Study of microturbulence in the TEXTOR Tokamak using CO2laser scattering

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Abstract
CO2 laser collective scattering has been used on TEXTOR to measure electron density fluctuation amplitude n2 (f,k) using both forward and far-forward scattering techniques. Measurements are presented for ohmically heated plasmas and for discharges with ICRF auxiliary heating. The frequency of maximum fluctuation amplitude and the spectral width in frequency at fixed k scales linearly with electron temperature. Wave number spectra decaying as k- alpha are observed, with alpha evolving during the plasma discharge and being approximately equal to 4 during the steady-state phase of the discharge. A density scaling experiment shows little dependence of the normalized turbulence level associated with one observation wave number on the gross energy confinement time, but indicates a strong effect of the electron temperature on (n)k/ne for a fixed value of tau E. Strong correlations between sawtooth oscillations and turbulence levels were measured using small-k scattering. Also, changes in the fluctuation level during ICRF heating were correlated to changes in the electron density profile.