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Featured researches published by B. Lyu.


Physical Review Letters | 2016

Nonlinear Transition from Mitigation to Suppression of the Edge Localized Mode with Resonant Magnetic Perturbations in the EAST Tokamak

Y. W. Sun; Y. Liang; Yueqiang Liu; Shuai Gu; Xu Yang; W. Guo; Tonghui Shi; M. Jia; L. Wang; B. Lyu; C. Zhou; A.D. Liu; Qing Zang; H. Liu; Nan Chu; Hui-Hui Wang; T. Zhang; J. Qian; Liuwei Xu; Kaiyang He; D. M. Chen; B. Shen; X.Z. Gong; X. Ji; Shouxin Wang; M. Qi; Yong Song; Q.P. Yuan; Zhi-Cai Sheng; Ge Gao

Evidence of a nonlinear transition from mitigation to suppression of the edge localized mode (ELM) by using resonant magnetic perturbations (RMPs) in the EAST tokamak is presented. This is the first demonstration of ELM suppression with RMPs in slowly rotating plasmas with dominant radio-frequency wave heating. Changes of edge magnetic topology after the transition are indicated by a gradual phase shift in the plasma response field from a linear magneto hydro dynamics modeling result to a vacuum one and a sudden increase of three-dimensional particle flux to the divertor. The transition threshold depends on the spectrum of RMPs and plasma rotation as well as perturbation amplitude. This means that edge topological changes resulting from nonlinear plasma response plays a key role in the suppression of ELM with RMPs.


Nuclear Fusion | 2015

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

Fukun Liu; B. J. Ding; J.G. Li; Baonian Wan; Jiafang Shan; M. Wang; L. Liu; L.M. Zhao; M. H. Li; Y. C. Li; Ying Yang; Z.G. Wu; J.Q. Feng; Huaichuan Hu; H. Jia; Y.Y. Huang; W. Wei; M. Cheng; Liuwei Xu; Qing Zang; B. Lyu; S. Y. Lin; Yanmin Duan; J.H. Wu; Y. Peysson; J. Decker; J. Hillairet; A. Ekedahl; Z.P. Luo; J. Qian

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 × 1019 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.


Review of Scientific Instruments | 2014

Upgrades of imaging x-ray crystal spectrometers for high-resolution and high-temperature plasma diagnostics on EAST

B. Lyu; F. D. Wang; X. Y. Pan; J.L. Chen; Jia Fu; Yingying Li; M. Bitter; K. W. Hill; L. F. Delgado-Aparicio; N. Pablant; S. G. Lee; Y. J. Shi; Minyou Ye; Baonian Wan

Upgrade of the imaging X-ray crystal spectrometers continues in order to fulfill the high-performance diagnostics requirements on EAST. For the tangential spectrometer, a new large pixelated two-dimensional detector was deployed on tokamaks for time-resolved X-ray imaging. This vacuum-compatible detector has an area of 83.8 × 325.3 mm(2), a framing rate over 150 Hz, and water-cooling capability for long-pulse discharges. To effectively extend the temperature limit, a double-crystal assembly was designed to replace the previous single crystals for He-like argon line measurement. The tangential spectrometer employed two crystal slices attached to a common substrate and part of He- and H-like Ar spectra could be recorded on the same detector when crystals were chosen to have similar Bragg angles. This setup cannot only extend the measurable Te up to 10 keV in the core region, but also extend the spatial coverage since He-like argon ions will be present in the outer plasma region. Similarly, crystal slices for He-like iron and argon spectra were adopted on the poloidal spectrometer. Wavelength calibration for absolute rotation velocity measurement will be studied using cadmium characteristic L-shell X-ray lines excited by plasma radiation. A Cd foil is placed before the crystal and can be inserted and retracted for in situ wavelength calibration. The Geant4 code was used to estimate X-ray fluorescence yield and optimize the thickness of the foil.


Review of Scientific Instruments | 2016

Measurement of helium-like and hydrogen-like argon spectra using double-crystal X-ray spectrometers on EAST

B. Lyu; J.L. Chen; R. J. Hu; F. D. Wang; Yingying Li; Jia Fu; Y. C. Shen; M. Bitter; K. W. Hill; L. F. Delgado-Aparicio; N. Pablant; S. G. Lee; Minyou Ye; Y. J. Shi; Baonian Wan

A two-crystal assembly was deployed on the tangential X-ray crystal spectrometer to measure both helium-like and hydrogen-like spectra on EAST. High-quality helium-like and hydrogen-like spectra were observed simultaneously for the first time on one detector for a wide range of plasma parameters. Profiles of line-integrated core ion temperatures inferred from two spectra were consistent. Since tungsten was adopted as the upper divertor material, one tungsten line (W XLIV at 4.017 Å) on the short-wavelength side of the Lyman-α line (Lα1) was identified for typical USN discharges, which was diffracted by a He-like crystal (2d = 4.913 Å). Another possible Fe XXV line (1.85 Å) was observed to be located on the long-wavelength side of resonance line (w), which was diffracted from a H-like crystal (2d = 4.5622 Å) on the second order. Be-like argon lines were also observable that fill the detector space between the He-like and H-like spectra.


