Table of Content

15 December 2013, Volume 33 Issue 4

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Plasma Physics

Liquid metal MHD film flow and its stability mechanism for the liquid first wall of fusion reactor

ZHANG Xiu-jie, PAN Chuan-jie, XU Zeng-yu

2013, 33(4):  289-296. 

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A mathematical and physical modeling of the liquid metal MHD film flow has been built and a related numerical code has been developed. Firstly, the code is validated by the related experimental results. Secondly, numerical simulation of the liquid metal MHD film flow is carried out by this code. The effects of the inlet velocity, the initial film thickness, the width of the bottom wall and the wall roughness on the flow state are presented. It is indicated that there is only one value of the inlet velocity and the substrate width when the film flow state is stable, and two initial film thickness values exist at the stable state, the wall roughness has little effect on the film flow state. In the end, the preliminary stable mechanism of the film MHD flow based on a equilibrium analysis is described, it is indicated that the increase of the substrate width is helpful to reduce the electromagnetic resistance and increase the MHD stability; the stable velocity firstly increases then decreases with the increase of the initial film thickness and it is greatly reduced compared to the no magnetic field case.

Simulation of runaway electron evolution during disruptions in HL-2A tokamak

WU Na1, WANG Zhong-tian2, SANG Chao-feng1 , ZHANG Yi-po2 , WANG De-zhen1

2013, 33(4):  297-303. 

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The simulation of runaway electron (RE) and electric field evolution during HL-2A disruption is presented using a self-consistent model, which is constituted by Maxwell’s equations and generation rate equation. The generation rate equation includes Dreicer and avalanche generation mechanisms of REs. The simulation shows that the electric field increases rapidly from 0.1~0.2ms after the disruption, reaches the maximum about 0.1 ms later, and lasts about 2.5ms. The simulation results also show that REs are produced mostly in the region around the magnetic axis and a RE beam forms at 1ms after disruption, tens of milliseconds steady-state current appearing after disruption is carried mainly by REs. Further, comparing between the simulation and the experimental results, it is found that 40%~60% of the Ohmic current is converted into runaway current (RC) during the disruption (discharge No. 15335) in HL-2A. Although the avalanche generation rate of REs is weaker than Dreicer generation mechanism in HL-2A, it plays a key role because of its larger action time than Dreicer generation mechanism.

Discrete Alfvén eigenmodes excited by energetic particles in JET

WANG Shuai, LONG Chao-yun, HU Shuang-hui, KONG Ran, CHEN Shu-ping , WANG Yi-ru

2013, 33(4):  304-311. 

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Resonant excitations of Alfvén eigenmodes by energetic particles in JET operation are investigated employing a gyrokinetic-magnetohydrodynamic(MHD) hybrid simulation code. Multiple branches of αTAEs can be kinetically destabilized by engetic particles. The influence to the resonant excitation which comes from energetic particle pressure and velocity is investigated. The physical characteristics of αTAE excited by energetic particles are investigated in different bootstrap current operation status as well as in distinct toroidal field ripple amplitude. We find that multiple branches of αTAEs are excited by energetic particles in ELMs regime compatible with ITB. It is showed that αTAE has a wide frequency spectrum and the isntability modes both higher-order and low-order αTAEs can be excited in various resonance conditions. It’s valuable to explore this kind of potential Alfvén instability, so its excitation and physical characteristics should be investigated under more operating condition in tokamak.

Absolute intensity calibration of soft X-ray spectrometer on EAST

ZHANG Hong-ming1, SHEN Yong-cai1, FU Jia1, LI Ying-ying1, XIONG Yan-wei1, WANG Fu-di1, Lü Bo1, WU Zhen-wei1, SHI Yue-jiang2, 3, WAN Bao-nian1

2013, 33(4):  312-319. 

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With the calibration method based on the bremsstrahlung of plasma, the absolute intensity calibration has been performed for the soft X-ray spectrometer on EAST. First, the bremsstrahlung intensity of EAST plasma has been measured with soft X-ray spectrometer. After that, the profile of the power density of bremsstrahlung has been calculated, based on the measured profiles of electron temperature, electron density and effective charge number, which are provided by other diagnostics. Then, the power density integrated along the sightline of soft X-ray spectrometer to calculate integrated intensity has been obtained. At last, by comparing the measurement and the calculated results of the intensity of bremsstrahlung, the absolute intensity calibration factor in the range of 10~50A has been obtained. After completing the absolute intensity calibration, the emission intensity of CⅥ at 33.73A has been measured with soft X-ray spectrometer. Combined with the calibration factor, the vertical profile of the emission intensity has been inferred from the measurement. Then, the radial profile has been obtained with the Abel inversion taking into count of the asymmetry of high filed side and low field side of the plasma cross section. This study shows the absolute intensity calibration method based on the bremsstrahlung is viable for the spectrometer working in the soft X-ray range. The obtained emission intensity of impurity can be used to study the impurity transport by combining some simulation codes.

