October 5, 2012, 12:00 pm - 1:00 pm

October 5, 12:00 pm - 1:00 pm

Calculating mode conversion by splitting rays

Dr. Steve Richardson, NRL

The ray optics (or WKB) approximation is the basis of the widely-used ray tracing method for simulating the propagation of electromagnetic waves in plasmas. The standard algorithm implemented in many ray tracing codes, however, cannot account for the transfer of energy between wave modes through the process of linear mode conversion. While mode conversion is accompanied by a local breakdown of the WKB approximation, methods have been developed which allow the mode conversion to be treated as a type of scattering problem; an incoming WKB wave splits into outgoing transmitted and converted WKB waves [Phys. Plasmas 14, 082102 (2007)]. In this talk, I will describe this scattering process, and how it can be used as the basis of a ray splitting algorithm. This splitting algorithm can identify the incoming and outgoing waves, and assign them the appropriate amplitudes and phases. By using this algorithm, ray tracing codes can now correctly handle linear mode conversion. Results using the code RAYCON will be shown for the example of mode conversion of RF waves in a tokamak [Plasma Phys. Control. Fusion 49, 43 (2007); http://github.com/arichar6/raycon].