Design and Emission Uniformity Studies of a 1.5 MW Gyrotron Electron Gun

We present the design and initial operation of a 96 kV, 40 A Magnetron Injection Gun (MIG) for a 1.5 MW, 110 GHz gyrotron. A critical parameter for the successful application of this electron gun is the uniformity of electron emission. The I-V curve of emission, at a series of temperatures, is measured. Analysis indicates that the work function of the emitter is 1.6 eV with a (total) spread of 0.07 +/0.01 eV. Measurement of the azimuthal emission uniformity with a rotating probe indicates that the work function variation around the azimuth, the global spread, is 0.04+/0.02 eV. The spread due to local (microscopic scale) work function variations is then calculated to be 0.06 +/0.02 eV. Temperature variation can be ruled out as the cause of the observed emission nonuniformity.