Ion cyclotron resonance heating on TEXTOR

Ion cyclotron heating on TEXTOR has now reached the Megajoule level. The heating scenario is normally mode conversion but occasionally minority heating in a D-(H) plasma. With appropriate wall conditioning by carbonization more than 1 MW of RF power has been injected for long pulse durations (approx. 1 s). The ICRF heated plasma is characterized by a quasi-stationarity of all plasma parameters, little or no impurity increase and a loop voltage reduction resulting in the total power coupled to the plasma reaching six times the remaining ohmic power input. Evidence of the coupling of the RF power to the plasma is obtained from the increase of the thermal load on the limiters and central energy deposition is supported from analysis of the sawtooth heating rate. The energy deposition profile appears to be broader than in the OH case. A detailed study of the global energy confinement time shows a degradation with additional RF heating which is found to scale with the power and the plasma parameters as in the case of neutral beam heating experiments performed in the L-mode regime with gettered walls. (author)