Confinement studies on the Wendelstein VII-AS stellarator

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Abstract
ECR heating at B0=2.5T has been extensively used in the 1990 experimental period of the W VII-AS stellarator. As it is a low-shear experiment the magnetic configuration (especially details of the rotational transform profile) depends sensitively on plasma currents (pressure driven, ohmic, EC driven, Ohkawa current) which in turn have a strong influence on energy and particle confinement properties. For the stationary phase a transport analysis has been performed, yielding the profiles of the electron heat conduction and the ion particle diffusion coefficients. The former was subjected to a statistical analysis resulting in phenomenological expressions for chi e and tau E. First experiments using neutral beam injection (ECRH target plasma) as well as combined heating (NBI+ECRH) are also discussed.