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Generation of Ultrahigh-Velocity Collisionless Electrostatic Shocks Using an Ultra-Intense Laser Pulse Interacting with Foil-Gas Target
Shu-Kai He, Jin-Long Jiao, Zhi-Gang Deng, Feng Lu, Lei Yang, Fa-Qiang Zhang, Ke-Gong Dong, Wei Hong, Zhi-Meng Zhang, Bo Zhang, Jian Teng, Wei-Min Zhou, Yu-Qiu Gu
Chin. Phys. Lett.    2019, 36 (10): .   DOI: 10.1088/0256-307X/36/10/105201
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Ultra high-velocity collisionless shocks are generated using an ultra-intense laser interacting with foil-gas target, which consists of copper foil and helium gas. The energy of helium ions accelerated by shock and the proton probing image of the shock electrostatic field show that the shock velocity is 0.02$c$, where $c$ is the light speed. The numerical and theory studies indicate that the collisionless shock velocity exceeding 0.1$c$ can be generated by a laser pulse with picosecond duration and an intensity of 10$^{20}$ W/cm$^{2}$. This system may be relevant to the study of mildly relativistic velocity collisionless shocks in astrophysics.
Comparison of ITG and TEM Microturbulence in DIII–D Tokamak
Wei Hu, Hong-Ying Feng, Wen-Lu Zhang
Chin. Phys. Lett.    2019, 36 (8): .   DOI: 10.1088/0256-307X/36/8/085201
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Microturbulence excited by ion temperature gradient (ITG)-dominant and trapped electron mode (TEM)-dominant instabilities is compared in the fusion plasmas using gyrokinetic simulations based on the realistic equilibrium data from DIII–D discharges. Collisions make a difference between two plasmas and give rise to similar results to those found in previous research experiments [Chin. Phys. Lett. 35 (2018) 105201]. The mode structures and frequency spectrum of the most unstable modes characterized by the ITG-dominant and TEM-dominant instabilities are excited in the lower and higher $T_{\rm e}$ plasmas in the linear simulations. In the nonlinear simulations, contour plots of the perturbed potential are shown in the saturated stage, with the radial correlation lengths being microscopic on the order of the ion thermal gyroradius $\rho_{\rm i}$ in both the ITG and the TEM microturbulences. The dominant mode wavelengths of the perturbed potential increase when evolving from linear to nonlinear stages in both simulations, with the fluctuation energy spreading from the linearly dominant modes to the nonlinearly dominant modes. The radial correlation lengths are about 4$\rho_{\rm i}$ and the electron density fluctuation intensities are about 0.85% in the nonlinear saturated stage, which are in agreement with the experimental results.
Electron-Electron Collision Term Describing the Reflections Induced Scattering in a Magnetized Plasma
Chao Dong, Ding Li, Chang Jiang
Chin. Phys. Lett.    2019, 36 (7): .   DOI: 10.1088/0256-307X/36/7/075201
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For an electron-electron collision with characteristic scale length larger than the relative gyro-radius of the two colliding electrons, when the initial relative parallel kinetic energy cannot surmount the Coulomb repulsive potential, reflection will occur with interchange of the parallel velocities of the two electrons after the collision. The Fokker–Planck approach is employed to derive the electron collision term $\mathcal{C}_{\rm R}$ describing parallel velocity scattering due to the reflections for a magnetized plasma where the average electron gyro-radius is much smaller than the Debye length but much larger than the Landau length. The electron parallel velocity friction and diffusion coefficients due to the reflections are evaluated, which are found not to depend on the electron perpendicular velocity. By studying the temporal evolution of the $H$ quantity due to $\mathcal{C}_{\rm R}$, it is found that $\mathcal{C}_{\rm R}$ eventually makes the system relax to a state in which the electron parallel velocity distribution is decoupled from the perpendicular velocity distribution.
