scholarly journals Some aspects of double layer formation in a plasma constrained by a magnetic mirror

1987 ◽  
Vol 5 (2) ◽  
pp. 315-324 ◽  
Author(s):  
W. Lennartsson
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Double Layer ◽  
Large Scale ◽  
Scale Effects ◽  
Distribution Functions ◽  
Electrons And Ions ◽  
Auroral Electrons ◽  
Complex Electric Field ◽  
Necessary And Sufficient

The discussion of parallel electric fields in the earth's magnetosphere has undergone a notable shift of emphasis in recent years, away from wave-generated anomalous resistivity towards the more large-scale effects of magnetic confinement of current carrying plasmas. This shift has been inspired in large part by the more extensive data on auroral particle distribution functions that have been made available, data that may often seem consistent with a dissipation-free acceleration of auroral electrons over an extended altitude range.Efforts to interpret these data have brought new vigor to the concept that a smooth and static electric field can be self-consistently generated by suitable pitch-angle anisotropies among the high-altitude particle populations, different for electrons and ions, and that such an electric field is both necessary and sufficient to maintain the plasma in a quasi-neutral steady state. This paper reviews and criticizes certain aspects of this concept, both from a general theoretical standpoint and from the standpoint of what we know about the magnetospheric environment. It is argued that this concept has flaws and that the actual physical problem is considerably more complicated, requiring a more complex electric field, possibly including double layer structures.

Intercomponent Momentum Transport and Electrical Conductivity of Collisionless Plasma

1973 ◽  
Vol 51 (24) ◽  
pp. 2604-2611 ◽  
Author(s):  
H. E. Wilhelm
Keyword(s):  
Electrical Conductivity ◽  
Electric Field ◽  
Collisionless Plasma ◽  
Electrical Current ◽  
Distribution Functions ◽  
Momentum Transport ◽  
Ion Drift ◽  
Moment Approximation ◽  
Electrons And Ions ◽  
Two Component

Based on the Lenard–Balescu equation, the interaction integral for the intercomponent momentum transfer in a two-component, collisionless plasma is evaluated in closed form. The distribution functions of the electrons and ions are represented in the form of nonisothermal, displaced Max wellians corresponding to the 5-moment approximation. As an application, the transport of electrical current in an electric field is discussed for infrasonic up to sonic electron–ion drift velocities.

scholarly journals Effect of double layers on magnetosphere–ionosphere coupling

1987 ◽  
Vol 5 (2) ◽  
pp. 351-366 ◽  
Author(s):  
Robert L. Lysak ◽  
Mary K. Hudson
Keyword(s):  
Wave Propagation ◽  
Electric Field ◽  
Double Layer ◽  
Large Scale ◽  
Debye Length ◽  
Plasma Temperature ◽  
Auroral Zone ◽  
Alfven Wave ◽  
Scale Model ◽  
Double Layers

The earth's auroral zone contains dynamic processes occurring on scales from the length of an auroral zone field line (about 10RE) which characterizes Alfven wave propagation to the scale of microscopic processes which occur over a few Debye lengths (less than 1 km). These processes interact in a time-dependent fashion since the current carried by the Alfven waves can excite microscopic turbulence which can in turn provide dissipation of the Alfven wave energy. This review will first describe the dynamic aspects of auroral current structures with emphasis on consequences for models of microscopic turbulence. In the second part of the paper a number of models of microscopic turbulence will be introduced into a large scale model of Alfven wave propagation to determine the effect of various models on the overall structure of auroral currents. In particular, we will compare the effect of a double layer electric field which scales with the plasma temperature and Debye length with the effect of anomalous resistivity due to electrostatic ion cyclotron turbulence in which the electric field scales with the magnetic field strength. It is found that the double layer model is less diffusive than the resistive model leading to the possibility of narrow, intense current structures.

scholarly journals The genomic basis of electrotaxis in Dictyostelium discoideum: Electric field sensitive amino acids are dynamically encoded en masse for the streaming-stage proteome

2015 ◽  
Author(s):  
Albert J Erives
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Electric Field ◽  
Electric Fields ◽  
Large Scale ◽  
Genetic Model ◽  
Critical Role ◽  
Axon Growth ◽  
Amino Acid Residues ◽  
Signaling Systems

