Numerical Optimization of the Cusp Gun for a $W$ -Band Second-Harmonic Gyro-TWA

This paper is intended to propose the numerical methodology in optimizing the cusp gun for a 70-kV, 1-A W-band gyrotron traveling wave amplifier working at the second-harmonic TE
₂₁
mode. Two numerical methods using the simulated annealing algorithm (SAA) and genetic algorithm (GA) are adopted to perform the gun optimization. Classical electron optics software EGUN is employed to compute the beam trajectories. Maintaining the velocity ratio around 1.6, the axial velocity spreads optimized by SAA and GA are 1.44% and 0.33%, respectively, which means a great improvement compared with the manually optimized value of 2.78%. An analysis of the impact of parametric fluctuation on beam quality indicates that this cusp gun can be stably operated within a reasonable parameter scope. This paper will help to enhance the efficiency of electron gun design for gyrotron devices.