First comparison between numerical predictions and experimental observations with Collective Thomson Scattering in FTU

Introduction Collective Thomson Scattering (CTS) emission has been studied to investigate the ion dynamics in the plasmas, exploiting the interaction between an injected high power microwave beam and the plasma collective fluctuations that scatter radiation with frequency spectra mainly characterised by ion features. Presently a CTS system is foreseen for ITER, with the main aim of characterizing Fusion born alpha particles [1]. CTS measurements of several bulk ion parameters as temperature, drift velocity and composition have been demonstrated in TEXTOR and in ASDEX [2-4]. The CTS system in FTU can operate in different "non-resonant" regimes, with the Electron Cyclotron resonances outside the plasma, as foreseen for the CTS system in ITER, allowing investigating bulk ions (thermal) features with low disturbance from ECE emission. Up to now, just few non-resonant discharges could be carried out in FTU as part of the experimental programme aimed at studying the effects of Parametric Decay Instabilities (PDIs) on ECH [5]. The scattering set up is described in section 1 and calibrated thermal spectra are compared (in section 2) for the first time with the power spectral densities (PSD) simulated with the Thermal Collective Scattering (TCS) code [6].