Impact of Sheath Boundary Conditions and Magnetic Flutter on Evolution and Distribution of Transient Particle and Heat Fluxes in the Edge-Localized Mode Burst by Experimental Advanced Superconducting Tokamak Simulation
Yan-Bin Wu, Tian-Yang Xia, Fang-Chuan Zhong, Bin Gui, EAST Team
Chin. Phys. Lett.    2019, 36 (4): .   DOI: 10.1088/0256-307X/36/4/045201
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To study the evolution and distribution of the transient particle and heat fluxes during the edge-localized modes (ELMs) burst on the experimental advanced superconducting tokamak (EAST), the BOUT$^{++}$ six-field two-fluid model with sheath boundary conditions (SBCs) and magnetic flutter terms in the parallel thermal conduction is used to simulate the evolution of the profiles and growing process of the fluxes at divertor targets. Although SBCs hardly play a role in the linear phase, in the nonlinear phase both SBCs and magnetic flutter can change the dominant toroidal mode. SBCs are able to broaden the frequency distribution of the turbulence. The magnetic flutter increases the ELM size from 2.8% to 8.4%, and it doubles the amplitudes of the radial heat and particle transport coefficients at outer midplane (OMP), at around 1.0 m$^{2}$s$^{-1}$. It is then able to increase the particle and heat flux at the divertor targets and to broaden the radial distribution of the parallel heat flux towards the targets.
Successive Picket Drive for Mitigating the Ablative Richtmyer–Meshkov Instability
Meng Li, Wen-Hua Ye
Chin. Phys. Lett.    2019, 36 (2): .   DOI: 10.1088/0256-307X/36/2/025201
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The ablative Richtmyer–Meshkov instability (ARMI) is crucial to the successful ignition implosion of the inertial confinement fusion (ICF) because of its action as the seed of the Rayleigh–Taylor instability. In usual ICF implosions, the first shock driven by various foots of the pulses plays a central role in the ARMI growth. We propose a new scheme for refraining from ARMI with a pulse of successive pickets. With the successive-picket pulse design, a rippled capsule surface is compressed by three successive shocks with sequentially strengthening intensities and ablated stabilization, and the ablative Richtmyer–Meshkov growth is mitigated quite effectively. Our numerical simulations and theoretical analyses identify the validity of this scheme.
Electron Magnetohydrodynamics Magnetic Reconnection Experiment on Keda Linear Magnetized Plasma Device
Feibin Fan, Jinlin Xie, Qiaofeng Zhang, Longlong Sang, Weixing Ding
Chin. Phys. Lett.    2019, 36 (1): .   DOI: 10.1088/0256-307X/36/1/015201
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We conduct an electron magnetohydrodynamics magnetic reconnection experiment with guide-field in our Keda linear magnetized plasma device, in which two pulsed currents with the same direction are conducted in parallel with the axial direction of the main chamber of the device using two long aluminum sticks. After approximately 5 μs, an X-type magnetic field line topology is formed at the center of the chamber. With the formation of the X-type topology of magnetic field lines, we can also find the rapid increase of the current and ratio of the common flux to the private flux in this area. Additionally, a reduction in the plasma density and the plasma density concentration along one pair of separatrices can also be found.
Particle Growth in an Experimental Dusty Plasma System
Shou-Zhi Jiang, Xue-Ni Hou, Jie Kong, Lorin S. Matthews, Truell W. Hyde, Feng Huang, Min-Juan Wang
Chin. Phys. Lett.    2018, 35 (12): .   DOI: 10.1088/0256-307X/35/12/125201
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The coagulation and growth process of dust particles is investigated through laboratory experiment in a plasma system. A large number of dust particles with different sizes and shapes are formed. The growth process is characterized by the scattering laser intensity and fractal dimension. The comparisons of dust particles and scattering laser intensity obtained at different rf powers are presented. The three-dimensional distribution of dust particles is also given. These results provide an experimental basis for dust growth investigation.
