Stober, J, Sips, ACC, Angioni, C, Forest, CB, Gruber, O, Hobirk, J, Horton, LD, Maggi, CF, Maraschek, M, Martin, P, Mc Carthy, PJ, Mertens, V, Na, YS, Reich, M, Staebler, A, Tardini, G, Zohm, H, ASDEX Upgrade Team;

2007

July

Nuclear Fusion

The Role of The Current Profile In The Improved H-Mode Scenario In Asdex Upgrade

Validated

()

47

8

728

737

Recent studies at ASDEX Upgrade aim to further characterize and understand the physics of the improved H-mode scenario. The main focus is on the influence of the ramp-up phase of the plasma current and heating on energy confinement and MHD-activity during the subsequent flat-top phase. Depending on the ramp-up scenario two different stationary plasmas can be generated, which show different equilibrated current profiles, although external control parameters are the same in the flat-top phase. The difference of the current profiles in the flat-top phase seems to be due to different MHD-modes. These MHD-modes set in during relaxation of the current profile, which itself depends on the ramp-up scenario. Also the stored energy is different. in the two cases as is the peaking of the temperature profiles.. Three mechanisms seem to play a role in linking the observed changes in MHD-behaviour and current profile to the changes of the kinetic profiles: the increased transport due to the MHD-modes themselves, the variation of the ratio of magnetic shear s to safety factor q, which modifies the critical temperature gradient length for the onset of ion temperature gradients, and effects on the H-mode pedestal pressure..

DOI 10.1088/0029-5515/47/8/002