Analysis of Carbon Deposition on the FirstWall of LHD by Monte Carlo Simulation

Deposition of impurities on surfaces of plasma confinement devices is one of essential issues in present devices and also future fusion devices. In the Large Helical Device (LHD), it is necessary to reveal fundamental characteristics of impurity transport and deposition by simulation studies along with experimental studies. In the present paper, simulation scheme of carbon deposition on the first wall of LHD and results are discussed. The geometry of the LHD divertor and the configuration of the plasma are newly implemented to the Monte Carlo code ERO. The profiles of the background plasma is calculated numerically by a ID two-fluid model along a magnetic field line. Spatial distributions of the carbon impurities are investigated for a typical set of plasma parameters in LHD. The simulation results indicate that the deposition is caused by neutral carbon particles from two facing divertor plates. The divertor opposite to the first wall makes less contributions than the adjacent one because of the ionization in the divertor plasma. Chemically sputtered impurities cause more deposition near the divertor than physical ones because atomic processes of methane molecules lead to isotropic particle velocities. (c) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim