Acoustic Disturbances in Galaxy Clusters

Galaxy cluster cores are pervaded by hot gas which radiates at far too high a rate to maintain any semblance of a steady state; this is referred to as the cooling flow problem. Of the many heating mechanisms that have been proposed to balance radiative cooling, one of the most attractive is dissipation of acoustic waves generated by Active Galactic Nuclei (AGN). Fabian (2005) showed that if the waves are nearly adiabatic, wave damping due to heat conduction and viscosity must be well below standard Coulomb rates in order to allow the waves to propagate throughout the core. Because of the importance of this result, we have revisited wave dissipation under galaxy cluster conditions in a way that accounts for the self limiting nature of dissipation by electron thermal conduction, allows the electron and ion temperature perturbations in the waves to evolve separately, and estimates kinetic effects by comparing to a semi-collisionless theory. While these effects considerably enlarge the toolkit for analyzing observations of wavelike structures and developing a quantitative theory for wave heating, the drastic reduction of transport coefficients proposed in Fabian (2005) remains the most viable path to acoustic wave heating of galaxy cluster cores

High-voltage space tether for enhanced particle scattering in Van Allen belts

New applications of space tethers (High-Voltage Tethered Satellite System project) are discussed in relation with ideal of an active experiment in the Earth's radiation belts. Two conducting strings are supposed to be tethered between the main satellite and two small subsatellites flying through the ERB. A large potential difference similar to 1MV is applied between the tethers by means of a generator carried on the main satellite. The tethers effectively scatter the high energy particles into loss cone of magnetic trap, providing a control of particle life time in ERB. The rigorous theory of the sheath layer formed by relatively cold plasma is developed, yielding the electric field profile,which is then used for the treatment of scattering problem. With the help of Fokker-Planck equation the average rate of particle losses, normalized per 1 km of the tether's length is found to be: (2.5 divided by 14) . 10(16) s(-1) km(-1) for electron belts and 1.8 . 10(14)divided by 2.5 . 10(20) s(-1) km(-1) for proton belts. New active experiments in space become possible under the joint realization of HVTSS and HAARP projects

The effect of boundary conditions on Rayleigh-Taylor instability

Laser experiments are widely used to investigate excitation of Rayleigh-Taylor modes, which are of great importance for astrophysical applications. Measured growth rates are normally compared with either the sharp interface or the smooth gradient model. In the present paper an analytical solution is obtained that is valid for arbitrary density gradient scale L. It is a further development of the Mikaelian & Lindl model. New explicit presentation omega(k) is found which describes all discrete modes at all transverse wavenumbers k with one parametric expression. A critical value of kL is shown to exist when two independent solutions for the fastest growing main mode become degenerate, in this case the growth rate is calculated exactly. The focus is on astrophysical applications when boundary conditions are at infinity. The case of rigid walls is also considered to study the interrelation with the Chandrasekhar model. Results are supposed to be used for nonlinear RT treatment to analyze mixing in supernovae and other RT-driven objects

The evolution of the magnetic moment in a corrugated magnetic field

In the first part, the equations of motion in a weakly corrugated, periodic magnetic field are linearized and solved by using paraxial approximation, to describe the model and the associated resonance condition. In the second part, the nonlinear evolution of the magnetic moment of resonant particles, in connection with their axial displacement is investigated analytically by using the multiple scale method. It is seen that the linear evolution is converted into a slow and periodic oscillation around the unperturbed value, with a considerable amplitude. The analytic expressions for the period and amplitude of the oscillations are derived and compared with the numerical simulations, which are also presented. Finally, the limitations of the paraxial approximation are concluded by investigating the numerical simulations, with actual field expressions. (C) 1997 American Institute of Physics

Radial motion of highly conducting sphere in magnetic field

Radial motion of a highly conducting sphere in external magnetic field is considered. It both perturbs the external magnetic field and generates an electric field. Exact analytic solution has been obtained previously for a uniformly expanding sphere. In the present paper a new exact solution is derived which is valid not only for expansion but for contraction as well. It allows us to calculate analytically the total electromagnetic energy irradiated by the sphere involved in periodical radial motion with arbitrary velocity. (C) 2000 American Institute of Physics. [S0022- 2488(00)04805-2]

Chaotic breather formation, coalescence, and evolution to energy equipartition in an oscillatory chain