Electrotaxis plays a critical role in developmental cell migration, axon growth cone guidance, epithelial wound healing, tissue regeneration, and the degree of invasiveness characterizing different cancer cell lines. During electrotaxis in a direct current electric field (EF), a cell migrates preferentially either towards the anode or cathode depending on the cell-type. However, the types and ranges of mechanisms coupling trans-cellular electric fields to cellular EF-sensitive signaling systems are largely unknown. To address this cell biological phenomenon, I use transcriptomic data from a developmental genetic model in which multicellular social aggregation is induced by starvation of amoeboid cells. I find that the developmental proteome expressed during the streaming aggregation stage is measurably and substantially enriched in charged and highly polar amino acids relative to the proteomes of either the unicellular amoeboid or the multicellular fruiting body. This large-scale coding augmentation of EF-sensitive amino acid residues in thousands of streaming-specific proteins is accompanied by a proportional coding decrease in the number of small, uncharged amino acid residues. I also confirm an expected coding increase of biosynthetically costly amino acids in the proteome of the satiated feeding-stage amoeboid. These findings suggest that electrotactic capability is encoded broadly in the genetically regulated deployment of a developmental proteome with augmented EF-sensitivity. These results signify that extreme, nonuniform, evolutionary constraints can be exerted on the amino acid composition of an organism’s proteome.

scholarly journals Vlasov simulations of trapping and loss of auroral electrons

2015 ◽  
Vol 33 (3) ◽  
pp. 279-293 ◽  
Author(s):  
H. Gunell ◽  
L. Andersson ◽  
J. De Keyser ◽  
I. Mann
Keyword(s):  
Double Layer ◽  
Electron Distribution ◽  
Electron Distribution Function ◽  
Distribution Functions ◽  
Initial State ◽  
Voltage Electron ◽  
Auroral Electrons ◽  
History Of ◽  
Auroral Current ◽  
Acceleration Voltage

Abstract. The plasma on an auroral field line is simulated using a Vlasov model. In the initial state, the acceleration region extends from one to three Earth radii in altitude with about half of the acceleration voltage concentrated in a stationary double layer at the bottom of this region. A population of electrons is trapped between the double layer and their magnetic mirror points at lower altitudes. A simulation study is carried out to examine the effects of fluctuations in the total accelerating voltage, which may be due to changes in the generator or the load of the auroral current circuit. The electron distribution function on the high potential side of the double layer changes significantly depending on whether the perturbation is toward higher or lower voltages, and therefore measurements of electron distribution functions provide information about the recent history of the voltage. Electron phase space holes are seen as a result of the induced fluctuations. Most of the voltage perturbation is assumed by the double layer. Hysteresis effects in the position of the double layer are observed when the voltage first is lowered and then brought back to its initial value.

Strong-field electrophoresis

2012 ◽  
Vol 701 ◽  
pp. 333-351 ◽  
Author(s):  
Ory Schnitzer ◽  
Ehud Yariv
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Double Layer ◽  
Strong Field ◽  
Salt Flux ◽  
Large Reynolds Number ◽  
Diffuse Part ◽  
Electrophoretic Velocity ◽  
Diffusive Boundary ◽  
Diffusive Fluxes

AbstractWe analyse particle electrophoresis in the thin-double-layer limit for asymptotically large applied electric fields. Specifically, we consider fields scaling as ${\delta }^{\ensuremath{-} 1} $, $\delta ~(\ll \hspace *{-2pt}1)$ being the dimensionless Debye thickness. The dominant advection associated with the intense flow mandates a uniform salt concentration in the electro-neutral bulk. The $O({\delta }^{\ensuremath{-} 1} )$ large tangential fields in the diffuse part of the double layer give rise to a novel ‘surface conduction’ mechanism at moderate zeta potentials, where the Dukhin number is vanishingly small. The ensuing $O(1)$ electric current emerging from the double layer modifies the bulk electric field; the comparable $O(1)$ transverse salt flux, on the other hand, is incompatible with the nil diffusive fluxes at the homogeneous bulk. This contradiction is resolved by identifying the emergence of a diffusive boundary layer of $O({\delta }^{1/ 2} )$ thickness, resembling thermal boundary layers at large-Reynolds-number flows. The modified electric field within the bulk gives rise to an irrotational flow, resembling those in moderate-field electrophoresis. At leading order, the particle electrophoretic velocity is provided by Smoluchowski’s formula, describing linear variation with applied field.

