Generalized bohm criterion for a multicomponent plasma

We have formulated the generalized Bohm criterion regulating the existence of a stationary charged near-electrode sheath in a multicomponent plasma with an infinitely large number of ion species. The criterion has the form of a set of inequalities one of which coincides with the Bohm criterion for a two-component plasma.     

Self-consistent expansion of a multicomponent plasma into a vacuum

The problem of the one-dimensional collisionless expansion of a multicomponent plasma into a vacuum is considered. In the hydrodynamic approximation, an approximate analytical solution for an arbitrary set of ion species with masses M₁,..., M_n and charge numbers Z₁e, Z₂e,..., Z_ne is found by using the technique of self-similar variables employed by Gurevich, Pariiskaya, and Pitaevskii for the case of single-species ions. A numerical iterative algorithm is developed in which the analytical solution is used as a first approximation.     

Distribution functions of a slightly nonideal multicomponent plasma

A regular perturbation theory technique is constructed using the plasma parameters of the equilibrium Bogolyubov-Born-Green-Kirkwood-Yvon (BBGKY) equation chain for a multicomponent plasma in which higher order terms are small at all admissable interparticle distances, in contrast to the Debye equations. As a result, two correlation radii appear in a charge-asymmetric plasma: the Debye radius D and 2 D. The divergence of correlation functions characteristic of Debye splitting is eliminated in any order of the perturbation theory. For the proposed theory to be applicable the plasma parameter must be limited more severely, the deeper the depth of the potential well which appears upon approach of oppositely charged ions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 53–58, May, 1988.     

Holographic recording of laser-induced plasma

We report on a holographic probing technique that allows for measurement of free-electron distribution with fine spatial detail. Plasma is generated by focusing a femtosecond pulse in air. We also demonstrate the capability of the holographic technique of capturing the time evolution of the plasma-generation process.     

Time resolved laser-induced plasma dynamics

The structure and evolution of the laser-induced vapor plume and shockwave were measured from femtosecond time resolved shadowgraph images. By changing the wavelength of the probe beam (400 and 800 nm), differences in the opacity of the vapor plume were measured as a function of delay time from the ablation laser pulse. The evolution of the temperature and electron number density during and after the ablation laser pulse were determined and compared for ablation in argon and helium background gases. A laser supported detonation wave (LSD) observed for ablation in argon, blocks the incoming laser energy and generates a high-pressure region above the vapor plume.     

Dynamics in a multicomponent plasma near the low-frequency cutoff

The distinctive feature of a multicomponent plasma is found to be a first order rotation of the light ion fluid with a characteristic frequency, Omega(r). A resonance at omega=Omega(r) results in plasma oscillation with unique properties. Coupling of the fast rotation time scale with the slow magnetosonic time scale leads to a nonlinear Schro dinger equation for the system and suggests the possibility of strong structural turbulence at MHD scales.     

Weak electron acoustic double layers in a multicomponent plasma

Formation of electron acoustic double layers in a magneto-plasma with two ion species is investigated. The existence of double layers propagating almost perpendicular to the magnetic field in a plasma with two distinct ion species and cold electron is discussed.     

Time-integrated photography of laser-induced plasma plumes

The shape of the plasma plume induced by KrF-laser irradiation of Y?Ba?Cu?O, Cu?O, and Cu targets in O₂ and N₂ atmosphere was investigated by time-integrated photography. The dependence on laser fluence, spot size, and pressure of the ambient gas was studied. Special emphasis was put on the ablation of YBCO in O₂ atmosphere under experimental conditions that are typical for thin-film deposition.     

Parameters of a slightly degenerate plasma

Summary This paper deals with some aspects of quantistic effects in a partially ionized plasma. A simplified Boltzmann-Vlasov equation is obtained, by taking into account the Pauli exclusion principle. Then two problems are analysed: the dispersion of electrostatic waves and the electrical conductivity. This work was supported in part by MPI (60%) grants of the Italian Ministry of education.     

Enhanced laser-induced plasma channels in air

Plasma is a significant medium in high-energy density physics since it can hardly be damaged. For some applications such as plasma based backward Raman amplification(BRA), uniform high-density and large-scale plasma channels are required. In the previous experiment, the plasma transverse diameter and density are 50–200 μm and 1–2 × 10~(19)cm~(-3),here we enhance them to 0.8 mm and 8 × 10~(19)cm~(-3), respectively. Moreover, the gradient plasma is investigated in our experiment. A proper plasma gradient can be obtained with suitable pulse energy and delay. The experimental results are useful for plasma physics and nonlinear optics.     

激光与介质薄膜作用过程的等离子体诊断

本文对YAG激光诱导介质薄膜产生的等离子体采用Mach-Zehnder干涉仪及光延迟装置进行时间序列分辨多幅干涉记录,并对序列干涉图进行电子密度及等离子体冲击波速度的计算.首次得到脉宽为15ns的1.06μm激光与介质薄膜作用在150ns以内的有关结果.     

