Optical diagnostics of femtosecond laser plasmas

Optical diagnostics of evolution of plasmas produced by ultrashort laser pulses is carried out using a femtosecond probing beam. The time sequence of plasma shadowgrams and interferograms are obtained. The filamentation instability in high-density region induces the local density modification. Large-scale toroidal magnetic fields confine plasma expansion in the transverse direction, resulting in the formation of a plasma jet. The plasma expansion along the target normal direction is found to scale as t^1/2.     

Charge density fluctuation of low frequency in a dusty plasma

The charge density fluctuation of low frequency in a dusty plasma, which is derived from the longitudinal dielectric permittivity of the dusty plasma, has been studied by kinetic theory. The results show that theP value, which describes the relative charge density on the dust in the plasma, and the charging frequency of a dust particle Ω _c , which describes the ratio of charge changing of the dust particles, determine the character of the charge density fluctuation of low frequency. For a dusty plasma ofP≪1, when the charging frequency Ω _c , is much smaller than the dusty plasma frequency ω_d, there is a strong charge density fluctuation which is of character of dust acoustic eigenwave. For a dusty plasma ofP≫1, when the frequency Ω _c , is much larger than ω _d there are weaker fluctuations with a wide spectrum. The results have been applied to the ionosphere and the range of radius and density of dust particles is found, where a strong charge density fluctuation of low frequency should exist.     

On the Attractive Plasma-Charge System in 2-d

We study a positively charged Vlasov-Poisson plasma in which N negative point charges are immersed. The attractiveness of the system forces us to consider a possibly unbounded plasma density near the charges. We prove the existence of a global in time solution, assuming a suitable initial distribution of the velocities of the plasma particles. Uniqueness remains unsolved.     

Trois formulations d'un modèle de plasma quasi-neutre avec courant non nul

In this Note, we propose three formulations of a model describing a quasi-neutral plasma with non-vanishing current. In order to study and compare the numerical efficiency of each formulation, two test-problems are implemented in one dimension. The first is a periodic perturbation of a uniform stationary plasma. The second is a case of plasma expansion in vacuum between two electrodes. To cite this article: P. Crispel et al., C. R. Acad. Sci. Paris, Ser. I 338 (2004).     

Un modèle d'expansion de plasma dans le videA model for plasma expansion in vacuum

In this paper, we propose a model describing the expansion of a plasma in vacuum. Our starting point consists of a 2-fluid Euler system (isentropic case) coupled with the Poisson equation. Since numerical simulations of this model are very expensive, we investigate a quasi-neutral limit of it. We show that electron emission happens at the plasma–vaccum interface. This emission is well modeled by a Child–Langmuir law. The difficulty consists in accounting for the motion of the plasma–vacuum interface. In this paper, we formally and numerically justify why electron emission produces a reaction pressure which slows down the plasma expansion. To cite this article: P. Degond et al., C. R. Acad. Sci. Paris, Ser. I 335 (2002) 399–404.     

Behavior of a plasma with the collision rate proportional to the electron velocity in an external electric field

We solve the problem of the behavior of a gas plasma in a half-space analytically using the kinetic equation with the collision rate proportional to the modulus of the electron velocity. The plasma is in a variable external electric field. The specular reflection of electrons from the plasma boundary is used as a boundary condition. We use the solution to find the screened electric field. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 153, No. 3, pp. 409–421, December, 2007.     

Stimulated Raman scattering in the presence of trapped particle instability

The behaviour of electron gas in a laser plasma corona is studied in the presence of stimulated Raman scattering (SRS). The 1D Vlasov–Maxwell model describing plasma relevant to the experiment PALS (Prague Asterix Laser System), where the nanosecond iodine laser with the wavelength of first harmonic λ_vac = 1.3152 and with the power density in the focal spot I = 10²⁰ W/m² is in operation. For the solution of Vlasov equation for the electron distribution function a Fourier–Hermite transform method is used. For the numerical stabilization a small collision term is added to the Vlasov equation keeping its value realistic for the condition relevant to the PALS experiment. The dominant wave modes in our model are both the backward (SRS-B) and the forward (SRS-F) Raman scattering, each of them accompanied by the forward going electron plasma wave. Several mechanisms were identified such as the SRS-B plasma wave spectral broadening due to a trapped particle instability (TPI) or the formation of an electrostatic quasi-mode by non-resonant interaction of SRS-B and SRS-F plasma waves.     

