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Title: Lower hybrid current drive at high density in the multi-pass regime

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 ({eta}=2.0-2.5 Multiplication-Sign 10{sup 19} AW{sup -1}m{sup -2} at n{sub e}=0.5 Multiplication-Sign 10{sup 20} m{sup -3}) on Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] under conditions (n{sub 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 n{sub e} to 1.0-1.5 Multiplication-Sign 10{sup 20} m{sup -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 themore » 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{sub e} in high density LH discharges results in higher non-thermal electron emission, as predicted by the models.« less

Authors:
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;  [1];  [2];  [3] more »; « less
  1. MIT Plasma Science and Fusion Center, Cambridge, Massachusetts 02139 (United States)
  2. CompX, Del Mar, California 92014 (United States)
  3. M.V. Lomonosov Moscow State University, Moscow (Russian Federation)
Publication Date:
OSTI Identifier:
22072465
Resource Type:
Journal Article
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 19; Journal Issue: 6; Other Information: (c) 2012 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 1070-664X
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ABSORPTION; ALCATOR DEVICE; BOOTSTRAP CURRENT; EFFICIENCY; ELECTRON EMISSION; EXPERIMENTAL DATA; FOKKER-PLANCK EQUATION; IONIZATION; ITER TOKAMAK; LOWER HYBRID CURRENT DRIVE; MAGNETIC FIELDS; PERFORMANCE; PLASMA SCRAPE-OFF LAYER; STEADY-STATE CONDITIONS; WAVE PROPAGATION

Citation Formats

Wallace, G. M., Faust, I. C., Meneghini, O., Parker, R. R., Shiraiwa, S., Baek, S. G., Bonoli, P. T., Hubbard, A. E., Hughes, J. W., LaBombard, B. L., Lau, C., Ma, Y., Reinke, M. L., Terry, J. L., Whyte, D. G., Wright, J. C., Wukitch, S. J., Schmidt, A. E., Harvey, R. W., Smirnov, A. P., and and others. Lower hybrid current drive at high density in the multi-pass regime. United States: N. p., 2012. Web. doi:10.1063/1.4729734.
Wallace, G. M., Faust, I. C., Meneghini, O., Parker, R. R., Shiraiwa, S., Baek, S. G., Bonoli, P. T., Hubbard, A. E., Hughes, J. W., LaBombard, B. L., Lau, C., Ma, Y., Reinke, M. L., Terry, J. L., Whyte, D. G., Wright, J. C., Wukitch, S. J., Schmidt, A. E., Harvey, R. W., Smirnov, A. P., & and others. Lower hybrid current drive at high density in the multi-pass regime. United States. doi:10.1063/1.4729734.
Wallace, G. M., Faust, I. C., Meneghini, O., Parker, R. R., Shiraiwa, S., Baek, S. G., Bonoli, P. T., Hubbard, A. E., Hughes, J. W., LaBombard, B. L., Lau, C., Ma, Y., Reinke, M. L., Terry, J. L., Whyte, D. G., Wright, J. C., Wukitch, S. J., Schmidt, A. E., Harvey, R. W., Smirnov, A. P., and and others. Fri . "Lower hybrid current drive at high density in the multi-pass regime". United States. doi:10.1063/1.4729734.
@article{osti_22072465,
title = {Lower hybrid current drive at high density in the multi-pass regime},
author = {Wallace, G. M. and Faust, I. C. and Meneghini, O. and Parker, R. R. and Shiraiwa, S. and Baek, S. G. and Bonoli, P. T. and Hubbard, A. E. and Hughes, J. W. and LaBombard, B. L. and Lau, C. and Ma, Y. and Reinke, M. L. and Terry, J. L. and Whyte, D. G. and Wright, J. C. and Wukitch, S. J. and Schmidt, A. E. and Harvey, R. W. and Smirnov, A. P. and and others},
abstractNote = {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 ({eta}=2.0-2.5 Multiplication-Sign 10{sup 19} AW{sup -1}m{sup -2} at n{sub e}=0.5 Multiplication-Sign 10{sup 20} m{sup -3}) on Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] under conditions (n{sub 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 n{sub e} to 1.0-1.5 Multiplication-Sign 10{sup 20} m{sup -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{sub e} in high density LH discharges results in higher non-thermal electron emission, as predicted by the models.},
doi = {10.1063/1.4729734},
journal = {Physics of Plasmas},
issn = {1070-664X},
number = 6,
volume = 19,
place = {United States},
year = {2012},
month = {6}
}