Relativistic Spherical Plasma Waves in a Collisional and Warm Plasma
Zhong-Kui Kuang, Li-Hong Cheng, Pan-Fei Geng, Rong-An Tang, Ju-Kui Xue
Chin. Phys. Lett.    2018, 35 (12): .   DOI: 10.1088/0256-307X/35/12/125202
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Under Lagrange coordinates, the relativistic spherical plasma wave in a collisional and warm plasma is discussed theoretically. Within the Lagrange coordinates and using the Maxwell and hydrodynamics equations, a wave equation describing the relativistic spherical wave is derived. The damped oscillating spherical wave solution is obtained analytically using the perturbation theory. Because of the coupled effects of spherical geometry, thermal pressure, and collision effect, the electron damps the periodic oscillation. The oscillation frequency and the damping rate of the wave are related to not only the collision and thermal pressure effect but also the space coordinate. Near the center of the sphere, the thermal pressure significantly reduces the oscillation period and the damping rate of the wave, while the collision effect can strongly influence the damping rate. Far away from the spherical center, only the collision effect can reduce the oscillation period of the wave, while the collision effect and thermal pressure have weak influence on the damping rate.
Collisional Effects on Drift Wave Microturbulence in Tokamak Plasmas
Wei Hu, Hong-Ying Feng, Chao Dong
Chin. Phys. Lett.    2018, 35 (10): .   DOI: 10.1088/0256-307X/35/10/105201
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Collisional effects on the microturbulence, excited by the electrostatic drift-wave instability, are investigated through first-principle large scale gyrokinetic particle simulations using the realistic discharge parameters of the DIII–D Tokamak. In the linear simulations, the growth rates of the drift waves are decreased by the collisions compared to the collisionless simulations in the lower and higher $T_{\rm e}$ plasmas. In the lower $T_{\rm e}$ plasma, the collisions can promote the transition of the drift wave regime from the TEM-dominant instability to the ITG-dominant instability. The zonal flows are excited by the microturbulence and work as a modulation mechanism for the microturbulence in the nonlinear simulations. Microturbulence can excite high frequency zonal flows in the collisionless plasmas, which is in agreement with the theoretical work. In the lower $T_{\rm e}$ plasma, the collisions decrease the microturbulence in the nonlinear saturated stage compared to the collisionless simulations, which are beneficial for the plasma confinement. In the higher $T_{\rm e}$ plasma, the final saturated microturbulence shows a slight change.
Electron Dynamics and Characteristics of Attosecond Electromagnetic Emissions in Relativistic Laser-Plasma Interactions
Yi-Ying Wu, Quan-Li Dong, Zhao-Hua Wang, Ping Liu, Cheng-Zhen Wang, Yi-Hui Zhang, Zheng-Ming Sheng, Jie Zhang
Chin. Phys. Lett.    2018, 35 (9): .   DOI: 10.1088/0256-307X/35/9/095201
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Generation of attosecond electromagnetic (EM) pulses and the associated electron dynamics are studied using particle-in-cell simulations of relativistic laser pulses interacting with over-dense plasma foil targets. The interaction process is found to be so complicated even in the situation of utilizing driving laser pulses of only one cycle. Two electron bunches closely involved in the laser-driven wavebreaking process contribute to attosecond EM pulses through the coherent synchrotron emission process whose spectra are found to follow an exponential decay rule. Detailed investigations of electron dynamics indicate that the early part of the reflected EM emission is the high-harmonics produced through the relativistic oscillating mirror mechanism. High harmonics are also found to be generated through the Bremsstrahlung radiation by one electron bunch that participates in the wavebreaking process and decelerates when it experiences the local wavebreaking-generated high electrostatic field in the moving direction.
Resistance and Reactance of Monopole Fields Induced by a Test Charge Drifting Off-Axis in a Cold and Collisional Cylindrical Plasma
M. S. Bawa'aneh, A. M. Al-Khateeb, Y. -c. Ghim
Chin. Phys. Lett.    2018, 35 (8): .   DOI: 10.1088/0256-307X/35/8/085101
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We study the interaction of a uniform, cold and collisional plasma with a test charged particle moving off-axis at a constant speed down a cylindrical tube with a resistive thick metallic wall. Upon matching the electromagnetic field components at all interfaces, the induced monopole electromagnetic fields in the plasma are obtained in the frequency domain. An expression for the plasma electric resistance and reactance is derived and analyzed numerically for some representative parameters. Near the plasma resonant frequency, the plasma resistance evolves with frequency like a parallel RLC resonator with peak resistance at the plasma frequency $\omega_{\rm pe}$, while the plasma reactance can be capacitive or inductive in nature depending on the frequency under consideration.
