Three-dimensional gyrokinetic particle simulation of low-frequency drift instabilities

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Abstract
The nonlinear behavior of drift-wave fluctuations driven unstable by trapped particles and pressure gradients is studied using three-dimensional gyrokinetic plasma simulation methods. In the linear stages of instability, the growth rates and the radial and poloidal ballooning mode structures agree reasonably well with theory. Saturation of the unstable modes occurs principally through quasilinear profile modification and mode coupling. Results of the growth and saturation phase of the instability are compared with a bounce-averaged electron drift model. The resultant anomalous particle and energy diffusion are estimated using the saturated mode spectrum.