The diffusion of macroparticles and criteria of phase transitions for dust structures in weakly ionized plasma

The dynamics of charged particles is investigated under conditions close to those of experiments in a weakly ionized laboratory gas-discharge dust plasma. The existing phenomenological criteria of phase transitions for dust structures in such a plasma are treated, and new criteria are suggested. The parameters responsible for the order and scaling of dynamic processes in Yukawa dissipative systems are determined. The relation for the diffusion coefficient D of macroparticles in strongly correlated liquid structures is derived.     

Convection in a weakly ionized plasma

The nonlinear dynamic stability of a weakly ionized plasma is investigated taking into account the spatial effects. Also obtained are the stability criteria.     

Nonlocal ion transport in a weakly ionized nonequilibrium plasma

Nonlocal ion transport in a weakly ionized plasma with a strong electric field is analyzed. It is assumed that charge-exchange interactions are the main mechanism of ion scattering. Ion density and drift velocity are determined for nonuniform time varying electric field by using both the direct solution of the kinetic equation and the Chapman-Enskog-type approach. The ion mean velocity is given by an integro-differential operator applied to the electric field. Ion density and drift velocity exhibit resonant behaviour when ω≃kW0, which corresponds to the resonance between ions moving with average velocity W₀ and wave traveling with the phase velocity ω/k     

Self-focusing of a laser beam in a strongly ionized plasma

In the presence of a strong Gaussian laser beam, the non-linearity in the dielectric constant of a strongly ionized plasma has been investigated. The non-linearity arises due to the heating and redistribution of the electrons; the loss of electron energy gained from the field has been assumed to be due to thermal conduction. This self-induced non-linearity causes a self-focusing and oscillatory waveguide propagation of the beam even when the non-linear dielectric constant does not fall in the saturating range. In a typical case of a 10¹⁰ W laser, the enhancement of axial intensity by a factor of 25 has been predicted in a length of 0.6 cm.Works supported by N.S.F. (USA).On leave from Malviya Regional Engeeniring College, Jaipur-4, India.     

Microscopic dynamics in a strongly interacting Bose-Einstein condensate

An initially stable 85Rb Bose-Einstein condensate (BEC) was subjected to a carefully controlled magnetic field pulse near a Feshbach resonance. This pulse probed the strongly interacting regime for the BEC, with the diluteness parameter (na(3)) ranging from 0.01 to 0.5. Condensate number loss resulted from the pulse, and for triangular pulses shorter than 1 ms, decreasing the pulse length actually increased the loss, until very short time scales (approximately 10 micros) were reached. The observed time dependence is very different from that expected in traditional inelastic loss processes, suggesting the presence of new microscopic BEC physics.     

Stimulated Brillouin effect in weakly ionized plasma

The stimulated Brillouin effect in gaseous plasma is investigated by means of classical coupledmode analysis. This process is described as interaction between an ion-acoustic plasma wave and two light waves. The threshold power levels calculated are achievable in giant-pulse lasers. However, the Brillouin effect may possibly be observable in the dense plasma or in the far infrared region of the electromagnetic spectrum.     

Nonequilibrium parton dynamics in the strongly interacting QGP

The dynamics of partons, hadrons and strings in relativistic nucleus-nucleus collisions is analyzed within the novel Parton-Hadron-String Dynamics (PHSD) transport approach, which is based on a dynamical quasiparticle model for partons (DQPM) matched to reproduce recent lattice-QCD results—including the partonic equation of state—in thermodynamic equilibrium. The transition from partonic to hadronic degrees of freedom is described by covariant transition rates for the fusion of quark-antiquark pairs or three quarks (antiquarks), respectively, obeying flavor current-conservation, color neutrality as well as energymomentum conservation. Since the dynamical quarks and antiquarks become very massive close to the phase transition, the formed resonant ‘pre-hadronic’ color-dipole states (q [`(q)]bar q or qqq) are of high invariant mass, too, and sequentially decay to the groundstate meson and baryon octets increasing the total entropy. When applying the PHSD approach to Pb + Pb colllisions at 158 A GeV we find a significant effect of the partonic phase on the production of multi-strange antibaryons due to a slightly enhanced s [`(q)]bar q pair production from massive time-like gluon decay and a larger formation of antibaryons in the hadronization process.     

