Destabilization of Fast Magnetoacoustic Waves by Circulating Energetic Ions in Toroidal Plasmas
Authors: V.S. Belikov, Ya. I. Kolesnichenko, and R.B. White
Date of PPPL Report: August 2003
Published in: Physics of Plasmas 10 (December 2003) 4771-4775.
An instability of fast magnetoacoustic waves (FMW) driven by circulating energetic ions in axisymmetric toroidal plasmas and characterized by the frequencies below the ion gyrofrequency is considered. An important role of the l = 0 resonance (l is the number of a cyclotron harmonic) in the wave-particle interaction is revealed: It is shown that this resonance considerably extends an unstable region in the space of the pitch-angles of the energetic ions and the wave frequencies. The analysis is carried out for a "slow" instability, which has the growth rate less than the bounce frequency of the energetic ions. Specific examples relevant to the National Spherical Torus Experiment (NSTX) [J. Spitzer et al., Fusion Technol. 30 (1996) 1337], where instabilities of this kind were observed, are considered.