scholarly journals Perpendicular Diffusion of Energetic Particles: A Complete Analytical Theory

2021 ◽  
Vol 923 (2) ◽  
pp. 209
Author(s):  
A. Shalchi
Keyword(s):  
Magnetic Field ◽  
Diffusion Coefficient ◽  
Correction Factor ◽  
Test Particle ◽  
Transport Theory ◽  
Energetic Particles ◽  
Analytical Theory ◽  
Nonlinear Transport ◽  
Particle Simulations ◽  
Perpendicular Diffusion

Abstract Over the past two decades scientists have significantly improved our understanding of the transport of energetic particles across a mean magnetic field. Due to test-particle simulations, as well as powerful nonlinear analytical tools, our understanding of this type of transport is almost complete. However, previously developed nonlinear analytical theories do not always agree perfectly with simulations. Therefore, a correction factor a 2 was incorporated into such theories with the aim to balance out inaccuracies. In this paper a new analytical theory for perpendicular transport is presented. This theory contains the previously developed unified nonlinear transport theory, the most advanced theory to date, in the limit of small Kubo number turbulence. New results have been obtained for two-dimensional turbulence. In this case, the new theory describes perpendicular diffusion as a process that is sub-diffusive while particles follow magnetic field lines. Diffusion is restored as soon as the turbulence transverse complexity becomes important. For long parallel mean-free paths, one finds that the perpendicular diffusion coefficient is a reduced field line random walk limit. For short parallel mean-free paths, on the other hand, one gets a hybrid diffusion coefficient that is a mixture of collisionless Rechester & Rosenbluth and fluid limits. Overall, the new analytical theory developed in the current paper is in agreement with heuristic arguments. Furthermore, the new theory agrees almost perfectly with previously performed test-particle simulations without the need of the aforementioned correction factor a 2 or any other free parameter.

Transport of energetic particles from reconnecting current sheets in flaring corona to the heliosphere

2021 ◽  
Author(s):  
Philippa Browning ◽  
Mykola Gordovskyy ◽  
Satashi Inoue ◽  
Eduard Kontar ◽  
Kanya Kusano ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Energetic Particles ◽  
Transport Processes ◽  
Data Driven ◽  
Current Sheets ◽  
Electrons And Ions ◽  
Data Driven Approach ◽  
Particle Simulations ◽  
The Magnetic Field

<p>In this study, we inverstigate the acceleration of electrons and ions at current sheets in the flaring solar corona, and their transport into the heliosphere. We consider both generic solar flare models and specific flaring events with a data-driven approach. The aim is to answer two questions: (a) what fraction of particles accelerated in different flares can escape into the heliosphere?; and (b) what are the characteristics of the particle populations propagating towards the chromosphere and into the heliosphere?</p><p>We use a combination of data-driven 3D magnetohydrodynamics simulations with drift-kinetic particle simulations to model the evolution of the magnetic field and both thermal and non-thermal plasma and to forward-model observable characteristics. Particles are accelerated in current sheets associated with flaring reconnection. When applied to a specific flare, the model successfully predicts observed features such as the location and relative intensity of hard X-ray sources and helioseismic source locations. This confirms the viability of the approach.</p><p>Using these MHD-particle models, we will show how the magnetic field evolution and particle transport processes affect the characteristics of both energetic electrons and ions in the the inner corona and the heliosphere. The implications for interpretation of in situ measurements of energetic particles by Solar Orbiter and Parker Solar Probe will be discussed.</p><p> </p><p> </p>

scholarly journals The cusp: a window for particle exchange between the radiation belt and the solar wind

2006 ◽  
Vol 24 (11) ◽  
pp. 3131-3137 ◽  
Author(s):  
X.-Z. Zhou ◽  
T. A. Fritz ◽  
Q.-G. Zong ◽  
Z. Y. Pu ◽  
Y.-Q. Hao ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Open Field ◽  
Test Particle ◽  
Radiation Belt ◽  
Magnetospheric Convection ◽  
Cusp Region ◽  
Particle Simulations ◽  
Particle Exchange ◽  
Field Lines

