Collective scattering of CO2-laser light from ion-acoustic turbulence

The spectral density function S(k,w) associated with spontaneous turbulence in a current-driven plasma of medium density (ne = 1019−10220 m −3) is measured with the scattering of the radiation of a cw low-power CO2- laser (Pi≃2 W, li = 10.6 mm). Optical homodyne detection has been used. A remarkable result is that the level of fluctuations with wave vectors k∥B is close to thermal; B is the magnetic field for plasma confinement. The level of fluctuations with k⊥B is several orders of magnitude larger than the thermal level. The phase velocity of these fluctuations is equal to the ion-acoustic velocity. A power law spectrum of the form n̄e/ne∼w−2 has been found. It is consistent with the spectrum below 1 MHz as measured by optical probes.