Direct measurement of the impurity radial flux in the FTU plasma core

A direct measurement of the impurity radial flux in the FTU plasma core has been obtained by observation of soft x-ray spectra from highly ionized charge states of intrinsic molybdenum. This measurement has been performed using the equation of continuity for Mo31+ and the radial density profiles of Mo32+, Mo31+ and Mo30+. The profiles of these ions have been obtained by inversion of the measured signal along six different lines of sight in a series of reproducible discharges. Other ions, such as Fe and Ni, which emit in the VUV range, are also monitored at different chords and confirm the picture given by the soft x-ray measurements. A collisional-radiative model developed at LLNL and JHU allowed the reconstruction, from the spectra, of the radial profiles for the three molybdenum ions. The resulting flux Γ₃₁₊ shows that the transport is negligible (within the experimental errors) in the central region r < 10 cm, but is very rapid in the intermediate region 10 < r < 20 cm, and is more than one order of magnitude greater than the neoclassical prediction. Defining an effective 'radial drift velocity' V_r = Γ₃₁₊/N₃₁₊, it is found that V_r has its maximum at half radius and there its value is about 0.4% of the thermal velocity.