[Zurück]

M. Dunne, L. Frassinetti, M. Beurskens, M. Cavedon, R. Fischer, G. Huijsmans, F. Laggner, R. McDermott, G. Tardini, E. Viezzer, E. Wolfrum, -. EUROfusion MST1 Team, . ASDEX Upgrade Team:
"Impact of nitrogen seeding on the AUG pedestal: experiments and modelling";
in: "Proc. 42nd EPS Conference on Plasma Physics, Europhys. Conf. Abstracts", Vol. 39E; EPS Conference on Plasma Physics, 2015, ISBN: 2-914771-98-3, S. 021091 - 021094.

Improved confinement with nitrogen seeding has been widely reported on AUG and JET in re-
cent years [1, 2]. However, despite intensive experimental and theoretical investigation on both
devices, an explanation for this phenomenology has thus far remained elusive. One currently
working hypothesis [3] for this effect starts with the assumption of a peeling-ballooning lim-
ited pedestal. When nitrogen is seeded, the edge current density is transiently reduced by the
increased Zeff, allowing access to a higher pedestal pressure gradient. This then propagates into
a higher thermal energy in the core plasma, which in turn acts to further stabilise the pedestal
via an increased Shafranov shift.
A set of experiments were carried out dur-
ing the last AUG experimental campaign with
the aim of experimentally testing this hypoth-
esis and providing data for modelling. Testing
of such a hypothesis involves both interpre-
tive and predictive modelling components to
verify the above mechanism.