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

The spectral density function S(k,¿) associated with spontaneous turbulence in a current-driven plasma of medium density (ne = 10 19 - 10220 m -3) is measured with the scattering of the radiation of a cw low-power CO2- laser (P i¿2 W, ¿i = 10.6 µm). 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 n¯e/ne ~¿-2 has been found. It is consistent with the spectrum below 1 MHz as measured by optical probes.