Nonuniform Magnetized Plasma Research Articles

Electromagnetic ion-temperature-gradient modes and anomalous transport in a nonuniform magnetized plasma with equilibrium flows

The linear and nonlinear properties of electrostatic and electromagnetic waves in the presence of ion-temperature gradient, magnetic-field gradient, density gradient, and velocity gradients are examined. In the linear limit, a dispersion relation is obtained that admits new instabilities of drift waves. It is found that parallel velocity shear couples the electrostatic and magnetostatic modes and can cause an instability. An estimate of the anomalous ion energy transport and particle flux on the basis of mixing length hypothesis is made and the results are discussed for some interesting limiting cases. Furthermore, stationary solutions of the nonlinear equations without dissipation are also presented. The findings of the present investigation should be useful in understanding fluctuations and transport phenomena in space and laboratory plasmas.

Nonlinear relativistic gyrokinetic Vlasov-Maxwell equations

A set of self-consistent nonlinear gyrokinetic equations is derived for relativistic charged particles in a general nonuniform magnetized plasma. Full electromagnetic-field fluctuations are considered with spatial and temporal scales given by the low-frequency gyrokinetic ordering. Self-consistency is obtained by combining the nonlinear relativistic gyrokinetic Vlasov equation with the low-frequency Maxwell equations in which charge densities and current densities are expressed in terms of moments of the gyrokinetic Vlasov distribution. For these self-consistent gyrokinetic equations, a low-frequency energy conservation law is also derived.

SMM analysis of reflection, absorption, and transmission from nonuniform magnetized plasma slab

An new analytical technique for obtaining a complete set of reflection, absorption, and transmission coefficients for a stratified plasma slab is presented, named the scattering matrix method (SMM). The nonuniform magnetized plasma slab is modeled by a number of subslabs. Each subslab has a fixed electron density. The overall density profile across the whole slab follows any practical distribution function. Because the field in each subslab can be represented by the sum of the reflected and incident components, the partial reflection and transmission coefficients can be obtained by successively matching boundary conditions at all interfaces. The partial and total reflected, absorbed, and transmitted powers as the functions of the electron density, collision frequency, and electron cyclotron frequency for typical parabolic and exponential density profiles are investigated.

Energy transfer from particles to low-frequency fields in a non-uniform magnetized plasma

Energy transfer from particles to low-frequency turbulent fields in the non-uniform magnetized plasma is studied. Sufficient conditions for plasma stability are derived taking account of magnetic field shear.

Nonlinear dynamics of electromagnetic turbulence in a nonuniform magnetized plasma

By using the hydrodynamic electron response with fixed (kinetic) ions along with Poisson’s equation as well as Ampère’s law, a system of nonlinear equations for low-frequency (in comparison with the electron gyrofrequency) long-(short-) wavelength electromagnetic waves in a nonuniform resistive magnetoplasma has been derived. The plasma contains equilibrium density gradient and sheared equilibrium plasma flows. In the linear limit, local dispersion relations are obtained and analyzed. It is found that sheared equilibrium flows can cause instability of Alfvén-like electromagnetic waves even in the absence of a density gradient. Furthermore, it is shown that possible stationary solutions of the nonlinear equations without dissipation can be represented in the form of various types of vortices. On the other hand, the temporal behavior of our nonlinear dissipative systems without the equilibrium density inhomogeneity can be described by the generalized Lorenz equations which admit chaotic trajectories. The density inhomogeneity may lead to even qualitative changes in the chaotic dynamics. The results of our investigation should be useful in understanding the linear and nonlinear properties of nonthermal electromagnetic waves in space and laboratory plasmas.

Nonlinear energy cascade in nonuniform media

The nonlinear energy cascade in a nonuniform magnetized plasma is studied by using a simple model allowing an analytical solution. The results are then confirmed by a more refined numerical investigation. It is shown that the propagation of moderate amplitude Alfvén waves interacting with the background may result in the dissipation of the equilibrium energy much faster than its standard resistive timescale.

Magnetic energy dissipation in the solar corona

In this paper we discuss the problem of small scale generation in a nonuniform magnetized plasma. In a MHD framework, we show that the free-energy stored in the inhomogenous, large scale coronal magnetic fields can be transferred on smaller and smaller scales up to the dissipative ones. This energy transfer is induced by the presence of MHD waves of “modest” amplitude (i.e. for which the non-linear time is much longer than the Alfvén time) which are likely to be generated in the solar athmosphere.

