Effect of neutral leaks on pumping efficiency in 3D DEMO divertor configuration

•Study on the pumping efficiency of a 3D DEMO divertor configuration based on the inter-cassette gaps.•The width of inter-cassette gaps is defined by the requirement to minimize the outflow of particles towards plasma.•The DIVGAS code is used to perform a sensitivity analysis of the DEMO divertor pumping efficiency.•For a 20 mm gap, 10 % reduction on the pumping efficiency is observed when compared with a completely sealed divertor.