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Ion and electron motions in the outer electron diffusion region of collisionless magnetic reconnection

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Earth and Planetary Physics 2024年第3期8卷 472-478页

作者： Cong Chang quanming lu San lu Kai Huang RongSheng Wang Deep Space Exploration Laboratory School of Earth and Space SciencesUniversity of Science and Technology of ChinaHefei 230026China Chinese Academy of Sciences(CAS)Center for Excellence in Comparative Planetology CAS Key Laboratory of Geospace EnvironmentHefei 230026China Collaborative Innovation Center of Astronautical Science and Technology Harbin 150001China

Two-dimensional particle-in-cell simulations are performed to study the coupling between ion and electron motions in collisionless magnetic *** electron diffusion region(EDR),where the electron motions are demagnetized,is found to have a two-layer structure:an inner EDR near the reconnection site and an outer EDR that is elongated to nearly 10 ion inertial lengths in the outflow *** the inner EDR,the speed of the electron outflow increases when the electrons move away from the X *** the outer EDR,the speed of the electron outflow first increases and then decreases until the electrons reach the boundary of the outer *** the boundary of the outer EDR,the magnetic field piles up and forms a depolarization *** the perspective of the fluid,a force analysis on the formation of electron and ion outflows has also been *** the X line,the electrons are accelerated by the reconnection electric field in the out-of-plane *** the electrons move away from the X line,we find that the Lorentz force converts the direction of the accelerated electrons to the x direction,forming an electron *** electric field forces and electron gradient forces tend to drag the electron *** acceleration along the x direction is caused by the Lorentz force,whereas the pressure gradient force tends to decelerate the ion *** these two terms are important,their effects on ions are almost *** Hall electric field force does positive work on ions and is not *** ions are continuously accelerated,and the ion and electron outflow velocities are almost the same near the depolarization front.

关键词： collisionless magnetic reconnection electron diffusion region force analysis particle-in-cell simulation

Study on electron stochastic motions in the magnetosonic wave field: Test particle simulations

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Earth and Planetary Physics 2021年第6期5卷 592-600页

作者： Kai Fan XinLiang Gao quanming lu Shui Wang CAS Key Laboratory of Geospace Environment Department of Geophysics and Planetary ScienceUniversity of Science and Technology of ChinaHefei 230026China CAS Center for Excellence in Comparative Planetology Hefei 230026China

Using the test particle simulation method, we investigate the stochastic motion of electrons with energy of 300 keV in a monochromatic magnetosonic(MS) wave field. This study is motivated by the violation of the quasi-linear theory assumption, when strong MS waves(amplitude up to ~1 nT) are present in the Earth's magnetosphere. First, electron motion can become stochastic when the wave amplitude exceeds a certain threshold. If an electron initially resonates with the MS wave via bounce resonance, as the bounce resonance order increases, the amplitude threshold of electron stochastic motion increases until it reaches the peak at about the 11 th order in our study, then the amplitude threshold slowly declines. Further, we find that the coexistence of bounce and Landau resonances between electrons and MS waves will significantly reduce the amplitude threshold. In some cases, the electron motion can become stochastic in the field of an MS wave with amplitudes below 1 nT. Regardless, if neither the bounce nor Landau resonance condition is satisfied initially, then the amplitude threshold of stochastic motion shows an increasing trend for lower frequencies and a decreasing trend for higher frequencies, even though the amplitude threshold is always very large(> 5 nT). Our study suggests that electron stochastic motion should also be considered when modeling electron dynamics regulated by intense MS waves in the Earth's magnetosphere.

关键词： magnetosonic waves electron stochastic motions bounce resonance test particle simulations

Two-stage acceleration of interstellar ions driven by high-energy lepton plasma flows

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Science China(Physics,Mechanics & Astronomy) 2015年第10期58卷 76-80页

作者： CUI YunQian SHENG ZhengMing lu quanming LI YuTong ZHANG Jie Beijing National Laboratory of Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Scottish Universities Physics Alliance Department of Physics University of Strathclyde Key Laboratory for Laser Plasmas (Mo E) and Department of Physics and Astronomy Shanghai Jiao Tong University IFSA Collaborative Innovation Center Shanghai Jiao Tong University School of Earth and Space Sciences University of Science and Technology of China

We present the particle-in-cell(PIC) simulation results of the interaction of a high-energy lepton plasma flow with background electron-proton plasma and focus on the acceleration processes of the protons. It is found that the acceleration follows a two-stage process. In the first stage, protons are significantly accelerated transversely(perpendicular to the lepton flow) by the turbulent magnetic field "islands" generated via the strong Weibel-type instabilities. The accelerated protons shows a perfect inverse-power energy spectrum. As the interaction continues, a shockwave structure forms and the protons in front of the shockwave are reflected at twice of the shock speed, resulting in a quasi-monoenergetic peak located near 200 Me V under the simulation parameters. The presented scenario of ion acceleration may be relevant to cosmic-ray generation in some astrophysical environments.

