen 14. The internal wall of the tube bears a conductive coating 15 made, for example, of graphite and extending from the screen 14 to the level of the dome-shaped electrode 12.

The sizes of the dome-shaped electrode 12 and its posit1o n within the tube are such that its geometric center colncides substantially with the center of the horizontal deflection, that is the virtual intersection point of the electlrm trajectories in the plane perpendicular to the plates A source of voltage, not shown, enables the filament 3 to be heated, while a direct-current potential source S1 enables the potentials of the various electrodes of the tube to be maintained at suitable values. The indicated values represent merely examples which may be considered as orders of magnitude.

The screen 14 of the tube and the conductive coating 15 are maintained at a high potential, of the order of 10 to 20 kv., with respect to ground by means of a source S2. The horizontal deiiection plates are connected to a time base, not shown, while the voltages or signals to be visualized on the screen are applied between the vertical plates 8.

FIGURE 2 shows the well known arrangement of an electron lens such as those designated by 9 and 11 in FIG- URE l. It is an electrostatic lens formed by four semicylindrical or hyperbolic electrodes 21, 22, 23 and 24.

3 The electrodes 21 and 23 are maintained at a potential -l-V, and the electrodes 22 and 24 at a potential -V. Polarized in this manner, the lens produces a divergent action in the direction X-X and a convergent action in the direction Y-Y. In the latter direction amplification is obtained by over-convergence.

For the voltages of the lenses 9 and 11 of FIGURE 1, the values of 100 and 300 volts, respectively, are indicated as an example.

In the tube of FIGURE l the quadrupolar lens 11 is the amplifying lens, properly speaking, while the lens 9 serves to correct the astigmatism produced by the main lens 11. Moreover, the position of lens 9 between the two pairs of plates 8 and 10 makes it possible for lens 9 to amplify the vertical deflection produced by the plates 8.

FIGURE 3 is an elevation of the dome-shaped electrode 12 with its slot 13, seen in section in FIGURE 1. The slot 13 has been represented in the rectangular form, but it may alternatively have an elliptical form, or the like.

In operation, if the voltages applied to the quadrupolar lens 11 are suitably chosen, all of the trajectories or paths of the electrons pass through the slot 13. In the vicinity of the dome-shaped electrode 12 the equipotential surfaces are substantially hemispheres having vas a center the center of the spherical dome, except in the space adjacent to the slot 13 where the equipotential surfaces are curved inwardly and form a thin convergent lens having its center at the level of the slot.

Under these conditions, the electrons emerge from the slot 13 without changing their direction. In eflect, in the horizontal plane there is no change of direction because all the trajectories of the electrons are perpendicular to the equipotential surfaces (hemispheres) and in the vertical plane all electrons traverse the thin convergent lens which does not effectively change their direction. Consequently, only acceleration is produced due to the very high voltage of screen 14 and coating 15, and thus the electrons impinge upon the screen with great energy. The spots produced on the fluorescent screen are therefore of a great brilliance and enable transistory phenomena of very short duration to be made visible.

Post-acceleration achieved in this manner does not have the defects which are inherent in the prior art systems wherein post-acceleration is accomplished by a helix or by a grid. Moreover, the arrangement in accordance with this invention presents the advantage of leaving the sensitivity of the tube independent from the high voltage applied to the screen.

While I have shown and described one embodiment in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to a person skilled in the art. For example, the present invention is not limited to the specific embodiment described herein but encompasses all modifications, for example, its applications to other prior art cathode ray tubes, as known to a person skilled in the art. Consequently, I do not wish to be limited to the details shown and described herein, but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

I claim:

1, A cathode ray tube comprising an envelope having a fluorescent screen, an electron gun for producing an electron beam directed toward said screen, a deflection system disposed along the path of said beam for deflecting said beam in two orthogonal directions, a quadrupolar electrostatic lens for amplifying the beam deflections, a dome-shaped electrode placed between said quadrupolar lens and said fluorescent screen so as to surround at least a portion of said electrostatic lens, a conductive coating on the internal wall of said envelope extending from said screen to the region adjacent said dome-shaped electrode5 and means for maintaining said conductive coating and said screen at a high direct-current potential with respect to said dome-shaped electrode, said dome-shaped electrode being provided with a slot whose median line coincides substantially with the locus of the cross-overs of the electrons that traverse said lens when the tube is operating, and the geometric center of said dome-shaped electrode coinciding substantially with the center of deflection of the nearest deflection system.

2. A cathode ray tube as claimed in claim 1, wherein said direct-current potential is of the order of l() to 20` kv.

3. In a cathode ray tube having beam generating means for generating an electron beam, beam deflecting means comprising a first and a second pair of plates for deflecting said electron beam, and a quadrupolar electrostatic lens means for amplifying said beam deflections, post-acceleration means for accelerating said beam subsequent to deilection thereot` comprising a first electrode of hemispherical shape having an aperture therein disposed in the path of said beam, a target to which said beam is directed and a second electrode encompassing the path of said beam beyond said first electrode to said target, said second electrode and said target being maintained at a high direct current potential.

4. The combination defined in claim 3 wherein said aperture is in the form of an elongated slot having its long dimension in substantial coincidence with the locus of points formed by the beam cross-overs resulting from said beam deflecting means.

5. The combination defined in claim 3 wherein the geometric center of said first electrode is in substantial coincidence with the center of deflection of said beam deflecting means.

6. The combination defined in claim 3, wherein a second quadrupolar electrostatic lens is disposed between said first and said second pair of plates.

References Cited UNITED STATES PATENTS 2,114,572 4/1938 Ressler 315-17 2,919,381 12/1959 Glaser 315-31 2,954,499 9/1960 `Gundert et al 313-78 X 3,042,832 7/1962 Owren 315-14 X 3,136,918 6/1964 Watson 315-14 3,373,310 3/1968 Worcester 313-78 X RODNEY D. BENNETT, IR., Primary Examiner MALCOLM F. HUBLER, Assistant Examiner US. Cl. X.R. 313-78