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

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 benefitedmore » from the changes of edge parameters. In addition, several possible methods are proposed to recover good efficiency in future experiments for EAST.« less
Authors:
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;  [1] ;  [2] ;
  1. Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China)
  2. CEA, IRFM, F-13108 Saint Paul-Lez-Durance (France)
Publication Date:
OSTI Identifier:
22304132
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 21; Journal Issue: 6; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
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