scholarly journals Plasma turbulence generated during particle acceleration in reconnection current sheets with magnetic islands

2020 ◽  
Author(s):  
Qian Xia ◽  
Valentina Zharkova
Keyword(s):  
Particle Acceleration ◽  
Plasma Turbulence ◽  
Magnetic Islands ◽  
Current Sheets

Fully kinetic PIC simulations of particle acceleration and non-Maxwellian distribution functions due to current sheets in solar wind turbulence

2021 ◽  
Author(s):  
Patricio A. Munoz ◽  
Jörg Büchner ◽  
Neeraj Jain
Keyword(s):  
Solar Wind ◽  
Particle Acceleration ◽  
Current Sheet ◽  
Plasma Turbulence ◽  
Distribution Functions ◽  
Heat Fluxes ◽  
Magnetic Islands ◽  
Ion Distribution ◽  
Current Sheets ◽  
Particle In Cell

<p>Turbulence is ubiquitous in solar system plasmas like those of the solar wind and Earth's magnetosheath. Current sheets can be formed out of this turbulence, and eventually magnetic reconnection can take place in them, a process that converts magnetic into particle kinetic energy. This interplay between turbulence and current sheet formation has been extensively analyzed with MHD and hybrid-kinetic models. Those models cover all the range between large Alfvénic scales down to ion-kinetic scales. The consequences of current sheet formation in plasma turbulence that includes electron dynamics has, however, received comparatively less attention. For this sake we carry out 2.5D fully kinetic Particle-in-Cell simulations of kinetic plasma turbulence including both ion and electron spectral ranges. In order to further assess the electron kinetic effects, we also compare our results with hybrid-kinetic simulations including electron inertia in the generalized Ohm's law. We analyze and discuss the electron and ion energization processes in the current sheets and magnetic islands formed in the turbulence. We focus on the electron and ion distribution functions formed in and around those current sheets and their stability properties that are relevant for the micro-instabilities feeding back into the turbulence cascade. We also compare pitch angle distributions and non-Maxwellian features such as heat fluxes with recent in-situ solar wind observations, which demonstrated local particle acceleration processes in reconnecting solar wind current sheets [Khabarova et al., ApJ, 2020].</p>

Current sheets, magnetic islands and associated particle acceleration in the solar wind as observed by Ulysses near the ecliptic plane

2020 ◽  
Author(s):  
Olga Malandraki ◽  
Olga Khabarova ◽  
Roberto Bruno ◽  
Gary Zank ◽  
Gang Li and the ISSI-405 team
Keyword(s):  
Solar Wind ◽  
Particle Acceleration ◽  
Magnetic Reconnection ◽  
Energetic Particle ◽  
Particle Flux ◽  
Energetic Particles ◽  
Magnetic Islands ◽  
Intermittent Turbulence ◽  
Current Sheets ◽  
Energetic Particle Flux

<p>Recent studies of particle acceleration in the heliosphere have revealed a new mechanism that can locally energize particles up to several MeV/nuc. Stream-stream interactions as well as the heliospheric current sheet – stream interactions lead to formation of large magnetic cavities, bordered by strong current sheets (CSs), which in turn produce secondary CSs and dynamical small-scale magnetic islands (SMIs) of ~0.01AU or less owing to magnetic reconnection. It has been shown that particle acceleration or re-acceleration occurs via stochastic magnetic reconnection in dynamical SMIs confined inside magnetic cavities observed at 1 AU. The study links the occurrence of CSs and SMIs with characteristics of intermittent turbulence and observations of energetic particles of keV-MeV/nuc energies at ~5.3 AU. We analyze selected samples of different plasmas observed by Ulysses during a widely discussed event, which was characterized by a series of high-speed streams of various origins that interacted beyond the Earth’s orbit in January 2005. The interactions formed complex conglomerates of merged interplanetary coronal mass ejections, stream/corotating interaction regions and magnetic cavities. We study properties of turbulence and associated structures of various scales. We confirm the importance of intermittent turbulence and magnetic reconnection in modulating solar energetic particle flux and even local particle acceleration. Coherent structures, including CSs and SMIs, play a significant role in the development of secondary stochastic particle acceleration, which changes the observed energetic particle flux time-intensity profiles and increases the final energy level to which energetic particles can be accelerated in the solar wind.</p>

scholarly journals Particle acceleration in coalescent and squashed magnetic islands

