US2173229A - Electric discharge device - Google Patents

Description

Sept. 19, 1939. 1.. E. FLORY ET AL ELECTRIC DISCHARGE bEvxcE Filed Jan. 28, 1957 2 Sheets-Sheet l Sept.- 19, 1939. E. FLORY El AL 2,173,229

. ELECTRIC DISCHARGE DEVICE Filed Jan. 28, 1937 '2 Sheets-Sheet 2 Zinnentors By M 0/96 amp/Fran (Ittorneg Patented Sept. 19, 1939 UNE E'EE STATES PATENT OFFiCE ELECTRIC DISCHARGE DEVICE Application January 28, 1937, Serial No. 122,690

'7 Claims.

Our invention relates to electric discharge devices, particularly to cathode ray tubes and has special reference to the provision of improvements in television transmitting tubes of the general type disclosed in our copending application Serial No. 33,330, filed July 26, 1935.

A cathode ray tube of the general type to which our invention more especially relates (though not limited thereto) comprises a target element, constituted by a plurality of minute photo-sensitive particles insulatingly supported upon a metallic back-plate, on which target element an optical image of a scene to be transmitted is projected. In addition the tube includes an electron source and means are provided whereby a beam of electrons from the source may be caused to scan the photo-sensitive particles whereby, when the device is in operation, the sequential neutralization of the electrical charges acquired by the particles produces a train of electrical impulses in an output circuit connected to the back-plate, which impulses correspond in amplitude to the light intensity of the elemental areas of the optical image.

Heretofore it has been generally customary to connect an output impedance device, such as a resistor, directly to the back-plate which supports the photo-sensitive elements and to impress upon external amplifier stages the potentials appearing across the resistor. As will be apparent to those skilled in the art, such connections to subsequent amplifier stages unavoidably introduce stray capacities to ground which tend to attenuate the higher frequencies appearing across the output resistor, and consequently, militate against definition in the scene when received at a distant point either by radio or over a wire channel. Also, as is well known to those skilled in the art, amplifiers of the thermionic type which, heretofore, have been utilized in connection with cathode ray transmitting tubes are inherently noisy. That is to say, the output current from a multi-stage amplifier will contain spurious frequencies occasioned by shot effect, thermo agitation in the coupling devices, etc., and also by reason of other obsure causes.

The above and certain other disadvantages inherent in tubes of the prior art are substantially obviated in accordance with our above identified copending application, by combining a television tube of the type manufactured by RCA Manufacturing Company, Inc., under the trade-mark Iconoscope with an electron multiplier device. The multiplier is so positioned with respect to the mosaic (upon which the image to be televised is impressed) that electrons released therefrom by the scanning beam are drawn into the multiplier to therein give rise to secondary electrons which, in turn, are utilized for the production of further secondary electrons in as many electronic amplifying stages as may be necessary.

Optimum. performance of improved tubes of the type described would be achieved in a device wherein the electrons leaving the mosaic are collected with equal effectiveness regardless of their exact point of origin. It would appear that this desire result could be substantially obtained by positioning the mouth or entrance of the multiplier in line with the center of the mosaic. Such arrangement would, however, interfere with the projection of the optical image upon the mosaic. In certain tubes constructed in accordance with our earlier invention, the practice has been to so position the multiplier that it is offset from the normal, with the result that greater per cent. of the electrons leaving the nearer portions of the mosaic are collected than those electrons originating at more remote points thereon.

The principal object, therefore, of the present invention is to increase the efficiency and uniformity of the collection of electrons from the emissive plate of a tube of the general type described, and this too without altering the optimum angle of impress of the optical image upon said electrode plate.

Another object of our invention is to provide a television tube wherein a plurality of electron multipliers are so coupled that the output currents therefrom may be mixed to give complete control of picture shading and background.

The above and other objects are accomplished in accordance with our invention by the provision of two or more electron multipliers so positioned with respect to the mosaic upon which the electrons originate, and so connected with respect to each other, that the combined output of the several multipliers constitutes a more uniform electron output with respect to the entire area of the mosaic than is possible of practical achievement with a single multiplier device.

Certain details of construction, together with other objects and advantages will be apparent and our invention itself will be best understood by reference to the following description taken in connection with the accompanying drawings, wherein Figure 1 is a view in perspective of a device constructed in accordance with our invention,

Figure 2 is a diagram exemplifying the connection of the various tube elements to potential sources during the operation of the device as a television transmitter.

