[Zurück]

L. Radovanovic, M. Dunne, E. Wolfrum, G. Harrer, M. Faitsch, R. Fischer, F. Aumayr, . ASDEX Upgrade Team:
"Developing a physics understanding of the quasi-continuous exhaust regime: pedestal profile and ballooning stability analysis";
Nuclear Fusion, 62 (2022), S. 08600401 - 08600412.

It has been experimentally observed that at ASDEX Upgrade (AUG) plasmas at relatively high
shaping, an increase of gas fuelling corresponds to an increase of the frequency and intensity
of the type-I edge localised modes (ELMs). At high enough fuelling, the plasma enters the
quasi continuous exhaust (QCE) regime.We have performed ideal ballooning n"#stability
analysis on four AUG discharges, comparing the type-I ELM dominated phases, with the
phases that are in the QCE regime. The results of this study show that as the gas puff increases,
the plasma gets more ballooning unstable in the pedestal region, especially very close to the
separatrix, at the pedestal bottom. On the contrary, in the middle of the pedestal, the discharges
are more ballooning stable. Here the locally negative magnetic shear has a stabilising effect on
ballooning modes, allowing access to the second stability region. Our analysis of the
ballooning stability and the con!nement factor H98 suggest that with optimisation of the
pedestal shape, good con!nement without type-I ELMs can be achieved. Necessary
ingredients are that the region of the highest pressure gradient is not ideal ballooning limited,
while the pedestal bottom is ballooning unstable. Ideal stability analysis of 36 simulated ITER
pro!les shows that, similarly to the experimental cases from AUG, a high pedestal top
pressure can be maintained concomitant with a ballooning instability at the pedestal bottom,
making QCE a promising scenario.

magnetic con!nement, pedestal stability, QCE regime, small ELMs, ballooning modes

http://dx.doi.org/10.1088/1741-4326/ac6d6a

https://publik.tuwien.ac.at/files/publik_304128.pdf