Experimental measurement of hydrogen and helium retention on liquid lithium on FLIRE

Experiments to measure particle pumping ability of liquid lithium have continued on the FLIRE facility. After the first extensive experimental campaign, an energy-dependent diffusion coefficient of 10^-3 cm²/s was measured for flow velocities of 80 and 215 cm/s, at a temperature of 250°C. Further experiments showed a diffusion coefficient on the order of 10^-3 10^-4 cm²/s. The goals of the second experimental campaign was to better understand the results previously observed, explain energy dependence of the diffusion coefficient obtained with He bombardment during the previous experiments, study the effect of having two Li streams overlapping after irradiation on the measurements, and take the preliminary steps to expand the work to hydrogen exposure. Further diffusion coefficient estimations based on the measured retention data were also performed. The addition of a new VTI magnetic sector gas analyzer to FLIRE drastically increased the detection in the low mass range compared to quadrupole instruments used in the past, hence making the data analysis more accurate. The new thermal desorption spectroscopy (TDS)/purification chamber in FLIRE, able to heat the exposed Li charge in a linear fashion up to 660°C, was installed and tested. Such addition allowed to detect long-term He trapping in the Li metal by accelerating the release. These thermal release studies will be even more critical to quantitatively measure hydrogen intake and the energetics of the trapped hydrogen for the case of hydrogen irradiation.