Particle Acceleration Asymmetry in a Reconnecting Nonneutral Current Sheet

2004 ◽  
Vol 604 (2) ◽  
pp. 884-891 ◽  
Author(s):  
Valentina V. Zharkova ◽  
Mykola Gordovskyy
Keyword(s):  
Particle Acceleration ◽  
Current Sheet

scholarly journals Hybrid numerical simulations of pulsar magnetospheres

2019 ◽  
Vol 491 (4) ◽  
pp. 5579-5585 ◽  
Author(s):  
Ioannis Contopoulos ◽  
Jerome Pétri ◽  
Petros Stefanou
Keyword(s):  
Particle Acceleration ◽  
Current Sheet ◽  
Electric Current ◽  
Hybrid Approach ◽  
High Energy ◽  
Basic Premise ◽  
Analytic Approximations ◽  
Polar Caps ◽  
Electron Positron ◽  
Field Lines

ABSTRACT We continue our investigation of particle acceleration in the pulsar equatorial current sheet (ECS). Our basic premise has been that the charge carriers in the current sheet originate in the polar caps as electron–positron pairs, and are carried along field lines that enter the ECS beyond the magnetospheric Y-point. In this work, we investigate further the charge replenishment of the ECS. We discovered that the flow of pairs from the rims of the polar caps cannot supply both the electric charge and the electric current of the ECS. The ECS must contain an extra amount of positronic (or electronic depending on orientation) electric current that originates in the stellar surface and flows outwards along the separatrices. We develop an iterative hybrid approach that self-consistently combines ideal force-free electrodynamics in the bulk of the magnetosphere with particle acceleration along the ECS. We derive analytic approximations for the orbits of the particles, and obtain the structure of the pulsar magnetosphere for various values of the pair formation multiplicity parameter κ. For realistic values κ ≫ 1, the magnetosphere is practically indistinguishable from the ideal force-free one, and therefore, the calculation of the spectrum of high energy radiation must rely on analytic approximations for the distribution of the accelerating electric field in the ECS.

scholarly journals Dissipation of the striped pulsar wind and non-thermal particle acceleration: 3D PIC simulations

2020 ◽  
Vol 642 ◽  
pp. A204
Author(s):  
Benoît Cerutti ◽  
Alexander A. Philippov ◽  
Guillaume Dubus
Keyword(s):  
Particle Acceleration ◽  
Current Sheet ◽  
Large Scale ◽  
Magnetic Energy ◽  
Rotation Axis ◽  
Moving Frame ◽  
Particle Spectrum ◽  
Secondary Current ◽  
Flux Ropes ◽  
Pulsar Wind

Context. The formation of a large-scale current sheet is a generic feature of pulsar magnetospheres. If the magnetic axis is misaligned with the star rotation axis, the current sheet is an oscillatory structure filling an equatorial wedge determined by the inclination angle, known as the striped wind. Relativistic reconnection could lead to significant dissipation of magnetic energy and particle acceleration, although the efficiency of this process is debated in this context. Aims. In this study, we aim at reconciling global models of pulsar wind dynamics and reconnection in the stripes within the same numerical framework in order to shed new light on dissipation and particle acceleration in pulsar winds. Methods. To this end, we perform large three-dimensional particle-in-cell simulations of a split-monopole magnetosphere, from the stellar surface up to 50 light-cylinder radii away from the pulsar. Results. Plasmoid-dominated reconnection efficiently fragments the current sheet into a dynamical network of interacting flux ropes separated by secondary current sheets that consume the field efficiently at all radii, even past the fast magnetosonic point. Our results suggest there is a universal dissipation radius solely determined by the reconnection rate in the sheet, lying well upstream from the termination shock radius in isolated pair-producing pulsars. The wind bulk Lorentz factor is much less relativistic than previously thought. In the co-moving frame, the wind is composed of hot pairs trapped within flux ropes with a hard broad power-law spectrum, whose maximum energy is limited by the magnetization of the wind at launch. Conclusions. We conclude that the striped wind is most likely fully dissipated when it enters the pulsar wind nebula. The predicted wind particle spectrum after dissipation is reminiscent of the Crab Nebula radio-emitting electrons.

scholarly journals PIC Simulations of Excited Waves in the Plasmoid Instability

2022 ◽  
Vol 8 ◽  
Author(s):  
Mahdi Shahraki Pour ◽  
Mahboub Hosseinpour
Keyword(s):  
Particle Acceleration ◽  
Kinetic Energy ◽  
Solar Corona ◽  
Current Sheet ◽  
Electromagnetic Waves ◽  
Magnetic Energy ◽  
Particle In Cell ◽  
Guide Field ◽  
Collisionless Regime ◽  
Accelerated Particles

Fragmentation of an elongated current sheet into many reconnection X-points, and therefore multiple plasmoids, occurs frequently in the solar corona. This speeds up the release of solar magnetic energy in the form of thermal and kinetic energy. Moreover, due to the presence of multiple reconnection X-points, the particle acceleration is more efficient in terms of the number of accelerated particles. This type of instability called “plasmoid instability” is accompanied with the excitation of some electrostatic/electromagnetic waves. We carried out 2D particle-in-cell simulations of this instability in the collisionless regime, with the presence of non-uniform magnetic guide field to investigate the nature of excited waves. It is shown that the nature and properties of waves excited inside and outside the current sheet are different. While the outside perturbations are transient, the inside ones are long-lived, and are directly affected by the plasmoid instability process.

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>

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