scholarly journals Adaptation of the de Hoffmann–Teller frame for quasi-perpendicular collisionless shocks

2015 ◽  
Vol 33 (3) ◽  
pp. 345-350 ◽  
Author(s):  
H. Comişel ◽  
Y. Narita ◽  
U. Motschmann
Keyword(s):  
Shock Wave ◽  
Electric Field ◽  
Shock Layer ◽  
Local Magnetic Field ◽  
Sliding Velocity ◽  
Collisionless Shock ◽  
Collisionless Shocks ◽  
Particle In Cell ◽  
Cell Simulation ◽  
High Mach

Abstract. The concept of the de Hoffmann–Teller frame is revisited for a high Mach-number quasi-perpendicular collisionless shock wave. Particle-in-cell simulation shows that the local magnetic field oscillations in the shock layer introduce a residual motional electric field in the de Hoffmann–Teller frame, which is misleading in that one may interpret that electrons were not accelerated but decelerated in the shock layer. We propose the concept of the adaptive de Hoffmann–Teller (AHT) frame in which the residual convective field is canceled by modulating the sliding velocity of the de Hoffmann–Teller frame. The electrostatic potential evaluated by Liouville mapping supports the potential profile obtained by electric field in this adaptive frame, offering a wide variety of applications in shock wave studies.

SIMULATION OF HIGH CURRENT FIELD EMISSION FROM VERTICALLY WELL-ALIGNED METALLIC CARBON NANOTUBES

2004 ◽  
Vol 03 (04n05) ◽  
pp. 677-684 ◽  
Author(s):  
W. S. KOH ◽  
L. K. ANG
Keyword(s):  
Electric Field ◽  
Space Charge ◽  
Field Enhancement ◽  
Smooth Transition ◽  
High Current ◽  
Simulation Code ◽  
Particle In Cell ◽  
Current Regime ◽  
Wide Range ◽  
Cell Simulation

We have studied the intense electron beams emitted from multiple metallic, vertical and well-aligned Carbon Nanotube (CNT) field emitters. A two-dimensional (2D) particle-in-cell simulation code MAGIC2D is used to obtain the I–V characteristics near to the apex of the emitters' surface for a given applied electric field and field enhancement factor over a wide range of parameters. The effects of electron space charge and electric field shielding from neighboring emitters are compared in low current and high current regimes. It is found that the electron space charge is dominant in high current regime, where the Fowler–Nordheim (FN) law becomes the 2D Child–Langmuir (CL) law. The emitter spacing, number of emitters, and emitter's uniformity are also particularly studied, and they are more critical in low current regime. Smooth transition from the FN law to CL law is demonstrated.

Full particle-in-cell simulation of the formation and structure of a collisional plasma shock wave

2021 ◽  
Vol 103 (2) ◽  
Author(s):  
Wen-shuai Zhang ◽  
Hong-bo Cai ◽  
Bao Du ◽  
Dong-guo Kang ◽  
Shi-yang Zou ◽  
...  
Keyword(s):  
Shock Wave ◽  
Collisional Plasma ◽  
Particle In Cell ◽  
Cell Simulation ◽  
Plasma Shock Wave ◽  
Plasma Shock

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 Theory of the formation of a collisionless Weibel shock: pair vs. electron/proton plasmas

2016 ◽  
Vol 34 (2) ◽  
pp. 362-367 ◽  
Author(s):  
A. Bret ◽  
A. Stockem Novo ◽  
R. Narayan ◽  
C. Ruyer ◽  
M. E. Dieckmann ◽  
...  
Keyword(s):  
Mean Free Path ◽  
Particle Accelerators ◽  
Incoming Flow ◽  
Collisionless Shock ◽  
Collisionless Shocks ◽  
Trapping Time ◽  
Particle In Cell ◽  
The Mean ◽  
The One ◽  
Overlapping Region

AbstractCollisionless shocks are shocks in which the mean-free path is much larger than the shock front. They are ubiquitous in astrophysics and the object of much current attention as they are known to be excellent particle accelerators that could be the key to the cosmic rays enigma. While the scenario leading to the formation of a fluid shock is well known, less is known about the formation of a collisionless shock. We present theoretical and numerical results on the formation of such shocks when two relativistic and symmetric plasma shells (pair or electron/proton) collide. As the two shells start to interpenetrate, the overlapping region turns Weibel unstable. A key concept is the one of trapping time τp, which is the time when the turbulence in the central region has grown enough to trap the incoming flow. For the pair case, this time is simply the saturation time of the Weibel instability. For the electron/proton case, the filaments resulting from the growth of the electronic and protonic Weibel instabilities, need to grow further for the trapping time to be reached. In either case, the shock formation time is 2τp in two-dimensional (2D), and 3τp in 3D. Our results are successfully checked by particle-in-cell simulations and may help designing experiments aiming at producing such shocks in the laboratory.

scholarly journals The properties and causes of rippling in quasi-perpendicular collisionless shock fronts

2003 ◽  
Vol 21 (3) ◽  
pp. 671-679 ◽  
Author(s):  
R. E. Lowe ◽  
D. Burgess
Keyword(s):  
Wave Mode ◽  
Fluid Simulation ◽  
Dimensional Structure ◽  
Simulation Studies ◽  
Collisionless Shock ◽  
Collisionless Shocks ◽  
One Dimensional ◽  
High Mach ◽  
Normal Magnetic Field ◽  
Shock Fronts

Abstract. The overall structure of quasi-perpendicular, high Mach number collisionless shocks is controlled to a large extent by ion reflection at the shock ramp. Departure from a strictly one-dimensional structure is indicated by simulation results showing that the surface of such shocks is rippled, with variations in the density and all field components. We present a detailed analysis of these shock ripples, using results from a two-dimensional hybrid (particle ions, electron fluid) simulation. The process that generates the ripples is poorly understood, because the large gradients at the shock ramp make it difficult to identify instabilities. Our analysis reveals new features of the shock ripples, which suggest the presence of a surface wave mode dominating the shock normal magnetic field component of the ripples, as well as whistler waves excited by reflected ions.Key words. Space plasma physics (numerical simulation studies; shock waves; waves and instabilities)

scholarly journals Collisional behaviors of astrophysical collisionless plasmas

2015 ◽  
Vol 81 (2) ◽  
Author(s):  
Antoine Bret
Keyword(s):  
Shock Wave ◽  
Equation Of State ◽  
Maxwellian Distribution ◽  
Collisionless Shocks ◽  
Astrophysical Plasmas ◽  
Length Scales ◽  
Particle In Cell ◽  
Two Fluids ◽  
Collisionless Plasmas ◽  
Binary Collisions

In collisional fluids, a number of key processes rely on the frequency of binary collisions. Collisions seem necessary to generate a shock wave when two fluids collide fast enough, to fulfill the Rankine–Hugoniot (RH) relations, to establish an equation of state or a Maxwellian distribution. Yet, these seemingly collisional features are routinely either observed or assumed, in relation with collisionlessastrophysical plasmas. This article will review our current answers to the following questions: How do colliding collisionless plasmas end-up generating a shock as if they were fluids? To which extent are the RH relations fulfilled in this case? Do collisionless shocks propagate like fluid ones? Can we use an equation of state to describe collisionless plasmas, like MHD codes for astrophysics do? Why are Maxwellian distributions ubiquitous in particle-in-cell simulations of collisionless shocks? Time and length scales defining the border between the collisional and the collisionless behavior will be given when relevant. In general, when the time and length scales involved in the collisionless processes responsible for the fluid-like behavior may be neglected, the system may be treated like a fluid.

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