The structure of the convection sustained ion sheath

1976 ◽  
Vol 54 (15) ◽  
pp. 1627-1636
Author(s):  
P. R. Smy
Keyword(s):  
Reynolds Number ◽  
Electric Field ◽  
Electron Temperature ◽  
Electron Density ◽  
Plasma Flow ◽  
Ion Mobility ◽  
Free Space ◽  
Characteristic Length ◽  
Electron Charge ◽  
Detailed Structure

The detailed structure of the convection sustained ion sheath has been examined. With Re = vfL/μikTe/e (the electric Reynolds number) and α = (ε0kTe/nee2)1/2(1/L), where vf = plasma flow velocity, μi = ion mobility, k = Boltzmann's constant, Te = electron temperature, e = electron charge, ε0 = permittivity of free space, ne = electron density, and L = characteristic length, it is found that for [Formula: see text], no 'presheath' or diminution of electron density outside the sheath is evident, whereas for [Formula: see text], a very substantial density gradient exists which is in fact similar to the quasi-neutral region which occurs in stationary plasmas. Calculations are presented which enable ion and electron densities and electric field and potential to be calculated through the presheath and sheath regions.

Hybrid simulation of instabilities in capacitively coupled RF CF4/Ar plasmas

2022 ◽  
Author(s):  
Wan Dong ◽  
Yi Fan Zhang ◽  
ZhongLing Dai ◽  
Julian Schulze ◽  
Yuan-Hong Song ◽  
...  
Keyword(s):  
Electric Field ◽  
Electron Temperature ◽  
Electron Impact ◽  
Electron Density ◽  
Etching Rate ◽  
Reaction Rates ◽  
High Energy ◽  
Density Fluctuations ◽  
Negative Ion ◽  
Capacitively Coupled

Abstract Radio frequency capacitively coupled plasmas (RF CCPs) sustained in fluorocarbon gases or their mixtures with argon are widely used in plasma-enhanced etching. In this work, we conduct studies on instabilities in a capacitive CF4/Ar (1:9) plasma driven at 13.56 MHz at a pressure of 150 mTorr, by using a one-dimensional fluid/Monte-Carlo (MC) hybrid model. Fluctuations are observed in densities and fluxes of charged particles, electric field, as well as electron impact reaction rates, especially in the bulk. As the gap distance between the electrodes increases from 2.8 cm to 3.8 cm, the fluctuation amplitudes become smaller gradually and the instability period gets longer, as the driving power density ranges from 250 to 300 W/m2. The instabilities are on a time scale of 16-20 RF periods, much shorter than those millisecond periodic instabilities observed experimentally owing to attachment/detachment in electronegative plasmas. At smaller electrode gap, a positive feedback to the instability generation is induced by the enhanced bulk electric field in the highly electronegative mode, by which the electron temperature keeps strongly oscillating. Electrons at high energy are mostly consumed by ionization rather than attachment process, making the electron density increase and overshoot to a much higher value. And then, the discharge becomes weakly electronegative and the bulk electric field becomes weak gradually, resulting in the continuous decrease of the electron density as the electron temperature keeps at a much lower mean value. Until the electron density attains its minimum value again, the instability cycle is formed. The ionization of Ar metastables and dissociative attachment of CF4 are noticed to play minor roles compared with the Ar ionization and excitation at this stage in this mixture discharge. The variations of electron outflow from and negative ion inflow to the discharge center need to be taken into account in the electron density fluctuations, apart from the corresponding electron impact reaction rates. We also notice more than 20% change of the Ar+ ion flux to the powered electrode and about 16% difference in the etching rate due to the instabilities in the case of 2.8 cm gap distance, which is worthy of more attention for improvement of etching technology.

scholarly journals Polar patches observed by ESR and their possible origin in the cusp region

2000 ◽  
Vol 18 (9) ◽  
pp. 1043-1053 ◽  
Author(s):  
A. M. Smith ◽  
S. E. Pryse ◽  
L. Kersley
Keyword(s):  
Energy Distribution ◽  
Electron Density ◽  
Plasma Flow ◽  
Plasma Temperature ◽  
Soft Particle ◽  
Polar Ionosphere ◽  
Polar Cap ◽  
Particle Precipitation ◽  
Cusp Region ◽  
Reconnection Site

