H J Sun

Publications (10)29.66 Total impact

• Article: Experimental evidence of the non-local response of transport to peripheral perturbations

  H.J. Sun, P.H. Diamond, Z.B. Shi, C.Y. Chen, L.H. Yao, X.T. Ding, B.B. Feng, X.L. Huang, Y. Zhou, J. Zhou, X.M. Song, the team
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  ABSTRACT: Qualitatively novel results on non-locality phenomena in perturbative transport experiments are reported. Here, non-locality means a rapid response in the core follows an edge perturbation on a time scale far shorter than any standard approximation to the global, diffusive model confinement time. Sequential firing of supersonic molecular beam injection on the HL-2A tokamak sustained the increase in the core temperature in response to the edge perturbation. O-mode reflectometers are introduced to measure density fluctuations and show that the central turbulence is suppressed during nonlocallity, suggesting that the interpretation of the phenomenon due to the formation of an 'ITB-like' structure is plausible. ECH switch-off experiments on the HL-2A tokamak demonstrated that the non-local response is sensitive to the deposition location. Taken together, these results suggest that non-locality phenomena have several aspects in common which can be linked to certain simple, generic elements of tokamak turbulence physics.
  Nuclear Fusion 10/2011; 51(11):113010. · 4.09 Impact Factor
• Article: Microwave Dielectric Properties of B-Site Modified CaTiO3 Ceramics

  J. Shen, J. Zhou, J. Zhu, H. J. Sun, H. X. Liu, W. Chen
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  ABSTRACT: Two kinds of B-site modified of CaTiO 3 were investigated with (Zn 1/3 Nb 2/3 ) 4+ and (Mg 1/3 Nb 2/3 ) 4+ which selected as B-site substitution cations respectively. The modified CaTiO 3 dielectric ceramics were prepared by solid state reaction method with niobate as precursor. Single perovskite structure can be found in the solid solutions, in both systems. As the substitution increased, ϵ r and τ ƒ decreased while Q× ƒ increased, which is consistent with the empirical rules. Optimal microwave dielectric properties are obtained at x = 0.6 in Ca[(Mg 1/3 Nb 2/3 ) x Ti 1 −x ]O 3 and at x = 0.7 in Ca[(Zn 1/3 Nb 2/3 ) x Ti 1 −x ]O 3 . The effect of structure on dielectric properties was discussed.
  Ferroelectrics 10/2011; 356(October 2007):111-114. · 0.39 Impact Factor
• Article: Overview of experimental results on the HL-2A tokamak

  L.W. Yan, X.R. Duan, X.T. Ding, J.Q. Dong, Q.W. Yang, Yi Liu, X.L. Zou, D.Q. Liu, W.M. Xuan, L.Y. Chen, [......], B.S. Yuan, K.J. Zhao, G.W. Zhong, J. Zhou, Y. Zhou, J.C. Yan, C.X. Yu, C.H. Pan, Yong Liu, the team
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  ABSTRACT: The physics experiments on the HL-2A tokamak have been focused on confinement improvement, particle and thermal transport, zonal flow and turbulence, filament characteristics, energetic particle induced modes and plasma fuelling efficiency since 2008. ELMy H-mode discharges are achieved in a lower density regime using a combination of NBI heating with ECRH. The power threshold is found to increase with a decrease in density, almost independent of the launching order of the ECRH and NBI heating power. The pedestal density profiles in the H-mode discharges are measured. The particle outward convection is observed during the pump-out transient phase with ECRH. The negative density perturbation (pump-out) is observed to propagate much faster than the positive one caused by out-gassing. The core electron thermal transport reduction triggered by far off-axis ECRH switch-off is investigated. The coexistence of low frequency zonal flow (LFZF) and geodesic acoustic mode (GAM) is observed. The dependence of the intensities of LFZFs and GAMs on the safety factor and ECRH power is identified. The 3D spatial structures of plasma filaments are measured in the boundary plasma and large-scale structures along a magnetic field line analysed for the first time. The beta-induced Alfvén eigenmodes (BAEs), excited by large magnetic islands (m-BAE) and by energetic electrons (e-BAE), are observed. The results for the study of fuelling efficiency and penetration characteristics of supersonic molecular beam injection (SMBI) are described.
  Nuclear Fusion 08/2011; 51(9):094016. · 4.09 Impact Factor
• Article: Observation of turbulence suppression after electron-cyclotron-resonance-heating switch-off on the HL-2A tokamak.

