Effects of plasma configuration, ELM and gas puffing on LHW coupling during H-mode in EAST

Kong, E. H.; Ding, Bingjun; Zhang, L; Liu, L; Qin, Chenghu; Gong, Xianzu; Xu, Guosheng; Li, M H; Wei, W.; Li, Y C; Wu, Ze; Gao, Wei; Shan, Jiafang; Liu, F K; Xu, Long; Zhao, Yanping; Zhao, Liang; Wang, M; Xu, H.; Feng, Jian; Yang, Yixin; Jia, H.; Hu, Haiping; Wang, X J; Wu, Dajun; Wu, Jinyong

doi:10.1088/0741-3335/55/6/065008

Cited by 8 publications

(9 citation statements)

References 21 publications

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“…This is a key asset particularly for long pulse operation when density control becomes of prime importance due to increased outgassing. Local deuterium puffing was first used to improve LH wave coupling in H-mode when the density drops at the edge [11,12]. After successful results on the lower hybrid system, the technique has been applied to improve ICRF wave coupling which is in general, difficult in EAST.…”

Section: Presentation Of East Parameters and Diagnostics Used In Thismentioning

confidence: 99%

Optimization of discharges with ion cyclotron range of frequencies using local gas injection in EAST

et al. 2019

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In view of improving Ion Cyclotron Range of Frequencies (ICRF) wave coupling in EAST (Experimental Advanced Superconducting Tokamak) necessary to obtain high-power discharges, two series of experiments in L-mode were devoted to the use of local gas injection as a tool to increase density in front of the antennas.During the first session, the quantity of deuterium simultaneously puffed from five different poloidal positions on each side of one ICRF antenna was gradually increased. Steady gas puffing on this antenna (~8.10 20 e/s) increased antenna coupling resistance by 100%, but puffing more gas did not provoke any further improvement.Plasma central electron density was not kept constant when using local puff but kept increasing during the discharges. During the second session, the global density was well-controlled and remained constant, the distance between the separatrix and the first wall was increased by 2cm allowing, the gas to spread better, and puffing more gas this time lead to better wave coupling. The same amount of gas was then puffed from three different locations and changes in SOL (Scrape-Off Layer) parameters were measured from several locations. Extensive analysis of the edge diagnostics made it possible to observe an electron density increase and a temperature decrease caused by the ionization of neutrals in the SOL. Heat loads on the divertor targets were slightly mitigated by gas injection, which is favorable from the perspective of long pulse scenario development. Injection at mid-plane led to the best results with the highest coupling simultaneously achieved for both antennas and smallest heat loads on the divertor target (below 1MW/m²). As far as wave coupling efficiency is concerned, most experimental trends were also successfully reproduced by antenna modelling with the RAPLICASOL finite element code with experimental density profiles from reflectometry as the main input.

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Section: Presentation Of East Parameters and Diagnostics Used In Thismentioning

confidence: 99%

Optimization of discharges with ion cyclotron range of frequencies using local gas injection in EAST

et al. 2019

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“…For the 2. 45 GHz system, many LHCD results have been reported [16,[22][23][24][25][26][27], including coupling and current drive at different conditions.…”

Section: Nuclear Fusionmentioning

confidence: 99%

First results of LHCD experiments with 4.6 GHz system toward steady-state plasma in EAST

Liu

Ding

et al. 2015

Nucl. Fusion

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A 4.6 GHz lower-hybrid current drive (LHCD) system has been firstly commissioned in EAST in the 2014 campaign. The first LHCD results with 4.6 GHz show that LHW can be coupled to plasma with a low reflection coefficient, drive plasma current and plasma rotation, modify the plasma current profile, and heat plasma effectively. By means of configuration optimization and local gas puffing near the LHW antenna, good LHW-plasma coupling with a reflection coefficient less than 5% is obtained. The maximum LHW power coupled to plasma is up to 3.5 MW. The current drive (CD) efficiency is up to 1.1 × 10 19 A m −2 W −1 and the central electron temperature is above 4 keV, suggesting that LH power could be mainly deposited in the core region, which is in agreement with code simulation. Experiments show that the current profile is effectively modified and toroidal rotation in the co-current direction is driven by the LHCD. Also, the CD efficiency and current profile depend on the launched wave spectrum, suggesting the possibility of controlling the current profile by changing the phase difference. Repeatable H-mode plasma is obtained by either the 4.6 GHz LHCD system alone, or together with a 2.45 GHz LHCD system, the NBI (neutral beam injection) system. The different ELM features of H-mode between the different heating methods are under investigation.

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“…The asymmetric density profiles in the poloidal direction modified by the LHW power were ascribed to the LHW induced E r_LH × B t drift. The above effects of E r × B t and E r_LH × B t have been preliminarily investigated [14,15] separately in EAST. Since LHW-plasma coupling is very important for LHCD experiments and E r × B t and E r_LH × B t are linked together, based on the previous studies, it is necessary to further discuss the effects of E r_LH and E r on grill density and coupling in EAST.…”

Section: Introductionmentioning

confidence: 99%

Investigations of LHW-plasma coupling and current drive at high density related to H-mode experiments in EAST

Ding

Zhang

et al. 2015

Nucl. Fusion

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Two important issues in achieving lower hybrid current drive (LHCD) high confinement plasma in EAST are to improve lower hybrid wave (LHW)-plasma coupling and to drive the plasma current at a high density. Studies in different configurations with different directions of toroidal magnetic field (B t) show that the density near the antenna is affected by both the radial electric field induced by plasma without a LHW (E r_plasma) in the scrape off layer (SOL), and the radial electric field induced by LHW power (E r_LH) near the grill. Investigations indicate that E r × B t in the SOL leads to a different effect of configuration on the LHW-plasma coupling and E r_LH × B t accounts for the asymmetric density behaviour in the SOL observed in the experiments, where E r is the total radial electric field in the SOL. Modelling of parametric instability (PI), collisional absorption (CA) and scattering from density fluctuations (SDF) in the edge region, performed considering the parameters of high density LHCD experiments in EAST, has shown that these mechanisms could be responsible for the low current drive (CD) efficiency at high density. Radiofrequency probe spectra, useful for documenting PI occurrence, show sidebands whose amplitude in the case of the lithiated vacuum chamber is smaller than in the case of poor lithiation, consistently with growth rates from PI modeling of the respective reference discharges. Since strong lithiation is also expected to diminish the parasitic effect on the LHCD of the remaining possible mechanisms, this appears to be a useful method for improving LHCD efficiency at a high density.

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Effects of plasma configuration, ELM and gas puffing on LHW coupling during H-mode in EAST

Cited by 8 publications

References 21 publications

Optimization of discharges with ion cyclotron range of frequencies using local gas injection in EAST

Optimization of discharges with ion cyclotron range of frequencies using local gas injection in EAST

First results of LHCD experiments with 4.6 GHz system toward steady-state plasma in EAST

Investigations of LHW-plasma coupling and current drive at high density related to H-mode experiments in EAST

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