scholarly journals Measurement of current density fluctuations and ambipolar particle flux due to magnetic fluctuations in MST

1992 ◽  
Author(s):  
Weimin Shen
Keyword(s):  
Current Density ◽  
Particle Flux ◽  
Density Fluctuations ◽  
Magnetic Fluctuations

scholarly journals On the structure of field-aligned currents in the mid-altitude cusp

2006 ◽  
Vol 24 (12) ◽  
pp. 3391-3401 ◽  
Author(s):  
A. Marchaudon ◽  
J.-C. Cerisier ◽  
J.-M. Bosqued ◽  
C. J. Owen ◽  
A. N. Fazakerley ◽  
...  
Keyword(s):  
Current Density ◽  
Particle Flux ◽  
Convective Motion ◽  
Magnetic Fluctuations ◽  
Current Sheets ◽  
Total Particle ◽  
Flux Measurements ◽  
Parallel Current ◽  
Particle Current ◽  
East West

Abstract. We analyse two crossings of the polar cusp at mid-altitudes (≈4 RE) by Cluster in order to study the structure of field-aligned currents associated with the injection of magnetosheath plasma. The current density is deduced independently from magnetic field and from particle flux measurements. In both cases the data are carefully tested. Magnetic fluctuations are analysed by discriminating between those compatible with the plane current sheet hypothesis under which the current density can be calculated safely, and those resulting from filamentary current structures. At medium transverse scales (80 km), the structure of the currents is more often tube-like than sheet-like, and current sheets are not systematically elongated in the east-west direction. The total particle current is calculated from the electron and ion measurements. For electrons, the full energy range is taken into account, from above the photoelectron threshold up to 32 keV. Magnetosheath plasma injections are well correlated with pairs of field-aligned currents. In both cases, the parallel current is mainly carried by electrons while ions contribute for about 20%. In the plane current sheets, the ratio between magnetic and particle currents shows large variations between 0.4 and 1.1. These fluctuations can be explained by the convective motion of the current sheets.

Laser Faraday rotation measurement of current density fluctuations and electromagnetic torque (invited)

2004 ◽  
Vol 75 (10) ◽  
pp. 3387-3392 ◽  
Author(s):  
W. X. Ding ◽  
D. L. Brower ◽  
B. H. Deng ◽  
D. Craig ◽  
S. C. Prager ◽  
...  
Keyword(s):  
Faraday Rotation ◽  
Current Density ◽  
Density Fluctuations ◽  
Electromagnetic Torque ◽  
Rotation Measurement

scholarly journals Current density fluctuations and ambipolarity of transport

1991 ◽  
Author(s):  
W. Shen ◽  
R.N. Dexter ◽  
S.C. Prager
Keyword(s):  
Current Density ◽  
Density Fluctuations

scholarly journals Simulating diverse instabilities of dust in magnetized gas

2020 ◽  
Vol 496 (2) ◽  
pp. 2123-2154 ◽  
Author(s):  
Philip F Hopkins ◽  
Jonathan Squire ◽  
Darryl Seligman
Keyword(s):  
Magnetic Fields ◽  
Radiation Pressure ◽  
Homogeneous Medium ◽  
Density Fluctuations ◽  
Charged Dust ◽  
Magnetic Fluctuations ◽  
Velocity Fluctuations ◽  
Drag Forces ◽  
Dust Plasma ◽  
External Acceleration

ABSTRACT Recently, Squire & Hopkins showed that charged dust grains moving through magnetized gas under the influence of a uniform external force (such as radiation pressure or gravity) are subject to a spectrum of instabilities. Qualitatively distinct instability families are associated with different Alfvén or magnetosonic waves and drift or gyro motion. We present a suite of simulations exploring these instabilities, for grains in a homogeneous medium subject to an external acceleration. We vary parameters such as the ratio of Lorentz-to-drag forces on dust, plasma β, size scale, and acceleration. All regimes studied drive turbulent motions and dust-to-gas fluctuations in the saturated state, rapidly amplify magnetic fields into equipartition with velocity fluctuations, and produce instabilities that persist indefinitely (despite random grain motions). Different parameters produce diverse morphologies and qualitatively different features in dust, but the saturated gas state can be broadly characterized as anisotropic magnetosonic or Alfvénic turbulence. Quasi-linear theory can qualitatively predict the gas turbulent properties. Turbulence grows from small to large scales, and larger scale modes usually drive more vigorous gas turbulence, but dust velocity and density fluctuations are more complicated. In many regimes, dust forms structures (clumps, filaments, sheets) that reach extreme overdensities (up to ≫109 times mean), and exhibit substantial substructure even in nearly incompressible gas. These can be even more prominent at lower dust-to-gas ratios. In other regimes, dust self-excites scattering via magnetic fluctuations that isotropize and amplify dust velocities, producing fast, diffusive dust motions.