Nuclear Fusion | 2017

Effort of lower hybrid current drive experiments toward to H-mode in EAST

B. J. Ding; M. H. Li; Fukun Liu; Jiafang Shan; Y. C. Li; M. Wang; L. Liu; L.M. Zhao; Y. Yang; Z. G. Wu; J. Q. Feng; Huaichuan Hu; H. Jia; M. Cheng; Qing Zang; B. Lyu; Yixiang Duan; S. Y. Lin; J.H. Wu; J. Hillairet; A. Ekedahl; Y. Peysson; M. Goniche; A.A. Tuccillo; R. Cesario; L. Amicucci; B. Shen; X.Z. Gong; G. Xu; H.L. Zhao

Lower hybrid current drive (LHCD) is an effective tool to achieve high confinement (H-mode) plasma in EAST. To utilize LHCD for accessing H-mode plasma, efforts have been made to improve LHW (lower hybrid wave)-plasma coupling and current drive capability at high density. Improved LHW-plasma coupling by means of local gas puffing and gas puffing from the electron side is routinely used during EAST operation with LHCD. High density experiments suggest that low recycling and high LH frequency are preferred for LHCD experiments at high density, consistent with previous results in other machines. The effect of LHCD on the current profile in EAST demonstrates that it is possible to control the plasma profile by optimizing the LHW spectrum. Repeatable H-mode plasma was obtained by LHCD and the maximum density during H-mode with the combination of 2.45 GHz and 4.6 GHz LH waves was up to 4.5 × 1019 m−3.


Nuclear Fusion | 2017

Edge localized mode control using n = 1 resonant magnetic perturbation in the EAST tokamak

M. Jia; H.L. Zhao; Ge Gao; W. Guo; Yun Li; D. M. Chen; X. Ji; Y. W. Sun; Hui-Hui Wang; Yueqiang Liu; Kaiyang He; Baonian Wan; Ge Li; T. Zhang; Qing Zang; M. Qi; B. Shen; Shouxin Wang; Tonghui Shi; Liuwei Xu; B. Lyu; Y. Liu; Yong Song; Peng Fu; Q.P. Yuan; Y. Liang; Zhi-Cai Sheng; Lianzhou Wang; X.Z. Gong; J. Qian

A set of in-vessel resonant magnetic perturbation (RMP) coil has been recently installed in EAST. It can generate a range of spectrum, and there is a relatively large window for edge localized mode (ELM) control according to the vacuum field modeling of the edge magnetic island overlapping area. Observation of mitigation and suppression of ELM in slow rotating plasmas during the application of an n = 1 RMP is presented in this paper. Strong ELM mitigation effect is observed in neutral beam injection heating plasmas. The ELM frequency increases by a factor of 5, and the crash amplitude and the particle flux are effectively reduced by a similar factor. Clear density pump-out and magnetic braking effects are observed during the application of RMP. Footprint splitting is observed during ELM mitigation and agrees well with vacuum field modelling. Strong ELM mitigation happens after a second sudden drop of plasma density, which indicates the possible effect due to field penetration of the resonant harmonics near the pedestal top, where the electron perpendicular rotation becomes flat and close to zero after the application of RMP. ELM suppression is achieved in a resonant window during the scan of the n = 1 RMP spectrum in radio-frequency (RF) dominant heating plasmas. The best spectrum for ELM suppression is consistent with the resonant peak of RMP by taking into account of linear magnetohydrodynamics plasma response. There is no mode locking during the application of n = 1 RMP in ELMy H-mode plasmas, although the maximal coil current is applied.


Review of Scientific Instruments | 2016

Validation of fast-ion D-alpha spectrum measurements during EAST neutral-beam heated plasmas

Jia-Qi Huang; W.W. Heidbrink; M. von Hellermann; L. Stagner; C. R. Wu; Y. M. Hou; J. F. Chang; S. Ding; Yue Chen; Y. B. Zhu; Z. Jin; Z. Xu; Wen Gao; J. F. Wang; B. Lyu; Qing Zang; G Q Zhong; L. Q. Hu; B. N. Wan; East Team

To investigate the fast ion behavior, a fast ion D-alpha (FIDA) diagnostic system has been installed on EAST. Fast ion features can be inferred from the Doppler shifted spectrum of Balmer-alpha light from energetic hydrogenic atoms. This paper will focus on the validation of FIDA measurements performed using MHD-quiescent discharges in 2015 campaign. Two codes have been applied to calculate the Dα spectrum: one is a Monte Carlo code, Fortran 90 version FIDASIM, and the other is an analytical code, Simulation of Spectra (SOS). The predicted SOS fast-ion spectrum agrees well with the measurement; however, the level of fast-ion part from FIDASIM is lower. The discrepancy is possibly due to the difference between FIDASIM and SOS velocity distribution function. The details will be presented in the paper to primarily address comparisons of predicted and observed spectrum shapes/amplitudes.


