Electron-ion Recombination Coefficient Research Articles

Numerical simulation of photocurrent transients generated from passive films and anodic films on pure Ti

A numerical simulation of photocurrent transient was proposed to estimate properties of passive films and anodic films formed on pure Ti. To simulate photocurrent transient, partial differential equations describing the change in the concentration and positions of photoexcited charge carriers with time were developed based on the generation, recombination, and transports of the carriers. Simulations were performed by screening several parameters. The electron mobility, donor density, recombination coefficient and interfacial reaction rate coefficient were estimated by fitting simulated photocurrent transients to experimentally obtained transients.

Predictions of circuit interruption including non-equilibrium electron densities

Calculations and predictions of arc properties, for example, for arc welding and circuit interruption, are generally made by solving the energy balance equation to obtain temperature profiles, assuming local thermodynamic equilibrium. Results for high power circuit breakers have needed to attribute turbulence as the principal energy loss, with larger turbulence parameters for SF6 than for air to fit the superior experimental performance of SF6. In the present paper, predictions of circuit interruption are obtained by solving the electron continuity equation together with the energy balance equation for a simple low current arc, with no imposed convective flow and thus no need for turbulence. It is found that circuit interruption depends critically on electron–ion recombination coefficients and also electron-neutral attachment coefficients, large values of which reduce electron densities and thus electrical conduction. SF6 is found to be superior to air because of its very large attachment coefficient. The results suggest that in the search for a replacement gas for SF6, because of its global warming potential of 24 000 times that of carbon dioxide, material properties of high electron recombination and attachment are desirable, as well as the high enthalpy density which follows from the results where convective flow is the principal energy loss.

Self-focusing of coaxial electromagnetic beams in a plasma with electron temperature dependent electron-ion recombination coefficient

An analytical formulation, describing the propagation of multiple coaxial Gaussian electromagnetic (em) beams in a self-formed plasma channel with dominant collisional nonlinearity has been developed; the generation/recombination of high energy plasma particles has been considered as an additional source of plasma non-linearity in addition to Ohmic heating. Well versed paraxial approach in the vicinity of the intensity maximum has been adopted to solve the wave equation and examine the non-linear propagation of em beams while the dielectric function in the presence of the em field is determined from the balance of partial pressure gradient of electron/ion gas with the space charge field and energy balance of plasma particles. On the basis of the analysis the influence of this novel non-linearity on the propagation features like electron temperature, dielectric function and critical curves are derived numerically and graphically presented. The inclusion of this novel nonlinearity results in reduced focusing effect. The three regime characteristic features viz. oscillatory focusing/defocusing and steady divergence of beam propagation have also been worked out.

Modification of ionospheric electron density by dust suspension

On the basis of a dynamic analysis the effectiveness of dust suspension for the reduction and enhancement of electron density in the E-layer of the ionosphere has been investigated in this paper. The analysis is based on the modelling of the E-layer as the Chapman α layer (validated earlier); the electron/ion production function, arrived at by Chapman and effective electron temperature-dependent electron–ion recombination coefficients in agreement with observations have been used. The balance of the charge on the particles and the number/energy balance of the constituents have been taken into account. The following is the physics of the change in electron density in the ionosphere by the suspension of dust. First, the dust provides a source (emission) and sink (accretion) of electrons. Second, the dust emits photoelectrons with energies much higher than those of ambient electrons, which enhances the electron temperature, leading to a reduced electron–ion recombination coefficient, and thus to a higher electron density. An interplay of these processes and the natural processes of electron production/annihilation determines the electron density and temperature in the dust suspension in the ionosphere. The numerical results, corresponding to suspension of dust of silicate (high work function) and Cs coated bronze (low work function) in the E-layer at are presented and discussed.

Effect of a novel nonlinearity, viz., electron temperature dependence of electron-ion recombination on electromagnetic wave. Plasma interaction: Nonlinear propagation in the E-layer

In this paper, we consider the nonlinearity in the propagation of electromagnetic (e.m.) waves in a plasma caused by the electron temperature dependence of the coefficient of recombination of electrons with ions; specifically, the ionospheric E layer has been investigated. The enhancement in electron temperature by an intense electromagnetic wave causes reduction of the electron-ion recombination coefficient and thereby enhancement of electron density, the electron collision frequency also gets enhanced. The equations for number and energy balance of electrons and the wave equation have been used to predict the dependence of electron density/collision frequency and the nonlinear refractive index and absorption coefficient on αE02 (proportional to wave irradiance). The dependence of the propagation parameters on αE02 has been used to investigate the nonlinear electromagnetic wave propagation in the ionosphere. The study concludes that the electron temperature dependence of the recombination coefficient should be considered in all analyses of nonlinear plasma-e.m. wave interaction.

