Study of lithium vapor flow in a detached divertor using DSMC code

Abstract

A detached divertor is predicted to be necessary to handle the heat fluxes of a demonstration fusion power plant. The lithium vapor box divertor localizes dense lithium vapor to cause stable detachment. This localization is formed by local evaporation and nearby condensation. We provide a simulation of lithium vapor flow using the SPARTA Direct Simulation Monte Carlo (DSMC) code. Simulations of a baffled vapor box divertor’s lithium mass flow are within a factor of two of an ideal-gas choked nozzle flow calculation. Lithium flow and density within each chamber are given for a 200 MW power input Demo-scaled vapor-box example configuration. We find the lithium exits the baffles of this configuration at a rate of ∼ 4 g/s. This should be acceptable since ionization of ∼ 60 g/s of lithium is taking place to cause detachment [3]. A simple model of the Fusion National Science Facility (FNSF) divertor plasma is also explored. We compare our simulations using SPARTA to a similar UEDGE simulation, showing the lithium ionizations rates can be emulated to a reasonable degree. The addition of baffles causes a decrease in far SOL ionization by a factor of eight. Changes in detachment front position over a range of 19cm can cause more than a factor of 18 increase in ionization rate, indicating detachment location is highly stable to variations in heatflux. Unbaffled results are more modest, but nonetheless promising with a factor of six change in ionization over the same region. Keywords: Divertor, Lithium, DSMC, Detachment