Speaker
Asger Schou Jacobsen
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1042.pdf
Investigating the effect of neoclassical tearing modes on fast ions in
ASDEX Upgrade: measurements and modelling
A. S. Jacobsen1 , B. Geiger1 , R. J. Akers2 , J. Buchanan2 , K. G. McClements2 , A. Snicker3 ,
V. Igochine1 , M. Salewski4 , M. Dunne1 , E. Poli1 , P. A. Schneider1 , G. Tardini1 ,
A. Jansen van Vuuren1 , M. Weiland1
the ASDEX Upgrade team and the EUROfusion MST1 team∗
1 Max-Planck-Institut für Plasmaphysik, D-85748 Garching, Germany
2 CCFE, Culham Science Centre, Abingdon OX14 3DB, United Kingdom
3 Department of Applied Physics, Aalto University, FI-00076 Aalto, Finland
4 Department of Physics, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark
Neoclassical tearing modes (NTMs) are pressure-driven MHD instabilities which degrade the
plasma performance and can lead to disruptions. They form at rational surfaces, typically ap-
pearing in plasmas with high βN values, and have been observed to be responsible for fast-ion
losses[1, 2, 3]. Here we present first measurements of the internal redistribution of neutral beam
injected fast ions caused by NTMs in ASDEX Upgrade, as inferred from tomographic recon-
structions and radial profiles of fast-ion Dα spectroscopy. Depending on its size and amplitude,
the NTM can cause a significant reduction of the fast-ion density. Neoclassical simulations using
an axisymmetric transport code have been performed, considering the NTM-induced modifica-
tion of plasma profiles, but not the structure of the magnetic perturbation itself. In this case the
simulated fast-ion transport is not sufficient to explain the observations and additional anoma-
lous diffusion is needed. This is especially the case for (m, n) = (2, 1) NTMs, where m and n
refer to the poloidal and toroidal mode numbers, respectively. To carry out more sophisticated
simulations, considering the 3D magnetic structure of the NTMs, we describe the perturbation
analytically, add it to the axisymmetric equilibrium and feed it into the full-orbit Monte Carlo
fast-ion codes LOCUST[4] and ASCOT[5]. The resulting predicted fast-ion redistribution is
presented and compared with the experimental results.
References
[1] H. E. Mynick, Physics of Fluids B 5, 1471 (1993)
[2] M. García-Muñoz et al., Nuclear Fusion 47, L10-L15 (2007)
[3] E. Poli et al., Physics of Plasmas 15, 032501 (2008)
[4] R. J. Akers et al., 39th EPS Conference & Int. Congress on Plasma Physics, P5.088 (2012)
[5] T. Kurki-Suonio et al., Nuclear Fusion 49, 095001 (2009)
∗ See author list of "H. Meyer et al 2017 Nucl. Fusion 57 102014"
