oward a multipacting-free cavity design for a very-high-frequency continuous-wave electron gun

very-high-frequency (VHF) photocathode electron gun serves as an electron source capable of generating high-repetition-rate, high-brightness electron bunches. It operates in continuous-wave mode with a 100\% microwave duty cycle, a configuration where multipacting emerges as a critical operational challenge requiring meticulous mitigation. The exponential amplification of secondary electrons within the electron gun may cause power dissipation, cavity material degradation, and beam quality deterioration, ultimately compromising both the performance and operational lifetime of the VHF gun. This study investigates the influence of radio-frequency (rf) cavity geometry and copper secondary electron yield on multipacting behavior through CST simulations. We present an equatorial cavity geometry exhibiting extremely low multipacting intensity, offering a promising approach for ensuring stable VHF electron gun operation.