scholarly journals Electron-magnetohydrodynamic simulations of electron scale current sheet dynamics in the Vineta.II guide field reconnection experiment

2017 ◽  
Vol 24 (9) ◽  
pp. 092312 ◽  
Author(s):  
Neeraj Jain ◽  
Adrian von Stechow ◽  
Patricio A. Muñoz ◽  
Jörg Büchner ◽  
Olaf Grulke ◽  
...  
Keyword(s):  
Current Sheet ◽  
Guide Field ◽  
Magnetohydrodynamic Simulations

scholarly journals Filaments and striations: anisotropies in observed, supersonic, highly magnetized turbulent clouds

2019 ◽  
Vol 492 (1) ◽  
pp. 668-685 ◽  
Author(s):  
James R Beattie ◽  
Christoph Federrath
Keyword(s):  
Magnetic Field ◽  
Column Density ◽  
Three Dimensional ◽  
High Density ◽  
Systematic Analysis ◽  
Guide Field ◽  
Degree Of Anisotropy ◽  
Mach Numbers ◽  
Magnetohydrodynamic Simulations ◽  
The Magnetic Field

ABSTRACT Stars form in highly magnetized, supersonic turbulent molecular clouds. Many of the tools and models that we use to carry out star formation studies rely upon the assumption of cloud isotropy. However, structures like high-density filaments in the presence of magnetic fields and magnetosonic striations introduce anisotropies into the cloud. In this study, we use the two-dimensional power spectrum to perform a systematic analysis of the anisotropies in the column density for a range of Alfvén Mach numbers ($\operatorname{\mathcal {M}_{\text{A}}}=0.1{\!-\!10}$) and turbulent Mach numbers ($\operatorname{\mathcal {M}}=2{\!-\!20}$), with 20 high-resolution, three-dimensional turbulent magnetohydrodynamic simulations. We find that for cases with a strong magnetic guide field, corresponding to $\operatorname{\mathcal {M}_{\text{A}}}\lt 1$, and $\operatorname{\mathcal {M}}\lesssim 4$, the anisotropy in the column density is dominated by thin striations aligned with the magnetic field, while for $\operatorname{\mathcal {M}}\gtrsim 4$ the anisotropy is significantly changed by high-density filaments that form perpendicular to the magnetic guide field. Indeed, the strength of the magnetic field controls the degree of anisotropy and whether or not any anisotropy is present, but it is the turbulent motions controlled by $\operatorname{\mathcal {M}}$ that determine which kind of anisotropy dominates the morphology of a cloud.

Effects of a guide field on the evolution of a current sheet

2006 ◽  
Vol 13 (10) ◽  
pp. 102902 ◽  
Author(s):  
C. L. Tsai ◽  
L. C. Lee ◽  
B. H. Wu
Keyword(s):  
Current Sheet ◽  
Guide Field ◽  
A Current

Gyrokinetic theory of electrostatic lower-hybrid drift instabilities in a current sheet with guide field

2014 ◽  
Vol 21 (5) ◽  
pp. 052104 ◽  
Author(s):  
K. Tummel ◽  
L. Chen ◽  
Z. Wang ◽  
X. Y. Wang ◽  
Y. Lin
Keyword(s):  
Current Sheet ◽  
Lower Hybrid ◽  
Guide Field ◽  
A Current

scholarly journals Thin current sheets with strong bell-shape guide field: Cluster observations and models with beams

2014 ◽  
Vol 32 (10) ◽  
pp. 1349-1360 ◽  
Author(s):  
I. Y. Vasko ◽  
A. V. Artemyev ◽  
A. A. Petrukovich ◽  
H. V. Malova
Keyword(s):  
Electron Beam ◽  
Current Sheet ◽  
Electron Beams ◽  
Ion Beam ◽  
Distribution Functions ◽  
Electron Velocity ◽  
Electron Current ◽  
Electron Velocity Distribution ◽  
Current Sheets ◽  
Guide Field

