DIVIMP modeling of the toroidally symmetrical injection of 13CH4 into the upper SOL of DIII-D

As part of a study of carbon-tritium co-deposition, we carried out an experiment on DIII-D involving a toroidally symmetric injection of (CH4)-C-13 at the top of a LSN discharge. A Monte Carlo code, DIVIMP-HC, which includes molecular breakup of hydrocarbons, was used to model the region near the puff. The interpretive analysis indicates a parallel flow in the SOL of M-parallel to similar to 0.4 directed toward the inner divertor. The CH4 is ionized in the periphery of the SOL and so the particle confinement time, tau(c), is not high, only similar to 5 ms, and about 4X lower than if the CH4 were ionized at the separatrix. For such a wall injection location, however, approximately 60-75% of the CH4 gets ionized to C+, C2+, etc., and is efficiently transported along the SOL to the inner divertor, trapping hydrogen by co-deposition there. (c) 2004 Elsevier B.V. All rights reserved.