Carbon chemical erosion in H-mode discharges in ASDEX Upgrade divertor IIb: flux dependence and local redeposition

Carbon erosion at the outboard divertor in ASDEX Upgrade has been investigated using the emission spectroscopy technique. The methane molecular influx was calibrated by simultaneous CD₄ puffing. In deuterium H-mode discharges a decrease of D/XB_CD←CD4 with increasing ion flux (decreasing temperature) is found at fluxes in the range 0.5–2 × 10²² m⁻² s⁻¹ and no dependence for higher fluxes. The corresponding obtained yields show a negative power law flux dependence with exponent γ = −0.46. To investigate the combined effect of re-deposition, re-erosion and local transport, known quantities of ¹³CH₄ were puffed at the end of the 2002/2003 experimental campaign. The amount of ¹³C locally redeposited has been measured by nuclear reaction analysis (NRA). The results show a strongly localised re-deposition near the puff location, with a downstream tail and a moderate downward drift with respect to the magnetic field line direction.