arXiv subjects

H. B. Nersisyan

Publications and source records attributed to H. B. Nersisyan.

At least 19 recordsLinked to original sources

arXiv2014

Dielectric function of a collisional plasma for arbitrary ionic charge

A simple model for the dielectric function of a completely ionized plasma with an arbitrary ionic charge, that is valid for long-wavelength high-frequency perturbations is derived using an approximate solution of a linearized Fokker-Planck kinetic equation for electrons with a Landau collision integral. The model accounts for both the electron-ion collisions and the collisions of the subthermal (cold) electrons with thermal ones. The relative contribution of the latter collisions to the dielectric function is treated phenomenologically, introducing some parameter $\varkappa$ that is chosen in such a way as to get a well-known expression for stationary electric conductivity in the low-frequency region and fulfill the requirement of a vanishing contribution of electron-electron collisions in the high-frequency region. This procedure ensures the applicability of our model in a wide range of plasma parameters as well as the frequency of the electromagnetic radiation. Unlike the interpolation formula proposed earlier by Brantov et al. [Brantov et al., JETP 106, 983 (2008)], our model fulfills the Kramers-Kronig relations and permits a generalization for the cases of degenerate and strongly coupled plasmas. With this in mind, a generalization of the well-known Lee-More model [Y. T. Lee and R. M. More, Phys. Fluids 27, 1273 (1984)] for stationary conductivity and its extension to dynamical conductivity [O. F. Kostenko and N. E. Andreev, GSI Annual Report No. GSI-2008-2, 2008 (unpublished), p. 44] is proposed for the case of plasmas with arbitrary ionic charge.

physics.plasm-ph↗

arXiv2013

Cooling force on ions in a magnetized electron plasma

Electron cooling is a well-established method to improve the phase space quality of ion beams in storage rings. In the common rest frame of the ion and the electron beam the ion is subjected to a drag force and it experiences a loss or a gain of energy which eventually reduces the energy spread of the ion beam. A calculation of this process is complicated as the electron velocity distribution is anisotropic and the cooling process takes place in a magnetic field which guides the electrons. In this paper the cooling force is calculated in a model of binary collisions (BC) between ions and magnetized electrons, in which the Coulomb interaction is treated up to second-order as a perturbation to the helical motion of the electrons. The calculations are done with the help of an improved BC theory which is uniformly valid for any strength of the magnetic field and where the second-order two-body forces are treated in the interaction in Fourier space without specifying the interaction potential. The cooling force is explicitly calculated for a regularized and screened potential which is both of finite range and less singular than the Coulomb interaction at the origin. Closed expressions are derived for monochromatic electron beams, which are folded with the velocity distributions of the electrons and ions. The resulting cooling force is evaluated for anisotropic Maxwell velocity distributions of the electrons and ions.

physics.plasm-ph↗

arXiv2013

Resistive MHD model for cylindrical plasma expansion in a magnetic field

The study of hot plasma expansion in a magnetic field is of interest for many laboratory and astrophysical applications. In this paper, an exactly solvable analytical model is proposed for an expanding resistive plasma in an external magnetic field in the regime in which the magnetic field does not perturb the plasma motion. The model is based on a class of exact solutions for the purely radial expansion of the plasma in the absence of a magnetic field. This approximation permits the reduction of the electromagnetic problem to consideration of a diffusion equation for the magnetic field. Explicit solutions are derived for a resistive cylindrical plasma expanding into a uniform ambient magnetic field. Some numerical examples related to the laser-produced plasma experiments are presented.

physics.plasm-ph↗

arXiv2013

An exact solution of the moving boundary problem for the relativistic plasma expansion in a dipole magnetic field

An exact analytic solution is obtained for a uniformly expanding, neutral, highly conducting plasma sphere in an ambient dipole magnetic field with an arbitrary orientation of the dipole moment in the space. Based on this solution the electrodynamical aspects related to the emission and transformation of energy have been considered. In order to highlight the effect of the orientation of the dipole moment in the space we compare our results obtained for parallel orientation with those for transversal orientation. The results obtained can be used to treat qualitatively experimental and simulation data, and several phenomena of astrophysical and laboratory significance.