We study the formation and evolution of chaotic breathers (CBs) on the Fermi-Pasta-Ulam oscillator chain with quartic nonlinearity (FPU-beta system). Starting with most of the energy in a single high-frequency mode, the mode is found to breakup on a fast time scale into a number of spatially localized structures (CBs) which, on a slower time scale, coalesce into a single CB. On a usually longer time scale, depending strongly on the energy, the CB gives up its energy to lower frequency modes, approaching energy equipartition among modes. We analyze the behavior, theoretically, using an envelope approximation to the discrete chain of oscillators. For fixed boundaries, periodic nonlinear solutions are found. The numerical structures formed after the fast breakup are found to approximate the underlying equilibrium. These structures are shown, theoretically, to undergo slow translational motions, and an estimated time for them to coalesce into a single chaotic breather are found to agree with the numerically determined scaling tau (B) alpha E-1. A previously developed theory of the decay of the CB amplitude to approach equipartition is modified to explicitly consider the interaction of the breather with background modes. The scaling to equipartition of T-eq alpha E-2 agrees with the numerical scaling and gives the correct order of magnitude of T-eq

Acoustic Disturbances in Galaxy Clusters

Galaxy cluster cores are pervaded by hot gas which radiates at far too high a rate to maintain any semblance of a steady state; this is referred to as the cooling flow problem. Of the many heating mechanisms that have been proposed to balance radiative cooling, one of the most attractive is dissipation of acoustic waves generated by Active Galactic Nuclei (AGN). Fabian (2005) showed that if the waves are nearly adiabatic, wave damping due to heat conduction and viscosity must be well below standard Coulomb rates in order to allow the waves to propagate throughout the core. Because of the importance of this result, we have revisited wave dissipation under galaxy cluster conditions in a way that accounts for the self limiting nature of dissipation by electron thermal conduction, allows the electron and ion temperature perturbations in the waves to evolve separately, and estimates kinetic effects by comparing to a semi-collisionless theory. While these effects considerably enlarge the toolkit for analyzing observations of wavelike structures and developing a quantitative theory for wave heating, the drastic reduction of transport coefficients proposed in Fabian (2005) remains the most viable path to acoustic wave heating of galaxy cluster cores

Modeling of the expansion of ultra-short-pulse laser-produced plasmas in magnetic fields

The study of hot plasma expansion in a uniform magnetic field is of interest for many astrophysical applications. In order to observe this process in laboratory, an experiment is proposed in which an ultrashort laser pulse produces a high-temperature plasma by irradiation of a jet of atomic clusters. The very high laser light absorption exhibited in such a gas of clusters facilitates the creation of a hot (> 5 keV), dense (10(19)-10(20) cm(-3)) plasma with a sharp boundary. The small scale of the plasma ( 1T). Pump-probe techniques can then be used to diagnose the density and magnetic field with high spatial and temporal resolution (<50fs). In the present work the expansion rate of the plasma and deceleration caused by the magnetic field are examined analytically. Electrodynamical aspects related to the radiation and transformation of energy are considered as well. The results obtained can be used in treating experimental data, studying magnetic R-T instabilities and other phenomena of astrophysical significance

MHD stability in axisymmetric multiple mirror geometry

The marginal stability of MHD modes is discussed in application for high beta multiple mirror experiments planned at Budker Institute of Nuclear Physics. Flute modes are dangerous in axisymmetric systems with beta beta(cr). A. very low ballooning margin is predicted in multiple mirror with the large number of cells: beta(cr) less than or equal to pi(2) /N-2. For the number of cells N similar or equal to 10: beta(cr) similar or equal to 5%. Results of the calculations are discussed in the context of old and new multiple mirror experiments

Axial shear instability in a "tachion" region

Plasma axial-shear flow instability arises due to a variation in an equilibrium E x B rotation along the axial direction in which the magnetic field is aligned. The two fluid MHD equations for incompressible perturbation (taking into account the FLR effects) being treated in WKB approximation in transversal direction yield one scalar Klein-Gordon type equation with one-dimensional effective potential U(s) and effective mass on(s). Only axisymmetric, paraxial geometry is analyzed in order to separate the desired effects from the effects related to a variation in cross-sectional shape of the magnetic flux tube. In this work the effective potential was considered for a semi-infinite bounded plasma, first in the form of a square well for analytical study and then in a linear nature to study in the so called "tachion" region. Growth rates as a function of the potential well depth and other parameters were calculated. The cases where effective mass is real and imaginary "tachion" regime were considered. The results obtained are interesting for the stability problem of such open devices as GDT, GAMMA-10 AMBAL-M and the scrape-off layer in tokamak divertors