Effect of cold plasma permittivity on the radiation of the dominant TEM‐wave by an impedance loaded parallel‐plate waveguide radiator

The effects of wall impedances on the radiation of the dominant transverse electromagnetic wave by an impedance loaded parallel‐plate waveguide radiator immersed in a cold plasma have been analyzed. The solution to the governing mathematical model in cold plasma is determined while using the Wiener–Hopf technique. It is observed that the amplitude of the radiated field increases with increasing permittivity of the plasma. The work presented may be of great interest to quantify the effects of ionosphere plasma on the communicating signals between Earth station and an artificial satellite in the Earth's atmosphere. Copyright © 2015 John Wiley & Sons, Ltd.     

On Plane Waves in Diluted Relativistic Cold Plasmas

We briefly report on some exact results (Fiore in J. Phys. A, Math. Theor. 47:225501, 2014) regarding plane waves in a relativistic cold plasma. If the plasma, initially at rest, is reached by a transverse plane electromagnetic travelling-wave, then its motion has a very simple dependence on this wave in the limit of zero density, otherwise can be determined by an iterative procedure whose accuracy decreases with time or the plasma density. Thus one can describe in particular the impact of a very intense and short laser pulse onto a plasma and determine conditions for the slingshot effect (Fiore et al. in arXiv:1309.1400, 2014) to occur. The motion in vacuum of a charged test particle subject to a wave of the same kind is also determined, for any initial velocity.     

Simulation of processes in an electrodynamic mass accelerator

Processes in a pulse plasma accelerator used as a mass accelerator are simulated in the magnetohydrodynamic approximation. Numerical calculations elucidate the dynamics of formation of a plasma piston. Two qualitatively different modes of plasma piston formation are identified, and the acceleration of the body in each mode is determined. Calculations show that the plasma dynamics mainly depends on the mass of the working substance, the dependence of plasma conductivity on the thermodynamic parameters, and the electrode cooling scheme.Translated from Matematicheskoe Modelirovanie i Reshenie Obratnykh Zadach Matematicheskoi Fiziki, pp. 201–207, 1993.     

Optimization of the MHH stellarator

The Modular Helias-like Heliac is a coil configuration selected two years ago for the U.S. Stellarator Power Plant Study. Since that time the design has been significantly improved by running a collection of three-dimensional plasma physics codes. An attractive choice seems to be three field periods, aspect ratio six for the plasma, and rotational transform ranging from 1/4 at the magnetic axis down to 1/5 at the separatrix. The torsion of the modular coils is low, and they are spaced well apart from each other and from the plasma. © 1997 John Wiley & Sons, Inc.     

Modeling and simulation of plasma jet by lattice Boltzmann method

In order to find a simple and efficient simulation for plasma spray process, an attempt of modeling was made to calculate velocity and temperature field of the plasma jet by hexagonal 7-bit lattice Boltzmann method (LBM) in this paper. Utilizing the methods of Chapman–Enskog expansion and multi-scale expansion, the authors derived the macro equations of the plasma jet from the lattice Boltzmann evolution equations on the basis of selecting two opportune equilibrium distribution functions. The present model proved to be valid when the predictions of the current model were compared with both experimental and previous model results. It is found that the LBM is simpler and more efficient than the finite difference method (FDM). There is no big variation of the flow characteristics, and the isotherm distribution of the turbulent plasma jet is compared with the changed quantity of the inlet velocity. Compared with the velocity at the inlet, the temperature at the inlet has a less influence on the characteristics of plasma jet.     

