Cathode arrangement

In an electron beam source for electron beam evaporation, which source comprises an electron emission cathode for electron optical picturing without distortion when the cathode is heated and cooled, said electron emission cathode, comprising:

• an electro-conductive emission body defining an emission surface, said emission body having at least two spaced conductive terminals for applying an electric current through said emission body for heating said emission body by Joule heat, and said emission body having a slit pattern therein formed by two helically arranged slits running substantially one beside the other from a periphery of said body toward a central area of said body defining said emission surface, said slit pattern forming out of said emission body a helical current path to be heated by said Joule heat and extending between said spaced conductive terminals at said periphery for receiving electric current, said conductive terminals being at opposite ends of said helical path and at the periphery, said conductive terminals also being near each other on one side of said body with respect to a diameter of said body, and said conductive terminals being off-set with respect to each other, at said periphery of said body and by the diameter across said body.