Fast ions in mode conversion heating ( ³He)-H plasmas in JET

Fast ions were analysed in experiments focusing on fundamental ³He minority and mode conversion (MC) in the ion cyclotron resonance range of frequencies (ICRF) in H plasmas and on second harmonic heating of ³He ions at 2.65T mimicking D-T plasma heating in ITER at half its nominal toroidal magnetic field. Gamma-ray spectrometry, neutral particle analysers and fast-ion loss diagnostics provided information on the generation of fast-ion populations and on the distribution of ICRH power among the species in various heating scenarios and for a large range of ³He concentrations. In the scenario with the fundamental ³He minority and MC wave heating at B _T(0)=3.41T and f32MHz, fast ³He ions accelerated by ICRH in the MeV energy range were detected in discharges with low ³He concentration. In the experiments with a ³He concentration scan it was found that at a ³He concentration of 2.2% the ³He ion losses disappeared while a population of energetic D ions gradually built up due to a redistribution of the ICRH power between species on reaching the first MC regime. Under those conditions the ICRF-heated D beam ions effectively absorbed the wave power at their Doppler shifted resonance, which was close to the plasma centre. In discharges with second harmonic heating of ³He ions at B _T(0)=2.65T and f52MHz, the confined energetic ³He ions were found in the MeV energy range. There is some evidence that the D ions were also accelerated by ICRF. This paper also demonstrates that the synergy of the various fast ion diagnostics allows making a broad picture of the physics of the redistribution of the absorbed ICRH power in complicated heating scenarios of JET.