On modulation instability of nonlinear Alfven waves

The modulation instability of nonlinear Alfven waves in high-temperature plasma with _{e i} = 1 with allowance for resonance particles is discussed. A dispersion equation is derived for longitudinal perturbations and instability increments in regions æ << æ ₀ ^* , æ >> æ ₀ ^* , and æ æ ₀ ^* . For short-wave perturbations æ >> æ ₀ ^* , the dispersion equation leads to the well-known formula for the Landau coefficient of nonlinear decay. As an example of application of the obtained formulas, the correlation and cross-correlation functions are calculated for perturbations of the transverse magnetic-field component of nonlinear Alfven waves propagated along the magnetic field.Chechno-Ingushskii State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 35, No. 8, pp. 663–670, August, 1992.     

Effect of limiting polarization in the Jovian inner magnetosphere

Jovian decameter emission is known to exhibit almost total polarization. We consider the elliptical polarization to be a consequence of linear-mode coupling in the Jovian magnetosphere outside the source region. We determine conditions of emission propagation along the ray path that are necessary for self-consistent explanatation of the polarization observations and show that the ellipticity (axial ratio of the polarization ellipse) is determined by the magnetospheric plasma density n_e in a small region a distance of about half the Jovian radius from the radiation source. The plasma density in the region is quite low, n_e<0.4 cm⁻³, and the geometrical-optics approximation of emssion propagation in front of the region converts to the vacuum approximation behind it. The latter means that the linear-mode coupling in the Jovian inner magnetosphere is manifested as the effect of limiting polarization. Sources of decameter emission emitting at different frequencies f are located at heights corresponding to gyrofrequency levels f _Be ≅f and at magnetic-force lines that belong to L-shells passing through the satellite Io. The location of the transitional region in the Jovian magnetosphere varies depending on the emission frequency and the time. For each given decameter radio emission storm occupying some region in frequencytime space, we have a number of transitional regions located in a certain region of the Jovian magnetosphere—the interaction region of the magnetosphere (IRM) for the given emission storm. The distribution of magnetospheric plasma in an IRM is found from data of observations of the polarization ellipiicity of the given decameter radio emission storm. By matching the calculated ellipticity of emission with the observed ellipticity at every point of frequency-time space of the emission dynamic spectrum one finds a recurrent relation between the local values of the magnetospheric plasma density N_c and the planetary magnetic field B in the IRM, which allows evaluation of the distribution of plasma density if a definite model of the Jovian magnetic field has been adopted. Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, Russia; Space Research Institute, Austrian Academy of Sciences, Austria. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 2, pp. 177–193, February, 1998.     

New Possibilities of Radioastronomical Diagnostics of the Jovian Magnetosphere Using the Observed Polarization of its Decameter Radio Emission

We discuss possibilities of diagnostics of the Jovian magnetosphere based on the results of measurements of the polarization characteristics of the decameter radio emission. It is shown that the essentially elliptical polarization of that radiation and its generation at frequencies near the local electron gyrofrequency opens new possibilities for radioastronomical diagnostics of the Jovian magnetosphere. The plasma distribution can be studied not only along the radiation path but also in the transverse direction, i.e., over latitudes. Moreover, since the relative position of the source and observer during a decameter noise storm is rather stable, it is possible to perform tomography of the magnetosphere (its diagnostics at different longitudes) using the planet rotation. We present the examples of diagnostics of different regions in the Jovian magnetosphere, such as sources of decameter radio emission, i.e., lower-magnetosphere regions located at a distance of about 1.5-2 R_J from the center of the planet, and the Io plasma torus located at a distance of about 6R_J from the center of the planet. It is pointed out that the number density of the magnetospheric plasma outside the Io magnetic flux tube is small (n 1 cm^-3 at the height of the gyroresonance level f_Be 30 MHz) while it is higher inside this flux tube at the same height: n 3 cm^-3. We estimate the variations in the number density of the plasma along the Io magnetic flux tube (n B, 1-1.8), determine the rate at which the integral plasma density varies over latitudes (d( n dz)/dh 2· 10³ cm^-3), and find the average number density of the plasma in the region where the radiation crosses the Io torus ( n 2· 10³ cm^-3).     

