Sawtooth period control by power modulation
M. Lauret, E. Schuster, M. De Baar, F. Felici, M. Heemels, A. Gomes, T. Goodman, D. Kim, O. Sauter, G. Vandersteen, G. Witvoet, M. Lennholm
Division of Plasma Physics (DPP) Annual Meeting of the American Physical Society (APS)
Savannah, GA, USA, November 16-20, 2015
Abstract
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It is foreseen that long sawtooth oscillations will occur during ITER
H-mode scenar- ios leading to confinement loss and even disruptions.
Sawtooth period control is therefore crucial. Most sawtooth period
control approaches depend on changing the deposition location of
electron-cyclotron current drive (ECCD) near r(q=1). In contrast to
this, several TCV and AUG experiments with fixed ECCD deposition
location show that ECCD power modulation, either periodic or feedback
controlled, can lead to fast and reliable period control. To understand
this nonlinear phe- nomenon, a reduced and ‘hybrid’ reset model has
been derived that models the nonlinear dynamics. Analysis reveals that
the sawtooth period can be controlled by power modulation, even in the
case of significant model uncertainties or when there is a significant
lengthening effect of the fast particles on the sawtooth period, as
there will be in ITER. The model can also be used to design period
control using ICRH influencing this fast particle effect.