Erosion/deposition in JET during the period 1999-2001

Coated divertor and wall tiles exposed in JET for the 1999–2001 operations have been used to assess erosion/deposition. Deposited films of up to 90 μm thickness at the inner wall of the divertor tiles are, for the most part, enriched in beryllium and other metals, whilst carbon is probably chemically sputtered from these tiles and transported to shadowed regions of the inner divertor. However, from the composition at the surface of the tiles, it appears that the chemical erosion was ‘switched off’ by reducing the JET vessel wall temperature for the last part of the operations to 200 °C. Thick powdery deposits localised at the ion transport limit at each corner of the divertor may be due to physical sputtering. Erosion of the coatings is seen at the outer divertor wall, and on all the inner wall and outer limiter tiles.