Nonlinear Phenomena of Plasma Waves Relevant to Inertial Fusion Energy

Jay E. Fahlen
Advisor: Warren Mori

Wednesday, February 24, 2010 at 2:00pm
Engr IV Room 67-124

Abstract:
Experiments soon to be performed at the National Ignition Facility require the understanding and control of stimulated Raman scattering (SRS) for their success. The SRS instability occurs when an incident laser decays into a backscattered light wave and an electron plasma wave. Recent computer simulations of SRS indicate that the daughter plasma waves have finite longitudinal and transverse extent and that they reach large amplitudes. The nonlinear behavior of such waves determines the growth, saturation, and recurrence of SRS. However, little attention has been paid to the behavior of plasma waves having these properties, and their study in SRS simulations is complicated by the large-amplitude light waves associated with the instability. Most theory and simulation work on SRS and its daughter plasma waves has been limited to infinite plane waves, often in the one-dimension limit. This thesis therefore studies isolated electron plasma waves over a wide range of parameters in one and multiple dimensions using particle-in-cell simulations. The simulations are performed with the goal of understanding the wave's behavior for parameters relevant to SRS. Accordingly, in all the simulations, an external ponderomotive driver generates traveling waves, driving them either continuously to study their peak amplitude and saturation mechanisms, or impulsively to study their propagation. Several novel effects are identified and characterized, including nonlinear resonance for driven waves, wave packet etching for finite-length waves, and localization and local damping for finite-width waves, among others. Where possible, simple physical models are proposed and carefully compared with the simulations over a wide range of parameters with the intention of deepening the understanding of plasma waves relevant to SRS.