[Zurück]

E. Wolfrum, F. Laggner, S. Keerl, J. Gnilsen, G. Birkenmeier, E. Fable, L. Guimaräis, F. Mink, -. EUROfusion MST1 Team, . ASDEX Upgrade Team:
"Pedestal particle transport during the ELM cycle at ASDEX Upgrade";
Poster: 44th EPS Conference on Plasma Physics, Belfast/United Kingdom; 26.06.2017; in: "Proceedings 44th EPS Conference on Plasma Physics, Europhys. Conf. Abstracts", 41F (2017), 979-10-96389-07; S. 1 - 4.

Edge localized modes (ELMs) appear in plasmas with steep pressure gradients in the edge
transport barrier. During an ELM crash the edge pressure relaxes, while heat and particles are
transported into the scrape-off layer (SOL) and to the divertor. Subsequently, the recovery of
the edge profiles of electron density (ne), electron temperature (Te) and ion temperature (Ti)
occurs on well separated time scales which have different durations [1,2,3]. The various
phases of the edge pedestal recovery are correlated with distinct signatures in the magnetic
signals at the mid-plane [2,4], changes in divertor conditions [5] and changes in the SOL
density at the high field side and the low field side [6].
A prominent feature of the inter-ELM pedestal development is the very fast recovery of the
pedestal top ne and Ti, which both occur before Te recovers. This behaviour has been found to
be universal at ASDEX Upgrade, i.e. at different collisionalities [2], for different isotope
species [7] and also for different plasma shapes [8]. The pedestal density behaviour is a
complex interplay of transport and sources. The divertor neutrals and the high field side high
density (HFSHD) region [9,10] influence the separatrix density. The SOL profiles determine
the transparency to neutrals and thus the ionisation source profile inside the separatrix, which
influences the gradient. Last but not least instabilities in the pedestal affect particle transport.
In this work, ELM resolved data at the mid-plane and in the divertor are analysed for an
exemplary ELM cycle. The measured profiles are modelled by the transport code ASTRA
[11] in order to determine whether a diffusively described particle transport changes during
the ELM cycle. The neutral source profile is not experimentally accessible and is therefore
modelled by four different temporal evolutions during the ELM cycle, taking into account
midplane or divertor SOL data. Also the energy of the neutral particles is changed so that the
modelling results can provide a comprehensive picture of the uncertainties of the obtained
diffusion coefficients.