Structures In Magnetized Plasma Research Articles

Mechanism and scaling for convection of isolated structures in nonuniformly magnetized plasmas

Large-scale radial advection of isolated structures in nonuniformly magnetized plasmas is investigated. The underlying mechanism considered is due to the nonlinear evolution of interchange motions, without any presumption of plasma sheaths. Theoretical arguments supported by numerical simulations reveal an inertial scaling for the radial velocity of isolated structures in the ideal limit. This velocity increases as the square root of the structure size relative to the length scale of the magnetic field. The magnitude of the radial advection velocity, as well as the dynamical evolution of the structures, compares favorably with recent experimental measurements of radially propagating blob structures in the scrape-off layer of magnetically confined plasmas.

GEOTAIL observation of tilted X-line formation during flux transfer events (FTEs) in the dayside magnetospheric boundary layers

Abstract. The magnetic field and plasma structures during two successive crossings of the subsolar magnetospheric boundary layers (i.e. MagnetoPause Current Layer (MPCL) and Low-Latitude Boundary Layer (LLBL)) under the southward-dawnward IMF are examined on the basis of the data obtained by the GEOTAIL spacecraft. A significant and interesting feature is found, that is, Flux Transfer Events (FTEs) occur in association with the formation of the tilted X-line. During the first inbound MPCL/LLBL crossing, the ion velocity enhancement (in particular, the Vl component negatively increases) can be observed in association with simultaneous typical bipolar signature (positive followed by negative) in the Bn component. In addition, a clear D-shaped ion distribution whose origin is the magnetosheath can also be found in the dawnward direction. A few minutes later, the satellite experiences outbound MPCL crossing. The negative enhancement of the Vm component can be found as well as the positive enhancement of the Vl component. Simultaneously, a typical bipolar signature with the polarity (negative followed by positive) opposite that observed in the first encounter can also be observed. The ions from the magnetosheath flow predominantly in the duskward direction, although the D-shaped ion distribution cannot be observed. These results indicate that the satellite initially observes one part of a reconnected flux tube formed by FTEs whose magnetospheric side is anchored to the Southern Hemisphere. The ions confined in this partial flux tube are flowing in the south-dawnward direction. Then, the satellite observes the other part of the reconnected flux tube whose magnetospheric side is anchored to the Northern Hemisphere. The ions confined in this flux tube flow dominantly in the north-duskward direction. Furthermore, it can be considered that the second MPCL crossing is a direct cut through the diffusion region of FTEs because the LLBL is absent in the vicinity of the MPCL. On the basis of these results, it can be concluded that the satellite was passing near the tilted X-line. The information obtained through this study is expected to be of great use in discriminating between the anti-parallel (steady-state) reconnection and tilted X-line models on the dayside MPCL.

A Direct Method to Estimate Magnetic Helicity in Magnetic Clouds

Magnetic clouds are extended and magnetized plasma structures that travel from the Sun toward the outer heliosphere, carrying an important amount of magnetic helicity. The magnetic helicity quantifies several aspects of a given magnetic structure, such as the twist, kink, and the number of knots between magnetic field lines, the linking between magnetic flux tubes, etc. Since the helicity is practically conserved in the solar atmosphere and the heliosphere, it is a useful quantity to compare the physical properties of magnetic clouds to those of their solar source regions. In this work we describe a method that, assuming a cylindrical geometry for the magnetic cloud structures, allows us to calculate their helicity (per unit length) content directly from the observed magnetic field values. We apply the method to a set of 20 magnetic clouds observed by the WIND spacecraft. To test its reliability we compare our results with the helicity computed using a linear force-free field model under cylindrical geometry (i.e. Lundquist's solution).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Effects of the dust charge variation and non-thermal ions on multi-dimensional dust acoustic solitary structures in magnetized dusty plasmas

Abstract The combined effects of both adiabatic dust charge variation and non-thermally (fast) distributed ions on dust acoustic solitary structures are studied in a magnetized dusty plasmas consisting of the negatively and variably charged hot dust fluid, Boltzmann distributed electrons and non-thermally distributed ions. By using the reductive perturbation method, we derive the Korteweg-de Vries (KdV) equation governing the dust acoustic solitary waves. It is shown that the dust charge variation and the presence of non-thermally distributed ions would modify the nature of dust acoustic solitary structures significantly and may excite both dust acoustic solitary holes (soliton with a density dip) and positive solitons (soliton with a density hump).

