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M. Mauel, J. Bialek, C. Cates, H. Dahi,
D. Maurer, D. Nadle, G. A. Navratil, M. Shilov, and
E. Taylor
Department of Applied Physics, Columbia University New York, NY 10027, USA
Abstract. Observations of the suppression of the amplitude of tearing
instabilities through the application of synchronous (closed loop) and
asynchronous (open loop) resonant magnetic perturbations are reported. These
observations extend our previous investigations of large changes of tearing
mode rotation induced by oscillating currents in small saddle coils. Although
mode suppression is achieved using several techniques, the most significant
decrease in the size of a magnetic island occurs when the island is made to
rotate faster or slower than its natural frequency. By comparing measurements
with time-dependent simulations, we find the observed mode suppression is
consistent with a dynamic stabilizing effect proportional to the square of the
difference between the island's instantaneous and time-averaged rate of
toroidal rotation. Our results suggest that internal modes may be controlled
more effectively by inducing rapid modulations of island rotation than by
applying phase-controlled active-feedback.
IAEA 2001
