Particle Acceleration in Reconnecting Current Sheets with a Nonzero Magnetic Field

1996 ◽  
Vol 462 ◽  
pp. 997 ◽  
Author(s):  
Yuri E. Litvinenko
Keyword(s):  
Magnetic Field ◽  
Particle Acceleration ◽  
Current Sheets

scholarly journals A global model of particle acceleration at pulsar wind termination shocks

2020 ◽  
Vol 642 ◽  
pp. A123
Author(s):  
Benoît Cerutti ◽  
Gwenael Giacinti
Keyword(s):  
Magnetic Field ◽  
Particle Acceleration ◽  
Shock Front ◽  
Large Scale ◽  
Particle Accelerators ◽  
Global Dynamics ◽  
Pulsar Wind Nebulae ◽  
Current Sheets ◽  
Pulsar Wind ◽  
Downstream Flow

Context. Pulsar wind nebulae are efficient particle accelerators, and yet the processes at work remain elusive. Self-generated, microturbulence is too weak in relativistic magnetized shocks to accelerate particles over a wide energy range, suggesting that the global dynamics of the nebula may be involved in the acceleration process instead. Aims. In this work, we study the role played by the large-scale anisotropy of the transverse magnetic field profile on the shock dynamics. Methods. We performed large two-dimensional particle-in-cell simulations for a wide range of upstream plasma magnetizations, from weakly magnetized to strongly magnetized pulsar winds. Results. The magnetic field anisotropy leads to a dramatically different structure of the shock front and downstream flow. A large-scale velocity shear and current sheets form in the equatorial regions and at the poles, where they drive strong plasma turbulence via Kelvin-Helmholtz vortices and kinks. The mixing of current sheets in the downstream flow leads to efficient nonthermal particle acceleration. The power-law spectrum hardens with increasing magnetization, akin to those found in relativistic reconnection and kinetic turbulence studies. The high end of the spectrum is composed of particles surfing on the wake produced by elongated spearhead-shaped cavities forming at the shock front and piercing through the upstream flow. These particles are efficiently accelerated via the shear-flow acceleration mechanism near the Bohm limit. Conclusions. Magnetized relativistic shocks are very efficient particle accelerators. Capturing the global dynamics of the downstream flow is crucial to understanding them, and therefore local plane parallel studies may not be appropriate for pulsar wind nebulae and possibly other astrophysical relativistic magnetized shocks. A natural outcome of such shocks is a variable and Doppler-boosted synchrotron emission at the high end of the spectrum originating from the shock-front cavities, reminiscent of the mysterious Crab Nebula gamma-ray flares.

Chaotic magnetic field lines and spontaneous development of current sheets

2017 ◽  
Vol 24 (8) ◽  
pp. 082902 ◽  
Author(s):  
Sanjay Kumar ◽  
R. Bhattacharyya ◽  
B. Dasgupta ◽  
M. S. Janaki
Keyword(s):  
Magnetic Field ◽  
Current Sheets ◽  
Field Lines

On the level surfaces of the magnetic field in a resistive plasma

2001 ◽  
Vol 65 (3) ◽  
pp. 161-170
Author(s):  
MANUEL NÚÑEZ
Keyword(s):  
Magnetic Field ◽  
Current Sheets ◽  
Resistive Plasma ◽  
Induction Equation ◽  
The Magnetic Field

An analysis of the induction equation shows that the level surfaces of the magnetic field in a resistive plasma satisfy a certain bound upon the time means of their areas. When this bound is applied to some configurations typical of chaotic plasmas, it is shown that the number of bidimensional sheets where the field reaches a extremum is bounded, whereas the number of extremal ropes or points need not be. This also applies to current sheets.

Transport of energetic particles from reconnecting current sheets in flaring corona to the heliosphere

2021 ◽  
Author(s):  
Philippa Browning ◽  
Mykola Gordovskyy ◽  
Satashi Inoue ◽  
Eduard Kontar ◽  
Kanya Kusano ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Energetic Particles ◽  
Transport Processes ◽  
Data Driven ◽  
Current Sheets ◽  
Electrons And Ions ◽  
Data Driven Approach ◽  
Particle Simulations ◽  
The Magnetic Field

<p>In this study, we inverstigate the acceleration of electrons and ions at current sheets in the flaring solar corona, and their transport into the heliosphere. We consider both generic solar flare models and specific flaring events with a data-driven approach. The aim is to answer two questions: (a) what fraction of particles accelerated in different flares can escape into the heliosphere?; and (b) what are the characteristics of the particle populations propagating towards the chromosphere and into the heliosphere?</p><p>We use a combination of data-driven 3D magnetohydrodynamics simulations with drift-kinetic particle simulations to model the evolution of the magnetic field and both thermal and non-thermal plasma and to forward-model observable characteristics. Particles are accelerated in current sheets associated with flaring reconnection. When applied to a specific flare, the model successfully predicts observed features such as the location and relative intensity of hard X-ray sources and helioseismic source locations. This confirms the viability of the approach.</p><p>Using these MHD-particle models, we will show how the magnetic field evolution and particle transport processes affect the characteristics of both energetic electrons and ions in the the inner corona and the heliosphere. The implications for interpretation of in situ measurements of energetic particles by Solar Orbiter and Parker Solar Probe will be discussed.</p><p> </p><p> </p>

scholarly journals Relativistic Particle Acceleration in Plerions

1994 ◽  
Vol 142 ◽  
pp. 797-806
Author(s):  
Jonathan Arons ◽  
Marco Tavani
Keyword(s):  
Magnetic Field ◽  
Particle Acceleration ◽  
Shock Waves ◽  
Shock Front ◽  
Heavy Ions ◽  
Surface Brightness ◽  
Crab Nebula ◽  
Electrons And Positrons ◽  
The Crab Nebula ◽  
The Magnetic Field

