Monte Carlo algorithm for calculating neutral gas transport in cylindrical plasmas

Monte Carlo techniques have been used to calculate neutral gas distributions in tokamaks. The algorithm uses track length estimators, suppression of absorption, and splitting with Russian roulette to reduce the variance, so that the algorithm is economic. The resultant package is small in memory requirements and relatively fast (approx.15 seconds of PDP-10 KI time per neutral density profile). The tokamak is modeled as an infinite cylinder, and the plasma parameters are specified as a function of the radial coordinate of the cylinder. The effects of wall reflection and sputtering yields can be easily computed within the model. The algorithm has been incorporated in a one-dimensional tokamak transport code. The code has also been used to predict the energy spectra of charge-exchange neutrals which form the basis for measurements of ion temperatures in tokamaks