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Title: Improved confinement in high-density H-modes via modification of the plasma boundary with lower hybrid wavesa)

Abstract

Injecting Lower Hybrid Range of Frequency (LHRF) waves into Alcator C-Mod's high-density H-mode plasmas has led to enhanced global energy confinement by increasing pedestal temperature and pressure gradients, decreasing the separatrix density, modifying the pedestal radial electric field and rotation, and decreasing edge turbulence. These experiments imply that edge LHRF can be used as an actuator to increase energy confinement via modification of boundary quantities. H98-factor increases of up to ~35% (e.g., H98 from 0.75 to 1.0) are seen when moderate amounts of LH power (PLH/Ptot~0.15) are applied to H-modes of densities $$\overline{n}$$e~3 × 1020 m–3, corresponding to values ~0.5 of the Greenwald density. However, the magnitude of the improvement is reduced if the confinement quality of the target H-mode plasma is already good (i.e., H98target ~ 1). Ray-tracing modeling and accessibility calculations for the LH waves indicate that they do not penetrate to the core. The LHRF power appears to be deposited in plasma boundary region, with a large fraction of the injected power increment appearing promptly on the outer divertor target. There is no evidence that the LH waves are driving current in these plasmas. The LHRF-actuated improvements are well correlated with suppressed pedestal density fluctuations in themore » 100–300 kHz range. Additionally, there is a correlation between the improved confinement and a drop in separatrix density, a correlation that is consistent with previous H-mode results with no LHRF.« less

Authors:
 [1];  [2]; ORCiD logo [1];  [1];  [3];  [1];  [1];  [1];  [4];  [4];  [1];  [1];  [1]; ORCiD logo [1];  [1];  [1];  [1];  [1];  [1];  [1] more »;  [1];  [1];  [1] « less
  1. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  2. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Univ. of York (United Kingdom)
  3. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Ecole Polytechnique Federale Lausanne (Switzlerland)
  4. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Publication Date:
Research Org.:
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)
Contributing Org.:
C-Mod Team
OSTI Identifier:
1547003
Alternate Identifier(s):
OSTI ID: 1228177
Grant/Contract Number:  
FC02-99ER54512; AC02-09CH11466
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 22; Journal Issue: 5; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Terry, J. L., Reinke, M. L., Hughes, J. W., LaBombard, B., Theiler, C., Wallace, G. M., Baek, S. G., Brunner, D., Churchill, R. M., Edlund, E., Ennever, P., Faust, I., Golfinopoulos, T., Greenwald, M., Hubbard, A. E., Irby, J., Lin, Y., Parker, R. R., Rice, J. E., Shiraiwa, S., Walk, J. R., Wukitch, S. J., and Xu, P. Improved confinement in high-density H-modes via modification of the plasma boundary with lower hybrid wavesa). United States: N. p., 2015. Web. doi:10.1063/1.4920964.
Terry, J. L., Reinke, M. L., Hughes, J. W., LaBombard, B., Theiler, C., Wallace, G. M., Baek, S. G., Brunner, D., Churchill, R. M., Edlund, E., Ennever, P., Faust, I., Golfinopoulos, T., Greenwald, M., Hubbard, A. E., Irby, J., Lin, Y., Parker, R. R., Rice, J. E., Shiraiwa, S., Walk, J. R., Wukitch, S. J., & Xu, P. Improved confinement in high-density H-modes via modification of the plasma boundary with lower hybrid wavesa). United States. https://doi.org/10.1063/1.4920964
Terry, J. L., Reinke, M. L., Hughes, J. W., LaBombard, B., Theiler, C., Wallace, G. M., Baek, S. G., Brunner, D., Churchill, R. M., Edlund, E., Ennever, P., Faust, I., Golfinopoulos, T., Greenwald, M., Hubbard, A. E., Irby, J., Lin, Y., Parker, R. R., Rice, J. E., Shiraiwa, S., Walk, J. R., Wukitch, S. J., and Xu, P. 2015. "Improved confinement in high-density H-modes via modification of the plasma boundary with lower hybrid wavesa)". United States. https://doi.org/10.1063/1.4920964. https://www.osti.gov/servlets/purl/1547003.
@article{osti_1547003,
title = {Improved confinement in high-density H-modes via modification of the plasma boundary with lower hybrid wavesa)},
author = {Terry, J. L. and Reinke, M. L. and Hughes, J. W. and LaBombard, B. and Theiler, C. and Wallace, G. M. and Baek, S. G. and Brunner, D. and Churchill, R. M. and Edlund, E. and Ennever, P. and Faust, I. and Golfinopoulos, T. and Greenwald, M. and Hubbard, A. E. and Irby, J. and Lin, Y. and Parker, R. R. and Rice, J. E. and Shiraiwa, S. and Walk, J. R. and Wukitch, S. J. and Xu, P.},
abstractNote = {Injecting Lower Hybrid Range of Frequency (LHRF) waves into Alcator C-Mod's high-density H-mode plasmas has led to enhanced global energy confinement by increasing pedestal temperature and pressure gradients, decreasing the separatrix density, modifying the pedestal radial electric field and rotation, and decreasing edge turbulence. These experiments imply that edge LHRF can be used as an actuator to increase energy confinement via modification of boundary quantities. H98-factor increases of up to ~35% (e.g., H98 from 0.75 to 1.0) are seen when moderate amounts of LH power (PLH/Ptot~0.15) are applied to H-modes of densities $\overline{n}$e~3 × 1020 m–3, corresponding to values ~0.5 of the Greenwald density. However, the magnitude of the improvement is reduced if the confinement quality of the target H-mode plasma is already good (i.e., H98target ~ 1). Ray-tracing modeling and accessibility calculations for the LH waves indicate that they do not penetrate to the core. The LHRF power appears to be deposited in plasma boundary region, with a large fraction of the injected power increment appearing promptly on the outer divertor target. There is no evidence that the LH waves are driving current in these plasmas. The LHRF-actuated improvements are well correlated with suppressed pedestal density fluctuations in the 100–300 kHz range. Additionally, there is a correlation between the improved confinement and a drop in separatrix density, a correlation that is consistent with previous H-mode results with no LHRF.},
doi = {10.1063/1.4920964},
url = {https://www.osti.gov/biblio/1547003}, journal = {Physics of Plasmas},
issn = {1070-664X},
number = 5,
volume = 22,
place = {United States},
year = {Mon May 18 00:00:00 EDT 2015},
month = {Mon May 18 00:00:00 EDT 2015}
}

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Works referenced in this record:

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New insights on boundary plasma turbulence and the quasi-coherent mode in Alcator C-Mod using a Mirror Langmuir Probe
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Hard x-ray diagnostic for lower hybrid experiments on Alcator C-Mod
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