Tungsten divertor erosion in all metal devices: Lessons from the ITER like wall of JET

Tungsten erosion in the outer divertor of the JET ITER like wall was quantified by spectroscopy. Effective sputtering yields of typically 10⁻⁴ were measured in L-mode at ∼30 eV attached divertor conditions and beryllium was identified as the main cause of sputtering. The signature of prompt redeposition was observed in the analysis of WI 400.9 nm and WII 364 nm line ratios and indicative of >50% redeposition fractions. Inter- and intra-ELM sputtering were compared for an example of 10 Hz ELMs with 13 MW NBI heating, in which intra-ELM sputtering was found to dominate by a factor of 5. 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 the initial 25 eV down to 15 eV.