Plasma Density Fluctuations in a Magnetic Field

1961 ◽  
Vol 122 (6) ◽  
pp. 1663-1674 ◽  
Author(s):  
E. E. Salpeter
Keyword(s):  
Magnetic Field ◽  
Plasma Density ◽  
Density Fluctuations

scholarly journals Interstellar Magnetohydrodynamic Waves as Revealed by Radio Astronomy

1990 ◽  
Vol 140 ◽  
pp. 176-176
Author(s):  
S. R. Spangler
Keyword(s):  
Magnetic Field ◽  
Wave Field ◽  
Plasma Density ◽  
Supernova Remnants ◽  
Density Perturbation ◽  
Density Fluctuations ◽  
Wave Intensity ◽  
Mhd Waves ◽  
Theoretical Understanding ◽  
Magnetohydrodynamic Waves

The plasma density fluctuations responsible for interstellar scintillations occur on the same scales as interstellar magnetohydrodynamic waves (Alfvén waves), which are responsible for many important processes such as the acceleration of the cosmic rays. This suggests that these density fluctuations represent a compressive component of MHD waves, and raises the exciting possibility that radioastronomical observations can provide more or less direct measurements of interstellar microphysical processes. Extraction of MHD wave properties from the radio scattering measurements requires a sound theoretical understanding of the relationship between the magnetic field in an MHD wave and the corresponding plasma density perturbation. We present a plasma kinetic theory treatment of the density compression associated with an MHD wave field. The density perturbation may be expressed as the sum of three terms. These terms are proportional to the wave amplitude, wave intensity, and sine transform of the wave intensity, respectively. The coefficients of these three terms are functions of the plasma β, the electron-to-ion temperature ratio, and the angle of wave propagation with respect to the large scale magnetic field. This relation can serve as the basis for inferring the MHD wave field given a radio scattering measurement of the density fluctuation statistics. In an attempt to apply these ideas to the interstellar plasma turbulence, we have made VLBI angular broadening measurements of sources whose lines of sight pass close to supernova remnants. The intensity of MHD waves is expected to be high in the vicinity of the shock waves associated with supernova remnants. We do not yet have unambiguous evidence of enhanced radio wave scattering due to shock-associated MHD waves. However, we have found anomalously high scattering for the source CL4, whose line of sight passes through the Cygnus Loop.

scholarly journals Radio remote sensing of the corona and the solar wind

2008 ◽  
Vol 4 (S257) ◽  
pp. 529-541 ◽  
Author(s):  
Steven R. Spangler ◽  
Catherine A. Whiting
Keyword(s):  
Magnetic Field ◽  
Remote Sensing ◽  
Solar Wind ◽  
Plasma Density ◽  
Faraday Rotation ◽  
Density Fluctuations ◽  
Line Of Sight ◽  
Small Scale ◽  
Radio Telescopes ◽  
The Magnetic Field

AbstractModern radio telescopes are extremely sensitive to plasma on the line of sight from a radio source to the antenna. Plasmas in the corona and solar wind produce measurable changes in the radio wave amplitude and phase, and the phase difference between wave fields of opposite circular polarization. Such measurements can be made of radio waves from spacecraft transmitters and extragalactic radio sources, using radio telescopes and spacecraft tracking antennas. Data have been taken at frequencies from about 80 MHz to 8000 MHz. Lower frequencies probe plasma at greater heliocentric distances. Analysis of these data yields information on the plasma density, density fluctuations, and plasma flow speeds in the corona and solar wind, and on the magnetic field in the solar corona. This paper will concentrate on the information that can be obtained from measurements of Faraday rotation through the corona and inner solar wind. The magnitude of Faraday rotation is proportional to the line of sight integral of the plasma density and the line-of-sight component of the magnetic field. Faraday rotation provides an almost unique means of estimating the magnetic field in this part of space. This technique has contributed to measurement of the large scale coronal magnetic field, the properties of electromagnetic turbulence in the corona, possible detection of electrical currents in the corona, and probing of the internal structure of coronal mass ejections (CMEs). This paper concentrates on the search for small-scale coronal turbulence and remote sensing of the structure of CMEs. Future investigations with the Expanded Very Large Array (EVLA) or Murchison Widefield Array (MWA) could provide unique observational input on the astrophysics of CMEs.

Plasma density accumulation on a conical surface for diffusion along a diverging magnetic field

2014 ◽  
Vol 21 (4) ◽  
pp. 043502 ◽  
Author(s):  
S. K. Saha ◽  
S. Chowdhury ◽  
M. S. Janaki ◽  
A. Ghosh ◽  
A. K. Hui ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Plasma Density ◽  
Conical Surface

A MODEL HIERARCHY FOR IONOSPHERIC PLASMA MODELING

2004 ◽  
Vol 14 (03) ◽  
pp. 393-415 ◽  
Author(s):  
CHRISTOPHE BESSE ◽  
PIERRE DEGOND ◽  
FABRICE DELUZET ◽  
JEAN CLAUDEL ◽  
GÉRARD GALLICE ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Plasma Density ◽  
Maxwell Equations ◽  
Ionospheric Plasma ◽  
Practical Interest ◽  
Plasma Modeling ◽  
Model Hierarchy ◽  
Great Practical Interest ◽  
Two Fluid ◽  
Insight Into

This paper deals with the modeling of the ionospheric plasma. Starting from the two-fluid Euler–Maxwell equations, we present two hierarchies of models. The MHD hierarchy deals with large plasma density situations while the dynamo hierarchy is adapted to lower density situations. Most of the models encompassed by the dynamo hierarchy are classical ones, but we shall give a unified presentation of them which brings a new insight into their interrelations. By contrast, the MHD hierarchy involves a new (at least to the authors) model, the massless-MHD model. This is a diffusion system for the density and magnetic field which could be of great practical interest. Both hierarchies terminate with the "classical" Striation model, which we shall investigate in detail.

scholarly journals Saturn's Plasma Density Depletions Along Magnetic Field Lines Connected to the Main Rings

2018 ◽  
Vol 45 (16) ◽  
pp. 8104-8110 ◽  
Author(s):  
W. M. Farrell ◽  
L. Z. Hadid ◽  
M. W. Morooka ◽  
W. S. Kurth ◽  
J.‐E. Wahlund ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Plasma Density ◽  
Field Lines
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