Nonlinear Modeling of Kinetic Plasma

Many kinetic plasma instabilities, in quite di erent physical systems, share a genuinely similar mathematical structure near isolated phase-space islands. For this reason, dynamical features such as faster-than-exponential growth of the instability, as well as nonlinear frequency sweeping, are found to be universal. Numerical f methods, which follow the evolution of the (nonlinear) perturbed distribution function along single-particle orbits, have been applied to analytic models which include a continuous particle source, resonant particle collisions, and wave damping. The result is a series of codes which can reliably model the nonlinear evolution of kinetic instabilities, including some speci c to tokamak plasmas, over experimentally relevant timescales. New results include: (i) nonlinear simulations of two-species, one-degree-of-freedom plasmas; (ii) simulations of shbone bursts in tokamak plasmas; (iii) nonlinear modeling of beam-driven toroidal Alfv en eigenmode activity in tokamaks. Typeset using REVTEX present address: General Atomics, P.O. Box 85608, San Diego, CA 92186-5608 ypermanent address: Politecnico di Torino, 10129 TORINO, Italy.