Measurement of the Vapor Pressure of Lithium Alloys in the Improved Lithium Alloy Vacuum Appliance (LAVA) Chamber

Liquid metals as a plasma facing component (PFC) in fusion reactors have become an attractive alternative to solid PFCs. Liquid lithium is the top among them due to the PFC’s low-Z nature, self-healing surface, and low hydrogen recycling.

However, the liquid lithium PFC can be hindered by its relatively high vapor pressure (about 1Pa at 800K). This introduces relatively high Z material into the bulk plasma, thereby decreasing the reactor’s efficiency. However, alloying lithium may substantially lower the vapor pressure (Pb₈₃Li₁₇ expected to be about 1mPa at 800K). Primary alloys of interest are Pb₈₄Li₁₆ and Sn₈₀Li₂₀.

 

Measurement of the vapor pressure is done using Knudsen effusion and a quartz crystal microbalance. The measurement of vapor pressure is done in the Lithium Alloy Vacuum Appliance (LAVA) at UIUC. LAVA has undergone various modifications and upgrades (dual turbo pump operation, ability to compensate for background noise, water cooling for increased sticking coefficients) in order to collect more reliable and accurate data. Initial results show a decrease in evaporation rate of Pb₈₄Li₁₆ as compared to lithium (at 750K, 100 mg/s down to 10 mg/s mass loss from the Knudsen cell) as well as a decrease in evaporate composition of lead as compared to the eutectic ratio (below 84 at. %).