Visible spectroscopy on the Tokamak de Varennes with high spatial resolution

A vertical slice of a tokamak plasma is imaged onto the entrance slit of a spectrometer, giving at the exit plane both the spectral (horizontal axis) and the spatial (vertical axis) distributions of the collected light. An intensified CID (charge injection device) camera is mounted at the exit plane to record the spatially and spectrally resolved emission profiles of low-Z impurities, with a temporal resolution of 1/60 s. The large number of lines of sight allows for inversion of chord-integrated signals to obtain local emissivities. Profiles from several ionization stages of carbon and oxygen are compared to the predictions of the impurity transport code MIST (multi-ionized species transport) to deduce impurity diffusion coefficients.