scholarly journals Control of Spreading Depression with Electrical Fields

2018 ◽  
Author(s):  
Andrew J. Whalen ◽  
Ying Xiao ◽  
Herve Kadji ◽  
Markus Dahlem ◽  
Bruce J. Gluckman ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Large Scale ◽  
Spreading Depression ◽  
Brain Slices ◽  
Propagation Path ◽  
Field Polarity ◽  
Biophysical Models ◽  
Control And Prevention ◽  
Cellular Swelling

AbstractSpreading depression or depolarization is a large-scale pathological brain phenomenon related to migraine, stroke, hemorrhage and traumatic brain injury. Once initiated, spreading depression propagates across gray matter extruding potassium and other active molecules, collapsing the resting membrane electro-chemical gradient of cells leading to spike inactivation and cellular swelling, and propagates independently of synaptic transmission. We demonstrate the modulation, suppression and prevention of spreading depression utilizing applied transcortical DC electric fields in brain slices, measured with intrinsic optical imaging and potassium dye epifluorescence. We experimentally observe a surface-positive electric field induced forcing of spreading depression propagation to locations in cortex deeper than the unmodulated propagation path, whereby further propagation is confined and arrested even after field termination. The opposite surface-negative electric field polarity produces an increase in propagation velocity and a confinement of the wave to more superficial layers of cortex than the unmodulated propagation path. These field polarities are of opposite sign to the polarity that blocks neuronal spiking and seizures, and are consistent with biophysical models of spreading depression. The results demonstrate the potential feasibility of electrical control and prevention of spreading depression.

scholarly journals Observations of the generation of eastward equatorial electric fields near dawn

2014 ◽  
Vol 32 (9) ◽  
pp. 1169-1175 ◽  
Author(s):  
M. C. Kelley ◽  
F. S. Rodrigues ◽  
R. F. Pfaff ◽  
J. Klenzing
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Plasma Density ◽  
Large Scale ◽  
Field Measurements ◽  
Equatorial Ionosphere ◽  
Winter Solstice ◽  
The Pacific ◽  
Density Perturbations ◽  
Forecasting System

Abstract. We report and discuss interesting observations of the variability of electric fields and ionospheric densities near sunrise in the equatorial ionosphere made by instruments onboard the Communications/Navigation Outage Forecasting System (C/NOFS) satellite over six consecutive orbits. Electric field measurements were made by the Vector Electric Field Instrument (VEFI), and ionospheric plasma densities were measured by Planar Langmuir Probe (PLP). The data were obtained on 17 June 2008, a period of solar minimum conditions. Deep depletions in the equatorial plasma density were observed just before sunrise on three orbits, for which one of these depletions was accompanied by a very large eastward electric field associated with the density depletion, as previously described by de La Beaujardière et al. (2009), Su et al. (2009) and Burke et al. (2009). The origin of this large eastward field (positive upward/meridional drift), which occurred when that component of the field is usually small and westward, is thought to be due to a large-scale Rayleigh–Taylor process. On three subsequent orbits, however, a distinctly different, second type of relationship between the electric field and plasma density near dawn was observed. Enhancements of the eastward electric field were also detected, one of them peaking around 3 mV m−1, but they were found to the east (later local time) of pre-dawn density perturbations. These observations represent sunrise enhancements of vertical drifts accompanied by eastward drifts such as those observed by the San Marco satellite (Aggson et al., 1995). Like the San Marco measurements, the enhancements occurred during winter solstice and low solar flux conditions in the Pacific longitude sector. While the evening equatorial ionosphere is believed to present the most dramatic examples of variability, our observations exemplify that the dawn sector can be highly variable as well.

scholarly journals Astrid-2 and ground-based observations of the auroral bulge in the middle of the nightside convection throat