Abstract. Observations by the EISCAT Svalbard radar in summer have revealed electron density enhancements in the magnetic noon sector under conditions of IMF Bz southward. The features were identified as possible candidates for polar-cap patches drifting anti-Sunward with the plasma flow. Supporting measurements by the EISCAT mainland radar, the CUTLASS radar and DMSP satellites, in a multi-instrument study, suggested that the origin of the structures lay upstream at lower latitudes, with the modulation in density being attributed to variability in soft-particle precipitation in the cusp region. It is proposed that the variations in precipitation may be linked to changes in the location of the reconnection site at the magnetopause, which in turn results in changes in the energy distribution of the precipitating particles.Key words: Ionosphere (ionosphere-magnetosphere interactions; plasma temperature and density; polar ionosphere)

scholarly journals Comparison of the measured and modelled electron densities and temperatures in the ionosphere and plasmasphere during 20-30 January, 1993

2000 ◽  
Vol 18 (10) ◽  
pp. 1257-1262 ◽  
Author(s):  
A. V. Pavlov ◽  
T. Abe ◽  
K.-I. Oyama
Keyword(s):  
Magnetic Field ◽  
Heat Flux ◽  
Electron Temperature ◽  
Field Line ◽  
Electron Density ◽  
Magnetic Field Line ◽  
New Approach ◽  
Additional Heating ◽  
Vibrational Levels ◽  
The Magnetic Field

Abstract. We present a comparison of the electron density and temperature behaviour in the ionosphere and plasmasphere measured by the Millstone Hill incoherent-scatter radar and the instruments on board of the EXOS-D satellite with numerical model calculations from a time-dependent mathematical model of the Earth's ionosphere and plasmasphere during the geomagnetically quiet and storm period on 20–30 January, 1993. We have evaluated the value of the additional heating rate that should be added to the normal photoelectron heating in the electron energy equation in the daytime plasmasphere region above 5000 km along the magnetic field line to explain the high electron temperature measured by the instruments on board of the EXOS-D satellite within the Millstone Hill magnetic field flux tube in the Northern Hemisphere. The additional heating brings the measured and modelled electron temperatures into agreement in the plasmasphere and into very large disagreement in the ionosphere if the classical electron heat flux along magnetic field line is used in the model. A new approach, based on a new effective electron thermal conductivity coefficient along the magnetic field line, is presented to model the electron temperature in the ionosphere and plasmasphere. This new approach leads to a heat flux which is less than that given by the classical Spitzer-Harm theory. The evaluated additional heating of electrons in the plasmasphere and the decrease of the thermal conductivity in the topside ionosphere and the greater part of the plasmasphere found for the first time here allow the model to accurately reproduce the electron temperatures observed by the instruments on board the EXOS-D satellite in the plasmasphere and the Millstone Hill incoherent-scatter radar in the ionosphere. The effects of the daytime additional plasmaspheric heating of electrons on the electron temperature and density are small at the F-region altitudes if the modified electron heat flux is used. The deviations from the Boltzmann distribution for the first five vibrational levels of N2(v) and O2(v) were calculated. The present study suggests that these deviations are not significant at the first vibrational levels of N2 and O2 and the second level of O2, and the calculated distributions of N2(v) and O2(v) are highly non-Boltzmann at vibrational levels v > 2. The resulting effect of N2(v > 0) and O2(v > 0) on NmF2 is the decrease of the calculated daytime NmF2 up to a factor of 1.5. The modelled electron temperature is very sensitive to the electron density, and this decrease in electron density results in the increase of the calculated daytime electron temperature up to about 580 K at the F2 peak altitude giving closer agreement between the measured and modelled electron temperatures. Both the daytime and night-time densities are not reproduced by the model without N2(v > 0) and O2(v > 0), and inclusion of vibrationally excited N2 and O2 brings the model and data into better agreement.Key words: Ionosphere (ionospheric disturbances; ionosphere-magnetosphere interactions; plasma temperature and density)  

Simulations of electric field at the initiation altitudes of sprites and halos generated by the thundercloud charge structure and lightning channels of causative return strokes

2021 ◽  
Author(s):  
Petr Kaspar ◽  
Ivana Kolmasova ◽  
Ondrej Santolik ◽  
Martin Popek ◽  
Pavel Spurny ◽  
...  
Keyword(s):  
Electromagnetic Field ◽  
Electric Field ◽  
Boundary Conditions ◽  
Free Space ◽  
Nonlinear Effects ◽  
Charge Structure ◽  
Transient Luminous Events ◽  
Lightning Channel ◽  
Free Parameters