Calibration of X-ray detector at 1750~3500eV energy range

YI Rong-qing1, SONG Tian-ming1, ZHAO Yi-dong2, ZHENG Lei2, MA Cheng-yan2

2013, 33(4):  320-323. 

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Using InTe crystal to replace Si crystal, homochromatic X-ray light source of 1750~3500eV energy range in the 4B7A X-ray beam line on BSRF was obtained. This light source has energy resolution of more than 5000, intensity of more than 1010 phs·s^{-1, harmonics wave less than 0.1%, and it fills in the domestic gap of X-ray calibration source at this energy range. We make some researches on calibration of XRD's sensitivity using X-ray at this energy range, get results of the uncertainty of XRD's sensitivity less than 3%.}

Nuclear Fusion Engineering and Technology

Preliminary design of basic equilibrium configuration for HL-2M tokamak

LI Jia-xian, CHEN Qian, ZHANG Jin-hua, PAN Yu-dong, MAO Rui, CHEN Liao-yuan

2013, 33(4):  324-330. 

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The equilibrium fiting code (EFIT) is used to design the basic configurations which include the limiter, double null divertor and single null divertor configurations. These configurations with high elongation and large triangularity, meet the main configuration parameters given by the physical target of HL-2M tokamak: the major radius is 1.78 m and the minor radius up to 0.65m. In consideration of the influence of CS coil current on configurations and the limits of PF coils current, several discharges waveforms of three basic configurations was designed with the plasma current equal to 1.2MA which is the normal current for the HL-2M discharge schemes. The other discharges waveforms with the plasma current equal to 3MA are designed also. In addition, the volt-seconds consumption is analyzed by tokamak simulation code (TSC) for the HL-2M discharge evolution process with the plasma current equal to 1.2MA.

Thermal and electromagnetic analysis for the new LHCD antenna on HL-2A tokamak

WEI Sen, BAI Xing-yu, ZHOU Jun, RAO Jun

2013, 33(4):  331-336. 

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A new LHCD antenna has been designed for HL-2A tokamak in passive active multijunction (PAM) form. Thermal analysis of the antenna has been done by finite element method，which shows that oxygen free copper can meet the thermal requirements. Electromagnetic analysis is carried out by analytic method under varying toroidal magnetic field and plasma current conditions. It is demonstrated that a pair of torque generated by the electromagnetic torsion may destroy the antenna when plasma disrupts, and stainless steel can satisfy the torque requirements. Combining oxygen free copper and stainless steel may be a reasonable solution in the practical manufacturing process. This work provides theoretical basis for the development of the new antenna.

Design and analysis of the vacuum vessel supports and limiting structure on EAST 4.6GHz LHCD system

LI Bo, WU Jie-feng, ZHU Wen-hua, LIU Liang

2013, 33(4):  337-341. 

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　　Presently, a remote steering antenna is building for 4.6GHz lower hybrid wave system on EAST, which needs 100mm movable distance and very strong basis as well as absolutely reliable limiting stroke. For reliable structure strength better than any section bar, this paper presents 3 kinds of different high-strength welding holder and support, which are named as support frame, fixed foundation, limiting stroke. All of them are made of 316L stainless steel. Three types of welding structures are employed designed as frame structure, plug-welding structure and portal strengthened square steel welding component. Result computed by ANSYS shows that structure strengthen of 3 supports is stable and firmly reliable.

Active feedback control used in plasma vertical unstable displacement for EAST

WANG Hai-xin1, WANG Feng-feng1, HUANG Hai-hong1, WU Yi-bing2

2013, 33(4):  342-347. 

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The feedback control system is restrained plasma vertical displacement on EAST. Fast control power supply excites active feedback coils, which produces magnetic field to control plasma’s displacement. To meet the requirement of large current and fast response, multi-inverters in parallel is presented. The validity of proposed scheme has been confirmed by experiments, the active feedback system can reach design demand.

Analysis of ITER poloidal field converter reliability

LIU Di1，DU Shao-wu1，JIANG Li2

2013, 33(4):  348-353. 

