Modeling of wall recycling effects on the global particle balance in magnetic fusion devices

A zero-dimensional particle balance model has been developed to compute hydrogen inventories in the four major reservoirs; core plasma, scraped-off layer (SOL), gas region, and wall of a magnetic fusion reactor system. This model takes as input separately calculated hydrogen reemission and reflection coefficients. Model applications have successfully reproduced the core plasma transient behavior with and without density decay observed in the large helical device (LHD). Particle balance modeling has also been done for a hypothetical steady-state reactor employing carbon as the plasma-facing material. Results indicate that codeposition-induced wall pumping is quite effective in controlling the core density although, on the other hand, the tritium inventory concerns environmental safety.