1 EX / P 6-8 Studies of Alfven Eigenmodes in the ITER Baseline Scenario , Sawtoothing JET Plasmas , and MAST Hydrogen-Deuterium Plasmas

Modelling with the HAGIS code is performed to compute stability of α-particle-driven TAEs and redistribution of α-particles in the 15 MA baseline ITER scenario. For this modelling, 129 TAEs with n’s from 1 to 35 were computed with the MISHKA code, and their damping was assessed with the CASTOR-K code. The self-consistent evolution of TAEs and α-particles results in TAE saturation amplitudes dBr/B0=3×10 -4 , with stochastic transport of α-particles localized in a narrow core region, and with α-particle redistribution beyond r/a=0.5 being minimal. Whilst these results are positive, their sensitivity to the sawtooth model used raises the issue of the hierarchy of various α-particle-driven Alfvén Eigenmodes (AEs) throughout the sawtooth cycle as well as the issue of re-distribution of α-particles by the sawtooth itself. Experiments on fusion products performed in JET sawtoothing plasmas give an indication of how AEs could vary throughout the sawtooth cycle in ITER. In these JET experiments, TAEs, EAEs, NAEs, and Alfvén Cascades were observed throughout the sawtooth cycle. Most often, core-localized TAEs inside the q=1 radius precede a sawtooth crash and cause a gradually increasing fast ion re-distribution/ losses seen in 2D -camera and scintillator. The sawtooth crash itself causes a strong short burst of lost fast ions followed by EAEs outside the q=1 radius, with EAE-induced losses. An inverse correlation between sawtooth crash times and sawtooth periods, crash (saw) - , 1≤ ≤2, is found using ECE diagnostics with ≤10 μs time resolution, facilitating the development of a model for sawtooth re-distribution of α-particles. In the field of energetic particle instabilities driven by velocity gradients, two recent developments are reported: i) a study of EAEs with n =0 observed in JET discharges, and ii) a study of compressional AEs (CAEs) in plasmas with mixed hydrogen isotopes. In the second case, deuterium-hydrogen plasmas with NBI-driven CAEs were obtained on MAST. A strong suppression effect of the D-H mixture was observed on CAEs in the ion-ion hybrid frequency range, BD< < BH; a similar effect may be expected in D-T plasmas.