2018 ◽  
Vol 620 ◽  
pp. A121 ◽  
Author(s):  
Q. Xia ◽  
V. Zharkova
Keyword(s):  
Particle Acceleration ◽  
Electric Field ◽  
Power Laws ◽  
Particle Energy ◽  
Energy Spectra ◽  
Magnetic Islands ◽  
Current Sheets ◽  
The Difference ◽  
Energy Gains ◽  
Electron Clouds

Aims. Magnetic reconnection in large Harris-type reconnecting current sheets (RCSs) with a single X-nullpoint often leads to the occurrence of magnetic islands with multiple O- and X-nullpoints. Over time these magnetic islands become squashed, or coalescent with two islands merging, as has been observed indirectly during coronal mass ejection and by in-situ observations in the heliosphere and magnetotail. These points emphasise the importance of understanding the basic energising processes of ambient particles dragged into current sheets with magnetic islands of different configuration. Methods. Trajectories of protons and electrons accelerated by a reconnection electric field are investigated using a test particle approach in RCSs with different 3D magnetic field topologies defined analytically for multiple X- and O-nullpoints. Trajectories, densities, and energy distributions are explored for 106 thermal particles dragged into the current sheets from different sides and distances. Results. This study confirms that protons and electrons accelerated in magnetic islands in the presence of a strong guiding field are ejected from a current sheet into the opposite semiplanes with respect to the midplane. Particles are found to escape O-nullpoints only through the neighbouring X-nullpoints along (not across) the midplane following the separation law for electrons and protons in a given magnetic topology. Particles gain energy either inside O-nullpoints or in the vicinity of X-nullpoints that often leads to electron clouds formed about the X-nullpoint between the O-nullpoints. Electrons are shown to be able to gain sub-relativistic energies in a single magnetic island. Energy spectra of accelerated particles are close to power laws with spectral indices varying from 1.1 to 2.4. The more squashed the islands the larger the difference between the energy gains by transit and bounced particles, which leads to their energy spectra having double maxima that gives rise to fast-growing turbulence. Conclusions. Particles are shown to gain the most energy in multiple X-nullpoints between O-nullpoints (or magnetic islands). This leads to the formation of electron clouds between magnetic islands. Particle energy gains are much larger in squashed islands than in coalescent ones. In summary, particle acceleration by a reconnection electric field in magnetic islands is much more effective than in an RCS with a single X-nullpoint.

Current Sheets, Magnetic Islands, and Associated Particle Acceleration in the Solar Wind as Observed by Ulysses near the Ecliptic Plane

2019 ◽  
Vol 881 (2) ◽  
pp. 116 ◽  
Author(s):  
Olga Malandraki ◽  
Olga Khabarova ◽  
Roberto Bruno ◽  
Gary P. Zank ◽  
Gang Li ◽  
...  
Keyword(s):  
Solar Wind ◽  
Particle Acceleration ◽  
Ecliptic Plane ◽  
Magnetic Islands ◽  
Current Sheets

Plasma turbulence generated during particle acceleration in magnetic islands

2021 ◽  
Author(s):  
Valentina Zharkova ◽  
Qian Xia
Keyword(s):  
Magnetic Field ◽  
Particle Acceleration ◽  
Current Sheet ◽  
Plasma Turbulence ◽  
Lower Hybrid ◽  
Diffusion Region ◽  
Magnetic Islands ◽  
Langmuir Waves ◽  
Kink Instability ◽  
Hybrid Waves

<div> <div> <div> <p>We investigate plasma turbulence generated during particle acceleration in magnetic islands within 3D Harris-type reconnecting current sheets (RCSs),using the particle-in-cell approach.  RCSs with a strong guiding magnetic field  ar shown to lead to separation of electrons and ions into the opposite sides from the current sheet mid-plane that significantly reduces kink instability along the guiding field direction. Particles with the same charge also have asymmetric trajectories forming two distinct populations of beams: ‘transit’ particles, which pass through RCS from one edge to another, become strongly energised and form nearly unidirectional beams; and ‘bounced’ particles, which are reflected from the diffusion region and move back to the same side they entered the current sheet, gaining much less energy and forming more dispersive spatial distributions. Thes transit and bounced particles form the ‘bump-on-tail’ velocity distributions that naturally generate plasma turbulence. Using the wavelet analysis of electric and magnetic field fluctuations in the frequency domain, we identified some characteristic waves produced by particle beams. In particular, we found thre are Langmuir waves near X-nullpoints produced by two electron beam instabilities, while the presence of anisotropic temperature variations inside magnetic islands lead to whistler waves. The lower-hybrid waves are generated inside the magnetic islands, owing to the two-stream instabilities of the ions. While the high-frequency fluctuations, upper hybrid waves, or electron Bernstein waves, pile up near X-nullpoints. The results can be beneficial for understanding in-situ observations with modern space missions of energetic particles in the heliosphere.</p> </div> </div> </div>

