Measurements of neutral gas fluxes under different plasma and divertor regimes in ASDEX Upgrade

Abstract

We report on neutral flux measurements in the full tungsten ASDEX Upgrade from the recently upgraded pressure gauge system in a wide range of plasma parameters and divertor conditions in L-mode plasmas. We compare these measurements with the ion and neutral fluxes in similar older discharges in presence of carbon target plates. We then show the qualitative relationship between the divertor poloidal distribution of the neutral flux density and the inner and outer divertor plasma regimes. During plasma density rise, when the plasma at one particular target detaches, the local flux increases abruptly producing a strong in–out asymmetry in the neutral flux distribution in the divertor. The neutral flux at the high field side increase linearly with the plasma density whereas at the low field side mid-plane it remains negligible in all the cases considered here. Finally, we compare detailed ion and neutral flux density profiles along the outer target from Langmuir probes, D α radiation and particle flux measurements obtained during vertical strike point sweeps.