MAGNETIC TURBULENCE IN TOKAMAKS

1977 ◽  
Vol 38 (C6) ◽  
pp. C6-103-C6-110
Author(s):  
A. SAMAIN
Keyword(s):  
Magnetic Turbulence

scholarly journals Pedestal magnetic turbulence measurements in ELMy H-mode DIII-D plasmas by Faraday-effect polarimetry

2021 ◽  
Vol 28 (2) ◽  
pp. 022506
Author(s):  
J. Chen ◽  
D. L. Brower ◽  
W. X. Ding ◽  
Z. Yan ◽  
M. Curie ◽  
...  
Keyword(s):  
Faraday Effect ◽  
Turbulence Measurements ◽  
Magnetic Turbulence

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.

scholarly journals Relative depolarization of the black hole photon ring in GRMHD models of Sgr A* and M87*

2021 ◽  
Vol 503 (3) ◽  
pp. 4563-4575
Author(s):  
A Jiménez-Rosales ◽  
J Dexter ◽  
S M Ressler ◽  
A Tchekhovskoy ◽  
M Bauböck ◽  
...  
Keyword(s):  
Black Hole ◽  
Relativistic Effects ◽  
Image Features ◽  
Black Hole Mass ◽  
Magnetic Turbulence ◽  
Intensity Images ◽  
General Relativistic ◽  
Sharp Image ◽  
Sgr A ◽  
Magnetohydrodynamic Simulations

ABSTRACT Using general relativistic magnetohydrodynamic simulations of accreting black holes, we show that a suitable subtraction of the linear polarization per pixel from total intensity images can enhance the photon ring feature. We find that the photon ring is typically a factor of ≃2 less polarized than the rest of the image. This is due to a combination of plasma and general relativistic effects, as well as magnetic turbulence. When there are no other persistently depolarized image features, adding the subtracted residuals over time results in a sharp image of the photon ring. We show that the method works well for sample, viable GRMHD models of Sgr A* and M87*, where measurements of the photon ring properties would provide new measurements of black hole mass and spin, and potentially allow for tests of the ‘no-hair’ theorem of general relativity.

Detailed analytical investigation of magnetic field line random walk in turbulent plasmas: II. Isotropic turbulence

2009 ◽  
Vol 75 (2) ◽  
pp. 183-192 ◽  
Author(s):  
I. KOURAKIS ◽  
R. C. TAUTZ ◽  
A. SHALCHI
Keyword(s):  
Magnetic Field ◽  
Random Walk ◽  
Field Line ◽  
Isotropic Turbulence ◽  
Mean Square Displacement ◽  
Analytical Investigation ◽  
Turbulence Spectrum ◽  
Quasilinear Theory ◽  
Magnetic Turbulence ◽  
Field Lines

AbstractThe random walk of magnetic field lines in the presence of magnetic turbulence in plasmas is investigated from first principles. An isotropic model is employed for the magnetic turbulence spectrum. An analytical investigation of the asymptotic behavior of the field-line mean-square displacement 〈(Δx)2〉 is carried out, in terms of the position variable z. It is shown that 〈(Δx)2〉 varies as ~z ln z for large distance z. This result corresponds to a superdiffusive behavior of field line wandering. This investigation complements previous work, which relied on a two-component model for the turbulence spectrum. Contrary to that model, quasilinear theory appears to provide an adequate description of the field-line random walk for isotropic turbulence.

Spatial Structure and Field-Line Diffusion in Transverse Magnetic Turbulence

1995 ◽  
Vol 75 (11) ◽  
pp. 2136-2139 ◽  
Author(s):  
W. H. Matthaeus ◽  
P. C. Gray ◽  
D. H. Pontius, Jr. ◽  
J. W. Bieber
Keyword(s):  
Spatial Structure ◽  
Field Line ◽  
Transverse Magnetic ◽  
Magnetic Turbulence ◽  
Line Diffusion

scholarly journals Magnetic turbulence and particle dynamics in the Earth’s magnetotail

2003 ◽  
Vol 21 (9) ◽  
pp. 1947-1953 ◽  
Author(s):  
G. Zimbardo ◽  
A. Greco ◽  
A. L. Taktakishvili ◽  
P. Veltri ◽  
L. M. Zelenyi
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Sheet Thickness ◽  
Particle Dynamics ◽  
Particle Simulation ◽  
Mhd Waves ◽  
Magnetic Fluctuations ◽  
Magnetic Turbulence ◽  
Magnetospheric Configuration And Dynamics ◽  
Interplanetary Physics

Abstract. The influence of magnetic turbulence in the near-Earth magnetotail on ion motion is investigated by numerical simulation. The magnetotail current sheet is modelled as a magnetic field reversal with a normal magnetic field com-ponent Bn , plus a three-dimensional spectrum of magnetic fluctuations dB which represents the observed magnetic turbulence. The dawn-dusk electric field Ey is also considered. A test particle simulation is performed using different values of Bn and of the fluctuation level dB/B0. We show that when the magnetic fluctuations are taken into account, the particle dynamics is deeply affected, giving rise to an increase in the cross tail transport, ion heating, and current sheet thickness. For strong enough turbulence, the current splits in two layers, in agreement with recent Cluster observations.Key words. Magnetospheric physics (magnetospheric configuration and dynamics) – Interplanetary physics (MHD waves and turbulence) – Electromagnetics (numerical methods)

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