scholarly journals On the growth of the thermally modified non-resonant streaming instability

2020 ◽  
Vol 500 (2) ◽  
pp. 2302-2315
Author(s):  
A Marret ◽  
A Ciardi ◽  
R Smets ◽  
J Fuchs
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Cosmic Rays ◽  
Magnetic Energy ◽  
Plasma Temperature ◽  
Ambient Plasma ◽  
Linear Evolution ◽  
Field Amplification ◽  
Streaming Instability ◽  
Wide Range

ABSTRACT The cosmic rays non-resonant streaming instability is believed to be the source of substantial magnetic field amplification. In this work, we investigate the effects of the ambient plasma temperature on the instability and derive analytical expressions of its growth rate in the hot, demagnetized regime of interaction. To study its non-linear evolution, we perform hybrid-PIC simulations for a wide range of temperatures. We find that in the cold limit, about two-thirds of the cosmic rays drift kinetic energy is converted into magnetic energy. Increasing the temperature of the ambient plasma can substantially reduce the growth rate and the magnitude of the saturated magnetic field.

scholarly journals Small-scale dynamo action in primordial halos

2012 ◽  
Vol 8 (S294) ◽  
pp. 237-248
Author(s):  
Jennifer Schober ◽  
Dominik R. G. Schleicher ◽  
Ralf S. Klessen ◽  
Christoph Federrath ◽  
Stefano Bovino ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Kinetic Energy ◽  
Magnetic Energy ◽  
Compressible Turbulence ◽  
Small Scale ◽  
Dynamo Action ◽  
Velocity Correlation ◽  
Field Amplification ◽  
First Galaxies

AbstractThe first galaxies form due to gravitational collapse of primordial halos. During this collapse, weak magnetic seed fields get amplified exponentially by the small-scale dynamo - a process converting kinetic energy from turbulence into magnetic energy. We use the Kazantsev theory, which describes the small-scale dynamo analytically, to study magnetic field amplification for different turbulent velocity correlation functions. For incompressible turbulence (Kolmogorov turbulence), we find that the growth rate is proportional to the square root of the hydrodynamic Reynolds number, Re1/2. In the case of highly compressible turbulence (Burgers turbulence) the growth rate increases proportional to Re1/3. With a detailed chemical network we are able to follow the chemical evolution and determine the kinetic and magnetic viscosities (due to Ohmic and ambipolar diffusion) during the collapse of the halo. This way, we can calculate the growth rate of the small-scale dynamo quantitatively and predict the evolution of the small-scale magnetic field. As the magnetic energy is transported to larger scales on the local eddy-timescale, we obtain an estimate for the magnetic field on the Jeans scale. Even there, we find that equipartition with the kinetic energy is reached on small timescales. Dynamically relevant field structures can thus be expected already during the formation of the first objects in the Universe.

scholarly journals On the linear and non-linear evolution of the relativistic MHD Kelvin–Helmholtz instability in a magnetically polarized fluid

2019 ◽  
Vol 490 (3) ◽  
pp. 4183-4193
Author(s):  
Oscar M Pimentel ◽  
Fabio D Lora-Clavijo
Keyword(s):  
Magnetic Field ◽  
Gamma Ray ◽  
Magnetic Energy ◽  
Linear Regime ◽  
Helmholtz Instability ◽  
Linear Evolution ◽  
Field Amplification ◽  
Non Linear ◽  
Open Question ◽  
The Magnetic Field

ABSTRACT The origin and strength of the magnetic field in some systems like active galactic nuclei or gamma-ray bursts is still an open question in astrophysics. A possible mechanism to explain the magnetic field amplification is the Kelvin–Helmholtz instability, since it is able to transform the kinetic energy in a shear flow into magnetic energy. Through this work, we investigate the linear and non-linear effects produced by the magnetic susceptibility in the development of the Kelvin–Helmholtz instability in a relativistic plasma. The system under study consists of a plane interface separating two uniform fluids that move with opposite velocities. The magnetic field in the system is parallel to the flows and the susceptibility is assumed to be homogeneous, constant in time, and equal in both fluids. In particular, we analyse the instability in three different cases, when the fluids are diamagnetic, paramagnetic, and when the susceptibility is zero. We compute the dispersion relation in the linear regime and found that the interface between diamagnetic fluids is more stable than between paramagnetic ones. We check the analytical results with numerical simulations, and explore the effect of the magnetic polarization in the non-linear regime. We find that the magnetic field is more amplified in paramagnetic fluids than in diamagnetic ones. Surprisingly, the effect of the susceptibility in the amplification is stronger when the magnetization parameter is smaller. The results of our work make this instability a more efficient and effective amplification mechanism of seed magnetic fields when considering the susceptibility of matter.

