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Lithium Research

NSTX is a world leader in studying lithium for particle pumping and power handling in diverted, NBI-heated, H-mode tokamak plasmas, and is the first toroidal device to deploy a liquid lithium divertor (LLD).

Research Priorities:

• Utilize MAPP diagnostic to characterize lithiated surface conditions, e.g. reactions with between evaporated lithium and residual gases as well as the plasma facing material itself
• Compare the effect of different surface conditions on plasma performance metrics, such as stored energy, confinement time, fueling efficiency, D pumping, recycling and impurities, and/or local plasma parameters (e.g. local Ne, Te, Ti)
• Assess the impact of lithiated, molybdenum inboard and outboard PFCs on plasma performance.
• Assess impact of novel Li delivery systems on plasma parameters such as stored energy, confinement time, fueling efficiency, impurities and/or local plasma parameters

Milestones:

R(12-1): Investigate the relationship between lithium-conditioned surface composition and plasma behavior.

Responsible TSGs: Lithium Research, Boundary Physics, Advanced Scenarios and Control

"The plasma facing surfaces in a tokamak have long been known to have a profound influence on plasma behavior. The development of a predictive understanding of this relationship has been impeded by the lack of diagnostics of the morphology and composition of the plasma facing surfaces. Recently, a probe has been used to expose samples to NSTX plasmas and subsequent post-run analysis has linked surface chemistry to deuterium retention. However, with very chemically active elements such as lithium, more prompt surface analysis is likely required to characterize the lithiated surface conditions during a plasma discharge. In support of prompt surface analysis, an in-situ materials analysis particle probe (MAPP) will be installed on NSTX. The MAPP probe will enable the exposure of various samples to the SOL plasma followed by ex-vessel but in-vacuo surface analysis within minutes of plasma exposure using state of the art tools. The reactions between evaporated lithium and plasma facing materials and residual gases in NSTX will be investigated. Correlations between the surface composition and plasma behavior will be explored and compared to laboratory experiments and modeling. Measurements of fueling efficiency and recycling will be made. The results will deepen the understanding of plasma-wall interactions and inform the plans for particle control in NSTX-Upgrade."

ITPA and BPO Participation:

• DSOL-21  Introduction of pre-characterized dust for dust transport studies in divertor and SOL