scholarly journals Regimes of cosmic-ray diffusion in Galactic turbulence

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
P. Reichherzer ◽  
L. Merten ◽  
J. Dörner ◽  
J. Becker Tjus ◽  
M. J. Pueschel ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Milky Way ◽  
Wave Spectrum ◽  
Cosmic Ray ◽  
Resonant Scattering ◽  
Guide Field ◽  
Parallel Diffusion ◽  
Perpendicular Diffusion ◽  
Field Lines ◽  
Ray Diffusion

AbstractCosmic-ray transport in astrophysical environments is often dominated by the diffusion of particles in a magnetic field composed of both a turbulent and a mean component. This process, which is two-fold turbulent mixing in that the particle motion is stochastic with respect to the field lines, needs to be understood in order to properly model cosmic-ray signatures. One of the most important aspects in the modeling of cosmic-ray diffusion is that fully resonant scattering, the most effective such process, is only possible if the wave spectrum covers the entire range of propagation angles. By taking the wave spectrum boundaries into account, we quantify cosmic-ray diffusion parallel and perpendicular to the guide field direction at turbulence levels above 5% of the total magnetic field. We apply our results of the parallel and perpendicular diffusion coefficient to the Milky Way. We show that simple purely diffusive transport is in conflict with observations of the inner Galaxy, but that just by taking a Galactic wind into account, data can be matched in the central 5 kpc zone. Further comparison shows that the outer Galaxy at $$>5$$ > 5  kpc, on the other hand, should be dominated by perpendicular diffusion, likely changing to parallel diffusion at the outermost radii of the Milky Way.

scholarly journals Turbulence-level dependence of cosmic ray parallel diffusion

2020 ◽  
Vol 498 (4) ◽  
pp. 5051-5064 ◽  
Author(s):  
P Reichherzer ◽  
J Becker Tjus ◽  
E G Zweibel ◽  
L Merten ◽  
M J Pueschel
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Coefficients ◽  
Cosmic Ray ◽  
Resonant Scattering ◽  
Homogeneous Magnetic Field ◽  
Resonant Interaction ◽  
Turbulence Level ◽  
Parallel Diffusion ◽  
Low Energies ◽  
Field Lines

ABSTRACT Understanding the transport of energetic cosmic rays belongs to the most challenging topics in astrophysics. Diffusion due to scattering by electromagnetic fluctuations is a key process in cosmic ray transport. The transition from a ballistic to a diffusive-propagation regime is presented in direct numerical calculations of diffusion coefficients for homogeneous magnetic field lines subject to turbulent perturbations. Simulation results are compared with theoretical derivations of the parallel diffusion coefficient’s dependences on the energy and the fluctuation amplitudes in the limit of weak turbulence. The present study shows that the widely used extrapolation of the energy scaling for the parallel diffusion coefficient to high turbulence levels predicted by quasi-linear theory does not provide a universally accurate description in the resonant-scattering regime. It is highlighted here that the numerically calculated diffusion coefficients can be polluted for low energies due to missing resonant interaction possibilities of the particles with the turbulence. Five reduced-rigidity regimes are established, which are separated by analytical boundaries derived in this work. Consequently, a proper description of cosmic ray propagation can only be achieved by using a turbulence-level-dependent diffusion coefficient and can contribute to solving the Galactic cosmic ray gradient problem.

scholarly journals Is there Evidence for Disk-Halo Connections in M31?

1991 ◽  
Vol 144 ◽  
pp. 233-236 ◽  
Author(s):  
Elly M. Berkhuijsen ◽  
Götz Golla ◽  
Rainer Beck
Keyword(s):  
Magnetic Field ◽  
Central Area ◽  
Cosmic Ray ◽  
Thick Disk ◽  
Significant Component ◽  
Southern Half ◽  
Ray Diffusion ◽  
The Magnetic Field ◽  
Uniform Disk

There is some evidence for disk-halo connections in M31, i.e.: (1) The central area seems inclined w.r.t. the main disk. (2) In several regions in the southern half the magnetic field has a significant component perpendicular to the disk. However, (3) any general emission from a thick disk at λ75 cm is ~100x weaker than that from our Galaxy. The uniform disk field seems to inhibit cosmic-ray diffusion perpendicular to the plane, and/or the field at high z is exceptionally weak.

scholarly journals Diffusion Coefficients, Short-Term Cosmic Ray Modulation, and Convected Magnetic Structures

