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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

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

Climate Signals from Tree Ring Chronologies of the Upper and Lower Treelines in the Dulan Region of the Northeastern Qinghai-Tibetan Plateau

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Journal of Integrative Plant Biology 2006年第3期48卷 278-285页

作者： lu-san Liu Xue-Mei Shao Er-Yuan Liang Institute of Geographic Sciences and Natural Resources Research the Chinese Academy of Sciences Beijing 100101 China Institute of Tibetan Plateau Research the Chinese Academy of Sciences Beijing 100085 China Graduate School of the Chinese Academy of Sciences Beijing 100039 China

The radial growth of trees In mountainous areas is subject to environmental conditions associated with changes In elevation. To assess the sensitivity of tree-ring growth to climate variation over a wide range of elevations, we compared the chronological characteristics of Sabina przewalskii Kom. and their relationships with climatic variables at the upper and lower treellnes In the Dulan region of the northeastern Qlnghal-Tlbetan Plateau. It was found that the radial growth in this region was controlled primarily by precipitation in late spring and early summer （from May to June）. In addition, a higher temperature from April to June could Intensify drought stress and lead to narrow tree rings. The significant similarity In climate-tree growth relationships at both the upper and lower treellnes Indicated that tree rings of S. przewalskU In this region are able to provide common regional climate information. However, the chronologies at the lower forest limits showed a higher standard deviation and more significant correlations with climatic factors, suggesting that the radial growth there was more significantly Influenced by climate variation. The first principal component of the four chronologies showed a common growth response to local climate. The second principal component showed a contrasting growth response between different sampling sites. The third principal component revealed different growth patterns In response to altitudinal variation. Further analysis Indicated that the precipitation In late spring and early summer controlled the growth of S. przewalskii on a regional scale and that other factors, such as mlcroenvlronment at the sampling sites, also affected the strength of the climatic response of tree growth.

关键词： dendroclimatology dendroecology Qinghai-Tibetan Plateau Sabina przewalskii treeline.

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

Global hybrid simulations of soft X-ray emissions in the Earth’s magnetosheath

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Earth and Planetary Physics 2024年第1期8卷 47-58页

作者： Jin Guo TianRan Sun san lu QuanMing lu Yu Lin XueYi Wang Chi Wang RongSheng Wang Kai Huang School of Earth and Space Sciences University of Science and Technology of ChinaHefei 230026China CAS Center for Excellence in Comparative Planetology/CAS Key Lab of Geospace Environment University of Science and Technology of ChinaHefei 230026China Collaborative Innovation Center of Astronautical Science and Technology Harbin 150001China National Space Science Center Chinese Academy of SciencesBeijing 100190China Physics Department Auburn UniversityAuburnALUSA

Earth’s magnetopause is a thin boundary separating the shocked solar wind plasma from the magnetospheric plasmas,and it is also the boundary of the solar wind energy transport to the *** X-ray imaging allows investigation of the large-scale magnetopause by providing a two-dimensional(2-D)global view from a *** performing 3-D global hybrid-particle-in-cell(hybrid-PIC)simulations,we obtain soft X-ray images of Earth’s magnetopause under different solar wind conditions,such as different plasma densities and directions of the southward interplanetary magnetic *** all cases,magnetic reconnection occurs at low latitude *** soft X-ray images observed by a hypothetical satellite are shown,with all of the following identified:the boundary of the magnetopause,the cusps,and the *** X-ray emissivity in the magnetosheath is characterized by large amplitude fluctuations(up to 160%);however,the maximum line-of-sight-integrated X-ray intensity matches the tangent directions of the magnetopause well,indicating that these fluctuations have limited impact on identifying the magnetopause boundary in the X-ray ***,the magnetopause boundary can be identified using multiple viewing *** also find that solar wind conditions have little effect on the magnetopause *** Solar wind Magnetosphere Ionosphere Link Explorer(SMILE)mission will provide X-ray images of the magnetopause for the first time,and our global hybrid-PIC simulation results can help better understand the 2-D X-ray images of the magnetopause from a 3-D perspective,with particle kinetic effects considered.

关键词： magnetopause X-ray emissivity X-ray imaging SMILE global hybrid-PIC simulation

Magnetotail dipolarization fronts and particle acceleration:A review

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Science China Earth Sciences 2020年第2期63卷 235-256页

作者： Huishan FU Elena EGRIGORENKO Christine GABRIELSE Chengming LIU san lu KJHWANG Xuzhi ZHOU Zhe WANG Fang CHEN School of Space and Environment Beihang UniversityBeijing 102206China Space Research Institute of RAS MoscowRussia Earth Planetaryand Space Sciences DepartmentUniversity of CaliforniaLos AngelesUSA Southwest Research Institute San AntonioUSA Institute of Space Physics and Applied Technology Peking UniversityBeijing 100871China

In this paper, the particle acceleration processes around magnetotail dipolarization fronts(DFs) were reviewed. We summarize the spacecraft observations(including Cluster, THEMIS, MMS) and numerical simulations(including MHD, testparticle, hybrid, LSK, PIC) of these processes. Specifically, we(1) introduce the properties of DFs at MHD scale, ion scale, and electron scale,(2) review the properties of suprathermal electrons with particular focus on the pitch-angle distributions,(3)define the particle-acceleration process and distinguish it from the particle-heating process,(4) identify the particle-acceleration process from spacecraft measurements of energy fluxes, and(5) quantify the acceleration efficiency and compare it with other processes in the magnetosphere(e.g., magnetic reconnection and radiation-belt acceleration processes). We focus on both the acceleration of electrons and ions(including light ions and heavy ions). Regarding electron acceleration, we introduce Fermi,betatron, and non-adiabatic acceleration mechanisms;regarding ion acceleration, we present Fermi, betatron, reflection, resonance, and non-adiabatic acceleration mechanisms. We also discuss the unsolved problems and open questions relevant to this topic, and suggest directions for future studies.

关键词： Dipolarization front Electron acceleration Ion acceleration Magnetic reconnection Review Reconnection front

Particle-in-Cell Simulations of Fast Magnetic Reconnection in Laser-Plasma Interaction

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Chinese Physics Letters 2013年第4期30卷 122-125页

作者： ZHANG Ze-Chen lu Quan-Ming DONG Quan-Li lu san HUANG Can WU Ming-Yu SHENG Zheng-Ming WANG Shui ZHANG Jie CAS Key Lab of Geoscience Environment University of Science and Technology of ChinaHefei 230026 School of Physics and Optoelectronic Engineering Ludong UniversityYantai 264025 Key Laboratory for Laser Plasmas(MoE and Department of Physics Shanghai Jiao Tong UniversityShanghai 200240

Recent experiments have observed magnetic reconnection in laser-produced high-energy-density(HED)plasma *** perform two-dimensional(2-D)particle-in-cell(PIC)simulations to investigate magnetic reconnection between two approaching HED plasma *** is found that the expanding velocity of the bubbles has a great influence on the process of magnetic *** the expanding velocity is small,a single X line reconnection is ***,when the expanding velocity is sufficiently large,we can observe a plasmoid in the vicinity of the X *** the same time,the structures of the electromagnetic field in HED plasma reconnection are similar to that in Harris current sheet reconnection.

关键词： expanding approaching sufficiently

Energy Budgets of the Dipolarization Front in Magnetic Reconnection through Kinetic Simulations

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Energy Budgets of the Dipolarization Front in Magnetic Recon...