<p><span>Sprites and halos are transient luminous events occurring above thunderclouds. They can be observed simultaneously or they can also appear individually. Circumstances leading to initiation of these events are still not completely understood. In order to clarify the role of lightning channels of causative lightning return strokes and the corresponding thundercloud charge structure, we have developed a new model of electric field amplitudes at halo/sprite altitudes. It consists of electrostatic and inductive components of the electromagnetic field generated by the lightning channel in free space at a height of 15 km. Above this altitude we solve Maxwell’s equations self-consistently including the nonlinear effects of heating and ionization/attachment of the electrons. At the same time, we investigate the role of a development of the thundercloud charge structure and related induced charges above the thundercloud. We show how these charges lead to the different distributions of the electric field at the initiation heights of the halos and sprites. We adjust free parameters of the model using observations of halos and sprites at the Nydek TLE observatory and using measurements of luminosity curves of the corresponding return strokes measured by an array of fast photometers. The latter measurements are also used to set the boundary conditions of the model.</span></p>

scholarly journals Effect of interchange instability on magnetic reconnection

2013 ◽  
Vol 20 (3) ◽  
pp. 365-377 ◽  
Author(s):  
W. Lyatsky ◽  
M. L. Goldstein
Keyword(s):  
Magnetic Fields ◽  
Electric Field ◽  
Magnetic Reconnection ◽  
Plasma Flow ◽  
Buoyancy Force ◽  
Strong Turbulence ◽  
Polarization Electric Field ◽  
Interchange Instability ◽  
Reconnection Layer ◽  
Fast Reconnection

Abstract. We present here the results of a study of interacting magnetic fields that involves a force normal to the reconnection layer. In the presence of such force, the reconnection layer becomes unstable to interchange disturbances. The interchange instability results in formation of tongues of heated plasma that leaves the reconnection layer through its wide surface rather than through its narrow ends, as is the case in traditional magnetic reconnection models. This plasma flow out of the reconnection layer facilitates the removal of plasma from the layer and leads to fast reconnection. The proposed mechanism provides fast reconnection of interacting magnetic fields and does not depend on the thickness of the reconnection layer. This instability explains the strong turbulence and bidirectional streaming of plasma that is directed toward and away from the reconnection layer that is observed frequently above reconnection layers. The force normal to the reconnection layer also accelerates the removal of plasma islands appearing in the reconnection layer during turbulent reconnection. In the presence of this force normal to the reconnection layer, these islands are removed from the reconnection layer by the "buoyancy force", as happens in the case of interchange instability that arises due to the polarization electric field generated at the boundaries of the islands.

Plane Wave Interaction with an Inhomogeneous Warm Plasma Column

1971 ◽  
Vol 49 (20) ◽  
pp. 2578-2588 ◽  
Author(s):  
Kanwal J. Parbhakar ◽  
Brian C. Gregory
Keyword(s):  
Electric Field ◽  
Electron Temperature ◽  
Plasma Column ◽  
Cold Plasma ◽  
Plane Electromagnetic Wave ◽  
Wave Interaction ◽  
Radial Electric Field ◽  
Main Resonance ◽  
At Resonance ◽  
Warm Plasma

The interaction of a plane electromagnetic wave with an inhomogeneous warm plasma column is studied as a boundary value problem using a wave matching method. The plasma is characterized by a uniform electron temperature T and a parabolic density distribution N00 (1 − αr2/α2), where N00 is the central line density, α the inhomogeneity parameter, and a the column radius. The coupled Maxwell's and first two moment equations, assuming scalar pressure, are solved numerically without the quasi-static assumption. The resonances cannot be characterized by a single parameter; the effects of α, T, and N00 are studied separately. The resonances are located by noting that the magnitude of the scattering coefficient is unity (for a unit amplitude incident wave) at resonance. The maxima in the scattering are associated with the maxima in the coupling.It is found that the dielectric or the main resonance is a reasonably good radiator, while the plasma wave resonances (Tonks–Dattner resonances) are rather poor radiators. A detailed analysis of the radial electric field inside the plasma indicates that the main resonance is essentially a cold plasma resonance. As for the resonant frequencies, our results are in good agreement with those of Parker, Nickel, and Gould.The radial electric field at resonance inside the plasma is very sensitive to electron temperature.For the main resonance the field distribution at low electron temperature approaches that of a uniform cold plasma at resonance.

scholarly journals SIMULATION OF THE ELECTRIC FIELD OF ION MOBILITY SPECTROMETER SENSOR

2016 ◽  
pp. 60-63
Author(s):  
A. V. Golikov ◽  
S. N. Petukhov ◽  
M. Yu. Yanchenkov
Keyword(s):  
Electric Field ◽  
Ion Mobility ◽  
Ion Mobility Spectrometer
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