Calibration-free laser-induced plasma analysis of a metallic alloy with self-absorption correction

Identification and concentration measurement of constituent elements of a metallic alloy is demonstrated by calibration-free laser-induced breakdown spectroscopy (CF-LIBS) according to a special peak intensity-based model and considering the self-absorption effect. In this procedure, which is based on the line pair ratio method, the effect of line widths, though needs to be theoretically considered, may be approximately ignored. This is mainly true for the multiplet lines, but this property, in the case of some generic spectral lines in a measured spectrum, can be sometimes regarded. Initially, the optical penetration depth and therefrom self-absorption coefficient of each selected spectral line is calculated using the experimental (self-absorbed) intensity of the line. Then, the true (non-self-absorbed) intensity, which is basis of the conventional CF-LIBS calculation, is obtained through a recursive algorithm implemented by the MATLAB programming. In the experimental examination, the recorded spectrum reflects that the metallic alloy is consisted of gold, copper and silver. The concentration of elements is calculated with and without regarding self-absorption correction using 27 trios of spectral lines related to the elements. The average concentrations signify that the measurement error relative to the certified value for the concentration of the gold is modified from 3.56 % in the normal way to 0.34 % after applying self-absorption correction.     

Observation of Peregrine solitons in a multicomponent plasma with negative ions

The experimental observation of Peregrine solitons in a multicomponent plasma with the critical concentration of negative ions is reported. A slowly amplitude modulated perturbation undergoes self-modulation and gives rise to a high amplitude localized pulse. The measured amplitude of the Peregrine soliton is 3 times the nearby carrier wave amplitude, which agrees with the theory. The numerical solution of the nonlinear Schr?dinger equation is compared with the experimental results.     

Generation and expansion of laser-induced plasma as a spectroscopic emission source

Laser-induced plasma represents today a widespread spectroscopic emission source. It can be easily generated using compact and reliable nanosecond pulsed laser on a large variety of materials. Its application for spectrochemical analysis for example with laser-induced breakdown spectroscopy (LIBS) has become so popular that one tends to forget the complex physical and chemical processes leading to its generation and governing its evolution. The purpose of this review article is to summarize the backgrounds necessary to understand and describe the laser-induced plasma from its generation to its expansion into the ambient gas. The objective is not to go into the details of each process; there are numerous specialized papers and books for that in the literature. The goal here is to gather in a same paper the essential understanding elements needed to describe laser-induced plasma as results from a complex process. These elements can be dispersed in several related but independent fields such as laser-matter interaction, laser ablation of material, optical and thermodynamic properties of hot and ionized gas, or plasma propagation in a background gas. We believe that presenting the ensemble of understanding elements of laser-induced plasma in a comprehensive way and in limited pages of this paper will be helpful for further development and optimized use of the LIBS technique. Experimental results obtained in our laboratory are used to illustrate the studied physical processes each time such illustration becomes possible and helpful.     

Propagation of waves in a multicomponent plasma having charged dust particles

Propagation of both low and high frequency waves in a plasma consisting of electrons, ions, positrons and charged dust particles have been theoretically studied. The characteristics of dust acoustic wave propagating through the plasma has been analysed and the dispersion relation deduced is a generalization of that obtained by previous authors. It is found that nonlinear localization of high frequency electromagnetic field in such a plasma generates magnetic field. This magnetic field is seen to depend on the temperatures of electrons and positrons and also on their equilibrium density ratio. It is suggested that the present model would be applicable to find the magnetic field generation in space plasma.     

Effect of multicomponent dust grains in a cold quantum dusty plasma

By employing the quantum hydrodynamic model for electron-ion-dust plasma,we derive a dispersion relation of the quantum dusty plasma.The effects of the dust size distribution on the dispersion relation in a cold quantum dusty plasma are studied.Both analytical and numerical results are given to compare the differences between the dusty plasma by considering the dust size distribution and the mono-sized dusty plasma.It is shown that many system parameters can significantly influence the dispersion relation of the quantum dusty plasma.     

Detection of broadband terahertz waves with a laser-induced plasma in gases

We report the experimental results and theoretical analysis of broadband detection of terahertz (THz) waves via electric-field-induced second-harmonic generation in laser-induced air plasma with ultrashort laser pulses. By introducing the second-harmonic component of the white light in the laser-induced plasma as a local oscillator, coherent detection of broadband THz waves with ambient air is demonstrated for the first time. Our results show that, depending on the probe intensity, detection of THz waves in air can be categorized as incoherent, hybrid, and coherent detection. Coherent detection is achieved only when the tunnel ionization process dominates in gases.     

Acceleration of a multicomponent plasma in the cathode region of a vacuum arc

A general solution to the problem of the steady-state spherical expansion of a current-carrying multicomponent plasma into a vacuum is derived. It is shown that, in vacuum arc discharges, the main force accelerating the cathode material, which becomes a plasma at distances of 1 to 300 μm from the cathode surface, is the electron pressure gradient force maintained by Joule heating. It is established that ions of different charges move with the same hydrodynamic velocity, which is uniquely determined by the mass and mean charge of the ions and the maximum electron temperature in the cathode region.