Submitted by jeffreyharris on Tue, 11/10/2020 - 17:29

M. Hirsch et al,  2000 Plasma Phys. Control. Fusion 42 A231

H-mode operation in the low-shear stellarator W7-AS is achieved for specific plasma

edge topologies characterized by three ‘operational windows’ of the edge rotational transform. An

explanation for this strong influence of the magnetic configuration could be the increase of viscous

damping if rational surfaces and thus island structures occur within the relevant plasma edge layer,

thereby impeding the development of an edge transport barrier. Prior to the final transition to

a quiescent state, the plasma edge passes a rich phenomenology of dynamic behaviour such as

dithering and ELMs. Plasma edge parameters indicate that a quiescent H-mode occurs if a certain

edge pressure is achieved.