[Zurück]

L. Frassinetti, M. Dunne, U. Sheikh, F. Orain, M. Bernert, G. Birkenmeier, P. Blanchard, D. Carralero, M. Cavedon, S. Coda, R. Fischer, M. Hoelzl, F. Laggner, M. McDermott, H. Meyer, A. Merle, C. Theiler, K. Verhaegh, E. Viezzer, E. Wolfrum, . ASDEX Upgrade Team, TCV Team, -. EUROfusion MST1 Team:
"Role of the scrape-off layer in the typeßI ELM dynamics in AUG and TCV";
Poster: 44th EPS Conference on Plasma Physics, Belfast/United Kingdom; 30.06.2017; in: "Proc. 44th EPS Conference on Plasma Physics, Europhys. Conf. Abstracts", 41F, 5.135 (2017), 979-10-96389-07; S. 1 - 4.

Recent results from the metal wall machines JET-ILW [1] and AUG [2,3] have shown that
the fast collapse of the pedestal energy during an ELM (time scale <1ms) can be followed by
a second collapse characterized by a longer time scale (≈2-5ms). Experimental results show
that the second collapse tends to disappear when nitrogen is seeded [1,2,3] and/or good
confinement is achieved [4]. These observations, due to the fact that N seeding leads to the
increase of the electron pedestal temperature Te
ped [5,6,7] might suggest that the presence of
the second collapse is correlated to low Te
ped. More recently, an empirical correlation
between the pre-ELM divertor temperature (Tdiv) and the energy losses of the second collapse
has been observed in AUG [3]. This has suggested that the divertor and/or the scrape-off
layer conditions can play a role in the ELM dynamics, as also noted in [2,4]. To date, the
origin of the second collapse is not clear yet and several questions are still open:
 is the second collapse correlated to Te
ped or to the pedestal pressure or to any pedestal
plasma parameter related to the temperature (such as resistivity or collisionality)?
 can the second collapse disappear only when the seeded species is nitrogen?
 is the presence of the second collapse correlated to the divertor and/or SOL conditions?
This work will try to answer these questions by investigating the ELM behavior in AUG and
TCV for plasmas in which nitrogen and neon have been seeded and in deuterium fuelling
scans.