Lithium surface conditioning and its impact on the scrape-off layer and fuel recycling in the Lithium Tokamak eXperiment-β

It is well established that the application of lithium to plasma facing components (PFCs) can improve plasma performance in tokamaks. Primarily, lithium PFCs improve plasma performance by reducing fuel recycling and the influx of high Z impurities sputtered from the underlying substrate. The Lithium Tokamak eXperiment (LTX) and its upgrade LTX-?? is the only tokamak in the world capable of operating with near complete coverage of lithium on its PFCs. LTX and LTX-?? have demonstrated plasma performance improvement due to both flat electron temperature profiles, attributed to lowered recycling and reduced radiative loss, attributed to lowered impurity levels. Experiments on LTX have demonstrated that high edge temperatures and low edge density, likely due to a low recycling boundary, lead to a low collisionality scrape-off layer (SOL). However, the connection between flattening electron temperature profiles and recycling, particularly as it relates to the SOL characteristics, remains to be made. To study this unique SOL and to quantify fuel recycling in LTX-?? a new, movable, low field side, off-midplane, swept single Langmuir probe is installed to measure SOL edge density and temperature. Additionally, the neutral particle influx from the high field side limiter is measured using a hydrogen Lyman-?? array. Core electron temperature and density are measured using the LTX-?? Thomson scattering system. The data from these diagnostics indicate a reduction in line integrated Lyman-?? emission intensity and an increase in edge temperature and energy confinement times after fueling termination. More complete analysis of the data using the neutral particle modeling code DEGAS2 will be presented.