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Test particle simulation on the ion and electron zebra stripes and their time evolution in inner radiation belt

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Science China(Technological Sciences) 2018年第4期61卷 623-632页

作者： WANG YongFu ZONG QiuGang ZHOU XuZhi State Key Laboratory of Nuclear physics and Technology School of Physics and Fusion Simulation CenterPeking University institute of Space physics and Applied Technology Peking University Key Laboratory of Earth and Planetary physics Chinese Academy of Sciences

During February 15–16, 2014, the energetic electron spectrogram for four successive inner radiation belt crossing show clearly the electron zebra structures and their time evolution which last for about 17 h. Unfortunately, the time of flight(TOF) in RBSPICE measurement is turned off below 3 RE, and the ion measurement is contaminated by electrons. Thus in this study we studied the differences between the ion and electron zebra stripe structures and their time evolution using simple theory and test particle simulation, combining the electron measurement from RBSIPICE onboard Van Allen Probes. Theoretical analysis predicts that the ion zebra stripe structures should lie at a higher energy range than the corresponding electron zebra stripe structures due to that the directions of gradient B drift and corotation E×B drift are the same for electrons while opposite for ions. Test particle simulation with the dipole magnetic field and Volland-Stern electric field model have shown that the ion and electron zebra stripe structures could be produced by the convection electric field penetrating into the inner magnetosphere in this event, with their time evolution determined by total drift velocity that are different for ions and electrons. The predicted differences between the ion and electron zebra stripe structures are partially verified through observation. The ion zebra stripe structures could have potential influence to the ring current.

关键词：电子污染条纹结构粒子模拟离子斑马时间进化测试

A Gyrokinetic simulation model for low frequency electromagnetic fluctuations in magnetized plasmas

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Science China(physics,Mechanics & Astronomy) 2021年第4期64卷 90-95页

作者： Liu Chen HaoTian Chen Fulvio Zonca Yu Lin institute for fusion theory and simulation and department of physics Zhejiang UniversityHangzhou 310027China department of physics and Astronomy University of CaliforniaIrvineCalifornia 92697USA institute of Space Science and Technology Nanchang UniversityNanchang 330031China Center for Nonlinear Plasma Science and C.R.ENEA Frascati-C.P.65 Frascati 00044Italy physics department Auburn UniversityAuburn AL 36849USA

We present a new model for simulating the electromagnetic fluctuations with frequencies much lower than the ion cyclotron frequency in plasmas confined in general magnetic configurations.This novel model(termed as GK-E&B)employs nonlinear gyrokinetic equations formulated in terms of electromagnetic fields along with momentum balance equations for solving fields.It,thus,not only includes kinetic effects,such as wave-particle interaction and microscopic(ion Larmor radius scale)physics;but also is computationally more efficient than the conventional formulation described in terms of potentials.As a benchmark,we perform linear as well as nonlinear simulations of the kinetic Alfvén wave;demonstrating physics in agreement with the analytical theories.

关键词： plasma kinetic equations Gyrokinetics Gyrokinetic simulations particle orbit and trajectory

Long-time evolution of charged grains in plasma under harmonic external force and after being withdrawn

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Chinese physics B 2022年第2期31卷 460-464页

作者：管苗陈志东李梦蝶刘忠茂汪友梅郁明阳 department of physics School of ScienceHangzhou Dianzi UniversityHangzhou 310016China College of Engineering physics CAMDTShenzhen Key Laboratory of Ultraintense Laser and Advanced Material TechnologyShenzhen Technology UniversityShenzhen 518118China institute for fusion theory and simulation Zhejiang UniversityHangzhou 310007China Theoretical physics I Ruhr UniversityBochum D-44780Germany

Evolution of the charged grains in a two-dimensional dusty plasma under a spatially harmonic external force,in particular,their long-time behaviors after the force has been withdrawn,is studied by using molecular dynamics simulation.Under an external force and a grain–grain interaction force,initially homogeneously distributed grains can reach a quasistationary state in the form of a disk crystal.After the external force is withdrawn,the disk moves initially with its size and shape nearly unchanged until it rapidly stops moving,and eventually the disk grain rotates like a vortex.The time needed to reach the final state increases with the strength of the initial external force increasing.