  Y Liu, Z B Shi, Y B Dong, H J Sun, A P Sun, Y G Li, Z W Xia, W Li, X T Ding, W W Xiao, Y Zhou, J Zhou, J Rao, Z T Liu, Q W Yang, X R Duan
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  ABSTRACT: The formation of a transient internal transport barrier (ITB) is observed after the electron-cyclotron-resonance-heating (ECRH) switch-off in the HL-2A plasmas, characterized by transient increase of central electron temperature. The newly developed correlation reflectometer provided direct measurements showing reduction of turbulence in the region of steepened gradients for the period of ITB formation triggered by the ECRH switch-off. Furthermore, the reduction of core turbulence is correlated in time with the appearance of a low-frequency mode with a spectrally broad poloidal structure that peaks near zero frequency in the core region. These structures have low poloidal mode number, high poloidal correlation, and short radial correlation and are strongly coupled with high-frequency ambient turbulence. Observation indicates that these structures play important roles in the reduction of the core turbulence and in improvements of the core transport after the off-axis ECRH is turned off.
  Physical Review E 07/2011; 84(1 Pt 2):016403. · 2.26 Impact Factor
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  Available from: swip.ac.cn

  Article: β-induced Alfvén eigenmodes destabilized by energetic electrons in a Tokamak plasma.

  W Chen, X T Ding, Q W Yang, Yi Liu, X Q Ji, Y P Zhang, J Zhou, G L Yuan, H J Sun, W Li, [......], Y Huang, J Q Dong, B B Feng, X M Song, Z B Shi, Z T Liu, X Y Song, L C Li, X R Duan, Y Liu
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  ABSTRACT: The β-induced Alfvén eigenmode (BAE) excited by energetic electrons has been identified for the first time both in the Ohmic and electron cyclotron resonance heating plasma in HL-2A. The features of the instability, including its frequency, mode number, and propagation direction, can be observed by magnetic pickup probes. The mode frequency is comparable to that of the continuum accumulation point of the lowest frequency gap induced by the shear Alfvén continuous spectrum due to finite β effect, and it is proportional to Alfvén velocity at thermal ion β held constant. The experimental results show that the BAE is related not only with the population of the energetic electrons, but also their energy and pitch angles. The results indicate that the barely circulating and deeply trapped electrons play an important role in the mode excitation.
  Physical Review Letters 10/2010; 105(18):185004. · 7.37 Impact Factor
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  Available from: Longwen Yan

  Article: Observation of a spontaneous particle-transport barrier in the HL-2A tokamak.

  W W Xiao, X L Zou, X T Ding, L H Yao, B B Feng, X M Song, S D Song, Y Zhou, Z T Liu, B S Yuan, [......], X Q Ji, Y D Gao, Y G Li, L W Yan, Q W Yang, Yi Liu, J Q Dong, X R Duan, Yong Liu, C H Pan
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  ABSTRACT: Using the profile analysis, the density perturbation transport analysis, and the Doppler reflectometry measurement, for the first time a spontaneous and steady-state particle-transport barrier has been evidenced in the Ohmic plasmas in the HL-2A tokamak with no externally applied momentum or particle input except the gas puffing. A threshold in density has been found for the observation of the barrier. The particle diffusivity is well-like, and the convection is found to be inward outside the well and outward inside the well. The formation of the barrier coincides with the transition between the trapped electron mode and the ion temperature gradient driven mode.
  Physical Review Letters 05/2010; 104(21):215001. · 7.37 Impact Factor
• Article: Overview of experimental results on HL-2A

