Extremum-Seeking Stabilization of Neoclassical Tearing Modes in Tokamak Plasmas
W. Wehner, E. Schuster
Division of Plasma Physics (DPP) Annual Meeting of the American Physical Society (APS)
Atlanta, Georgia, November 2-6, 2009
Abstract
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Current injection by Electron Cyclotron Current Drive (ECCD) has been
proved experimentally as an effective method to stabilize neoclassical
tearing modes (NTM). The effectiveness of this method is limited in
practice by the uncer- tainties in the width of the island, the
alignment between the island and the EC beam, and the EC power
threshold for NTM stabilization. Heuristic search and sup- press
algorithms have been proposed and shown effective to improve the
alignment of the EC beam with the island by just using an estimate of
the island width. Making use of this estimate, a real-time,
non-model-based, extremum-seeking, optimization algorithm is proposed
in this work for EC beam steering and modulation in order to minimize
the time (control energy) required for NTM stabilization. A model is
proposed for the dynamic response of the island width to different
parameters of the EC beam such as alignment, width, power, modulation
duty-cycle and modulation phase. The efficiency of the proposed method
is compared with traditional search and suppress algorithms.