Simulation of Neutral Gas Flow in the JET Sub-Divertor and Comparison with Experimental Results
ABSTRACT. The present work includes a comparative study of the neutral gas dynamics in the JET sub-divertor. A complex model of the sub-divertor geometry is implemented and successful comparisons between corresponding numerical and experimental data have been performed. The experimental data represent the neutral gas pressure obtained by the KT5P pressure gauge. The Direct Simulation Monte Carlo (DSMC) code is able to predict qualitatively and quantitatively the behaviour of the flow including macroscopic quantities of practical interest as for instance the pressure, temperature and bulk velocity. For all presented plasma cases, the deduced flow pattern is strongly non-isothermal and covers the free molecular up to the transition flow regime. The relative difference between the measured pressure and the pressure in the sub-divertor area varies between 6-40% depending on the gas species and the plasma upstream conditions. Furthermore, for low and medium electron upstream density simulations, recirculation effects occur through gaps between the target tiles in the lower-high-field-side while for the highest electron upstream density case recirculation occurs only through gaps in the upper-low-field-side.