April 4-6

Abstract Details

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Author: Samuel Frank
Requested Type: Poster
Submitted: 2022-03-03 15:43:44

Co-authors: S.J.Wukitch, J.C.Wright, P.T.Bonoli

Contact Info:
Massachusetts Institute of Technology
56 Gardner St. Apt. 14
Boston, MA   02134

Abstract Text:
Lower-hybrid current drive (LHCD) is an important current drive actuator in present-day tokamak experiments, and because of its high current drive efficiency LHCD is used in a number of fusion pilot plant designs. However, interpreting the results of LHCD experiments remains difficult due to the phase velocity downshift process known as the spectral gap closure. The closure of the spectral gap dictates lower-hybrid wave damping in most current tokamaks where the lower-hybrid wave is weakly damped. Here, using the largest tokamak RF heating simulations ever performed, we demonstrate spectral gap closure induced by full-wave effects for the first time in weakly damped LHCD experiments in EAST. Furthermore, in the strongly damped reactor-like high-field-side LHCD experiment on DIII-D and in a number of damping regimes in C-Mod we show using comparisons with full-wave simulations that raytracing simulations of LHCD can have excellent validity in regimes with stronger damping. These results indicate that raytracing will be an effective tool in the design of future fusion reactors and help to provide a fundamental understanding of the spectral gap closure process in weakly damped LHCD experiments.