76
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Nosenko V, Nunomura S, Goree J. Nonlinear compressional pulses in a 2D crystallized dusty plasma. PHYSICAL REVIEW LETTERS 2002; 88:215002. [PMID: 12059479 DOI: 10.1103/physrevlett.88.215002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2002] [Indexed: 05/23/2023]
Abstract
Compressional pulses were launched in a two-dimensional Yukawa lattice, a hexagonal monolayer of polymer microspheres suspended in a plasma. The pulsed wave was excited by a laser beam, and nonlinear effects were observed for Mach numbers M>0.07 and for variation of particle number density delta(n)/n>0.1, but no steepening of the pulse was detected. The pulse propagation speed was found to be comparable to the sound speed of compressional waves launched with sinusoidal excitation.
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77
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Quinn RA, Goree J. Particle interaction measurements in a Coulomb crystal using caged-particle motion. PHYSICAL REVIEW LETTERS 2002; 88:195001. [PMID: 12005638 DOI: 10.1103/physrevlett.88.195001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/29/2001] [Indexed: 05/23/2023]
Abstract
A technique for characterizing the particle interaction potential of a Coulomb crystal is developed. The mean-square displacement (MSD) is measured, showing both caged- and superdiffusive-particle motions. By subtracting the center of mass of neighboring particles in computing MSD, only short-wavelength particle motions are retained. This yields the lattice Einstein frequency, which contains information about the interparticle forces and potentials. Video measurements of particle motions in a complex (dusty) plasma are used to demonstrate the technique.
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78
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Nosenko V, Goree J, Ma ZW, Piel A. Observation of shear-wave Mach cones in a 2D dusty-plasma crystal. PHYSICAL REVIEW LETTERS 2002; 88:135001. [PMID: 11955103 DOI: 10.1103/physrevlett.88.135001] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/2001] [Indexed: 05/23/2023]
Abstract
Mach cones composed of shear waves were observed experimentally in a two-dimensional screened-Coulomb crystal. Highly charged microspheres suspended in a plasma and interacting with a repulsive Yukawa potential arranged themselves in a triangular lattice with hexagonal symmetry. Mach cones were excited by applying a force from the radiation pressure of a moving laser beam. They had a single-cone structure, which is explained by the almost dispersionless character of shear waves. The cone's opening angle obeyed the Mach-cone-angle relation. Results are compared to a molecular-dynamics simulation.
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79
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Quinn RA, Goree J. Experimental test of two-dimensional melting through disclination unbinding. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2001; 64:051404. [PMID: 11735920 DOI: 10.1103/physreve.64.051404] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2000] [Revised: 05/30/2001] [Indexed: 05/23/2023]
Abstract
A two-dimensional (2D) melting transition has been studied in a nonequilibrium experimental model system. The system used was a complex or dusty plasma consisting of microspheres suspended in a glow-discharge plasma, where we have mapped the topological defects during the transition. The role of the defects in the melting transition is evaluated and the arrangement of the defects in the lattice is quantified in a new way. It is found that defect density increases dramatically during the melting; at all stages the defects tend to be clustered together rather than widely dispersed; the clustering tends to take the form of chain or string-like structures. We compare these results for the defect structure with the assumptions of the popular 2D melting theory of Halperin and Nelson, rather than the predictions, as is more common.
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80
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Tsytovich VN, Vladimirov SV, Morfill GE, Goree J. Theory of collision-dominated dust voids in plasmas. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2001; 63:056609. [PMID: 11415033 DOI: 10.1103/physreve.63.056609] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2000] [Indexed: 05/23/2023]
Abstract
A dust void, i.e., the dust-free region in a dusty plasma, results from the balance of the electrostatic and plasma (such as the ion drag) forces acting on a dust particle. The properties of dust voids depend on the ratio of the void size to the mean free path of plasma ions colliding with neutral species of a weakly ionized plasma. For many plasma-processing and plasma-crystal experiments, the size of the void is much larger than the ion-neutral mean free path. The theory and numerical results are presented for such a collisional case including the situations in which the plasma is quasineutral in the void region or the plasma quasineutrality is violated, as well as the case in which the ion ram pressure is insignificant.
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81
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Samsonov D, Ivlev AV, Morfill GE, Goree J. Long-range attractive and repulsive forces in a two-dimensional complex (dusty) plasma. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2001; 63:025401. [PMID: 11308534 DOI: 10.1103/physreve.63.025401] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2000] [Indexed: 05/23/2023]
Abstract
An interaction of a negatively biased wire with a monolayer lattice of negatively charged particles has been studied experimentally. The particles levitated at the height of the wire in a sheath of an rf discharge. It was found that the particles close to the wire were repelled from it electrostatically, while the far particles were attracted due to the drag of the ion flow deflected toward the wire. The ion drag force prevails far from the wire, whereas the electrostatic force is stronger close to the wire. The range of the forces is one to two orders of magnitude greater than the screening length.