Study of dust particle charging in weakly ionized inert gases taking into account the nonlocality of the electron energy distribution function

The charging of dust particles in weakly ionized inert gases at atmospheric pressure has been investigated. The conditions under which the gas is ionized by an external source, a beam of fast electrons, are considered. The electron energy distribution function in argon, krypton, and xenon has been calculated for three rates of gas ionization by fast electrons: 1013, 1014, and 1015 cm s−1. A model of dust particle charging with allowance for the nonlocal formation of the electron energy distribution function in the region of strong plasma quasi-neutrality violation around the dust particle is described. The nonlocality is taken into account in an approximation where the distribution function is a function of only the total electron energy. Comparative calculations of the dust particle charge with and without allowance for the nonlocality of the electron energy distribution function have been performed. Allowance for the nonlocality is shown to lead to a noticeable increase in the dust particle charge due to the influence of the group of hot electrons from the tail of the distribution function. It has been established that the screening constant virtually coincides with the smallest screening constant determined according to the asymptotic theory of screening with the electron transport and recombination coefficients in an unperturbed plasma.

Effective recombination coefficient and solar zenith angle effects on low-latitude D-region ionosphere evaluated from VLF signal amplitude and its time delay during X-ray solar flares

Excess solar X-ray radiation during solar flares causes an enhancement of ionization in the ionospheric D-region and hence affects sub-ionospherically propagating VLF signal amplitude and phase. In first part of the work, using the well known LWPC technique, we simulated the flare induced excess lower ionospheric electron density by amplitude perturbation method. Unperturbed D-region electron density is also obtained from simulation and compared with IRI-model results. Using these simulation results and time delay as key parameters, we calculate the effective electron recombination coefficient ($\alpha_{eff}$) at solar flare peak region. Our results match with the same obtained by other established models. In the second part, we dealt with the solar zenith angle effect on D-region during flares. We relate this VLF data with the solar X-ray data. We find that the peak of the VLF amplitude occurs later than the time of the X-ray peak for each flare. We investigate this so-called time delay ($\bigtriangleup t$). For the C-class flares we find that there is a direct correspondence between $\bigtriangleup t$ of a solar flare and the average solar zenith angle $Z$ over the signal propagation path at flare occurrence time. Now for deeper analysis, we compute the $\bigtriangleup t$ for different local diurnal time slots $DT$. We find that while the time delay is anti-correlated with the flare peak energy flux $\phi_{max}$ independent of these time slots, the goodness of fit, as measured by $reduced$-$\chi^2$, actually worsens as the day progresses. The variation of the $Z$ dependence of $reduced$-$\chi^2$ seems to follow the variation of standard deviation of $Z$ along the $T_x$-$R_x$ propagation path. In other words, for the flares having almost constant $Z$ over the path a tighter anti-correlation between $\bigtriangleup t$ and $\phi_{max}$ was observed.

Study of laser induced plasma grating dynamics in gases

The relaxation of a plasma grating resulting from the interference of two crossing laser filaments in molecular and atomic gases is studied experimentally. Dissipation of the grating fringes is dominated by ambipolar diffusion in atomic gases and by a combination of ambipolar diffusion and collision-assisted free electron recombination in molecular gases. A theoretical model of the grating evolution is developed and compared to experimental results. Good agreement with simulations allows extracting plasma properties such as electron density, diffusion and recombination coefficients in Ne, Ar, Kr, Xe, N2, O2, CO2 and air at atmospheric pressure.

Electron distribution function and recombination coefficient in ultracold plasma in a magnetic field

The electron distribution function and diffusion coefficient in energy space have been calculated for the first time for a weakly coupled ultracold plasma in a magnetic field in the range of magnetic fields B = 100−50000 G for various temperatures. The dependence of these characteristics on the magnetic field is analyzed and the distribution function is shown to depend on the electron energy shift in a magnetic field. The position of the “bottleneck” of the distribution function has been found to be shifted toward negative energies with increasing magnetic field. The electron velocity autocorrelators as a function of the magnetic field have been calculated; their behavior suggests that the frequency of collisions between charged particles decreases significantly with increasing magnetic field. The collisional recombination coefficient αB has been calculated in the diffusion approximation for a weakly coupled ultracold plasma in a magnetic field. An increase in magnetic field is shown to lead to a decrease in αB and this decrease can be several orders of magnitude.

The parameters that play role in numerical parameter variation in two-center holographic recording in photorefractive lithium niobate (LiNbO3 ) and strontium barium niobate (Sr x Ba1 − x Nb2 O6 )

We have conducted a numerical study of the dependence of nonvolatile data storage on the holographic parameter variation for a two-center holographic recording (TCHR) process. Parameters of the photorefractive crystals and the experimental conditions such as the electron mobility in the conduction band, the level concentrations, the electron-recombination coefficients, the bulk photovoltaic coefficient, the spatial period of modulation, the dielectric constant, and the modulation depth are studied numerically. The results of the numerical calculations showed that the significant parameters are the electron mobility in the conduction band, the electron-recombination coefficient, and the concentrations of the dopant levels (levels created due to the dopants) in the TCHR process. It seems that the electron-recombination coefficient for deep levels plays a more important role than the other parameters.

