Observation of fast and slow modes associated with ICRF heating in the TFR tokamak by CO₂laser scattering

Abstract

Using a CO2 forward-scattering experiment during ICRF heating in a D2-H2 plasma, fast and slow waves associated with the heating mechanism are observed. The fast wave, with long wavelength, is observed through a coupling between the fast wave and drift waves. A measure of the corresponding electric field is given. When approaching the ion-ion hybrid layer, the fast wave is slowed down and an electric field increase is observed (swelling) . Afterwards, the fast wave undergoes conversion and becomes a slow one, which is directly observed and analysed. Its corresponding electric field is measured. 'Sawtooth relaxations' are also observed on this signal. The importance of the hybrid layer and the rotational transform in the process is outlined.