High power ICRF heating on the divertor tokamak ASDEX

Abstract

First ICRF experiments on ASDEX have been performed at 67 MHz, corresponding to 2 Omega _CH-heating of a hydrogen plasma at B₀=2.2 T. Despite divertor operation ICRH is accompanied by a significant increase of impurity production which can drastically be reduced by means of wall carbonisation. RF power up to 2.3 MW is routinely coupled to the plasma for pulse lengths of up to 1 sec. The RF heating is found to depend strongly on plasma preheating. In combination with neutral beam injection the ICRF heating efficiency is even higher than the one of NI. Confinement degrades with ICRH to values in between NI-L-type and OH confinement.