Table of Content

15 December 2010, Volume 30 Issue 4

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Plasma Physics

Numerical simulation of lower hybrid current drive on EAST tokamak

DUAN Wen-xue, MA Zhi-wei, WU Bin

2010, 30(4):  289-294. 

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The modified code is used to numerically simulate the lower hybrid current drive (LHCD) on EAST tokamak. The results indicate that the injection location, power spectrum of the lower hybrid wave (LHW) and plasma temperature and density can importantly affect the power deposition and current drive profiles. The power deposition and current drive profiles can be controlled by selecting the proper LHW spectrum, plasma temperature and density.

Preliminary study on plasma discharge prediction on EAST tokamak

LIU Cheng-yue, CHEN Mei-xia, WU Bin, SONG Feng-quan

2010, 30(4):  295-300. 

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The discharge simulations are carried out with tokamak simulation code (TSC) before experiments and the expected plasma discharge process and some important parameter evolution wave are obtained, such as poloidal field coil current、plasma current and plasma position etc.. These obtained parameter waves will be applied to guide experiments by plasma control system (PCS). The predictive simulations on plasma R position control、coil current control and plasma RZIp control follow a good agreement with experiments, which identifies that TSC has high predictability and reliability and affords some reference for EAST tokamak further physical experiments in the future.

Modulational instability of intense laser beam in magnetized plasma

CHEN Hua-ying, LIU San-qiu, LI Xiao-qing

2010, 30(4):  301-305. 

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The nonlinear dispersion relation is derived for an intense left-hand elliptically polarized laser beam propagating through magnetized plasma by means of the Lorentz transformation. In terms of the Karpman method, the nonlinear governing equation for the envelope of the laser field is obtained. The modulational instability of the intense left-hand elliptically polarized laser beam in magnetized plasma is analyzed and the temporal growth rate of modulational instability is found. The analysis shows that the maximum growth rate of self-modulation instability is obviously smaller for magnetized plasma compared to the unmagnetized case. It is also shown that the temporal growth rate of modulational instability is increased significantly near the critical surface in a laser-plasma.

Effect of the plasma pressure on growth rate and eigenfunction of line-tied kink instability

DAI Yu-jie, LIU Jin-yuan, WANG Xue-hui

2010, 30(4):  306-311. 

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The evolution of growth rate and two-dimensional radial eigenfunction of line-tied kink instability in cylindrical geometry is studied by using semi-analytical method for the three cases of p₀=0,p₀=const and p₀=f(r) respectively. The ranges of axial wave number k are same for the two cases of p₀=0 and p₀=const, and the growth rate of p₀= const is less than that of p₀=0. The ranges of axial wave number k and growth rate of p₀=f(r) are greater than that of p₀=0, and the magneto- hydrodynamic (MHD) velocity has a great change. Therefore, the case of p₀=f(r) is closed to the actual physical model (for example, the coronal mass ejections).

  

 

 

 

Molecular dynamics simulation of carbon atoms redeposition on the hydrocarbon film in the fusion reactor

ZHAO Cheng-li, SUN Wei-zhong, LIU Hua-min, ZHANG Jun-yuan, Lü Xiao-dan, QIN You-min, NING Jian-ping, HE Ping-ni, PAN Yu-dong, GOU Fu-jun

2010, 30(4):  312-316. 

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Molecular dynamics method was used to investigate the interactions of C continuously bombarding the hydrocarbon film surface. The Brenner potential was chosen. The simulation results show that the amorphous carbon-rich layer was formed on the hydrocarbon surface. The thickness of the carbon-rich layer decreases with increasing incident energy. In the formed layer, C atoms bond chiefly with C_sp2-C_sp2 and C_sp2-C_sp3. With increasing incident energy, the hybridization of C atoms converts from C_sp2-C_sp2 to C_sp2-C_sp3.

Molecular dynamics simulation of the effects of the samples’ temperature on Ar⁺ interactions with SiC surface

SUN Wei-zhong, ZHAO Cheng-li, LIU Hua-min, ZHANG Jun-yuan, Lü Xiao-dan, PAN Yu-dong, GOU Fu-jun

2010, 30(4):  317-322. 

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Molecular dynamics simulations were performed to investigate the effects of surface temperature on Ar⁺ interactions with the SiC surface. The simulation results show that the number of Si atoms removed increases with increasing surface temperature, while the number of C atoms removed slightly changes. The sputtering yield of Si atoms is greater than that of C atoms. It is found that most of Si and C atoms removed come from the surface region. After modified by Ar⁺ ions, a Si-rich amorphous layer is formed.

Influence of the laser energy and photo-acoustic signal intensity by the change of the solid temperature under Compton scattering

PI Xiao-li, HAO Xiao-fei, HAO Dong-shan

2010, 30(4):  323-326. 

