Electron gun for a high power klystron

An electron gun for a high power klystron which includes a cathode which emits electrons; a focus electrode which, connected to the cathode through a supporting member composed of a material of high electric resistivity, makes the electrons emitted from the cathode produce an electron beam; and an anode which accelerates the electron beam produced by the focus electrode. The supporting member composed of a material of high electric resistivity may alternately be provided between the first and the second portions of the focus electrode, or between the cathode and the second focus electrode portion, wherein the two focus electrode portions are arranged adjacently to each other in the axial direction of the device, and wherein the first focus electrode portion is directly connected to the cathode.