Ordinary wave propagation in a tokamak with random density fluctuations

Electromagnetic waves with ordinary polarization, propagating almost perpendicularly to the magnetic field in a tokamak with random density fluctuations, are investigated numerically. The fluctuations are assumed to be located mainly at the plasma edge, as is appropriate for drift wave type fluctuations. The wave propagation in this fluctuating plasma is described in the limit of geometrical optics by a ray tracing code. Even low levels of relative density fluctuations (around 1%) result in significant scattering of the incoming wave beam. The variations in the wave intensity are investigated by analysing the relative dispersion of rays. Caustic formation is demonstrated in localized regions, where the amplitude predictions based on geometrical optics break down. A statistical analysis of the results is performed by tracing many rays for a wide range of fluctuation parameters and subsequently averaging the ray trajectories. The results may be relevant to tokamak plasma heating experiments and current generation schemes. Analytical results for the statistics of the ray propagation are presented for simplified geometries.