Effect of lithium in the DIII-D SOL and plasma-facing surfaces

Abstract

Lithium has been introduced into the DIII-D tokamak, and migration and retention in graphite have been characterized since no lithium was present in DIII-D initially. A new regime with an enhanced edge electron pedestal and H 98y2 ≤ 2 has been obtained with lithium. Lithium deposition was not uniform, but rather preferentially deposited near the strike points, consistent with previous 13 C experiments. Edge visible lithium light (LiI) remained well above the previous background during the entire DIII-D campaign, decaying with a 2600 plasma-second e-fold, but plasma performance was only affected on the discharge with lithium injection.Lithium injection demonstrated the capability of reducing hydrogenic recycling, density, and ELM frequency.Graphite and silicon samples were exposed to a lithium-injected discharge, using the DiMES system and then removed for ex-situ analysis. The deposited lithium layer remained detectable to a depth up to 1 m. Abstract length (150 words):142 currently

Enhanced H-mode pedestals with lithium injection in DIII-D

“…The emission from neutral Li, Li I, occurring outside the separatrix, from an MDS spectrometer [37] chord viewing the divertor and poloidally the injection region, but at a different toroidal location (figure 2), is plotted in figure 6(d). Note that emission is present before Li is injected, but no Li is observed in the plasma core until after injection starts at 2 s. This is consistent with LiI emission slowly decaying for hundreds of pulses after Li injection, even though it is not detected in the plasma core, and has no effect on subsequent discharges [42]. The level of edge Li I emission is better correlated with the appearance of the long ELM-free periods in the discharge with 18 mg s −1 injection rate since the Li I emission remains low at 9 mg s −1 .…”