physics.plasm-ph↗

arXiv2011

Stopping of ions in a plasma irradiated by an intense laser field

The inelastic interaction between heavy ions and an electron plasma in the presence of an intense radiation field (RF) is investigated. The stopping power of the test ion averaged with a period of the RF has been calculated assuming that $ω_{0} >ω_{p}$, where $ω_{0}$ is the frequency of the RF and $ω_{p}$ is the plasma frequency. In order to highlight the effect of the radiation field we present a comparison of our analytical and numerical results obtained for nonzero RF with those for vanishing RF. It has been shown that the RF may strongly reduce the mean energy loss for slow ions while increasing it at high-velocities. Moreover, it has been shown, that acceleration of the projectile ion due to the RF is expected at high-velocities and in the high-intensity limit of the RF, when the quiver velocity of the plasma electrons exceeds the ion velocity.

physics.plasm-ph↗

arXiv2011

Self-similar analytical model of the plasma expansion in a magnetic field

The study of hot plasma expansion in a magnetic field is of interest for many astrophysical applications. In order to observe this process in laboratory, an experiment is proposed in which an ultrashort laser pulse produces a high-temperature plasma by irradiation of a small target. In this paper an analytical model is proposed for an expanding plasma cloud in an external dipole or homogeneous magnetic field. The model is based on the self-similar solution of a similar problem which deals with sudden expansion of spherical plasma into a vacuum without ambient magnetic field. The expansion characteristics of the plasma and deceleration caused by the magnetic field are examined analytically. The results obtained can be used in treating experimental and simulation data, and many phenomena of astrophysical and laboratory significance.

physics.plasm-ph↗

arXiv2010

Microfield Fluctuations and Spectral Line Shapes in Strongly Coupled Two-Component Plasmas

The spectral line shapes for hydrogen-like heavy ion emitters embedded in strongly correlated two-component electron-ion plasmas are investigated with numerical simulations. For that purpose the microfield fluctuations are calculated by molecular dynamics simulations where short range quantum effects are taken into account by using a regularized Coulomb potential for the electron-ion interaction. The microfield fluctuations are used as input in a numerical solution of the time-dependent Schroedinger equation for the radiating electron. In distinction to the standard impact and quasistatic approximations the method presented here allows to account for the correlations between plasma ions and electrons. The shapes of the Ly-alpha line in Al are investigated in the intermediate regime. The calculations are in good agreement with experiments on the Ly-alpha line in laser generated plasmas.

physics.plasm-ph↗

arXiv2010

Energy transfer in binary collisions of two gyrating charged particles in a magnetic field

Binary collisions of the gyrating charged particles in an external magnetic field are considered within a classical second-order perturbation theory, i.e., up to contributions which are quadratic in the binary interaction, starting from the unperturbed helical motion of the particles. The calculations are done with the help of a binary collisions treatment which is valid for any strength of the magnetic field and involves all harmonics of the particles cyclotron motion. The energy transfer is explicitly calculated for a regularized and screened potential which is both of finite range and nonsingular at the origin. The validity of the perturbation treatment is evaluated by comparing with classical trajectory Monte Carlo (CTMC) calculations which also allow to investigate the strong collisions with large energy and velocity transfer at low velocities. For large initial velocities on the other hand, only small velocity transfers occur. There the nonperturbative numerical CTMC results agree excellently with the predictions of the perturbative treatment.

physics.plasm-ph↗

arXiv2009

Predicted thermal superluminescence in low-pressure air

It is shown that due to the dissociation of the molecular oxygen it is possible to obtain inverted population in low pressure air by heating. As a result of the quenching of the corresponding levels of the atomic oxygen the thermal superluminescent radiation is generated. It has been found that the threshold of the overpopulation is exceeded at the air temperature 2300-3000 K. Using this effect a possible mechanism for the generation of the flashes of the radiation in air observed on the airframe of the space shuttle during its descent and reentry in the atmosphere is suggested.

