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

1997 ◽  
Vol 15 (1) ◽  
pp. 24-28 ◽  
Author(s):  
S. Kumar ◽  
S. K. Dixit ◽  
A. K. Gwal
Keyword(s):  
Growth Rate ◽  
Electric Field ◽  
Electric Fields ◽  
Electron Cyclotron ◽  
Wave Excitation ◽  
Parallel Electric Field ◽  
Excitation Process ◽  
Auroral Plasma ◽  
Auroral Electrons ◽  
Electron Cyclotron Waves

Abstract. 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.

scholarly journals Double layers in the downward current region of the aurora

2003 ◽  
Vol 10 (1/2) ◽  
pp. 45-52 ◽  
Author(s):  
R. E. Ergun ◽  
L. Andersson ◽  
C. W. Carlson ◽  
D. L. Newman ◽  
M. V. Goldman
Keyword(s):  
Magnetic Field ◽  
Electron Beam ◽  
Phase Space ◽  
Electric Field ◽  
Electric Fields ◽  
Double Layers ◽  
Parallel Electric Field ◽  
Electrostatic Waves ◽  
Current Region ◽  
Decisive Evidence

Abstract. Direct observations of magnetic-field-aligned (parallel) electric fields in the downward current region of the aurora provide decisive evidence of naturally occurring double layers. We report measurements of parallel electric fields, electron fluxes and ion fluxes related to double layers that are responsible for particle acceleration. The observations suggest that parallel electric fields organize into a structure of three distinct, narrowly-confined regions along the magnetic field (B). In the "ramp" region, the measured parallel electric field forms a nearly-monotonic potential ramp that is localized to ~ 10 Debye lengths along B. The ramp is moving parallel to B at the ion acoustic speed (vs) and in the same direction as the accelerated electrons. On the high-potential side of the ramp, in the "beam" region, an unstable electron beam is seen for roughly another 10 Debye lengths along B. The electron beam is rapidly stabilized by intense electrostatic waves and nonlinear structures interpreted as electron phase-space holes. The "wave" region is physically separated from the ramp by the beam region. Numerical simulations reproduce a similar ramp structure, beam region, electrostatic turbulence region and plasma characteristics as seen in the observations. These results suggest that large double layers can account for the parallel electric field in the downward current region and that intense electrostatic turbulence rapidly stabilizes the accelerated electron distributions. These results also demonstrate that parallel electric fields are directly associated with the generation of large-amplitude electron phase-space holes and plasma waves.

scholarly journals Parallel electric field structures associated with the low-frequency oscillations in the auroral plasma

2006 ◽  
Vol 58 (9) ◽  
pp. 1227-1232 ◽  
Author(s):  
R. V. Reddy ◽  
S. V. Singh ◽  
G. S. Lakhina ◽  
R. Bharuthram
Keyword(s):  
Electric Field ◽  
Low Frequency ◽  
Parallel Electric Field ◽  
Low Frequency Oscillations ◽  
Auroral Plasma

scholarly journals THE EFFECT OF CRITICAL ELECTRIC FIELDS ON THE ELECTRONIC DISTRIBUTION OF BILAYER ARMCHAIR GRAPHENE NANORIBBONS

2021 ◽  
pp. 98-112
Author(s):  
Lam Thuy Duong Nguyen ◽  
Thi Kim Quyen Nguyen ◽  
Nguyen Huu Hanh Pham ◽  
Dang Khoa Le ◽  
Van Chinh Ngo ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Energy Band ◽  
Graphene Nanoribbons ◽  
Strong Impact ◽  
Parallel Electric Field ◽  
Electronic Distribution ◽  
Wide Range ◽  
Armchair Graphene Nanoribbons ◽  
Armchair Graphene

We employed tight-binding calculations and Green’s function formalism to investigate the effect of applied electric fields on the energy band and electronic properties of bilayer armchair graphene nanoribbons (BL-AGNRs). The results show that the perpendicular electric field has a strong impact on modifying and controlling the bandgap of BL-AGNRs. At the critical values of this electric field, distortions of energy dispersion in subbands and the formation of new electronic excitation channels occur strongly. These originate from low-lying energies near the Fermi level and move away from the zero-point with the increment of the electric field. Phase transitions and structural changes clearly happen in these materials. The influence of the parallel electric field is less important in changing the gap size, resulting in the absence of the critical voltage over a very wide range [–1.5 V; 1.5 V] for the semiconductor-insulator group. Nevertheless, it is interesting to note the powerful role of the parallel electric field in modifying the energy band and electronic distribution at each energy level. These results contribute to an overall picture of the physics model and electronic structure of BL-AGNRs under stimuli, which can be a pathway to real applications in the future, particularly for electronic devices.

scholarly journals Study of Electron Beam on Electron Cyclotron Waves with AC Field in the Magnetosphere of Uranus

2017 ◽  
Vol 6 (4) ◽  
pp. 90-100
Author(s):  
R. Kaur ◽  
R. S. Pandey
Keyword(s):  
Growth Rate ◽  
High Energy ◽  
Electron Cyclotron ◽  
Magnetic Field Direction ◽  
Number Density ◽  
Temperature Anisotropy ◽  
Real Frequency ◽  
Oblique Propagation ◽  
High Energy Tail ◽  
Electron Cyclotron Waves

