Laser Profiling for Liquid Metal Fast Channel Flow Surface Wave Diagnostics*

Liquid-metal plasma facing components (LM-PFCs) show greater efficacy for managing the high heat flux and radiative damage present in a tokamak in comparison to their solid counterparts. Liquid lithium is one of the most promising liquid metal candidates as it is low Z, reduces particle recycling, and aids fuel cycle in conserving unused hydrogen isotopes. However, design of LM-PFCs suffer from potential ejection and sputtering of the liquid metal into the core of the plasma, due to the instabilities under the effect of electromagnetic forces and surface tension, introducing impurities and decreasing performance. In particular, surface waves in fast channel flow LM-PFCs are emblematic of these instabilities and require careful characterization. So far, existing methods for measuring surface waves lack resolution and consistency. Experiments on the Liquid Metal eXperiment Upgrade (LMX-U) investigated surface wave formation in a flow of Galinstan, an alloy of gallium, indium, and tin. Novel diagnostics and analysis techniques for surface waves in liquid metal using a Keyence LJ-8080X laser profiler are demonstrated. A mount was designed to facilitate replicable, consistent diagnostics. Surface wave measurements are taken at various Hartmann and Reynolds numbers, processed with spectral analysis, and compared to theoretical predictions.