XP should quantify modifications to SOL profiles under varying pumping scenarios

1. XP should quantify modifications to SOL profiles under varying pumping scenarios • LLD exists to create a low recycling surface that improves plasma performance through persistent pumping • Previous lithium usage has demonstrably lowered midplane edge densities as seen by SOL reflectometer • some, but limited, reciprocating probe data give midplane SOL temperature profiles • almost no SOL data at target, as only available diagnostic was a single Langmuir probe at R=.79m, far from most discharges • Desire to measure SOL temperatures and densities at the divertor target as function of plasma interaction with lithium • includes state of lithium (solid vs. liquid), temperature of lithium, flux to pumping surfaces, local recycling coefficients • main knobs are temperature of LLD, LITER deposition, and ROSP

2. Experimental capabilities and possible pathways • Utilize probe array proximity to strike point in intermediate triangularity discharge (ROSP = .63m) with 1-2 MW NBI to characterize density, temperature, and flux under cold and warm Li conditions • Do not evaporate between discharges in both cases to test persistence of Li surface • evaluate need for re-evaporation when surface becomes passive • SOL density and temperature profiles as obtained by LP array will inform on plasma response • Once baseline established, and depending on results of characterization, move strike point outboard in 1-2 cm increments (up to ROSP=.70m) to increase flux to LLD • establish stable SGI or HFS fueling scenario and document perpendicular SOL density and temperature gradients with array • if power is low enough, can reciprocating probe and/or reflectometer be used to obtain midplane measurements up to separatrix? • ability to control strike point may be required, but low enough li may allow use of pre-programmed PF2L currents