Observation of Efficient Lower Hybrid Current Drive at High Density in Diverted Plasmas on the Alcator C-Mod Tokamak

Dataset · Fri Jan 18 04:00:00 EST 2019

DOI:https://doi.org/10.7910/DVN/PZOMOI· OSTI ID:1881223

Baek, S. G. ^[1]; Wallace, G. M.; Bonoli, P. T.; Brunner, D.; Faust, I. C.; Hubbard, A. E.; Hughes, J. W.; LaBombard, B.; Parker, R. R.; Porkolab, M.; Shiraiwa, S.; Wukitch, S.

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1. OSTI

Efficient lower hybrid current drive (LHCD) is demonstrated at densities up to ne≈1.5×10^20 m^-3 in diverted plasmas on the Alcator C-Mod tokamak by operating at increased plasma current - and therefore reduced Greenwald density fraction. This density exceeds the nominal "LH density limit" at ne≈1.0×10^20 m^-3 reported previously, above which an anomalous loss of current drive efficiency was observed. The recovery of current drive efficiency to a level consistent with engineering scalings is correlated with a reduction in density shoulders and turbulence levels in the far scrape-off layer. Concurrently, rf wave interaction with the edge and/or scrape-off-layer plasma is reduced, as indicated by a minimal broadening of the wave frequency spectrum measured at the plasma edge. These results have important implications for sustaining steady-state tokamak operation and indicate a pathway forward for implementing efficient LHCD in a reactor.

• Research Organization: Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center
• Sponsoring Organization: USDOE Office of Science (SC), Fusion Energy Sciences (FES)
• DOE Contract Number: FC02-99ER54512
• OSTI ID: 1881223
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY