Atomic hydrogen production in a cold plasma for application in a metal foil pump

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.