Plasma-launcher interaction during lower hybrid current drive and heating on JT-60

This paper describes the experimental investigation of the heat load on a lower hybrid (LH) launcher in divertor plasma. It was found that a good coupling of the reflection coefficient, ρ=15-20%, was obtained by pushing the launcher head a few mm from the first wall even though the distance δ between the separatrix and the launcher head was more than 10 cm. In this condition, the heat load on the launcher head rapidly decreased at δ>5 cm and was estimated to be about 0.4-0.6 kW/cm2 at δ=10 cm anti ne<2x1013 cm-3 during only LH injection. A higher heat load was observed on the ion side of the launcher guard limiter during combined NB+LH heating at anti ne>3x1013 cm-3 when fast ions were observed at the plasma edge due to parametric decay instability. We discuss the implication of these results with respect to LH application on a high power heated plasma. (orig.)