physics.atom-ph↗

arXiv2009

Collisionless plasma expansion in the presence of a dipole magnetic field

The collisionless interaction of an expanding high-energy plasma cloud with a magnetized background plasma in the presence of a dipole magnetic field is examined in the framework of a 2D3V hybrid (kinetic ions and massless fluid electrons) model. The retardation of the plasma cloud and the dynamics of the perturbed electromagnetic fields and the background plasma are studied for high Alfven-Mach numbers using the particle-in-cell method. It is shown that the plasma cloud expands excluding the ambient magnetic field and the background plasma to form a diamagnetic cavity which is accompanied by the generation of a collisionless shock wave. The energy exchange between the plasma cloud and the background plasma is also studied and qualitative agreement with the analytical model suggested previously is obtained.

physics.plasm-ph↗

arXiv2009

Interaction of fast charged projectiles with two-dimensional electron gas: Interaction and disorder effects

The results of a theoretical investigation on the stopping power of ions moving in a disordered two-dimensional degenerate electron gas are presented. The stopping power for an ion is calculated employing linear response theory using the dielectric function approach. The disorder, which leads to a damping of plasmons and quasiparticles in the electron gas, is taken into account through a relaxation time approximation in the linear response function. The stopping power for an ion is calculated in both the low- and high-velocity limits. In order to highlight the effects of damping we present a comparison of our analytical and numerical results, in the case of point-like ions, obtained for a non-zero damping with those for a vanishing damping. It is shown that the equipartition sum rule first formulated by Lindhard and Winther for three-dimensional degenerate electron gas does not necessarily hold in two-dimensions. We have generalized this rule introducing an effective dielectric function. In addition some new results for two-dimensional interacting electron gas have been obtained. In this case the exchange-correlation interactions of electrons are considered via local-field-corrected dielectric function.

physics.plasm-ph↗

arXiv2008

Binary collisions of charged particles in a magnetic field

Binary collisions between charged particles in an external magnetic field are considered in second-order perturbation theory, starting from the unperturbed helical motion of the particles. The calculations are done with the help of an improved binary collisions treatment which is valid for any strength of the magnetic field, where the second-order energy and velocity transfers are represented in Fourier space for arbitrary interaction potentials. The energy transfer is explicitly calculated for a regularized and screened potential which is both of finite range and non-singular at the origin, and which involves as limiting cases the Debye (i.e., screened) and Coulomb potential. Two distinct cases are considered in detail. (i) The collision of two identical (e.g., electron-electron) particles; (ii) and the collision between a magnetized electron and an uniformly moving heavy ion. The energy transfer involves all harmonics of the electron cyclotron motion. The validity of the perturbation treatment is evaluated by comparing with classical trajectory Monte--Carlo calculations which also allows to investigate the strong collisions with large energy and velocity transfer at low velocities. For large initial velocities on the other hand, only small velocity transfers occur. There the non-perturbative numerical classical trajectory Monte--Carlo results agree excellently with the predictions of the perturbative treatment.

physics.plasm-ph↗

arXiv2007

Renormalized cluster expansion of the microfield distribution in a strongly coupled two-component plasmas

The electric microfield distribution (MFD) at an impurity ion is studied for two-component (TCP) electron-ion plasmas using molecular dynamics simulation and theoretical models. The particles are treated within classical statistical mechanics using an electron-ion Coulomb potential regularized at distances less than the de Broglie length to take into account quantum-diffraction effects. Corrections to the potential-of-mean-force exponential (PMFEX) approximation recently proposed for MFD in a strongly coupled TCP [Phys. Rev. E 72, 036403 (2005)] are obtained and discussed. This has been done by a generalization of the standard Baranger-Mozer and renormalized cluster expansion techniques originally developed for the one-component plasmas to the TCPs. The results obtained for a neutral point are compared with those from molecular dynamics simulations. It is shown that the corrections do not help to improve the PMFEX approximation for a TCP with low ionic charge Z. But starting with Z > 5 the PMFEX model is substantially improved and the agreement with numerical simulations is excellent. We have also found that with increasing coupling the PMFEX approximation becomes invalid to predict the MFD at a neutral point while its corrected version agrees satisfactory with the simulations.

