Experimental findings to contribute to the preliminary design of a metal foil pump for fuel separation in the Direct Internal Recycling loop of the DEMO fusion device are presented. In parametric studies on a small-scale superpermeation experiment with a microwave plasma source and two different metal foil materials, niobium Nb and vanadium V, a substantial increase in permeation with plasma power and with a decrease in pressure was observed. To ease operation in the typical fusion environment, in-situ heating procedures were developed to recover from impurity contamination. The temperature independence of plasma-driven permeation from 600 to 900 °C metal foil temperature was demonstrated. No proof of an isotopic effect for plasma-driven permeation of protium and deuterium could be found. The highest repeatable permeation flux achieved was 6.7 Pa∙m³/(m²∙s) or ~5.5 × 10⁻³ mol H/(m²∙s). The found compression ratios do safely allow the operation of the metal foil pump using ejector pumps as backing stages for the permeate. In a dedicated experimental setup, the operation of the plasma source in a strong magnetic field was tested. Parametric studies of pressure, power input, magnetic flux density, field gradient and field angle are presented.

It is a challenging but key task to reduce the tritium inventory in EU-DEMO to levels that are acceptable for a nuclear regulator. As solution to this issue, a smart fuel cycle architecture is proposed based on the concept of Direct Internal Recycling (DIR), in which the Metal Foil Pump (MFP) will play an important role to separate the unburnt hydrogen isotopes coming from the divertor by exploiting the superpermeation phenomenon. In this study, we will present the assessment of the performance of the lower port of EU-DEMO after the integration of the MFP. For the first time, a thorough comparison of three different MFP (parallel long tubes, sandwich and halo) designs is performed regarding conductance for helium molecules, the pumping speed and the separation factor for deuterium molecules under different physical and geometric parameters. All simulations were carried out in supercomputer Marconi-Fusion with our in-house Test Particle Monte Carlo (TPMC) simulation code ProVac3D because the code had been parallelized with high efficiency. These results are essential for the development of a suitable MFP design in the vacuum-pumping train of EU-DEMO.

Any good design of fuel cycles for thermonuclear fusion reactors, which operate on deuterium-tritium fusion, comes with minimized tritium inventory. The direct internal recycling concept can significantly reduce the tritium inventory of a fusion power plant by introducing a bypass for most of the unburned fuel from the torus exhaust. It requires a technology that can sharply separate hydrogen isotopes from other gases in the given environment in the reactor's pump duct. The prime candidate for this task is a metal foil pump (MFP) using plasma-driven permeation. A workflow toward a performance predicting modeling tool of a MFP is introduced. It is based on the characterization of the employed cold plasma by using a plasma simulation, which is experimentally validated using optical emission spectroscopy and the actinometry method. The used approach accounts for the radial inhomogeneity of the linearly extended plasma. We determine the atomic hydrogen content down to pressures of 1 Pa and condense the complex processes that contribute to the hydrogen atom production into a single excitation probability. This value can be used in Monte Carlo based modeling approaches to determine the particle exhaust performance of the vacuum pump.