Simulation of redeposition patterns of hydrocarbons released from carbon target in divertors

摘要

Transport of various hydrocarbons, i.e. CH_4, C_2H_2, C_2H_4, C_2H_6 and C_3H_6, in divertor plasmas and their redeposition on a wall surface are investigated by computer simulations. At high plasma temperature ( > tens of eV), the redeposition is dominated by ionized carbon and hydrocarbon fragments so that the redeposition patterns distribute mainly in the toroidal direction. At low plasma temperature (～a few eV), a much higher neutral fraction is redeposited and the neutral species liberated from a magnetic constrain redeposit widely in both toroidal and poloidal directions. The redeposition patterns distribute over several tens of cm at low plasma temperature (3 eV) and low plasma density (10~(18) m~(-3)). The trends are similar for all species of hydrocarbons calculated. Due to dominant redeposition of neutral species, at the low plasma temperature, the redeposition occurs deeply inside the gaps between the tiles and no asymmetry is calculated between the toroidal and poloidal gaps.