What post mortem analysis tells us of plasma surface interactions in JET

Periodic removal of beryllium and tungsten plasma facing components (PFCs) from the JET tokamak allows for surface analysis to be carried out. Measurement of components from around the vessel enable both local erosion, deposition and fuel retention phenomena to be characterised and global material migration and fuel retention to be mapped. Whilst extraction of PFCs within operating periods and systematic parameter studies of materials are not possible on JET, the samples that are removed at the end of an operating period are unique in that they represent long term PFC exposure in a tokamak. The analysis and interpretation of JET PFCs for this reason is challenging as they result from a varied plasma programme. Despite this, valuable insight into the global parameters affecting material migration and fuel retention may be obtained and bench marking of models is possible. An overview of post mortem analysis in JET shows the influence of plasma configuration on deposition patterns - with fuel retention being dominated by co-deposition at the upper inner divertor, evidence of prompt deposition of eroded materials and longer-range migration to remote areas where mirrors are degraded, dust inventories and related sources and potential PFC lifetime issues from melt events and erosion.