Ultrashort-pulse reflectometry for density profile measurement of a steady state plasma

An ultrashort pulse reflectometry using an impulse generator as a source is applied to an inductively-coupled steady-state plasma. The reflectometer signal is directly recorded to a digitizing scope with 50 GHz bandwidth, and analyzed by a wavelet transform based phase extraction method and a tomographic method which relies on a row signal waveform rather than on the group delay of each frequency. The line-integrated values of reconstructed density profiles are in good agreement with those measured by a 4-mm interferometer. The results demonstrate the potential of current system for the time resolved density profile measurement of LHD plasmas as well as low temperature processing plasmas. (author)