Acceleration of cold ions at separatrices of symmetric collisionless magnetic reconnection

2020 ◽  
Author(s):  
Evgeny Gordeev ◽  
Andrey Divin ◽  
Ivan Zaitsev ◽  
Vladimir Semenov ◽  
Yuri Khotyaintsev ◽  
...  
Keyword(s):  
Electric Field ◽  
Magnetic Reconnection ◽  
Electric Fields ◽  
Electrostatic Potential ◽  
Potential Drop ◽  
Local Electron ◽  
One Dimensional ◽  
Particle In Cell ◽  
Background Population ◽  
Cold Ions

<p>Separatrices of magnetic reconnection host intense perpendicular Hall electric fields produced by decoupling of ion and electron components and associated with the in-plane electrostatic potential drop between inflow and outflow regions. The width of these structures is several local electron inertial lengths, which is small enough to demagnetize ions as they cross the layer. We investigate temperature dependence of ion acceleration at separatrices by means of 2D Particle-in-Cell (PIC) simulations of magnetic reconnection with only cold or hot ion background population. The separatrix Hall electric field is balanced by the inertia term in cold background simulations, the effect indicative of the quasi-steady local perpendicular acceleration. The electric field introduces a cross-field beam of unmagnetized particles which makes the temperature strongly non-gyrotropic and susceptible to sub-ion scale instabilities. This acceleration mechanism nearly vanishes for hot ion background simulations. Particle-in-cell simulations are complemented by one-dimensional test particle calculations, which show that the hot ion particles experience scattering in energies after crossing the accelerating layer, whereas cold ions are uniformly energized up to the energies comparable to the electrostatic potential drop between the inflow and outflow regions.</p>

Ionospheric ions in the magnetosphere: Important at large and small scales

2020 ◽  
Author(s):  
Mats André ◽  
Sergio Toledo-Redondo ◽  
Andrew W Yau
Keyword(s):  
Electric Field ◽  
Magnetic Reconnection ◽  
Energy Transport ◽  
Small Scale ◽  
Diffusion Region ◽  
Positive Ions ◽  
Small Scales ◽  
Outflow Rate ◽  
Long Time ◽  
Cold Ions

<p><span lang="EN-US">Cold (eV) ions of ionospheric origin dominate the number density of most of the volume of the magnetosphere during most of the time. </span><span lang="EN-US">Supersonic flows of cold positive ions are common and can cause a negatively charged wake behind a positively charged spacecraft. The associated induced electric field can be observed and can be used to study the cold ions. We present observations from the Cluster and MMS spacecraft showing how a charged satellite, and also individual charged wire booms of  an electric field instrument, can be used to investigate cold ion populations. </span><span lang="EN-US">Ionospheric ions affect large scales, including the Alfvén velocity and </span><span lang="EN-US"> </span><span lang="EN-US">thus energy transport with waves and the magnetic reconnection rate. These ions also affect small-scale kinetic plasma physics, including the Hall physics and wave instabilities associated with magnetic reconnection. Concerning large scales, we summarize observations from several spacecraft and show that a typical total outflow rate of ionospheric ions is 10<sup>26</sup> ions/s and that many of these ions stay cold also after a long time in the magnetosphere.  Concerning small scales, we show examples of how cold ions modify the Hall physics of thin current sheets, including magnetic reconnection separatrices. On small kinetic scales the cold ions introduce a new length-scale, a gyro radius between the gyro radii of hot (keV) ions and electrons. </span><span lang="EN-US">The Hall currents carried by electrons can be partially cancelled by the cold ions when electrons and the magnetized cold ions ExB drift together. Also, close to a reconnection X-line an additional diffusion region can be formed (regions associated with hot and cold ions, and with electrons, total of three).</span></p>

How does dissipation work in the electron diffusion region of asymmetric magnetic reconnection

2020 ◽  
Author(s):  
Michael Hesse ◽  
Cecilia Norgren ◽  
Paul Tenfjord ◽  
James Burch ◽  
Yi-Hsin Liu ◽  
...  
Keyword(s):  
Electric Field ◽  
Magnetic Reconnection ◽  
Stagnation Point ◽  
Electric Fields ◽  
Current Density ◽  
Electron Flow ◽  
Diffusion Region ◽  
Density Maximum ◽  
Density Peak ◽  
Electron Diffusion

<p>At some level, magnetic reconnection functions by means of a balance between current dissipation, and current maintenance due to the reconnection electric field. While this dissipation is well understood process in symmetric magnetic reconnection, the way nonideal electric fields interact with the current density in asymmetric reconnection is still unclear. In symmetric reconnection, the current density maximum, the X point location, and the nonideal electric field determined by the divergence of the electron pressure tensor usually coincide. In asymmetric reconnection, however, the electric field at the X point can be partly provided by bulk inertia terms, implying that the X point cannot be the dominant location of dissipation. On the other hand, we know that the nongyrotropic pressure-based electric field must dominate at the stagnation point of the in-plane electron flow, and that electron distributions here feature crescents. The further fact that the current density peak is shifted off the position of the X point indicates that there may be a relation between this current density enhancement, the location of the stagnation point, and the electron nongyrotropies. In this presentation we report on further progress investigating the physics of the electron diffusion region in asymmetric reconnection with a focus on how to explain the dissipation operating under these conditions. </p>

scholarly journals Perpendicular Current Reduction Caused by Cold Ions of Ionospheric Origin in Magnetic Reconnection at the Magnetopause: Particle‐in‐Cell Simulations and Spacecraft Observations

