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 2.65 T 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 BT(0) = 3.41 T and f ≈ 32 MHz, 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 BT(0) = 2.65 T and f ≈ 52 MHz, 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.