Showing papers on "Relativistic plasma published in 2018"

Particle Acceleration in Relativistic Plasma Turbulence

Abstract: Due to its ubiquitous presence, turbulence is often invoked to explain the origin of nonthermal particles in astrophysical sources of high-energy emission. With particle-in-cell simulations, we study decaying turbulence in magnetically dominated (or, equivalently, "relativistic") pair plasmas. We find that the generation of a power-law particle energy spectrum is a generic by-product of relativistic turbulence. The power-law slope is harder for higher magnetizations and stronger turbulence levels. In large systems, the slope attains an asymptotic, system-size-independent value, while the high-energy spectral cutoff increases linearly with system size; both the slope and the cutoff do not depend on the dimensionality of our domain. By following a large sample of particles, we show that particle injection happens at reconnecting current sheets; the injected particles are then further accelerated by stochastic interactions with turbulent fluctuations. Our results have important implications for the origin of nonthermal particles in high-energy astrophysical sources.

System-size Convergence of Nonthermal Particle Acceleration in Relativistic Plasma Turbulence

Abstract: We apply collisionless particle-in-cell simulations of relativistic pair plasmas to explore whether driven turbulence is a viable high-energy astrophysical particle accelerator. We characterize nonthermal particle distributions for varying system sizes up to $L/2\pi\rho_{e0} = 163$, where $L/2\pi$ is the driving scale and $\rho_{e0}$ is the initial characteristic Larmor radius. We show that turbulent particle acceleration produces power-law energy distributions that, when compared at a fixed number of large-scale dynamical times, slowly steepen with increasing system size. We demonstrate, however, that convergence is obtained by comparing the distributions at different times that increase with system size (approximately logarithmically). We suggest that the system-size dependence arises from the time required for particles to reach the highest accessible energies via Fermi acceleration. The converged power-law index of the energy distribution, $\alpha \approx 3.0$ for magnetization $\sigma = 3/8$, makes turbulence a possible explanation for nonthermal spectra observed in systems such as the Crab nebula.

Particle acceleration in explosive relativistic reconnection events and Crab Nebula gamma-ray flares

Abstract: We develop a model of gamma-ray flares of the Crab Nebula resulting from the magnetic reconnection events in a highly magnetised relativistic plasma. We first discuss physical parameters of the Crab Nebula and review the theory of pulsar winds and termination shocks. We also review the principle points of particle acceleration in explosive reconnection events [Lyutikov et al., J. Plasma Phys., vol. 83(6), p. 635830601 (2017a); J. Plasma Phys., vol. 83(6), p. 635830602 (2017b)]. It is required that particles producing flares are accelerated in highly magnetised regions of the nebula. Flares originate from the poleward regions at the base of the Crab’s polar outflow, where both the magnetisation and the magnetic field strength are sufficiently high. The post-termination shock flow develops macroscopic (not related to the plasma properties on the skin-depth scale) kink-type instabilities. The resulting large-scale magnetic stresses drive explosive reconnection events on the light-crossing time of the reconnection region. Flares are produced at the initial stage of the current sheet development, during the X-point collapse. The model has all the ingredients needed for Crab flares: natural formation of highly magnetised regions, explosive dynamics on the light travel time, development of high electric fields on macroscopic scales and acceleration of particles to energies well exceeding the average magnetic energy per particle.

Electron Trapping from Interactions between Laser-Driven Relativistic Plasma Waves.

