1996
Authors
Havnes O. Li F. Melandso F. Aslaksen T. Hartquist TW. Morfill GE. Nitter T. Tsytovich V.Title
DIAGNOSTIC OF DUSTY PLASMA CONDITIONS BY THE OBSERVATION OF MACH CONES CAUSED BY DUST ACOUSTIC WAVESSource
Journal of Vacuum Science & Technology A-Vacuum Surfaces & Films.Abstract
14(2):525-528, 1996 Mar-Apr.
The theory of dust acoustic waves in dusty plasmas is well developed for conditions with monosized dust particles. It was proposed [O. Havnes et al., J. Geophys. Res. 100, 1731 (1995)] that such waves may be generated in planetary dust rings by boulders moving through the dust at a velocity that is somewhat higher than the dust acoustic velocity. In this manner Mach cones can form with an opening angle that is dependent on the boulder velocity and the local dust acoustic velocity. Measurements of this opening angle will therefore provide additional information on dusty plasma conditions since the dust acoustic velocity can be determined when the boulder velocity is known. We suggest that this method may also be applied under laboratory conditions if a suitable controlled disturbance can be made and we discuss how the dust acoustic velocity and resulting Mach cones are affected if the dusty plasma have a distribution of dust sizes. (C) 1996 American Vacuum Society. [References: 13]
Authors
Thomas HM. Morfill GE.Title
SOLID LIQUID GASEOUS PHASE TRANSITIONS IN PLASMA CRYSTALSSource
Journal of Vacuum Science & Technology A-Vacuum Surfaces & Films.Abstract
14(2):501-505, 1996 Mar-Apr.
We present further observations of the solid/liquid and liquid/gaseous phase transition in plasma crystals. Plasma crystal is the term used to describe the recently discovered "state" that a colloidal plasma may assume under certain conditions-a state which has properties resembling those of metals. During the melting transition from solid to liquid the system passes through an intermediate "flow and flee" stage that has not been observed in other model crystals before. It may well be that this intermediate stage is a general feature of the solid/liquid phase transition in crystals. In this case it is clearly important. The fact that this stage could be detected for the first time is a consequence of the unique properties of plasma crystals: global charge neutrality, very fast response and little damping, easy experimental control, detailed imaging, and fine time resolution of the dynamics of individual particles ("atoms"). (C) 1996 American Vacuum. [References: 26]
Authors
Zuzic M. Thomas HM. Morfill GE.Title
WAVE PROPAGATION AND DAMPING IN PLASMA CRYSTALSSource
Journal of Vacuum Science & Technology A-Vacuum Surfaces & Films.Abstract
14(2):496-500, 1996 Mar-Apr.
Wave propagation through plasma crystals provides an interesting experimental approach towards understanding strongly coupled plasmas as well as certain solid state properties of crystals. In order to build up our basic understanding of conditions and processes, oscillation modes of one- and two-particle systems are investigated first, and the damping process is identified by studying the amplitude variations of the oscillations as a function of the excitation frequency. Next, single layer plasma crystals are investigated using the same techniques. An induced spontaneous transition from the solid to the gas phase is observed, and its possible origin is discussed. (C) 1996 American Vacuum Society. [References: 10]
Authors
Morfill GE. Thomas H.Title
PLASMA CRYSTALSource
Journal of Vacuum Science & Technology A-Vacuum Surfaces & Films.Abstract
14(2):490-495, 1996 Mar-Apr.
