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 1MW 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. (C) 2019 The Japan Society of Plasma Science and Nuclear Fusion Research