Abstract. We study the kinetic structure of intense ion-scale current sheets with strong electron currents and the guide field having a bell-shape profile. We consider four crossings of the Earth magnetotail current sheet by the Cluster mission in 2003. The thickness of these current sheets is about the ion inertial length and significantly smaller than the characteristic ion gyroradius. We analyze the asymmetry of the electron velocity distribution functions and show that the electron current is provided by the small electron subpopulation interpreted as an electron beam or two counter-streaming electron beams. The beam (counter-streaming beams) has a bulk velocity of the order of the electron thermal velocity and a density (difference of beam densities) of about 1–5% of the plasma density. To describe the observed current sheets we develop a kinetic model with particle beams. The model predicts different thickness of the current sheet for different types of current carriers (one electron beam or two counter-streaming electron beams). The observed ion-scale current sheets can be explained assuming that the current is carried by one electron beam and a co-streaming ion beam. Although the ion beam does not carry a significant current, this beam is required to balance the electron current perpendicular to the current sheet neutral plane. The developed model explains the dominance of the electron current and the ion scales of the current sheets.

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.

scholarly journals Asymmetry in the current sheet and secondary magnetic flux ropes during guide field magnetic reconnection

2012 ◽  
Vol 117 (A7) ◽  
pp. n/a-n/a ◽  
Author(s):  
Rongsheng Wang ◽  
Rumi Nakamura ◽  
Quanming Lu ◽  
Aimin Du ◽  
Tielong Zhang ◽  
...  
Keyword(s):  
Magnetic Flux ◽  
Magnetic Reconnection ◽  
Current Sheet ◽  
Magnetic Flux Ropes ◽  
Guide Field ◽  
Flux Ropes

scholarly journals Bifurcated Current Sheet Observed on the Boundary of Kelvin-Helmholtz Vortices

2021 ◽  
Vol 8 ◽  
Author(s):  
K-J. Hwang ◽  
K. Dokgo ◽  
E. Choi ◽  
J. L. Burch ◽  
D. G. Sibeck ◽  
...  
Keyword(s):  
Current Sheet ◽  
Layer Structure ◽  
Velocity Shear ◽  
Current Layer ◽  
Combined Effects ◽  
Slow Mode ◽  
Flow Shear ◽  
Current Sheets ◽  
Guide Field ◽  
Line Region

On May 5, 2017 MMS observed a bifurcated current sheet at the boundary of Kelvin-Helmholtz vortices (KHVs) developed on the dawnside tailward magnetopause. We use the event to enhance our understanding of the formation and structure of asymmetric current sheets in the presence of density asymmetry, flow shear, and guide field, which have been rarely studied. The entire current layer comprises three separate current sheets, each corresponding to magnetosphere-side sunward separatrix region, central near-X-line region, and magnetosheath-side tailward separatrix region. Two off-center structures are identified as slow-mode discontinuities. All three current sheets have a thickness of ∼0.2 ion inertial length, demonstrating the sub-ion-scale current layer, where electrons mainly carry the current. We find that both the diamagnetic and electron anisotropy currents substantially support the bifurcated currents in the presence of density asymmetry and weak velocity shear. The combined effects of strong guide field, low density asymmetry, and weak flow shear appear to lead to asymmetries in the streamlines and the current-layer structure of the quadrupolar reconnection geometry. We also investigate intense electrostatics waves observed on the magnetosheath side of the KHV boundary. These waves may pre-heat a magnetosheath population that is to participate into the reconnection process, leading to two-step energization of the magnetosheath plasma entering into the magnetosphere via KHV-driven reconnection.

scholarly journals The evolution of electron current sheet and formation of secondary islands in guide field reconnection

2011 ◽  
Vol 18 (5) ◽  
pp. 727-733 ◽  
Author(s):  
C. Huang ◽  
Q. Lu ◽  
Z. Yang ◽  
M. Wu ◽  
Q. Dong ◽  
...  
Keyword(s):  
Electric Field ◽  
Current Sheet ◽  
Diffusion Region ◽  
Two Dimensional ◽  
Electron Current ◽  
Particle In Cell ◽  
Field Force ◽  
Guide Field ◽  
Tearing Instability ◽  
Electric Field Force

Abstract. Two-dimensional (2-D) particle-in-cell (PIC) simulations are performed to investigate the evolution of the electron current sheet (ECS) in guide field reconnection. The ECS is formed by electrons accelerated by the inductive electric field in the vicinity of the X line, which is then extended along the x direction due to the imbalance between the electric field force and Ampere force. The tearing instability is unstable when the ECS becomes sufficiently long and thin, and several seed islands are formed in the ECS. These tiny islands may coalesce and form a larger secondary island in the center of the diffusion region.

