H-MODE OF W7-AS STELLARATOR

In W7-AS the H-mode has been observed for the first time in a currentl ess stellarator plasma. H-modes are achieved with 0.4 MW Electron Cycl otron Resonance Heating with 140 GHz at 2.5 T and high density, with 7 0 GHz at 1.25 T and lower density and with neutral beam injection. The H-phases display all characteristics known from tokamak H-modes inclu ding the development of an edge transport barrier, an increase of the poloidal impurity flow velocity at the edge, the reduction of edge tur bulence and ELMs. The power threshold for the H-mode seems to be lower than that in tokamaks and is in agreement With an n(e)B(T)BAR scaling . Major differences to the divertor H-mode is the small increase in en ergy content of maximally 30%, the lack of a strong isotope effect bot h in threshold and in H-mode characteristics and a peculiarly narrow o perational range in iota.