Liquid Lithium Divertor Development for the National Spherical Torus Experiment

Laura Berzak, Princeton University

The National Spherical Torus Experiment (NSTX) is a unique magnetic fusion device designed to study the physics principles of spherically shaped plasmas. The low aspect ratio configuration permits higher plasma pressure with lower magnetic fields yielding higher power densities. In 2005, NSTX began investigating the effects on plasma performance of lithium as a plasma-facing surface. Through lithium pellet injection and then direct lithium evaporation on plasma-facing surfaces, NSTX has achieved dramatic improvements in plasma behavior. This included increased energy confinement times and electron temperature profiles that were higher and broader. These successful results with solid lithium plasma-facing surfaces have led NSTX to pursue the concept of a liquid lithium divertor (LLD). The divertor is the region where plasma-surface interactions are expected to have the largest effect on the plasma density in NSTX. The LLD will be a new divertor structure composed of molybdenum, stainless steel, and copper, heated and coated with a thin liquid lithium film. Initial materials testing was performed during my practicum at Sandia National Laboratories/New Mexico. The purpose of the LLD will be to provide pumping on the outer divertor to control the plasma density and improve the efficiency of neutral beams in driving plasma currents. In the long term, LLD research will be used to develop plasma-facing surfaces for handling power levels during long-pulses and high heat fluxes.

Abstract Author(s): Laura Berzak