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

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.

doi:10.1063/1.4920964

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

Journal Article · Mon May 18 00:00:00 EDT 2015 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4920964· OSTI ID:1547003

Terry, J. L. ^[1]; Reinke, M. L. ^[2];

^[1]; LaBombard, B. ^[1]; Theiler, C. ^[3]; Wallace, G. M. ^[1]; Baek, S. G. ^[1]; Brunner, D. ^[1]; Churchill, R. M. ^[4]; Edlund, E. ^[4]; Ennever, P. ^[1]; Faust, I. ^[1]; Golfinopoulos, T. ^[1];

^[1]; Hubbard, A. E. ^[1]; Irby, J. ^[1]; Lin, Y. ^[1]; Parker, R. R. ^[1]; Rice, J. E. ^[1]; Shiraiwa, S. ^[1] more »

Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Univ. of York (United Kingdom)
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Ecole Polytechnique Federale Lausanne (Switzlerland)
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)

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 (P_LH/P_tot~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., H₉₈^target ~ 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.

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Research Organization:: Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Fusion Energy Sciences (FES)

Contributing Organization:: C-Mod Team

Grant/Contract Number:: FC02-99ER54512; AC02-09CH11466

OSTI ID:: 1547003

Alternate ID(s):: OSTI ID: 1228177

Journal Information:: Physics of Plasmas, Vol. 22, Issue 5; ISSN 1070-664X

Publisher:: American Institute of Physics (AIP)Copyright Statement

Country of Publication:: United States

Language:: English

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Cited by: 6 works

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