MAGNETIC FIELD AMPLIFICATION BY RELATIVISTIC SHOCKS IN AN INHOMOGENEOUS MEDIUM

2012 ◽  
Vol 08 ◽  
pp. 364-367
Author(s):  
YOSUKE MIZUNO ◽  
MARTIN POHL ◽  
JACEK NIEMIEC ◽  
BING ZHANG ◽  
KEN-ICHI NISHIKAWA ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Inhomogeneous Medium ◽  
Magnetic Energy ◽  
Small Scale ◽  
Two Dimensional ◽  
Filamentary Structure ◽  
Field Amplification ◽  
Relativistic Shocks ◽  
Field Lines ◽  
Magnetohydrodynamic Simulations

We perform two-dimensional relativistic magnetohydrodynamic simulations of a mildly relativistic shock propagating through an inhomogeneous medium. We show that the postshock region becomes turbulent owing to preshock density inhomogeneity, and the magnetic field is strongly amplified due to the stretching and folding of field lines in the turbulent velocity field. The amplified magnetic field evolves into a filamentary structure in two-dimensional simulations. The magnetic energy spectrum is flatter than the Kolmogorov spectrum and indicates that the so-called small-scale dynamo is occurring in the postshock region. We also find that the amplitude of magnetic-field amplification depends on the direction of the mean preshock magnetic field.

scholarly journals Magnetic Rayleigh–Taylor instability at a contact discontinuity with an oblique magnetic field

2020 ◽  
Vol 634 ◽  
pp. A96
Author(s):  
E. Vickers ◽  
I. Ballai ◽  
R. Erdélyi
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Dispersion Relation ◽  
Contact Discontinuity ◽  
Homogeneous Magnetic Field ◽  
Taylor Instability ◽  
Wide Range ◽  
Rayleigh Taylor Instability ◽  
The Magnetic Field ◽  
Theoretical Results

Aims. We investigate the nature of the magnetic Rayleigh–Taylor instability at a density interface that is permeated by an oblique homogeneous magnetic field in an incompressible limit. Methods. Using the system of linearised ideal incompressible magnetohydrodynamics equations, we derive the dispersion relation for perturbations of the contact discontinuity by imposing the necessary continuity conditions at the interface. The imaginary part of the frequency describes the growth rate of waves due to instability. The growth rate of waves is studied by numerically solving the dispersion relation. Results. The critical wavenumber at which waves become unstable, which is present for a parallel magnetic field, disappears because the magnetic field is inclined. Instead, waves are shown to be unstable for all wavenumbers. Theoretical results are applied to diagnose the structure of the magnetic field in prominence threads. When we apply our theoretical results to observed waves in prominence plumes, we obtain a wide range of field inclination angles, from 0.5° up to 30°. These results highlight the diagnostic possibilities that our study offers.

scholarly journals Preliminary study for the laboratory experiment of cosmic-rays driven magnetic field amplification

2019 ◽  
Vol 32 ◽  
pp. 31-43
Author(s):  
Chun-Sung Jao ◽  
Sergei Vafin ◽  
Ye Chen ◽  
Matthias Gross ◽  
Mikhail Krasilnikov ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Cosmic Rays ◽  
Laboratory Experiment ◽  
Field Amplification ◽  
Preliminary Study

scholarly journals The Formation of Discontinuities in Gas Flows in the ISM and its Relation to the Galactic Synchrotron Radio Emission

1990 ◽  
Vol 140 ◽  
pp. 159-162
Author(s):  
V.G. Berman ◽  
L.S. Marochnik ◽  
Yu.N. Mishurov ◽  
A.A. Suchkov
Keyword(s):  
Magnetic Field ◽  
Cosmic Rays ◽  
Radio Emission ◽  
Large Scale ◽  
Field Energy ◽  
Gas Flows ◽  
Interstellar Gas ◽  
Gas Density ◽  
Magnetic Field Energy ◽  
Wide Range

We show that large–scale motions of the interstellar gas, such as those associated with galactic density waves, easily develop, over a wide range of scales, shocks and discontinuities which are expected to generate turbulence. The latter is supposed to evoke diffusion of magnetic fields and cosmic rays on scales down to a few parsecs. We suggest that these processes may be of major importance in discussions of interconnections between the observed radio emission of the disks of spiral galaxies and the gas density distribution within them. In particular, we predict that the density of cosmic rays and magnetic field energy must be much less contrasted (on scales of ~1 pc and up to the scales of galactic shocks) than the gas density, hence the synchrotron radio emission is not as contrasted as is predicted under the hypothesis of a fully frozen-in magnetic field.

scholarly journals Modelling coronal electron density and temperature profiles of the Active Region NOAA 11855

