Nuclear Fusion and Plasma Physics

SHI Bing-ren

2012, 32(2): 97-102.

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It is shown that the variation of the kinetic energy for Suydam instability of a cylindrical plasma derived from the energy principle is infinite，implying that the growth rate of such instability is zero. Realistic physical meaning of the Suydam instability can be correctly explained by the solution of the Hain-Lust equations. Accomplished works so far are simply commented. Finally, a method is suggested to determine the stability of the externally kink modes for a tokamak plasma when in its internal region the Suydam criterion is unsatisfied.

Characteristics of ions in a collisional plasma sheath with two species of positive ions

ZHAO Xiao-yun, DUAN Ping, LIU Jin-yuan, WANG Chun-xiao

2012, 32(2): 103-108.

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A fluid model is developed in a collisional plasma sheath including two species of positive ions. It is discussed that collisions which consist of ion-neutral collision and secondary electron emitted from the wall affect the density distribution and velocity. Numerical results are obtained through a fourth-order-Rung-Kutta method. It is shown that by increasing the collision frequency of one of two ions with neutrals, the density distribution and velocity of this ion will take on the fluctuation in the sheath. The density increases, then decreases. But the velocity is in verse. The other ion is completely monotone. It is discovered that the position where the density of the ion presents the transformation by the collision between this kind of positive ions and neutral particles in the sheath will be away from the sheath edge if the ion’s density is less at the sheath edge. It is also found that the abatement of this ion density distribution is very small when the collision between the less ion and neutral particles increases. In addition, the coefficient of secondary electron emission affects the density distribution of the lighter ion species greatly in two different masses of positive ions.

Two dimensional high-order CIP numerical method and applications

ZHU Ting-ru, PENG Xiao-dong, WANG Gang, ZHAO Xiao-ming, TANG Chang-jian

2012, 32(2): 109-116.

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Employing a function and its derivatives to construct a fifth-order interpolation function to approximate to the real solution in a cell, we have improved the CIP (Constrained Interpolation Profile) numerical algorithm. A direct two-dimensional high-order CIP method differing from adopting a time-splitting technology has been developed on the basis of the previous one-dimensional case. The improved method is an explicit scheme with the fifth-order accuracy.

Computational research on fast wave minority species heating

ZHU Xue-guang, DING Bo-jiang, KUANG Guang-li, XIE Ji-kang, LIU Yan-li

2012, 32(2): 117-121.

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Advances of research on then domain of ion cyclotron wave heating are introduced, and mode conversion of fast wave minority heating, as well as the factor to influence the fraction and position of absorption is analyzed in detail. By means of controlling wave frequency and minority concentration, it is possible for the wave to be propagated near tokamak plasma central ion hybrid resonance region and effectively absorbed by the plasma by being converted to ion Bernstein wave, so the heating effect is improved.

The effect of the electric drift upon the resonant interaction between energetic ions and neoclassical tearing modes

HE Da-jian, GONG Xue-yu

2012, 32(2): 122-127.

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The effect of the electric drift upon the resonant interaction of passing energetic ions with neoclassical tearing mode (NTM) has been studied. Using a drift-kinetic approach, we reconsider the role of the electric drift and obtain the toroidal torque exerting on island produced by the resonant interaction. We find that, according to the net balance of toroidal momentum associated with the magnetic island motion, the passing energetic ions with v >0 tend to reduce the mode frequency when the magnetic island moves along the electron diamagnetic drift direction, on the opposite, the ones with v<0 tend to increase the mode frequency, the total toroidal torque produced by them is almost zero. In the following calculation, only the torque produced by the passing energetic ions with v>0 has been included in the coupled equations which consist of the net balance of toroidal momentum equation associated with the magnetic island motion and the modified Rutherford equation. Numerical calculation show that the stable limit cycle describing nonlinear oscillations of the mode frequency and amplitude dose not exit.

N₂-Ar rf discharge surface nitriding plasma characteristics simulation

SUN Qian, YANG Ying, ZHAO Hai-tao, HAO Ying-ying, ZHANG Lian-zhu, ZHAO Guo-ming

2012, 32(2): 128-132.

