Film condensation study of liquid lithium on materials relevant to fusion reactors

Lithium is becoming a very strong candidate for the implementation of liquid components and walls in magnetic confinement fusion devices, due to its ability to getter impurities and its dramatic effect on reactor operation. However, the implementation of schemes based in flowing liquid lithium requires expanding the knowledge of thermohydraulic behavior of liquid lithium, in particular for free surface scenarios. A facility for studying the condensation of lithium vapor on hot surfaces was designed, developed and constructed at CICATA-Querétaro. The facility has a tantalum evaporator that can reach temperatures up to 1600 °C, and it is used to generate the lithium vapor. The evaporator operates in a vacuum of 10^-6 Torr. The lithium vapor condensates in a stainless steel AISI 316 plate, where various temperature gradients can be produced by a 5-zone set of cartridge heaters, and the steel plate can hold other materials such as graphite and refractory metals for future studies. The experimental arrangement consist in a vacuum chamber with 40 cm of diameter and 38 cm length; the chamber is also equipped to measure lithium surface passivation with an in-situ ellipsometer, and an optical diagnostic to monitor condensation conditions and film deposition onset as well as thickness based on dispersive reflectivity will be implemented. Results on complementary measurements of wetting angle as a function of temperature under vacuum conditions carried out in this facility will be presented as well.