The Evolution of Collisionless Magnetic Reconnection from Electron Scales to Ion Scales

2021 ◽  
Vol 922 (1) ◽  
pp. 51
Author(s):  
Dongkuan Liu ◽  
Kai Huang ◽  
Quanming Lu ◽  
San Lu ◽  
Rongsheng Wang ◽  
...  
Keyword(s):  
Magnetic Reconnection ◽  
Current Sheet ◽  
High Speed ◽  
Two Dimensional ◽  
Ion Outflow ◽  
Particle In Cell ◽  
Electron Kinetics ◽  
Guide Field ◽  
Cell Simulation ◽  
The Magnetic Field

Abstract It is generally accepted that collisionless magnetic reconnection is initiated on electron scales, which is mediated by electron kinetics. In this paper, by performing a two-dimensional particle-in-cell simulation, we investigate the transition of collisionless magnetic reconnection from electron scales to ion scales in a Harris current sheet with and without a guide field. The results show that after magnetic reconnection is triggered on electron scales, the electrons are first accelerated by the reconnection electric field around the X line, and then leave away along the outflow direction. In the Harris current sheet without a guide field, the electron outflow is symmetric and directed away from the X line along the center of the current sheet, while the existence of a guide field will distort the symmetry of the electron outflow. In both cases, the high-speed electron outflow is decelerated due to the existence of the magnetic field B z , then leading to the pileup of B z . With the increase of B z , the ions are accelerated by the Lorentz force in the outflow direction, and an ion outflow at about one Alfvén speed is at last formed. In this way, collisionless magnetic reconnection is transferred from the electron scales to the ion scales.

scholarly journals Effect of guide field on three-dimensional electron shear flow instabilities in electron current sheets

2015 ◽  
Vol 81 (6) ◽  
Author(s):  
Neeraj Jain ◽  
Jörg Büchner
Keyword(s):  
Shear Flow ◽  
Current Sheet ◽  
Three Dimensional ◽  
Sheet Thickness ◽  
Electron Current ◽  
Tearing Mode ◽  
Current Sheets ◽  
Tearing Modes ◽  
Guide Field ◽  
Half Thickness

We examine, in the limit of electron plasma ${\it\beta}_{e}\ll 1$, the effect of an external guide field and current sheet thickness on the growth rates and nature of three-dimensional (3-D) unstable modes of an electron current sheet driven by electron shear flow. The growth rate of the fastest growing mode drops rapidly with current sheet thickness but increases slowly with the strength of the guide field. The fastest growing mode is tearing type only for thin current sheets (half-thickness ${\approx}d_{e}$, where $d_{e}=c/{\it\omega}_{pe}$ is the electron inertial length) and zero guide field. For finite guide field or thicker current sheets, the fastest growing mode is a non-tearing type. However, growth rates of the fastest 2-D tearing and 3-D non-tearing modes are comparable for thin current sheets ($d_{e}<\text{half thickness}<2\,d_{e}$) and small guide field (of the order of the asymptotic value of the component of magnetic field supporting the electron current sheet). It is shown that the general mode resonance conditions for tearing modes depend on the effective dissipation mechanism. The usual tearing mode resonance condition ($\boldsymbol{k}\boldsymbol{\cdot }\boldsymbol{B}_{0}=0$, $\boldsymbol{k}$ is the wavevector and $\boldsymbol{B}_{0}$ is the equilibrium magnetic field) can be recovered from the general resonance conditions in the limit of weak dissipation. The conditions (relating current sheet thickness, strength of the guide field and wavenumbers) for the non-existence of tearing mode are obtained from the general mode resonance conditions. We discuss the role of electron shear flow instabilities in magnetic reconnection.

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