Initial studies of the divertor dome effect on pumping efficiency in DEMO

In this paper we analyze the gas dynamics effect on the pumping efficiency in the European DEMO 1 ITER-like divertor configuration with and without dome. The achievement of detachment at given upstream heat flux and upstream density under burning conditions depends on the level of neutral pressure in the divertor private flux region (PFR) and on the required throughput at actual pumping speed. The principle effect of the dome on neutral compression in the PFR is assessed by using the DIVGAS code based on direct Monte Carlo simulation [1]. The numerical analysis includes the calculation of neutral density in the PFR and the overall conductance of the sub-divertor structure, which consequently affects the estimation of the effective pumping speed and, ultimately, the achievement of detachment. It is shown that the configuration with dome requires a higher pumping efficiency and that the dome impedes the detachment onset. The dome position can be further optimized to ensure good pumping of impurities and ease detachment onset. DIVGAS is demonstrated to be a most suitable tool to do further parametric and detail studies.