关键词： particle acceleration Fermi acceleration collisionless shock lepton plasma flow

Collisionless magnetic reconnection in the magnetosphere

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Chinese Physics B 2022年第8期31卷 101-116页

作者： quanming lu Huishan Fu Rongsheng Wang San lu CAS Key Laboratory of Geospace Environment School of Earth and Space SciencesUniversity of Science and Technology of ChinaHefei 230026China CAS Center for Excellence in Comparative Planetology Hefei 230026China School of Space and Environment Beihang UniversityBeijing 100191China Key Laboratory of Space Environment Monitoring and Information Processing Ministry of Industry and Information TechnologyBeijing 100191China

Magnetic reconnection underlies the physical mechanism of explosive phenomena in the solar atmosphere and planetary magnetospheres, where plasma is usually collisionless. In the standard model of collisionless magnetic reconnection,the diffusion region consists of two substructures: an electron diffusion region is embedded in an ion diffusion region,in which their scales are based on the electron and ion inertial lengths. In the ion diffusion region, ions are unfrozen in the magnetic fields while electrons are magnetized. The resulted Hall effect from the different motions between ions and electrons leads to the production of the in-plane currents, and then generates the quadrupolar structure of out-of-plane magnetic field. In the electron diffusion region, even electrons become unfrozen in the magnetic fields, and the reconnection electric field is contributed by the off-diagonal electron pressure terms in the generalized Ohm’s law. The reconnection rate is insensitive to the specific mechanism to break the frozen-in condition, and is on the order of 0.1. In recent years, the launching of Cluster, THEMIS, MMS, and other spacecraft has provided us opportunities to study collisionless magnetic reconnection in the Earth’s magnetosphere, and to verify and extend more insights on the standard model of collisionless magnetic reconnection. In this paper, we will review what we have learned beyond the standard model with the help of observations from these spacecraft as well as kinetic simulations.

关键词： collisionless magnetic reconnection magnetosphere

Ray-tracing simulations of whistler-mode wave propagation in different rescaled dipole magnetic fields

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Earth and Planetary Physics 2022年第6期6卷 555-562页

作者： YangGuang Ke quanming lu XinLiang Gao HuaYue Chen Rui Chen CAS Key Laboratory of Geoscience Environment School of Earth and Space SciencesUniversity of Science and Technology of ChinaHefei 230026China CAS Center for Excellence in Comparative Planetology Hefei 230026China Collaborative Innovation Center of Astronautical Science and Technology Harbin 150001China

Kinetic simulation is a powerful tool to study the excitation and propagation of whistler-mode waves in the Earth’s inner *** method typically applies a scaled-down dipole magnetic field to save computational ***,it remains unknown whether whistler wave propagation in the scaled-down dipole field is consistent with that in the realistic dipole *** this work,we develop a ray-tracing code with a scalable dipole magnetic field to address this *** simulation results show that parallel whistler waves at different frequencies gradually become oblique after leaving the equator and propagate in different raypaths in a dipole magnetic *** their propagation,the higher frequency waves tend to have larger wave normal angles at the same *** with the wave propagation in a realistic dipole field,the wave raypath and wave normal remain the same,whereas the wave amplification or attenuation is smaller because of the shorter propagation time in a scaled-down dipole *** study provides significant guidance for kinetic simulations of whistler-mode waves.

关键词： whistler wave ray tracing propagation dipole magnetic field magnetosphere

Simulation of mode conversion at the magnetopause

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Chinese Science Bulletin 2012年第12期57卷 1375-1383页

作者： LIN Yu JOHNSON Jay WANG XueYi lu quanming Physics Department Auburn University Auburn 36849 USA Department of Geophysics and Planetary Science University of Science and Technology of China Hefei 230026 China princeton Plasma Physics Laboratory Princeton University Princeton 08543 USA

Two-dimensional(2-D)and three-dimensional(3-D)hybrid simulations are carried out for mode conversion from fast mode compressional wave to kinetic Alfvn waves(KAWs)at the inhomogeneous magnetopause *** cases in which the incident fast wave propagates in the xz plane,with the magnetopause normal along x and the background magnetic field pointing along z,the 2-D (xz)simulation shows that KAWs with large wave number kxρi～1 are generated near the Alfve′n resonance surface,whereρi is the ion Larmor *** nonlinear wave properties are manifest in the mode conversion *** of the driver frequency are *** a result of nonlinear wave interaction,the mode conversion region and its spectral width are *** the 3-D simulation,after this first stage of the mode conversion to KAWs with large kx,a subsequent generation of KAW modes of finite ky is observed in the later stage,through a nonlinear parametric decay *** the nonlinear cascade to ky can lead to massive transport at the magnetopause,the simulation results provide an effective transport mechanism at the plasma boundaries in space as well as laboratory plasmas.