physics.plasm-ph↗

arXiv2006

The moving boundary problem in the presence of a dipole magnetic field

An exact analytic solution is obtained for a uniformly expanding, neutral, infinitely conducting plasma sphere in an external dipole magnetic field. The electrodynamical aspects related to the radiation and transformation of energy were considered as well. The results obtained can be used in analyzing the recent experimental and simulation data.

physics.plasm-ph↗

arXiv2005

Microfield distributions in strongly coupled two-component plasmas

The electric microfield distribution at charged particles is studied for two-component electron-ion plasmas using molecular dynamics simulation and theoretical models. The particles are treated within classical statistical mechanics using an electron-ion Coulomb potential regularized at distances less than the de Broglie length to take into account the quantum-diffraction effects. The potential-of-mean-force (PMF) approximation is deduced from a canonical ensemble formulation. The resulting probability density of the electric microfield satisfies exactly the second-moment sum rule without the use of adjustable parameters. The correlation functions between the charged radiator and the plasma ions and electrons are calculated using molecular dynamics simulations and the hypernetted-chain approximation for a two-component plasma. It is shown that the agreement between the theoretical models for the microfield distributions and the simulations is quite good in general.

physics.plasm-ph↗

arXiv1999

Stopping of ion beam in a temperature anisotropic magnetized plasma

Using the dielectric theory for a weakly coupled plasma we investigate the stopping power of the ion in a temperature anisotropic magnetized electron plasma. The analysis is based on the assumption that the energy variation of the ion is much less than its kinetic energy. The obtained general expression for stopping power is analyzed for weak and strong magnetic fields (i.e., for the electron cyclotron frequency less than and greater than the plasma frequency), and for low and high ion velocities. It is found that the friction coefficient contains, in addition to the usual velocity independent friction coefficient, an anomulous term which diverges logarithmically as the projectile velocity approaches zero. The physical origin of this anomulous term is the coupling between the cyclotron motion of the electrons and the long-wave length, low-frequency fluctuations produced by the projectile ion.

physics.plasm-ph↗

arXiv1999

Spectrum of surface-mode contributions to the excitation probability for electron beam interacting with sharp-edged dielectric wedges

The interaction of a nonrelativistic charged particle beam, travelling parallel to the surface of a sharp-edged dielectric wedge is analyzed. The general expressions for excitation probability are obtained for a beam moving along the direction of a symmetry axis, either outside or inside the dielectric wedge. The dielectric function of the medium is assumed to be isotropic, and numerical results are given for the materials of experimental interest.

cond-mat.mtrl-sci↗

arXiv1999

Excitation of nonlinear one-dimensional wake waves in underdense and overdense magnetized plasma by a relativistic electron bunch

The excitation of wake waves by a relativistic homogeneous electron bunch passing through cold magnetized plasma at equilibrium is studied for arbitrary values of the ratio of bunch density to plasma density. The analysis is based on the assumption that the magnetic field is sufficiently strong ($ω_B\gg ω_p$, where $ω_p$ and $ω_B$ are the electron plasma and cyclotron frequences respectively). The periodic and nonperiodic solutions for the momentum of plasma electrons inside and outside the bunch are analyzed. It was shown that the presence of strong external magnetic field may increase the amplitude of wake waves and the maximum transformer ratio, the latter being reached at densities of bunch lower than that in the absence of magnetic field. The optimum conditions for obtaining the maximum values of the wake field amplitude and of the transformer ratio are found.

physics.plasm-ph↗