Computer Simulation of Plasma-Surface Interactions in Fusion Devices

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A computer simulation code which treats plasma-surface interactions for divertor plates in magnetic confine-went fusion devices. The simulation code allows simultaneous incidence of different ion species as well as a Maxwellian velocity distribution and different charge states of the ions. The dynamic composition change of the surface layer due to ion implantation and redeposition of released impurities due to their ionization and gyromotion in an edge plasma.Particle release from a W test limiter exposed to deuterium edge plasma, containing impurities C and O, in the tokamak TEXTOR-94 is studied by using this simulation code. The release of W impurities from the limiter is strongly suppressed by prompt redeposition, whereas low Z impurities (C and O) are much less influenced. Expert- mentally observed radial distributions of WI and CII line intensities in front of the limiter can be explained by physical sputtering of W and deposited C, in addition to high-energy reflection of impurit … More y C ions. On the other hand, the CII line emission observed in front of graphite as a limiter is attributed to many low-energy atoms due to chemical sputtering by impact of D ions, which is strongly suppressed by deposition of high-Z impurities, such as W.Erosion of boron out of a thin film exposed to deuterium edge plasmas and the simultaneous carbon deposition in TEXTOR-94 is studied by simulation. The implantation of carbon impurities strangly changes the effective boron sputtering yield of the film, which results into a lowering of the film erosion and a formation of thick carbon deposits. A strong decrease in the experimentally observed Bill line emission around a surface location far from the plasma edge can be explained by a carbon deposition on the film. The cauculated carbon depth proflies in die film are in resonable agreement with measurements by AES.A combined Monte Carlo simulation of secondary electron emission from solids and transport of secondary electrons in a plasma sheath is performed for analyzing a relationship between the secondary electron yield and sheath voltage formed on the wall in magnetic fusion devices. Less