ECRH system upgrade design using dual frequency gyrotrons for EAST

Abstract The ECRH (Electron Cyclotron Resonance Heating) system was used in the EAST (Experimental Advanced Superconducting Tokamak) experiments for several years, and some good experimental results have been obtained. However, the performance of the gyrotrons is degraded and the ability to stabilize output RF (Radio Frequency) power is reduced. Two single-frequency 140 GHz gyrotrons are planned to be repaired in order to improve the performance of the gyrotrons. At the same time, some internal components of the gyrotrons (such as collectors, electron guns, mode conversion mirrors) will be upgraded to make the gyrotrons have the output capability of 0.6 MW/1 MW at 105 GHz/140 GHz. The MOUs (Matching Optical Units), transmission lines, the low voltage power supplies, the measurement and control system, and the water-cooling system also need to be modified for the dual-frequency operation of the new gyrotrons. The retrofitted design of the EAST ECRH system using dual-frequency gyrotrons is discussed in the paper. The upgraded ECRH system will be used for future EAST experiments to explore the range of low q95 and high βN, to study the steady-state operation mode for the future nuclear fusion power plants.