2018 ◽  
Vol 45 (19) ◽  
pp. 10,033-10,042 ◽  
Author(s):  
Sergio Toledo‐Redondo ◽  
Jérémy Dargent ◽  
Nicolas Aunai ◽  
Benoit Lavraud ◽  
Mats André ◽  
...  
Keyword(s):  
Magnetic Reconnection ◽  
Particle In Cell ◽  
Cold Ions ◽  
Current Reduction

scholarly journals Effects on magnetic reconnection of a density asymmetry across the current sheet

2008 ◽  
Vol 26 (8) ◽  
pp. 2471-2483 ◽  
Author(s):  
K. G. Tanaka ◽  
A. Retinò ◽  
Y. Asano ◽  
M. Fujimoto ◽  
I. Shinohara ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Magnetic Reconnection ◽  
Current Sheet ◽  
Three Dimensional ◽  
Flow Region ◽  
Electron Acceleration ◽  
Particle In Cell ◽  
Line Structure ◽  
Simulation Results

Abstract. The magnetopause (MP) reconnection is characterized by a density asymmetry across the current sheet. The asymmetry is expected to produce characteristic features in the reconnection layer. Here we present a comparison between the Cluster MP crossing reported by Retinò et al. (2006) and virtual observations in two-dimensional particle-in-cell simulation results. The simulation, which includes the density asymmetry but has zero guide field in the initial condition, has reproduced well the observed features as follows: (1) The prominent density dip region is detected at the separatrix region (SR) on the magnetospheric (MSP) side of the MP. (2) The intense electric field normal to the MP is pointing to the center of the MP at the location where the density dip is detected. (3) The ion bulk outflow due to the magnetic reconnection is seen to be biased towards the MSP side. (4) The out-of-plane magnetic field (the Hall magnetic field) has bipolar rather than quadrupolar structure, the latter of which is seen for a density symmetric case. The simulation also showed rich electron dynamics (formation of field-aligned beams) in the proximity of the separatrices, which was not fully resolved in the observations. Stepping beyond the simulation-observation comparison, we have also analyzed the electron acceleration and the field line structure in the simulation results. It is found that the bipolar Hall magnetic field structure is produced by the substantial drift of the reconnected field lines at the MSP SR due to the enhanced normal electric field. The field-aligned electrons at the same MSP SR are identified as the gun smokes of the electron acceleration in the close proximity of the X-line. We have also analyzed the X-line structure obtained in the simulation to find that the density asymmetry leads to a steep density gradient in the in-flow region, which may lead to a non-stationary behavior of the X-line when three-dimensional freedom is taken into account.

Coherent ion acceleration at a density gradient

1975 ◽  
Vol 13 (3) ◽  
pp. 553-562 ◽  
Author(s):  
Shiew L. Hsieh ◽  
Howard W. Bloomberg ◽  
S. Peter Gary
Keyword(s):  
Steady State ◽  
Electric Field ◽  
Density Gradient ◽  
Ion Acceleration ◽  
Applied Potential ◽  
One Dimensional ◽  
Order Of Magnitude ◽  
Cold Electrons ◽  
Cold Ions

The paper describes a model, in which ions are accelerated against the direction of the electric field at a density gradient. A one-dimensional, inhomogeneous, steady-state is constructed, in which cold electrons stream relative to cold ions. The wavenumber and amplitude of the fluctuating potential are calculated, then used to compute the trajectories of representative ions trapped in the potential troughs. Ion acceleration to energies an order of magnitude greater than the applied potential is demonstrated.

Research on Charge Transport in One-Dimensional Organic Semiconductors Material

2012 ◽  
Vol 531 ◽  
pp. 231-234 ◽  
Author(s):  
Wen Liu
Keyword(s):  
Electric Field ◽  
Charge Transport ◽  
Organic Semiconductors ◽  
Electric Fields ◽  
One Dimensional ◽  
Organic Semiconductor Materials ◽  
Insulator Metal Transition ◽  
The Family ◽  
High Electric Fields ◽  
Ssh Model

1D conjugated polymers belong to the family of organic semiconductor materials, in which the charge carriers are polarons or bipolarons. Charge transport in 1D organic semiconductors in the presence of high electric fields is studied within the SSH model. It is found that under a sufficiently high electric field, the polaron is dissociated into free-like electron. The electron performs Bloch oscillation (BO) in the organic semiconductors. By enhancing the electric field, BO will be destroyed and electrons can transit from the valence band to the conduction band, which is Zener tunneling in organic semiconductors. The results also indicate a field-induced insulator-metal transition.