Low-frequency instability of an inhomogeneous weakly ionized plasma in crossed electric and inhomogeneous magnetic fields

The paper discusses the drift dissipative instability that arises in a weakly ionized inhomogeneous plasma in crossed electric and magnetic fields. The potential perturbations are studied in the WKB (Wentzel-Krammers-Brillouin) approximation, i.e. for k = d lnn ₀/dx. The critical magnetic field, beyond the value of which the plasma is again stable against the studied perturbations, is computed. The effect of the inhomogeneity of the magnetic field modelled by a gravitational field is analyzed and the effect of a magnetic field, growing in the direction opposite to that of the plasma density, is pointed out. Under certain circumstances similar phenomena also arise in the current-convective instability.The author wishes to express his thanks to J. Václavík, K. Jungwirth and J. Preinhaelter for their stimulating discussions and comments.     

Propagation of self-gravitating density waves in the deDonder gauge on a gravitational background field

Arguments are given for using the deDonder instead of the synchronous gauge in describing the propagation of density perturbations in a preexisting gravitational field. Since in the deDonder gauge the corresponding reference frame is fixed on the background, the physical interpretation of results is obvious, while in the synchronous gauge it is at least very difficult to extract the physical consequences from the results. For the propagation of density perturbations, with large spatial extension, a decisive difference is found between the two gauges. While in the synchronous gauge there is a growing mode in the density contrast (at least for adiabatic perturbations on a background matter substratum withp as equation of state), in the deDonder gauge there is not. The calculation in deDonder gauge leads to upper boundaries for the spatial extension of unstable density perturbations, and thus may give a hint for upper boundaries of galaxy masses.     

Structure of the magnetic field of the Jovian magnetosphere

We exactly solved the problem of the interaction between the rotating magnetic field of Jupiter and the equatorial plasma disk formed by the gases flowing from the Jovian satellite Io. The disk is shown to expel the Jovian magnetic field in both directions, inward, toward Jupiter, compressing its dipole magnetic field, and outward. Jupiter spins up the disk up to velocities that correspond to nearly constant angular rotation, but with an angular frequency lower than the angular frequency of Jupiter itself. The radial velocity of the plasma in the disk approaches its azimuthal velocity. We determined the power of Jupiter’s rotational energy losses. Part of this energy is transferred to the disk, and the other part goes into heating the Jovian ionosphere. We show that the Pedersen surface conductivity of the Jovian ionosphere must have a lower limit to maintain the electric current that arises in the disk-rotating magnetic field system. This current in the Jovian magnetosphere flows only along the preferential magnetic surfaces that connect the inner and outer edges of the disk to the ionosphere.     

Hydromagnetic transverse instability of two highly viscous fluid-particle flows with finite ion Larmor radius corrections

A linear analysis of the combined effect of viscosity, finite ion Larmor radius and suspended particles on Kelvin-Helmholtz instability of two superposed incompressible fluids in the presence of a uniform magnetic field is carried out. The magnetic field is assumed to be transverse to the direction of streaming. A general dispersion relation for such a configuration has been obtained using appropriate boundary conditions. The stability analysis is discussed analytically, and the obtained results are numerically confirmed. Some special cases are recovered and corrected. The limiting cases of absence of suspended particles (or fluid velocities) and finite Larmor radius, absence of suspended particles are discussed in detail. In both cases, all other physical parameters are found to have stabilizing as well as destabilizing effects on the considered system. In the former case, the kinematic viscosity is found to has a stabilizing effect, while in the later case, the finite Larmor radius is found to has a stabilizing influence for a vortex sheet. It is shown also that both finite Larmor radius and kinematic viscosity stabilizations for interchange perturbations are similar to the stabilization effect due to a magnetic field for non-interchange perturbations. Received 13 January 2003 Published online 24 April 2003 RID="a" ID="a"Also at: Department of Mathematics, Faculty of Education, Ain Shams University, Roxy, Cairo, Egypt. e-mail: m.elsayed@uaeu.ac.ae     

The effect of plasma drift on the electromagnetic cyclotron instability

It is shown that the drift of plasma across a homogeneous magnetic field causes the generation of a wave electric field which, for waves propagating along the magnetic field in the whistler mode, is in the direction of the magnetic field. This leads to Landau damping of the wave field by the background electron distribution, simultaneously with amplification via the electromagnetic cyclotron instability. The drift velocity of the plasma for zero net growth of a whistler mode signal is calculated. It is suggested that such a process occurs in the equatorial region of the magnetosphere during a geomagnetic storm and accounts for the missing band of emissions at half the equatorial gyrofrequency.     

