Effect Of Electron-ion Collisions Research Articles

The effect of electron-ion collisions on the breaking of cylindrical plasma oscillations

The effect of electron-ion collisions on the breaking of cylindrical plasma oscillations

Longitudinal fluctuations in a nonuniform collisional plasma with nonequilibrium particle distributions

The amplitudes of high-frequency longitudinal fluctuations excited by a nonequilibrium source in a nonuniform plasma are calculated. The results obtained are applicable to arbitrary nonequilibrium distributions of plasma particles in the absence of parametric instabilities. The spectra of probing waves scattered by fluctuations in a linear ionospheric plasma layer under conditions typical of experiments on incoherent radio wave scattering are found. The effects of electron-ion collisions and electron temperature anisotropy on the scattering intensity are demonstrated.

Scaling of saturated stimulated Raman scattering with temperature and intensity in ignition scale plasmas

Measurements show the scaling of stimulated Raman scattering (SRS) with laser intensity and plasma electron temperature under the conditions expected in ignition experiments. The scaling of the scattered energy with each parameter follows a power law with a small exponent (of order 1). Comparison with simulations suggests SRS is nonlinearly saturated in these cases. Further experiments with high Z dopants showed that the effect of electron-ion collisions on the measured SRS is primarily due to the inverse bremsstrahlung absorption of the scattered light.

Simulations of heating and electron energy distributions in optical field ionized plasmas.

The heating in underdense plasmas produced by optical field ionization and the resulting electron energy distributions have been calculated using Monte Carlo simulations. Though the magnitude of collisional heating is found to be low in plasmas with densities of interest for recombination x-ray lasers, the effect of electron-ion collisions on the shape of the electron energy distribution is important. The consequences that the calculated energy distributions have on three-body recombination rates are found to be dramatic.

Effect of electron-ion collisions on generation of ionospheric irregularities by thermal source

On montre que les collisions electron-ion amortissent les sources thermiques et on determine les seuils d'instabilite dans la generation des irregularites ionospheriques d'echelle depassant la vingtaine de metres

Effect of electron-ion collisions on the nonlinear state of the relativistic two-stream instability

The analysis outlines conditions for the hydrodynamic interaction, including foil scattering and beam self-magnetic field effects. For the hydrodynamic interaction, the oblique coupling coefficient model is extended to include the effect of a finite electron-ion collision rate on the nonlinear state. Partial numerical simulation results are found to be in agreement with the model. Limitations due to temperature inhomogeneity along the deposition length and to increased deposition length are also discussed. It is found that an intense relativistic electron beam can couple its energy via the two-stream instability to a high density 1017–1020 cm−3 plasma. It is required that the plasma be fully ionized, with an initial electron temperature of ≳10 eV for 1017 cm−3, 10–20 eV for 1018 cm−3, 15–50 eV for 1019 cm−3, and ∼100 eV for 1020 cm−3.

A non-linear study of the possible effects of electron-ion collisions on the diffusion of a cylindrical column of ionisation in the Earth's ionosphere

The possible effects of electron—ion collisions on the diffusion of a cylindrical plasma irregularity orientated at right angles to the geomagnetic field lines, at altitude 300 km, are discussed. The results obtained indicate that the diffusion may proceed at a rate rather greater than for a case for which the effects of collisions of electrons with ions are assumed to be negligible. Furthermore, it is suggested that if the plasma density is great enough, the production of a 'fin' of ionisation along the magnetic field direction may be inhibited by the action of electron—ion collisions.

“Universal” Drift Instability in a Collisional Plasma

The effect of electron-ion collisions on the “universal” drift instability in an inhomogeneous plasma, using a Fokker-Planck collision operator is considered and compared with the results obtained using the Bhatnagar, Gross, and Krook model. It is found that for small collision frequency, the BGK model gives a destabilizing effect while the Fokker-Planck model indicates a stabilizing effect. For larger values of collision frequency, growth rates for collisional drift waves increase in both models but the growth rate obtained from the Fokker-Planck model is not nearly as high as would be expected from the results derived from the Krook model calculations. For very large collision frequency, growth rates tend to vanish in both models.