Referring now to Fig. 1 of the drawings, a cathode ray tube of the type to which our invention pertains is constituted by a bulbous evacuated container I having an elongated neck portion 3 wherein is mounted an electron source of the type commonly designated an electron gun. The electron gun comprises a thermionic cathode 2 (now shown in Fig. 1 but exemplified in Fig. 2) surrounded by a grid element 5 coaxial therewith and includes a cylindrical first anode 1 coaxial with the grid element. The specific construction of the gun forms no part of our present invention and it is now so well known to those skilled in the art as to need no further explanation.

A cathode or target 9, of the mosaic type, is mounted in the bulbous portion of the container and is so oriented with respect to the electron gun as to be accessible to the electron stream, or cathode ray, during the scanning operation. The target is constituted by a sheet of insulating material H such as mica, the surface of which, exposed to the electron stream, carries a large number of minute. discrete photo-sensitive metallic particles IS. The mica sheet, in turn, is supported from a metallic back-plate l5 which is provided with a lead i? that extends through a wall of the tube to the exterior thereof. In the drawing, which is a view of our improved device looking down into it from the top thereof, the target appears foreshortened; it is to be understood, of course, that in the actual device the target is substantially square or rectangular.

The inner surface of the neck portion of the container, adjacent to the end of the first anode, is provided with a metallic coating Hi, to which is connected an exteriorily extending conductor 2!. The coating has the double function of focus ing the cathode ray to a fine spot upon the target and of accelerating photo and secondary electrons away from the photo-sensitive globules during the. scanning operation. The metallic coating may also extend over the Whole inner surface of t the bulb, with the exception of an area 20 sufficiently large to permit focusing of an optical image on the target. The more extensive coating, if utilized, prevents the walls of the tube from acquiring charges and gives rise to optimum field conditions.

- Attention is also directed to the fact that, in order to simplify the drawings, the ray deflecting coils, usually four in number, one pair for horizontal and one pair for vertical deflection, are omitted.

' During the utilization of the device to transmit or televise a scene, an optical image of the scene is focused sharply upon the surface of the target carrying the photo-sensitive particles. The light causes emission from the particles of photoelectrons which are accelerated toward the conductive coating within the neck portion of the tube. It is our belief that, as a result of the emission of photo-electrons, each minute globule acquires a charge proportional to the light intensity of the elemental area of the optical image that is focused upon it. During the scanning operation, as each globule is struck by the beam, its charge is neutralized and, at the same time, secondary electrons are emitted from the globules, their number varying in proportion to the neutralized charge.

In order to make use of the secondary electrons (rather than the changes in the electrical condition of the device occasioned by the successive neutralizing of the minute charges acquired by the particles), we connect to the container two or more electron multiplier devices in such manner that the vacuous spaces of the main cathode ray tube and of the multipliers are continuous. In the illustrated embodiments of our invention, but two multipliers are employed. They are mounted within the vacous extensions A and B of the main body of the container. The axes a, b (Fig. 2) of the entrances through which the electrons enter the multipliers form an angle of substantially 40 to a plane normal to the center of the mosaic 9. These axes and the normal preferably lie in a common plane. This plane is at a right angle to the plane defined by the normal and the axis g of the electron gun.

In tubes constructed in accordance with our present invention, the precise angles (with respect to the normal of the mosaic) at which the electron multipliers are disposed is not critical. The lower limit of the permissible range of angles is determined by the necessary presence of the window 20 through which the optical image is impressed upon the mosaic 9. Ordinarily, the electron multipliers will be so disposed that their axes will form angles of from 30 to 50 with the normal, though they may be mounted up to substantially 90 without rendering the device inoperative. It is preferable to mount the multipliers symmetrically about the normal, though this is not essential since it is the combined or average output of all of the multipliers that is utilized.

The electron multipliers which we prefer to employ are of the electrostatic type. It is not to be inferred, however, that we are limited to multipliers of the electrostatic type. Any other multiplier may be utilized, such, for example, as one having focusing devices of the electromagnetic type. The latter we do not believe to be quite so good as those of the electrostatic type since the focusing fields tend to interfere with the ray deflecting fields.

