Neutral atom transport in tokamak plasmas by multigroup discrete ordinates methods

The numerical calculations consist of two parts: the generation of the neutral multigroup cross sections, and the transport equation solutions. A code, GIMUXS, was written to provide multigroup cross section libraries for the standard MGDO transport code ANISN. It is found that ANISN can treat all important aspects of neutral transport. From the results of a parameter survey a standard operating procedure is arrived at for neutral transport problems. Of particular interest are the neutral profiles generated as an integral part of larger plasma system simulation codes. To determine the appropriateness of utilizing ANISN for this purpose, results are compared with the neutral transport module of the Duechs plasma code. For a typical TFTR plasma, predicted neutral densities differ by a maximum factor of three on axis and outfluxes at the plasma boundary by approx. 40%. This is found to be significant for a neutral transport module. Possible sources of the observed discrepancies are indicated from an analysis of the approximations used in the Duechs model