US2864020A - Electron discharge device - Google Patents

Description

Dec. 9, 1958 P. RUDNICZK ET AL ELECTRON DISCHARGE DEVICE Filed Oct. 16, 1956 panmapamvpnnaaannaanu 1 A Y I 2,864,020 Fatented Dec. 9, 1958 ELECTRON DISCHARGE DEVICE Paul Rudnick and Michael F. Toohig, Fort Wayne, Ind., assignors to International Telephone and Telegraph Corporation Application October 16, 1956, Serial No. 616,294

2 Claims. (Cl. 313-71) This invention relates to an electron discharge device, and is particularly directed to electron discharge devices of the storage tube type.

In display cathode ray tubes commonly characterized as storage tubes or cathode ray amplifiers, as disclosed in Farnsworth Patents Nos. 2,228,388 and 2,754,449, a planar storage electrode of extended area is uniformly bombarded 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 electron beam. To transfer the charge 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 the screen 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 both guns 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.

An object of this invention is to provide an improved electron discharge device having an electron flood gun and a writing gun in which the two guns are each symmetrically disposed with respect to the tube axis and the screen to be flooded.

It is another object of this invention to provide uniform flood beam current density distribution over the entire storage screen area, this uniformity taking into consideration the fact that at each incremental area on the screen the individual electrons are approaching from different directions (angular distribution). This uniform current distribution results in an image on the phosphor face plate which is of uniform brightness; i. e., the displayed image will possess greater exactness in shading and contrast to the object being reproduced.

It is still another object of this invention to provide a unique annular flood gun arrangement which emits an annular stream of electrons, each arcuate segment of this stream spreading or flooding the entire storage screen area.

In the accomplishment of this invention there is provided a cathode ray tube of the storage type comprising an extended planar storage screen, a writing gun and a flood gun symmetrically arranged with respect to a line passing perpendicularly through the center of the screen, the flood gun being of annular configuration surrounding the beam path'of the writing gun, means for flooding the entire screen area from each arcuate segment of the flood gun, and means for scanning the beam from the writing gun over the entire screen area for impressing a charge image thereon.

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:

Fig. 1 is a cross-section of an electron discharge device embodying this invention, diagrammatically illustrating flood beam divergence from each arcuate 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 gun assembly of Fig. 2.

Referring to Fig. 1, there is shown a cathode ray tube in which the combined 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. The tube comprises an evacuated glass envelope 1 having an end plate 2 inteiorly located with an aluminized phosphor. Immediately adjacent the phosphor layer is a storage screen 3 of conventional construction comprising a fine mesh metallic screen having an insulating material on the lefthand side thereof (gun side). 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 conventional lead-in conductors, not shown.

At the other end of the envelope, and centrally located 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 beam of electrons-which may be scanned in the usual manner over the screen 3 for impressing an electrical charge image thereon. Deflection electrodes or coils (not shown) may be employed to scan the usual raster 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 annular 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 generating a stream of electrons. The shell 7 is fabricated of inner and outer metallic sleeves 10 and 11, respectively, which are radiused inwardly toward cathode 9 as shown to provide the slot 8. The sleeves are secured together by means of a metallic annular backing 12 suitably provided with apertures 13 for receiving suitable 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 suitable means to the envelope 1, thus mounting the flood gun assembly 6.

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 conductively connected 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 from, the coating 18. These coatings may comprise any of the conventional coating materials such as conductive graphite, more commonly referred to as Aquadag.

These coatings 18 and 19 serve as accelerating and forming electrodes for the beam issuing from the ficod gun 7 and act, in conjunction with a center sleeve electrode 20 inside the gun 7, to distribute the electron emission 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 by means of the ceramic supports 16. Electrodes 18 and 19 could if desired comprise end-to-end metallic sleeves. The sleeve electrode 20 has a separate lead-in for establishing the desired potential thereo i 3 "Inanbperativeembodiment of this invention, suitable physieal dimensions are as follows: Diameter of phosphor plate 2-approx. two (2) inches;

Axial-distance between screen 3 and :front of ringgun'*6- approx. 'two' and five-eighths (2% inches; Lengths'of carbon coatings 18 and 19- 'one and one-half (1 /2 inches and three-quarters inch, respectively; Inner'and outer diameters of flood gun 6-0.812 inch and 1.312 inches, respectively;