AbstractWe discuss recent research on the structure and particle acceleration properties of relativistic shock waves in which the magnetic field is transverse to the flow direction in the upstream medium, and whose composition is either pure electrons and positrons or primarily electrons and positrons with an admixture of heavy ions. Particle-in-cell simulation techniques as well as analytic theory have been used to show that such shocks in pure pair plasmas are fully thermalized—the downstream particle spectra are relativistic Maxwellians at the temperature expected from the jump conditions. On the other hand, shocks containing heavy ions which are a minority constituent by number but which carry most of the energy density in the upstream medium do put ~20% of the flow energy into a nonthermal population of pairs downstream, whose distribution in energy space is N(E) ∝ E−2, where N(E)dE is the number of particles with energy between E and E + dE.The mechanism of thermalization and particle acceleration is found to be synchrotron maser activity in the shock front, stimulated by the quasi-coherent gyration of the whole particle population as the plasma flowing into the shock reflects from the magnetic field in the shock front. The synchrotron maser modes radiated by the heavy ions are absorbed by the pairs at their (relativistic) cyclotron frequencies, allowing the maximum energy achievable by the pairs to be γ±m±c2 = mic2γ1/Zi, where γ1 is the Lorentz factor of the upstream flow and Zi, is the atomic number of the ions. The shock’s spatial structure is shown to contain a series of “overshoots” in the magnetic field, regions where the gyrating heavy ions compress the magnetic field to levels in excess of the eventual downstream value.This shock model is applied to an interpretation of the structure of the inner regions of the Crab Nebula, in particular to the “wisps,” surface brightness enhancements near the pulsar. We argue that these surface brightness enhancements are the regions of magnetic overshoot, which appear brighter because the small Larmor radius pairs are compressed and radiate more efficiently in the regions of more intense magnetic field. This interpretation suggests that the structure of the shock terminating the pulsar’s wind in the Crab Nebula is spatially resolved, and allows one to measure γ1, and a number of other properties of the pulsar’s wind. We also discuss applications of the shock theory to the termination shocks of the winds from rotation-powered pulsars embedded in compact binaries. We show that this model adequately accounts for (and indeed predicted) the recently discovered X-ray flux from PSR 1957+20, and we discuss several other applications to other examples of these systems.Subject headings: acceleration of particles — ISM: individual (Crab Nebula) — relativity — shock waves

Particle Acceleration at Corotating Shocks: Ulysses Magnetic Field and Particle Observations

2008 ◽  
Author(s):  
Edward J. Smith ◽  
Xiaoyan Zhou ◽  
Gang Li ◽  
Qiang Hu ◽  
Olga Verkhoglyadova ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Particle Acceleration

scholarly journals Nonlinear equilibrium structure of thin currents sheets: influence of electron pressure anisotropy

2004 ◽  
Vol 11 (5/6) ◽  
pp. 579-587 ◽  
Author(s):  
L. M. Zelenyi ◽  
H. V. Malova ◽  
V. Yu. Popov ◽  
D. Delcourt ◽  
A. S. Sharma
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Magnetic Energy ◽  
Plasma Pressure ◽  
Quasi Equilibrium ◽  
Electrostatic Effects ◽  
Current Sheets ◽  
Thin Current Sheet ◽  
Field Lines ◽  
The Magnetic Field

Abstract. Thin current sheets represent important and puzzling sites of magnetic energy storage and subsequent fast release. Such structures are observed in planetary magnetospheres, solar atmosphere and are expected to be widespread in nature. The thin current sheet structure resembles a collapsing MHD solution with a plane singularity. Being potential sites of effective energy accumulation, these structures have received a good deal of attention during the last decade, especially after the launch of the multiprobe CLUSTER mission which is capable of resolving their 3D features. Many theoretical models of thin current sheet dynamics, including the well-known current sheet bifurcation, have been developed recently. A self-consistent 1D analytical model of thin current sheets in which the tension of the magnetic field lines is balanced by the ion inertia rather than by the plasma pressure gradients was developed earlier. The influence of the anisotropic electron population and of the corresponding electrostatic field that acts to restore quasi-neutrality of the plasma is taken into account. It is assumed that the electron motion is fluid-like in the direction perpendicular to the magnetic field and fast enough to support quasi-equilibrium Boltzmann distribution along the field lines. Electrostatic effects lead to an interesting feature of the current density profile inside the current sheet, i.e. a narrow sharp peak of electron current in the very center of the sheet due to fast curvature drift of the particles in this region. The corresponding magnetic field profile becomes much steeper near the neutral plane although the total cross-tail current is in all cases dominated by the ion contribution. The dependence of electrostatic effects on the ion to electron temperature ratio, the curvature of the magnetic field lines, and the average electron magnetic moment is also analyzed. The implications of these effects on the fine structure of thin current sheets and their potential impact on substorm dynamics are presented.

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