Simulation of Electron Density Profile Reconstruction on Ultrashort-Pulse Reflectometry

For the reconstruction of electron density profiles in the Sustained Spheromak Physics Experiment plasma, ultrashort-pulse reflectometry signals are numerically generated solving a one-dimensional wave equation by means of the central difference scheme. The signals cover an O-mode cutoff frequency range of 33--93 GHz. The lower frequencies (6--18 GHz) of a chirped waveform are up-converted to higher frequencies using four mixers. The reflected signals are down-converted to the lower frequency signals, thereby permitting band-pass filters to compute the time delays of different frequency components. A variety of density profiles are assumed to examine the performance of density profile reconstruction.