scholarly journals Tripolar electric field Structure in guide field magnetic reconnection

2018 ◽  
Vol 36 (2) ◽  
pp. 373-379 ◽  
Author(s):  
Song Fu ◽  
Shiyong Huang ◽  
Meng Zhou ◽  
Binbin Ni ◽  
Xiaohua Deng
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Magnetic Reconnection ◽  
Electric Fields ◽  
Particle Simulation ◽  
Space Plasma Physics ◽  
Guide Field ◽  
Substantial Modification ◽  
Reconnection Layer ◽  
The Magnetic Field

Abstract. It has been shown that the guide field substantially modifies the structure of the reconnection layer. For instance, the Hall magnetic and electric fields are distorted in guide field reconnection compared to reconnection without guide fields (i.e., anti-parallel reconnection). In this paper, we performed 2.5-D electromagnetic full particle simulation to study the electric field structures in magnetic reconnection under different initial guide fields (Bg). Once the amplitude of a guide field exceeds 0.3 times the asymptotic magnetic field B0, the traditional bipolar Hall electric field is clearly replaced by a tripolar electric field, which consists of a newly emerged electric field and the bipolar Hall electric field. The newly emerged electric field is a convective electric field about one ion inertial length away from the neutral sheet. It arises from the disappearance of the Hall electric field due to the substantial modification of the magnetic field and electric current by the imposed guide field. The peak magnitude of this new electric field increases linearly with the increment of guide field strength. Possible applications of these results to space observations are also discussed. Keywords. Space plasma physics (magnetic reconnection)

scholarly journals Collisions of acoustic solitons and their electric fields in plasmas at critical compositions

2019 ◽  
Vol 85 (1) ◽  
Author(s):  
Frank Verheest ◽  
Willy A. Hereman
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Soliton Solution ◽  
Electrostatic Potential ◽  
Kdv Equation ◽  
Mkdv Equation ◽  
Perturbation Scheme ◽  
Cubic Nonlinearity ◽  
Analytic Treatment ◽  
Reductive Perturbation

Acoustic solitons obtained through a reductive perturbation scheme are normally governed by a Korteweg–de Vries (KdV) equation. In multispecies plasmas at critical compositions the coefficient of the quadratic nonlinearity vanishes. Extending the analytic treatment then leads to a modified KdV (mKdV) equation, which is characterized by a cubic nonlinearity and is even in the electrostatic potential. The mKdV equation admits solitons having opposite electrostatic polarities, in contrast to KdV solitons which can only be of one polarity at a time. A Hirota formalism has been used to derive the two-soliton solution. That solution covers not only the interaction of same-polarity solitons but also the collision of compressive and rarefactive solitons. For the visualization of the solutions, the focus is on the details of the interaction region. A novel and detailed discussion is included of typical electric field signatures that are often observed in ionospheric and magnetospheric plasmas. It is argued that these signatures can be attributed to solitons and their interactions. As such, they have received little attention.

scholarly journals Collisionless magnetic reconnection: analytical model and PIC simulation comparison

2009 ◽  
Vol 27 (3) ◽  
pp. 905-911 ◽  
Author(s):  
V. Semenov ◽  
D. Korovinskiy ◽  
A. Divin ◽  
N. Erkaev ◽  
H. Biernat
Keyword(s):  
Electric Field ◽  
Magnetic Reconnection ◽  
Analytical Model ◽  
Analytical Study ◽  
Spatial Scales ◽  
Magnetospheric Substorms ◽  
Particle In Cell ◽  
Shafranov Equation ◽  
Cell Simulation ◽  
Particles Trajectories

Abstract. Magnetic reconnection is believed to be responsible for various explosive processes in the space plasma including magnetospheric substorms. The Hall effect is proved to play a key role in the reconnection process. An analytical model of steady-state magnetic reconnection in a collisionless incompressible plasma is developed using the electron Hall MHD approximation. It is shown that the initial complicated system of equations may split into a system of independent equations, and the solution of the problem is based on the Grad-Shafranov equation for the magnetic potential. The results of the analytical study are further compared with a two-dimensional particle-in-cell simulation of reconnection. It is shown that both methods demonstrate a close agreement in the electron current and the magnetic and electric field structures obtained. The spatial scales of the acceleration region in the simulation and the analytical study are of the same order. Such features like particles trajectories and the in-plane electric field structure appear essentially similar in both models.

scholarly journals Electron Acceleration by Strong DC Electric Fields in Extragalactic Jets

2000 ◽  
Vol 195 ◽  
pp. 311-312
Author(s):  
Y. E. Litvinenko
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Magnetic Reconnection ◽  
Current Sheet ◽  
Electric Fields ◽  
Electron Acceleration ◽  
Acceleration Time ◽  
Extragalactic Jets ◽  
Dc Electric Field ◽  
The Magnetic Field

Fast magnetic reconnection in extragalactic jets leads to electron acceleration by the DC electric field in the reconnecting current sheet. The maximum electron energy (γ > 106) and the acceleration time (< 106 s) are determined by the magnetic field dynamics in the sheet.

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