Enhanced microwave pulse backscattering off externally excited lower-hybrid waves

Enhanced scattering is a sensitive diagnostic tool for detecting small-scale density fluctuations in small tokamaks as well as in laboratory plasmas with high spatial resolution. It makes use of a hybrid resonance in which the wavenumbers as well as the amplitudes of the incident probe wave and the backscattered wave increase strongly. The pulse (RADAR) modification of the enhanced scattering diagnostic additionally permits the measurement of the wavenumber spectra of the fluctuations. This method is experimentally studied on an RF generated linear discharge at which externally excited lower-hybrid waves serving as test fluctuations are diagnosed.