Abstract: Interactions of large-amplitude relativistic plasma waves were investigated experimentally by propagating two synchronized ultraintense femtosecond laser pulses in plasma at oblique crossing angles to each other The electrostatic and electromagnetic fields of the colliding waves acted to preaccelerate and trap electrons via previously predicted, but untested injection mechanisms of ponderomotive drift and wake-wake interference High-quality energetic electron beams were produced, also revealing valuable new information about plasma-wave dynamics

Spectral control of high harmonics from relativistic plasmas using bicircular fields

Abstract: We introduce two-color counterrotating circularly polarized laser fields as a way to spectrally control high harmonic generation (HHG) from relativistic plasma mirrors Through particle-in-cell simulations, we show that only a selected group of harmonic orders can appear owing to the symmetry of the laser fields and the related conservation laws By adjusting the intensity ratio of the two driving field components, we demonstrate the overall HHG efficiency, the relative intensity of allowed neighboring harmonic orders, and that the polarization state of the harmonic source can be tuned The HHG efficiency of this scheme can be as high as that driven by a linearly polarized laser field

System-size convergence of nonthermal particle acceleration in relativistic plasma turbulence

Abstract: We apply collisionless particle-in-cell simulations of relativistic pair plasmas to explore whether driven turbulence is a viable high-energy astrophysical particle accelerator. We characterize nonthermal particle distributions for varying system sizes up to $L/2\pi\rho_{e0} = 163$, where $L/2\pi$ is the driving scale and $\rho_{e0}$ is the initial characteristic Larmor radius. We show that turbulent particle acceleration produces power-law energy distributions that, when compared at a fixed number of large-scale dynamical times, slowly steepen with increasing system size. We demonstrate, however, that convergence is obtained by comparing the distributions at different times that increase with system size (approximately logarithmically). We suggest that the system-size dependence arises from the time required for particles to reach the highest accessible energies via Fermi acceleration. The converged power-law index of the energy distribution, $\alpha \approx 3.0$ for magnetization $\sigma = 3/8$, makes turbulence a possible explanation for nonthermal spectra observed in systems such as the Crab nebula.

Isolated elliptically polarized attosecond soft X-ray with high-brilliance using polarization gating of harmonics from relativistic plasmas at oblique incidence

Abstract: The production of intense isolated attosecond pulse is a major goal in ultrafast research. Recent advances in high harmonic generation from relativistic plasma mirrors under oblique incidence interactions gave rise to photon-rich attosecond pulses with circular or elliptical polarization. However, to achieve an isolated elliptical attosecond pulse via polarization gating using currently available long driving pulses remains a challenge, because polarization gating of high harmonics from relativistic plasmas is assumed only possible at normal or near-normal incidence. Here we numerically demonstrate a scheme around this problem. We show that via control of plasma dynamics by managing laser polarization, it is possible to gate an intense single attosecond pulse with high ellipticity extending to the soft X-ray regime at oblique incidence. This approach thus paves the way towards a powerful tool enabling high-time-resolution probe of dynamics of chiral systems and magnetic materials with current laser technology.

Explosive X-point collapse in relativistic magnetically-dominated plasma

Abstract: The extreme properties of the gamma ray flares in the Crab Nebula present a clear challenge to our ideas on the nature of particle acceleration in relativistic astrophysical plasma. It seems highly unlikely that standard mechanisms of stochastic type are at work here and hence the attention of theorists has switched to linear acceleration in magnetic reconnection events. In this series of papers, we attempt to develop a theory of explosive magnetic reconnection in highly-magnetized relativistic plasma which can explain the extreme parameters of the Crab flares. In the first paper, we focus on the properties of the X-point collapse. Using analytical and numerical methods (fluid and particle-in-cell simulations) we extend Syrovatsky's classical model of such collapse to the relativistic regime. We find that the collapse can lead to the reconnection rate approaching the speed of light on macroscopic scales. During the collapse, the plasma particles are accelerated by charge-starved electric fields, which can reach (and even exceed) values of the local magnetic field. The explosive stage of reconnection produces non-thermal power-law tails with slopes that depend on the average magnetization $\sigma$. For sufficiently high magnetizations and vanishing guide field, the non-thermal particle spectrum consists of two components: a low-energy population with soft spectrum, that dominates the number census; and a high-energy population with hard spectrum, that possesses all the properties needed to explain the Crab flares.