Density and magnetic field fluctuations observed by ISEE 1-2 in the quiet magnetosheath

1995 ◽  
Vol 13 (4) ◽  
pp. 343-357 ◽  
Author(s):  
C. Lacombe ◽  
G. Belmont ◽  
D. Hubert ◽  
C. C. Harvey ◽  
A. Mangeney ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Phase Relation ◽  
Dynamic Pressure ◽  
Density Fluctuations ◽  
Distribution Functions ◽  
Linear Wave ◽  
Magnetic Fluctuations ◽  
Ion Distribution ◽  
Maxwellian Plasma ◽  
The Magnetic Field

Abstract. We analyse the fluctuations of the electron density and of the magnetic field in the Earth's magnetosheath to identify the waves observed below the proton gyrofrequency. We consider two quiet magnetosheath crossings i.e. 2 days characterized by small-amplitude waves, for which the solar wind dynamic pressure was low. On 2 August 1978 the spacecraft were in the outer magnetosheath. We compare the properties of the observed narrow-band waves with those of the unstable linear wave modes calculated for an homogeneous plasma with Maxwellian electron and bi-Maxwellian (anisotropic) proton and alpha particle distributions. The Alfvén ion cyclotron (AIC) mode appears to be dominant in the data, but there are also density fluctuations nearly in phase with the magnetic fluctuations parallel to the magnetic field. Such a phase relation can be explained neither by the presence of a proton or helium AIC mode nor by the presence of a fast mode in a bi-Maxwellian plasma. We invoke the presence of the helium cut-off mode which is marginally stable in a bi-Maxwellian plasma with α particles: the observed phase relation could be due to a hybrid mode (proton AIC+helium cut-off ) generated by a non-Maxwellian or a non-gyrotropic part of the ion distribution functions in the upstream magnetosheath. On 2 September 1981 the properties of the fluctuations observed in the middle of the magnetosheath can be explained by pure AIC waves generated by protons which have reached a bi-Maxwellian equilibrium. For a given wave mode, the phase difference between B\\Vert and the density is sensitive to the shape of the ion and electron distribution functions: it can be a diagnosis tool for natural and simulated plasmas.

Study of Radial Particle Flux due to Phase Difference Between Potential and Density Fluctuations

2009 ◽  
Vol 55 (2T) ◽  
pp. 168-171 ◽  
Author(s):  
Yoshiaki Miyata ◽  
Masayuki Yoshikawa ◽  
Masanori Mizuguchi ◽  
Youhei Oono ◽  
Yousuke Nakashima ◽  
...  
Keyword(s):  
Phase Difference ◽  
Particle Flux ◽  
Density Fluctuations

Electromagnetic turbulence in increased β plasmas in the Large Plasma Device

2021 ◽  
Vol 87 (4) ◽  
Author(s):  
G.D. Rossi ◽  
T.A. Carter ◽  
B. Seo ◽  
J. Robertson ◽  
M.J. Pueschel ◽  
...  
Keyword(s):  
Dynamic Pressure ◽  
Relative Magnitude ◽  
Density Fluctuations ◽  
Magnetized Plasma ◽  
Strongly Correlated ◽  
Magnetic Fluctuations ◽  
Pressure Balance ◽  
Plasma Device ◽  
Field Fluctuations ◽  
Large Plasma Device

The variation of pressure-gradient-driven turbulence with plasma $\beta$ (up to $\beta \approx 15\,\%$ ) is investigated in linear, magnetized plasma. The magnitude of magnetic fluctuations is observed to increase substantially with increasing $\beta$ . More importantly, parallel magnetic fluctuations are observed to dominate at higher $\beta$ values, with $\delta B_\parallel / \delta B_\perp \approx 2$ and $\delta B / B_0 \approx 1\,\%$ . Parallel magnetic fluctuations are strongly correlated with density fluctuations and the two are observed to be out of phase. The relative magnitude of and cross-phase between density and parallel magnetic field fluctuations are consistent with the dynamic pressure balance ( $P+{B_{0}^2}/{2\mu _0} = \textrm {constant}$ ). A local slab model theory for electromagnetic, modified drift Alfvén waves, including parallel magnetic fluctuations, shows partial agreement with experimental observations.

Magnetic fluctuations associated with density fluctuations in the tokamak edge

1989 ◽  
Vol 29 (1) ◽  
pp. 99-103 ◽  
Author(s):  
Y.J. Kim ◽  
K.W. Gentle ◽  
C.P. Ritz ◽  
T.L. Rhodes ◽  
R.D. Bengtson
Keyword(s):  
Density Fluctuations ◽  
Magnetic Fluctuations ◽  
Tokamak Edge

Magnetohydrodynamic parametric instabilities driven by a standing Alfvén wave in a low-β plasma

1996 ◽  
Vol 56 (2) ◽  
pp. 251-264 ◽  
Author(s):  
L. P. L. Oliveira ◽  
A. C.-L. Chian
Keyword(s):  
Mode Coupling ◽  
Wave Equations ◽  
Maximum Growth ◽  
Finite Amplitude ◽  
Maximum Growth Rate ◽  
Density Fluctuations ◽  
Alfven Wave ◽  
Magnetic Fluctuations ◽  
Parametric Instabilities ◽  
The Stability

The stability of a finite-amplitude standing Alfvén wave of circular polarization in a low-β plasma is studied using a set of nonlinearly coupled MHD wave equations. In the presence of a standing Alfvén pump, two distinct gratings associated with the density fluctuations are excited: those due to the ponderomotive beating of the pump magnetic field, and those due the induced magnetic fluctuations. The roles played by the two gratings in the mode coupling are analysed. Both convective and purely growing regimes of the MHD parametric instabilities can be produced by a standing Alfvén wave. In both regimes, the maximum growth rate increases as the pump amplitude increases, and decreases as increases. Tn the presence of the second grating, a new unstable convective regime appears that widens the overall instability bandwidth.

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