Microwave Scattering From an Underdense Turbulent Plasma

The bistatic radar cross section of an underdense, inhomogeneous turbulent plasma was measured at X‐band and the results were compared with a theoretical model. The turbulent plasma was formed by seeding a premixed ethylene‐oxygen flame in a combustion chamber and exhausting it through an expansion nozzle into a low‐pressure vessel. Electrostatic probes, biased for ion collection, were used to map the variation of the mean and rms electron density throughout the turbulent regions and to measure the correlation coefficient of the plasma fluctuations. A theoretical scattering model was constructed using the Born approximation and the results of the diagnostic measurement program. Good agreement between theory and experiment has been obtained for the dependence of cross section on bistatic angle and for the spectrum of fluctuations of the scattered microwave signal. The predicted cross section underestimates the measured cross section by 6 to 11 dB when the measured cross sections are in the range from 10−8 to 10−5 m2. The measured cross section was observed to have a square‐law dependence on electron density in agreement with the Born model for densities up to one percent of the critical electron density. For densities beyond this, the Born approximation breaks down and the cross‐section dependence becomes linear.