Experimental observation of a tripolar vortex in a plasma

Okamoto, Atsushi; Hara, Kazuhiro; Nagaoka, K.; Yoshimura, S.; Vranjes, Jovo; Kono, Mitsuo; Tanaka, MY

doi:10.1063/1.1571059

Cited by 57 publications

(41 citation statements)

References 18 publications

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“…Such equilibrium density gradients are in fact a rather common feature of various laboratory plasmas. 16,17 Note that an axial density inhomogeneity has also been detected. Yet, in view of very different axial and radial lengths of the chamber, that inhomogeneity may be neglected without losing much of essential physics.…”

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confidence: 99%

Global convective cell formation in pair-ion plasmas

Vranjes

Poedts

2008

Physics of Plasmas

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The global electrostatic mode in pair-ion plasmas is discussed for cylindric geometry and for a radially inhomogeneous equilibrium density. In the case of a Gaussian radial density profile, exact analytical eigensolutions are found in terms of the Kummer confluent hypergeometric functions. The mode is identified as a convective cell propagating in the poloidal and axial direction, having at the same time a standing wave structure in the radial direction. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2907160͔A new research field and a new area of increasing scientific activity have emerged recently after a series of experiments [1][2][3][4] in which a pure pair-ion plasma has been produced; i.e., a plasma without electrons. The two ions, i.e., C 60 Ϯ , are produced in a simultaneous process of impact ionization and electron attachment, and further collected by a magnetic filtering effect; i.e., by a diffusion in the radial direction ͑perpendicular to the magnetic field lines͒. Being separated from electrons, the ions are then collected in a narrow and elongated chamber ͑90 cm long and with a diameter of 8 cm͒. In Refs. 2-4, several types of modes have been reported in such plasmas; viz., the ion plasma wave, the ion acoustic wave ͑IAW͒, and the so-called intermediate frequency wave. The detailed measurements presented in the most recent Refs. 3 and 4, reveal that the IAW actually has two separate branches, and is accompanied by some additional backward propagating mode between these two branches. Some features of the experimentally observed modes still remain unexplained. These experimental works have been followed by numerous studies, 5-14 dealing with various aspects of linear and nonlinear waves and instabilities in pair-ion plasmas. In addition to this, the recent successful production of a pairhydrogen plasma, 4 which is even more attractive because of the small ion mass and the obvious consequences related to this, indicates that the number of experiments and analytical studies in this particular field will grow even further. The topic is interesting also in view of the fact that a similar pair plasma, comprising much lighter particles ͑electrons and positrons͒ in the past years has also been created under laboratory conditions. 15 The knowledge of processes in such plasmas will help us to understand the physics of some pairplasmas in space, comprising electrons and positrons, as in the atmospheres of pulsars and in active galactic nuclei, and even in flares in the lower solar atmosphere.So far, studies dealing with waves and instabilities 5-14 have been carried out mainly in the framework of a local mode analysis and in Cartesian geometry. However, the experimental conditions mentioned above 1-4 are such that, in some domains of frequencies and wavelengths, the proper cylindric geometry is to be used and the effects of the plasma boundary on the modes are to be taken into account. Therefore, in the present work we shall focus on frequencies below the ion gyrofrequency, on the effect of radial densi...

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confidence: 99%

Global convective cell formation in pair-ion plasmas

Vranjes

Poedts

2008

Physics of Plasmas

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“…The spontaneous formation of a tripolar vortex has been observed and analyzed in many other numerical studies. [5][6][7][8][9][10][11] The first experimental evidence of a tripolar vortex was given by van Heijst and Kloosterziel. 12 This study was soon followed by other observations of tripolar vortices in the laboratory [13][14][15][16] and in satellite imagery. 17 Higher-order vortices are less commonly observed.…”

Section: Introductionmentioning

confidence: 99%

Laboratory experiments on multipolar vortices in a rotating fluid

2010

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The instability properties of isolated monopolar vortices have been investigated experimentally and the corresponding multipolar quasisteady states have been compared with semianalytical vorticity-distributed solutions to the Euler equations in two dimensions. A novel experimental technique was introduced to generate unstable monopolar vortices whose nonlinear evolution resulted in the formation of multipolar vortices. Dye-visualization and particle imaging techniques revealed the existence of tripolar, quadrupolar, and pentapolar vortices. Also evidence was found of the onset of hexapolar and heptapolar vortices. The observed multipolar vortices were found to be unstable and generally broke up into multipolar vortices of lesser complexity. The characteristic flow properties of the quadrupolar vortex were in close agreement with the semianalytical model solutions. Higher-order multipolar vortices were observed to be susceptible to strong inertial oscillations.

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“…Such equilibrium density gradients are a rather common feature of various laboratory plasmas. [18][19][20] In the experiments in Refs. 2-4, the modes are initiated by a cylindric exciter at one end of the chamber, and they also appear to propagate almost parallel to the magnetic field vector, i.e., they may include a ͑small͒ wave number component in the perpendicular direction as well, as commented in Ref.…”

Section: Modelmentioning

confidence: 99%

Electrostatic modes in multi-ion and pair-ion collisional plasmas

et al. 2008

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The physics of plasmas containing positive and negative ions is discussed with special attention to the recently produced pair-ion plasma containing ions of equal mass and opposite charge. The effects of the density gradient in the direction perpendicular to the ambient magnetic field vector are discussed. The possible presence of electrons is discussed in the context of plasma modes propagating at an angle with respect to the magnetic field vector. It is shown that the electron plasma mode may become a backward mode in the presence of a density gradient, and this behavior may be controlled either by the electron number density or the mode number in the perpendicular direction. In plasmas with hot electrons an instability may develop, driven by the combination of electron collisions and the density gradient, and in the regime of a sound ions' response. In the case of a pure pair-ion plasma, for lower frequencies and for parameters close to those used in the recent experiments, the perturbed ions may feel the effects of the magnetic field. In this case the plasma mode also becomes backward, resembling features of an experimentally observed but yet unexplained backward mode.

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Experimental observation of a tripolar vortex in a plasma

Cited by 57 publications

References 18 publications

Global convective cell formation in pair-ion plasmas

Global convective cell formation in pair-ion plasmas

Laboratory experiments on multipolar vortices in a rotating fluid

Electrostatic modes in multi-ion and pair-ion collisional plasmas

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