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

G. M. Wallace; I. C. Faust; O. Meneghini; R. R. Parker; S. Shiraiwa; S. G. Baek; P. T. Bonoli; A. E. Hubbard; J. W. Hughes; B. L. Labombard; C. Lau; Y. Ma; M. L. Reinke; J. L. Terry; D. G. Whyte; J. C. Wright; S. J. Wukitch; R. W. Harvey; A. E. Schmidt; A. P. Smirnov; J. R. Wilson

doi:10.1063/1.4729734

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

G. M. Wallace, I. C. Faust, O. Meneghini, R. R. Parker, S. Shiraiwa, S. G. Baek, P. T. Bonoli, A. E. Hubbard, J. W. Hughes, B. L. Labombard, C. Lau, Y. Ma, M. L. Reinke, J. L. Terry, D. G. Whyte, J. C. Wright, S. J. Wukitch, R. W. Harvey, A. E. Schmidt, A. P. SmirnovJ. R. Wilson

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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 19 AW ^-1 m ^-2 at n̄ _e 0.5 × 10 ²⁰m ^-3) on Alcator C-Mod [I. H. Hutchinson, Phys. Plasmas 1, 1511 (1994)] under conditions (n e, magnetic field and topology, and LHCD frequency) relevant to ITER [S. Shiraiwa, 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 n̄ _e to 1.0 - 1.5 × 10 ²⁰m ^-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 e in high density LH discharges results in higher non-thermal electron emission, as predicted by the models.

Original language	English
Article number	062505
Journal	Physics of Plasmas
Volume	19
Issue number	6
DOIs	https://doi.org/10.1063/1.4729734
State	Published - Jun 2012
Externally published	Yes

Funding

The authors would like to thank the C-Mod LHCD engineering team for their efforts in keeping the system running. This work was supported by US Department of Energy awards DE-FC02-99ER54512 and DE-AC02-09CH11466.

Funders	Funder number
U.S. Department of Energy	DE-AC02-09CH11466, DE-FC02-99ER54512

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

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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., Harvey, R. W., Schmidt, A. E., ... Wilson, J. R. (2012). Lower hybrid current drive at high density in the multi-pass regime. Physics of Plasmas, 19(6), Article 062505. https://doi.org/10.1063/1.4729734

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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 (η 2.0 - 2.5 × 10 19 AW -1 m -2 at {\=n} e 0.5 × 10 20m -3) on Alcator C-Mod [I. H. Hutchinson, Phys. Plasmas 1, 1511 (1994)] under conditions (n e, magnetic field and topology, and LHCD frequency) relevant to ITER [S. Shiraiwa, 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} e to 1.0 - 1.5 × 10 20m -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 e in high density LH discharges results in higher non-thermal electron emission, as predicted by the models.",

author = "Wallace, {G. M.} and Faust, {I. C.} and O. Meneghini and Parker, {R. R.} and S. Shiraiwa and Baek, {S. G.} and Bonoli, {P. T.} and Hubbard, {A. E.} and Hughes, {J. W.} and Labombard, {B. L.} and C. Lau and Y. Ma and Reinke, {M. L.} and Terry, {J. L.} and Whyte, {D. G.} and Wright, {J. C.} and Wukitch, {S. J.} and Harvey, {R. W.} and Schmidt, {A. E.} and Smirnov, {A. P.} and Wilson, {J. R.}",

year = "2012",

month = jun,

doi = "10.1063/1.4729734",

language = "English",

volume = "19",

journal = "Physics of Plasmas",

issn = "1070-664X",

publisher = "American Institute of Physics",

number = "6",

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Wallace, GM, Faust, IC, Meneghini, O, Parker, RR, Shiraiwa, S, Baek, SG, Bonoli, PT, Hubbard, AE, Hughes, JW, Labombard, BL, Lau, C, Ma, Y, Reinke, ML, Terry, JL, Whyte, DG, Wright, JC, Wukitch, SJ, Harvey, RW, Schmidt, AE, Smirnov, AP & Wilson, JR 2012, 'Lower hybrid current drive at high density in the multi-pass regime', Physics of Plasmas, vol. 19, no. 6, 062505. https://doi.org/10.1063/1.4729734

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T1 - Lower hybrid current drive at high density in the multi-pass regime

AU - Wallace, G. M.

AU - Faust, I. C.

AU - Meneghini, O.

AU - Parker, R. R.

AU - Shiraiwa, S.

AU - Baek, S. G.

AU - Bonoli, P. T.

AU - Hubbard, A. E.

AU - Hughes, J. W.

AU - Labombard, B. L.

AU - Lau, C.

AU - Ma, Y.

AU - Reinke, M. L.

AU - Terry, J. L.

AU - Whyte, D. G.

AU - Wright, J. C.

AU - Wukitch, S. J.

AU - Harvey, R. W.

AU - Schmidt, A. E.

AU - Smirnov, A. P.

AU - Wilson, J. R.

PY - 2012/6

Y1 - 2012/6

N2 - 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 19 AW -1 m -2 at n̄ e 0.5 × 10 20m -3) on Alcator C-Mod [I. H. Hutchinson, Phys. Plasmas 1, 1511 (1994)] under conditions (n e, magnetic field and topology, and LHCD frequency) relevant to ITER [S. Shiraiwa, 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 n̄ e to 1.0 - 1.5 × 10 20m -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 e in high density LH discharges results in higher non-thermal electron emission, as predicted by the models.

AB - 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 19 AW -1 m -2 at n̄ e 0.5 × 10 20m -3) on Alcator C-Mod [I. H. Hutchinson, Phys. Plasmas 1, 1511 (1994)] under conditions (n e, magnetic field and topology, and LHCD frequency) relevant to ITER [S. Shiraiwa, 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 n̄ e to 1.0 - 1.5 × 10 20m -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 e in high density LH discharges results in higher non-thermal electron emission, as predicted by the models.

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

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