2001 ◽  
Vol 19 (6) ◽  
pp. 633-641 ◽  
Author(s):  
G. T. Marklund ◽  
T. Karlsson ◽  
P. Eglitis ◽  
H. Opgenoorth
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Large Scale ◽  
Current Model ◽  
Energetic Electron ◽  
Auroral Oval ◽  
Plasma Convection ◽  
Magnetometer Data ◽  
Electric Fields And Currents ◽  
Good Agreement

Abstract. Results concerning the electrodynamics of the nightside auroral bulge are presented based on simultaneous satellite and ground-based observations. The satellite data include Astrid-2 measurements of electric fields, currents and particles from a midnight auroral oval crossing and Polar UVI images of the large-scale auroral distribution. The ground-based observations include STARE and SuperDARN electric fields and magnetic records from the Greenland and MIRACLE magnetometer network, the latter including stations from northern Scandinavia north to Svalbard. At the time of the Astrid-2 crossing the ground-based data reveal intense electrojet activity, both to the east and west of the Astrid-2 trajectory, related to the Polar observations of the auroral bulge but not necessarily to a typical substorm. The energetic electron fluxes measured by Astrid-2 across the auroral oval were generally weak being consistent with a gap observed in the auroral luminosity distribution. The electric field across the oval was directed westward, intensifying close to the poleward boundary followed by a decrease in the polar cap. The combined observations suggests that Astrid-2 was moving close to the separatrix between the dusk and dawn convection cells in a region of low conductivity. The constant westward direction of the electric field across the oval indicates that current continuity was maintained, not by polarisation electric fields (as in a Cowling channel), but solely by localized up- and downward field-aligned currents in good agreement with the Astrid-2 magnetometer data. The absence of a polarisation electric field and thus of an intense westward closure current between the dawn and dusk convection cells is consistent with the relatively weak precipitation and low conductivity in the convection throat. Thus, the Cowling current model is not adequate for describing the electrodynamics of the nightside auroral bulge treated here.Key words. Ionosphere (auroral ionosphere; electric fields and currents; plasma convection)

scholarly journals Equatorial electrojet as part of the global circuit: a case-study from the IEEY

1998 ◽  
Vol 16 (6) ◽  
pp. 698-710 ◽  
Author(s):  
A. T. Kobea ◽  
C. Amory-Mazaudier ◽  
J. M. Do ◽  
H. Lühr ◽  
E. Houngninou ◽  
...  
Keyword(s):  
Electric Field ◽  
Geomagnetic Storm ◽  
Electric Fields ◽  
High Latitude ◽  
Large Scale ◽  
Equatorial Electrojet ◽  
Doppler Frequency ◽  
Time Interval ◽  
Ground Field ◽  
Equatorial Latitude

Abstract. Geomagnetic storm-time variations often occur coherently at high latitude and the day-side dip equator where they affect the normal eastward Sq field. This paper presents an analysis of ground magnetic field and ionospheric electrodynamic data related to the geomagnetic storm which occured on 27 May 1993 during the International Equatorial Electrojet Year (IEEY) experiment. This storm-signature analysis on the auroral, mid-latitude and equatorial ground field and ionospheric electrodynamic data leads to the identification of a sensitive response of the equatorial electrojet (EEJ) to large-scale auroral return current: this response consists in a change of the eastward electric field during the pre-sunrise hours (0400-0600 UT) coherently to the high-, mid-, and equatorial-latitude H decrease and the disappearance of the EEJ irregularities between the time-interval 0800-0950 UT. Subsequent to the change in h'F during pre-sunrise hours, the observed foF2 increase revealed an enhancement of the equatorial ionization anomaly (EIA) caused by the high-latitude penetrating electric field. The strengthening of these irregularities attested by the Doppler frequency increase tracks the H component at the equator which undergoes a rapid increase around 0800 UT. The ∆H variations observed at the equator are the sum of the following components: SR, DP, DR, DCF and DT.Keywords. Equatorial electrojet · Magnetosphere-ionosphere interactions · Electric fields and currents · Auroral ionosphere · Ionospheric disturbances

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