Second harmonic deuteron heating in the ion cyclotron range of frequency (ICRF) was evaluated based on neutron measurements newly installed before a deuterium experimental campaign of the LHD. In deuteron plasmas, it was confirmed that the neutron emission rate increased with higher ICRF injection power. Fast deuterons with energy above 500 keV could be measured by a diamond neutral particle analyzer, when the minority proton ratio was less than 1%. On the other hand, a significant increase in the neutron emission rate, due to fast deuterons produced by ICRF second harmonic heating, was not observed, even in the case of ICRF superimposing on neutral beam injection (NBI). In experiments when the ICRF resonance layer was located near the magnetic axis, fast-ion driven instabilities due to the ICRF heating were observed for the first time at the LHD.
SEKI et al. (Wed,) studied this question.