scholarly journals Acceleration of Charged Particles in Astrophysical Plasmas

2021 ◽  
Vol 8 ◽  
Author(s):  
Siming Liu ◽  
J. Randy Jokipii
Keyword(s):  
Particle Acceleration ◽  
Magnetic Fields ◽  
Electric Fields ◽  
Charged Particles ◽  
High Energy ◽  
Shock Acceleration ◽  
High Energy Particle ◽  
Acceleration Of Particles ◽  
Diffusive Shock Acceleration ◽  
Astrophysical Plasmas

The origin of high-energy particles in the Universe is one of the key issues of high-energy solar physics, space science, astrophysics, and particle astrophysics. Charged particles in astrophysical plasmas can be accelerated to very high energies by electric fields. Based on the characteristics of interactions between charged particles and electric fields carried by the background plasma, the mechanisms of charged particle acceleration can be divided into several groups: resonant interactions between plasma waves and particles, acceleration by electric fields parallel to magnetic fields, and acceleration caused by drift of the guiding center of particle gyro-motion around magnetic fields in magnetic field in-homogeneity-related curvature and gradient, etc. According to macroscopic energy conversion mechanisms leading to acceleration of particles, several theories of particle acceleration have been developed: stochastic particle acceleration by turbulent electromagnetic fields, diffusive shock acceleration of particles, and particle acceleration during magnetic re-connections. These theories have their own assumptions and characteristics and find applications in different astrophysical contexts. With advances in high-energy astrophysical observations and in combination with analyses of characteristics of high-energy particle acceleration and radiation, we can better understand the underlying physical processes in dramatically evolving astrophysical environments.

The Role of Magnetic Reconnection–associated Processes in Local Particle Acceleration in the Solar Wind

2021 ◽  
Author(s):  
Laxman Adhikari ◽  
Gary Zank ◽  
Lingling Zhao
Keyword(s):  
Solar Wind ◽  
Particle Acceleration ◽  
Magnetic Reconnection ◽  
Electric Fields ◽  
Charged Particles ◽  
Heliospheric Current Sheet ◽  
Shock Acceleration ◽  
Small Scale ◽  
Diffusive Shock Acceleration ◽  
Theoretical Predictions

<p>Recent studies of unusual or atypical energetic particle flux events (AEPEs) observed at 1 au show that another mechanism, different from diffusive shock acceleration, can energize particles locally in the solar wind. The mechanism proposed by Zank et al. is based on the stochastic energization of charged particles in regions filled with numerous small-scale magnetic islands (SMIs) dynamically contracting or merging and experiencing multiple magnetic reconnection in the super-Alfvénic solar wind flow. A first- and second-order Fermi mechanism results from compression-induced changes in the shape of SMIs and their developing dynamics. Charged particles can also be accelerated by the formation of antireconnection electric fields. Observations show that both processes often coexist in the solar wind. The occurrence of SMIs depends on the presence of strong current sheets like the heliospheric current sheet (HCS), and related AEPEs are found to occur within magnetic cavities formed by stream–stream, stream–HCS, or HCS–shock interactions that are filled with SMIs. Previous case studies comparing observations with theoretical predictions were qualitative. Here we present quantitative theoretical predictions of AEPEs based on several events, including a detailed analysis of the corresponding observations. The study illustrates the necessity of accounting for local processes of particle acceleration in the solar wind.</p>

scholarly journals An Introduction to Particle Acceleration in Shearing Flows

Galaxies ◽  
2019 ◽  
Vol 7 (3) ◽  
pp. 78 ◽  
Author(s):  
Frank Rieger
Keyword(s):  
Particle Acceleration ◽  
Large Scale ◽  
Shear Flows ◽  
Charged Particles ◽  
Shock Acceleration ◽  
Diffusive Shock Acceleration ◽  
Astrophysical Plasmas ◽  
Particle Distributions ◽  
Recent Developments ◽  
Type Particle

Shear flows are ubiquitously present in space and astrophysical plasmas. This paper highlights the central idea of the non-thermal acceleration of charged particles in shearing flows and reviews some of the recent developments. Topics include the acceleration of charged particles by microscopic instabilities in collisionless relativistic shear flows, Fermi-type particle acceleration in macroscopic, gradual and non-gradual shear flows, as well as shear particle acceleration by large-scale velocity turbulence. When put in the context of jetted astrophysical sources such as Active Galactic Nuclei, the results illustrate a variety of means beyond conventional diffusive shock acceleration by which power-law like particle distributions might be generated. This suggests that relativistic shear flows can account for efficient in-situ acceleration of energetic electrons and be of relevance for the production of extreme cosmic rays.

