Speaker
Marc Goniche
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1057.pdf
Role of MHD activity triggered by fast ions in tungsten transport in JET
hybrid discharges
M.Goniche1, P.Buratti2, R.Dumont1, C.Challis3, J. Graves4, P.Jacquet3, E.Lerche5,
M.Mantsinen6, T.Pütterich7 and JET Contributors*
Eurofusion Consortium JET, Culham Science Centre, Abingdon, OX14 3DB, UK
1
CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France.
2
ENEA, C.R. Frascati, 00044 Frascati (RM), Italy
3
CCFE, Culham Science Centre, Abingdon, OX14 3DB, UK
4
1Barcelona Supercomputing Center(BSC),Barcelona, Spain
5
Laboratory for Plasma Physics, Brussels, Belgium,
6
EPFL, Swiss Plasma Center (SPC), CH-1015 Lausanne, Switzerland
7
Max-Planck-Institut für Plasmaphysik, Garching, Germany
MHD activity is known to be acting on impurity transport and in particular the sawtooth
crash is found to flush out the tungsten accumulated inside the q=1 surface. On JET, when
ICRH power is added to a NBI-heated H-mode discharge, the resulting increase of fast ion
pressure gradient inside the q=1 surface may trigger the fishbone instability. When a regime
with large amplitude and frequency span of the fishbones is achieved, the tungsten profile
peaking decreases strongly and flat profiles can be observed before the sawtooth crash.
In the hybrid scenario (Bt=2.8-3.2T, Ip=2.0-2.4MA, PNBI+ICRH=25-32MW) with on-axis
ICRH power exceeding 3MW, fishbones are also triggered in 40% of the 39 analysed
pulses. The fishbone structure (amplitude, frequency span, cycling time) varies during the
high power phase and the mode may alternate with the continuous (1,1) internal kink mode.
In that latter case, the tungsten peaking increases strongly with the continuous mode. On
average for this data base, it is found that the tungsten peaking of the pulses with fishbone
activity is lower than those with no fishbones and is compatible with operation at high
normalized beta (βN>2) for more than 4 s. In fishbone-free discharges, the tungsten
transport is found to be dominated by neo-classical transport unless tearing modes, mainly
with toroidal number n=2 or n=3, are triggered and strong tungsten peaking occurs in the
plasma core.
*See the author list of “X. Litaudon et al 2017 Nucl. Fusion 57 102001″
