Study on lower hybrid current drive efficiency at high density towards long-pulse regimes in Experimental Advanced Superconducting Tokamak

Journal Article · Sun Jun 15 00:00:00 EDT 2014 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4883640· OSTI ID:22304132

Li, M. H.; Ding, B. J.; Zhang, J. Z.; Gan, K. F.; Wang, H. Q.; Zhang, L.; Wei, W.; Li, Y. C.; Wu, Z. G.; Ma, W. D.; Jia, H.; Chen, M.; Yang, Y.; Feng, J. Q.; Wang, M.; Xu, H. D.; Shan, J. F.; Liu, F. K. ^[1]; Peysson, Y. ^[2]; others, and

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1. Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China)
2. CEA, IRFM, F-13108 Saint Paul-Lez-Durance (France)

Significant progress on both L- and H-mode long-pulse discharges has been made recently in Experimental Advanced Superconducting Tokamak (EAST) with lower hybrid current drive (LHCD) [J. Li et al., Nature Phys. 9, 817 (2013) And B. N. Wan et al., Nucl. Fusion 53, 104006 (2013).]. In this paper, LHCD experiments at high density in L-mode plasmas have been investigated in order to explore possible methods of improving current drive (CD) efficiency, thus to extend the operational space in long-pulse and high performance plasma regime. It is observed that the normalized bremsstrahlung emission falls much more steeply than 1/n{sub e-av} (line-averaged density) above n{sub e-av} = 2.2 × 10{sup 19} m{sup −3} indicating anomalous loss of CD efficiency. A large broadening of the operating line frequency (f = 2.45 GHz), measured by a radio frequency (RF) probe located outside the EAST vacuum vessel, is generally observed during high density cases, which is found to be one of the physical mechanisms resulting in the unfavorable CD efficiency. Collisional absorption of lower hybrid wave in the scrape off layer (SOL) may be another cause, but this assertion needs more experimental evidence and numerical analysis. It is found that plasmas with strong lithiation can improve CD efficiency largely, which should be benefited from the changes of edge parameters. In addition, several possible methods are proposed to recover good efficiency in future experiments for EAST.

• OSTI ID: 22304132
• Journal Information: Physics of Plasmas, Vol. 21, Issue 6; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
BREMSSTRAHLUNG
EFFICIENCY
GHZ RANGE 01-100
H-MODE PLASMA CONFINEMENT
HT-7U TOKAMAK
L-MODE PLASMA CONFINEMENT
LOWER HYBRID CURRENT DRIVE
LOWER HYBRID HEATING
NUMERICAL ANALYSIS
PLASMA
PLASMA SCRAPE-OFF LAYER
RADIOWAVE RADIATION