In this paper, we investigate the electromagnetic electron cyclotron (EMEC) waves in the magnetosphere of Uranus. By using the method of characteristic solution, the expression for dispersion relation is drawn. Following kinetic approach, the growth rate and real frequency of EMEC waves is studied theoretically, considering the injection of cold plasma beam in the Uranian system. The observations made by a space probe launched by NASA, Voyager 2, showed unusual orientation of planet’s spin axis and presence of more particles in high energy tail in Uranian magnetospheric plasma. Therefore, in this paper Kappa distribution is employed instead of usual Maxwellian distribution. The study is extended to the parallel as well as the oblique propagation of EMEC waves with variation in temperature anisotropy, number density of electrons and angle of propagation with respect to magnetic field direction. It is found that these parameters support the growth rate of EMEC waves. But response of real frequency of these waves is not same as that of growth rate for all the cases. Numerical analysis also revealed that as the ratio of number density of cold to hot plasma increases growth rate of EMEC waves also increases. Thus, denser the beam is injected, more the growth can be observed. These results are appropriate for applications to space plasma environments and magnetospheric regimes for detailed comparative planetary study.

Auroral ionization and incident magnetospheric electrons

1970 ◽  
Vol 48 (21) ◽  
pp. 2537-2541 ◽  
Author(s):  
J. R. Catchpoole
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Equatorial Plane ◽  
Pitch Angle ◽  
Magnetic Line ◽  
Parallel Electric Field ◽  
Energetic Electrons ◽  
Significant Control ◽  
Isotropic Distribution

A model is studied in which the supply of energetic electrons from a spiralling magnetospheric path to auroral atmospheric heights is considered. In particular, a calculation is made of the effect on atmospheric penetration which might be expected as a result of the combined influence of two magnetospheric accelerating mechanisms: (a) magnetic line convergence and (b) the superposition of a parallel electric field. This determination depends on details of energy and pitch angle distributions for precipitated electrons, and is made with reference to an isotropic distribution in the equatorial plane. Results indicate the significant control by magnetospheric electric fields on auroral ionization.

scholarly journals Downward ion acceleration at auroral latitudes: cause of parallel electric field

2002 ◽  
Vol 20 (8) ◽  
pp. 1117-1136 ◽  
Author(s):  
B. Hultqvist
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Pitch Angle ◽  
Difference Set ◽  
Potential Difference ◽  
Local Times ◽  
Parallel Electric Field ◽  
Energetic Electrons ◽  
Field Lines ◽  
Set Up

Abstract. Observations with the Freja satellite at about 1700 km altitude of downward accelerated ions in the keV and sub-keV energy range are described and analysed. The observations show the following: (1) Processes involving velocity dispersion are not important; (2) Ion pitch-angle distributions are mostly somewhat field aligned but not far from isotropic, so the ions are effectively spread in pitch-angle; (3) As all ion species, H +, O +, and He +, are found to be accelerated to the same energy, the only possible known acceleration mechanism is a potential difference along the magnetic field lines; (4) No significant Birkeland current features are associated with the ion precipitation; (5) Precipitation of energetic electrons from the plasma sheet is always present when the downward accelerated ions are observed; (6) Ion precipitation is generally not seen in regions with primary auroral Birkeland currents associated with electron inverted-V distributions; (7) Precipitated ions are mostly observed at low and medium disturbance levels, but they are also found in strongly disturbed conditions; (8) Downward accelerated ions occur fairly frequently at auroral latitudes near Freja apogee altitudes and are seen at all local times. The present investigation is limited to the nightside. The above observational results are found to be consistent with the physical mechanism for producing a downward-pointing parallel electric field proposed by Hultqvist (1971). That mechanism is basically one of an ambipolar potential difference set up by the energetic electrons from the plasma sheet.Key words. Magnetospheric physics (electric fields; energetic particles, precipitating; magnetosphere – ionosphere interactions)

VLF emission stimulated by parallel electric fields

1985 ◽  
Vol 34 (1) ◽  
pp. 47-66 ◽  
Author(s):  
B. Juhl ◽  
R. A. Treumann
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Electromagnetic Waves ◽  
Resonant Interaction ◽  
Alfven Wave ◽  
Emission Region ◽  
Parallel Electric Field ◽  
Loss Cone ◽  
Excitation Region ◽  
Cone Field

We study the influence of a weak quasi-static parallel electric field on the stability of electromagnetic plasma waves. Using an operator calculus to solve the Boltzmann-Maxwell equations we derive a dispersion relation for the electromagnetic waves. Assuming that the electrons have a loss-cone distribution, the real frequency of waves in the whistler band is not changed by the presence of the electric field. Resonant interaction damps the HF waves for propagation parallel to the electric field. In the case of opposite propagation, a new HF excitation is found at frequencies ω ≲ ωce The width of the excitation region depends on the width of the loss cone, field strength and collision frequency. This result is applied to observations of the splitting of VLF emissions under natural conditions in the magnetosphere. It is found that the observed splitting could have been caused by the presence of the weak parallel electric field of a kinetic (shear) Alfvén wave in the emission region, which is quasi-stationary compared with the growth of the observed VLF emission.

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