Relativistic turbulence with strong synchrotron and synchrotron self-Compton cooling

Abstract: Many relativistic plasma environments in high-energy astrophysics, including pulsar wind nebulae, hot accretion flows onto black holes, relativistic jets in active galactic nuclei and gamma-ray bursts, and giant radio lobes, are naturally turbulent. The plasma in these environments is often so hot that synchrotron and inverse-Compton (IC) radiative cooling becomes important. In this paper we investigate the general thermodynamic and radiative properties (and hence the observational appearance) of an optically thin relativistically hot plasma stirred by driven magnetohydrodynamic (MHD) turbulence and cooled by radiation. We find that if the system reaches a statistical equilibrium where turbulent heating is balanced by radiative cooling, the effective electron temperature tends to attain a universal value $\theta = kT_e/m_e c^2 \sim 1/\sqrt{\tau_T}$, where $\tau_T=n_e\sigma_T L \ll 1$ is the system's Thomson optical depth, essentially independent of the strength of turbulent driving or magnetic field. This is because both MHD turbulent dissipation and synchrotron cooling are proportional to the magnetic energy density. We also find that synchrotron self-Compton (SSC) cooling and perhaps a few higher-order IC components are automatically comparable to synchrotron in this regime. The overall broadband radiation spectrum then consists of several distinct components (synchrotron, SSC, etc.), well separated in photon energy (by a factor $\sim \tau_T^{-1}$) and roughly equal in power. The number of IC peaks is checked by Klein-Nishina effects and depends logarithmically on $\tau_T$ and the magnetic field. We also examine the limitations due to synchrotron self-absorption, explore applications to Crab PWN and blazar jets, and discuss links to radiative magnetic reconnection.

Wave dispersion in pulsar plasma: 1. Plasma rest frame

Abstract: Wave dispersion in a pulsar plasma (a 1D, strongly magnetized, pair plasma streaming highly relativistically with a large spread in Lorentz factors in its rest frame) is discussed, motivated by interest in beam-driven wave turbulence and the pulsar radio emission mechanism. In the rest frame of the pulsar plasma there are three wave modes in the low-frequency, non-gyrotropic approximation. For parallel propagation these are referred to as the X, A and L modes, with the X and A modes having dispersion relation $z=z_A\approx1-1/2\beta_A^2$, where $z=\omega/k_\parallel c$ is the phase speed and $\beta_Ac$ is the Alfven speed. The L mode dispersion relation is determined by a relativistic plasma dispersion function, $z^2W(z)$, which is negative for $ z z_0$, to form the O and Alfven modes for oblique propagation ($\theta eq0$). For $z_A z_0^2-z_A^2$. The L mode is the nearest counterpart to Langmuir waves in a nonrelativistic plasma, but we argue that there are no `Langmuir-like' waves in pulsar plasma, identifying three features of the L~mode (dispersion relation, ratio of electric to total energy and group speed) that are not Langmuir-like. A beam-driven instability requires a beam speed equal to the phase speed of the wave. This resonance condition can be satisfied for the O mode, but only for an implausibly energetic beam and only for a tiny range of angles for the O~mode around $\theta\approx0$. The resonance is also possible for the Alfven mode but only near a turnover frequency that has no counterpart for Alfven waves in a nonrelativistic plasma.

