Speaker
Basil Duval
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1093.pdf
Plasma rotation and low-Z impurity transport across sawteeth in TCV
B.P. Duval, C. Marini, A. Karpushov, Y. Andrebe, O. Sauter and the TCV teama
Ecole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC)
CH-1015 Lausanne, Switzerland
The local particle and heat transport increase across sawteeth (ST) crashes in a tokamak
plasma is well documented. Although plasma momentum transport, often estimated from
radially resolved plasma rotation, is often modelled as a continuous process that depends on
the plasma parameters and their gradients, MHD has long been shown to strongly affect
TCV’s experimental profile, and that in many other machines. For similar conditions
(plasma shape density and temperature) the rotation profile gradient outside the ST-mixing
radius was seen to be reasonably constant whereas the average profile is flattened inside,
with what appeared to be a co-plasma current core-weighted additional component, and this
for a wide range of plasma currents. In the experiments reported in this paper, the natural
ST period (~2ms) was lengthened by precision X2 ECCD deposition close to the q=1
surface stabilising the ST to obtain regular ST periods in the range of 8-40ms. A diagnostic
neutral beam system based CXRS system measured the Carbon intrinsic impurity rotation
profiles, in the absence of a perturbing external torque, with a 2ms temporal resolution.
Acquisition was synchronised to the ST crashes where conditional resampling was then
particularly appropriate to decrease the measured rotation profile uncertainties. The ST
event was found to reset the rotation profile to similar values independently of the ST
period with the whole rotation profile then increasing at similar rates after each crash so
that the pre-ST profile peaks with increasing ST period. The behaviour of the ion
temperature and Carbon impurity density measured during the ST crash is also presented
showing that this low-Z impurity is preferentially evacuated from the plasma core,
compared to the Deuterium working gas. Together, these measurements underline how a
description and prediction of plasma rotation and impurity transport must include the effect
of ST and, most probably, all other strong MHD activity.
a See the author list of S. Coda et al, 2017 Nucl. Fusion 57 102011
