Abstract
Lithium coatings in the Lithium Tokamak eXperiment (LTX) led to flat temperature profiles. The flat temperature profiles were observed along with a hot, low density edge, implying a broad, collisionless scrape-off layer (SOL). Additionally, in vacuo X-ray photoelectron spectroscopy (XPS) measurements established that lithium coatings evaporatively deposited onto high-Z plasma facing components (PFCs) became oxidized while retaining the ability to achieve good plasma performance long after lithium was applied to the PFCs. Longstanding theory predicted flat temperature profiles with low recycling walls, which was presumed to be due to hydrogen binding with elemental lithium to form lithium hydride. The presence of oxidized lithium, however, raised questions regarding the exact mechanism of hydrogen retention in LTX. To investigate these questions, the upgraded facility LTX- ß includes a new sample exposure probe (SEP) for more detailed in vacuo analysis of PFC samples. The SEP is equipped with a vacuum suitcase capable of transporting samples representative of the LTX- ß outer midplane PFCs to a stand-alone XPS system while maintaining pressures lower than the LTX- ß base vacuum to limit the contamination between sample exposure and analysis. The low-energy resolution XPS system used in past experiments could only enable the determination of elemental percentages on the PFC sample surfaces. Because the new XPS system has higher energy resolution, it is more direct to assign chemical compounds to the measured binding energies. This capability has been confirmed by comparing XPS data from PFC test samples with measurements using a commercial high-resolution XPS system. Quartz crystal microbalances (QCMs) were used to quantify the thickness of the deposited lithium on the LTX- ß PFCs. This article describes the application of the SEP to characterize the PFC surfaces using XPS and their relationship to plasma conditions.
Original language | English |
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Article number | 9102425 |
Pages (from-to) | 1463-1467 |
Number of pages | 5 |
Journal | IEEE Transactions on Plasma Science |
Volume | 48 |
Issue number | 6 |
DOIs | |
State | Published - Jun 2020 |
Funding
Manuscript received July 19, 2019; revised January 2, 2020; accepted January 18, 2020. Date of publication May 27, 2020; date of current version June 10, 2020. This work was supported by the U.S. DOE under Grant DE-AC02-09CH11466, Grant DE-AC05-00OR22725, Grant DE-AC52-07NA27344, and Grant DE-SC0019308. The review of this article was arranged by Senior Editor G. H. Neilson. (Corresponding author: Anurag Maan.) Anurag Maan, Robert Kaita, and David Donovan are with the Department of Nuclear Engineering, University of Tennessee, Knoxville, TN 37996 USA (e-mail: [email protected]).
Keywords
- Lithium
- plasma chemistry
- plasma confinement
- plasma diagnostics
- tokamaks