  The lithium vapor box divertor is a concept for handling the extreme divertor
heat fluxes in magnetic fusion devices. In a baffled slot divertor, plasma
interacts with a dense cloud of Li vapor which radiates and cools the plasma,
leading to recombination and detachment. Before testing on a tokamak the
concept should be validated: we plan to study detachment and heat
redistribution by a Li vapor cloud in laboratory experiments. Mass changes and
temperatures are measured to validate a Direct Simulation Monte Carlo model of
neutral Li. The initial experiment involves a 5 cm diameter steel box
containing 10 g of Li held at 650 degrees C as vapor flows out a wide nozzle
into a similarly-sized box at a lower temperature. Diagnosis is made
challenging by the required material compatibility with lithium vapor. Vapor
pressure a steep function of temperature, so to validate mass flow models to
within 10%, absolute temperature to within 4.5 K is required. The apparatus is
designed to be used with an analytical balance to determine mass transport.
Details of the apparatus and methods of temperature and mass flow measurements
are presented.