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Using the model of the multi-photon nonlinear Compton scattering，the influence of laser energy and photo-acoustic signal intensity is studied by the change of solid temperature. The result shows that when the intensity and frequency of the coupling optical formed by between Compton scattering and incident optical beams have not changed，the photo-acoustic signal intensity will be quickly and nonlinearly increased along with the ascending of the solid temperature. When the solid temperature has not changed，the photo-acoustic signal intensity will nearly be zero along with the increasing of the coupling laser intensity and frequency.

The effect of curl B on magnetic field drift

XU Lao-li, HOU Bi-hui

2010, 30(4):  327-331. 

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The drift of particle guiding centre caused by curl B in a static inhomogeneous magnetic field is investigated by means of three-dimensional vector arithmetic. The drift related to the charged particle velocity perpendicular to the magnetic field is divided into two terms, respectively described by B curvature and curl B. Consequently the representation of curl B drift in a toroidal magnetic field is given, and the possible effect on orbits of passing particle and trapped particle due to curl B drift in a toroidal magnetic field is discussed. The results demonstrate that the drift due to the charged particle velocity perpendicular to the magnetic field is mainly determined by B curvature, and the effect of the curl B on the drift is minor.

Experimental investigation of the suppression of runaway electrons by ramp-up the initial plasma density

ZHU Jin-xia, DUAN Zhuo-qi, JU Hong-jun, CAI Wu-de, ZHU Jun, CHEN Zhong-yong

2010, 30(4):  332-334. 

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The effect of initial plasma density on the generation of runaway electrons at the startup phase has been investigated by hard X-ray diagnostics in the HT-7 tokamak. It is found that higher initial plasma density can effectively suppress the generation of runaway electrons.

Nuclear Fusion Engineering and Technology

Error field calculation on HL-2M tokamak

SUN Ai-ping, CHEN Qian, PENG Xiao-dong, PAN Yu-dong, ZHANG Jin-hua

2010, 30(4):  335-338. 

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Error field caused by non-coaxiality among poloidal and toroidalfield coils on HL-2M tokamak is calculated with SURFMN and SURFMN_TFCOIL code. According to the coil installation error chosen by international tokamak and the installation experience of HL-2A tokamak, the maximum shift distance of poloidal- and toroidal-field coils on HL-2M tokamak is chosen 3~8mm, and the maximum tilt angle of that is 0.05~0.1 degree. The probability density and accumulative probability of error field are calculated with the maximum shift distance 3mm, 5mm and 8mm respectively, and the maximum tilt angle 0.05, 0.075 and 0.1 degree respectively. The results show that: (1) the probability density distribution become flat and the range of error field B_3-mode/B_T is enlarged significantly with the increase of maximum shift distance of field coils; (2) the shift of poloidal- and toroidal-field coils influences error field more heavily than tilt does; (3) when the shift of poloidal- and toroidal-field coils reaches 5mm, especially 8mm, the error field is more possibly reach 2×10^-4.

Design of the new antenna of ECRH system on HL-2A tokamak

WANG Chao, ZHOU Jun, ZENG Jian-er, CHEN Gang-yu, RAO Jun

2010, 30(4):  339-344. 

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Using the principle of quasi-optic, the new antenna of the electron cyclotron resonant heating(ECRH) system on the tokamak HL-2A has been designed. After being focused by the elliptical mirror and reflected by the plane mirror, 4 68GHz/500kW/1s electron cyclotron wave beams would be injected into the tokamak from one Æ350mm port to accomplish heating to the plasma. Based on the propagating theory of the fundamental Gaussian beam, it is gotten that at the centre of the cross section of the tokamak, the power density of each beam is 158MW•m^-2, and the power density radius, which means that the power density is reduced by a factor 1/e² compared to the power density at the centre of the beam, is 31.7mm. On the mirror, due to the focusing and reflecting, the ohmic loss and diffraction loss of the microwave beams are 0.27% and 0.64%, respectively. By the finite element analysis software ANSYS, some thermal analysis of the mirror have been done. The result shows that the highest temperature increase would be only 0.47℃ under 1s pulse load, so there is no need of any cooling.

Improvement of arcing detector for ECRH system on the HL-2A tokamak

Lu Bo, RAO Jun, WANG Ming-wei

2010, 30(4):  345-349. 

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The improvement of the arcing detector for the ECRH system in HL-2A tokomak is presented in this paper. Two types of photoelectric conversion module, four different operator amplifiers are investigated and the anti-self-excitation capacitor is quantitatively studied in this improvement. The GGOE-2 photoelectric converter and OPA128LM operator amplifier are finally chosen. The anti-self-excitation capacity is determined to be 30pF. 30 arcing detectors were produced and tested to satisfy the requirement of the HL-2A tokomak in 2009. The measured average response time is 1.2μs, which is shorter than the former’s. The arcing detectors work properly in different level of background light and in complicated electromagnetic environment.

