Experiments in W 7AS and projections to W 7X

Beginning October 1988, after magnetic surface mapping, first plasma experiments were conducted in the advanced stellarator W 7AS. During the first phase of operation, ECF 70 GHz was used to generate and heat a 'currentless' plasma, which was maintained in quasi-steady state for typically 0.5 s. Up to now the magnetic field had to be restricted to 1.25 T. Therefore, for second harmonic heating the accessible density range is determined by the cut-off density: n≤31019 m-3. Restricted by the density limitations for ECF-applications central values of β≤0.5% were achieved. Effects of the magnetic configuration on the confinement and measures to deal with the observed plasma current (bootstrap current) by ohmic heating and ECF-current drive were investigated. Preliminary results of transport analysis were compared with predictions of transport models. (orig.)