Lower hybrid current drive at high density in Alcator C-Mod
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Whyte_Lower hybrid.pdf
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Author(s)
Harvey, R. W.
Meneghini, Orso-Maria Cornelio
Schmidt, A. E.
Smirnov, A. P.
Wilson, J. R.
Wallace, Gregory Marriner
Hubbard, Amanda E.
Bonoli, Paul T.
Faust, Ian Charles
Hughes, Jerry W.
Date Issued
July 2011
Journal
Nuclear Fusion
Publisher
IOP Publishing
Citation
Wallace, G.M. et al. “Lower Hybrid Current Drive at High Density in Alcator C-Mod.” Nuclear Fusion 51.8 (2011): 083032.
Version
Author's final manuscript
Abstract
Experimental observations of lower hybrid current drive (LHCD) at high density on the Alcator C-Mod tokamak are presented in this paper. Bremsstrahlung emission from relativistic fast electrons in the core plasma drops suddenly above line-averaged densities of 10[superscript 20] m[superscript −3] (ω/ω[subscript LH] ~ 3) in single null discharges with large (≥8 mm) inner gaps, well below the density limit previously observed on limited tokamaks (ω/ω[subscript LH] ~ 2). Modelling and experimental evidence suggest that the absence of LHCD driven fast electrons at high density may be due to parasitic collisional absorption in the scrape-off layer (SOL). Experiments show that the population of fast electrons produced by LHCD at high density ([bar over n][subscript e] > 10[superscript 20] m[superscript -3]) can be increased by operating with an inner gap of less than ~5 mm with the strongest non-thermal emission in inner wall limited plasmas. A change in plasma topology from single to double null produces a modest increase in non-thermal emission at high density. Increasing the electron temperature in the periphery of the plasma (0.8 > r/a > 1.0) also results in a modest increase in non-thermal electron emission above the density limit. Ray tracing/Fokker–Planck simulations of these discharges predict the observed sensitivity to plasma position when the effects of collisional absorption in the SOL are included in the model.
MIT Department
Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science
Massachusetts Institute of Technology. Department of Nuclear Science and Engineering
Massachusetts Institute of Technology. Plasma Science and Fusion Center
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Creative Commons Attribution-Noncommercial-Share Alike 3.0
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DOI of Published Version
https://doi.org/10.1088/0029-5515/51/8/083032