Plasma Physics and Controlled Fusion | 2016

The behavior of neutron emissions during ICRF minority heating of plasma at EAST

G Q Zhong; Hongrui Cao; Liqun Hu; R. J. Zhou; Min Xiao; Kai Li; Neng Pu; J. Huang; Guangzhu Liu; S. Y. Lin; B. Lyu; Haiqing Liu; Xinjun Zhang; East Team

Ion cyclotron radio frequency (ICRF) wave heating is a primary method to heat ions in the Experimental Advanced Superconducting Tokamak (EAST). Through neutron diagnostics, effective ion heating was observed in hydrogenminority heating (MH) scenarios. At present, investigation of deuterium–deuterium (DD) fusion neutrons is mostly based on time-resolved flux monitor and spectrometer measurements. When the ICRF was applied, the neutron intensity became one order higher. The H/H + D ratio was in the range of 5–10%, corresponding to the hydrogen MH dominated scenario, and a strong high energy tail was not displayed on the neutron spectrum that was measured by a liquid scintillator. Moreover, ion temperature in the plasma center (T i) was inversely calculated by the use of neutron source strength (S n) and the plasma density based on classical fusion reaction equations. This result indicates that T i increases by approximately 30% in L-mode plasma, and by more than 50% in H-mode plasma during ICRF heating, which shows good agreement with x-ray crystal spectrometer (XCS) diagnostics. Finally, the DD neutron source strength scaling law, with regard to plasma current (I P) and ICRF coupling power (P RF) on the typical minority heating condition, was obtained by statistical analysis.


Plasma Physics and Controlled Fusion | 2016

Density limits investigation and high density operation in EAST tokamak

X.W. Zheng; Jiangang Li; Jiansheng Hu; Haiqing Liu; Yinxian Jie; Shouxin Wang; Jiahong Li; Yanming Duan; M. H. Li; Yongchun Li; Ling Zhang; Yang Ye; Qingquan Yang; Tao Zhang; Yingjie Cheng; Jichan Xu; Liang Wang; Liqing Xu; H.L. Zhao; Fudi Wang; S. Y. Lin; Bin Wu; B. Lyu; Guosheng Xu; X. Gao; Tonghui Shi; Kaiyang He; H. Lan; Nan Chu; Bin Cao

Increasing the density in a tokamak is limited by the so-called density limit, which is generally performed as an appearance of disruption causing loss of plasma confinement, or a degradation of high confinement mode which could further lead to a H → L transition. The L-mode and H-mode density limit has been investigated in EAST tokamak. Experimental results suggest that density limits could be triggered by either edge cooling or excessive central radiation. The L-mode density limit disruption is generally triggered by edge cooling, which leads to the current profile shrinkage and then destabilizes a 2/1 tearing mode, ultimately resulting in a disruption. The L-mode density limit scaling agrees well with the Greenwald limit in EAST. The observed H-mode density limit in EAST is an operational-space limit with a value of . High density H-mode heated by neutral beam injection (NBI) and lower hybrid current drive (LHCD) are analyzed, respectively. The constancy of the edge density gradients in H-mode indicates a critical limit caused perhaps by e.g. ballooning induced transport. The maximum density is accessed at the H → L transition which is generally caused by the excessive core radiation due to high Z impurities (Fe, Cu). Operating at a high density () is favorable for suppressing the beam shine through NBI. High density H-mode up to could be sustained by 2 MW 4.6 GHz LHCD alone, and its current drive efficiency is studied. Statistics show that good control of impurities and recycling facilitate high density operation. With careful control of these factors, high density up to 0.93 stable H-mode operation was carried out heated by 1.7 MW LHCD and 1.9 MW ion cyclotron resonance heating with supersonic molecular beam injection fueling.


Review of Scientific Instruments | 2017

Development of beam emission spectroscopy diagnostic on EAST.

Wang H; Yan Yu; R. Chen; Y.F. Wu; Boda Yuan; S.B. Gong; Q. J. Yu; B. Lyu; Y.J. Shi; Minyou Ye; Bo Wan

Beam Emission Spectroscopy (BES) diagnostic based on Neutron Beam Injection (NBI) on the Experimental Advanced Superconducting Tokamak has been developed. This system consists of 16 × 8 channels which can diagnose the density fluctuation in a rectangular area of about 20 × 10 cm2 in the cross section, whose radial position is adjustable from the core to edge just by means of changing the angle of the rotation mirror. The spatial resolution is about 1-3 cm according to the diagnosed radial position. The temporal resolution is 1 μs. Space calibration of the diagnostic system is done based on the reversibility of the optical path. The NBI modulation experiment shows the success of BES development.

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Qing Zang

Chinese Academy of Sciences

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Baonian Wan

Chinese Academy of Sciences

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Minyou Ye

University of Science and Technology of China

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Yingying Li

Chinese Academy of Sciences

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J. Qian

Chinese Academy of Sciences

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Jia Fu

Chinese Academy of Sciences

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X.Z. Gong

Chinese Academy of Sciences

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Bo Wan

Chinese Academy of Sciences

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Tonghui Shi

Chinese Academy of Sciences

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Fudi Wang

Chinese Academy of Sciences

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