Abstract. The study focuses on a single particle dynamics in the cusp region. The topology of the cusp region in terms of magnetic field iso-B contours has been studied using the Tsyganenko 96 model (T96) as an example, to show the importance of an off-equatorial minimum on particle trapping. We carry out test particle simulations to demonstrate the bounce and drift motion. The "cusp trapping limit" concept is introduced to reflect the particle motion in the high latitude magnetospheric region. The spatial distribution of the "cusp trapping limit" shows that only those particles with near 90° pitch-angles can be trapped and drift around the cusp. Those with smaller pitch angles may be partly trapped in the iso-B contours, however, they will eventually escape along one of the magnetic field lines. There exist both open field lines and closed ones within the same drift orbit, indicating two possible destinations of these particles: those particles being lost along open field lines will be connected to the surface of the magnetopause and the solar wind, while those along closed ones will enter the equatorial radiation belt. Thus, it is believed that the cusp region can provide a window for particle exchange between these two regions. Some of the factors, such as dipole tilt angle, magnetospheric convection, IMF and the Birkeland current system, may influence the cusp's trapping capability and therefore affect the particle exchanging mechanism. Their roles are examined by both the analysis of cusp magnetic topology and test particle simulations.

scholarly journals Mercury’s Ring Current: MESSENGER Observations and Test-Particle Simulations

2021 ◽  
Author(s):  
Jiutong Zhao ◽  
Qiugang Zong ◽  
Chao Yue ◽  
Weijie Sun ◽  
Hui Zhang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Test Particle ◽  
Ring Current ◽  
Current System ◽  
Wind Forcing ◽  
Particle Simulation ◽  
Space Environment ◽  
Magnetic Field Model ◽  
Particle Simulations

Abstract Energetic protons can carry a longitudinal electric current via their gradient and curvature drift around a planet and form a current system known as the ring current. The ring current has been observed in the intrinsic magnetosphere of Earth, Jupiter, and Saturn. However, there is still lacking evidence of ring current in Mercury’s magnetosphere, which contains significantly weaker and oppressive “dipolar” magnetic field and the charged particles are thought able to efficiently escape the magnetosphere through magnetopause shadowing and/or directly hitting the surface. Here we present the first observational evidence of Mercury ring current with the measurement of MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER). The ring current is bifurcated under moderate solar wind forcing, which is caused by the off-equatorial magnetic minima on the noon side and tends to vanish during weak solar wind forcing. This morphology is validated by a test-particle simulation with a Mercury’s dynamic magnetic field model. The total energy stored in the ring current exceeds 5x1010 J during active times, indicating that magnetic storms may also occur in Mercury’s magnetosphere.

Particle energization inside plasmoids: numerical and analytical investigations

2021 ◽  
Author(s):  
Xiaozhou Zhao ◽  
Rony Keppens ◽  
Fabio Bacchini
Keyword(s):  
Test Particle ◽  
Large Scale ◽  
Mass Density ◽  
Magnetic Islands ◽  
Chaotic Flow ◽  
Reynolds Decomposition ◽  
Particle Simulations ◽  
Particle Energization ◽  
Periodic Setting ◽  
A Current

