Measurement of lower hybrid drift fluctuations in the boundary layer of a high-beta plasma by collective CO₂laser light scattering

The wavenumber and frequency spectrum of LHD-instabilities were measured by coherent CO2 laser light scattering in the boundary layer of a theta-pinch plasma. The 9-m-long theta pinch produced a stationary plasma for up to 20 μs. These conditions allowed the LHD-wave to be examined in the low-drift-velocity regime and a comparison to be carried out with the linearized theory. The fluctuation density amplitudes and the wavenumber spectrum as functions of the discharge parameters indicated that ion trapping is likely to be the limiting saturation mechanism.