Solitary vortices in a rotating plasma

Horton, W.; Liu, J.; Meiss, James D.; Sedlak, Joseph E.

doi:10.1063/1.865898

Cited by 44 publications

(26 citation statements)

References 12 publications

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“…Experiments using thin soap films and electrolyte have observed similar vortices, despite non-2D effects associated with the boundary layers and free surfaces [2,3]. Theoretical studies have analyzed coherent structures, such as drift-wave vortices, in various plasma systems [4,5]. Experimentally, the existence of such plasma structures is generally inferred from point probe measurements [6][7][8][9], and it is often presumed that these structures are destroyed by shear in the background flow.…”

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confidence: 99%

Coherent Vorticity Holes from 2D Turbulence Decaying in a Background Shear Flow

1995

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Freely decaying 2D turbulence in magnetized electron columns has been measured using a phosphor screen͞CCD camera diagnostic. The relaxation towards axisymmetric equilibrium is hindered by medium-sized coherent vorticity holes which persist for hundreds of column rotations despite the strong negative rotational shear. These holes tend to settle into symmetric configurations in the column, give a negative skew to the measured vorticity fluctuations, and are eventually destroyed due to a slow outward radial creep. PACS numbers: 47.27.Jv, 47.32.Cc, 52.25.Wz, 52.35.Ra Coherent structures are important in the dynamics and transport of many flows. In two-dimensional (2D) freely decaying Navier-Stokes turbulence, computer simulations have demonstrated that self-coherent vortices emerge from random initial conditions and dominate the late-time relaxation [1]. Experiments using thin soap films and electrolyte have observed similar vortices, despite non-2D effects associated with the boundary layers and free surfaces [2,3]. Theoretical studies have analyzed coherent structures, such as drift-wave vortices, in various plasma systems [4,5]. Experimentally, the existence of such plasma structures is generally inferred from point probe measurements [6][7][8][9], and it is often presumed that these structures are destroyed by shear in the background flow. 2D quasigeostrophic models of sheared planetary atmospheres exhibit vortices [10,11], and computer simulations [11] and driven fluid experiments [12] have demonstrated the persistence of prograde vortices.In this paper, we characterize freely decaying 2D turbulence in magnetized electron columns, and find that coherent density holes (i.e., prograde vortices) survive for hundreds of column rotations. An initially hollow column exhibits instabilities, transport, and fine-scale turbulence [13], then relaxes to an axisymmetric minimum enstrophy metaequilibrium with essentially no energy loss, the "selective decay" consistent with hypothesis [14].Here, we show that this relaxation is slow because it is hindered by the longevity of elliptical density holes. The orientation and shape of these holes agree with an inviscid equilibrium model for vorticity patches in a background shear flow [15]. Hole interactions lead to a preferred configuration of two diametrically opposed holes on a distorted core (a "tripole"). On a time scale of hundreds of column bulk rotations, these holes creep radially outward and are eventually destroyed. Because of these coherent holes, the observed fluctuation relaxation rate is about 50 times slower than expected from simple passive tracer mixing, and the measured fluctuations are negatively skewed from Gaussian. Figure 1 shows the experimental device with the imaging diagnostic. Electrons from a tungsten filament are trapped in a series of conducting cylinders (radius R w 3.05 cm) enclosed in a vacuum chamber (ϳ10 29 torr). The electrons are contained axially by negative voltages (2150 V) on the two end cylinders, and confined radially by a uniform axia...

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confidence: 99%

Coherent Vorticity Holes from 2D Turbulence Decaying in a Background Shear Flow

1995

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“…Equations ͑14͒-͑16͒ are the generalization of Horton et al 10 to include the effects of the parallel electron dynamics and charged dust impurities.…”

Section: ͑1͒mentioning

confidence: 99%

Drift-ballooning modes in the presence of charged dust impurities in a nonuniform rotating magnetoplasma

et al. 1998

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The linear and nonlinear properties of drift-ballooning modes in the presence of an equilibrium electric field and stationary charged dust grains are examined. It is found that the presence of these two contribute to the stability of the ballooning mode. Furthermore, the nonlinear coupling between finite amplitude drift-ballooning modes gives rise to different types of coherent vortex structures, which can affect the transport properties of an inhomogeneous magnetized plasma. The relevance of the investigation to laboratory and astrophysical plasmas is discussed.

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“…One class, the dipolaf drift mode vortex [Makino et al 1981;Horton et al 1986] occurs for the case where the plasma corotates at both the inner and outer radial boundaries of the torus. One class, the dipolaf drift mode vortex [Makino et al 1981;Horton et al 1986] occurs for the case where the plasma corotates at both the inner and outer radial boundaries of the torus.…”

Section: Sd (1988) Use Periodograms and Statistical Analysis Ofmentioning

confidence: 99%

“…In this work we show that in a geometry which idealizes that of the Io plasma torus, we find at least two classes of large-scale solitary vortex structures. One class, the dipolaf drift mode vortex [Makino et al 1981;Horton et al 1986] occurs for the case where the plasma corotates at both the inner and outer radial boundaries of the torus. The speed of propagation of the dipole vortex depends on the unperturbed density profile of the torus, and is compatible with the observed lag of 3-5% for the n-kom source.…”

Section: Sd (1988) Use Periodograms and Statistical Analysis Ofmentioning

confidence: 99%

Solitary vortices in the Io plasma torus

Horton¹,

Smith²

1988

J. Geophys. Res.

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Coupling of radial plasma gradients to the centrifugal and Coriolis forces are shown to give rise to localized, nonlinear vortex structures in rotating plasmas. The vortex density and potential structures are derived along with the nonlinear dispersion relation that relates the scale size of the vortex to its speed of propagation. The hypothesis is advanced that the vortex structures may be associated with certain localized emission features observed in the EUV and the narrow band kilometric radio emission observed in the Io plasma torus. The parameters for a vortex lagging corotation by 3% are derived for comparison with the features of a region of localized emission as given by this idealized model.

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Solitary vortices in a rotating plasma

Cited by 44 publications

References 12 publications

Coherent Vorticity Holes from 2D Turbulence Decaying in a Background Shear Flow

Coherent Vorticity Holes from 2D Turbulence Decaying in a Background Shear Flow

Drift-ballooning modes in the presence of charged dust impurities in a nonuniform rotating magnetoplasma

Solitary vortices in the Io plasma torus

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