Lithium vapour-box divertor module design for investigating vapour shielding performance and lithium transport in linear plasma generator Magnum-PSI

The vapour box divertor concept aims to handle the tremendous high heat flux in a tokamak fusion power plant by strongly evaporating lithium with and into the plasma for cooling and using a closed divertor structure to limit lithium migration. To test this concept, a vapour box module (VBM) was designed for the first time for use with the Magnum-PSI linear plasma device, which is capable of producing plasma with divertor-relevant conditions. The goal was to reduce the total heat load from the plasma beam on the target of 3 kW by 50% and recapture lithium to minimize migration and protect diagnostics. The VBM consists of a heated central box with a lithium reservoir and two cold side boxes to promote recondensation. Simulations made with the direct simulation Monte Carlo code SPARTA determined optimal operating temperatures of 800–1000 K and highlighted the importance of the nozzle diameter and side box length in controlling lithium migration. Thermal modelling showed that a 2 kW conduction heater would efficiently reach the desired temperature. Based on these findings, an engineering design for the VBM was developed to evaluate the concept in Magnum-PSI, advancing the vapour box divertor towards practical use.