Propagation and Damping of Two-Fluid Magnetohydrodynamic Waves in Stratified Solar Atmosphere
Yong-Jian Jin, Hui-Nan Zheng, Zhen-Peng Su
Chin. Phys. Lett.    2018, 35 (7): .   DOI: 10.1088/0256-307X/35/7/075201
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An extreme ultra-violet (EUV) wave is characterized as a bright pulse that has emanated from the solar eruption source and can propagate globally in the solar corona. According to one leading theory, the EUV wave is a fast magnetoacoustic wave, as the coronal counterpart of the Moreton wave in the chromosphere. However, previous observations have shown that the EUV wave differs significantly from the Moreton wave in both velocity and lifetime. To reconcile these differences, here we analyze the wave characteristics of a two-fluid MHD model in the stratified solar atmosphere with a height-dependent ionization rate. It is found that the collision between neutral and ionized fluids is able to attenuate the wave amplitude, while causing a slight change in its propagation velocity. Because the chromosphere has the lower ionization rate and the stronger magnetic fields than the corona, the velocity of the Moreton wave is much higher than that of the EUV wave. In contrast to the Moreton waves damped strongly by the collision between neutral and ionized fluids, the EUV wave in the fully ionized corona is able to propagate globally on a time scale of several hours. Our results support the previous theory that fast magnetoacoustic waves account for both EUV and Moreteon waves in the different layers of the solar atmosphere.
Dynamics of Ring-to-Volume Discharge Transition in $H$ Mode in Inductively Coupled Plasma Torches at Atmospheric Pressure
Qi-Jia Guo, Guo-Hua Ni, Lin Li, Qi-Fu Lin, Yan-Jun Zhao, Si-Yuan Sui, Hong-Bing Xie, Wen-Xue Duan, Yue-Dong Meng
Chin. Phys. Lett.    2018, 35 (7): .   DOI: 10.1088/0256-307X/35/7/075202
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The transition process in ring-to-volume discharge in $H$ mode in inductively coupled plasma torches at atmospheric pressure is investigated by analyzing the time resolved image taken by a high speed camera. The effects of input power, plasma working gas flow rate, and its composition on the transition dynamics are also discussed. The results show that the discharge plasma has experienced ring discharge, and the development stage diffused from the boundary to the center in the confinement tube, and steady volume discharge after entering the $H$ mode. Increasing input power, sheath gas flow rate and hydrogen contents in plasma working gas are all able to lessen the time consumed in the transition process in ring-to-volume discharge.
Effect of Hyper-Resistivity on Nonlinear Tearing Modes
Wen Yang, Ding Li, Xue-qiao Xu
Chin. Phys. Lett.    2018, 35 (6): .   DOI: 10.1088/0256-307X/35/6/065201
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We analytically investigate nonlinear tearing modes with the anomalous electron viscosity or, as it is normally called, hyper-resistivity. In contrast to the flux average method used by previous work, we employ the standard singular perturbation technique and a quasilinear method to obtain the time evolution equation of tearing modes. The result that the magnetic flux grows with time in a scaling as $t^{2/3}$ demonstrates that nonlinear tearing modes with the hyper-resistivity effect alone have a weaker dependence on time than that of the corresponding resistive case.
Weakly Nonlinear Rayleigh–Taylor Instability in Cylindrically Convergent Geometry
Hong-Yu Guo, Li-Feng Wang, Wen-Hua Ye, Jun-Feng Wu, Wei-Yan Zhang
Chin. Phys. Lett.    2018, 35 (5): .   DOI: 10.1088/0256-307X/35/5/055201
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The Rayleigh–Taylor instability (RTI) in cylindrical geometry is investigated analytically through a second-order weakly nonlinear (WN) theory considering the Bell–Plesset (BP) effect. The governing equations for the combined perturbation growth are derived. The WN solutions for an exponentially convergent cylinder are obtained. It is found that the BP and RTI growths are strongly coupled, which results in the bubble-spike asymmetric structure in the WN stage. The large Atwood number leads to the large deformation of the convergent interface. The amplitude of the spike grows faster than that of the bubble especially for large mode number $m$ and large Atwood number $A$. The averaged interface radius is small for large mode number perturbation due to the mode-coupling effect.
