Erosion/deposition issues at JET

Deposition and H-isotope retention in JET is highly asymmetric, with deposi tion predominantly in the inner divertor, where flaking deposits form on wa ter-cooled louvres shadowed from the plasma, The asymmetry implies drift in the SOL of JET from outboard to inboard under normal operating conditions, which has been measured. In order to model the amounts of deposition, assu mptions have to be made about the transport at the inner target, Analysis o f divertor tiles shows that material from the main chamber travels along th e SOL to the inner divertor wall, from where carbon is preferentially remov ed leaving a beryllium-rich film. The carbon travels to shadowed areas (suc h as the louvres) where deposits with high H-isotope content accrue. The an alysis indicates that chemical processes must be important. (C) 2001 JET Jo int Undertaking. Published by Elsevier Science B.V. All rights reserved.