关键词：模拟模式磁层顶等离子体边界模式转换非线性波非线性参数波动力学混合模拟

Electrostatic Structure of the Electron Phase-space Holes Generated by the Electron Two-stream Instability with a Finite Width

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空间科学学报 2017年第5期37卷 517-523页

作者： SANG Longlong WU Mingyu lu quanming CAS Key Laboratory of Geospace Environment School of Earth and Space Sciences University of Science and Technology of China

Space satellite observations in an electron phase-space hole(electron hole) have shown that bipolar structures are discovered at the parallel cut of parallel electric field, while unipolar structures spring from the parallel cut of perpendicular electric field. Particle-in-cell(PIC) simulations have demonstrated that the electron bi-stream instability induces several electron holes during its nonlinear evolution. However, how the unipolar structure of the parallel cut of the perpendicular electric field formed in these electron holes is still an unsolved problem,especially in a strongly magnetized plasma(Ω_e >ω_(pe), where Ω_e is defined as electron gyrofrequency and ω_(pe) is defined as plasma frequency, respectively). In this paper, with two-dimensional(2D) electrostatic PIC simulations, the evolution of the electron two-stream instability with a finite width in strongly magnetized plasma is investigated. Initially, those conditions lead to monochromatic electrostatic waves, and these waves coalesce with each other during their nonlinear evolution. At last, a solitary electrostatic structure is formed. In such an electron hole, a bipolar structure is formed in the parallel cut. of parallel electric field, while a unipolar structure presents in the parallel cut of perpendicular electric field.

关键词： Electron phase-space hole Two-stream instability PIC simulation

Electron dynamics in collisionless magnetic reconnection

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Chinese Science Bulletin 2011年第12期56卷 1174-1181页

作者： lu quanming WANG RongSheng XIE JinLin HUANG Can lu San WANG Shui CAS Key Laboratory of Basic Plasma Physics School of Earth and Space Sciences University of Science and Technology of China Hefei 230026 China Institute of Geology of Geophysics Chinese Academy of Sciences Beijing 100029 China CAS Key Laboratory of Basic Plasma Physics School of Physical Sciences University of Science and Technology of China Hefei 230026 China

Magnetic reconnection provides a physical mechanism for fast energy conversion from magnetic energy to plasma kinetic energy. It is closely associated with many explosive phenomena in space plasma, usually collisionless in character. For this reason, researchers have become more interested in collisionless magnetic reconnection. In this paper, the various roles of electron dynamics in collisionless magnetic reconnection are reviewed. First, at the ion inertial length scale, ions and electrons are decoupled. The resulting Hall effect determines the reconnection electric field. Moreover, electron motions determine the current system inside the reconnection plane and the electron density cavity along the separatrices. The current system in this plane produces an out-of-plane magnetic field. Second, at the electron inertial length scale, the anisotropy of electron pressure determines the magnitude of the reconnection electric field in this region. The production of energetic electrons, which is an important characteristic during magnetic reconnection, is accelerated by the reconnection electric field. In addition, the different topologies, temporal evolution and spatial distribution of the magnetic field affect the accelerating process of electrons and determine the final energy of the accelerated electrons. Third, we discuss results from simulations and spacecraft observations on the secondary magnetic islands produced due to secondary instabilities around the X point, and the associated energetic electrons. Furthermore, progress in laboratory plasma studies is also discussed in regard to electron dynamics during magnetic reconnection. Finally, some unresolved problems are presented.

关键词：电子动力学磁重联碰撞空间等离子体磁场能量磁场重联电场加速能量转换

The effects of the guide field on the structures of electron density depletions in collisionless magnetic reconnection

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Chinese Science Bulletin 2011年第1期56卷 48-52页

作者： lu San lu quanming CAO Yang HUANG Can XIE JinLin WANG Shui CAS Key Laboratory of Basic Plasma Physics School of Earth and Space Sciences University of Science and Technology of China Hefei 230026 China State Key Laboratory of Space Weather Chinese Academy of Sciences Beijing 100190 China CAS Key Laboratory of Basic Plasma Physics School of Physics University of Science and Technology of China Hefei 230026 China

Two-dimensional particle-in-cell simulations are performed to investigate the formation of electron density depletions in collisionless magnetic *** anti-parallel reconnection,the quadrupole structures of the out-of-plane magnetic field are formed,and four symmetric electron density depletion layers can be found along the separatrices due to the effects of magetic *** the increase of the initial guide field,the symmetry of both the out-of-plane magnetic field and electron density depletion layers is *** the initial guide field is sufficiently large,the electron density depletion layers along the lower left and upper right separatrices *** parallel electric field in guide field reconnection is found to play an important role in forming such structures of the electron density depletion *** structures of the out-of-plane magnetic field By and electron depletion layers in anti-parallel and guide field reconnection are found to be related to electron flow or in-plane currents in the separatrix *** anti-parallel reconnection,electrons flow towards the X line along the separatrices,and are directed away from the X line along the magnetic field lines just inside the *** guide field reconnection,electrons can only flow towards the X line along the upper left and lower right separatrices due to the existence of the parallel electric field in these regions.

关键词：磁场重联电子密度无碰撞结构模拟分析耗尽层电子流平行