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82
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Zuzic M, Ivlev AV, Goree J, Morfill GE, Thomas HM, Rothermel H, Konopka U, Sütterlin R, Goldbeck DD. Three-dimensional strongly coupled plasma crystal under gravity conditions. PHYSICAL REVIEW LETTERS 2000; 85:4064-4067. [PMID: 11056625 DOI: 10.1103/physrevlett.85.4064] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2000] [Indexed: 05/23/2023]
Abstract
Experiments were carried out to investigate a three-dimensional (3D) plasma crystal. A method of determining the positions of each individual microparticle has been developed. A crystal volume of about 2x10(4) particles in 19 horizontal planes was analyzed. Direct imaging and the 3D pair correlation function show that "domains" of fcc and hcp lattices coexist in the crystal. Other structures, in particular, the theoretically predicted bcc lattice, were not observed.
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83
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Melzer A, Nunomura S, Samsonov D, Ma ZW, Goree J. Laser-excited mach cones in a dusty plasma crystal. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 2000; 62:4162-4176. [PMID: 11088945 DOI: 10.1103/physreve.62.4162] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2000] [Indexed: 05/23/2023]
Abstract
Experimental studies of the formation and structure of Mach cones in a plasma crystal are presented. Plasma crystals are ordered structures of charged microspheres trapped in the sheath of an rf discharge plasma. Using a monolayer crystal with a hexagonal lattice, Mach cones were excited by the radiation pressure of a focused laser beam. The beam was swept at a supersonic speed through the crystal, in a controlled and repeatable manner. A multiple Mach cone structure was observed, with at least three distinct Mach cones. The Mach angle relation was verified over a wide range of Mach numbers, for both the first and second cones. The sound speed, measured from the first Mach angle, was found to increase with the particle number density. Two methods of determining the particle charge and screening distance are developed, making use of the sound speed and an assumption of a Yukawa interparticle potential. Molecular-dynamics simulations of the experiment were carried out, using a monolayer of particles interacting through a Yukawa potential, and these show close agreement with the experiment.
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84
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Nunomura S, Samsonov D, Goree J. Transverse waves in a two-dimensional screened-coulomb crystal (Dusty plasma). PHYSICAL REVIEW LETTERS 2000; 84:5141-5144. [PMID: 10990887 DOI: 10.1103/physrevlett.84.5141] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2000] [Indexed: 05/23/2023]
Abstract
Transverse shear waves were observed experimentally in a two-dimensional screened Coulomb crystal. They were excited by applying a chopped laser beam to a 2D dusty plasma, i.e., a monolayer of charged microspheres levitated in a plasma. Measurements of the dispersion relation reveal an acoustic, i.e., nondispersive, character over the entire range of wave numbers measured, 0.2<k(r)a/pi<0.7, where a is the interparticle spacing. Comparison to theory provides a measurement of the particles' charge.
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85
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Samsonov D, Goree J, Thomas HM, Morfill GE. Mach cone shocks in a two-dimensional Yukawa solid using a complex plasma. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 2000; 61:5557-5572. [PMID: 11031610 DOI: 10.1103/physreve.61.5557] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/1999] [Indexed: 05/23/2023]
Abstract
Mach cones were studied experimentally in a two-dimensional Yukawa solid consisting of charged micrometer particles suspended as a layer in a plasma. These cones were V-shaped shocks produced spontaneously by a supersonic particle moving below the main two-dimensional particle layer. The cones had a double structure. The first cone was compressional and particles moved forward, and it was followed by a second cone, which was rarefactional, where particles moved backward. Over the limited range of speed V attained by the supersonic particles in this experiment, the angle mu of the cone was found to obey the Mach cone rule sin mu = c/V, where c is the medium's sound speed. The cones caused only elastic deformations in the crystal lattice, except in a narrow track behind the cone's vertex. The wings of the cones can be analyzed as linear shocks in two dimensions. Using spatially resolved measurements of the particle number density and velocity and applying the Hugoniot relations for shocks in two dimensions, we found that the pressure inside the first Mach cone was greater than in the undisturbed medium by a factor of 1.3-1.6. The cone angle was also used to measure the charge in this experiment.