Referring now to Fig. 1, wherein the electron multipliers are mounted within the vacuous extensions A and B, respectively, of the main body of the tube. These multipliers are of duplicate construction'so that a description of one serves as a description of both. Each of the extensions A, B terminates in a press P through which six conductive leads 30 to 35 inclusive pass. Lead 3% supports an orificed disc 48 out of short-circuiting contact with the film l9 which constitutes the second anode of the device. An insulating extension M on wire 3i forms an auxiliary support for disc 40. A conductive arm on wire 3! supports a funnel-shaped electron collector 45 which extends through without touching the disc 45. The inner surface of this electron collector is rendered secondarilyemissive as by an application of caesium or the like. The wide mouth of the funnel preferably terminates in a plane adjacent or substantially adjacent the plane of that surface of 'disc 4% which faces the mosaic 9.

Elements 4!? and 4| facilitate the collection of electrons from the mosaic 9. Since such arrangement may be employed in collecting electrons from any surface of large area they form no part of the present invention but are described and claimed in our copending application, Serial No. 128,050 filed February 27, 1937.

Leads 32, 33 and 34 support T-shaped hollow multiplying electrodes 42, 43 and 44, respectively. One open end of electrode 42 is, presented to the inner end of the funnel-shaped electrode 4|, and the other open end of electrode 42 is presented to the mount of the next multiplying electrode 43. Similarly, the other end of electrode 43 is aligned with an opening in electrode 44, which electrode has its terminal hollow end presented to an output electrode 45, which is supported on lead 35. Each of the multiplying electrodes 42, 42, 43 and 44 will be understood to have their inner surfaces treated, as with caesium, to enhance secondary emission. To facilitate such treatment during the construction of the device, parts of these electrodes may be of meshed construction, as shown.

For the purpose of concentrating, accelerating and, directing electrons from one multiplying electrode to the next multiplying electrode, an electron lens is disposed between adjacent hollow electrode terminals. These lenses are constituted, respectively, by the electrostatic field which is set up between the spaced terminals of the adjacent electrodes when appropriate positive potentials are applied therebetween.

Referring now to Fig. 2 of the drawings, in the operation of our improved device it is preferable to connect duplicate electrodes (other than the discs 49) of the separate multipliers in parallel and to so supply potentials to the various electrodes that a potential gradient exists between the parallel connected output electrodes 45 and the electron emissive cathode 2 of the cathode ray tube per se.

Such potentials may be supplied from any well regulated direct current potential source, as exemplified by a potential divider 5G--5ta to the negative end of which the grid or control element 5 of the cathode ray tube is connected and to the positive end of which the common lead 35 of the output electrodes 45 of the multipliers is connected over a circuit including an impedance device 5| connected between the grid 52 and cathode 53 of an output amplifier tube 54. From an inspection of Fig. 2 it will be noted that the cathode 2 of the transmitting tube is variably connected by lead 20, to the potential source Sta at a point more positive than the connection 5a to the source of the grid or control element 5. Such variable connection is for the purpose of properly adjusting the static bias on the transmitting tube to the best operating point.

It is also to be understood that the common leads 3! to 35 inclusive for the multiplying electrodes 4| to 45 may be connected, respectively, to points upon the potential source successively more positive than the connection thereto of the grid or control element in the cathode ray tube. The separate leads 30a and 30b from the disc elements 4%, respectively, are variably connected to source 59 at points intermediate the points to which lead 2| from the second anode l9 and lead 3| from the funnel-shaped collecting elements 4| are connected.

When an optical image is focused upon the layer of particles in the transmitting tube each particle, according to our present understanding, emits photo-electrons which leave the illuminated particles l3, thus causing the said particles to acquire charges, respectively, that are proportional to the light intensity of the elemental areas of the optical image. During the scanning operation, whereby a cathode ray or beam of electrons is caused to repeatedly traverse the photo-sensitized surface in two directions simultaneously, the charges are sequentially released and at the same time secondary electrons are emitted in an amount varying in proportion to the neutralized charges. According to our present understanding of the manner in which our improved device functions the secondary 'electrons are drawn over into the separate multipliers by reason of the fact that the discs 40 and funnel-shaped collecting electrodes 4| are each maintained at potentials which are high relative to the potential of the second anode IS. The potential on each funnel-shaped electrode is higher than the potentials of the discs 40 so that substantially all of the electrons from the mosaic enter these electrons 4| where they may strike the emissive walls to release additional secondary electrons which, together with the non-impinging electrons, are accelerated towards and enter the first T-shaped multiplying electrodes 42 by reason of the higher positive potentials applied thereto. The electrostatic field existing between the adjacent edges of electrodes 4| and 42 constitute an electron lens which focuses and directs the electrons in their passage therebetween.