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The poloidal field (PF) converter belongs to the critical systems of ITER, thus its reliability and availability should maintain a high state through the two decades operation life of ITER. This paper is aiming at improving these two abilities with the RAMI (Reliability, Availability, Maintainability and Inspectability) analysis method. The system functional breakdown is performed at first, then the reliability model is established based on it. The initial reliability and availability of the PF converter is obtained by analysing this model. Finally, by improving the reliability and availability of subsystems, the scheme of the PF converter satisfied the requirements of ITER.

Thermo-mechanical simulation and analysis of W/Cu mono-block for ITER divertor

XUE Kui1, 2, CHEN Jun-ling2 , ZHU Da-huan2

2013, 33(4):  353-358. 

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Thermo-mechanical analysis was performed under the superposition effect of steady state and transient heat flux for the ITER W/Cu mono-block model by finite-element analysis code ANSYS. Numerical results proved the structure to be safe and reliable under the steady state heat flux, while under the transient heat flux, there occurred plastic deformation on the surface of W, and the corresponding heat flux was 320_{MW·m^{-2(lasts for 0.5ms). The results can be useful for the design and improvement of ITER divertor.}}

ITER project and fusion energy development strategy

ZHANG Yi-ming1, ZENG Li-ping1, SHEN Xin-yuan2, ZHANG Li1, DING Ya-qing1, XIAO Cheng-xin1, KANG Wei-hong1, WANG Hai1

2013, 33(4):  359-365. 

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The international thermonuclear experimental reactor (ITER), currently under construction in Cadarache of France, and its project were introduced. Seven members’ purposes of participation in the ITER project and their fusion development strategies focusing on the ITER project were analyzed.

Non-Fusion Plasma Applications

Experimental research on the characteristic of plasma aerodynamic actuation and flow separation control on a compressor cascade

WANG Xue-de1, ZHAO Xiao-hu1, WANG Lu-cheng2, LU Jia-wu3, LIN Ya-ming3

2013, 33(4):  366-373. 

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To discover the characteristic of nanosecond pulsed plasma aerodynamic actuation (PAA) as well as the effect and influence law of flow separation control on a highly loaded compressor cascade by PAA, experimental investigations of PIV measurements, high-speed Schlieren visualization and pressure measurements were conducted. Results show that a shock wave is induced by nanosecond pulsed PAA to spread outward and can last only about 80μs. Nanosecond pulsed PAA can effectively prevent the flow separation in a highly loaded compressor cascade, and the control effect enhances with the increase of lower electrode width and actuation discharge as well as the shape of curved electrodes. The relative reduction of pitch-averaged total pressure loss coefficient is up to 8.4%. The actuation frequency is one key factor affecting the control effect of nanosecond pulsed PAA, and the optimal actuation frequency is 4kHz. The streamwise PAA on the suction surface can mainly change the flow characteristic at midspan, but has weak impact on corner separation. The pitchwise PAA on the endwall can reduce the accumulation of low-energy fluids at the suction surface and endwall corner by inhibiting the cross flow. The control effect of streamwise PAA on the suction surface combined with pitchwise PAA on the endwall is the best.

Experimental investigation on the characteristics of dielectric barrier discharge with a large gap width at atmospheric pressure

LI Xue-chen, LIU Run-fu, JIA Peng-ying, ZHAO Huan-huan, CHANG Yuan-yuan

2013, 33(4):  374-378. 

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A dielectric barrier discharge with a fairly large gap width is realized in atmospheric pressure argon because the critical voltage value for gas gap breakdown is sharply lowered through using a wedged gas gap. The discharge behavior is investigated experimentally through analyzing images taken with exposure time of several milliseconds. Results indicate that a stripe pattern with a homogeneous corona around can be observed under a lower voltage, and the discharge turns quite homogeneous at a higher voltage. It has been found that the micro-discharges tend to be generated at the region with small gap width, and then move to the region with large gap width along the flowing gas. Therefore, dielectric barrier discharge with a fairly large gap width can be obtained at a rather lowered voltage. Based on the visualization of the discharge with exposure time of several microseconds, it has been found that micro-discharge filament consists of the volumetric discharge between the two electrodes and the stochastic surface discharge on the dielectric for the filamentary discharge. The stripe on the image taken with exposure time of several milliseconds results from the moving of the volumetric discharge along the gas flow, and the homogeneous corona is a superimposition of the surface discharge at different half cycles. These results are of great importance for industrial applications of the atmospheric pressure uniform discharge.