Patent ID: 7486009

Claim:
An electron gun, comprising: at least three emissive cathodes supported by electrode supports, a first electrode (G 1 ) and a second electrode (G 2 ) for control and shaping of the electron beam emitted by the cathode, a third electrode (G 3 ) for focusing or pre-focusing the electrons, and a fourth electrode (G 4 ) for accelerating the electron beam, wherein the first, second and fourth electrodes are made of a non-oxidizing alloy whose coefficient of expansion between 20° C. and 300° C. lies between 4×10 −6 /° C. and 13×10 −6 /° C. and wherein the third electrode is made of FeNi whose coefficient of thermal expansion is smaller than the coefficient of thermal expansion of G 1 , G 2 , and G 4 .