The impact electrons emitted by the first T-shaped multiplying electrodes 42 are directed and focused upon the next multiplying electrodes 43, by reason of a similar electrostatic field existing therebetween. Upon reaching the second T-shaped multiplying electrodes 43 the secondary electrons, in turn, drive out further secondary electrons which are similarly focused and drawn to the next multiplying electrodes 44 from whence they are drawn over to the output electrodes 45 and give rise to a fluctuating current in the output resistor 5| that is a greatly amplified replica of the electron currents which enter the multipliers from the transmitting tube.

As previously set forth the leads 30 to the discshaped accelerating electrodes 40 are preferably separately connected to the source 50. This permits of control of the quantity of secondaryelectrons, from the mosaic, entering the separate multipliers whereby complete control of picture shading and background is achieved. Thus, should the surface of the mosaic be unevenly activated during manufacture, or should it or the multipliers be misaligned with the result that more electrons would ordinarily enter one multiplier than the other, such inequalities may be compensated for by altering the potential applied to one or another of the discs 40, whereby the electrons from the mosaic are equally distributed among the several multipliers. Again, should it be desirable to shade a portion of the televised image in a manner other than that dictated by the shading of the optical image, the potentials on the discs may be separately varied to increase the quantity of electrons entering that multiplier on the side of the mosaic containing that portion of the image which is to be intensified.

Obviously, the number of separate multipliers employed may be greater than two, the maximum number being limited only by the physical dimensions of the tube and by the mechanical difficulties incident to connecting a large number of multipliers to the tube without obstructing the window through which the optical image enters the device. Further, we may employ as many multiplying stages in the separate multipliers as are desirable without departing from the spirit of our invention.

We are aware of many other physical modifications of our device and many other possible uses therefor that at once will be apparent to sm'face to emit secondary-electrons, and a plurality of electron multipliers mounted remote from said target on opposite sides of a plane which is normal to the plane of the said emissive'surface.

2. An electric discharge device comprising an evacuated container in which. are mounted a target electrode having a plane surface capable of emitting secondary electrons, means for bombarding said target with electrons to cause said electrode to emit secondary electrons, and a plu- 'rality of electron multipliers mounted remote from and on the bombarded side of the target,

the axes of the entrance of said multipliers bearing substantially the same angular relation to 25 the plane of said emissive surface.

3. An electric discharge device comprising an evacuated container in which are mounted a target electrode having a plane surface capable of emitting secondary-electrons, means for bombarding said target with electrons to cause said electrode to emit secondary-electrons, and a plurality of electron multipliers so disposed on opposite sides of the normal of the plane of said emissive surface that the axes of their entrances form angles of from substantially 30 to substantially 90 with said normal.

4. Theinventign assetforth in claim 3 whereinjthe angle formed by the intersection of the axis-of the entrance of oneof said electron multiplierswithsaid normal is substantially 40.

5. The invention set forth in claim 3 wherein the angles formed by the axes of the entrances of said electron multipliers with said normal are substantially equal 6. Anelectron discharge device comprising an evacuated receptacle containing a mosaic of lightsensitive elements, an electron-gun mounted along an axiswhich intercepts the plane of said mosaic for bombarding said mosaic with electrons to cause said light-sensitive elements to release secondary-electrons, and a plurality of electron multipliers mounted on opposite sides of the normal of said mosaic with the axes of their entrances lying in a plane containing said normal, said plane being substantially at a right angle to a plane defined by said normal and the axis along which said electron-gun is mounted 7. An electric discharge device comprising an evacuated container in which are disposed a mosaic of light-sensitive elements, an electron gun, and a pair of electron multipliers mounted on opposite sides of a plane which is normal to the surface of said mosaic, end means constituting that portion of said container which is normal to an axiswhich is intermediate corresponding ends of said pair of multipliers permitting the impress of an optical image upon said mosaic.

LESLIE E. FLORY. GEORGE A. MORTON.

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