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R. Ding, P. Stangeby, D. Rudakov, J. Elder, D. Tskhakaya, W. Wampler, A. Kirschner, A. McLean, H. Guo, V. Chan, P. Snyder:
"Simulation of gross and net erosion of high-Z materials in the DIII-D divertor";
Nuclear Fusion, 56 (2016), 0160211 - 01602110.

The three-dimensional Monte Carlo code ERO has been used to simulate dedicated DIII-D
experiments in which Mo and W samples with different sizes were exposed to controlled and welldiagnosed
divertor plasma conditions to measure the gross and net erosion rates. Experimentally, the
net erosion rate is significantly reduced due to the high local redeposition probability of eroded high-Z
materials, which according to the modelling is mainly controlled by the electric field and plasma
density within the Chodura sheath. Similar redeposition ratios were obtained from ERO modelling
with three different sheath models for small angles between the magnetic field and the material
surface, mainly because of their similar mean ionization lengths. The modelled redeposition ratios
are close to the measured value. Decreasing the potential drop across the sheath can suppress both
gross and net erosion because sputtering yield is decreased due to lower incident energy while the
redeposition ratio is not reduced owing to the higher electron density in the Chodura sheath. Taking
into account material mixing in the ERO surface model, the net erosion rate of high-Z materials is
shown to be strongly dependent on the carbon impurity concentration in the background plasma;
higher carbon concentration can suppress net erosion. The principal experimental results such as net
erosion rate and profile and redeposition ratio are well reproduced by the ERO simulations.

erosion, redeposition, high-Z material