Suprathermal Effects in ECRH Experiments on Thor Tokamak

ECRH experiments on the Thor Tokamak aimed at the investigation of r.f. absorption by suprathermal electrons are discussed. At the lowest densities (ne=3*1012 cm-3) the damping of the injected wave is shown to be dominated by a r.f. enhanced suprathermal population in the presence of a bulk with very low optical thickness, so that a rather pure suprathermal interaction regime occurs. At higher density, localization of heating is lost due to refractive effects and multiple reflections. No evidence is found of conversion into electrostatic electron Bernstein waves of the extraordinary mode propagating quasiperpendicularly from the inner side of the torus.