Electron beam heated thermionic cathode

A thermionic cathode comprising:

• (a) a planar electron emissive body having a front and a rear electron emissive surface;
• (b) a planar heating body disposed adjacent said rear electron emissive surface for substantially uniformly radiatively heating said electron emissive body;
• (c) first means for variably heating said heating body to a temperature sufficient to effect heating of said rear electron emissive surface to an electron emission temperature;
• and
• (d) second means including means for variably applying a voltage between said emissive body and said heating body effective to cause electrons emitted by said rear electron emitting surface to flow to said heating body to heat said heating body to a temperature effective to raise the temperature of said front emissive surface to a temperature providing a predetermined rate of emission from said front emissive surface.

The method of providing a predetermined rate of electron emission from an emissive front surface of a thermionic cathode comprising the steps of:

• (a) providing an emissive rear surface on said cathode;
• (b) disposing a heating body adjacent said emissive rear surface for radiatively heating said cathode;
• (c) heating said emissive rear surface to an electron emission temperature;
• and
• (d) applying an adjustable voltage between said cathode and said heating body effective to cause electrons emitted by said emissive rear surface to flow to said heating body to heat said heating body to a temperature effective to raise the temperature of said emissive front surface to provide therefrom said predetermined rate of electron emission.