关键词： dusty plasma external force long-time behavior molecular dynamics(MD)simulation

An Island Coalescence Scenario for Near-Earth Current Disruption in the Magnetotail

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Chinese physics Letters 2009年第8期26卷 385-388页

作者：马志为路兴强 institute of Plasma physics Chinese Academy of Sciences Hefei 230031 institute for fusion theory and simulation Zhejiang University Hangzhou 310027

A current disruption and dipolarization scenario associated with island coalescences in the near-Earth region is proposed. The thin and elongated current-sheet built up during the growth phase is unstable due to a tearing mode instability that leads to formation of multiple magnetic islands （or magnetic flux ropes in the three dimensional case） in the near-Earth region. The growth rate of the tearing mode shoual be different in different locations because the rate is in general determined by the external driving force and the local plasma sheet properties. When the rate of the magnetic reconnection in the mid-tail region around 20RE is much larger than that in other locations, the strong bulk earthward flows resulting from the fast reconnection in the mid-tail drive the earthward convection and the coalescence of the magnetic islands. Consequently, the cross-tail current in the near-Earth region is suddenly disrupted and the geometry of the magnetic field changes from tall-like to dipolar-like in the ideal time scale. This proposed scenario is tested by Hall MHD simulation and is compared with the observations.

关键词： sea surface nonliear interaction numerical method

Theoretical investigations of half-metallic ferromagnetism in new Half-Heusler YCrSb and YMnSb alloys using first-principle calculations

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Chinese physics B 2016年第10期25卷 386-392页

作者： M Atif Sattar Muhammad Rashid M Raza Hashmi S A Ahmad Muhammad Imran Fayyaz Hussain department of physics simulation Laboratory the Islamia University of Bahawalpur department of physics COMSATS Institute of Information Technology department of physics Bahauddin Zakariya University

Structural,electronic,and magnetic properties of new predicted half-Heusler YCrSb and YMnSb compounds within the ordered MgAgAs Clb-type structure are investigated by employing first-principal calculations based on density functional theory.Through the calculated total energies of three possible atomic placements,we find the most stable structures regarding YCrSb and YMnSb materials,where Y,Cr(Mn),and Sb atoms occupy the(0.5,0.5,0.5),(0.25,0.25,0.25),and(0,0,0) positions,respectively.Furthermore,structural properties are explored for the non-magnetic and ferromagnetic and anti-ferromagnetic states and it is found that both materials prefer ferromagnetic states.The electronic band structure shows that YCrSb has a direct band gap of 0.78 eV while YMnSb has an indirect band gap of 0.40 eV in the majority spin channel.Our findings show that YCrSb and YMnSb materials exhibit half-metallic characteristics at their optimized lattice constants of 6.67  and 6.56 ,respectively.The half-metallicities associated with YCrSb and YMnSb are found to be robust under large in-plane strains which make them potential contenders for spintronic applications.

关键词： electronic structures density functional theory metals and alloys other ferromagnetic metals and alloys

Viscous effects on plasmoid formation from nonlinear resistive tearing growth in a Harris sheet

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Plasma Science and Technology 2022年第1期24卷 18-29页

作者： Nisar AHMAD 朱平 Ahmad ALI 曾市勇 CAS Key Laboratory of Geospace Environment and department of Engineering and Applied physics University of Science and Technology of ChinaHefei 230026People's Republic of China International Joint Research Laboratory of Magnetic Confinement fusion and Plasma physics State Key Laboratory of Advanced Electromagnetic Engineering and TechnologySchool of Electrical and Electronic EngineeringHuazhong University of Science and TechnologyWuhan 430074People's Republic of China department of Engineering physics University of Wisconsin-MadisonMadisonWisconsin 53706United States of America Pakistan Tokamak Plasma Research institute Islamabad 44000Pakistan department of Plasma physics and fusion Engineering University of Science and Technology of ChinaHefei 230026People’s Republic of China

In this work,the evolution of a highly unstable m=1 resistive tearing mode,leading to plasmoid formation in a Harris sheet,is studied in the framework of full MHD model using the Non-Ideal Magnetohydrodynamics with Rotation,Open Discussion simulation.Following the initial nonlinear growth of the primary m=1 island,the X-point develops into a secondary elongated current sheet that eventually breaks into plasmoids.Two distinctive viscous regimes are found for the plasmoid formation and saturation.In the low viscosity regime(i.e.P_(r)■1),the plasmoid width increases sharply with viscosity,whereas in the viscosity dominant regime(i.e.P_(r)■1),the plasmoid size gradually decreases with viscosity.Such a finding quantifies the role of viscosity in modulating the plasmoid formation process through its effects on the plasma flow and the reconnection itself.

关键词： viscosity reconnection plasmoids Prandtl number

simulation of the Quasi-Monoenergetic Protons Generation by Parallel Laser Pulses Interaction with Foils

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Chinese physics Letters 2014年第11期31卷 103-106页

作者：王伟权银燕邹德滨余同普徐涵郁明阳马燕云 College of Science National University of Defense Technology Changsha 410073 College of Computer Science National University of Defense Technology Changsha 410073 institute for fusion theory and simulation Zhejiang University Hangzhou 310027

A new scheme of radiation pressure acceleration for generating high-quality protons by using two overlappingparallel laser pulses is proposed. Particle-in-cell simulation shows that the overlapping of two pulses with identical Caussian profiles in space and trapezoidal profiles in the time domain can result in a composite light pulse with a spatial profile suitable for stable acceleration of protons to high energies. At～2.46 × 10^21 W/cm^2 intensity of the combination light pulse, a quasi-monoenergetic proton beam with peak energy ,～200 MeV/nucleon, energy spread 〈15%, and divergency angle 〈4° is obtained, which is appropriate for tumor therapy. The proton beam quality can be controlled by adjusting the incidence points of two laser pulses.

