COMPUTATIONAL STUDY OF ULTRA-SHORT-PULSE REFLECTOMETRY

Ultra-short-pulse reflectometry is studied by means of the numerical i ntegration of a one-dimensional full-wave equation for ordinary modes propagating in a plasma. The numerical calculations illustrate the pot ential of using the reflection of ultra-short-pulse microwaves as an e ffective probe of the density profile even in the presence of density fluctuations in a plasma. The difference in time delays of differing f requency components of the microwaves can be used to deduce the densit y profile. The modification of the reflected pulses in the presence of density fluctuations is examined and can be understood based on consi derations of Bragg resonance. A simple and effective profile-reconstru ction algorithm using the zero-crossings of the reflected pulse and su bsequent Abel inversion is demonstrated. The robustness of the profile reconstruction algorithm in the presence of a sufficiently small-ampl itude density perturbation is assessed. The reconstruction algorithm b egins to fail when the scaled density perturbation is large enough to invalidate the first Born approximation description of scattering by d ensity fluctuations.