The THESEUS facility — A test environment for the Torus exhaust vacuum pumping system of a fusion power plant

At KIT Karlsruhe, a new vacuum pump concept for fusion power plants is under development. This concept consists of three pump types, namely a vapour diffusion pump as primary pump, a metal foil pump that provides a sharp gas separation of unburnt fuel (pure deuterium/tritium) and a liquid ring pump as backing pump. As special feature, diffusion pump and ring pump apply mercury as working fluid due to its perfect tritium compatibility. All three pump types require a proof-of-principle testing as their performance cannot be predicted easily. For these experiments, a dedicated experimental facility called THESEUS is currently being set up. This facility allows experiments with nitrogen, argon, hydrogen, deuterium and helium as fusion relevant test gases in a pressure range from 10³ to as low as 10^-9 mbar. Hence, the performance of both primary pumps and backing pumps can be tested. The use of mercury and flammable gases in the facility asks for demanding safety pre-cautions and a well-designed safety system. This paper presents the test facility in full detail. It describes the safety system as well as the Supervised Control And Data Acquisition (SCADA) system, and the gas analysing system that monitors the mercury release and - migration inside the facility.