Presence Of Parallel Electric Fields Research Articles

Accelerated aqueous nano-film rupture and evaporation induced by electric field: A molecular dynamics approach

The interfacial heat and mass transfer at nano-scale are the key procedure of various phase changes phenomena, and are of significant importance for both science and engineering applications. In the present work, molecular dynamics simulations were applied to investigate the influence of external electric field on the rupture and evaporation of aqueous thin films, which is crucial for bubble coalescence within the context of flotation. The properties of pure water and saline liquid thin films at the absence and presence of parallel electric fields were examined with field intensity ranging from 0.1 to 10V/nm. It was observed that for relatively thick film, which is very stable (4×4×1.45nm) with infinite life time under the electric-field free condition, by incorporating an electric field, the rupture process was significantly accelerated with increases in the field strength. With the field strength reaches up to a threshold at 2–2.5V/nm, the rupture occurred nearly instantly and temperature increased due to molecular friction, a further increase of strength resulted in thermostat’s improper working and the evaporation of molecules. The surface tension exhibits a decreasing trend when the field strength is below 1V/nm, surface tension cannot be correctly measured when the field intensity is above 2V/nm due to the influence of rupture and evaporation. This result provides a theoretical guidance with external electric field for nano-electric transfer, regarding the potential of electro-coalescence between bubbles during flotation process.

Kinetic Alfven wave in the presence of parallel electric field with general loss-cone distribution function: A kinetic approach

In past, kinetic Alfven waves are widely investigated regarding the transfer of energy from the magnetosphere to the ionosphere. These waves are supposed to be responsible for the acceleration of auroral electrons to exhibit auroral phenomena. The existence of parallel electric fields is always reported in association with the kinetic Alfven waves. In the present investigation, assuming parallel electric fields developed by different mechanism, the dispersion relation and growth/damping rate of the kinetic Alfven Wave (KAW) in the presence of parallel electric field are evaluated with general loss-cone distribution using the kinetic approach. The wave frequency w and growth/damping rate gL are obtained for two regimes of propagation k^ri 1, where k^ is perpendicular wave number andri is the ion-gyro radius. The results of the present study show that the frequency w and growth/damping rate of wave depend upon the distribution indices, parallel electric field and k^ri. The generation of kinetic Alfven wave by the combined effect of parallel electric field and loss-cone distribution indices (J), at a particular range of k^ri is noticed. Thus the propagation of kinetic Alfven wave and loss of the Poynting flux from plasma sheet boundary layer (PSBL) to the ionosphere can be explained more effectively on the basis of present investigation. The results of the present study show that the parallel electric field in the presence of loss-cone distribution index is an important parameter to study KAW in the PSBL. The finding of the present investigation is to report that auroral phenomena are suitably described by kinetic Alfven wave in the presence of parallel electric field and the general loss-cone distribution function. Key words: Kinetic Alfven wave, Plasma-sheet-boundary-layer, Parallel electric field, Kinetic theory, Loss-cone distribution function.

Solar wind electron interaction with the dayside lunar surface and crustal magnetic fields: Evidence for precursor effects

Electron distributions measured by Lunar Prospector above the dayside lunar surface in the solar wind often have an energy dependent loss cone, inconsistent with adiabatic magnetic reflection. Energy dependent reflection suggests the presence of downward parallel electric fields below the spacecraft, possibly indicating the presence of a standing electrostatic structure. Many electron distributions contain apparent low energy (<100 eV) upwardgoing conics (58% of the time) and beams (12% of the time), primarily in regions with non-zero crustal magnetic fields, implying the presence of parallel electric fields and/or wave-particle interactions below the spacecraft. Some, but not all, of the observed energy dependence comes from the energy gained during reflection from a moving obstacle; correctly characterizing electron reflection requires the use of the proper reference frame. Nonadiabatic reflection may also play a role, but cannot fully explain observations. In cases with upward-going beams, we observe partial isotropization of incoming solar wind electrons, possibly indicating streaming and/or whistler instabilities. The Moon may therefore influence solar wind plasma well upstream from its surface. Magnetic anomaly interactions and/or non-monotonic near surface potentials provide the most likely candidates to produce the observed precursor effects, which may help ensure quasi-neutrality upstream from the Moon.