Design and realization of the control system of the auxiliary heating high-voltage power supply on HL-2A

MAO Xiao-hui, LI Qing, WANG Ya-li, XUAN Wei-min, YAO Lie-ying

2010, 30(4):  350-354. 

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The AC regulated high-voltage power supply and the neutral point control high-voltage power supply are designed for LHCD and ECRH. The high-voltage pulse modulators are used in these power supplies. The wave head compensation, the feed forward control and the feedback control methods are adopted to compensate the dynamic characteristic fault of the power supply and the output voltage instability of the generators. The stability of output voltage is better than 1%. The main circuit and the control system are described. Good controlling properties and reliable protective properties of the control system are proven by the experiment results.

Analysis of strain distribution and critical current of superconductors based on a strain-critical current measurement system

LIU Fang, WU Yu, LONG Feng

2010, 30(4):  355-359. 

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Based on Pacman device which is widely used to investigate the axial strain dependence of the critical current in superconductors, the finite element analysis method is employed to carry out the force analysis of the spring and the superconducting strand, thereby the axial and lateral strain distributions of the superconducting strand are obtained. According to the two extreme assumptions (low inter-filament resistance and high inter-filament resistance), the effects of the strain homogeneity at the cross section of the superconductor on the critical current is analyzed combined with the Nb₃Sn deviatoric strain-critical current scaling law.

Calibration of magnetic probe parameters

DAI Xiao-jing, SHEN Biao, LIU Guang-jun

2010, 30(4):  360-364. 

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In order to calibrate the offset of the magnetic probe position and loop gain of the electromagnetic measurement system in EAST tokamak, the discharge mode of the poloidal field coils is designed through the analysis of the error sources.The measurement data is preprocessed by Green function, then using the simplified Taylor linear expansion ideas, combined with least squares method with weights, the offset of the magnetic probe position and the loop gain is fitted after cycle-iteration. Experimental results show that this calibration method is reasonable.

Non-Fusion Plasma Applications

Study of discharge properties and parameters of high power pulsed unbalanced magnetron sputtering

MU Zong-xin, WANG Chun, JIA Li, MU Xiao-dong, ZANG Hai-rong, LIU Bing-bing, DONG Chuang

2010, 30(4):  365-369. 

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The deep extent discharge has been formed by spontaneous transcend discharge. The magnetic trap above target captures the second electrons leading to a drift current. A circular planar electron biased -100V opposite to target was used to measure saturation ion current. A Langmuir probe located at 14cm from target was used to measure floating potential. An oscilloscope was used to pick the pulsed signal of discharge voltage, current, float potential and saturation ion current. The pulsed discharge power reached above 0.9MW, and a peak frequency value is about 40Hz. The limited condition of space charge is the control mechanism for the electron current and ion current respectively.

Plasma immersion ion implantation for ultra low energy doping

WANG Ming-gang, LIU Jie, YANG Wei-feng, LI Chao-bo, XIA Yang

2010, 30(4):  370-373. 

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A plasma immersion ion implantation(PIII) system based on inductively coupled plasma(ICP) technology was designed. The PIII system had a cylindrical chamber, and a radio frequency(RF) power was used to sustain discharge and a pulsed voltage source was provided to bias the wafer. The RF power was coupled into chamber by a non-coplanar two-turn circular structure coil. A Langmuir probe was connected to the PIII system to diagnose the plasma parameters. The probe diagnosis indicated that plasma ion density of the system achieves 10¹⁷m^-3, the uniformity of the ion density along radial direction achieves 3.53%. Boron (B) and phosphorus (P) doping experiments were performed on the system. Results from second ion mass spectrum (SIMS) tests showed that the measured injection depth is about 10nm and the shallowest is 8.6 nm (at 10¹⁸cm^-3), the peak ion concentration is below the surface of the wafer, and the ion dose reaches above10¹⁵cm^-2 and the abrupt 2.5 nm/decade.

Investigation on an open microwave resonant cavity measurement system in a ballistic range

MA Ping, LIU Sen, TANG Pu, ZENG Xue-jun, SHI An-hua, HUANG Jie

2010, 30(4):  374-378. 

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The principle and experimental results of the open microwave resonant cavity measurement system were introduced. The models were steel ball models and the ball models coated with copper. The diameter of the models was 10mm. The models were launched in ballistic range. The model velocity was 5.44 km.s^-1. The wake electron density of the models was obtained. The experimental results presents that the response time of the open microwave resonant cavity measurement system was quicker than 1ms. The results showed the wake electron density ranged from 10⁹cm^-3 to 10¹¹cm^-3 could be achieved.