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F. Laggner, E. Wolfrum, M. Cavedon, M. Dunne, G. Birkenmeier, R. Fischer, M. Willensdorfer, F. Aumayr, -. EUROfusion MST1 Team, . ASDEX Upgrade Team:
"Plasma shaping and its impact on the pedestal of ASDEX Upgrade: edge stability and inter-ELM dynamics at varied triangularity";
Nuclear Fusion, 58 (2018), 4; 04600801 - 04600813.

behaviour of edge localised modes (ELMs) and the pre-ELM pedestal stability for different
plasma shapes. Generally, at higher δ the pedestal top electron density (ne) is enhanced and
the ELM repetition frequency (fELM) is reduced. For all δ, the pedestal top ne is already fully
established to its pre-ELM value during the initial recovery phase of the ne pedestal, which
takes place immediately after the ELM crash. The lowering of the fELM with increasing δ is
related to longer pedestal recovery phases, especially the last pre-ELM phase with clamped
pedestal gradients (after the recovery phases of the ne and electron temperature (Te) pedestal)
is extended. In all investigated discharge intervals, the pre-ELM pedestal profiles are in
agreement with peeling-ballooning (PB) theory.
Over the investigated range of δ, two well-separated fELM bands are observed in several
discharge intervals. Their occurrence is linked to the inter-ELM pedestal stability. In both
kinds of ELM cycles the pedestal evolves similarly, however, the `fast´ ELM cycle occurs
before the global plasma stored energy (WMHD) increases, which then provides a stabilising
effect on the pedestal, extending the inter-ELM period in the case of the `slow´ ELM cycle. At
the end of a `fast´ ELM cycle the ne profile is radially shifted inwards relative to the ne profile
at the end of a `slow´ ELM cycle, leading to a reduced pressure gradient. The appearance of
two fELM bands suggests that the pedestal becomes more likely PB unstable in certain phases
of the inter-ELM evolution. Such a behaviour is possible because the evolution of the global
plasma is not rigidly coupled to the evolution of the pedestal structure on the timescales of an
ELM cycle.

tokamak, H-mode, edge localised modes, plasma shaping, ELM behaviour