Estimates of global recycling coefficients for LTX-β discharges

Maan, A.; Boyle, D. P.; Majeski, R.; Wilkie, G. J.; Francisquez, M.; Banerjee, S.; Kaita, R.; Maingi, R.; LeBlanc, B. P.; Abe, S.; Jung, E.; Perez, E.; Capecchi, W.; Ostrowski, E. T.; Elliott, D. B.; Hansen, C.; Kubota, S.; Soukhanovskii, V.; Zakharov, L.

doi:10.1063/5.0177604

Title: Estimates of global recycling coefficients for LTX-β discharges

Journal Article · 15 February 2024 · Physics of Plasmas

DOI: https://doi.org/10.1063/5.0177604 · OSTI ID:2305594

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Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
Univ. of Wisconsin, Madison, WI (United States)
Princeton Univ., NJ (United States)
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Columbia Univ., New York, NY (United States)
Univ. of California, Los Angeles, CA (United States)
Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
LiWall Fusion, Princeton, NJ (United States)

We report the first observation of global recycling coefficient R near 0.5 in the Lithium Tokamak eXperiment-β (LTX-β), significantly below the minimum R previously reported in other devices. In a series of experiments with varied Li wall conditioning, estimates of the recycling coefficient have been made using a Lyman-α array and DEGAS2 modeling. A progressive reduction in Lyman-α emission with increased lithium and an increase in edge electron temperature are observed. It is also observed that with increasing Li coating thickness, the effective particle confinement time τ_p^* is reduced and approaches TRANSP calculated energy confinement time (τ_E), with τ_p^* near τ_E,TRANSP for the lowest recycling coefficients. Edge temperatures approaching core plasma temperatures, first reported in LTX, can now be directly connected to estimates of the recycling coefficient and qualitatively agree with previous UEDGE simulations. The particle flux to the limiting surfaces appears to be significantly reduced in comparison with fluid scrape-off layer (SOL) models, indicating that a large fraction of the SOL ions are mirror trapped. SOL collisionality drops more than an order of magnitude below the banana regime boundary, indicating the importance of kinetic effects. Full-f 1x2v gyrokinetic simulations of SOL field lines with the GKEYLL code indicate that the fraction of ions trapped along field lines increases as collisionality drops, as a result of increased lithium evaporation.

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Research Organization:: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)

Sponsoring Organization:: USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Fusion Energy Sciences (FES)

Grant/Contract Number:: AC52-07NA27344; AC02-09CH11466; AC05-00OR22725; SC0023481; SC0019006; SC0019239; SC0019308

OSTI ID:: 2305594

Report Number(s):: LLNL-JRNL-854653; 1083264; TRN: US2409026

Journal Information:: Physics of Plasmas, Vol. 31, Issue 2; ISSN 1070-664X

Publisher:: American Institute of Physics (AIP)Copyright Statement

Country of Publication:: United States

Language:: English

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