10.7910/DVN/PZOMOI S. G. Baek, G. M. Wallace, P. T. Bonoli, D. Brunner, I. C. Faust, A. E. Hubbard, J. W. Hughes, B. LaBombard, R. R. Parker, M. Porkolab, S. Shiraiwa, S. Wukitch Harvard Dataverse 2019 Physics lower hybrid heating &amp; current drive parametric decay instability scattering of waves by turbulence scrape off layer tokamak plasma 2019-01-18 10.7910/DVN/PZOMOI/KQHCWB 10.7910/DVN/PZOMOI/BBH1RP 10.7910/DVN/PZOMOI/DNB7OQ 10.7910/DVN/PZOMOI/Z0FM3L 10.7910/DVN/PZOMOI/8WLKUB 10.7910/DVN/PZOMOI/FMZ7CN 31056 1340456 31056 26640 1623514 480912 application/x-hdf5 application/x-hdf5 application/x-hdf5 application/x-hdf5 application/pdf application/x-hdf5 1.0 Custom terms specific to this dataset 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 &quot;LH density limit&quot; 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. <a href="http://library.psfc.mit.edu/catalog/reports/2010/18ja/18ja022/abstract.php">PSFC REPORT PSFC/JA-18-22</a><br /><br />This research was conducted on Alcator C-Mod, a DOE Office of Science User Facility, and is supported by DOE Contract No. DE-FC02-99ER54512