Mass selected cluster deposition in strongly or weakly interacting media

Mass selected cluster deposition is discussed with respect to three questions: what is the integrity of the clusters after deposition; are they uniform in terms of size and isomerisation; and finally what is the influence of the support on the clusters? The answer to these questions will depend on the strength of cluster media interaction and we have chosen two extreme cases the inert rare gases on one hand and metal surfaces on the other. Three examples are given: Raman studies as well as low-temperature STM give structural information on the deposited clusters, while other optical spectroscopies (absorption and fluorescence) yield information on the electronic structure of the clusters. To cite this article: W. Harbich, C. Félix, C. R. Physique 3 (2002) 289–300.     

Macroscopic velocity of ions in a weakly ionized plasma in the crossed fields

Macroscopic velocity of energetic ions from energy spectra measured with electrostatic microanalyzer in the direction along and against the drift was found. It turned out, that in the investigated range of velocities a little below the critical one it is possible to describe the macroscopic motion of ions by the drift theory.The authors wish to thank Dr JanVáa and Prof.Jií Kracík for their interest and support, DrPavel unka for many helpful discussions, Mr J.Dvoák for his technical assistance throughout the work and Mr J.Zubec for manufacturing of the microanalyzer.     

Dynamo transformation of the collisional R–T in a weakly ionized plasma

Theoretical prediction of a new kind of normal mode behaviour of electro-mechanical nature was first time reported by Dwivedi and Das in 1992 in the context of mesospheric modeling of observed neutral induced turbulence. Local dynamo action (due to relative neutral flow) governs the basic physical principle for linear excitation of the neutral induced low frequency instability (NILF) in mesospheric plasma, which comprises of weakly ionized inhomogeneous gas confined by the external gravity and ambient magnetic field. The present contribution offers physical explanation in terms of dynamo transformation of neutral drag effect as a source to understand complete suppression of the usual collisional R-T and in turn linear driving of the NILF. It is therefore emphasized, worth calling it as the dynamo instability.     

Kinetic approach to the propagation of electromagnetic waves in a weakly ionized plasma

Summary High-frequency wave phenomena in a partially ionized plasma are analysed in the frame of the kinetic theory without resorting to perturbation techniques. In particular, we obtain the electron distribution function in an external electric field alternating in both time and position, and then the electrical conductivity and the dispersion relation. Corrections to the results of the macroscopic theory are evaluated up to any desired order.

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Riassunto Il fenomeno della propagazione di un'onda elettromagnetica in un plasma parzialmente ionizzato è analizzato nell'ambito della teoria cinetica. Il metodo proposto consente di ricavare la funzione di distribuzione degli elettroni senza dover ricorrere a tecniche perturbative. Si riportano le espressioni esatte della conducibilità elettrica e della legge di dispersione e, quindi, le correzioni da apportare ai risultati ottenuti con la teoria macroscopica.

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Резюме В рамках кинетической теории анализизируется явление распространения электромагнитных волн в частично ионизованной плазме. Предложенный метод позволяет получить электронную функцию распределения во внешнем электрическом поле без использования теории возмущений. Затем определяются электрическая проводимость и дисперсионное соотношение. Поправки к резулятатам макроскопической теории оцениваются в любом желаемом порядке.

     

Dynamics of heating of weakly ionized plasma in a self-consistent electric field

The dynamics of heating of a weakly ionized plasma in a pulsed discharge with allowance for the back reaction of the currents excited in the plasma on the field is analyzed on the basis of a kinetic equation with the Bhatnagar-Gross-Krook (BGK) model elastic collision integral. It is shown that the nature of the heating depends essentially on the ratio of the frequency of elastic collisions of an electron with neutrals and the plasma frequency. Analytic expressions for the dynamic electron distribution function and its moments are obtained. The limits of applicability of the approximation used are determined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 12–16, June, 1986.     

Incoherent scattering of electromagnetic waves by a weakly ionized plasma layer

Institute of Theoretical Physics of the Ukrainian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 33, No. 12, pp. 1327–1341 December, 1990