Diaceleric structures in magnetized plasmas

The existence of novel confinement configurations in magnetized plasmas, coined diaceleric structures, is predicted. The conditions for these configurations to emerge are derived and shown to depend on the functional relation between the so-defined material flux fraction and central velocity pitch. The analysis is based upon the application of the coercive criterion, followed by the adjustment procedure, developed by other authors, to a variational method approach. A complete description of Lagrange multipliers and Beltrami eigenvalues in terms of strictly physical parameters is presented. The model recovers the diamagnetic and reversed field pinch structures, investigated by those authors, leading to a comprehensive classification of the relaxed states in magnetized plasmas.

Early life of coronal mass ejections

Coronal mass ejections (CMEs) are large-scale magnetized plasma structures ejected from closed magnetic field regions of the Sun. White light coronagraphic observations from ground and space have provided extensive information on CMEs in the outer corona. However, our understanding of the solar origin and early life of CMEs is still in an elementary stage because of lack of adequate observations. Recent space missions such as Yohkoh and Solar and Heliospheric Observatory (SOHO) and ground-based radioheliographs at Nobeyama and Nancay have accumulated a wealth of information on the manifestations of CMEs near the solar surface. We review some of these observations in an attempt to relate them to what we already know about CMEs. Our discussion relies heavily on non-coronagraphic data combined with coronagraphic data. Specifically, we discuss the following aspects of CMEs: (i) coronal dimming and global disk signatures, (ii) non-radial propagation during the early phase, (iii) Photospheric magnetic field changes during CMEs, and (iv) acceleration of fast CMEs. The relative positions and evolution of coronal dimming, arcade formation, prominence eruption will be discussed using specific events. The magnitude and spatial extent of CME acceleration may be an important parameter that distinguishes fast and slow CMEs.

Multi-dimensional instability of electrostatic solitary structures in magnetized nonthermal dusty plasmas

A rigorous theoretical investigation has been made of multi-dimensional instability of obliquely propagating electrostatic solitary structures in a hot, magnetized, non-thermal dusty plasma which consists of a negatively charged hot dust fluid, Boltzmann distributed electrons and nonthermally distributed ions. The Zakharov–Kuznetsov equation for the electrostatic solitary structures that exist in such a dusty plasma system is derived by the reductive perturbation method. The multi-dimensional instability of these solitary waves is also studied by the small- k (long wavelength plane wave) perturbation expansion method. The nature of these solitary structures, the instability criterion and their growth rate depending on dust-temperature, external magnetic field and obliqueness are discussed. The implications of these results to some space and astrophysical dusty plasma situations are briefly mentioned.

Vortex Dynamics in Inhomogeneous Plasmas

The dynamics of vortical structures in magnetized plasmas with nonuniform density is investigated numerically. In particular the dynamics of monopolar vortices is considered and the results are discussed in terms of the conservation of potential vorticity. It is found that individual vortex structures tend to transport density up the gradient in contrast to structures embedded in developed turbulence, which on the average will lead to a flattening of the density gradient. The role of vortical structures in connection with electrostatic plasma turbulence and the associated cross-field plasma transport is also addressed.