关键词： Proton beams

Runaway electron dynamics in Experimental Advanced Superconducting Tokamak helium plasmas

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Chinese physics B 2023年第7期32卷 62-70页

作者：罗晨曦曾龙朱翔唐天仇志勇林士耀张涛刘海庆石同辉张斌丁锐高伟王敏锐高伟提昂赵海林周天富钱金平孙有文吕波臧庆揭银先梁云峰高翔 institute of Plasma physics Hefei Institutes of Physics ScienceChinese Academy of SciencesHefei 230031China University of Science and Technology of China Hefei 230031China department of Engineering physics Tsinghua UniversityBeijing 100084China Advanced Energy Research Center Shenzhen UniversityShenzhen 518060China institute for fusion theory and simulation Zhejiang UniversityHangzhou 310000China Forschungszentrum Jülich GmbH Institute of Energy and Climate Research Plasma Physics(IEK-4)Jülich 52425Germany

The generation of runaway electrons(REs)is observed during the low-density helium ohmic plasma discharge in the Experimental Advanced Superconducting Tokamak(EAST).The growth rate of hard x-ray(HXR)is inversely proportional to the line-average density.Besides,the RE generation in helium plasma is higher than that in deuterium plasma at the same density,which is obtained by comparing the growth rate of HXR with the same discharge conditions.The potential reason is the higher electron temperature of helium plasma in the same current and electron density plateau.Furthermore,two Alfvén eigenmodes driven by REs have been observed.The frequency evolution of the mode is not fully satisfied with the Alfvén scaling and when extension of the Alfvén frequency is towards 0,the high frequency branch is~50 kHz.The different spatial position of the two modes and the evolution of the helium concentration could be used to understand deviation between theoretical and experimental observation.

关键词： helium plasma runaway electron toroidal Alfvén eigenmode(TAE) Experimental Advanced Superconducting Tokamak(EAST)

Edge and Core Impurity Transport Study With Spectroscopic Instruments in LHD

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Plasma Science and Technology 2009年第4期11卷 402-408页

作者： Shigeru MORITA Motoshi GOTO Masahiro KOBAYASHI Sadatsugu MUTO Malay Bikas CHOWDHURI 董春凤周航宇崔正英 Keisuke FUJII Akihiro FURUZAWA Masahiro HASUO AtsushiI WAMAE 揭银先 Mohammed KOUBITI Ikuya SAKURAI Yuzuru TAWARA 万宝年吴振伟 Naohiro YAMAGUCHI National institute for fusion Science department of fusion Science Graduate University for Advanced Studies Southwestern institute of physics department of Engineering physics Kyoto University EcoTopia Science institute Nagoya University institute of Plasma physics Chinese Academy of Sciences PIIM University of Province physics Laboratory Graduate School of Medicine and Pharmaceutical SciencesUniversity of Toyama

Impurity transport was investigated at both edge and core regions in large helical de- vice （LHD） with developed spectroscopic instruments which can measure one- and two-dimensional distributions of impurities. The edge impurity behavior was studied recently using four carbon resonant transitions in different ionization stages of CIII （977A）, CIV （1548A）, CV （40.3A） and CVI （33.7A）. When the line-averaged electron density, ne, is increased from 1 to 6 × 10^13 cm-3, the ratio of （CIII^CIV）/ne increases while the ratio of （CV＋CVI）/ne decreases. Here, CIII^CIV （CV＋CVI） expresses the sum of CIII （CV） and CIV （CVI） intensities. The CIII＋CIV indicates the carbon influx and the CV＋CVI indicates the emissions through the transport in the ergodic layer. The result thus gives experimental evidence on the impurity screening by the ergodic layer in LHD, which is also supported by a three-dimensional edge particle simulation. The core impu- rity behavior is also studied in high-density discharges （ne 〈 1 × 10^15 cm 3） with multi H2-pellets injection. It is found that the ratio of V/D （V： convection velocity, D： diffusion coefficient） decreases after pellet injection and Zeff profile shows a flat one at values of 1.1,-1.2. These results confirm no impurity accumulation occurs in high-density discharges. As a result, the iron density, rife, is analyzed to be 6 × 10^-7（=- nFe/ne） of which the amount can be negligible as radiation source even in such high-density discharges. One- and two-dimensional impurity distributions from space-resolved VUV and EUV spectrometers newly developed for further impurity transport study are also presented with their preliminary results.

关键词： impurity transport screening effect VUV spectroscopy