Data and extended diffusion theories for neutral particle transport in tokamak divertors

A formalism is developed that incorporates the anisotropic effects on the neutral atom and molecule transport of collisions with plasma ions flowing toward the divertor into Legendre representations of the scattering, charge-exchange, and recombination processes. These anisotropic directed flow effects and the anisotropic effects of neutral particles recycling from the divertor plate or streaming across low-density regions are incorporated into a differential transport formalism, which retains the computational advantages of an extended diffusion theory. The available collision and wall reflection data that are needed for implementation of the model for deuterium are reviewed, and recommended reaction rates and reflection coefficients are presented. Model problem calculations illustrate the importance of these anisotropic effects.