Non-linear MHD simulations of sawteeth and their control by current and power depositions

Olivier Février (1, 2) , T. Nicolas (1) , P. Maget (2) , J-H. Ahn (3, 2) , X. Garbet (2) , H. Lütjens (4)

1 EPFL - Ecole Polytechnique Fédérale de Lausanne
2 IRFM - Institut de Recherche sur la Fusion par confinement Magnétique
3 Department of Applied Physics and Applied Mathematics [New York]
4 CPHT - Centre de Physique Théorique [Palaiseau]

Sawteeth in tokamak plasmas correspond to periodic relaxations of the temperature and density in the central region of the plasma, caused by the internal kink mode. They are a key player in core confinement and impurity transport in the central region of a tokamak discharge, and can trigger secondary instabilities. Being able to control their dynamics is therefore important. In this article, we explore by means of MHD simulations the control of sawteeth, relying on Electron Cyclotron Resonant Heating (ECRH) or Electron Cyclotron Current Drive (ECCD) deposition in the vicinity of the $q = 1$ surface. To do so, simulations with the full-MHD code XTOR-2F [1], which features power and current source terms mimicking the effects of ECCD and ECRH, are performed. Simulations show that deposition of current inside the inversion radius leads to an increase of the sawtooth frequency whereas deposition near or outside the inversion radius leads to a decrease of the sawtooth period. The modification of the sawtooth shape in presence of additional heating or current drive is also investigated. Finally, we briefly explore possible scenarios for the triggering of magnetic islands, and show that controlling the sawteeth can indeed help to prevent the triggering of tearing instabilities.

Domaines: Physique des plasmas [physics.plasm-ph]

Olivier Février, T. Nicolas, P. Maget, J-H. Ahn, X. Garbet, et al.. Non-linear MHD simulations of sawteeth and their control by current and power depositions. 2018. ⟨hal-01707731⟩