Spectroscopic study of neon emission and retention in the Tore Supra ergodic divertor

In order to assess the capability of the Tore Supra ergodic divertor (ED) to retain impurities in the low confinement edge region, spectroscopic observations of a divertor neutraliser plate are reported. The neutral neon density is deduced from these measurements; it increases strongly (up to 1.5x1017 m-3 per injected Pa l) when the plasma approaches detachment. The central neon density is approximately independent of the plasma edge conditions. A 2D model confirms the relatively weak measured dependence of the neutral neon penetration on edge electron density and temperature. Comparison of BBQ (3D scrape-off layer Monte-Carlo code) results with 1D impurity radial transport modelling suggests a possible mechanism for the observed weak dependence of core content on edge impurity influx: enhanced exchange between the ergodized layer of the core and the neutraliser region