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Measuring the Effects of Lithium Wall-coatings on Impurities in LTX

Author: Dennis P. Boyle
Requested Type: Poster Only
Submitted: 2014-05-30 17:27:57

Co-authors: R.E. Bell, R. Kaita, R. Majeski, PPPL, T.M. Biewer, T.K. Gray, ORNL, K.Tritz, JHU, K. Widmann, LLNL

Contact Info:
PPPL
Stellarator Road
Princeton, NEW JERSEY   08540
United States

Abstract Text:
The Lithium Tokamak Experiment (LTX) is designed to study the low-recycling regime through the use of close-fitting, lithium-coated, heatable shell quadrants surrounding the plasma volume. Lithium coatings can getter and bury impurities, but they can also become covered by impurity compounds. Liquefied coatings can either dissolve impurity compounds or bring them to the surface, while sputtering and evaporation rates increase strongly with temperature. Here, we use spectroscopic measurements to assess the effects of varying wall conditions on plasma impurities.
As part of a long-standing collaboration with PPPL, ORNL has a large role in spectroscopy in LTX, including fast filterscopes and compact visible spectrometers. Upgraded optics and fiber arrays for the ORNL passive Doppler spectroscopy system view the core plasma toroidally (r/a<0.7) and poloidally (0.2<r/a<0.9). Spectra are measured with high sensitivity and time resolution using an ORNL fixed-wavelength spectrometer as well as a novel spectrometer with similar performance which can be adjusted between shots to measure any impurity lines in the visible range, including Li I-III, C I-IV, and O I-III. In addition, extreme ultraviolet spectroscopy with survey and high-resolution LLNL grazing-incidence spectrometers and a JHU transmission grating imaging radiometer detect emission from higher charge states, especially O IV-VI, Li II-III, and C IV.
Preliminary results show that fresh Li coatings generally reduced C and O emission. C emission decreased sharply following the first solid Li coatings. Inversions of toroidal profiles in a discharge with solid Li coatings show peaked Li III emissivity and temperature profiles. Recently, experiments with fresh liquid coatings led to especially strong O reduction. These results and further analysis will be presented, along with developments in supporting diagnostics and interpretive modeling.
Supported by US DOE contracts DE-AC02-09CH11466 and DE-AC05-00OR22725

Characterization: 1.4

Comments:
Place with other LTX posters by Majeski, Schmitt, and Jacobson

Workshop on Exploratory Topics in Plasma and Fusion Research (EPR) and US-Japan Compact Torus (CT) Workshop
August 5-8, 2014
Madison, Wisconsin

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