US2189998A - Tube electrode - Google Patents

Description

Feb. 13, 1940. D. SCHENK 2,189,998

TUBE ELECTRODE Filed July 16, 1936 Fig.3 fig. 2

Ana-5r INVENTOR DAN KWART SCHENK ATTORNEY Patented Feb. 13, 19 40 FFlCE,

TUBE ELECTRODE Dankwart Schenk, Berlin-Reinickendorf, Germany, assignor to Allgemeine Elektricitats- Gesellschaft, a corporation of Germany Application July 16, 1936, Serial No. 90,837

In Germany July 29, 1985 i I Claims. 01. 250-475) This invention relates to tube electrodes and inv particular to a new, useful, and improved electron emitting cathode for use in electron discharge tubes.

This invention is concerned with a method and means adapted to operate electron-optic discharge vessels whose cathodes operated either upon the heating or photo-electric principle are to be imaged upon a fluorescent screen by the aid of electrons issuing therefrom. The cathodes are here activated frequently by the application of a very tenuous metallic coat or film, say, of barium or caesium, especially where an investigation of the structure of the cathode material is concerned. These thin metallic films, however, are of but short life. In fact, they are subject to destruction due to vaporization and also ionic bombardment, and the result is that the entire cathode and thus also the discharge tube itself are rapidly rendered unserviceable.

Now, this drawback may be obviated by that, according to the idea underlying the present invention, the electron-emissive material is constantly and uninterruptedly replenished by the fact that, during the very operation of the tube, it is produced upon an auxiliary electrode whence it is transferred onto the cathode to be investigated or to be imaged by virtue of evaporation. The life or" the cathode is thereby greatly increased, for it depends no longer upon the quantity of active material placed upon it, but upon the supply of material capable of being accom The active metal vapor is preferably produced by the heating of the auxiliary electrode or else by virtue of electrolysis. What is important in all arrangements is that the auxiliary electrode carrying a supply of active material is so dis- .posed in the electron-optic discharge tube that the fields" of potential prevailing between the cathode and the rest of the electrodes constituting a lens system will not be disturbed.

Figs. 1a and 1b show in side and front elevation a cathode arrangement of the kind serviceable, for instance, for electron-optic structure investigations. The cathode l which is ,to be examined, by the use and aid of lens electrodes tron-emissive material,

(or electrodes possessing lenticular actions) is to be imagedupon a fluorescent screen (also not shown). The cathode is here of the incandesced type. The heating current is supplied to it at 2.

In order to insure a constant potential field, the cathode, as known from the prior art, is surrounded by a ring or shield 3 which. is kept at cathode potential. This ring has an annular slit 5 below which the auxiliary electrode 4 of groove v shape is disposed which serves to accommodate 10 the supply of eleotron-emissive material. The said annular groove is heated by means of a current supplied at ends 5, 5. The groove 4 itself is connected at one point with the shield 3 so that it is substantially at the same potential as the shield.

Fig. 2 shows an arrangement in which the groove-shaped auxiliary electrode 4 surrounds the anode ll (auxiliary anode, gun, or accelerator anode) in the form of a ringand has the same voltage as the anode 6. Through a slit provided in the cylindrical shell of the anode, the elecwhen electrode 4. is heated by means of an electriccurrent supplied at 5, flows into the interior of the cyllndrical anode or gun, whence it is able to reach the cathode.

Another exemplified embodiment is illustrated in Fig.13 of the annexed drawing. In this instance, a small area is recessed in the anode 5 which area is replaced by the auxiliary electrode' l which also is here of planar form. The

storage or supply electrode also in the present instance is at anode potential, and it is heated by the aid of a current supplied at 5, 5. Also in r this arrangement the potential field set up between the cathode I andthe gun 6 will not be influenced by the accommodation in the assembly of the supply electrode 4.

The evaporable material consists preferably of a light metal compound which is capable of being decomposed thermally with great ease, more parthen preferably in the form of a small cup or of a groove into which projects a second electrode planar end apertured and lying in the same plane as the disk, and storage means spaced from 'said disk holding an easily decomposable metallic compound positioned symmetrically about the disk, said storage means being adapted to deposit emissive material onto said disk by decomposition of the stored metallic compound.

' 2. An electron emitter comprising an apexed filametary heater, a disk aflixed to the apex of the heater, a cylindrical electrode planarly closed at one end and positioned coaxially with the axis of said disk, said electrode having its planar end apertured and lying in the same plane as the disk, storage means positioned coaxially with the axis of said disk for holding an easily decomposable metallic compound and means for electrolytically decomposing the metallic compound.

3. An electron emitter comprising an apexed filamentary heater, a disk afiixed to the apex of the heater, a cylindrical electrode planarly closed at one end and positioned coaxially with the axis of said disk, said electrode having the planar end apertured and lying in the same plane as the disk, storage means positioned coaxially with the axis of said disk for holding an easily decomposable metallic compound and electrical heating means for decomposing the metallic compound.

4. An electron emitter comprising an apexed filamentary heater, a disk member operatively associated with said heater and having thereon an electron emissive material, a cylindrical shield electrode substantially embracing said disk memher, and at least one holding means positioned adjacent said disk and containing an easily decomposable metallic compound, said electron emissive material and said metallic compound being independently spaced apart whereby decomposition 01' said metallic compound deposits emissive material onto said disk member.

5. Apparatus in accordance with claim 4 wherein there is provided in addition means for decomposing the metallic compound.

DANKWART SCHENK.

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