  X.R. Duan, X.T. Ding, J.Q. Dong, Q.W. Yang, L.W. Yan, Yi Liu, X.L. Zou, D.Q. Liu, W.M. Xuan, L.Y. Chen, [......], K.J. Zhao, Y.Z. Zheng, G.W. Zhong, C.P. Zhou, J. Zhou, Y. Zhou, J.C. Yan, C.X. Yu, C.H. Pan, Yong Liu
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  ABSTRACT: Significant experimental advances have been made on the HL-2A tokamak along with substantial improvement and development of the hardware. A spontaneous particle transport barrier has been observed in Ohmic discharges without any external momentum input. The barrier was evidenced by a density perturbation study using modulated supersonic molecular beam injection (SMBI) and microwave reflectometry. The new features of the non-local transport effect induced with SMBI have been analysed. The three-dimensional spectral structures of the low frequency zonal flow, the geodesic acoustic mode (GAM) and the quasi-mode-like low frequency fluctuations have been observed simultaneously for the first time. In addition, the spectral structure of the density fluctuations of GAM was also identified. The e-fishbone instability excited by energetic electrons deviated from Maxwellian distribution has been investigated via a 10-channel CdTe hard x-ray detector. It was found that the e-fishbone was correlated with the existence of energetic electrons of 30–70 keV. The MHD experiment has indicated that the suppression of m/n = 2/1 tearing modes may be sustained by ECRH modulation at a frequency of about 10 Hz.
  Nuclear Fusion 09/2009; 49(10):104012. · 4.09 Impact Factor
• Article: The features of the electron heat transport during high power ECRH & SMBI on HL-2A

  H J Sun, X T Ding, L H Yao, J Rao, Z T Liu, Y Liu, Y Huang, C F Dong, W Li, X R Duan, Q W Yan
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  ABSTRACT: With high power ECRH and supersonic molecular beam injection (SMBI), the electron heat transport has been investigated on HL-2A. This paper will show features of the electron transport during ECRH, especially new non-local phenomena triggered by SMBI, in which an electron transport barrier is formed and the confinement is improved. The diffusion coefficient both from steady-state analysis (χhp) and the heat pulse propagation (χpb) increase with the ECRH power and decrease with the electron density, which is in agreement with the L-mode scaling. The ratio χhp/χpb is about 2.8 in Ohmic discharges; it increases to 3.3 with low power ECRH and decreases to 1.7 with the high power ECRH. The non-local transport phenomena induced by SMBI have been observed firstly on HL-2A. The density limit beyond which the phenomena disappear is apparently higher in the ECRH regime than in the Ohmic regime. Both the bolometer radiation and the Haemission decrease when the non-local effect appears. After the appearance of the non-local effect, it can be found that the region outside r/a ~ 0.5, just like usual result, is cooled by SMBI, while the core Te increasing gives a surprise. The core Te is increased by about 18 %. This suggests that the injection of SMBI triggers the internal transport barriers.
  Journal of Physics Conference Series 08/2008; 123(1):012016.
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  Available from: swip.ac.cn

  Article: Siliconization for wall conditioning and its effect on plasma performance in HL-2A tokamak

  X R Duan, Z Cao, C H Cui, X Cai, H J Sun, X T Ding, Y D Pan, M X Wang, Q W Yang, X M Song, D Q Liu, Y Liu, X Q Ji, Z Y Cui, Y Zhou, Yong Liu, Team
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  ABSTRACT: Wall conditioning with siliconization has been performed in the HL-2A tokamak to improve the plasma performance. It was based on the plasma chemical vapor deposition by using a four-anode glow discharge cleaning system and gas mixture of 90% He + 10% SiH 4 . It was found that the main components of the residual gas were CO, H 2 and H 2 O. The amount of H 2 O was reduced from 49.5% to 24.5%. After siliconization, the impurity fluxes released from the first wall were reduced, especially the oxygen level (till to 10%) and high z impurities like Cu were decreased significantly. The total radiated power measured by the bolometer was decreased from 70% to 35%. A high density exceeding the Greenwald limit and energy confinement improvement have been achieved. The plasma operational region of HL-2A has been effectively broadened.
  5225.
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  Available from: Longwen Yan

  Article: Present Progress of Plasma Transport Study on HL-2A

  X T Ding, W W Xiao, X L Zou, H J Sun, Yi Liu, L H Yao, J Rao, B B Feng, Z T Liu, Y Zhou, Q W Yang, L W Yan, J Q Dong, X R Duan, Team
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  ABSTRACT: The recent experiments of HL-2A tokamak have been focused on studying the physics of turbulence and transport. A spontaneous particle transport barrier has been observed in Ohmic discharges without any external momentum input. The barrier was evidenced by density perturbation study using modulated supersonic molecular beam injection (SMBI) and microwave reflectometry. The new features of the non-local transport effect induced with SMBI have been analyzed. The suppression of m/n = 2/1 tearing modes may be sustained by ECRH modulation at a frequency about 10 Hz. Continuous confinement improvement was observed after the mode suppression.