| Budget Amount *help |
¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 2005: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 2004: ¥1,600,000 (Direct Cost: ¥1,600,000)
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| Research Abstract |
A dynamic Monte Carlo simulation code, Erosion and Deposition based on a DYnamic model (EDDY), which combines ion reflection and sputtering of plasma-facing materials with transport of released particles in a plasma, was developed. The surface composition changes due to impurity deposition, collisional mixing, and thermal diffusion of the deposited impurities at elevated temperatures were taken into account. Ionization and dissociation of released atoms and molecules and their gyromotion were calculated in the plasma, so that prompt and local redepositions were simulated. This enables the simulation of erosion and redeposition patterns, the impurity depth profile of plasma facing materials.
Using the code, the material mixing effects on the erosion and deposition processes of tungsten and carbon under simultaneous bombardment with deuterium ions and a small amount of carbon and beryllium ions were investigated. The transition from deposition to erosion occured abruptly for tungsten when the plasma temperature was increased. The erosion and deposition patterns observed on the tungsten-carbon twin test limiter exposed to TEXTOR edge plasmas were reproduced.
The EDDY code also simulated the divertor plasma transport of chemically eroded hydrocarbons from a carbon target and their redeposition on divertor tiles. The erosion and deposition patterns on inner and outer regions in the divertor of JT-60U were investigated. In the simulation, transport of various hydrocarbons in the divertor plasmas and their redeposition on a wall surface were calculated. Furthermore, redeposition patterns and species of hydrocarbons in the gap between divertor tiles and the shadowed area by the neighboring tile and the hole on the tile were calculated. One of further important results is that an asymmetry in hydrogen concentration in the codeposition between the toroidal and poloidal gaps.
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