Gravitational collapse with charge and small asymmetries I. Scalar perturbations

A recent analysis by Richard Price of spherical collapse with small nonspherical perturbations is here generalized to the case of an electrically charged collapsing star (0¦Q¦-M). The perturbations are confined to a scalar field generated by a nonspherical distribution of scalar charge in the star. As in the electrically neutral case, the scalar perturbations are probably a prototype for all others — electromagnetic, gravitational, and higherspin. The collapse is shown to produce a Reissner-Nordström black hole, and the scalar-field perturbations are shown to radiate completely away; but they die out more slowly the larger is the star's electric charge. For charge ¦Q¦M, the -pole part of the perturbation at fixedr and late times is dominated by a tail that dies out ast ^{–(2+ 2)}. But for ¦Q¦=M, the primary outgoing waves emitted from the star's surface are everywhere larger than the tail. At fixedr and late times they die as t^–(+2). Also, a calculation of the redshift shows that a collapsing star becomes black more slowly the larger is the star's electric charge.Supported in part by the National Science Foundation (GP-27304, GP-28027, GP-19887).     

Numerical Simulation of Plasma Edge Turbulence Due to E×B Flow Velocity Shear

A numerical code is used to study the nonlinear evolution of the Kelvin-Helmholtz instability, and the existence and time evolution of a charge separation with the self-consistent electric field at a plasma edge. Both ions and electrons are described by gyrokinetic equations that include the ions finite Larmor radius correction and the polarization drift. We present results for the case where the plasma layer is two-dimensional, and the magnetic field makes an angle very close to the normal to the plane of the plasma. At = 88.5°, the nonlinear evolution of the Kelvin-Helmholtz instability shows a spectrum which is turbulent and is dominated by higher harmonics, saturates at low level and has little effect on the electrons and ions initial equilibrium density profiles. At an angle of the magnetic field closer to 90°, when the component of the motion of the electrons along the magnetic field decreases, the behavior is in accordance with some basic physics associated with the set of equations describing the behavior of a guiding center plasma in a strong magnetic field, namely the energy condensing in the lowest k modes (inverse cascades). The results show the sensitivity of the turbulent spectrum to the motion of the electrons along magnetic field lines. In particular, we study the effect of different algorithms to compute this sensitive electrons motion, and their effect on the turbulent spectrum. We show that Eulerian Vlasov codes associated with cubic spline interpolations perform favorably when compared to other methods.     

Magnetic propulsion of intense lithium streams in a tokamak magnetic field

This paper describes the effect and gives the theory of magnetic propulsion which allows driving free surface plasma facing liquid lithium streams in tokamaks. In the approximation of a thin flowing layer the MHD equations are reduced to one integrodifferential equation which takes into account the propulsion effect, viscosity, and the drag force due to magnetic pumping and other interactions with the magnetic field. A stability criterion is obtained for stabilization of the "sausage" instability of the streams by centrifugal force.     

Observations of an ion-driven instability in non-neutral plasmas confined on magnetic surfaces

The first detailed experimental study of an instability driven by the presence of a finite ion fraction in an electron-rich non-neutral plasma confined on magnetic surfaces is presented. The instability has a poloidal mode number m=1, implying that the parallel force balance of the electron fluid is broken and that the instability involves rotation of the entire plasma, equivalent to ion-resonant instabilities in Penning traps and toroidal field traps. The mode appears when the ion density exceeds approximately 10% of the electron density. The measured frequency decreases with increasing magnetic field strength, and increases with increasing radial electric field, showing that the instability is linked to the E x B flow of the electron plasma. The frequency does not, however, scale exactly with E/B, and it depends on the ion species that is introduced, implying that the instability consists of interacting perturbations of ions and electrons.     

Exact solution of the totally asymmetric simple exclusion process: Shock profiles

The microscopic structure of macroscopic shocks in the one-dimensional, totally asymmetric simple exclusion process is obtained exactly from the complete solution of the stationary state of a model system containing two types of particles-first and second class. This nonequilibrium steady state factorizes about any second-class particle, which implies factorization in the one-component system about the (random) shock position. It also exhibits several other interesting features, including long-range correlations in the limit of zero density of the second-class particles. The solution also shows that a finite number of second-class particles in a uniform background of first-class particles form a weakly bound state.     

Mach's Principle and Minkowski Spacetime

It is shown that when the Minkowski metric is approached by a limiting process using two different static, spherically-symmetric, closed cosmological models, that although the energy-stress tensors for the Einstein-Friedmann field equations vanishes, their integral does not. Since part of this integral consists of the mass of the incoherent dust background, which is the same in both models, the Minkowski metric obtained by this limiting process cannot be regarded as anti-Machian, since there is an infinite amount of ponderable matter in the background, albeit at vanishing density. One of the models is the Einstein static universe with its cosmological term. The other model does not employ this term, but instead uses a tensor that has vanishing trace, negative energy density and negative pressure. Gravitational energy is also studied, and it is pointed out that for both models, this energy becomes infinitely negative in the Minkowski limit.     