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N₂-Ar rf discharge plasma is used in numerous widespread applications, such as the etching in microelectronics industry, the preparation of nitrides film and the metal surface nitriding and so on. A PIC/MC model for the N2-Ar mixture gas capacitively coupled rf discharge processes was developed, in which we describe the behaviour of the main charged particles(e^-, N₂⁺, N⁺, Ar⁺)and take into account 21 kinds of collisions of charged particles(e^-, N₂⁺, N⁺, Ar⁺)with ground-state neutral N₂ and Ar. It turned out that however in the N₂-Ar mixture gas discharge or N₂ gas discharge, the density of charged particles all has the maximum in the plasma region, especially, N₂⁺ is the main particle. In the N₂ gas capacitively coupled rf discharge, with the adding of 10% Ar, the mean energy of N⁺ is increasing, and the high-energy proportion of the two particles (N₂⁺, N⁺) in the rf electrode are both increasing. So it was important for us to know the microscopic mechanism of N₂-Ar rf discharge.

Study on the properties of tunable prohibited band gaps for one-dimensional ternary magnetized plasma photonic crystals

ZHANG Hai-feng, ZHENG Jian-ping, ZHU Rong-jun

2012, 32(2): 133-139.

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The transfer matrix method was applied to study on the properties of tunable prohibited band gaps for one-dimensional ternary magnetized plasma photonic crystals with TE wave arbitrary incident under ideal conditions. TE wave would be divided into left-handed circularly polarized wave and right-handed circularly polarized wave after propagation through one-dimensional ternary magnetized plasma photonic crystals. The calculated transmission coefficients were used to analyze the effects of parameter of plasma, plasma filling factor, incident angle and relative dielectric constant for dielectric layer on the properties of tunable prohibited band gap. The results illustrate that the width of band gaps can not be broadened by increasing plasma collision frequency, the numbers and width of band gaps can be tuned by changing plasma frequency, plasma filling factor and relative dielectric constant for dielectric layer. The band gaps for right-handed circularly polarized wave can be tuned by the plasma gyro frequency, but band gaps for the left-handed circularly polarized wave can’t influenced. Low-frequency region of band gaps will be broadened, while high-frequency region of band gaps will be firstly narrow and then broaden with increasing incident angle.

Discrete Alfvén eigenmodes in high performance discharges in the DⅢ-D tokamak

WANG Yi-ru, HU Shuang-hui, YAO Long-bao, CHEN Shu-ping

2012, 32(2): 140-147.

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The physical features of the discrete Alfvén eigenmodes are investigated in the DⅢ-D tokamak plasmas for the high performance discharge conditions, including the negative magnetic shear configuration, the high power heating, the co- and counter- neutral beam injection (NBI), the internal transport barrier, the high bootstrap current fraction case, and the VH-mode discharge. These Alfvén eigenmodes exist in a wide radial range of the DⅢ-D plasma with a broad frequency spectrum in the advanced operation regime with the negative magnetic shear. The high power heating, the co-NBI, and the internal transport barrier can help form multiple deep potential wells, thus efficiently trapping the Alfvén eigenmodes. These Alfvén bound states can be found in even more extended radial range with relatively high frequencies for both the high bootstrap fraction discharge and the VH-mode discharge. These discrete Alfvén eigenmodes, developed during the DⅢ-D high performance discharges with a broad scope of operating parameters, would be the potential instability which can exist widely in the experiments on the large similar tokamaks.

Influences on attenuation characteristics of laser in plasma by Compton scattering

SUN Fu-hao, HAO Xiao-Fei, HAO Dong-Shan

2012, 32(2): 148-152.

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Using the model of multi-photon nonlinear Compton scattering, the influences on attenuation characteristics of electromagnetism wave in plasma by Compton scattering is studied. It is advanced that Compton scattering is an important influence mechanism on the attenuation characteristics of electromagnetism wave in plasma, and the formulas on attenuations of the electromagnetism wave energy and power are derived and simulated numerically. The results show that Compton scattering can take bigger influences on the attenuation of electromagnetism wave in plasma, and the results between the theory computation and numerical simulation are very coincident. The results can give the theory basis for deciding the Compton scattering taking place in the plasma.

The cooling calculation and optimization of HL-2M ohmic test coil

JIANG Jia-ming, LIU De-quan, LI Guang-sheng, XIE Yan-feng, ZOU Hui, CAI Li-jun

2012, 32(2): 153-157.

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The models of HL-2M ohmic test coil and the cooling water have been built by using ANSYS CFX finite element software, and the coil temperature rise and water cooling have been calculated by the fluid-solid coupling with the boundary of heat conduction and convective heat transfer equation. As a result, the ohmic coil maximum temperature rise caused by the joule heat, has close relationship with current density and the equivalent running time, and has little relationship with cooling water flow; cooling water flow decides mainly the length of the ohmic coil cooling time interval, maximum cooling time interval is 5min.

