Studies of the localization paradox of fluctuation reflectometry via multidimensional SOFTSTEP simulations (abstract)

The initial value problem of the scalar wave equation modeling the propagation and scattering of O modes in a fluctuating plasma is solved numerically. Using split operator and FFT techniques, SOFTSTEP codes solve the slow temporal envelope equations that describe fluctuation reflectometry in the presence of space and time varying density profiles. Previous studies have revealed an inexplicable sensitivity of the scattered phase signal to input microwave frequency. This might suggest that the fluctuations that give rise to the scattered signals are highly localized in space, much more so than one might expect on physical grounds. Our simulations attempt to resolve this paradox by demonstrating the existence of additional interference between various signals that contribute to the same measured phase. As the launching and detecting antennas are a few wavelengths wide, the measured phase is an average over their surface areas. This results in added sensitivity and wavelength selectivity which might be overcome if more than one detector is used to simultaneously measure the scattered signal at various angles.