Recent Advances in ICRF Heating of Mixture Plasmas: Survey of JET and AUG Experiments and Extrapolation to JET-DT and ITER

Full text: This contribution summarizes recent theoretical and experimental developments of a novel "three-ion species" heating scheme that have opened new promising avenues for the application of ICRF in fusion plasmas. Following successful proof-of-principle demonstration on the Alcator C-Mod and JET tokamaks, this scenario has also been recently established on AUG. A small amount of ³He ions (∼ 1% and below) was injected into H-D plasmas to absorb RF power and heat the plasma. In JET experiments, effective plasma heating was observed both at extremely low ³He concentrations of ∼ 0.1–0.2% (maximized fast-ion content) and at moderate concentrations of ∼ 1–1.5%. We further enhanced the efficiency for fast-ion generation and plasma heating by changing the configuration of ICRH antennas from dipole to +τ/2 phasing. Heating AUG plasmas with this ICRF scenario requires ³He ions to be less energetic than in JET. The combination of moderate ³He concentrations of ∼ 1% and off-axis ³He resonance was successfully applied to reduce fast-ion energies and thus improve confinement of RF-heated ions in AUG. ICRH modelling with the state-ofthe- art codes SCENIC and TORIC-SSFPQL has been used extensively to validate JET and AUG experimental observations. In a next-step,we also successfully demonstrated effective heating of JET H-D mixtures using the fast injected D-NBI ions as resonant "third" species. The scenariowas tuned such that D-NBI ions with injection energy of 100 keV absorbed most of launched RF power and were accelerated with ICRF up to ∼ 2 MeV. The observed 10-fold increase in the neutron rate and its temporal evolution were successfully reproduced with the time-dependent TRANSP modelling. The established technique of accelerating NBI ions in mixture plasmas to higher energies can be applied to generate alpha particles in D ³He plasmas and to maximize DT fusion reactivity. Finally, we conclude with a discussion of the application of these novel ICRF scenarios for future JET-DT and ITER operations. (author)