scholarly journals Particle acceleration in coalescent and squashed magnetic islands

2020 ◽  
Vol 635 ◽  
pp. A116 ◽  
Author(s):  
Q. Xia ◽  
V. Zharkova
Keyword(s):  
Particle Acceleration ◽  
Current Sheet ◽  
Test Particle ◽  
Pitch Angle ◽  
Magnetic Islands ◽  
Current Sheets ◽  
Aspect Ratios ◽  
Energy Gains ◽  
Particle Approach ◽  
Accelerated Particles

Aims. Particles are known to have efficient acceleration in reconnecting current sheets with multiple magnetic islands that are formed during a reconnection process. Using the test-particle approach, the recent investigation of particle dynamics in 3D magnetic islands, or current sheets with multiple X- and O-null points revealed that the particle energy gains are higher in squashed magnetic islands than in coalescent ones. However, this approach did not factor in the ambient plasma feedback to the presence of accelerated particles, which affects their distributions within the acceleration region. Methods. In the current paper, we use the particle-in-cell (PIC) approach to investigate further particle acceleration in 3D Harris-type reconnecting current sheets with coalescent (merging) and squashed (contracting) magnetic islands with different magnetic field topologies, ambient densities ranging between 108 − 1012 m−3, proton-to-electron mass ratios, and island aspect ratios. Results. In current sheets with single or multiple X-nullpoints, accelerated particles of opposite charges are separated and ejected into the opposite semiplanes from the current sheet midplane, generating a strong polarisation electric field across a current sheet. Particles of the same charge form two populations: transit and bounced particles, each with very different energy and asymmetric pitch-angle distributions, which can be distinguished from observations. In some cases, the difference in energy gains by transit and bounced particles leads to turbulence generated by Buneman instability. In magnetic island topology, the different reconnection electric fields in squashed and coalescent islands impose different particle drift motions. This makes particle acceleration more efficient in squashed magnetic islands than in coalescent ones. The spectral indices of electron energy spectra are ∼ − 4.2 for coalescent and ∼ − 4.0 for squashed islands, which are lower than reported from the test-particle approach. The particles accelerated in magnetic islands are found trapped in the midplane of squashed islands, and shifted as clouds towards the X-nullpoints in coalescent ones. Conclusions. In reconnecting current sheets with multiple X- and O-nullpoints, particles are found accelerated on a much shorter spatial scale and gaining higher energies than near a single X-nullpoint. The distinct density and pitch-angle distributions of particles with high and low energy detected with the PIC approach can help to distinguish the observational features of accelerated particles.

scholarly journals Effects of plasma turbulence on the nonlinear evolution of magnetic island in tokamak

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Minjun J. Choi ◽  
Lāszlo Bardōczi ◽  
Jae-Min Kwon ◽  
T. S. Hahm ◽  
Hyeon K. Park ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Nonlinear Evolution ◽  
Plasma Turbulence ◽  
Magnetized Plasmas ◽  
Tokamak Plasmas ◽  
Magnetic Islands ◽  
Magnetic Island ◽  
Reconnection Site ◽  
Ambient Turbulence

AbstractMagnetic islands (MIs), resulting from a magnetic field reconnection, are ubiquitous structures in magnetized plasmas. In tokamak plasmas, recent researches suggested that the interaction between an MI and ambient turbulence can be important for the nonlinear MI evolution, but a lack of detailed experimental observations and analyses has prevented further understanding. Here, we provide comprehensive observations such as turbulence spreading into an MI and turbulence enhancement at the reconnection site, elucidating intricate effects of plasma turbulence on the nonlinear MI evolution.

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