Impurity density profile measurements with a fast filter spectrometer and a modulated diagnostic beam on Tore Supra by charge exchange recombination spectroscopy

A simple interference filter spectrometer, together with a modulated neutral diagnostic beam is used on the Tore Supra tokamak for the measurement of carbon impurity profiles by charge exchange spectroscopy. A temporal resolution of 8 ms with a good signal to noise ratio is obtained with a neutral hydrogen beam of about 1 A equivalent neutral current at the plasma edge at 45 kV. Experimental results with ion cyclotron heating show that fast changes of the heating power are followed by transient modifications of the carbon impurity profile. The evolution of the C6+ profile from peaked to hollow and back to normal can be followed step by step and a typical diffusion time of about 30 ms is measured.