scholarly journals Bohm Diffusion and Cosmic-Ray-Modified Shocks

1994 ◽  
Vol 142 ◽  
pp. 981-983
Author(s):  
Peter Duffy
Keyword(s):  
Particle Acceleration ◽  
Cosmic Rays ◽  
Cosmic Ray ◽  
Shock Acceleration ◽  
Back Reaction ◽  
Acceleration Of Particles ◽  
Diffusive Shock Acceleration ◽  
Spacetime Structure ◽  
Wide Range ◽  
Self Consistent

AbstractA numerical solution to the problem of self-consistent diffusive shock acceleration is presented. The cosmic rays are scattered, accelerated and exert a back-reaction on the gas through their interaction with turbulence frozen into the local fluid frame. Using a grid with a hierarchical spacetime structure the physically interesting limit of Bohm diffusion (к ∝ pv), which introduces a wide range of diffusion lengthscales and acceleration timescales, can be studied. Some implications for modified shocks and particle acceleration are presented.Subject headings: acceleration of particles — cosmic rays — diffusion — shock waves

scholarly journals Probing Magnetic Fields and Acceleration Mechanisms in Blazar Jets with X-ray Polarimetry

Galaxies ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 37
Author(s):  
Fabrizio Tavecchio
Keyword(s):  
Particle Acceleration ◽  
Magnetic Fields ◽  
Numerical Simulations ◽  
High Energy ◽  
Acceleration Of Particles ◽  
Synchrotron Emission ◽  
Relativistic Jets ◽  
X Ray ◽  
The Earth ◽  
Shock Fronts

X-ray polarimetry promises us an unprecedented look at the structure of magnetic fields and on the processes at the base of acceleration of particles up to ultrarelativistic energies in relativistic jets. Crucial pieces of information are expected from observations of blazars (that are characterized by the presence of a jet pointing close to the Earth), in particular of the subclass defined by a synchrotron emission extending to the X-ray band (so-called high synchrotron peak blazars, HSP). In this review, I give an account of some of the models and numerical simulations developed to predict the polarimetric properties of HSP at high energy, contrasting the predictions of scenarios assuming particle acceleration at shock fronts with those that are based on magnetic reconnection, and I discuss the prospects for the observations of the upcoming Imaging X-ray Polarimetry Explorer (IXPE) satellite.

scholarly journals Diagnosing particle acceleration in relativistic jets

2014 ◽  
Vol 10 (S313) ◽  
pp. 153-158
Author(s):  
Markus Böttcher ◽  
Matthew G. Baring ◽  
Edison P. Liang ◽  
Errol J. Summerlin ◽  
Wen Fu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Particle Acceleration ◽  
Lorentz Factor ◽  
High Energy ◽  
Shock Acceleration ◽  
Relativistic Jets ◽  
Diffusive Shock Acceleration ◽  
Magnetic Field Generation ◽  
Particle Distributions ◽  
Particle In Cell

AbstractThe high-energy emission from blazars and other relativistic jet sources indicates that electrons are accelerated to ultra-relativistic (GeV - TeV) energies in these systems. This paper summarizes recent results from numerical studies of two fundamentally different particle acceleration mechanisms potentially at work in relativistic jets: Magnetic-field generation and relativistic particle acceleration in relativistic shear layers, which are likely to be present in relativistic jets, is studied via Particle-in-Cell (PIC) simulations. Diffusive shock acceleration at relativistic shocks is investigated using Monte-Carlo simulations. The resulting magnetic-field configurations and thermal + non-thermal particle distributions are then used to predict multi-wavelength radiative (synchrotron + Compton) signatures of both acceleration scenarios. In particular, we address how anisotropic shear-layer acceleration may be able to circumvent the well-known Lorentz-factor crisis, and how the self-consistent evaluation of thermal + non-thermal particle populations in diffusive shock acceleration simulations provides tests of the bulk Comptonization model for the Big Blue Bump observed in the SEDs of several blazars.

scholarly journals Hybrid modeling of diffusive shock acceleration in collisionless shocks in multispecies plasma