Demonstration of a Shock-Timing Experiment in a CH Layer at the ShenGuang III Laser Facility
Feng WANG, Yu-Long Li, Zhe-Bin Wang, Tao Xu, Wei-Yi Zha, Dong Yang
Chin. Phys. Lett.    2018, 35 (5): .   DOI: 10.1088/0256-307X/35/5/055202
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Shock-timing experiments are indispensable to inertial confinement fusion mainly because the timing of multiple shock waves is crucial to understanding the processes of laser irradiation of targets. Investigations into shock waves driven by a two-step radiation pulse in polystyrene (CH) capsule targets are experimentally conducted at the ShenGuang III laser facility. Differing from the traditional shock-timing implementation in which one shock wave could catch up with another one in solid CH, in this experiment, the second shock front in a rarefaction CH layer is observed through velocity interferometry. This second shock could also be made to converge with rarefaction waves within only a few micrometers of the CH capsule by designing the two-shock coalescence time. A shock-timing diagnostic technique to tune the multi-shock convergence in the CH capsule can thereby be achieved. The experimental results in the CH layer are quasi-quantitatively interpreted using streamlines simulated with the Multi-1D program. The experimental results are expected to offer important information for target structure and laser pulse design, both of which are important for realizing inertial confinement fusion.
Mechanism of Electromagnetic Flow Control Enhanced by Electro-Discharge in Water
Yan-Liang Ji, Ben-Mou Zhou, Ya-Dong Huang
Chin. Phys. Lett.    2018, 35 (5): .   DOI: 10.1088/0256-307X/35/5/055203
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Pulsed discharge utilized to achieve large current density in the electromagnetic flow control is numerically studied. A mathematic discharge model is established to calculate the plasma channel, and an actuator is designed to generate the Lorentz force in the micro plasma channel. During the discharge process, the resistance in the channel decreases rapidly and a large current density appears between the discharge electrodes. After the actuator is applied in the leading edge of a flat plate, the separation region and downstream turbulent boundary layer on the plate disappear. Meanwhile, a skin-friction drag force reduction is achieved.
Extraordinary Electromagnetic Waves in Weakly Relativistic Degenerate Spin-1/2 Magnetized Quantum Plasmas
Chun-Hua Li, Shao-Wei Wang, Yun-Hao Liu, Zhen-Wei Xia, Xiao-Hui Zhang, Dan-Dan Zou
Chin. Phys. Lett.    2018, 35 (4): .   DOI: 10.1088/0256-307X/35/4/045201
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By using the relativistic quantum magnetohydrodynamic model, the extraordinary electromagnetic waves in magnetized quantum plasmas are investigated with the effects of particle dispersion associated with the quantum Bohm potential effects, the electron spin-1/2 effects, and the relativistic degenerate pressure effects. The electrons are treated as a quantum and magnetized species, while the ions are classical ones. The new general dispersion relations are derived and analyzed in some interesting special cases. Quantum effects are shown to affect the dispersion relations of the extraordinary electromagnetic waves. It is also shown that the relativistic degenerate pressure effects significantly modify the dispersive properties of the extraordinary electromagnetic waves. The present investigation should be useful for understanding the collective interactions in dense astrophysical bodies, such as the atmosphere of neutron stars and the interior of massive white dwarfs.
Effect of Parallel-Plate Geometry on Mode Transition Behavior in Argon Microplasmas: Two-Dimensional Simulation
Xiang-Mei Liu, Yuan-Hong Song, Wei Jiang, Wen-Zhu Jia
Chin. Phys. Lett.    2018, 35 (4): .   DOI: 10.1088/0256-307X/35/4/045202
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A two-dimensional self-consistent fluid model is employed to investigate radio-frequency process parameters on the plasma properties in Ar microdischarges. The neutral gas density and temperature balance equations are taken into account. We mainly investigate the effect of the electrode gap on the spatial distribution of the electron density and electron temperature profiles, due to a mode transition from the $\gamma$ regime (secondary electrons emission is responsible for the significant ionization) to the $\alpha$ regime (sheath oscillations and bulk electrons are responsible for sustaining discharge) induced by a sudden decrease of electron density and electron temperature. The pressure, radio-frequency sources frequency and voltage effects on the electron density are also elaborately investigated.
