Recovery of ion temperature profiles from the analysis of energy-resolved neutral-flux measurements

In this paper, results of two approaches to account for the neutral density are reported, which substitute the time-consuming Monte Carlo simulations. In the first approach, the neutral density is estimated by transport formulas applicable to a planar slab model. This model is a somewhat crude approximation to the real situation in ASDEX Upgrade. The second approach, consists in empirically estimating the neutral density profile simultaneously with the ion temperature profile, while imposing a low-order parametric class of neutral-density profiles (of the neutrals stemming from the wall) along the line of sight. The class of functions (a variant of exponential survival functions) has been selected by investigating various fits to results results of a Monte-Carlo based Ti evaluation program, for some ASDEX-Upgrade discharges. The procedure roughly captures global features of the 'survival profile' of the atomic neutral density due to the wall sources, from the central region of the plasma up to the region close to the separatrix. The neutrals from volume recombination, which are important in the center of the plasma, are calculated separately. (orig.)