<div> <div> <div> <p>In an idealized system where four magnetic islands interact in a two-dimensional periodic setting, we follow the detailed evolution of current sheets forming in between the islands, as a result of an enforced large-scale merging by magnetohydrodynamic (MHD) simulation. The large-scale island merging is triggered by a perturbation to the velocity field, which drives one pair of islands move towards each other while the other pair of islands are pushed away from one another. The "X"-point located in the midst of the four islands is locally unstable to the perturbation and collapses, producing a current sheet in between with enhanced current and mass density. Using grid-adaptive resistive magnetohydrodynamic (MHD) simulations, we establish that slow near-steady Sweet-Parker reconnection transits to a chaotic, multi-plasmoid fragmented state, when the Lundquist number exceeds about 3×10<sup>4</sup>, well in the range of previous studies on plasmoid instability. The extreme resolution employed in the MHD study shows significant magnetic island substructures. Turbulent and chaotic flow patters are also observed inside the islands. We set forth to explore how charged particles can be accelerated in embedded mini-islands within larger (monster)-islands on the sheet. We study the motion of the particles in a MHD snapshot at a fixed instant of time by the Test-Particle Module incorporated in AMRVAC (). The planar MHD setting artificially causes the largest acceleration in the ignored third direction, but does allow for full analytic study of all aspects leading to the acceleration and the in-plane, projected trapping of particles within embedded mini-islands. The analytic result uses a decomposition of the test particle velocity in slow and fast changing components, akin to the Reynolds decomposition in turbulence studies. The analytic results allow a complete fit to representative proton test particle simulations, which after initial non-relativistic motion throughout the monster island, show the potential of acceleration within a mini-island beyond (√2/2)c≈0.7c, at which speed the acceleration is at its highest efficiency. Acceleration to several hundreds of GeVs can happen within several tens of seconds, for upward traveling protons in counterclockwise mini-islands of sizes smaller than the proton gyroradius.</p> </div> </div> </div><div></div><div></div>

scholarly journals A GENERALIZED DIFFUSION TENSOR FOR FULLY ANISOTROPIC DIFFUSION OF ENERGETIC PARTICLES IN THE HELIOSPHERIC MAGNETIC FIELD

2012 ◽  
Vol 750 (2) ◽  
pp. 108 ◽  
Author(s):  
F. Effenberger ◽  
H. Fichtner ◽  
K. Scherer ◽  
S. Barra ◽  
J. Kleimann ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Anisotropic Diffusion ◽  
Diffusion Tensor ◽  
Energetic Particles ◽  
Heliospheric Magnetic Field

scholarly journals On the Turbulent Reduction of Drifts for Solar Energetic Particles

2021 ◽  
Vol 922 (2) ◽  
pp. 200
Author(s):  
J. P. van den Berg ◽  
N. E. Engelbrecht ◽  
N. Wijsen ◽  
R. D. Strauss
Keyword(s):  
Pitch Angle ◽  
Cosmic Ray ◽  
Energetic Particles ◽  
Solar Energetic Particles ◽  
Particle Distributions ◽  
Magnetic Turbulence ◽  
Field Diffusion ◽  
Background Magnetic Field ◽  
Perpendicular Diffusion ◽  
Inner Heliosphere

Abstract Particle drifts perpendicular to the background magnetic field have been proposed by some authors as an explanation for the very efficient perpendicular transport of solar energetic particles (SEPs). This process, however, competes with perpendicular diffusion caused by magnetic turbulence, which can also disrupt the drift patterns and reduce the magnitude of drift effects. The latter phenomenon is well known in cosmic-ray studies, but not yet considered in SEP models. Additionally, SEP models that do not include drifts, especially for electrons, use turbulent drift reduction as a justification of this omission, without critically evaluating or testing this assumption. This article presents the first theoretical step for a theory of drift suppression in SEP transport. This is done by deriving the turbulence-dependent drift reduction function with a pitch-angle dependence, as is applicable for anisotropic particle distributions, and by investigating to what extent drifts will be reduced in the inner heliosphere for realistic turbulence conditions and different pitch-angle dependencies of the perpendicular diffusion coefficient. The influence of the derived turbulent drift reduction factors on the transport of SEPs are tested, using a state-of-the-art SEP transport code, for several expressions of theoretically derived perpendicular diffusion coefficients. It is found, for realistic turbulence conditions in the inner heliosphere, that cross-field diffusion will have the largest influence on the perpendicular transport of SEPs, as opposed to particle drifts.

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