Response of topside radio sounding signals to small-scale field-aligned ionospheric irregularities

Abstract Small-scale ionospheric irregularities produce numerous observed effects during high-frequency radio wave sounding from a satellite. Scattering of z-mode waves radiated by an ionosonde, which results in the occurrence of characteristic traces on ionograms, are among the most complex of them. In the present paper the factors determining the power characteristics of such signals are considered. These are the size and shape of the surface of orthogonality for a family of z-mode waves radiated from a satellite, features of the radiating and propagating radio waves in a non-uniform magnetized plasma, and the details of the scattering process. Simple but adequate physical models for each of these factors are presented and a numerical calculation algorithm of the power of the z-mode scattered signals received by the satellite sounder receiver has been constructed. Values for this calculated quantity are presented as a function of time delay, sounding frequency, and magnetic latitude. A synthesis of topside ionograms showing z-mode scattered traces has been performed. The results support new diagnostic methods of detecting small-scale ionospheric irregularities using topside-sounder z-mode signal returns and the concept that the sounder radiation can, under certain conditions, stimulate artificial plasma turbulence. In addition, it was shown that z-mode scattering may contribute to the resonance observed at the plasma frequency on topside ionograms.

Velocity shear effect on Rayleigh–Taylor vortices in nonuniform magnetized plasmas

In this paper, the effect of velocity shear on Rayleigh–Taylor vortices has been demonstrated. An inhomogeneous plasma is considered with a density profile such that the diamagnetic drift velocity Vn=(cTe/eB)dn0/dx is a constant and includes the effect of an ambient poloidal shear flow Veq(x)=V⊥0′(x−x0)y. The final equation describing the stationary Rayleigh–Taylor vortex is shown to have the structure of a nonlinear Poisson equation, where the nonlinearity arises essentially because of the velocity shear term. This equation has been solved numerically and it has been shown that qualitatively new two-dimensional monopole vortex solutions may be obtained in the appropriate parameter space. Therefore, a new important nonlinear effect related to equilibrium shear flow has been identified in the calculations of Rayleigh–Taylor vortices which results in monopole-like solutions in plasmas.

Electromagnetic instability in nonuniform resistive electron magnetohydrodynamics

A local dispersion relation for electromagnetic modes in a nonuniform collisional magnetized electron plasma with fixed ion background is derived, taking into account equilibrium magnetic field and pressure gradients, as well as impurity radiation losses. The dispersion relation is then analyzed both analytically as well as numerically. It is found that for a low-β plasma, the principal source for the generation of unstable modes is the impurity radiation loss; whereas for a high-β plasma, the various effects such as the electron streaming, the electron–ion collisions, finite electron thermal conductivity, and impurity radiation losses are shown to be responsible for unstable perturbations. The results should be useful in the interpretation of nonthermal electromagnetic fluctuations in nonuniform collision-dominated magnetoplasmas with impurities.

Quasiparticle concept for non-uniformly magnetized plasmas

A quasiparticle concept [Sosenko P P and Decyk V K 1993 Physica Scripta 47 258] is generalized for the case of non-uniformly magnetized plasma. Exact and reduced continuity equations for the microscopic density in the quasiparticle phase space are derived, and the nature of quasiparticles is analyzed. The theory is developed for the general case of relativistic particles in electromagnetic fields, besides non-uniform but stationary magnetic fields.

Formation of vortex chains in a nonuniform magnetized electron plasma

It is shown that the equations governing the dynamics of weakly interacting medium-frequency electrostatic waves in a nonuniform magnetoplasma with a fixed ion background can have localized vortex chain solutions.

Variational theory of the cyclotron-emission source distribution from a mode-conversion layer

This paper presents the theory of an inhomogeneous source of cyclotron emission from a three-branch mode-conversion layer in a non-uniformly magnetized plasma. The physical formulation of the problem is based on the generalized Kirchhoff's law that relates, branch by branch, the emission to the absorption. General integral expressions for both absorbed and emitted energy fractions along each wave branch are obtained. A discrete multi-point model of absorbers and emitters is analysed. A variational principle for the integral of the emitted power is formulated.

A two-nonlinearity model of dissipative drift wave turbulence

A simple, one-field, two-nonlinearity, drift wave model equation is derived to describe the dynamics of a nonuniform magnetized plasma by taking into account the effects of dissipative trapped electron response in the turbulence dynamics. Because of the nonadiabatic response of trapped electrons, mode couplings by both the E×B drift and the polarization drift nonlinearities are present. In this work, the statistical dynamics for this dissipative drift wave turbulence is investigated using the EDQNM (eddy-damped quasinormal Markovian) closure scheme. In particular, apart from the eddy viscosity, a large nonlinear frequency shift is shown to be induced by cross coupling of the two nonlinearities. Thus instability drive is modified by this turbulent back reaction. By taking into account this self-consistency effect, a wave kinetic equation is derived, and the density fluctuation spectrum is obtained in different parameter ranges. The results show that the dynamics of dissipative drift wave turbulence is fundamentally different from that of the familiar Hasegawa–Mima model, because E×B drift nonlinearity blocks the low-k condensation of fluctuation energy. It is shown that both the E×B drift nonlinearity and the nonlinear frequency shift effect transfer energy nonlocally from large to small scales and, in contrast to the predictions of dimensional analysis, their contribution to the nonlinear transfer processes are actually of the same order as that of the polarization drift nonlinearity, even within the Hasegawa–Mima regime. This results in a significant modification of the Hasegawa–Mima spectrum for the short-wavelength drift waves.

