On the determination of edge Ti profiles by a supersonic He beam in TJ-II

Abstract In the present work, a new diagnostic for the simultaneous measurement of ne, Te and Ti profiles at the edge of a fusion plasma is proposed and tested. First, the propagation of a supersonic He beam is self-consistently simulated from the electron parameter profiles reconstructed from the line ratio method. The radial profile of excited HeII ions, measured simultaneously with the HeI lines, is then compared with the simulated profile and the total effective ion loss rate from the observation volume is deduced, which is function of Ti and the local plasma parameters. The values so obtained are normalized to those from passive CX measurements (NPA). Steeper gradients and lower values are found in the Ti profile compared to those in the Te profiles. The implication of these findings in ion transport at the edge of the TJ-II stellarator is addressed.