(TH/P3-10) Partial Stabilization and Control of Neoclassical Tearing Modes in Burning Plasmas

Abstract.  Neoclassical tearing modes (NTMs) are magnetic islands which increase locally the radial transport and therefore degrade the plasma performance. They are self-sustained by the bootstrap current perturbed by the enhanced radial transport. The confinement degradation is proportional to the island width and to the position of the resonant surface. The q=2 NTMs are much more detrimental to the confinement than the 3/2 modes due to their larger radii. NTMs are metastable in typical scenarios with β_N > 1 and in the region where the safety factor is increasing with radius. This is due to the fact that the local pressure gradient is sufficient to self-sustain an existing magnetic island. The main questions for burning plasmas are whether there is a trigger mechanism which will destabilize NTMs, and what is the best strategy to control/avoid the modes. The latter has to take into account the main aim which is to maximize the Q factor, but also the controllability of the scenario. In this paper we present different aspects of the above questions, in particular the role of partial stabilization of NTMs, the possibility to control NTMs at small size with little electron cyclotron heating (ECH) power and the differences between controlling NTMs at the resonant surface or controlling the main trigger source, that is the sawteeth.

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