Designing a Lithium Evaporator for a Lithium Vapor Divertor in a Short-Pulse Tokamak

The Lithium Vapor Divertor concept is being developed to achieve divertor detachment with minimal impurity contamination of the core plasma. By directing a flow of lithium vapor from the private flux side of the divertor leg toward the outer strike point, the radiative cooling of the plasma by lithium impurities can be localized to occur downstream of the x-point. SOLPS-ITER modeling has shown that during plasma operation a substantial fraction of the evaporated lithium will be redeposited on the evaporator, along with significant plasma radiated power, which makes control of the evaporator temperature more challenging during the plasma discharge phase. Further, operation of a Lithium Vapor Divertor in a short-pulse tokamak requires that the evaporative source of lithium be ramped up and down quickly in concert with the plasma discharges to minimize the amount of lithium that is evaporated between discharges. To address these challenges, an updated design for the evaporator system is being studied where the evaporator has been moved out of the direct line of sight of the plasma, improving the temperature controllability of the lithium evaporator. The impact of the lithium redeposition and direct radiative heating of the evaporator system is evaluated in this work through dedicated modeling of the system's thermal response to cycled operation under a variety of plasma conditions.