Particle Trajectory Integrator in Guiding Center Phase Space
Jing-Bo Lin, Wen-Lu Zhang, Peng-Fei Liu, Chao Dong, Jin-Tao Cao, Ding Li
Chin. Phys. Lett.    2018, 35 (2): .   DOI: 10.1088/0256-307X/35/2/025201
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A trajectory integrator is developed based on a particle's guiding center Hamiltonian. It is verified by a series of benchmarks, which are in good accordance with theoretical prediction. This integrator can be used as the guiding center trajectory integrator of a particle-in-cell simulation platform, such as the newly developed VirtEx. It can also be used as a stand-alone tool to investigate particle dynamics in a given background field.
Formation of Nonlinear Solitary Vortical Structures by Coupled Electrostatic Drift and Ion-Acoustic Waves
L. Z. Kahlon, I. Javaid
Chin. Phys. Lett.    2017, 34 (12): .   DOI: 10.1088/0256-307X/34/12/125201
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Propagation of coupled electrostatic drift and ion-acoustic waves (DIAWs) is presented. It is shown that nonlinear solitary vortical structures can be formed by low-frequency coupled electrostatic DIAWs. Primary waves of distinct (small, intermediate and large) scales are considered. Appropriate set of 3D equations consisting of the generalized Hasegawa–Mima equation for the electrostatic potential (involving both vector and scalar nonlinearities) and the equation of motion of ions parallel to magnetic field are obtained. According to experiments of laboratory plasma mainly focused to large scale DIAWs, the possibility of self-organization of DIAWs into the nonlinear solitary vortical structures is shown analytically. Peculiarities of scalar nonlinearities in the formation of solitary vortical structures are widely discussed.
Effects of Three Typical Resistivity Models on Pulsed Inductive Plasma Acceleration Modeling
Xin-Feng Sun, Yan-Hui Jia, Tian-Ping Zhang, Chen-Chen Wu, Xiao-Dong Wen, Ning Guo, Hai Jin, Yu-Jun Ke, Wei-Long Guo
Chin. Phys. Lett.    2017, 34 (12): .   DOI: 10.1088/0256-307X/34/12/125202
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The effects of three different typical resistivity models (Spitzer, Z&L and M&G) on the performance of pulsed inductive acceleration plasma are studied. Numerical results show that their influences decrease with the increase of the plasma temperature. The significant discriminations among them appear at the plasma temperature lower than 2.5 eV, and the maximum gap of the pulsed inductive plasma accelerated efficiency is approximately 2.5%. Moreover, the pulsed inductive plasma accelerated efficiency is absolutely related to the dynamic impedance parameters, such as voltage, inductance, capacitance and flow rate. However, the distribution of the efficiency as a function of plasma temperature with three resistivity models has nothing to do with the dynamic impedance parameter.
Microstructure and Deuterium Retention of Tungsten Deposited by Hollow Cathode Discharge in Deuterium Plasma
Zhong-Chao Sun, Zi-Wei Lian, Wei-Na Qiao, Jian-Gang Yu, Wen-Jia Han, Qing-Wei Fu, Kai-Gui Zhu
Chin. Phys. Lett.    2017, 34 (12): .   DOI: 10.1088/0256-307X/34/12/125203
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Tungsten has been chosen as one of the most promising candidates as the plasma-facing material in future fusion reactors. Although tungsten has numerous advantages compared with other materials, issues including dust are rather difficult to deal with. Dust is produced in fusion devices by energetic plasma-surface interaction. The re-deposition of dust particles could cause the retention of fuel atoms. In this work, tungsten is deposited with deuterium plasma by hollow cathode discharge to simulate the dust production in a tokamak. The morphology of the deposited tungsten can be described as a film with spherical particles on it. Thermal desorption spectra of the deposited tungsten show extremely high desorption of the peak positions. It is also found that there is a maximum retention of deuterium in the deposited tungsten samples due to the dynamic equilibrium of the deposition and sputtering process on the substrates.
