Forward cw CO2-laser scattering on a high density plasma column

Wave-number and frequency spectra S(k,ω) associated with spontaneous electrostatic fluctuations in a high-density (5 x 1021 m-3) current-driven plasma are measured using forward CO2-laser scattering with homodyne detection. Scattering measurements during the quiescent plateau phase of the discharge show fluctuation levels several orders of magnitude above the thermal level with k-4 and ω-2 spectral amplitude dependences. The fluctuations are found to be isotropic in a plane transverse to the magnetic axis with S(k/sub parallel/,ω)<<S(k/sub perpendicular/,ω). The scattering apparatus is also shown to be a valuable diagnostic tool for basic studies of plasma current transport across magnetic field lines. In fact, a clear correlation is observed between the appearance of strong fluctuations and the rapid current penetration during fast plasma current reversal experiments. Finally, cw scattering results are used to find a set of experimental conditions suitable for the measurement of the ion temperature using a CO2 pulsed scattering system