Characterization of Tungsten Sputtering in the JET Divertor
Tungsten erosion in the outer divertor of the JET ITER like wall was quantified by spectroscopy. Effective sputtering yields of ~10­4 were measured in L-mode at ~30eV low recycling divertor conditions and Be was identified as the main species causing the sputtering. The signature of prompt redeposition was observed in the analysis of WI 400.9nm and WII 364nm line ratios indicating >50% redeposition fraction. Inter- and intra-ELM sputtering were compared for an example of 10Hz ELMs with 13MW NBI heating, in which intra-ELM sputtering was found to dominate by a factor of 9. Nitrogen seeding initially increased the tungsten sputtering threefold due to higher extrinsic impurity levels and effectively reduced the tungsten sputtering when the divertor plasma temperature was decreased from 25eV to 15eV.