IOP PUBLISHING and INTERNATIONAL ATOMIC ENERGY AGENCY NUCLEAR FUSION Nucl. Fusion 50 (2010) 054008 (11pp) doi:10.1088/0029-5515/50/5/054008 Effects of resonant magnetic perturbations on the dynamics of transport barrier relaxations in fusion plasmas M. Leconte 1,2 , P. Beyer 1 , X. Garbet 3 and S. Benkadda 1 1 International Institute for Fusion Science, CNRS-Universit´ e de Provence, Centre St. J´ erˆ ome, Case 321, 13397 Marseille Cedex 20, France 2 Physique Statistique et Plasmas, Universit´ e Libre de Bruxelles, Campus de la Plaine, CP 231 Bd du Triomphe, 1050 Brussels, Belgium 3 CEA/IRFM, 13108 St.Paul-Lez-Durance, France E-mail: michleco@ulb.ac.be Received 22 July 2009, accepted for publication 11 February 2010 Published 21 April 2010 Online at stacks.iop.org/NF/50/054008 Abstract The dynamics of transport barrier relaxation oscillations in the presence of resonant magnetic perturbations (RMPs) is investigated with a 3D global fluid code which simulates resistive ballooning turbulence in tokamak edge plasmas. The results reproduce qualitatively the stabilizing effect of RMPs and share common characteristics with ELM control experiments. It is found that this stabilization is due to a modification of the geometrical properties of the barrier. PACS numbers: 52.35.Ra, 52.25.Xz, 52.25.Fi, 52.55.Fa (Some figures in this article are in colour only in the electronic version) 1. Introduction In divertor tokamak plasmas, an edge transport barrier (ETB) forms during the transition from low to high confinement (L–H transition) when the heating power reaches a critical value P c [1]. Such a barrier is characterized by a strong pressure gradient at the plasma edge. The H regime is promising for the next generation of tokamak experiments such as ITER. However, an instability known as edge localized mode (ELM) develops usually as soon as the threshold P c is reached. ELMs are characterized by intermittent bursts in the heat flux, therefore causing the transport barrier to relax quasi-periodically. Over the last decade, the possibility of controlling ELMs has become more and more plausible, as recent experiments were carried out on DIII-D using I-coils [2, 3], on JET using error field correction coils [4] and on the TEXTOR tokamak using an ergodic divertor [5, 6]. These experimental studies obtained a qualitative control over the ELMs by imposing resonant magnetic perturbations (RMPs) at the plasma edge. However, a deeper understanding needs numerical analysis. Studies have contributed to the understanding of the effects of RMPs on the stability of so-called peeling–ballooning modes [7]. Numerical investigations were also performed using turbulence simulations with RMPs but no transport barriers [8–10]. The simulations [8, 9], restricted to an electrostatic model, revealed the presence of stationary E × B convection cells, and these features were also observed in [10] using a more general electromagnetic four field model. In [11], we presented numerical results showing the control of transport barrier relaxation oscillations by RMPs. The main conclusions of this previous paper are that RMPs have a stabilizing effect on relaxation oscillations, and that this effect is due mainly to a modification of the pressure profile linked to the presence of both residual magnetic island chains and a stochastic layer. Our electrostatic treatment of the plasma is a restriction in our model, since it does not permit modelling of plasma response currents, and implicitly supposes total penetration of the external fields into the plasma. However, note that in the experiments, the magnetic field lines are connected to the wall. This effect is not included in our model, but experimental observations show that the plasma current response to the RMPs is restrained by the large sheath resistivity which builds up at the wall intersection and the plasma magnetic response is 0029-5515/10/054008+11$30.00 1 © 2010 IAEA, Vienna Printed in the UK & the USA