Plasma crystal is the term used to describe the recently discovered ordered state that a colloidal plasma may assume under certain conditions. This state resembles metals, to some extent, with the ''atoms'' represented by the highly negatively charged and highly ordered colloidal particles and the ''electrons'' by the mobile plasma ions and electrons-perhaps ''heavy metal'' might be an appropriate description. Plasma crystals are formed in a colloidal plasma if two conditions are met: (1) The Coulomb coupling parameter (the ratio of the Coulomb energy between neighboring particles to their kinetic energy) exceeds a certain threshold and (2) the lattice parameter (the ratio of the particle separation to the Debye length) is smaller than unity. These conditions are easy to generate in rf discharge plasmas and plasma crystallization then proceeds spontaneously. Plasma crystals have some unique properties, which make them exciting systems to study. (1) In their own right, as a hitherto unknown form of condensed plasma, they may provide many insights into basic plasma physical processes and transport effects. (2) As model systems for the detailed investigation of phase transitions, lattice defects, annealing, doping, etc., they may provide new information for a better understanding of solid state physics. (3) As test systems they may be useful for investigating nonlinear effects in ''nanocrystals'' (crystals with less than approximately 100 lattice planes). The unique properties, which enable these investigations and possibly many more, are (1) global charge neutrality, (2) very fast response, (3) very little damping, and (4) easy experimental control and diagnostics, i.e., detailed imaging and high temporal resolution of the dynamics of individual particles (''atoms''). We present here an overview of recent developments in this new research field. (C) 1996 American Vacuum Society. [References: 28]
Authors
Quinn RA. Cui C. Goree J. Pieper JB. Thomas H. Morfill GE.Title
STRUCTURAL ANALYSIS OF A COULOMB LATTICE IN A DUSTY PLASMASource
Physical Review A. 53(3):R2049-R2052, 1996 Mar.Abstract
Pair and bond-orientational correlation functions and structure factors, as used in colloidal science, are applied as quantitative indicators of the phase of the newly discovered ''plasma crystals.'' These Coulomb-lattice structures are formed by charged microspheres levitated in glow discharge plasmas and are imaged photographically. Static structural analysis is demonstrated on the experimental data of Thomas et al. [Phys. Rev. Lett. 73, 652, (1994)] and interpreted in the context of a two-dimensional (2D) dislocation-unbinding melting theory and a 2D density-wave melting theory. [References: 27]
Authors
Shukla PK. Morfill G.Title
IONIZATION INSTABILITY OF DUST-ACOUSTIC WAVES IN WEAKLY IONIZED COLLOIDALSource
PLASMAS
Physics Letters A. 216(1-5):153-156, 1996 Jun 17.Abstract
It is shown that dust-acoustic waves in an unmagnetized dusty plasma can be excited on account of an ionization instability. The expressions for the growth rates and thresholds are given explicitly. [References: 14]
Authors
Thomas HM. Morfill GE.Title
MELTING DYNAMICS OF A PLASMA CRYSTALSource
Nature. 379(6568):806-809, 1996 Feb 29.Abstract
Plasmas have long been regarded as the most disordered state of matter; nevertheless, a set of colloidal particles introduced into a charge-neutral plasma can spontaneously exhibit ordered crystalline structures(1,2) -- so-called 'plasma crystals'. Such systems, which reach equilibrium very rapidly and can be easily tuned between their ordered and disordered states, are ideally suited for investigating the processes underlying the solid-to-liquid phase transition. Here we report the results of experiments on 'flat' plasma crystals (with thicknesses of only a few lattice planes) which suggest that the melting transition occurs through two fundamental intermediate stages. On melting, the crystal first enters a state characterized by islands of crystalline order about which streams of particles flow. The crystalline regions then dissolve as the vibrational energy of the system increases, but this is accompanied by a temporary increase in orientational order before the system finally enters a disordered, liquid state. The unexpected 'vibrational' phase, characterized by enhanced orientational order, might arise as a consequence of the mixed two- and three-dimensional nature of the flat plasma crystals. Alternatively, it may indicate the existence of a new intermediate state in melting transitions more generally. [References: 25]
Authors
Birk GT. Kopp A. Shukla PK. Morfill G.Title
NONLINEAR FLUID EQUATIONS FOR LOW-FREQUENCY PHENOMENA IN PARTIALLY IONIZED DUSTY MAGNETOPLASMASSource
Physica Scripta. 54(6):625-626, 1996 Dec.Abstract
A set of five coupled held equations governing the nonlinear dynamics of low-frequency (in comparison with the ion gyrofrequency) phenomena in partially ionized collisional dusty magnetoplasmas has been derived These are the continuity and the momentum transfer equations for the neutral and dust fluids as well as an appropriate Ampere's law for partially ionized dusty gases. The presented set of nonlinear magnetohydrodynamic (MHD) equations should be useful for a self-consistent description of linear and nonlinear wave and instability phenomena in dusty magnetoplasmas whose constituents are negatively charged dust grains,single charged positive ions, as well as neutral atoms. [References: 15]
Updated: 2004-11-18
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