Complex (dusty) plasmas: current status, open issues, perspectives

In recent decades particular interest in applications of nonequilibrium plasma for the problems of plasma-assisted ignition and plasma-assisted combustion has been observed. A great amount of experimental data has been accumulated during this period which provided the grounds for using low temperature plasma of nonequilibrium gas discharges for a number of applications at conditions of high speed flows and also at conditions similar to automotive engines. The paper is aimed at reviewing the data obtained and discusses their treatment. Basic possibilities of low temperature plasma to ignite gas mixtures are evaluated and historical references highlighting pioneering works in the area are presented. The first part of the review discusses plasmas applied to plasma-assisted ignition and combustion. The paper pays special attention to experimental and theoretical analysis of some plasma parameters, such as reduced electric field, electron density and energy branching for different gas discharges. Streamers, pulsed nanosecond discharges, dielectric barrier discharges, radio frequency discharges and atmospheric pressure glow discharges are considered. The second part depicts applications of discharges to reduce the ignition delay time of combustible mixtures, to ignite transonic and supersonic flows, to intensify ignition and to sustain combustion of lean mixtures. The results obtained by different authors are cited, and ways of numerical modelling are discussed. Finally, the paper draws some conclusions on the main achievements and prospects of future investigations in the field.

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Plasma assisted ignition and combustion

1 The Equations of Gas Dynamics 2 Magnetoplasma Dynamics 3 Waves in Magnetoplasmas 4 Magnetoplasma Stability 5 Transport in Magnetoplasmas 6 Extensions of Theory Bibliography Index

Physics of plasmas

Atomic Spectra Database

Complex (dusty) plasmas are composed of a weakly ionized gas and charged microparticles and represent the plasma state of soft matter. Complex plasmas have several remarkable features: Dynamical time scales associated with microparticles are ``stretched'' to tens of milliseconds, yet the microparticles themselves can be easily visualized individually. Furthermore, since the background gas is dilute, the particle dynamics in strongly coupled complex plasmas is virtually undamped, which provides a direct analogy to regular liquids and solids in terms of the atomistic dynamics. Finally, complex plasmas can be easily manipulated in different ways---also at the level of individual particles. Altogether, this gives us a unique opportunity to go beyond the limits of continuous media and study---at the kinetic level---various generic processes occurring in liquids or solids, in regimes ranging from the onset of cooperative phenomena to large strongly coupled systems. In the first part of the review some of the basic and new physics are highlighted which complex plasmas enable us to study, and in the second (major) part strong coupling phenomena in an interdisciplinary context are examined. The connections with complex fluids are emphasized and a number of generic liquid and solid-state issues are addressed. In summary, application oriented research is discussed.

Complex plasmas: An interdisciplinary research field

Experimental determination of the charge on dust particles forming Coulomb lattices

Measurements of the melting transition of a Coulomb crystal consisting of dust particles immersed in an rf parallel plate discharge in helium were performed. The dust crystal is shown to be solid at higher gas pressure (120 Pa) and low discharge power (10--20 W). Reducing the gas pressure or increasing the discharge power leads to fluid states of the dust ensemble. Even gaslike states are observed at low pressures of about 40 Pa. The transition is attributed to an increasing effective particle temperature. The phase transition is compared with one-component-plasma and Yukawa models, and with basic predictions of theories for two-dimensional melting. \textcopyright{} 1996 The American Physical Society.

Experimental investigation of the melting transition of the plasma crystal.

The screening of dust particles immersed in the sheath of a parallel plate rf discharge in helium is studied by excitation of waves in a linear chain arrangement. The waves are excited by the radiation pressure of a modulated laser beam. The measured dispersion relation is compared with a one-dimensional dust lattice wave to obtain the shielding length. Dust acoustic waves are not compatible with the measured dispersion relation. {copyright} {ital 1997} {ital The American Physical Society}

Determination of the dust screening length by laser-excited lattice waves

First experimental investigations of spherical three-dimensional plasma crystals consisting of hundreds or thousands of micrometer-sized polymer particles suspended in a radio-frequency gas discharge are described. These ``Coulomb balls'' are not subject to the formation of dust-free regions (voids) and have an unusual structure of nested crystalline shells. While small systems are in a solid phase, large systems show melting effects.

Dust Coulomb balls: three-dimensional plasma crystals.

The electrostatic interaction of a system of two single dust particles in a plasma-sheath environment with flowing ions has been investigated quantitatively It is shown that attractive net ``binding'' forces between the negatively charged particles exist, leading to the formation of a dust molecule By laser manipulation of the dust particles, it is demonstrated that the attraction is asymmetric in such a way that it acts only on one of the particles Moreover, the net forces between the particles can be reversibly changed between attraction and repulsion

André Melzer

Papers

Experimental determination of the charge on dust particles forming Coulomb lattices

Experimental investigation of the melting transition of the plasma crystal.

Determination of the dust screening length by laser-excited lattice waves

Dust Coulomb balls: three-dimensional plasma crystals.

Transition from Attractive to Repulsive Forces between Dust Molecules in a Plasma Sheath