Plasma density feedback control system in HL-2A tokamak

GAO Xiao-yan, TIAN Pei-hong, CUI Cheng-he, CAI Xiao

2012, 32(2): 158-164.

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The design of the plasma density feedback control system (PDFCS) is described. The design requirements of the feedback control system including hardware and software are proposed to approach the plasma density reference value and then a discussion of “how to realize the feedback control” is given. The experimental results show that the feedback control system satisfies the real-time and stable control.

The ohmic field power supply system of SUNIST based on IGBT

YANG Gui-xiang, TAN Yi, GONG Xue-yu, PENG Xiao-wei, GAO Zhe, SUNIST Zu

2012, 32(2): 165-170.

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The double swing fluxes of the ohmic field must be utilized in order to extend the flat top of plasma current in the SUNIST spherical tokamak. This requires an upgrade of the power system of the ohmic field. An H-bridge bidirectional discharge circuit is introduced, which is based on four high-current low-frequency switches composed of multiple parallel IGBTs. The key components of the circuit, 3kV/10kA class IGBT switches has been developed. In addition，both the single-phase and three-phase quasi-constant current charging circuit for the energy storage capacitor banks of the upgraded power supply are investigated. After the upgrade，the double swing current, e. g., +10kA to ?6kA, in the ohmic field coils was obtained. The waveforms of plasma current were also improved obviously.

Analysis of phase shift of the EAST fast control power supply

TANG Ke, GAO Ge, LIU Hui, WU Yi-bing

2012, 32(2): 171-176.

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The Fast Control Power Supply(FCPS) is employed to maintain the balance of plasma movement at vertical direction in the Experimental Advanced Superconducting Tokamak (EAST). FCPS is composed of H-bridge inverters. Phase shift is adopted to increase voltage levels and to guarantee that FCPS works safely and smoothly. The characteristics of PWM as well as the basic principle of phase shift were studied by introducing dual Fourier transform. The relationship between voltage levels and modulation ratio is also studied; meanwhile, a new modulation method is suggested to increase voltage levels. Simulation result using MATLAB verifies the validity of analysis.

Experiments of helium and deuterium resolution performance using a quadrupole mass spectrometer

HUANG Xiang-mei, CAO Zeng, CAI Xiao, XU Zheng-hua

2012, 32(2): 177-182.

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Base on the gas analysis and testing system of quadrupole mass spectrometer, experiments of resolution performance for helium and deuterium was carried out. The mass spectrograms were recorded when the vacuum vessel was filled with gas. The results show that the peak position for He⁺ is (4.0022±0.0006)amu and D₂⁺ is (4.0246±0.0006)amu, respectively. Within the pressure range of 10^-6～10^-4Pa, it is found that the mass resolution of He (and D₂) decreases with its partial pressure increase. Under a leak of 10^-7Pa•m³•s^-1 and adjusting the quantity of deuterium, the helium is discriminated if the peak ratio He⁺/D₂⁺ is in the order of 10^-1.

Energy spectrum of ions generated by femtosecond laser and plasmas interaction at the back-side of target

CHEN Xiao-xu, TANG Cui-ming, HONG Wei, GU Yu-qiu, WANG Guang-chang

2012, 32(2): 183-186.

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In the ultra-short and ultra-intense laser interaction with 7μm Cu target, we use CR39 and Thomson spectrometer to detect the energy spectrum of protons and carbon ions at the normal direction of target back. Protons, C⁴⁺, C³⁺, C²⁺ and C¹⁺ ions have been observed experimentally. In addition, the results show that the ions are emitted along the target rear-side normal direction and the ions were cut-off at a certain energy. What is more, the yield of proton is much higher than the one of carbon ions, and the ratio of the maximum cut-off energy of the C⁴⁺, C³⁺, C²⁺ and C¹⁺ ions is about 4: 3: 2: 1.

The study of plasma jet characteristics

ZHA Bai-lin, JIANG Peng, YUAN Xiao-jing, QIAO Su-lei, HUANG Ding-yuan

2012, 32(2): 187-192.

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The operating parameters of plasma generator under various regimes were measured by a newly developed digital plasma measurement system, which can test the flowrate of working gas, temperature rise of cooling water, arc voltage and arc current. According to energy balance principle, plasma average enthalpy, plasma average temperature and its distribution at the plasma generator exit were calculated. The results show that at the plasma generator exit, the distribution of jet temperature is parabolic. Increasing gas flowrate, plasma jet enthalpy and temperature will decline, and while adding hydrogen as a supplementary gas, the enthalpy and temperature will increase significantly.

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