Ion cyclotron range of frequency (ICRF) heating has been a reliable tool for steady-state plasma heating with high RF power of several tens of megawatts. However, a sudden increase in the reflected RF power during ICRF heating experiments with ELMy H-mode plasmas is an issue which must be solved for future fusion experimental devices or fusion reactors. This paper describes an innovative ICRF heating system using a frequency feedback control to reduce the reflected power in response to the rapid change in the plasma impedance in the ELMy H-mode plasma. A twin stub tuner has been newly invented for this purpose. The feasibility of keeping the reflected RF power fraction at a low level, e.g. 1%, is demonstrated even with a large change in plasma resistance, e.g. 2 ∼ 8Ω. Calculated and experimental results are presented for the conventional double stub tuner impedance matching system equipped with the twin stub tuner.
ICRF heating of TFTR plasmas fuelled by deuterium - tritium neutral beam injection