Simulation Analysis of Carbon Deposition Profile in the Closed Helical Divertor Configuration in the Large Helical Device

Recent long pulse plasma discharges in the Large Helical Device have been interrupted by radiation collapse induced by large amounts of dusts released from a closed divertor region. Traces of exfoliation of carbon‐rich mixed material deposition layers were found in the divertor region after the experimental campaigns, indicating that the thickly accumulated deposited layers were exfoliated and broken into dusts. Simulation of the density profiles of carbon deposition in the divertor region by EMC3‐EIRENE reasonably explains the observation of the exfoliation of the deposition layers. It shows that the positions of the exfoliated layers correspond to the area where the density of the carbon deposition is high. It also proves that change of the configuration of target plates in the closed divertor is effective for controlling the accumulation of the carbon deposition, and carbon atoms released from the new target plates does not influence the main plasma confinement region. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)