Surface Fitting for Three-Dimensional DEGAS 2 Modeling

The \urllink{DEGAS 2}{http://w3.pppl.gov/degas2} neutral transport code is proving to be a valuable tool in modeling the edge regions of plasma devices. To date, the code has been applied to two dimensional or nearly axisymmetric three-dimensional systems. The logical next step is to perform fully three-dimensional simulations. A new geometry definition code consisting of a hermite interpolation and singular value decomposition algorithm has been developed for this purpose. The algorithm is used to fit the Fourier moments representation commonly used for stellarator plasma flux surfaces and vacuum vessel components to the quadratic surfaces required by DEGAS 2. This fitting technique will be applied to model neutral transport in the National Compact Stellarator Experiment (NCSX) being built at the Princeton Plasma Physics Laboratory (PPPL).