US1955894A - Electron discharge apparatus - Google Patents

Description

April 24, 1934. SPENCER 1,955,894

ELECTRON DISCHARGE APPARATUS Filed July 16, 1928 I5 I l v INVENTOQ P5067 Jam/cs2 T'TOBNCY Patented Apr. 24, 1934 UNITED STATES PATENT OFFICE 7 1,955,804 amoraou msomaca maaa'rcs Delaware Application July 1c, 1928, Serial No. 293,214

2 Claims. (01. 250-475) My invention relates to electron discharge apparatus and more particularly to gas filled rectifiers. In a patent of Vannevar Bush, No. 1,880,014, dated September 2'7, 1932, having the same assignee as this case, is disclosed a gaseous conduction rectifier, in which a hollow cathode substantially encloses a plurality of cooperating anodes. To reduce the potential drop across the electrodes of this type of tube, various metallic vapors have been introduced, the most desirable being that of caesium, in addition to the usual inert gas content. However, for the caesium vapor to function, it is necessary that there be an adsorbed film on the cathode surface, and that the cathode be operated in such a way that this adsorbed film remain there.

With the ordinary tube, trouble has been experienced in retaining the film of caesium on the cathode surface. It seems that the bombardment of the cathode surface by ions of the rare gases or mercury, if used, results in stripping the caesium film from the surface. As this stripping action goes on, the drop through the tube increases. The heavier the current through the tube, and thus the more intense the discharge, the more rapidis the stripping action.

I have discovered that by treating the cathode surface in such a manner as to more firmly retain the caesium film thereon, that this stripping action is effectually eliminated and that intense discharges may occur without denuding the cathode surface of its coating.

Broadly I accomplish this by providing the bare cathode with a surface which is highly electronegative. The alkali vapors being electro-positive, are retained very tenaciously on said cathode surface by virtue of the interplay of electric forces between the atoms of the cathode surface and vapor.

Referring to the drawing, the single figure is a sectional view of a tube embodying my invention.

Within an evacuated envelope 1 of glass or other suitable material is a press 2 upon which are -mounted the various electrodes. Two anodes 3 are mounted on the press, lead wires 31 of which go through glass stems 15, upon which are mounted insulating lavas 4. The anodes may be of any suitable material as iron, aluminum, carbon, nickel, tantalum, etc. The insulators have mean free path spacing around the anodes as at 5 in order to protect them from bombardment. Surrounding the anodes is a cathode 7. The bottom of this cathode is composed of a dished metallic member 6, the inside portion of which surrounds the edges of the insulator and approaches to within mean free path-spacing of the anodes. Suitably supported as from the cathode 7 is capsule 9 which contains necessary chemicals for liberation of some alkali vapor, preferably caesium.

In accordance with usual practice, while the tube is being evacuated, this capsule is heated by bombardment and the vapor is liberated therefrom. Then, one or more gases, either of the rare group or hydrogen, is admitted to the desired pressure and the tube is then sealed. The top of cathode 7 is covered by screen 8, the purpose of which is to retain the region of discharge within the confines of the inner cathode surface.-

At the same time this screen allows the alkali vapor from capsule 9 to diffuse through the screen and enter the region of discharge, there to condense on the cathode surface and partake of the discharge in general. The cathode is connected by lead wire 1'7. The tube has the usual base 10 :Vitls prongs connected to the electrodes by the In order to retain the film of alkali vapor on the active surface of the cathode, I have found that by oxidizing this surface, the film is very tenaciously held thereon and allows a greater discharge. In one instance the cathode was composed of nickel, the inner surface of which was oxidized.

The coating of oxide may be formed by heating the cathode in the presence of air before assembly or by bombardment during evacuation. The surface becomes oxidized and thus adapted to retain an adsorbed layer of caesium tenaciously.

In this way the amount of caesium or other vapor released need not be as great as in prior devices because the amount present is more effectively used.

I claim:

1. A unidirectional gaseous discharge device comprising a gas tight envelope containing a gas, an anode, a hollow cathode enclosing said anode for maintaining in the enclosed cathode space a unidirectional discharge, a source of discharge promoting vapor supported outside said cathode above the same for supplying vapor upon heating, the upper side of said cathode comprising an extended wall portion including a plurality of perforations underlying said source adapted to permit free access of the vapor into the interior of the cathode but preventing extension of the discharge outside the interior of the cathode.

2. A unidirectional gaseous discharge device comprising a gas tight envelope containing a gas,

portion including a plurality of perforations underlying said source adapted to permit free access or the vapor into the interior of the cathode but preventing extension of the discharge outside the interior of the cathode.

PERCY L. SPENCER.

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