US2217448A - Cathode - Google Patents

Description

Oct. 8, 1940. E. MULLER CATIIODE Filed March 19, 1938 WITNESSES:

INVENTOR E win Miller ATTORNE @earcn Patented Oct. 8, 1940 UNITED STATES Search PATENT OFFICE CATHODE Application March 19, 1938, Serial No. 196,924

Germany May 15, 1937 2 Claims.

The invention relates to cathodes and particularly pointed cathodes for high vacuum tubes.

An object of the invention is to provide a cathode whereby the value of the necessary anode potential to create a discharge is decreased.

Other objects and advantages of the invention will be apparent from the following description and drawing, in which Figures 1 and 2 are views partly in cross section and partly in elevation of tubes embodying the invention.

The invention concerns the utilization of a cold cathode and especially a pointed cathode since in such a case, by reason of the inhomogeneity of the electric field, a discharge is possible at low potentials, and also without an external source of energy providing a heating current for the cathode. The invention also includes a cathode, preferably constructed as a point, being sub-divided by means of cathode disintegration in an electric discharge into a large number of individual sub-microscopic fine points. A great decrease in the necessary operating potential is possible by this multiple sub-division of the oathode surface. It is desirable, of course, not to operate the cathode with too high current strengths because a too great specific current loading at the fine cathode points will ruin the points. The invention particularly concerns high vacuum tubes because the points are apt to be destroyed by the ion bombardment which takes place in the gas or vapor.

In Figure 1 is disclosed the discharge vessel I with an anode 2 and a pointed cathode 3. The vacuum-tight envelope has a tubulation indicated at 4 for the application of the pump or gas supply utilized in the formation of the tube. This tubulation 4 is preferably sealed off when the tube is ready for operation. The discharge vessel is preferably first filled with a gas, for example, argon, the pressure of which is preferably below 10- millimeters. A discharge is then passed between the cathode and anode for a relatively long time and the surface of the cathode points is coarsened by the rebound of ions. When this process is finished, the vessel is evacuated through the tubulation 4 which is sealed oif and the tube is ready for operation.

As materials for the cathode, high melting metals such, for example, as tungsten, tantalum or molybdenum are particularly suitable. Under certain circumstances the coarsened cathode surface may be vaporized with a light metal increasing the electron emitting activity such as barium, for example. Furthermore, an activation with thorium may also take place or a thoriated tungsten wire used for the cathode. By the activation of the cathode, the necessary operating potential value is further decreased and this decreased operating potential still further protects the very large number of tiny points on the oathode. The necessary operating anode potential may be volts and lower.

A heating of the cathode may be necessary under certain circumstances, such as for the purpose of degasifying the cathode or other measures necessary in the protection of the oathode. For such purposes, at least two cathode points may be arranged as illustrated in Fig. 2. A heating current may be supplied through the conductor 5, the contact point of the two cathode parts 6 and the conductor 1.

It may be desirable to provide the cathode not only with one but with a plurality or even with a large number of individual points which are connected in parallel with reference to the anode current. With this arrangement, a higher operating current is obtained while at the same time the maximum advantage of the efiect of the point in decreasing the necessary anode potential is obtained.

It is apparent that many modificaions may be made in the form, arrangement and application of the invention. Accordingly, it is desired that only such limitations be placed on the following claims as is necessitated by the prior art.

I claim as my invention:

1. The method of preparing a pointed cathode which comprises causing an electrical discharge in a gas between said cathode and a less pointed electrode until said cathode is surfaced with a large number of sub-microscopic small points, said gas being of less than 10- mm. pressure.

2. The method of preparing a pointed cathode which comprises causing an electrical discharge in a gas between said cathode and a less pointed electrode until said cathode is surfaced with a large number of sub-microscopic small points, said gas being argon of less than 10- mm. pressure.

ERWIN MtiLLER.

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