Lower hybrid current drive at high density in the multi-pass regime
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Whyte_Lower hybrid current.pdf
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Author(s)
Meneghini, Orso-Maria Cornelio
Lau, C.
Ma, Y.
Harvey, R. W.
Schmidt, A. E.
Smirnov, A. P.
Wilson, J. R.
Wallace, Gregory Marriner
Faust, Ian Charles
Parker, Ronald R.
Date Issued
June 2012
Journal
Physics of Plasmas
Publisher
American Institute of Physics (AIP)
Citation
Wallace, G. M. et al. “Lower Hybrid Current Drive at High Density in the Multi-pass Regime.” Physics of Plasmas 19.6 (2012): 062505.
Version
Author's final manuscript
Abstract
Assessing the performance of lower hybrid current drive (LHCD) at high density is critical for developing non-inductive current drive systems on future steady-state experiments. Excellent LHCD efficiency has been observed during fully non-inductive operation (η = 2.0 − 2.5 × 10[superscript 19] AW[superscript –1] m[superscript –2] at [¯ over n][subscript e] = 0.5 × 10[superscript 20] m[superscript –3]) on Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas1, 1511 (1994)] under conditions (n[subscript e], magnetic field and topology, and LHCD frequency) relevant to ITER [S. Shiraiwa et al., Nucl. Fusion 51, 103024 (2011)]. To extend these results to advanced tokamak regimes with higher bootstrap current fractions on C-Mod, it is necessary to increase [¯ over n][subscript e] to 1.0 − 1.5 × 10[superscript 20] m[superscript −3]. However, the number of current-carrying, non-thermal electrons generated by LHCD drops sharply in diverted configurations at densities that are well below the density limit previously observed on limited tokamaks. In these cases, changes in scrape off layer (SOL)ionization and density profiles are observed during LHCD, indicating that significant power is transferred from the LH waves to the SOL.Fokker-Planck simulations of these discharges utilizing ray tracing and full wave propagation codes indicate that LH waves in the high density, multi-pass absorption regime linger in the plasma edge, and SOL region, where absorption near or outside the LCFS results in the loss of current drive efficiency. Modeling predicts that non-thermal emission increases with stronger single-pass absorption. Experimental data show that increasing T[subscript e] in high density LH discharges results in higher non-thermal electron emission, as predicted by the models.
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/10.1063/1.4729734