Effect of parallel electric field on Alfven wave in thermal magnetoplasma

Dispersion relation, dissipation and growth of Alfven wave in the presence of parallel electric field and electron thermal velocity have been obtained by investigating the trajectories of the charged particles. The effect of parallel electric field is included with the zeroth-order distribution function through modification of the electron thermal velocity parallel to ambient magnetic field. It is found that the parallel electric field and thermal velocity of the electrons enhance the damping/growth rate of the wave according to the direction of electric field. The applicability of theory to explain auroral acceleration in the space plasma has been discussed.

Role of magnetic shear on the electrostatic current driven ion-cyclotron instability in the presence of parallel electric field

Recent observation and theoretical investigations have led to the significance of electrostatic ion cyclotron (EIC) waves in the electrodynamics of acceleration process. The instability is one of the fundamental of a current carrying magnetized plasma. The EIC instability has the lowest threshold current among the current driven instabilities. On the basis of local analysis where inhomogeneities like the magnetic shear and the finite width current channel, have been ignored which is prevalent in the magnetospheric environment. On the basis of non-local analysis interesting modification has been incorporated by the inclusion of magnetic shear. In this paper we provide an analytical approach for the non-local treatment of current driven electrostatic waves in presence of parallel electric field. The growth rate is significantly influenced by the field aligned electron drift. The presence of electric field enhances the growth of EIC waves while magnetic shear stabilizes the system.

Momentum transfer in the combined release and radiation effects satellite plasma injection experiments: The role of parallel electric fields

Optical observations of the combined release and radiation effects satellite (CRRES) plasma injection experiments have revealed signatures of the coupling processes between the injected and ambient plasmas. The elongation of the ion cloud along the geomagnetic field indicated the presence of parallel electric fields. A dense core of ions polarized and E×B drifted along the satellite trajectory for 6–10 s. In an effort to understand the momentum coupling between the two plasma populations, a three-dimensional hybrid code is used. The simulation, which neglected electron inertia, showed a very efficient transfer of momentum via Alfvén waves and the skidding ion core was stopped within 2 s. To reconcile the difference between the observed and simulated skidding times, we propose that the cloud must have been decoupled from the ambient plasma via parallel electric fields. The parallel fields may be associated with inertial Alfvén waves propagating in filamentary current layers at the edges of the ion cloud, or due to a variety of possible plasma instabilities. The results of this study can be applied to coupling processes in other geophysical and astrophysical systems such as cometary environments, Io’s plasma torus, and the auroral regions of the ionosphere and magnetosphere.

Electron cyclotron waves in the presence of parallel electric fields in the Earth's auroral plasma

Abstract. The electron cyclotron waves that originate at low altitudes (&lt;0.5 RE) and observed by ground facilities have been studied in the presence of a weak parallel electric field in auroral magnetoplasma consisting of trapped energetic auroral electrons and cold background electrons of ionospheric origin. The model distribution for auroral trapped electrons is taken as Maxwellian ring distribution. An expression for the growth rate has been obtained in the presence of parallel electric field assuming that the real frequency in the whistler mode is not affected by the presence of the electric field. The results show that waves grow (or damp) in amplitude for a parallel (or antiparallel) electric field. The influence of the electric field is more pronounced at a shorter wavelength spectrum. An increase in population of energetic electrons increases the growth rate and thus, plays a significant role in the wave excitation process in the auroral regions.

Electron cyclotron waves in the presence of parallel electric fields in the Earth’s auroral plasma

The electron cyclotron waves that originate at low altitudes (<0.5 RE) and observed by ground facilities have been studied in the presence of a weak parallel electric field in auroral magnetoplasma consisting of trapped energetic auroral electrons and cold background electrons of ionospheric origin. The model distribution for auroral trapped electrons is taken as Maxwellian ring distribution. An expression for the growth rate has been obtained in the presence of parallel electric field assuming that the real frequency in the whistler mode is not affected by the presence of the electric field. The results show that waves grow (or damp) in amplitude for a parallel (or antiparallel) electric field. The influence of the electric field is more pronounced at a shorter wavelength spectrum. An increase in population of energetic electrons increases the growth rate and thus, plays a significant role in the wave excitation process in the auroral regions.

