Nonlinear RF processes in plasma

This report is a final progress report for a research contract with Lawrence Livermore Laboratory entitled Nonlinear RF Processes in Plasma. The purpose of this research contract was to establish some understanding of nonlinear radiofrequency (RF) effects in magnetized and unmagnetized plasma environments driven by strong electromagnetic fields. This research was particularly directed at the development of a nonlinear ray tracing method. This method can be applied to vector wave propagation problems such as electromagnetic wave propagation in plasma. A key issue in this development was the treatment of the nonlinear term in the plasma wave equation by an equivalent nonlinear dielectric tensor epsilon sub 2 E vector, omega, x vector which could then fit into our basic formalism. Calculating a nonlinear dielectric tensor of this form for the relevant driven plasma systems was included as another theoretical task. This was effected by using a computer simulation method known as f-moving, whereby the distribution function f of a plasma system with RF fields present was simulated using an equilibrium distribution function f(sub 0) and directly integrating the Vlasov equation along characteristics in order to obtain the perturbed distribution function f. This approach results in a relatively inexpensive but accurate method for obtaining the plasma response including parametric instabilities caused by strong RF drive. From these simulations, the equivalent epsilon sub 2 could be calculated and used in the nonlinear ray tracing. A third task in this contract was the integration of these techniques (the f-moving and nonlinear ray tracing) to generate a complete ray tracing package for the simulation of lower hybrid wave propagation in compact toroids. The results of these investigations are described below, separated into the three tasks.