Behavior of suprathermal electrons accelerated by the lower hybrid wave in the presence of giant sawteeth

The dynamics and localization of fast electrons accelerated by the lower hybrid wave in the presence of giant sawteeth are for the first time investigated by measuring the non-thermal Bremsstrahlung emission using a hard X-ray tomographic system recently installed on the TORE SUPRA tokamak [Equipe TORE SUPRA, in Proceedings of the 15. Conference on Plasma Physics and Controlled Nuclear Fusion Research, Seville (International Atomic Energy Agency, Vienna, 1995), 1, AIEA-CN-60 / A1-5, p. 105]. This study is carried out in high-density helium plasmas - ηe0 = 6.0 x 10+19 m-3 - strongly heated by several MW of ion cyclotron radio-frequency power, in the hydrogen minority scheme, together with 2-3 MW of LH power. While sawtooth activity is clearly observed on the thermal bulk contribution, no modulation is detected on the intensity of radiations emitted by the suprathermal population. This original effect is investigated in details experimentally, and also in the light of simulations of the lower hybrid wave propagation and absorption by using a ray-tracing code coupled with a two-dimensional relativistic Fokker Planck solver. (author)