US2185395A - Apertured electrode for thermionic tubes - Google Patents

Description

Jan. 2,1949.. H, s BAMFORD 2,185,395

HARRY S. EMFORD.

W ATToRNEYs.

A in sharp contrast the anode aperture 5, by means of which signals from an input lead 9 may be utilized to control the intensity of the beam passing through the anode aperture.

The cathode is energized by cathode heating w battery lO and an accelerating potential is placed upon anode 4 by anode source ll. In case additional acceleration 'is desired an'auxliary accelerating electrode may be used, and I prefer to position this electrode between anode 4 and the fluorescent screen 1. This accelerating electrode embodies my present invention and comprises an electrode support ring |2, across which ist stretched a kntted fabric id. The fabric is maintained in position, preferably by splitting support l2, placing the fabric across one half of the ring, placing the other half over the fabric, and welding both halves to fix the fabric between the two half rings. The fabric M is lmitted, and I have found that the fabric may be knitted on standard knitting machines, such as, for example, those utilized to make silk stockings, and the Wire utilized for the accelerating fabric may be, for example, molybdenum, tantalum, tungsten, nickel, or any ductile metal of lower melting points, in case the accelerating electrode is not subjected to heavy bombardments.

Inasmuch as the aceelerating electrode here is used only for the production of an accelerating field, it is obvious that within certain limits.

the mesh aperture should be large in proportion to the wire diameter; in other words, here it is desirecl that the large majority of the electrons shall pass through the electrode, and as few as possible intercepted thereby. This is, of course, to the two above-mentioned patents, where it was desired to intercept vas many (electrons as possible in order to produce bombardment of the fabric. I therefore utilize very fine wire for the fabric and make the meshes `relatively large, and I have found that it is possible to make a satisfactory accelerating electrode fabric where the ratio of Wire diameter to mesh' aperture diameter is to 1.

After the accelerating electrode has been mounted in the desired position, an exterior lead |5 is provided so that the electrode may be given an' accelerating potential from auxiliary source IS. 'Ijhe tube is then exhausted, and when placed in operation the beam from anode 4 may be deflected over the screen in a pattern as predetermined by the action on the beam of scanning oscillatorsv ll and IB, energizing magnetic deflection coils .|9 and 20, respeotively.

It will thus be seen that the accelerating electrode l4 is subject to differential heating which, if not compensated for, will tend to buckle or displace the fabric out of its normal plane, therebychanging the electrostatic field set up by it and distorting the image produced on the screen 1. The loops of the knitted fabric, however, quickly absorb the expansion and contraction of the wires due to the passage thereover of the beam, and prevent any substantial distortion from the normal plane of the fabric as a whole. I have thus been able to utlize, without welding at cross-overs, a fabric screen electrode having exceptionally fine wire slzes, without breaking and without any substantial deviation from the normal plane.

In the example given above, the differential heating of the screen occurs by reason of the passage thereover of a moving electron beam.

In the example shown in Figure 2, however, the

differential heating is caused by an entirely different factor. Here I have shown, in its very simplest form, a photoelectric tube comprising a cathode and an anode 2|. case comprises a support |2, exactly similar to that previously described, and a knitted fabric |4 supported thereby in exactly the same manner as previously described, except that in this case I prefer to form the wires of the fabric from silver and to make the wire-to-aperture-size ratio between l to 5 and l to '100, depending upon circumstances, and I have found that there is no difficulty in knitting fine silver Wire to the smallei' mesh. The silver cathode, in this case,`is supported on a stem 22, the anode 2| is supported from the wall by lead 23, and the difference of potential is placed between the cathode and anode by source 24 Operating through output device 25, which may well be a work circuit. After the silver fabric has been mounted in position it may then be oxidized and sensitized from a source of caesium or other material 26 having a low work function, as is well known in theV art.

The cathode in this' If, then, an image from light source 21 is l thrown on the silver screen 14 through a lens 28, different parts of the silver screen will be illumnated to a greater or lesser degree and, in consequence, heated to a greater or lesser degree; and if the knitted fabric is utilized here the entire cathode Will maintain its normal plane in spite of its differential heating, and thus the field between the anode and cathode will not become distorted. Electrons emitted on the front surface of the fabric |4 will be pulled through the apertures by the accelerating potential and over to anode 2|, and if it is desired, a focusing coil or other focusing device may be utilized between anode and cathode to maintain the electrons in parallel relationship so that an electron image may be formed which can be utilized in any desired manner, although my cathode screen in this case is not by any means limited to use in forming such an electron image.

I have therefore provided and given two instances of electrodes Within a thermionic tube envelope which are subjected to differential heating, and vwhich will, if made of knitted fabric, maintain their normal planes under such differential heating without the necessity of welding cross-overs, thus allowing an extremely fine Wire to be utilized in making the fabric. I have thus been able to greatly reduce the area of the electrode as far as Wire size is concerned, and have provided an exceptionally strong screen and one which cannot be warped or distorted in use, thereby preventing field distortions when energized.

I claim:

1. An electrical discharge tube having an envelope containing an electrode comprising a fabric of refractory wire, said fabric having a single Wire formed into a single chain of loops through which another row of loops of said wire is passed `to produce a Warp knit fabric, and a cooperating electrode.

2. An electron discharge tube having an envvelope' containing an electrode comprising a

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