Enhancement of Heat-Resistance of Carbonyl Iron Particles by Coating with Silica and Consequent Changes in Electromagnetic Properties
Zhao-Wen Ren, Hui Xie, Ying-Ying Zhou
Chin. Phys. Lett.    2017, 34 (10): .   DOI: 10.1088/0256-307X/34/10/105201
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Silica-coated carbonyl iron particles (CIPs) are fabricated with the Stober method to improve their heat-resistance and wave-absorption properties. The morphology, heat-resistance, electromagnetic properties and microwave absorption of raw-CIPs and silica-coated CIPs are investigated using a scanning electron microscope, an energy dispersive spectrometer, a thermal-gravimetric analyzer, and a network analyzer. The results show that the heat-resistance of silica-coated CIPs is better than that of raw CIPs. The reflection losses exceeding $-$10 dB of silica-coated CIPs are obtained in the frequency range 9.3–12.4 GHz for the absorber thickness of 2.3 mm, and the same reflection losses of uncoated CIPs reach the data in the lower frequency range for the same thickness. The enhanced microwave absorption of silica-coated CIPs can be ascribed to the combination of proper electromagnetic impedance match and the decrease of dielectric permittivity.
Heat Flux on EAST Divertor Plate in H-mode with LHCD/LHCD+NBI
Bo Shi, Zhen-Dong Yang, Bin Zhang, Cheng Yang, Kai-Fu Gan, Mei-Wen Chen, Jin-Hong Yang, Hui Zhang, Jun-Li Qi, Xian-Zu Gong, Xiao-Dong Zhang, Wei-Hua Wang
Chin. Phys. Lett.    2017, 34 (9): .   DOI: 10.1088/0256-307X/34/9/095201
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Based on the surface temperature measured by the infrared camera on the experimental advanced superconducting tokamak (EAST), the heat fluxes on the lower outer divertor target plate during H-mode with the lower-hybrid wave current drive (LHCD) only and with the LHCD combined with the neutral beam injection (NBI) are calculated by the DFLUX code and compared. The analyzed discharges are lower single null divertor configuration discharges. In the case with the LHCD only ($I_{\rm p}\sim 400$ kA, $P_{\rm LHCD}\sim2$ MW), ELM-free appears after L-H transition with the peak heat flux on the lower outer target plate less than 1 MW/m$^{2}$. However, there is no ELM-free appearing after the L-H transition in the case with the LHCD+NBI ($I_{\rm p}\sim300$ kA, $P_{\rm LHCD}+P_{\rm NBI}\sim2$ MW). The results show that the peak heat fluxes on the lower outer target plate in the LHCD+NBI H-mode cases are larger than those in the LHCD H-mode under the similar auxiliary heating power. This is because the heat flux profiles of the lower outer target plate as a function of plate location in ELMing with the LHCD+NBI are narrower than those with the LHCD only. The results are consistent with the results in terms of the scrape-off layer width observed in the EAST.
High-Yield High-Efficiency Positron Generation in High-$Z$ Metal Targets Irradiated by Laser Produced Electrons from Near-Critical Density Plasmas
Wei Song, Rong-Hao Hu, Yin-Ren Shou, Zheng Gong, Jin-Qing Yu, Chen Lin, Wen-Jun Ma, Yan-Yin Zhao, Hai-Yang Lu, Xue-Qing Yan
Chin. Phys. Lett.    2017, 34 (8): .   DOI: 10.1088/0256-307X/34/8/085201
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An improved indirect scheme for laser positron generation is proposed. The positron yields in high-$Z$ metal targets irradiated by laser produced electrons from near-critical density plasmas and underdense plasma are investigated numerically. It is found that the positron yield is mainly affected by the number of electrons of energies up to several hundreds of MeV. Using near-critical density targets for electron acceleration, the number of high energy electrons can be increased dramatically. Through start-to-end simulations, it is shown that up to $6.78\times10^{10}$ positrons can be generated with state-of-the-art Joule-class femtosecond laser systems.
