Edge transport barrier formation and ELM phenomenology in the W7-AS stellarator
In NBI discharges with density ramps in W7-AS, the quiescent H-mode is restricted to the same ranges of the edge rotational transform as in ECRH discharges and occurs above threshold densities = 10(20) m(-3) which increase with heating power. Higher power needs higher density for stabilization. The approach to the quiescent H-mode often occurs, with increasing density and decreasing power flow through the edge, from grassy through dithering states to bursts of ELMs and, in a few cases, quasi-periodic ELMs. This goes parallel with increasing radial gradients of the plasma pressure and E-field at the edge. Higher heating power reduces in particular the T(i) gradients and hence the E-field gradients, which effect can be compensated by higher density. The correlations found are fairly consistent when an E x B flow shear de-correlation of the turbulent transport is assumed.
Bibliographic Reference: An article published in: Elsevier; Journal of Nuclear Materials, 290-293 (2001) pp.1009-1012
Availability: An article published in: Elsevier; Journal of Nuclear Materials, 290-293 (2001) pp.1009-1012
Record Number: 200013452 / Last updated on: 2001-06-27
Original language: en
Available languages: en