Speaker
Michail Anastopoulos-Tzanis
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1047.pdf
Perturbative 3D Ideal MHD Stability of Tokamak Plasmas
M.S. Anastopoulos-Tzanis 1,2 , B.D. Dusdson 1 , C.J. Ham 2 , C.C. Hegna 3 ,
P.B. Snyder 4 , H.R. Wilson 1,2
1) York Plasma Institute, Department of Physics, University of York, York, YO10 5DD, UK
2) Culham Science Centre, Abingdon, Oxon OX14 3DB, UK
3) Departments of Engineering Physics and Physics, University of Wisconsin-Madison,
Madison, Wisconsin 53706, USA
4) General Atomics, San Diego, California 92186-5608, USA
Control of edge localised modes (ELMs) is required for ITER to prevent damage to the di-
vertor. One method of control is the application of non-axisymmetric resonant magnetic per-
turbations (RMPs). Experimentaly either ELM mitigation (increase of frequency) or complete
suppression (removal) is seen. However, the physics mechanism responsible for the occurrence
of those states is still an open question. In this work, the non-axisymmetric part of the equilib-
rium is postulated to have the key impact on MHD instabilities, potentially modifying stability
boundaries. Linear perturbation theory is employed to study the 3D ideal MHD stability follow-
ing the formalism of [C.C. Hegna, Physics of Plasmas 21, 2014]. The symmetry breaking due
to the non-axisymmetric equilibrium geometry induces toroidal mode coupling. A numerical
framework for the calculation of coupling is developed, based on the ideal MHD stability code
ELITE [H.R. Wilson et al., Physics of Plasmas 9, 2002] that provides axisymmetric toroidal
modes and fixed boundary non-axisymmetric equilibria. To validate result, the nonlinear MHD
code BOUT++ [B.D. Dudson et al., Computer Physics Communications 180, 2009] is employed
to simulate mode coupling and qualitative agreement is observed. The external 3D field has a
strong impact on stability above a certain threshold and decrease of MHD growth rates was
observed due to stronger coupling with higher toroidal modes. Such a result could provide vital
insight for understanding the exact mechanism responsible for ELM suppression and optimal
RMP coil design.
The author wishes to thank all collaborators for fruitful discussions and advice. This work has been
carried out within the framework of the EUROfusion Consortium and has received funding from the
Euratom research and training programme 2014-2018 under grant agreement No 633053 and from
the RCUK Energy Programme [grant number EP/P012450/1], as well as the Fusion CDT programme
through the EPSRC grant [EP/L01663X/1]. To obtain further information on the data and models under-
lying this paper please contact PublicationsManager@ukaea.ac.uk.
