Nonlinear theory for fishbone modes
- Polytechnic Institute of Turin (Italy)
- Univ. of Texas, Austin, TX (United States); and others
We present a nonlinear theory for fishbone activity, on the basis of a recently developed weak turbulence model of beam driven plasma waves with a discrete spectrum near the instability threshold. Fishbone oscillations are triggered by an internal kink mode driven unstable by the resonant interaction with trapped fast ions. We focus on the regime where the mode frequency is close to the thermal ion diamagnetic frequency. In this regime, a (stable) internal kink mode exists in the absence of the fast ions, which can therefore be treated perturbatively. A Lagrangian formalism for the nonlinear wave-particle interaction is used. The oscillatory behavior of the resonant ions trapped in a finite amplitude toroidal wave is discussed on the basis of a nonlinear pendulum model. Numerical estimates of saturation levels and resonant fishbone losses for present Tokamak experiments are obtained.
- DOE Contract Number:
- FG03-96ER54346
- OSTI ID:
- 489453
- Report Number(s):
- CONF-960354--
- Country of Publication:
- United States
- Language:
- English
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