Speaker
Nils Leuthold
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1109.pdf
Investigation of the pump-out effect by resonant magnetic
perturbations in ASDEX Upgrade
N. Leuthold1, W. Suttrop1, M. Willensdorfer1, M. Cavedon1, M. Dunne1, L. Guimarais2, T.
Happel1, A. Kirk3, the ASDEX Upgrade4 and MST15 teams
1
Max Planck Institute for Plasma Physics,Boltzmannstrasse 2, 85748 Garching, Germany,
2
Instituto de Plasmas e Fusao Nuclear, Instituto Superior Tecnico, Universidade de Lisboa,
Portugal, 3 CCFE, Culham Science Centre, Abingdon, Oxon, OX14 3DB, U.K., 4 See A.
Kallenbach et al, Nucl. Fusion 57 (2017) 102015, 5 See H. Meyer et al, Nucl. Fusion 57
(2017) 102014
E-mail: nils.leuthold@ipp.mpg.de
Resonant magnetic perturbations (RMPs) are considered as an efficient method to mitigate
(in the sense of reduced stored energy losses) or suppress the Edge Localized Mode (ELM)
instability in tokamaks. However, a clear reduction of plasma density (‘pump-out’) is often
observed when RMPs are applied, which leads to deterioration of the H-mode edge pedestal
pressure and therefore reduced confinement.
Recent experiments in ASDEX Upgrade aimed to characterize the pump-out effect and its
parameter dependencies. When magnetic perturbations penetrate to resonant surfaces,
magnetic field lines and equipotential field lines get perturbed locally. This in turn can lead to
enhanced radial transport by changes in the ExB drift velocity [1]. In scans of the safety
factor, no singular behavior such as an increase of the RMP induced particle transport was
found if rational surfaces resonant with the magnetic perturbation were moved through the
zero crossings of the electron perpendicular velocity and radial electric field at the pedestal
top. If cross-field flows vanish at rational surfaces, no shielding currents for the MP are
induced, and therefore a resistive plasma response can develop.
In ELM suppressed H-modes, however, enhanced fluctuations in the edge transport barrier
region are observed with conventional reflectometers. Experiments with rigid rotations of the
RMP field reveal their toroidally asymmetric amplitude, indicating that the enhanced
fluctuation levels are an effect of the 3D perturbation field. Discharges with a modulation of
the RMP field strength were performed in order to identify the plasma layer in which particle
transport is modified by the RMPs. The phase profiles of the plasma density response to the
modulation suggest that particle transport is modified in the H-mode edge transport barrier
region. The implications of these observations for models of the pump-out effect will be
discussed.
[1] Heyn et al, Nucl. Fusion 54 (2014) 064005