Parallel electric field-induced instability in the magnetospheric ion-electron plasma

A complete dispersion relation for a whistler mode wave propagation in an anisotropic warm ion-electron magnetoplasma in the presence of parallel electric field using the dispersion relation for a circularly polarized wave has been derived. The dispersion relation includes the effect of anisotropy for the ion and electron velocity distribution functions. The growth rate of electron-ion cyclotron waves for different plasma parameters observed atL = 6.6REhas been computed and the results have been discussed in detail in the light of the observed features of VLF emissions and whistlers. The role of the combination of ion-cyclotron and whistler mode electromagnetic wave propagation along the magnetic field in an anisotropic Maxwellian weakly-ionized magnetoplasma has been studied.

Optically thin H Lyman alpha production on outer planets: Low‐energy proton Acceleration in parallel electric fields and neutral H atom precipitation from ring current

A Monte Carlo model has been constructed to describe the energization and energy degradation of low‐energy protons in an H2 atmosphere in the presence of parallel electric field. The energy spectrum of Ly α collision events is employed to determine the volume emission rate (VER) of H Ly α emissions. Numerical experiments have been performed to study the effect of initial proton energy, electric field, neutral number density, initial pitch angle, and cutoff limit on H Ly α VER. The present study demonstrates that energization of solar EUV‐generated low‐energy protons by parallel electric fields is incapable of producing optically thin Ly α emissions on Uranus through direct collision with H2. However, nonthermal H atoms, produced through acceleration of protons in parallel electric fields, play an important role in enhancing the Ly α intensity through resonant scattering of solar Ly α flux: resulting emissions are consistent with the broadening of the Ly α line observed on Jupiter by IUE. The Monte Carlo model is also applied to the problem of Doppler‐shifted H Ly α emissions from the auroral atmosphere of Jupiter. Energetic neutral H precipitation from the ring current is discussed as a possible source of optically thin H Ly α emissions on outer planets. Estimates are also given for Hα, Hβ, and H2 band emissions resulting from the impact of fast H (of ring current origin) on H2. The input energies and fluxes of precipitating ring current particles are, however, too uncertain to permit definite conclusions.

Jovian magnetospheric ion cyclotron instability in the presence of parallel electric field

A dispersion relation for left hand circularly polarized electromagnetic wave propagation in an anisotropic magnetoplasma in the presence of a very weak parallel electrostatic field has been derived with the help of linearized Vlasov and Maxwell equations. An expression of the growth rate has been derived in presence of parallel electric field for ion-cyclotron electromagnetic wave in an anisotropic media. The modification made in the growth rate by introducing parallel electric field and temperature anisotropy has been studied for fully ionized hydrogen plasma with the help of observations made on Jovian ionosphere and magnetosphere atL = 5.6 Rj. It is concluded that the growth (damping) of ion-cyclotron electromagnetic wave is possible when the wave vector is parallel (antiparallel) to the static electric field and effect is more pronounced at higher wave number.

Excitation of electrostatic wave instability by dc electric field in Earth's magnetoplasma

The dispersion relation for electrostatic wave propagation in an anisotropic warm collisionless magnetoplasma, in the presence of weak parallel (d c) electric field, has been derived analytically. An expression for the growth rate of the electrostatic wave and the marginal stability condition are also derived. The modifications introduced in the growth rate by the electric field and the temperature anisotropy are discussed using plasma parameters observed in the magnetospheric region (4 &lt; L &lt; 10). The effect of the electric field is to increase the growth rate of the electrostatic waves at different electron cyclotron harmonics, whereas the effect of the temperature anisotropy is to decrease the growth rate. The presence of parallel electric field may excite the electrostatic emissions at different electron cyclotron harmonics. The most unstable band of wave frequencies obtained with the aid of computations lies between 5 kHz and 10 kHz. These wave frequencies are well within the experimentally observed frequencies of electrostatic emissions. Therefore such a study would not only explain the observed satellite features of the electrostatic wave emissions but would also account for the diagnostics of the magnetospheric plasma parameters.

