US2927235A - Electron discharge device - Google Patents

Description

March 1, 1960 G. PAPP I 2,927,235

ELECTRON DISCHARGE DEVICE Filed Dec. :5, 1956 INVENTOR. GEORGE PAPP ATTORNEY 2,921,235 ga tented Mar.

ELECTRON DISCHARGE DEVICE George Papp, Fort Wayne, Ind., assignor to International Telephone and Telegraph Corporation Application December 3, 1956, Serial No. 625,665

2 Claims. (Cl. 313-70) This invention relates to an electron discharge device,

and more particularly to an electron gun assembly for producing a relatively broad, uniform density electron beam.

In display cathode ray tubes, commonly characterized as storage tubes or cathode ray amplifiers, as disclosed in Farnsworth Patents Nos. 2,228,388 and 2,754,- 499, a planar storage electrode of extended area is uniformly flooded throughout one' side with a flood beam of electrons. In one storage type tube, the planar electrode is a fine mesh screen (see the above Farnsworth patents) coated on the gun side with an insulating material on which a charge image may be written with a sharply focused pencil-like beam. To transfer thecharge image on the screen to a closely spaced parallel phosphor face plate, an electron beam of broad cross-section is flooded over the surface of thescreen and is modulated upon passing therethrough into an electron beam image which corresponds to the charge image. This electron beam image is focused onto the phosphor plate and visibly reproduces the image.

Heretofore, the flood gun and the writing gun of the tube have been mounted side-by-side facing the screen,

necessitating that one or bothguns be displaced from the perpendicular center line of the screen. If the writing gun is inclined to and offset from the center line, keystone and other distorting effects inevitably appear in the electron pattern on the screen. 7

An object of this invention is to provide an improved electron discharge device which is capable of emitting a relatively broad cross-section beam which will flood a given area or electrode with uniform density and distribution.

Another object of this invention is to provide an electron gun which emits a beam of annular configuration and directs the electrons from each elemental segment of the annular beam onto a given area'whereby' such area will be flooded uniformly by the entire beam.

It is still another object of this'invention to provide an annularly shaped flood electron gun for a storage type tube which is operative to produce a visible display possessing uniform brightness throughout its extent.

In the accomplishment of this invention, there is'provided an electron discharge device comprising an annular anode shell having front and back sides, and an annular cathode concentrically disposed inside and in sulated from said anode shell, said shell having an annular beam-limiting aperture in the front side thereof for forming and directing an annular beam onto a given surface or area. This invention has particular utility in storage type tubes wherein it is desired to flood an electrostatically charged planar electrode with an electron beam of uniform cross-section.

The above-mentioned and'other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction:

with the accompanying drawings, wherein: by I Fig. 1 is a cross-sectional view of an electron discharge device embodying this invention, diagrammatically illus-;

trating flood beam divergence from each elemental segment of the annular gun;

Fig. 2 is a sectional view of the flood gun assembly of this invention; and

Fig. 3 is a plan view of the gunassembly of Fig. 2.

Referring to Fig. 1, there is shown a cathode ray tube in which the writing gun and flood gun of this invention are conveniently employed. The particular tube'is of;

the storage type as disclosed in Farnsworth Patents Nos. 2,228,388 and 2,754,449, and comprises an-evacuated glass envelope 1 having an end plate 2 interiorly provided with an aluminized phosphor or a thin phosphor layer on a transparent conductive surface on end plate 2. Immediately adjacent the phosphor layer is a storage screen 3 of conventional construction comprisingafinej' mesh'metallic' screen having an insulating material on the To the left of the storage screen 3 is the collector 'screen' electrode 4. The. storage screen 3, collector screen 4, and phosphor plate 2 have separate and couventioiiallead-in conductors, not

left-hand side thereof (gun side).

shown.

- At the other end of 'the envelope, and centrally cated therein, on a perpendicular line through the center of the screen 3, is mounted a writing gun 5.. This gun 5 is of conventional design and provides a pencil-like V beam of electrons which may be scanned in the usual manner over the screen 3 for impressing an electrostatic charge image thereon.

pattern on the screen 3.

Immediately adjacent the writing gun 5 and concentrically arranged about the tube axis is an annular flood gun 6 which comprises, as shown in Fig. 2, an annularf anodic shell 7 having a forwardly opening annular slot 8. Positioned inside the shell 7 is an annular cathode:

9 suitably arranged to be heated for generatinga stream of electrons. The shell 7 is fabricated of; inner and outer metallic sleeves 10ancl 11, respectively, which are curved inwardly as shown to provide the slot 8. The

sleeves are secured together by means of a metallic an i nular backing 12 suitably provided with apertures 13 for receiving mounting ribbons 14 which support the cathode 9 from a supporting ring 15. The backing 12, hence the anode shell 7, is also mounted on ring 15 by means of a suitable number of radially positioned ceramic spacers 16. The supporting ring 15 is fastened by some suitablemeans to the envelopel thus mountingthe flood .gun asselmblyf6. p n Referring again to Fig.1, an annular electrode; 17 is placed approximately in the plane of the forwardmost edge of the anode shell or anode 7 and is conductivelyconnected to a conductive coating '18 on the inner wall of envelope 1. A second similar "conductive coating 19' on the inner wall is spaced from, and thereby insulated sion from each arcuate segment of the cathode 9 over'the entire' area of the storage screen 3. The sleeve electrode 20 is concentrically positioned inside the gun 7 bymeans of the ceramic supports 16. Electrodes 18 and 19 could. The: sleeveelectrodezll'has a; separate lead-in for establishing.-

if. desired comprise end-to end-metallic sleeves.

the desired potential thereon.

