Self-inhibiting thermal conduction in high-beta, whistler-unstable plasma

A heat flux in a high-$\beta$ plasma with low collisionality triggers the whistler instability. Quasilinear theory predicts saturation of the instability in a marginal state characterized by a heat flux that is fully controlled by electron scattering off magnetic perturbations. This marginal heat flux does not depend on the temperature gradient and scales as $1/\beta$. We confirm this theoretical prediction by performing numerical particle-in-cell simulations of the instability. We further calculate the saturation level of magnetic perturbations and the electron scattering rate as functions of $\beta$ and the temperature gradient to identify the saturation mechanism as quasilinear. Suppression of the heat flux is caused by oblique whistlers with magnetic-energy density distributed over a wide range of propagation angles. This result can be applied to high-$\beta$ astrophysical plasmas, such as the intracluster medium, where thermal conduction at sharp temperature gradients along magnetic-field lines can be significantly suppressed. We provide a convenient expression for the amount of suppression of the heat flux relative to the classical Spitzer value as a function of the temperature gradient and $\beta$. For a turbulent plasma, the additional independent suppression by the mirror instability is capable of producing large total suppression factors (several tens in galaxy clusters) in regions with strong temperature gradients.Comment: accepted to JP

On integration of the Kowalevski gyrostat and the Clebsch problems

For the Kowalevski gyrostat change of variables similar to that of the Kowalevski top is done. We establish one to one correspondence between the Kowalevski gyrostat and the Clebsch system and demonstrate that Kowalevski variables for the gyrostat practically coincide with elliptic coordinates on sphere for the Clebsch case. Equivalence of considered integrable systems allows to construct two Lax matrices for the gyrostat using known rational and elliptic Lax matrices for the Clebsch model. Associated with these matrices solutions of the Clebsch system and, therefore, of the Kowalevski gyrostat problem are discussed. The Kotter solution of the Clebsch system in modern notation is presented in detail.Comment: LaTeX, 24 page

Passive mode-locking of a fiber laser operating in the regime of undumped regular spiking

Computer simulation is used to investigate a new regime of oscillation of fiber lasers in which passive mode-locking takes place simultaneously with the regime of regular undumped spiking induced by an intracavity saturable absorber. Such a superposition regime takes place when part of the output radiation of the laser operating in the regime of spiking is propagated through a fiber-optic delay line and is coupled back into the laser cavity in a time interval equal to the time interval between adjacent spikes. The advantages of the proposed regime of oscillation relative to other means of achieving passive mode-locking in fiber lasers are discussed. The proposed regime is of interest for obtaining reproducible high-energy light pulses

Quantization of binding energy of structural solitons in passive mode-locked fiber lasers

On basis of numerical simulation of fiber laser passive mode locking, we have determined the quantum binding-energy levels for a pair of interacting structural solitons. These solitons have powerful wings and correspondingly large binding energies. It has been found that the field amplitude functions for steady states corresponding to neighboring energy levels have opposite parity. We have pointed out the analogy between the energy quantization for laser bound solitons and for a particle moving in potential well. The possibility of a coexistence of in-, opposite-, and π/2-phase soliton pairs has been found. In the case of multiple soliton trains, we have demonstrated the realization of highly stable soliton sequences with any required distribution along the soliton train of various types of bonds between neighboring pulses

Regimes of Passive Mode-Locking of Fiber Lasers

We present results of a numerical simulation and analysis of various regimes of passive mode-locking of fiber lasers including a single pulse  and multipulse operation, bound states of solitons, and harmonic passive mode-locking. Our results on the multipulse regimes consist of the multihysteresis dependences of a number of pulses in the laser cavity, of pulse peak intensities and an intracavity radiation energy on a pump power. The analysis of mechanisms of an intersoliton interaction in the laser cavity has been performed. The opportunity of the coding of information with the use of bound soliton sequences has been demonstrated. Various mechanisms for control of intersoliton interactionr are proposed

Dissipative Soliton Resonance in Passive Mode-Locked Lasers

By numerical simulation it is found that the dissipative soliton resonance prevents to an appearance in generation of new pulses with increasing pump power. It can be used for generation of high-energy pulses

Polarization of Sunyaev-Zeldovich signal due to electron pressure anisotropy in galaxy clusters

We describe polarization of the Sunyaev-Zel'dovich (SZ) effect associated with electron pressure anisotropy likely present in the intracluster medium (ICM). The ICM is an astrophysical example of a weakly collisional plasma where the Larmor frequencies of charged particles greatly exceed their collision frequencies. This permits formation of pressure anisotropies, driven by evolving magnetic fields via adiabatic invariance, or by heat fluxes. SZ polarization arises in the process of Compton scattering of the cosmic microwave background (CMB) photons off the thermal ICM electrons due to the difference in the characteristic thermal velocities of the electrons along two mutually orthogonal directions in the sky plane. The signal scales linearly with the optical depth of the region containing large-scale correlated anisotropy, and with the degree of anisotropy itself. It has the same spectral dependence as the polarization induced by cluster motion with respect to the CMB frame (kinematic SZ effect polarization), but can be distinguished by its spatial pattern. { For the illustrative case of a galaxy cluster with a cold front, where electron transport is mediated by Coulomb collisions, we estimate the CMB polarization degree at the level of 10$^{-8}$ ($\sim 10$ nK). An increase of the effective electron collisionality due to plasma instabilities will reduce the effect. Such polarization, therefore, may be an independent probe of the electron collisionality in the ICM, which is one of the key properties of a high-$\beta$ weakly collisional plasma from the point of view of both astrophysics and plasma theory.Comment: 13 pages, 5 figures, accepted for publication in MNRA