The Diffusion Coefficient Using Sawtooth Oscillation in IR-T1 Tokamak
N. Hasanvand, S. Meshkani, M. Ghoranneviss
Chin. Phys. Lett.    2017, 34 (8): .   DOI: 10.1088/0256-307X/34/8/085202
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The investigation of runaway electrons is expanded by different methods. The aim of this study is to show sawtooth oscillations of hard x-ray emission and with the help of sawtooth oscillations to obtain radial diffusion coefficient and magnetic fluctuations. In the same way, the hard x-ray spectral evaluation is compared in several time intervals and it is shown that during discharge, the energy of the runaway electrons is less than 200 keV. Also, for typical plasmas, population of runaway electrons is measured at seven time intervals of 5 ms and temporal evaluation of runaway electron mean energy. The sawtooth-like shape is observed in the hard x-ray range (10–1000 keV). By the sawtooth oscillation method, the RE diffusion coefficient in radial transport in the IR-T1 plasma is $D_{\rm r}\sim 0.5$ m$^2$s$^{-1}$. The magnetic field fluctuation due to magnetic diffusion $D_{\rm m}$ is given as $\frac{b_{\rm r}}{B_{\rm t}}\sim 10^{-4}$.
A Method of Using a Carbon Fiber Spiral-Contact Electrode to Achieve Atmospheric Pressure Glow Discharge in Air
Wen-Zheng Liu, Shuai Zhao, Mao-Lin Chai, Jiang-Qi Niu
Chin. Phys. Lett.    2017, 34 (8): .   DOI: 10.1088/0256-307X/34/8/085203
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During discharge, appropriately changing the development paths of electron avalanches and increasing the number of initial electrons can effectively inhibit the formation of filamentary discharge. Based on the aforementioned phenomenon, we propose a method of using microdischarge electrodes to produce a macroscopic discharge phenomenon. In the form of an asymmetric structure composed of a carbon fiber electrode, an electrode structure of carbon fiber spiral-contact type is designed to achieve an atmospheric pressure glow discharge in air, which is characterized by low discharge voltage, low energy consumption, good diffusion and less ozone generation.
Jeans Gravitational Instability with $\kappa $-Deformed Kaniadakis Distribution
Hui Chen, Shi-Xuan Zhang, San-Qiu Liu
Chin. Phys. Lett.    2017, 34 (7): .   DOI: 10.1088/0256-307X/34/7/075101
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The Jeans instabilities in an unmagnetized, collisionless, isotropic self-gravitating matter system are investigated in the context of $\kappa$-deformed Kaniadakis distribution based on kinetic theory. The result shows that both the growth rates and critical wave numbers of Jeans instability are lower in the $\kappa$-deformed Kaniadakis distributed self-gravitating matter systems than the Maxwellian case. The standard Jeans instability for a Maxwellian case is recovered under the limitation $\kappa=0$.
Linear Growth of Rayleigh–Taylor Instability of Two Finite-Thickness Fluid Layers
Hong-Yu Guo, Li-Feng Wang, Wen-Hua Ye, Jun-Feng Wu, Wei-Yan Zhang
Chin. Phys. Lett.    2017, 34 (7): .   DOI: 10.1088/0256-307X/34/7/075201
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The linear growth of Rayleigh–Taylor instability (RTI) of two superimposed finite-thickness fluids in a gravitational field is investigated analytically. Coupling evolution equations for perturbation on the upper, middle and lower interfaces of the two stratified fluids are derived. The growth rate of the RTI and the evolution of the amplitudes of perturbation on the three interfaces are obtained by solving the coupling equations. It is found that the finite-thickness fluids reduce the growth rate of perturbation on the middle interface. However, the finite-thickness effect plays an important role in perturbation growth even for the thin layers which will cause more severe RTI growth. Finally, the dependence of the interface position under different initial conditions are discussed in some detail.
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