Dynamics of plasma gratings in atomic and molecular gases

The decay of the plasma grating formed at the intersection of two femtosecond filaments is measured in several molecular and atomic gases. The grating evolution is ruled by ambipolar diffusion in atomic gases and by a combination of ambipolar diffusion and collision-assisted free electron recombination in molecular gases. Electron diffusion and recombination coefficients are extracted for Ne, Ar, Kr, Xe, N2, O2, CO2, and air at 1 bar.

Effective electron recombination coefficient in ionospheric D-region during the relaxation regime after solar flare from February 18, 2011

In this paper, we present a model for determination of a weakly time dependent effective recombination coefficient for the perturbed terrestrial ionospheric D-region plasma. We study consequences of a class M1.0 X-ray solar flare, recorded by GOES-15 satellite on February 18, 2011 between 14:00 and 14:15UT, by analyzing the amplitude and phase real time variations of very low frequency (VLF) radio waves emitted by transmitter DHO (located in Germany) at frequency 23.4kHz and recorded by the AWESOME receiver in Belgrade (Serbia). Our analysis is limited to ionospheric perturbations localized at altitudes around 70km where the dominant electron gain and electron loss processes are the photo-ionization and recombination, respectively.

Screening of a moving charge in a nonequilibrium plasma

Based on the model of point sinks, we consider the problem on the screening of the charge of a moving macroparticle in a nonequilibrium plasma. The characteristic formation times of the polarization cloud around such a macroparticle have been determined by the method of a three-dimensional integral Fourier transformation in spatial variables and a Laplace transformation in time. The screening effect is shown to be enhanced with increasing macroparticle velocity. We consider the applicability conditions for the model of point sinks and establish that the domain of applicability of the results obtained expands with decreasing gas ionization rate and macroparticle size. We consider the problem of charge screening at low velocities and establish that the stationary potential of the moving charge has a dipole component that becomes dominant at large distances. We show that the direction of the force exerted on the dust particle by the induced charges generally depends on the relationship between the transport and loss coefficients of the plasma particles in a plasma. When the Langevin ion recombination coefficient β iL = 4πeμ i exceeds the electron-ion recombination coefficient β ei , this force will accelerate the dust particles in the presence of sinks. In the absence of sinks or when β ei > β iL , this force will be opposite in direction to the dust particle velocity. We also consider the problem on the energy and force of interaction between a moving charged macroparticle and the induced charges.

Plasma decay in air and N2 : O2 : CO2 mixtures at elevated gas temperatures

Plasma decay after a high-voltage nanosecond discharge has been studied experimentally and numerically behind incident and reflected shock waves in high temperature (600–2400 K) air and N2 : O2 : CO2 mixtures for pressures between 0.05 and 1.2 atm. Time-resolved electron density history was measured by a microwave interferometer for initial electron densities in the range (1–3) × 1012 cm−3 and the effective electron–ion recombination coefficient was determined. A numerical simulation was carried out to describe the temporal evolution of the densities of charged and neutral particles under the conditions considered. It was shown that the loss of electrons in this case is determined by dissociative recombination with ions, whereas the effect of complex ions is negligible. Electron attachment to O2 to form negative ions is not important because of fast electron detachment in collisions with O atoms produced in the discharge. In the absence of O atoms the electron density could decay as if the loss of charged particles were governed by electron–ion recombination with the effective rate coefficient being much higher than the dissociative recombination coefficient.

Upper-mesospheric temperatures measured during intense substorms in the declining phase of the January 2005 solar proton events

Abstract. Temperature measurements from the ALOMAR Weber Na lidar together with cosmic radio noise absorption measurements from IRIS and particle measurements from NOAA 15, 16 and 17 are used to study effects of geomagnetic activity on the polar winter upper-mesospheric temperature. On 21–22 January 2005 we have 14 h of continuous temperature measurement with the Na lidar coinciding with strong geomagnetic activity in the declining phase of one of the hardest and most energetic Solar Proton Event (SPE) of solar cycle 23. According to measurements by the imaging riometer IRIS in northern Finland, the temperature measurements coincide with two periods of increased cosmic radio noise absorption. Particle measurements from the three satellites, NOAA 15, 16 and 17 that pass through and near our region of interest confirm that the absorption events are probably due to particle precipitation and not due to changes in e.g. the electron recombination coefficient. The measured temperature variation at 85 and 90 km is dominated by a 7.6-h wave with downward phase propagation and a vertical wavelength of approximately 10 km. Assuming that the wave is due to a lower altitude source independent of the particle precipitation, we do not find any temperature modification that seems to be related to the absorption events. The average temperature is larger than expected above 90 km based on MSIS and the monthly mean from falling spheres, which could be due to particle precipitation and Joule heating prior to our measurement period. There is also a possibility that the identified wave phenomenon is an effect of the geomagnetic activity itself. Earlier studies have reported of similar wavelike structures in wind observations made by the EISCAT VHF radar during SPEs, and found it conceivable that the wave could be excited by the effect of energetic particles precipitating into the mesosphere.

