(TH/P8-9) Electromagnetic Self-Organization and Transport Barrier Relaxations in Fusion Plasmas

G. Fuhr1), S. Benkadda1), 2), P. Beyer1), 2), M. Leconte1), 2), X. Garbet3), I. Sandberg4), H. Isliker5), D. Reiser6), I. Caldas7), Z.O. Guimaraes-Filho7), S. Hamaguchi8), 1)
 
1)France-Japan Magnetic Fusion Lab., LIA 336 CNRS, France
2)P.I.I.M. Lab. , UMR 6633 CNRS Universite de Provence, Marseille, France
3)I.R.F.M., Ass. EURATOM, CEA, CEA Cadarache, France
4)N. T. U. A. , Ass. Euratom-Hellenic Republic, Dept of Electrical and Computer Engineering GR-157 73 Athens, Greece
5)Department of Physics, Aristotle University of Thessaloniki, GR-541 24 Thessaloniki, Greece
6)Institut fur Energieforschung-Plasmaphysik, Forschungszentrum Julich GmbH, EURATOM Ass., Germany
7)Universidade de Sao Paulo, Brazil
8)Center for Atomic and Molecular Technologies, Osaka University, Japan

Abstract.  In hot magnetized plasmas, the cross-field transport is dominated by the presence of instabilities which give rise to both, electrostatic and magnetic fluctuations. Experimental measurements of fluctuation levels on typical fusion devices reveal that magnetic perturbations are typically much smaller than electrostatic perturbations. However, as even small magnetic fluctuations can locally modify the topology of the magnetic surfaces, they play an important role with respect to the transport properties of the plasma. In this work, we show results from turbulence simulations at a tokamak plasma edge, realized with EMEDGE3D, a three dimensional global code in toroidal geometry. This code evolves self-consistently electromagnetic fluctuations as well as the pressure and E×B velocity profiles. The level of magnetic fluctuations is linked to the β parameter (the ratio between the kinetic pressure and the magnetic pressure). Using statistical tools (structure functions, Extended Self-Similarity), we analyze the impact of the electromagnetic fluctuations and we show that finite β effects may cause an increase of the irregularity in the redistribution of the energy in the turbulent cascade, leading in this way to an increased degree of intermittency. The competitive mechanisms (Reynolds and Maxwell stresses) that are responsible for the generation of the large scale flows, which regulate the level of the turbulent fluctuations in the plasma, are investigated. It is found that with increasing beta, the steady state component of the flow is reduced and replaced by an oscillatory behavior. We also focus on the dynamics of transport barriers at the plasma edge. The presence of a transport barrier is a key element of high confinement modes (H-modes) in fusion devices. In the present work we report the first barrier relaxations obtained in the general electromagnetic case including magnetic fluctuations effects. The main mechanisms inducing these relaxations in a purely electrostatic case are also present here, i.e., a transitory growth of a mode localized at the barrier center. In addition, peaks of the magnetic flux and strong magnetic fluctuations are associated to such relaxations events, in agreement with experimental observations.

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