Magnetosonic waves in structured atmospheres with steady flows

The magnetosonic modes of magnetic plasma structures in the solar atmosphere are considered taking into account steady flows of plasma in the internal and external media and using a slab geometry. The investigation brings nearer the theory of magnetosonic waveguides, in such structures as coronal loops and photospheric flux tubes, to realistic conditions of the solar atmosphere. The general dispersion relation for the magnetosonic modes of a magnetic slab in magnetic surroundings is derived, allowing for field-aligned steady flows in either region. It is shown that flows change both qualitatively and quantitatively the characteristics of magnetosonic modes. The flow may lead to the appearance of a new type of trapped mode, namelybackward waves. These waves are the usual slab modes propagating in the direction opposite to the internal flow, but advected with the flow. The disappearance of some modes due to the flow is also demonstrated.

Waves in cosmic magnetic structures taking into account the anisotropic plasma pressure

This paper provides an analysis of magneto-sonic eigenwaves travelling in magnetic plasma structures based on the Chew-Goldberger-Low approximation, for which the plasma kinetic pressure is different along and across the magnetic field. The anisotropy does not lead to the emergence of new modes. The dependence of phase velocities of the waves, trapped by a single magnetic surface, on the pressure anisotropy is investigated. For a magnetic slab with field-free surroundings, the dispersion relations for the eigenwaves are obtained. The pressure anisotropy may change dispersion relations of such modes significantly. In particular, backward waves are possible in the case of strong anisotropy. The dependences of the thresholds for the mirror and hose instabilities on the system parameters are obtained. In particular, hose and mirror instabilities of such waves are absent for some wave number regions. The results are used to obtain the eigenwave characteristics in coronal loops and chromospheric flux tubes.

Vortex structures in magnetized plasmas with sheared dust flow

Using a kinetic description for the ion fluid and the hydrodynamic models for the electron and dust fluids, we derive nonlinear equations for shortwavelength electrostatic fluctuations in the presence of equilibrium density and magnetic field-aligned dust flow gradients in multicomponent dusty magnetoplasmas. It is shown that possible stationary solutions of the nonlinear equations are dipolar vortices.

Nonlinear coupling between electromagnetic fields in a strongly magnetized electron-positron plasma

The nonlinear coupling between electromagnetic fields in a strongly magnetized electron-positron plasma is considered. We point out that compressional magnetic field perturbations are excited by the rotational part of the nonlinear current, and derive a new nonlinear system of equations that is basic for studies of modulational instabilities and coherent nonlinear structures in magnetized electron-positron plasmas.

The influence of the magnetic field and plasma structures in the earth magnetosphere on some properties of the hydromagnetic waves in the 0.1–1.0 Hz frequency band

By using an image-dipole magnetic field model for a variety of plasma density profiles we study the latitude effect of the 0.1–1.0 Hz hydromagnetic wave propagation in the Earth magnetosphere. By comparing the results of group delay time calculations for dipole and model magnetic firld with ground and satellite observations we have obtained some propagation characteristics of Pc1's and have localized the regions of their generation. It has been shown that nondipole geometry of geomagnetic field in outer magnetosphere (at geomagnetic latitudes φ 0 > 66, L > 6) has strong effect on the hydromagnetic wave propagation.

Non-turbulent electric fields in soliton and shock-like structures in magnetized plasmas

A new treatment of soliton and laminar shock-like structures in single ion species and counter-streaming plasmas in perpendicular magnetic fields is presented. Charge separation effects are treated exactly, and may become important for high Alfvén Mach number flows. The theory contains the familiar quasi-neutrality theory in the limitB20≪ Μ0nmec2and the Longmire theory in the limitB20≫ Μ0nmec2. The introduction of the potential ψ as the primary dependent variable, instead of the magnetic fieldB, clarifies the role of ion dynamics. New pseudo-potential functions are defined which generate classes of solutions for single ion species, rigid piston problems, and multispecies problems. They also provide information about the evolution of particle piston solutions. Results include the fact that a small amount of resistivity allows shock solutions for very large Mach numbers, and for zero dissipation the parameterdoes not affect the solutions except in the scale length.