SCALAR RADIATIVE TRANSPORT MODEL FOR MICROWAVE SCATTERING FROM A TURBULENT PLASMA

The scalar radiative transport equation is solved in an iterative manner for the backscattered reflected intensity. A model for the direct and cross-polarized cross section is derived in terms of the first two terms of the iterated series. Model calculations agree to good approximation with an experiment where microwaves are scattered from a turbulent plasma column. At very low plasma density fluctuations (less than 0.01 of the critical plasma density) a single scatter regime exists where the direct cross section is proportional to the square of the plasma density fluctuations and the cross-polarized cross section is much less than the direct cross section. As the fluctuations increase, this single scatter regime is followed by a regime where multiple scattering makes a significant contribution to the backscattered signal; here, the magnitude of the cross-polarized cross section is approximately 0.1 of the magnitude of the direct cross section. Finally, when the plasma density fluctuations are about 0.1 of the critical plasma density, the wave is strongly attenuated by scattering and the cross sections saturate as a function of the plasma density fluctuations. The model also predicts the observed variation of the cross section with angle of incidence. Suggestions for future work are made.