Liquid metals have received increased attention within the fusion community as of late. Liquid lithium, especially, has been the target of much interest for its ability to getter impurities and cold hydrogenic species at the walls of fusion devices. Lithium has been shown in several fusion devices to increase energy confinement times and to reduce the frequency of edge localized modes, plasma instabilities which cause large deposits of energy to the first wall of fusion devices. Inclusion of liquid metals in a fusion device requires, however, that the liquid metal wet the substrate on which it is placed. Beading of the liquid is undesirable.
The Materials Characterization Test Stand (MCATS) chamber at CPMI was specifically designed to investigate the wetting phenomena of liquid metals on various fusion relevant substrates. A moveable stage mounted either on a plate heater, or with strip heaters attached to the back side allows for placement of several droplets of liquid metal on various surfaces, in order to study the contact angle of a liquid metal on the surface. Contact angles of liquid lithium on various fusion relevant surfaces have been studied, as well as methods for the reduction of the critical wetting temperature of lithium on these surfaces.
MCATS also allows for the study of the compatibility of liquid metals with various solid surfaces. A pool of liquid metal in a stainless steel cup is mounted on the stage. A rotary motion feedthrough driven by an external motor allows for study of erosion of different solid materials in liquid metal. Most recently, this device showed the strong attack of copper by liquid gallium.