Lower hybrid current drive experiments on Tore Supra in the ergodic divertor configuration

Abstract

Lower hybrid current drive experiments in the ergodic divertor (ED) configuration have been carried out on Tore Supra for 9 years (1991–1999). This paper gives an overview of the results regarding both the current drive and the divertor efficiencies: waves coupling, current drive efficiency and fast particle confinement, energy confinement, thermal load on the ED plasma facing components, impurity screening. It is shown that the coupling remains good enough for high power transmission up to 26 MW m−2. The current drive efficiency, measured on not fully non-inductive discharges, is only marginally affected by the loss of fast electrons due to the perturbed magnetic structure which is documented from hard x-ray measurements. Electron confinement follows, as in the limiter case, the Rebut–Lallia–Watkins scaling without any losses related to the width of the ergodic layer extending to 15% of the minor radius. The heat flux on the divertor neutralizers from both thermal particles and fast electrons accelerated near the antennae is detailed. Plasma contamination due to carbon and oxygen is analysed from a large database: it is shown that, for a large enough gap between the ED modules and the antennae, the contamination by these species is reduced by a factor of ∼3 with respect to the limiter case.