Asymptotic solution of the Fokker-Planck equation at low collision frequency

An asymptotic solution has been obtained for the case of low collision frequency using a Fokker-Planck collision operator suitable for the study of the effect of electron-ion collisions on the 'Universal' instability in an inhomogeneous plasma. The solution, obtained under certain approximations, contains fractional powers of the collision-rate coefficient and this eliminates the divergence occurring in the expression for physical quantities like perturbed density when obtained by using a direct iterative method. Also, an approximate study of the solutions over various ranges of the velocity variable is given.

Enhancement of Plasma Density Fluctuations by Nonthermal Electrons

In a plasma in thermal equilibrium, the spectrum of electron density fluctuations that have a wavelength longer than the Debye length has a sharp maximum near the electron plasma frequency. In this paper, the effect of a non-Maxwellian electron velocity distribution on the spectrum of electron density fluctuations is computed for frequencies near the electron plasma frequency. The electron velocity distribution is assumed to be isotropic but not necessarily Maxwellian and the effects of electron-ion collisions are included. The results show how the presence of a small number of energetic electrons can enhance the intensity of the fluctuations near the plasma frequency, provided the Landau damping resulting from these energetic electrons is greater than both the collision damping and the Landau damping caused by the ambient electrons. The results are applied to the ionosphere radar-backscatter experiments, where the energetic electrons are photoelectrons produced by solar uv radiation. In the case of the Arecibo radar experiments, the intensity of the fluctuations near the electron plasma frequency is estimated to be enhanced at plasma frequencies greater than about 4 or 5 Mc/sec.

Corrigendum [to “ Effect of electron-ion collisions in theFregion of the ionosphere on the absorption of cosmic radio noise at 25 Mc/s at Ahmedabad changes in absorption associated with magnetic storms” by Ramanathan, Bhonsle, and Degaonkar

Corrigendum [to “ Effect of electron-ion collisions in the<i>F</i>region of the ionosphere on the absorption of cosmic radio noise at 25 Mc/s at Ahmedabad changes in absorption associated with magnetic storms” by Ramanathan, Bhonsle, and Degaonkar

Effect of electron-ion collisions in theFregion of the ionosphere on the absorption of cosmic radio noise at 25 Mc/s at Ahmedabad changes in absorption associated with magnetic storms

Measurements of cosmic radio noise at 25 Mc/s, being made at the Physical Research Laboratory, Ahmedabad, since March 1957, have shown much larger values of absorption than those observed by Shain and Mitra in Australia. This fact, together with the empirically known dependence of the absorption on the critical frequency of the F region, and the effect of magnetic storms on the absorption found from the Ahmedabad observations have led us to examine the different possible parameters that may affect cosmic-noise absorption. It is found that electron-ion collisions in the F region both below and above the level of maximum electron density contribute in a substantial way to the absorption of cosmic radio noise. The values of hourly absorption due to collisions of electrons with neutral particles and with ions have been calculated for a period of 6 days in August–September 1957, when there were three magnetic storms. The results obtained show a depletion of electrons above F maximum on the day following the commencement of the magnetic storm and a refilling on later days. The results are discussed in relation to findings from satellite observations about particle fluxes in the Van Allen belts during magnetic storms.

Space Charge Neutralization by Positive Ions in Diodes

The neutralization of electron space charge in diodes is analyzed on the basis of the assumption that the ion density is proportional to e−eV/kT, where V is the local potential and T is the cathode temperature. The neglect of electron-ion collisions enables solutions for the potential variation between electrodes to be obtained by a single numerical quadrature. Curves are presented for the potential as a function of position for a series of values of the ratio α of ion to electron density at the potential minimum. It is shown that for a large range of tube parameters, the electron current reaches two-thirds of its saturated value when the ion density at the cathode is about one-third the quantity Is/ev0, where Is is the saturation current and v0 = (2kT/πm)½. The electron current saturates completely when the ion density at the cathode is slightly above 0.81 Is/ev0 for large electrode spacing and slightly below Is/ev0 for small spacing. The anomalous behavior of the potential as a function of position when α lies between 0.81 and unity leads to the possibility of more than one mode of operation for a given ion density at the cathode and also causes the tube current to increase rather than decrease with increasing electrode spacing under certain conditions. Since these phenomena occur only over a narrow range of tube parameters, the effect of electron ion collisions may prevent them from being observed experimentally.