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86
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Konopka U, Samsonov D, Ivlev AV, Goree J, Steinberg V, Morfill GE. Rigid and differential plasma crystal rotation induced by magnetic fields. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 2000; 61:1890-8. [PMID: 11046474 DOI: 10.1103/physreve.61.1890] [Citation(s) in RCA: 192] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/1999] [Indexed: 11/07/2022]
Abstract
Observations show that plasma crystals, suspended in the sheath of a radio-frequency discharge, rotate under the influence of a vertical magnetic field. Depending on the discharge conditions, two different cases are observed: a rigid-body rotation (all the particles move with a constant angular velocity) and sheared rotation (the angular velocity of particles has a radial distribution). When the discharge voltage is increased sufficiently, the particles may even reverse their direction of motion. A simple analytical model is used to explain qualitatively the mechanism of the observed particle motion and its dependence on the confining potential and discharge conditions. The model takes into account electrostatic, ion drag, neutral drag, and effective interparticle interaction forces. For the special case of rigid-body rotation, the confining potential is reconstructed. Using data for the radial dependence of particle rotation velocity, the shear stresses are estimated. The critical shear stress at which shear-induced melting occurs is used to roughly estimate the shear elastic modulus of the plasma crystal. The latter is also used to estimate the viscosity contribution due to elasticity in the plasma liquid. Further development is suggested in order to quantitatively implement these ideas.
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87
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Goree J, Morfill GE, Tsytovich VN, Vladimirov SV. Theory of dust voids in plasmas. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1999; 59:7055-67. [PMID: 11969694 DOI: 10.1103/physreve.59.7055] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/1998] [Indexed: 04/18/2023]
Abstract
Dusty plasmas in a gas discharge often feature a stable void, i.e., a dust-free region inside the dust cloud. This occurs under conditions relevant to both plasma processing discharges and plasma crystal experiments. The void results from a balance of the electrostatic and ion drag forces on a dust particle. The ion drag force is driven by a flow of ions outward from an ionization source and toward the surrounding dust cloud, which has a negative space charge. In equilibrium the force balance for dust particles requires that the boundary with the dust cloud be sharp, provided that the particles are cold and monodispersive. Numerical solutions of the one-dimensional nonlinear fluid equations are carried out including dust charging and dust-neutral collisions, but not ion-neutral collisions. The regions of parameter space that allow stable void equilibria are identified. There is a minimum ionization rate that can sustain a void. Spatial profiles of plasma parameters in the void are reported. In the absence of ion-neutral collisions, the ion flow enters the dust cloud's edge at Mach number M=1. Phase diagrams for expanding or contracting voids reveal a stationary point corresponding to a single stable equilibrium void size, provided the ionization rate is constant. Large voids contract and small voids expand until they attain this stationary void size. On the other hand, if the ionization rate is not constant, the void size can oscillate. Results are compared to recent laboratory and microgravity experiments.
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88
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Pieper JB, Goree J, Quinn RA. Three-dimensional structure in a crystallized dusty plasma. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1996; 54:5636-5640. [PMID: 9965751 DOI: 10.1103/physreve.54.5636] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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89
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Pieper JB, Goree J. Dispersion of Plasma Dust Acoustic Waves in the Strong-Coupling Regime. PHYSICAL REVIEW LETTERS 1996; 77:3137-3140. [PMID: 10062143 DOI: 10.1103/physrevlett.77.3137] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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90
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Quinn RA, Cui C, Goree J, Pieper JB, Thomas H, Morfill GE. Structural analysis of a Coulomb lattice in a dusty plasma. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1996; 53:R2049-R2052. [PMID: 9964604 DOI: 10.1103/physreve.53.r2049] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/01/2023]
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91
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Melandso F, Goree J. Polarized supersonic plasma flow simulation for charged bodies such as dust particles and spacecraft. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1995; 52:5312-5326. [PMID: 9964030 DOI: 10.1103/physreve.52.5312] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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92
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Sheridan TE, Goree J. Langmuir-probe characteristic in the presence of drifting electrons. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1994; 50:2991-2996. [PMID: 9962343 DOI: 10.1103/physreve.50.2991] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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93
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Thomas H, Morfill GE, Demmel V, Goree J, Feuerbacher B, Möhlmann D. Plasma crystal: Coulomb crystallization in a dusty plasma. PHYSICAL REVIEW LETTERS 1994; 73:652-655. [PMID: 10057503 DOI: 10.1103/physrevlett.73.652] [Citation(s) in RCA: 305] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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94
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Goree J. Ion trapping by a charged dust grain in a plasma. PHYSICAL REVIEW LETTERS 1992; 69:277-280. [PMID: 10046632 DOI: 10.1103/physrevlett.69.277] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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95
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Goeckner MJ, Goree J, Sheridan TE. Measurements of ion velocity and density in the plasma sheath. ACTA ACUST UNITED AC 1992. [DOI: 10.1063/1.860074] [Citation(s) in RCA: 61] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
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96
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Goeckner MJ, Goree J, Sheridan TE. Laser‐induced fluorescence characterization of a multidipole filament plasma. ACTA ACUST UNITED AC 1991. [DOI: 10.1063/1.859924] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
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97
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98
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Goree J, Ono M, Colestock P, Horton R, McNeill D, Park H. Fast-wave current drive in a toroidal plasma. PHYSICAL REVIEW LETTERS 1985; 55:1669-1672. [PMID: 10031888 DOI: 10.1103/physrevlett.55.1669] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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