2016 ◽  
Vol 12 (S328) ◽  
pp. 149-151
Author(s):  
J. M. Rodríguez Gómez ◽  
L. E. Antunes Vieira ◽  
A. Dal Lago ◽  
J. Palacios ◽  
L. A. Balmaceda ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Physical Mechanism ◽  
Magnetic Energy ◽  
Plasma Temperature ◽  
Coronal Magnetic Field ◽  
Flux Emergence ◽  
Vector Magnetic Field ◽  
Atmospheric Phenomena ◽  
Coronal Electron

AbstractThe magnetic flux emergence can help understand the physical mechanism responsible for solar atmospheric phenomena. Emerging magnetic flux is frequently related to eruptive events, because when emerging they can reconnected with the ambient field and release magnetic energy. We will use a physic-based model to reconstruct the evolution of the solar emission based on the configuration of the photospheric magnetic field. The structure of the coronal magnetic field is estimated by employing force-free extrapolation NLFFF based on vector magnetic field products (SHARPS) observed by HMI instrument aboard SDO spacecraft from Sept. 29 (2013) to Oct. 07 (2013). The coronal plasma temperature and density are described and the emission is estimated using the CHIANTI atomic database 8.0. The performance of the our model is compared to the integrated emission from the AIA instrument aboard SDO spacecraft in the specific wavelengths 171Å and 304Å.

scholarly journals ENVIRONMENTS FOR MAGNETIC FIELD AMPLIFICATION BY COSMIC RAYS

2010 ◽  
Vol 709 (2) ◽  
pp. 1412-1419 ◽  
Author(s):  
Ellen G. Zweibel ◽  
John E. Everett
Keyword(s):  
Magnetic Field ◽  
Cosmic Rays ◽  
Field Amplification

scholarly journals Velocity Shear Instabilities in the Anisotropic Solar Wind

1985 ◽  
Vol 107 ◽  
pp. 371-374
Author(s):  
Stefano Migliuolo
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Solar Wind ◽  
Magnetic Energy ◽  
Equilibrium Temperature ◽  
Acoustic Mode ◽  
Plasma Pressure ◽  
Velocity Shear ◽  
Linear Growth Rate ◽  
Quasilinear Theory

The linear and quasilinear theory of perturbations in finite-β (β is the ratio of plasma pressure to magnetic energy density), collisionless plasmas, that have sheared (velocity) flows, is developed. A simple, one-dimensional magnetic field geometry is assumed to adequately represent solar wind conditions near the sun (i.e., at R ≃ 0.3 AU). Two modes are examined in detail: an ion-acoustic mode (finite-β stabilized) and a compressional Alfven mode (finite-β threshold, high-β stabilization). The role played by equilibrium temperature anisotropies, in the linear stability of these modes, is also presented. From the quasilinear theory, two results are obtained. First, the feedback of these waves on the state of the wind is such as to heat (cool) the ions in the direction perpendicular (parallel) to the equilibrium magnetic field. The opposite effect is found for the electrons. This is in qualitative agreement with the observed anisotropies of ions and electrons, in fast solar wind streams. Second, these quasilinear temperature changes are shown to result in a quasilinear growth rate that is lower than the linear growth rate, suggesting saturation of these instabilities.

scholarly journals The role of the sonic scale in the growth of magnetic field in compressible turbulence

2020 ◽  
Vol 493 (3) ◽  
pp. 4400-4408
Author(s):  
Itzhak Fouxon ◽  
Michael Mond
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Large Scale ◽  
Compressible Turbulence ◽  
Small Scale ◽  
Integral Scale ◽  
Time Model ◽  
Turbulent Eddies ◽  
Field Amplification ◽  
The Magnetic Field

ABSTRACT We study the growth of small fluctuations of magnetic field in supersonic turbulence, the small-scale dynamo. The growth is due to the smallest and fastest turbulent eddies above the resistive scale. We observe that for supersonic turbulence these eddies are localized below the sonic scale ls, defined as the scale where the typical velocity of the turbulent eddies equals the speed of sound, and are therefore effectively incompressible. All previous studies have ignored the existence of the sonic scale and consequently treated the entire inertial range as made up of compressible eddies. However, at large Mach numbers ls is much smaller than the integral scale of the turbulence so the fastest growing mode of the magnetic field belongs to small-scale incompressible turbulence. We determine this mode and the associated growth rate numerically with the aid of a white noise in time model of turbulence whose approximate validity for the description of the Navier–Stokes turbulence is explained. For that purpose, we introduce a new non-dimensional number Rsm that we name the magnetosonic Reynolds number that describes the division of the magnetic field amplification range between small-scale incompressible eddies and large-scale supersonic ones. We show that indeed, as Rsm grows (which means that the incompressible eddies occupy a larger portion of the magnetic field amplification range) the growth rate of the fastest growing mode increases, while the spatial distribution of the growing magnetic field shifts to smaller scales. Our result implies the existence of small-scale dynamo for compressible homogeneous turbulence.

Sign in / Sign up

Export Citation Format

Share Document