W. Suttrop , F. Ryter , V. Mertens , O. Gruber ,
H. Murmann , H. Salzmann , J. Schweinzer and
ASDEX Upgrade Team
Max-Planck-Institut für Plasmaphysik, EURATOM-IPP Association,
D-85740 Garching, Germany
Abstract
H-mode operational boundaries and H-mode confinement are
investigated on ASDEX Upgrade . The local edge parameter threshold for H-mode
holds independent of divertor geometry and changes little with ion mass. The
deviation of the H-mode power threshold at densities near the
Greenwald limit can be understood as a consequence of a confinement
deterioration,
caused by ``stiff'' temperature profiles and lack of core density gradients
in gas puff fuelled discharges. Ion and electron temperature profiles can be
described by a lower limit of gradient length .
IAEA 1999