Effect of neutral screening on pumping efficiency in the DEMO divertor

Abstract The neutral gas screening by plasma on the top of the private flux region of the DEMO divertor configuration without dome is analysed by using the direct simulation Monte Carlo method (DSMC). Calculations show that a strong neutral outflux from the private flux region towards the confined plasma can be supressed because the neutral pressure is balanced by the magnetized plasma in the scrape-off layer. The neutral pressure in the divertor plenum rises when interaction with the plasma is taken into account and the neutral outflux is reduced with increasing plasma density and temperature at the separatrix. However, the neutral screening effect turns out to be insufficient for increasing the pumping efficiency. To achieve this goal, a dome structure has to be introduced. The DEMO divertor dome structure can be further optimized by taking into account the neutral screening effect at the top of private flux region.