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
John J. Quenby ◽  
Tamitha Mulligan ◽  
J. Bernard Blake ◽  
Diana N. A. Shaul
Keyword(s):  
Diffusion Coefficients ◽  
Particle Interaction ◽  
Flux Rope ◽  
Cosmic Ray ◽  
Magnetic Scattering ◽  
High Data ◽  
Cosmic Ray Modulation ◽  
Parallel Diffusion ◽  
Data Rates ◽  
Ray Diffusion

Three cases of large-amplitude, small spatial-scale interplanetary particle gradients observed by the anticoincidence shield (ACS) aboard the INTEGRAL spacecraft in 2006 are investigated. The high data rates provided by the INTEGRAL ACS allow an unprecedented ability to probe the fine structure of GCR propagation in the inner Heliosphere. For two of the three cases, calculating perpendicular and parallel cosmic ray diffusion coefficients based on both field and particle data results in parallel diffusion appearing to satisfy a convection gradient current balance, provided that the magnetic scattering of the particles can be described by quasi-linear theory. In the third case, perpendicular diffusion seems to dominate. The likelihood of magnetic flux rope topologies within solar ejecta affecting the local modulation is considered, and its importance in understanding the field-particle interaction for the astrophysics of nonthermal particle phenomena is discussed.

scholarly journals Evolution of magnetic helicity under kinetic magnetic reconnection: Part II B ≠ 0 reconnection

2002 ◽  
Vol 9 (2) ◽  
pp. 139-147 ◽  
Author(s):  
T. Wiegelmann ◽  
J. Büchner
Keyword(s):  
Magnetic Field ◽  
Magnetic Reconnection ◽  
Hall Current ◽  
Neutral Line ◽  
Magnetic Helicity ◽  
Perpendicular Magnetic Field ◽  
Guide Field ◽  
Magnetic Neutral Line ◽  
Field Lines ◽  
The Magnetic Field

Abstract. We investigate the evolution of magnetic helicity under kinetic magnetic reconnection in thin current sheets. We use Harris sheet equilibria and superimpose an external magnetic guide field. Consequently, the classical 2D magnetic neutral line becomes a field line here, causing a B ≠ 0 reconnection. While without a guide field, the Hall effect leads to a quadrupolar structure in the perpendicular magnetic field and the helicity density, this effect vanishes in the B ≠ 0 reconnection. The reason is that electrons are magnetized in the guide field and the Hall current does not occur. While a B = 0 reconnection leads just to a bending of the field lines in the reconnection area, thus conserving the helicity, the initial helicity is reduced for a B ≠ 0 reconnection. The helicity reduction is, however, slower than the magnetic field dissipation. The simulations have been carried out by the numerical integration of the Vlasov-equation.

scholarly journals A bisymmetric spiral magnetic field in the Milky Way

1985 ◽  
Vol 106 ◽  
pp. 251-252
Author(s):  
Y. Sofue ◽  
M. Fujimoto
Keyword(s):  
Magnetic Field ◽  
Faraday Rotation ◽  
Large Scale ◽  
Milky Way ◽  
Radio Sources ◽  
Extragalactic Radio Sources ◽  
Large Scale Magnetic Field ◽  
Rotation Measure ◽  
The Galaxy ◽  
Field Lines

The distribution of Faraday rotation measure (RM) of extragalactic radio sources shows that a large-scale magnetic field in the Galaxy is oriented along the spiral arms. The field lines change direction from one arm to the next in the inter-arm region.

scholarly journals Theory of cosmic ray modulation

2008 ◽  
Vol 4 (S257) ◽  
pp. 429-438 ◽  
Author(s):  
Stefan E. S. Ferreira
Keyword(s):  
Magnetic Field ◽  
Three Dimensional ◽  
Cosmic Ray ◽  
Transport Parameters ◽  
Cosmic Ray Modulation ◽  
Field Lines ◽  
Jovian Electrons ◽  
Globally Distributed ◽  
The Magnetic Field ◽  
Inner Heliosphere

AbstractThis work aims to give a brief overview on the topic of cosmic ray modulation in the heliosphere. The heliosphere, heliospheric magnetic field, transport parameters and the transport equation together with modulation models, which solve this equation in various degree of complexity, are briefly discussed. Results from these models are then presented where first it is shown how cosmic rays are globally distributed in an asymmetrical heliosphere which results from the relative motion between the local interstellar medium and the Sun. Next the focus shifts to low-energy Jovian electrons. The intensities of these electrons, which originate from a point source in the inner heliosphere, exhibit a unique three-dimensional spiral structure where most of the particles are transported along the magnetic field lines. Time-dependent modulation is also discussed where it is shown how drift effects together with propagating diffusion barriers are responsible for modulation over a solar cycle.

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