Monte Carlo simulation of photoelectron energization in parallel electric fields: Electroglow on Uranus

A Monte Carlo simulation of photoelectron energization and energy degradation in H2 gas in the presence of parallel electric fields has been carried out. Numerical yield spectra which contain information about the electron energy degradation process and can be used to calculate the yield for any inelastic event are obtained. The variation of yield spectra with incident electron energy, electric field, pitch angle, and cutoff limit has been studied. The yield function is employed to determine the photoelectron fluxes. H2 Lyman and Werner band excitation rates and integrated column intensity are computed for three different electric field profiles taking various low‐energy cutoff limits. It is found that an electric field profile with peak value of 4 mV/m at neutral number density of 3×1010 cm−3 produces enhanced volume emission rates of H2 bands [λ &lt; 1100 Å] explaining about 20% of the observed electroglow emission on Uranus. The effect of solar zenith angle and solar cycle variation on peak excitation rate is discussed.

Effect of spectral distribution of energetic electrons on wave-particle interaction and precipitated energy input

The precipitated energy flux as affected by the presence of parallel electric field and geomagnetic field distortions have been obtained using a complete kinetic treatment of pitch angle scattering by whistler waves. Four different energy spectra have been used to show that the precipitated energy flux depends on the spectral details of the interacting electron ensemble.

Effect of parallel electric field on charged particle precipitation

Considering the presence of electric field parallel to geomagnetic field in the magnetosphere, the problem of wave-particle interaction has been considered. Dispersion equation of whistler mode wave in presence of parallel electric field has been derived. Using the effective dispersion equation, the wave-particle interaction has been reformulated to account for the effect of parallel electric field. Using charged particle energy spectrum and magnetospheric field and plasma models, the flux of electron precipitation has been computed. It is shown that the parallel electric field plays an important role and may work in simultaneity with other processes known for enhancement of electron precipitation.

On the lowest altitude S3‐3 observations of electrostatic shocks and parallel electric fields

S3‐3 satellite observations of low altitude electrostatic shocks on auroral zone field lines indicate the presence of parallel electric fields below an altitude of 2000 km and probably below 1100 km. These conclusions result from the direct observation of parallel fields, from inference based on the V‐shaped equipotential contours associated with some shocks, and from the fact that perpendicular fields with magnitudes as large as those observed in shocks are not seen in the ionosphere.

On the modifications of the whistler mode instability in the magnetosphere in the presence of parallel electric field by cold plasma injection

Dispersion relation for the whistler mode waves in an anisotropic warm magnetoplasma in the presence of a parallel electric field has been derived. The modifications in the whistler mode instability produced by cold plasma injection to an infinite uniform anisotropic plasma (A &lt;1) in the presence of a parallel electric field have been studied. This study has been performed with the plasma parameters similar to those observed in the equatorial magnetosphere at 6.6 RE. The electric field is found to have pronounced effect for small values of nc/nw and extends the range of instability in k space toward higher wavelengths. The cold plasma injection increases the range of instability in k space toward lower wave lengths. The effects of electric field seem to be insignificant for large values of nc/nw.

A comparison between N2+4278-Å emission and electron flux in the auroral zone

Visual airglow and low-energy electron experiment data from the Atmosphere Explorer D satellite are used to measure variations in N2(+) density and mixing in the nighttime auroral zone. The intensity of the 4278-A N2(+) emission, proportional to energy flux deposited in N2 by energetic electrons, is determined by a method which corrects for ground reflection affecting the satellite data. Calculations related to electron energy flux are found to show a slight variance from the theoretical predictions of Rees and Luckey (1974). Evidence for high-energy proton precipitation on the southern edge of the aurora and for the presence of parallel electric fields in the altitude range 150 to 800 km is also discussed.

Effect of parallel electric fields on the whistler mode wave propagation in the magnetosphere

The effect of parallel electric fields on whistler mode wave propagation has been studied. To account for the parallel electric fields, the dispersion equation has been analyzed, and refractive index surfaces for magnetospheric plasma have been constructed. The presence of parallel electric fields deforms the refractive index surfaces which diffuse the energy flow and produce defocusing of the whistler mode waves. The parallel electric field induces an instability in the whistler mode waves propagating through the magnetosphere. The growth or decay of whistler mode instability depends on the direction of parallel electric fields. It is concluded that the analyses of whistler wave records received on the ground should account for the role of parallel electric fields.