Development of a Liquid Lithium Level Sensor and 3D Modeling for a Single Pre-filled Lithium Vapor Divertor Tile in NSTX-U

The lithium vapor box divertor is a high recycling heat mitigation concept that has been shown, through SOLPS-ITER modeling, to be able to reduce 90 MW/m² unmitigated heat flux to <10MW/m² while minimizing the upstream lithium density in NSTX-U. Pre-filled single lithium vapor divertor tile tests are planned to assess performance of lithium vapor box divertor technology before a future full toroidal system could be installed. This necessitates the need for a non-contact liquid lithium level sensor to be optimized and tested, as well as 3D modeling of a non-axisymmetric system to take place. A non-contact level sensor that measures the inductive response of liquid lithium inside a stainless-steel reservoir has been tested with tin as a lithium stand-in and results have been compared to theoretical predictions made with ANSYS 3D Maxwell simulations with good success. The theoretical predictions have thus been extended to a potential single pre-filled lithium vapor divertor tile geometry to predict the inductive response of the sensor in NSTX-U tests. Furthermore, 3D modeling of a non-axisymmetric lithium vapor divertor system with the code SolEdge3X has begun to predict the expected heat mitigation in future single tile tests. These preliminary results will be compared to previous results from SOLPS-ITER simulations.