Modeling of neutral transport for self-consistent transport simulations in tokamaks

A model of the neutral transport in tokamaks has been developed suitable for a one-dimensional transport code, TASK/TX. The model consists of the one-dimensional diffusion equations for slow, thermal and halo neutrals, which are simultaneously solved together with two-fluid equations and Maxwell's equation. The behavior of the slow neutrals is easily modelled by a one-dimensional diffusion equation owing to short mean free path, while that of the thermal neutrals with long mean free path is not straightforwardly. The development of the way to evaluate an effective mean free path reflecting their two-dimensional motion and velocity realized the reasonable estimation of the thermal neutral diffusivity for a one-dimensional diffusion modeling. The validity of the model has been confirmed by a Monte Carlo code in the cases with various plasma parameters. (author)