Energetic Particle Physics with Applications in Fusion and Space Plasmas
Author: C.Z. Cheng
Energetic particle physics is the study of the effects of energetic particles on "collective" electromagnetic (EM) instabilities and energetic particle transport in plasmas. Anomalously large energetic particle transport is often caused by low-frequency MHD instabilities, which are driven by these energetic particles in the presence of a much denser background of thermal particles. The theory of collective energetic particle phenomena studies complex wave-particle interactions in which particle kinetic physics involving small spatial and fast temporal scales can strongly affect the MHD structure and long-time behavior of plasmas. The diffculty of modeling kinetic-MHD multiscale coupling processes stems from the disparate scales which are traditionally analyzed separately: the macroscale MHD phenomena are studied using the fluid MHD framework, while microscale kinetic phenomena are best described by complicated kinetic theories. We have developed a kinetic-MHD model that properly incorporates major particle kinetic effects into the MHD fluid description. For tokamak plasmas a nonvariational kinetic-MHD stability code, the NOVA-K code, has been successfully developed and applied to study problems such as the excitation of fishbone and Toroidal Alfvén Eigenmodes (TAE) and the sawtooth stabilization by energetic ions in tokamaks.
In space plasmas, we have employed the kinetic-MHD model to study the energetic particle effects on the ballooning-mirror instability which explains the multisatellite obervation of the stability and field-aligned structure of compressional Pc 5 waves in the magnetospheric ring current plasma.