Erosion and re-deposition processes in JET tiles studied with ion beams

Plasma facing components in fusion reactor chambers will operate under extreme conditions. Among the processes with implications on the material lifetime are erosion and re-deposition due to plasma interactions. This work will address the behaviour of both JET divertor and outer poloidal limiters (OPL) under plasma irradiation. The limiters comprise about 50 pairs of tiles in a poloidal stack, each of which has a plasma facing surface about 25 mm (poloidal) by 350 mm (toroidal) and is about 50 mm thick. The divertor tiles are located at the bottom of the chamber and withstand high fluxes of radiation and heat. Standard carbon-fibre composite (CFC) tiles coated with a thin layer of W overlaid with a 10 μm layer of C were studied with RBS/PIXE to understand the erosion/re-deposition processes occurring in these regions of the reactor chamber. High resolution surface morphology was assessed through SEM with and without tilting of the sample. The retention of hydrogen isotopes in the tiles were studied combining NRA and ERDA techniques – this is mostly 2H from the fuelling gas, but 3H is also present as a result of 2H–2H fusion reactions, and 1H coming from the atmospheric exposure.