Material transport from marker tiles in the JET divertor
The JET ITER-like Wall (ILW) divertor mostly consists of CFC tiles coated with a thick tungsten (W) layer over a molybdenum (Mo) interlayer. Poloidal sets of tiles are additionally coated with ~3 microns of Mo and ~4 microns of W to act as markers to measure the erosion/deposition during ILW campaigns. A few of the marker tiles only have the Mo coating to facilitate transport studies of Mo and W within the divertor.
Transport to and from one of these Mo markers (tile 14ING3B – a tile3 from the lower part of the inner divertor wall) to tile 14BNG4D (an innermost base tile4) has been extensively studied using SIMS and IBA techniques including RBS and HIERDA. There was measurable erosion from the top of 14ING3B after the first ILW campaign (ILW1) as for the majority of discharges the inner strike point was at the top of tile 3/bottom of tile 1 whereas for ILW 2+3 the inner strike point was usually nearer the bottom corner of the divertor. However, in each case the amount of Mo transferred to 14BNG4D was comparable and was located towards the top of the tile (s-coordinates ~840mm).
Migration of W was observed onto Mo marker tiles from adjacent tiles and showed similar localised transport behaviour to Mo, however the main plasma impurities such as beryllium (Be) also display a much less restrictive transport component.