Deflection electrodes or coils (not shown) may be employed to scan the usual raster.

In an operative embodiment of this invention, suitable physical dimensions are as follows:

Suitable operating potentials may be as follows:

Volts Electrode 20 3 to 10 Anode 7 12 to 16 Rings 17 and wall coating 18 12 to 16 Wall coating 19 30 to 80 Qollector support ring 21 and collector "screen 4 125 to 200 Backing or storage screen 3 10 to 20 Phosphor plate 4,000 Cathode 9 The flood gun 6 and the associated electrodes 17, 18, 19, 20 and 21 are designed so that electrons from each arcuate segment S (see Fig. 3) will flood the entire storage screen area. This is graphically illustrated by the dashed incremental beam boundaries in Fig. 1 wherein the line 22 which extends from the flood gun slot 8 parallel to the tube axis defines an approximate angle of fourteen degrees (14) with the upper beam boundary and an approximate angle of twenty-seven degrees (27) with the lower beam boundary. While these angular values are given, it will be understood by those skilled in the art that these may vary in order to meet the desired operating characteristics wherein the incremental beam from each flood gun segment S floods the entire storage screen area and not appreciably more nor less than this area. The potentials on the various electrodes, the size of slot 8 and the like all constitute variables which may be adjusted to obtain the precise incremental flooding characteristics desired.

As a consequence of this coverage of the storage screen area from each incremental segment of the flood gun 6, the total flood beam which reaches the collector screen 4 and also the storage screen 3 and phosphor face plate 2 is uniform both in current density and in angular distribution. While the angular paths of the various electrons at individual points over the screen 4 may differ, yet the average effect of these electrons is uniform since each point on the screen is flooded by electrons from each point of the cathode and the axial component of each of these electrons is the same at every point of the screen. This results in a displayed image on the phosphor face plate, which has an essentially uniform brightness characteristic.

Prior art tubes of the storage type conventionally collimate the flood beam just prior to its covering the storage screen; however, this present invention is unique in the respect that it does not collimate the flood beam but instead conversely operates to provide a uniform, non-collimated beam which floods the entire screen area. However, as stated at the end of the previous paragraph, care must be taken that the forward or axial component of electron velocity is substantially constant over the entire flood beam area from every point of the cathode.

This results in the production of an image on the phosphor face plate 2 of essentially uniform brightness, a condition quite difficult to achieve in the use of prior art collimated beams.

In operation, with the various operating potentials applied as described hereinabove, the writing gun 5 of the tube of Fig. 1 is fed with an image signal which modulates the pencil-like beam issuing therefrom. The deflecting plates, or deflecting coils, whichever may be preferred, serve to scan the modulated beam in a pattern over the storage screen 3, thereby producing an electrostatic charge image in a manner now well understood and explained also in the aforementioned Farnsworth patents. After this charge image is applied to the storage screen 3, the writing gun 5, by some means, may be dis abled. The flood gun 6 is active at all times, producing the annular beam of electrons, as previously described, which floods the entire screen 3 from each incremental segment thereof. Because of the relatively high potential on the phosphor plate 2, these flood electrons will be drawn through the openings in the screen 3 and are modulated by the individual charges around these openings. There then results an extended electron image which impinges the phosphor plate 2 and produces a visible image conforming to the charge image on the screen 3.

Essentially the same results could be obtained using various shapes and arrangements of the gun parts, e.g., concentric cylinders and the like. The mode of operation of a storage tube as just described is well known and understood by a person skilled in the art. There are many different variations in this operation; however, it will be apparent that the flood-beam producing system of this invention may be utilized in conjunction with any conventional mode of operation as well as any conventional design of storage tube. Thus it is not necessary to elaborate the various modes of operation.

The electron optics incorporated in the tube structure shown in Fig. 1 of the drawing including the center sleeve electrode 20, annular electrode 17 and conductive coatings 18 and 19 are not apartofmy invention, being the invention of Paul Rudnick andMichael F. Toohig as described and illustrated in their Patent No. 2,864,020, issued December 9, 1953,'and.assigned to the assignee of the present application; my invention rather resides in the construction and arrangement of the annular flood gun 6 which, in combination with the electron optics arrangement of the aforesaid Rudnick and T oohig patent provides the flooding of the entire areaof the screen 3 from each incremental segment of flood gun 6.

While the principles of the invention have been described in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of the invention.

What is claimed is:

1. An annular flood gun for a charge storage cathode ray tube having a planar electrode, said gun comprising: a hollow annular anode shell; and an "annular cathode arranged within said anode shell; said anode shell having a narrow concentric annular slot formed in one side thereof facing said electrode, said slot having a radial width substantially smaller than the greatest radial width of said anode shell and being disposed with respect to said cathode so that the electrons emitted from each elemental segment of said cathode flood the entire area of said electrode.

2. An annular flood gun for .a,charge storage cathode ray tube having a planar. electrode, said gun comprising: a hollow annular anodeshell having two metallic annular sleeves disposed concentrically one within the other, and an annular metallic backing platmone edge of each of. said sleeves. being secured to .said backing plate, the other edges of said sleeves being respectively curved toward each ot er and be r di l y p ed p t q e ies References Cited in the file of this patent UNITED STATES PATENTS Gaebel Nov. 22, 1938 Beintema May 29, 1956 'F-arnsworth July 10, 1956 Hansen Apr. 9, 1957 Rudnick et a1. Dec. 9, 1958

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