Uniform boundedness of the magnetic field in a resistive plasma

While the magnetic energy in a plasma can be easily bounded by classical energy inequalities, the behaviour of the maximum of the magnetic field is less clear. In fact, the field in chaotic flows appears to concentrate in progressively smaller regions of the domain, so that conceivably it could grow there without limit. However, we prove that as long as the magnetic energy and the plasma remain bounded, so does the magnetic field. The dependence of these bounds on the main plasma parameters is analysed. Copyright © 2003 John Wiley & Sons, Ltd.     

Virial type blow-up solutions for the Zakharov system with magnetic field in a cold plasma

In this paper, we study blow-up solutions of virial type to the Zakharov system with magnetic field in a cold plasma in RN (N=2,3). After obtaining some a priori estimates on those terms generated by the magnetic field, we obtain a virial type blow-up result to the system under consideration. The result suggests that the magnetic field in a cold plasma doesn?t affect the virial type blow-up character of the Zakharov system.     

Stabilization of axisymmetric instability in a tokamak with a diverter

We consider the stabilization of vertical instability of a toroidal plasma pinch using passive ring conductors. The analysis is conducted by two techniques: by numerical solution of the system of linearized MHD equations and by applying the energy principle. We investigate the dependence of plasma stability on the location and the number of conductors and examine the effect produced by closing the conductors into sections. For an INTOR plasma pinch we show that a small number N 4 of properly placed conductors of reasonable size may suppress vertical instability.Translated from Vychislitel'naya Matematika i Matematicheskoe Obespechenie EVM, pp. 130–138, 1985.     

Zustandsgrössen eines schweren Plasmas in Abhängigkeit von temperatur und Dichte

Summary Assuming thermodynamic equilibrium we calculate ion and electron densities of a uranium plasma in the temperature range between 0,5 keV and 50 keV for densities around 10²³ ions per cm³ using a simplified Saha equation. The ionization energies are found by extrapolation from known data or by a Slater approximation.The ratios of the partition functions of two successive stages of ionization are set equal to one. A depression of the ionization energies caused by electrostatic interactions is considered. The numerical results include the internal energy of the plasma as a function of temperature.     

Sulla instabilità gravitazionale secondo Jeans di un plasma dissipativo in presenza di effetto Hall

Summary In this paper we study Jeans' gravitational instability of a dissipative Hall plasma, i.e., of a viscous, heat-conducting plasma with finite electrical conductivity, described by the magnetofluiddynamic equations in the presence of the Hall effect. The critical value of the wavelength is determined and the condition for the gravitational instability is discussed. Several noteworthy particular cases are then examined.

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Facoltà di Ingegneria dell'Università.

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Entrata in Redazione il 7 settembre 1977.     

Oscillations in quasineutral plasmas

Abstract The purpose of this article is to describe the limit, as the vacuum electric permittivity goes to zero, of a plasma physics system, deduced from the Vlasov—Poisson system for special initial data (distribution functions which are analytic in the space variable, with compact support in velocity), a limit also called "quasineutral regime'' of the plasma, and the related oscillations of the electric field, with high frequency in time.     

Analytical construction of peaked solutions for the nonlinear evolution of an electromagnetic pulse propagating through a plasma

Abstract

We obtain analytical solutions, by way of the homotopy analysis method, to a nonlinear wave equation describing the nonlinear evolution of a vector potential of an electromagnetic pulse propagating in an arbitrary pair plasma with temperature asymmetry. As the method is analytical, we are able to construct peaked structures which propagate through the pair plasma, analogous to peakon solutions. These solutions are obtained through a novel matching of inner and outer homotopy solutions. In order to ensure that our analytical results are valid over the whole real line, we also discuss the convergence of the analytical results to the true solution, through minimization of the residual errors resulting from an approximate analytical solution. These results demonstrate the existence of peaked pulses propagating through a pair plasma. The algebraic decay rate of the pulses are determined analytically, as well. The method discussed here can be applied to approximate solutions to similar nonlinear partial differential equations of nonlinear Schr¨odinger type.