Paulo Hiroshi Sakanaka

Coronal loop heating by discrete Alfvén waves

We have modeled the solar coronal loop heating by discrete Alfven waves. Discrete Alfven waves (DAW) are a new class of Alfven waves which can be describe by the two fluid model with finite ion cyclotron frequency or the MHD model with plasma current along the magnetic field line as shown by Appert, Vaclavik and Villar (1984). We have modeled the coronal loop as a semi-toroidal plasma. We have shown that the absorptions of the discrete Alfven wave by the plasma through the viscosity can account for at least 20% of the necessary coronal power density of 10–9 erg cm -3 s -1.

A nonlinear model for auroral density cavities

A nonlinear model for the short-scale auroral density cavity (SSADC) is presented. Specifically, it is shown that the SSADC is associated with nonlinear short wavelength (in comparison with the collisionless electron skin depth) dispersive convective cells (DCCs) whose frequencies are much smaller than the ion gyrofrequency. In a stationary frame, the relevant equations governing the dynamics of the nonlinear DCCs are put in the form of an energy integral with an effective potential. The latter is analyzed to demonstrate the existence of density cavities (or holes). Larger amplitude cavities are necessarily quasi-stationary. The present theoretical model is capable of describing the salient features of SSADCs that are seen in data from the Freja satellite.

Discrete Alfvén waves in solar loop prominences

It is shown that a discrete Alfvén wave can explain the natural oscillations of solar loop prominences by considering the existence of a current flow. Discrete Alfvén waves are a new class of Alfvén waves which is described by the inclusion of the finite ion cyclotron frequency (ω/ωcl≠0) and/or the equilibrium plasma current. In this paper we consider only the effect of the current since in solar prominences (ω/ωcl≈0). We have modeled the solar prominences as a cylindrical plasma, surrounded by vacuum (corona), with L ≫ a where L and a are the plasma column, length, and radius, respectively. We have calculated the spectrum of the discrete Alfvén waves as function of the magnitude and shape of the plasma current.

Soliton and Double Layer Solutions for Four Component Dusty Plasmas

In dusty plasmas with warm electrons, warm positive ions, and negative and positively charged cold dust grains which are simultaneously present, it is shown that stationary solutions of the fluid equations combined with Poisson’s equation can be expressed in terms of the energy integral of a classical particle with a modified Sagdeev potential. We found that in four component dusty plasma there are changes in the nonlinear properties of the DAW. Compressive dust‐acoustic solitons exist only when there is at least a trace of positively charged dust grains. The four fluid dusty plasma system, with both the negatively and positively charged dust grains, provides the ambient to excite double layers. These are analyzed both analytically and numerically. The parametric regions of solitons, cavitons and double layers are given, and their profiles are displayed graphically. At the end, we have analysed the case in which the dust charge is introduced self‐consistently, using a simple charging model. The result of ...

Formation of quadrupolar vortices in ion-temperature-gradient modes

Nonlinear equations which govern the dynamics of low-frequency (ω≪ωci), ion-temperature gradient modes in the presence of equilibrium density, temperature, magnetic field, and electrostatic potential gradients are derived. For some specific profiles of the equilibrium flow velocity, number density, temperature, and magnetic field, new type of solutions in the form of quadrupole vortices are found for a nondissipative plasma. The results can have relevance to the understanding of the salient features of anomalous ion thermal transport and coherent vortex structure formation in magnetically confined plasmas, such as in tokamaks.

Study of nonlinear phenomena in four-component dusty plasma with charge fluctuation

The presence of a small quantity of positive dust component in a negatively charged dusty plasma gives rise to the double layers (DLs), which otherwise are absent. The parametric regions of solitons and DLs are given so as to guide experimenters to find this higher order nonlinear phenomenon experimentally. We also considered the case with the negative charge fluctuation so as to find in which conditions the charging equilibrium is reached and what is the consequence of the presence of the charge fluctuation on the linear dispersion relation.

Formation of vortices in the presence of sheared electron flows in the earth's ionosphere

Abstract It is shown that sheared electron flows can generate long as well as short wavelength (in comparison with the ion gyroradius) electrostatic waves in a nonuniform magnetplasma. For this purpose, we derive dispersion relations by employing two-fluid and hybrid models; in the two-fluid model the dynamics of both the electrons and ions are governed by the hydrodynamic equations and the guiding center fluid drifts, whereas the hybrid model assumes kinetic ions and fluid electrons. Explicit expressions for the growth rates and thresholds are presented. Linearly excited waves attain finite amplitudes and start interacting among themselves. The interaction is governed by the nonlinear equations containing the Jacobian nonlinearities. Stationary solutions of the nonlinear mode coupling equations can be represented in the form of a dipolar vortex and a vortex street. Conditions under which the latter arise are given. Numerical results for the growth rates of linearly excited modes as well as for various types of vortices are displayed for the parameters that are relevant for the F-region of the Earths ionosphere. It is suggested that the results of the present investigation are useful in understanding the properties of nonthermal electrostatic waves and associated nonlinear vortex structures in the Earths ionosphere.

On plasma processes in the solar corona

Abstract This paper reviews theoretical research on the solar corona performed in Brazil. Three coronal processes are discussed: (1) coronal heating by surface Alfven waves, (2) coronal heating by global Alfven waves, and (3) generation of type III radio emission. The surface Alfven waves can power, directly, at least 10% of the required coronal flux density; in the case of mode conversion into kinetic Alfven waves the bulk of energy flux density can be provided. The global waves can power at least 20% of the required coronal energy flux density. It is shown that the electromagnetic oscillating two-stream instability driven by intense Langmuir waves, can be a likely generation mechanism of type −III radio bursts.

Formation of solitary waves and oscillatory shocklets in a two-temperature electron κ–distributed plasma

Large-amplitude electron acoustic (EA) waves and shocklets are investigated in a two-temperature electron plasma. For this purpose, dynamical cold electrons are described by the fully nonlinear continuity and momentum equations, while superthermal (hot) inertialess electrons are described by the κ –distribution function with a neutralizing background of static positive ions. The fluid equations along with a quasineutrality equation are solved to obtain a set of two characteristic wave equations that admit analytical and numerical solutions. It is shown that variation due to hot electron superthermality and hot-to-cold electron density ratio strongly affects the profiles of nonlinear EA structures in terms of negative potential, cold electron velocity and density. In particular, at time τ = 0 , symmetric solitary pulses are formed, which develop into oscillatory shocklets with the course of time. Our results should be useful for understanding solitary excitations and associated nonstationary large-amplitud...

High‐Mode Configuration Solutions from Generalized Beltrami Equation

It was reported by Dasgupta and Sakanaka that starting with a warm, homogeneous, non‐relativistic electron‐positron plasma, described by the two‐fluid model, a Triple Beltrami equation is derived, describing its steady‐state solution with flow. This is equivalent to the Simple Beltrami equation shown by J.B. Taylor to model the force‐free relaxed state of plasma, a static solution of plasma, and the Double Beltrami equation shown by S.M. Mahajan and Z. Yoshida to model a steady‐state solution of electron‐ion plasma with flow velocity. We explore the eigenvalue solutions obtained by imposing a consistent set of boundary values for the magnetic and velocity fields.