Inner and'outer "diameters of slot l-l'0.948 inch and 1.118 inches, respectively;

Suitable operating" potentials inay be as follows:

Electrode 20--3 to 10 volts; Anode 7-- 12 to 1 6 volts;

The floodgun 6 and the associated'electrodes 17, 18,

'19,:20,'and21 aredesignedso that electrons fromeach :a'rcuate "segment S '(see'Fig. 3') will flood the entire storage screen area. This is graphically illustrated by the' dashed incremental beamboundar'ies in Fig. lwhe'rein'the line 22' whichextends from'the flood gunners 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 'val'ues aregiven, it will be'understood by those slsilled in the'a'rt'that these may vary inorder to meet the desired operating characteristics wherein theincremental beam from each flood gun segments floods the entire storage screen area a'nd not appreciably morenor less thanthis area. Thepotentials on the various electrodes, the size of slot 8 and the like'all constitute variables whichmay be adjusted to obtain the precise incremental flooding characteristics desired. v V V s V V As a consequenceot thiscoverage of the storagescreen area from each incremental segment of the flood gun 6, the total flood beam which'reaches the collector screen 7 4 and also the storage "screen .3 and phosphor face plate 2 is uniform both in current density and inangular distribution. While the angular paths of the various electrons at individual points over "the screenareas'may differ, yet the average effect of these electrons is uniform providing a displayedimage onithe phosphorface plate which is free of unwanted shading or contrast characteristics.

Prior art tubes of the storage type conventionally collimate the flood beam just prior to its covering the storage screen; however, this present inventionis unique in the respect that it does not collimate the flood beam but instead conversely operates to providela uniform, noncollimated beam which floods the entire screen area. This results in the production of an image on the phosphor face plate 2 of uniform brightness, a condition quite diflicult to achieve in the use of prior art collimated beams.

In operation, with the various operating potentials applied as described hereinabove, the writing 'gun S ofthe tube of Fig. 1 is fed with an image signal which modulates the pencil-like beam issuing therefrom. The defleeting plates, or deflecting coils, whichever may be preferred, serve to scan the modulated beam in a conventional television faster or other pattern over the storage screen '3, thereby producing an "electrostatic charge image in a manner now' well-'understood'andexplained 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 disabled. The flood gun 6 produces the annular beam of electrons, as previously described, which floods the entire screen 3 from each incremental segment thereof. Because of the relatively high potetnial on'thei phosphor plate 2, these flood electrons will be drawn through the openings in the screen3 and are'mo'dulatedby the individual charges around these-openings. There then results an extended electron image which impinges the phosphorplate 2 and produces a visible image conforming to the'charge'image on the screen 3.

The mode of oper'ation'of a storage tube as just described is well known and understood by persons skilled in the art. There are many difierent variations in this operation; however, it will be apparent that the floodbeam producing system of this invention may be utilized in conjunction witha'ny'conventional mode of operation enclosing an'a'nnular cathode, a sleeve electrode concentric inside of "said shell, an annular electrode concentric outside of "said shell and approximately in-the plane of the forward edge thereof; and a pair of 'jspacedapart accelerating and forming electrode sleeves arranged endto-end between said annular electrodeand said planar electrode, said annular electrode being connected to 'the adjacent one of said accelerating and forming electrodes, said accelerating and forming electrodes cooperating with said ring gun and said annular and sleeve electrodes -to distribute the electron emission from each elemental segment of said ring cathode over'the entire area of said planar electrode.

2. An electron discharge device comprising: an envelope; a phosphor plate and parallel screens across one end of said-envelope; a writing gun centrally located at the other end' of said envelope; a ring gun concentric about the axis of and immediately adjacent said-tube and located in front of said'writing gun; two bands of conductive material coated on the inside of said envelope between said ring gun and said screen, the axial length of the band adjacent said-screen end of said envelope being less than the axial length of said other bandya ring electrode radially inside said ring gun, saidring gun having a mask; provided with an annular maskingaperture; an annular electrode concentrically arranged outside of said ring gun and approximately in a plane with said masking aperture, said annular electrode being connected to the adjacent band of conductive material; said ring. gun-cooperating with said ring and annular elec- 2,452,569 "sziklai Feb. 22, 1949 2,748,312 Beinterna May 29,1956 2,754,449 'Farnsworth July '10," 1956

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