Stimulated scattering instability in a relativistic plasma

Abstract: We study the stimulated scattering instabilities of an intense linearly polarized electromagnetic wave (EMW) in a relativistic plasma with degenerate electrons. Starting from a relativistic hydrodynamic model and the Maxwell's equations, we derive coupled nonlinear equations for low-frequency electron and ion plasma oscillations that are driven by the EMW's ponderomotive force. The nonlinear dispersion relations are then obtained from the coupled nonlinear equations which reveal stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS), and modulational instabilities (MIs) of EMWs. It is shown that the thermal pressure of ions and the relativistic degenerate pressure of electrons significantly modify the characteristics of SRS, SBS, and MIs.We study the stimulated scattering instabilities of an intense linearly polarized electromagnetic wave (EMW) in a relativistic plasma with degenerate electrons. Starting from a relativistic hydrodynamic model and the Maxwell's equations, we derive coupled nonlinear equations for low-frequency electron and ion plasma oscillations that are driven by the EMW's ponderomotive force. The nonlinear dispersion relations are then obtained from the coupled nonlinear equations which reveal stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS), and modulational instabilities (MIs) of EMWs. It is shown that the thermal pressure of ions and the relativistic degenerate pressure of electrons significantly modify the characteristics of SRS, SBS, and MIs.

Effect of non-thermality of electron and negative ion on the polarity of shock waves in a relativistic plasma

Abstract: Considering the effect of non-thermality of electrons and negative ions, the evolution of shock waves and their characteristics in a relativistic plasma is investigated by deriving a three-dimensional Burgers' (3D-Burgers') equation Based on the stationary solution of the 3D-Burgers' equation, the nature of propagation of shock waves for different suitable physically admissible ranges of plasma parameters, is carried out Both compressive and rarefactive shock waves are found to propagate in such plasma under different combinations of non-thermal plasma parameters The critical values of non-thermal electron and negative ion parameters, normalized electron, and negative ion density under which the non-linear co-efficient vanishes is sought The nature of propagation of shock waves, below, above, and at the critical parameters is carried out The non-thermal population of negative ions and electrons as well as normalized electron and negative ion density plays a pivotal role in controlling the polarity of the shock wave propagation Compressive and rarefactive shock is found to propagate simultaneously with the non-thermal population of negative ions for different chosen values of normalized negative ion density at the critical value of normalized electron density

Fast magnetic reconnection: The ideal tearing instability in classic, Hall, and relativistic plasmas.

Abstract: Magnetic reconnection is believed to be the driver of many explosive phenomena in Astrophysics, from solar to gamma-ray flares in magnetars and in the Crab nebula. However, reconnection rates from classic MHD models are far too slow to explain such observations. Recently, it was realized that when a current sheet gets sufficiently thin, the reconnection rate of the tearing instability becomes "ideal", in the sense that the current sheet destabilizes on the "macroscopic" Alfvenic timescales, regardless of the Lundquist number of the plasma. Here we present 2D compressible MHD simulations in the classical, Hall, and relativistic regimes. In particular, the onset of secondary tearing instabilities is investigated within Hall-MHD for the first time. In the frame of relativistic MHD, we summarize the main results from Del Zanna et al. [1]: the relativistic tearing instability is found to be extremely fast, with reconnection rates of the order of the inverse of the light crossing time, as required to explain the high-energy explosive phenomena.

Dispersion relation of longitudinal oscillation in relativistic plasmas with nonextensive distribution

Abstract: The theory and application of nonextensive statistical mechanics (NESM) have underwent rapid development since the nonextensive entropy is put forward in 1988; its tentacles are almost throughout all areas of physics and has been a huge success. The nonextensive distribution function, however, as a basic part of NESM theory and application foundation, suffers a controversy: two different mathematical definitions of nonextensive distributions. Here, we show that the one dimensional nonextensive distribution function has the form of [ 1 + ( 1 − q ) x 2 ] 1 q − 1. We are starting from the nonextensive entropy, derive the nonextensive distribution function adopting the Maxwellian method, and prove the correctness of the form, and illustrate the physical meaning of the nonextensive parameter q as the fractal dimension when the Euclidean dimension is one. Furthermore, we derive the three-dimensional distribution function and the relativistic nonextensive distribution function, which perfect the theory of NESM and lay a solid application foundation of the NESM. We use the relativistic nonextensive distribution function to investigate the dispersion relations of relativistic longitudinal oscillation in nonextensive plasma and obtain the analytical expression of long wave dispersion relations under the ultra-relativistic case and the complete numerical dispersion curves. These results under an extensive limit reproduce Maxwellian statistical results. The proposed theory provides a method to measure the dimension of a plasma system, which may greatly promote our understanding for complex nonlinear plasma systems and thus, promote the understanding and solving of nonlinear problems such as turbulence, chaos, and soliton. This work also is the application foundation of nonextensive statistical mechanics to high energy physics such as relativistic plasma, M-theory, and so on in physical and mathematical aspects.

