Thermal Deformation Analysis and Electron Beam Optics Simulation for a Thermionic Electron Gun Design

When the thermionic electron gun of the klystron operates, the structure around the cathode is subjected to thermal deformation due to the high operating temperature of the cathode. A thermal deformation analysis of the existing electron gun with ‘cold’ dimensions (dimension on fabrication) was done using the ANSYS code to get the ‘hot’ dimensions of the electron gun on operation. After that, the optics of the emitted electron beam were simulated using two codes (EGUN and CST-PS) for the two cases of the ‘cold’ dimension and the ‘hot’ dimension. We compared the beam trajectories of the above two cases to investigate the change in the physical quantities, which would have a strong effect on the klystron performance due to the thermal deformation. The thermal deformation was found to cause a perveance change as large as 15%. The scalloping behavior was also investigated with an applied magnetic field for the two cases of cold and hot dimensions.