3D Design and Thermal Analysis of a Pre-filled Lithium Vapor Divertor Tile for NSTX-U

The lithium vapor divertor is a divertor concept that has been predicted to reduce the peak heat flux in NSTX-U from 90MW/m^2 to less than 10MW/m^2 by inducing radiative cooling of the divertor plasma using lithium impurities. In order to test key physics questions for a lithium vapor divertor, a private flux region tile was designed with the ability to heat and subsequently evaporate a pre-filled reservoir of lithium into the divertor plasma. The liquid lithium is wicked up from the reservoir through a stainless steel Capillary Porous System (CPS), and a high power density heater is placed in a slot directly behind the CPS. Efficient heating of the lithium in the CPS requires good thermal contact between the heater and the CPS, which is achieved via wedges secured by set screws. Thermal cycling of the tile was analyzed in ANSYS Mechanical throughout a plasma shot cycle, which includes a variable heater ramp-up, five second plasma pulse, and twenty minute cooldown. Both a stainless steel 316 and a Titanium-Zirconium-Molybdenum (TZM) alloy tile were simulated, with each being found to have its own respective advantages. Repeated-cycle analysis will be done to assess temperature ratcheting of the tile body from the start of one cycle to the start of the next.