Gibbs and Markov random systems with constraints

This paper concerns random systems made up out of a finite collection of elements. We are interested in how a fixed structure of interactions reflects on the assignment of probabilities to overall states. In particular, we consider two simple models of random systems: one generalizing the notion of Gibbs ensemble abstracted from statistical physics; the other, Markov fields derived from the idea of a Markov chain. We give background for these two types, review proofs that they are in fact identical for systems with nonzero probabilities, and explore the new behavior that arises with constraints. Finally, we discuss unsolved problems and make suggestions for further work.     

High-frequency sum-rules for classical relativistic plasmas in a magnetic field

High-frequency sum rules for the transverse elements of classical relativistic plasmas in a magnetic field are derived. The relativistic effect reduces the plasma mode frequency by a factor of ^–1(1 –v²/3c².     

Global particle simulation for a space weather model: present andfuture

The authors report progress in the long-term effort to represent the interaction of the solar wind with the Earth's magnetosphere using a three-dimensional electromagnetic particle model (EMPM) as a space weather model. Magnetohydrodynamic (MHD) simulation models have been refined to establish quantitative global modeling in comparison with observations. The EMPM has become more feasible as the power and speed of supercomputers have improved in recent years. Simulations with southward and dawnward turning IMFs have revealed the fundamental processes which have been confirmed by MHD simulations and observations. After a quasisteady state is established with an unmagnetized solar wind, a southward IMF is switched on, which causes the magnetosphere to stretch with reconnection at the dayside magnetopause. The plasma sheet in the near-Earth magnetotail clearly thins. The cross-field current also thins and intensifies, which excites a kinetic (drift kink) instability along the dawn-dusk direction. As a result of this instability the electron compressibility effect appears to be reduced and to allow the collisionless tearing to grow rapidly with the reduced B_z component. Later, magnetic reconnection also takes place in the near-Earth magnetotail. In the case where the northward IMF is switched gradually to dawnward, magnetic reconnection takes place at both the dawnside and duskside. The arrival of dawnward IMF at the magnetopause creates a reconnection groove which causes particle entry into the deep region of the magnetosphere via field lines that go near the magnetopause. The flank weak-field region joins onto the plasma sheet and the current sheet to form a geometrical feature called the cross-tail S that structurally integrates the magnetopause and the tail interior     

Theory for the laser-induced femtosecond phase transition of silicon and GaAS

We analyze he femtosecond instability of the chamond lattice of silicon and GaAs, which is induced by a dense electron-hole plasma after excitation by a very imense laser pulse. We obtain that the electron-hole plasma causes an instability of both transverse acoustic and longitudinal optical phonons. So, within less than 200fs, the atoms are displaced more than 1 Å from their equilibrium position. The gap between the conduction and the valence band then vanishes and the symmetries of the diamond structure are destroyed, which has important effects on the optical reflectivity and second-harmonic generation. After that, the crystal melts very rapidly because of the high kinetic energy of the atoms. Note that mis is in good agreement with recent experiments done on Shand GaAs using a pump laser to excite a dense electron hole plasma and a probe laser to observe the resulting changes in the atomic and electronic structure.Paper presented at the 129th WE-Heraeus-Seminar on Surface Studies by Nonlinear Laser Spectroscopies, Kassel, Germany, May 30 to June 1, 1994     

Calculation of Out‐of‐Plane Vibrations of a Porphin Molecule

Using the DFT/B3LYP method with the base set 631G^**, we carried out calculation of the frequencies of the normal vibrations of porphin and of its five isotopic types. Scaling of force constants for outofplane vibrations has been performed in independent natural coordinates. The symmetry coordinates are introduced and a force field for outof plane vibrations of a porphin molecule in independent coordinates of symmetry is obtained. A new correlation of the frequencies of vibrations in the type of the symmetry B _1u for the isotopic type of the d ₂ porphin molecule is suggested on the basis of discrete analysis of the distribution of a potential energy.     

The interplay between relativistic gravitational,centrifugal and electric forces: a simple example

We show that some striking properties of the circular motion of charged, ultrarelativistic particles close to the circular photon orbit around a charged black hole (found by Balek, Biák and Stuchlík) can be easily understood in terms of the centrifugal force vanishing at the circular photon orbit. We also comment briefly on a possible non-uniqueness of the recently-proposed operational definition of the centrifugal force in static spacetimes.