Study of lower-hybrid wave propagation by CO2-scattering and r.f. probe diagnostics

Abstract

Coherent CO2-scattering as well as phase-sensitive probe diagnostics are applied to investigate small-amplitude lower-hybrid (LH) waves launched by a slow-wave antenna to a linear plasma column. Special attention is focussed on the detailed description of the LH wave field in the plasma taking into account the wavenumber spectrum of the antenna. With the knowledge of the LH density perturbations, the r.f. detector current is computed under the actual scattering conditions. To fit the theoretical results to the experimental results, an effective collisional frequency nu eff for electron momentum transfer is introduced. The observed LH wave damping is considerably higher than expected from collisional and electron Landau damping, but it is correlated with the level of low-frequency fluctuations. In particular, the scattering and the probe signals are strongly affected by the damping as well as by the low-frequency turbulence itself.