Author/Authors :
Grigull، نويسنده , , P. and Hirsch، نويسنده , , M. and Baldzuhn، نويسنده , , J. and Ehmler، نويسنده , , H. and Gadelmeier، نويسنده , , F. and Giannone، نويسنده , , L. and Hartfuss، نويسنده , , H.-J. and Hildebrandt، نويسنده , , D. and Jaenicke، نويسنده , , R. and Kisslinger، نويسنده , , J. and Koenig، نويسنده , , R. and McCormick، نويسنده , , K. and Wagner، نويسنده , , F. and Weller، نويسنده , , A. and Wendland، نويسنده , , Ch.، نويسنده ,
Abstract :
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 ⩾1020 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 Ti gradients and hence the E-field gradients, which effect can be compensated by higher density. The correlations found are fairly consistent when an E×B flow shear decorrelation of the turbulent transport is assumed.
