Code development for calculating electron beams in the cavities of the future high-power gyrotrons

This study develops a computational code for evaluating the operations of high-power gyrotrons with high-current electron beams. The analytical model describes the electromagnetic fields and electrons by the Maxwell equations and cold-fluid equations, respectively. Specifically, it estimates the output power of the gyrotron with electron-beam fluctuations, which occur under high beam currents. The effects of fluctuations of the intense electron flows in nonuniform magnetic fields are studied in a 1 MW gyrotron for electron cyclotron resonance plasma heating and current drive in large devices, such as the tandem mirror plasma device GAMMA10/PDX and the Large Helical Device (LHD). The rate of fluctuation growth of the electron beam and the output power of the high-power gyrotron with a fluctuated beam are calculated. In gyrotrons with a higher operating frequency (e.g., 154 GHz), significant deterioration of the electron beam and gyrotron operation is expected at beam currents exceeding 120 A. (author)