Low-frequency temperature-dependent plasma discharge instabilities in the presence of external constant electric and magnetic fields

AbstractBy calculating the dielectric permittivity of a magnetoactive plasma discharge in the presence of an external electric field, low-frequency instabilities resulting from the dependency of the electron-neutral collision frequency, electron-ion recombination coefficient and ionization frequency on the electron temperature are investigated. Furthermore, it is shown that some of these instabilities depend on the sign change of the derivative of the kinetic coefficients with respect to the electron temperature. Finally, it is shown how frequency spectra and the development of instabilities are changed by increasing the strength of the external magnetic field.

Local plasma processes and enhanced electron densities in the lower ionosphere in magnetic cusp regions on Mars

Both the MARSIS ionospheric sounder and the charged particle instrument package ASPERA-3 are experiments on board the Mars Express spacecraft. Joint observations have shown that events of intense ionospheric electron density enhancements occur in the lower ionosphere of magnetic cusp regions, and that these enhancements are not associated with precipitation of charged particles above a few hundred electron volts (<300 eV). To account for the enhancement by particle precipitation, electron fluxes are required with mean energy between 1 and 10 keV. No ionizing radiation, neither energetic particles nor X-rays, could be identified, which could produce the observed density enhancement only in the spatially limited cusp regions. Actually, no increase in ionizing radiation, localized or not, was observed during these events. It is argued that the process causing the increase in density is controlled mainly by convection of ionosphere plasma driven by the interaction between the solar wind and crustal magnetic field lines leading to excitation of two-stream plasma waves in the cusp ionosphere. The result is to heat the plasma, reduce the electron–ion recombination coefficient and thereby increase the equilibrium electron density.

Plasma decay in N2, CO2 and H2O excited by high-voltage nanosecond discharge

Plasma decay after a high-voltage nanosecond discharge was studied experimentally and numerically in room temperature N2, CO2 and H2O for pressures between 1 and 10 Torr. The time-resolved electron density was measured by a microwave interferometer for initial electron densities in the range 8 × 1011–3 × 1012 cm−3 and the effective electron–ion recombination coefficient was determined. It was shown that this coefficient varies in time and depends on pressure. A numerical simulation was carried out to describe the temporal evolution of the densities of charged particles under the conditions considered. A good agreement was obtained between the calculated and the measured electron density histories. It was shown that the loss of electrons is governed by dissociative recombination with complex ions, their density being dependent on pressure. In N2 at low pressures, a hindered electron thermalization in collisions with molecules led to a delay in the plasma decay. This effect was observed both experimentally and theoretically.

Charge screening in a plasma with an external ionization source

An asymptotic theory for the screening of the electric field of a dust particle or a spherical probe in a plasma with an external steady and/or internal (proportional to the electron density) gas ionization source has been developed for the first time. It has been established that the screening of the charge of a spherical body adsorbing the charge of the incident plasma particles is described by a superposition of two exponentials with different screening constants. The two exponentials are retained even in the absence of nonequilibrium fluxes on the macroparticle and only in the special case of an isothermal plasma does the screening become Debye one. The screening length is determined by the ratio of the electron-ion, βei, and Langevin, βL = 4πeμi (where μi is the ion mobility), recombination coefficients. If βL ≫ βei, then it is much larger than the electron Debye length. The ions in an isothermal plasma have been found to give the same contribution to the screening as the electrons if the electron-ion recombination coefficient exceeds the Langevin ion recombination coefficient by a factor of 2 or more, βei ≥ 2βL. The Vlasov equation is used to analyze the asymptotic behavior of the macroparticle potential in a collisionless plasma.

Theoretical Analysis on Effect of Adding Argon to Hydrogen Plasma

An increased of H- ion beam current whenever argon gas is added has been observed. The physics behind argon effect is that in the production of more H atoms, a part of H atoms will be converted to H2*(v > 4) to increase H- density. Increase of nH depends on the rate of added Ar η%, primary filling pressure P, electron density neAr and recombination coefficient γ of H atom. Adding 25% Ar is optimal, although there have been assumed various parameters. Increase of nH depends on decreased recombination coefficient γ, and increased primary filling pressure P. The increase of nH is small when the pressure P < 0.3 Pa. Optimized volume size L/R ∼ 2 is optimal for obtaining a maximum Ar effect.