Monte Carlo analysis of the low-temperature adsorption facility TITAN and its pumping characteristics

Within the framework of the European Fusion Technology Programme, the Karlsruhe research centre (FZK) has been charged with the development of the primary vacuum pumping system for the International Thermonuclear Experimental Reactor ITER. To support the design and operation of the cryopump, an experimental campaign for pump component testing was started at the TITAN test facility available in FZK. The primary objective was to investigate, under ITER-relevant conditions, the pumping speed of the designed cryosorption panels coated with activated carbon. The experiments performed at TITAN allow to determine the relationship between the pumping speed of the gas, the gas load and the pressure during pumping. The pumping speed strongly depends on the arrival rate of the gas, the geometry of the pumping system, the cold surface, the type of sorbent used, the temperature and the gas load. In order to quantify the geometry impact on the measured pumping speed in the molecular flow regime, the Monte Carlo method was applied. To analyse the rarefied gas flow in the TITAN test facility, the general Monte Carlo code MOVAK3D was employed. A series of simulations was performed to determine the conductance of the entire TITAN vacuum structure, to evaluate the capture probability depending on the panel pumping characteristics, to gain an insight into the relative pressure variation within the structure and finally to study the influence of panel arrangement on the TITAN overall pumping performance. (orig.)