Numerical Simulations of Particle Acceleration at Interplanetary Quasi-perpendicular Shocks

Kong

Zhang

2018

ApJ

Self Cite

Using test particle simulations we study electron acceleration at collisionless shocks with a two-component model turbulent magnetic field with slab component including dissipation range. We investigate the importance of shock normal angle θ Bn , magnetic turbulence level (b/B 0 ) 2 , and shock thickness on the acceleration efficiency of electrons. It is shown that at perpendicular shocks the electron acceleration efficiency is enhanced with the decreasing of (b/B 0 ) 2 , and at (b/B 0 ) 2 = 0.01 the acceleration becomes significant due to strong drift electric field with long time particles staying near the shock front for shock drift acceleration (SDA). In addition, at parallel shocks the electron acceleration efficiency is increasing with the increasing of (b/B 0 ) 2 , and at (b/B 0 ) 2 = 10.0 the acceleration is very strong due to sufficient pitch-angle scattering for first-order Fermi acceleration, as well as due to large local component of magnetic field perpendicular to shock normal angle for SDA. On the other hand, the high perpendicular shock acceleration with (b/B 0 ) 2 = 0.01 is stronger than the high parallel shock acceleration with (b/B 0 ) 2 = 10.0, the reason might be the assumption that SDA is more efficient than first-order Fermi acceleration. Furthermore, for oblique shocks, the acceleration efficiency is small no matter the turbulence level is low or high. Moreover, for the effect of shock thickness on electron acceleration at perpendicular shocks, we show that there exists the bend-over thickness, L diff,b . The acceleration efficiency does not change evidently if the shock thickness is much smaller than L diff,b . However, if the shock thickness is much larger than L diff,b , the acceleration efficiency starts to drop abruptly.

Section: Modelmentioning

confidence: 99%

Section: Modelmentioning

confidence: 99%

Effects of Shock and Turbulence Properties on Electron Acceleration

Kong

Zhang

2018

ApJ

Self Cite

“…Therefore, in our simulation, when a shock reaches an observer there is no significant increase of flux compared to the observations. In the future, we will include the shock acceleration process (e.g., Kong et al 2017;Qin et al 2018) in our modeling work to make it more realistic.…”

Section: Particlementioning

confidence: 99%

“…There are different ways to deal with the origin of SEPs produced by the shock. The details of the acceleration of SEPs by the shock have been investigated (e.g., Lee 1983;Gordon et al 1999;Zuo et al 2011Zuo et al , 2013Kong et al 2017;Qin et al 2018). However, in other studies, the ICME shock was assumed to be a moving SEP source (Kallenrode & Wibberenz 1997;Kallenrode 2001), so that the propagation of the particles could be focused on without considering the acceleration process (e.g., Heras et al 1992Heras et al , 1995Lario et al 1998;Wang et al 2012;Qin et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Numerical simulation and data analysis of the 23 July 2012 SEP event observed by ACE, STEREO-A, and STEREO-B

2020

A&A

Self Cite

An extremely powerful, superfast interplanetary coronal mass ejection (ICME) from the Sun on 23 July 2012 was detected by widely separated multiple spacecraft, namely STEREO-A, STEREO-B, and ACE, together with the ICME-driven shock and associated solar energetic particles (SEPs). We use the Parker spiral magnetic field model to analyze the relationship between the propagation of the shock and the SEP flux. Furthermore, we simulate the SEP event by numerically solving the three-dimensional focused transport equation of SEPs considering the shock as the moving source of energetic particles. To deal with the fact that protons and electrons behave completely differently for both parallel and perpendicular diffusion, for simplicity, we use the same diffusion model format for the simulations of protons and electrons but with different parameters. We find that the analysis can qualitatively explain the important features of the SEP flux observed by the multiple spacecraft simultaneously. In addition, the numerical results for both energetic protons and electrons approximately agree with multi-spacecraft observations.

“…We adopt a numerical code developed by Sun et al (2007) (also used in Kong et al (2017) and Qin et al (2018)) using an adjustable time step fourth-order Runge-Kutta method with an accuracy of 10 −9 to obtain test particle trajectories by solving the equation of motion of particles, Equation (7). A total of 60,000…”

Section: Simulation Modelsmentioning

confidence: 99%

Study of Time Evolution of the Bend-over Energy in the Energetic Particle Spectrum at a Parallel Shock

Kong

et al. 2019

ApJ

Self Cite

Shock acceleration is considered one of the most important mechanisms for the acceleration of astrophysical energetic particles. In this work, we calculate the trajectories of a large number of test charged particles accurately in a parallel shock with magnetic turbulence. We investigate the time evolution of the accelerated-particle energy spectrum in the downstream of the shock in order to understand the acceleration mechanism of energetic particles. From simulation results we obtain power-law energy spectra with a bend-over energy, E 0 , increasing with time. With the particle mean acceleration time and mean momentum change during each cycle of the shock crossing from diffusive shock acceleration model (following Drury), a time-dependent differential equation for the maximum energy, E acc , of particles accelerated at the shock, can be approximately obtained. We assume the theoretical bendover energy as E acc . It is found that the bend-over energy from simulations agrees well with the theoretical bend-over energy using the non-linear diffusion theory, NLGCE-F, in contrast to that using the classic quasi-linear theory (QLT).