2D imaging of Li and O impurity emissions in LTX-β

High speed filtered impurity emissions from Li and O in LTX-β reveal 3-D effects from ribs of the inner shell structure, melt dynamics of Li deposited on the walls, and up to 5 times more emission when the walls are pre-heated to above the Li melting temperature. The mission of the Lithium Tokamak eXperiment β upgrade is to demonstrate plasma operation in a low recycling environment, leading to nearly flat temperature profiles out to the edge of limited plasmas. This scenario leads to strong gradients for impurities eroded at the edge, making interrogation of impurity emissions critical for understanding the low recycling regime. High speed Phantom cameras are used to observe dynamics of these emissions at the plasma edge, showing increased emission with hot walls consistent with greater evaporation and increased physical erosion for Li above the 180ºC melting point. Melting of lithium in shadowed regions between the shell ribs is observed by progressive changes in emissivity, as well as droplet formation and release and subsequent breakup into the core plasma. Comparisons and analysis are shown for imaging of LTX-β for cases of walls pre-heated and not, as well as cases with 'fresh' vs. passivated Li walls.