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The variation of the density profile shape of H-modes in ASDEX Upgrade is governed by time constants much larger than tau E. A method to determine these time constants is presented. Especially high density discharges with moderate heating and constant gas puff show very long phases of increasingly peaking density profiles which may not reach a steady state, although the H-mode pedestal remains constant during the peaking process. If heated more centrally with ICRH the peaking is strongly reduced and a steady state is reached. The behaviour can be well modelled using D approximately equal to 0.1chi and the neoclassical Ware-pinch. Strongly peaked density profiles lead to an earlier onset of neoclassical tearing modes (NTMs) in agreement with theoretical predictions of the strong influence of [gradient operator] n/n on the bootstrap current. Also for impurities an effect of the heat flux profile is observed: central heating with ECRH leads to a reduction of heavy ions in the plasma core.

Additional information

Authors: STOBER J ET AL, Max-Planck-Institut für Plasmaphysik, EURATOM Association, Garching (DE)
Bibliographic Reference: An article published in: Plasma Physics and Controlled Fusion, 44, (May 2002), pp.A159-A164.
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Record Number: 200214943 / Last updated on: 2002-07-09
Original language: en
Available languages: en