Convective cells in nonuniform dusty plasmas

It is shown that purely damped convective cell modes acquire a real frequency in the presence of static charged dust grains in a nonuniform magnetized dusty plasma. The frequency of the two-dimensional mode is induced by the plasma density gradient and corresponds to charge density waves arising out of the plasma non-neutrality. The dynamics of weakly interacting finite-frequency convective cell modes is governed by the generalized Navier–Stokes equation. The presence of the new term arising from the dust inhomogeneity in the latter provides the possibility of a two-dimensional dipolar vortex solution in dusty plasmas.

Cyclotron emission from nonuniformly magnetized plasmas.

A new quantitative representation of the generalized Kirchhoff's law relating the emission from each propagating branch to the absorption along the corresponding branch is established, including for the first time the effects of inhomogeneous magnetic fields on cyclotron and synchrotron radiation from mode conversion theory. The concept of optical depth is revised to include effects of reflection and conversion in addition to transmission. Via the use of a variational principle, the source distribution function for the inhomogeneous emitting layer is calculated.

Gyrokinetic theory of fast wave transmission with arbitrary parallel wave number in a nonuniformly magnetized plasma

The gyrokinetic theory of ion cyclotron resonance is extended to include propagation at arbitrary angles to a straight equilibrium magnetic field with a linear perpendicular gradient in strength. The case of the compressional Alfvén wave propagating in a D(3He) plasma is analyzed in detail. A self-consistent local dispersion relation is obtained using a single mode description; this approach enables three-dimensional effects to be included and permits efficient calculation of the transmission coefficient. The dependence of this quantity on the species density ratio, minority temperature, plasma density, magnetic field, and equilibrium scale length is obtained. A self-consistent treatment of the variation of the field polarization across the resonant region is included. Families of transmission curves are given as a function of the normalized parallel wave number for parameters relevant to JET [see, for example, J. Jacquinot et al., Plasma Phys. 30, 1467 (1988)]. Perpendicular absorption by the minority ions is also discussed, and shown to depend on a single parameter, the ratio of the ion thermal velocity to the Alfvén speed.

New mode coupling equations for nonlinear drift waves

New mode coupling equations for nonlinear electrostatic drift waves are derived taking into account the electron temperature perturbation that is self-consistently produced due to the compression of the electron fluid as well as the E × B 0 convection of the equilibrium electron temperature gradient in nonuniform magnetized plasmas.

Gyrokinetic theory of perpendicular cyclotron resonance in a nonuniformly magnetized plasma

The extension of gyrokinetic theory to arbitrary frequencies by Chen and Tsai [Phys. Fluids 26, 141 (1983); Plasma Phys. 25, 349 (1983)] is used to study cyclotron absorption in a straight magnetic field with a perpendicular, linear gradient in strength. The analysis includes the effects of magnetic field variation across the Larmor orbit and is restricted to propagation perpendicular to the field. It yields the following results for propagation into the field gradient. The standard optical depths for the fundamental O-mode and second harmonic X-mode resonances are obtained from the absorption profiles given in this paper, without invoking relativistic mass variation [see also Antonsen and Manheimer, Phys. Fluids 21, 2295 (1978)]. The compressional Alfvén wave is shown to undergo perpendicular cyclotron damping at the fundamental minority resonance in a two-ion species plasma and at second harmonic resonance in a single-ion species plasma. Ion Bernstein waves propagating into the second harmonic resonance are no longer unattenuated, but are increasingly damped as they approach the resonance. It is shown how the kinetic power flow affects absorption profiles, yielding information previously obtainable only from full-wave theory. In all cases, the perpendicular cyclotron damping arises from the inclusion of magnetic field variation across the Larmor orbit.

Nonlinear fluid equations for fully toroidal electromagnetic waves in nonuniform magnetized plasmas.

By means of the two-fluid model of Braginskii [Reviews of Plasma Physics, edited by M. A. Leontovich (Consultants Bureau, New York, 1965), Vol. I, p. 205], this paper derives a set of nonlinear differential equations governing the dynamics of fully toroidal low-frequency electromagnetic waves in an inhomogeneous electron-ion plasma immersed in a nonuniform magnetic field. The effects of equilibrium electron and ion pressure gradients, magnetic drifts caused by the nonuniform magnetic field, as well as the contribution of heat fluxes in the particle-energy transport equations are incorporated. In the linear limit, expressions for the ion and electron number-density perturbations together with a new dispersion relation for fully toroidal electromagnetic waves are obtained. A new long-wavelength electromagnetic drift wave instability is shown to exist in a nonuniform magne- tized electron plasma. The formation of dipolar vortices in the two-dimensional ion-temperature-gradient-driven electrostatic drift wave turbulence has been demonstrated.