2018 ◽  
pp. 373-378
Author(s):  
J. A. Kropotina ◽  
A. M. Bykov ◽  
V. E. Ermolina ◽  
S. M. Osipov ◽  
V. I. Romansky
Keyword(s):  
Heavy Ions ◽  
Supernova Remnants ◽  
Gamma Ray ◽  
Hydrogen Plasma ◽  
High Energy ◽  
Shock Acceleration ◽  
High Energy Particle ◽  
Diffusive Shock Acceleration ◽  
Particle Injection ◽  
Initial Flow

Diffusive shock acceleration (DSA) is a very efficient mechanism of high energy particle acceleration in heliosphere, supernova remnants, stellar winds and gamma-ray bursts. We present microscopic simulation of particle injection and diffusive shock acceleration which is performed with 3D divergence-conserving second-order accurate hybrid code "Maximus". Hydrogen plasma with admixture of various heavy ions is considered. The injection process is found to start through shock reflection for both hydrogen and heavier ions. However, the reflection process depends on charge-to-mass ratio. While hydrogen ions reflection appears at shock ramp and is governed by the cross-shock potential, the reflection of ions with greater A=Z proceeds deeper down-stream via gyration in perpendicular magnetic field component. The heavy ions appear to inject into the DSA preferentially, but this chemical enhancement saturates with growing A=Z. The protons injection efficiency is estimated within various approaches, and it is shown that about 20% of initial flow energy goes into accelerated particles.

scholarly journals A Theoretical Review of Diffusive Shock Acceleration

1994 ◽  
Vol 142 ◽  
pp. 561-565
Author(s):  
Frank C. Jones
Keyword(s):  
Particle Acceleration ◽  
Shock Waves ◽  
Power Law ◽  
Second Order ◽  
Shock Acceleration ◽  
Acceleration Of Particles ◽  
Diffusive Shock Acceleration ◽  
Stochastic Acceleration ◽  
Universal Power Law ◽  
Subject Headings

AbstractWe discuss the fundamental ideas of particle acceleration in plasma shocks with emphasis on those features that are required to produce the “universal” power-law spectrum. We compare shock acceleration with the more familiar second-order or stochastic acceleration and see that they are not too different in many respects. We discuss the features of shock acceleration that make it appealing and some of its problems as well.Subject headings: acceleration of particles — MHD — plasmas — shock waves

Particle Motions in Planetary Magnetic Fields: Europlanet Service

2020 ◽  
Author(s):  
Patrick Guio ◽  
Nicholas Achilleos ◽  
Nicolas André
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Charged Particles ◽  
High Energy ◽  
Particle Energy ◽  
Curvature Radius ◽  
High Energy Particle ◽  
Field Curvature ◽  
Planetary Magnetic Fields ◽  
Field Lines

<p>The trapping of charged particles in planetary magnetic fields is a process which underpins many important aspects of planetary magnetospheres, such as ring current evolution, particle acceleration, and the flow of current through the system, both free and bound. As part of our effort for the Europlanet project, the UCL group have developed codes which accurately model the trajectories of charged particles in magnetic field models appropriate for the magnetospheres of Jupiter and Saturn. These will form the basis of a service for the SPIDER task. In this presentation, we show examples of ion trajectories at both planets for representative 'start values' of equatorial distance, pitch angle, and values of particle energy. The simulations provide an indication of how particle orbits become less adiabatic as one approaches energies where gyroradii become comparable to magnetic field curvature radius. The disk-like fields of the gas giants are particularly effective at 'scattering' adequately high-energy particle trajectories as they cross the equator, where the field lines are most 'pinched' and have the smallest length scales.</p>

ENERGY ORDERING EFFECTS IN THE ARRIVAL DIRECTIONS OF ULTRA-HIGH ENERGY COSMIC RAYS MEASURED BY THE PIERRE AUGER OBSERVATORY

2011 ◽  
Vol 20 (supp02) ◽  
pp. 50-56
Author(s):  
◽  
PETER SCHIFFER
Keyword(s):  
Cosmic Rays ◽  
Magnetic Fields ◽  
Charged Particles ◽  
High Energy ◽  
Pierre Auger Observatory ◽  
Ultra High Energy ◽  
High Energy Cosmic Rays ◽  
Ordering Effects ◽  
Arrival Directions

The Pierre Auger Observatory is the world's largest experiment for the measurement of ultra-high energy cosmic rays (UHECRs). These UHECRs are assumed to be to be charged particles, and thus are deflected in cosmic magnetic fields. Recent results of the Pierre Auger Observatory addressing the complex of energy ordering of the UHECRs arrival directions are reviewed in this contribution. So far no significant energy ordering has been observed.

Sign in / Sign up

Export Citation Format

Share Document