Abstract
Fusion reactors are generating energy by nuclear fusion between deuterium and tritium. In order to evacuate the high gas throughputs from the plasma exhaust, large pumping speed systems are required. Within the European Fusion Programme, the Karlsruhe Institute of Technology (KIT) has taken the lead to design a three-stage cryogenic pump that can provide a separation function of hydrogen isotopes from the remaining gases; hence limiting the tritium inventory in the machine. A primary input parameter for the detailed design of a cryopump is the sticking coefficient between the gas and the pumping surface. For this purpose, the so-called TIMO open panel pump experiment was conducted in the TIMO-2 test facility at KIT in order to measure pumping speeds on an activated carbon surface cooled at temperatures between 6 K and 22 K, for various pure gases and gas mixtures, under fusion relevant gas flow conditions, and for two different geometrical pump configurations. The influences of the panel temperature, the gas throughput and the intake gas temperature on the pumping speed have been characterized, providing valuable qualitative results for the design of the three-stage cryopump. In a future work, supporting Monte Carlo simulations should allow for derivation of the sticking coefficients.
Highlights
Fusion reactors are generating energy by nuclear fusion between deuterium and tritium
This configuration should allow for investigation on two effects which are to be expected under fusion relevant conditions, namely high specific flow rate and high gas intake temperature
Within EUROfusion, a three-stage cryopump has to be developed for DEMO
Summary
Fusion reactors are generating energy by nuclear fusion between deuterium and tritium. Particular attention should be paid on the reduction of the cryogenic operational costs, one of the main drawbacks of cryopumps These new requirements can be tackled using several pumping stages cooled at different operating temperatures: two pumping stages coated with activated carbon – at 12 K – 22 K for hydrogenic species adsorption and below 5 K for helium adsorption – and tightly. The sticking coefficient is a primary parameter for the vacuum design of a cryogenic pump, and its proper characterization is essential For this purpose, the so-called TIMO open panel experiment was conducted in the large and versatile cryogenic-vacuum TIMO-2 test facility at KIT in order to measure pumping speeds of various pure gases and gas mixtures on an activated carbon adsorption surface, at various sorbent temperatures and under fusion relevant gas flow conditions. This paper summarizes the experimental pumping speed results and the conclusions drawn from this experiment
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