Exploration of Strong Field Physics with Multi-PW Lasers

Abstract: At the Center for Relativistic Laser Science (CoReLS) petawatt (PW) lasers have been developed for the investigations of strong field physics. The CoReLS has successfully upgraded one of the existing PW laser beamlines to a 4 PW laser at 20 fs. From laser-driven charged-particle acceleration experiments, multi-GeV electrons and 90-MeV protons can be generated using the laser wakefield acceleration and the radiation pressure acceleration schemes, respectively. The GeV electron beam can be, in turn, used for Compton backscattering with another PW laser. Such a Compton scattering process can be examined for other quantum electrodynamics (QED) effects, including the radiation reaction effect and the Breit-Wheeler pair production process. PW lasers have, thus, offered new opportunities to pursue novel physics research in relativistic plasma physics, strong field quantum electrodynamics, nuclear physics and laboratory astrophysics.

Overlapping of the harmonics of the cyclotron frequency in the Bernstein waves due to relativistic effects

Abstract: By using the generalized expression for the plasma conductivity tensor, the general dispersion relation for the Bernstein waves is derived. To investigate the Bernstein waves for a weakly relativistic plasma, the Maxwell-Boltzmann-Juttner distribution function is employed. The propagation characteristics of the electron Bernstein waves (overlapping, propagation regions, and harmonic structures) are examined by using different values of η (ratio of rest mass energy to thermal energy) and ω p e ω c e (ratio of the plasma frequency to the cyclotron frequency). It is observed that the relativistic effects are the main cause of the harmonic overlapping which reduces the region of propagation.

Splitter target for controlling magnetic reconnection in relativistic laser plasma interactions

Abstract: The utilization of a conical target irradiated by a high power laser is proposed to study fast magnetic reconnection in relativistic plasma interactions. Such target, placed in front of the near critical density gas jet, splits the laser pulse, forming two parallel laser pulses in the 2D case and a donut shaped pulse in the 3D case. The magnetic annihilation and reconnection occur in the density downramp region of the subsequent gas jet. The magnetic field energy is converted into the particle kinetic energy. As a result, a backward accelerated electron beam is obtained as a signature of reconnection. The above mechanisms are demonstrated using particle-in-cell simulations in both 2D and 3D cases. Facilitating the synchronization of two laser beams, the proposed approach can be used in designing the corresponding experiments on studying fundamental problems of relativistic plasma physics.

Two-dimensional structures of electron bunches in relativistic plasma cavities

Abstract: The spatial structure of an ultralow-emittance electron bunch in a plasma wakefield blowout regime is studied. The full Li\'enard-Wiechert potentials are considered for mutual interparticle interactions in the framework of the equilibrium slice model. This model uses the quasistatic theory which allows one to solve the Li\'enard-Wiechert potentials without knowledge of the electrons' history. The equilibrium structure we find is similar to already observed hexagonal lattices but shows topological defects. Scaling laws for interparticle distances are obtained from numerical simulations and analytical estimations.

3D Burgers Equation in Relativistic Plasma in the Presence of Electron and Negative Ion Trapping: Evolution of Shock Wave

Abstract: The characteristics of shock waves in a relativistic plasma in the presence of nonisothermal electrons and nonisothermal negative ions is investigated by deriving the evolution equation in terms of a modified 3D Burgers equation, or trapped 3D Burgers equation. The solution of this equation is examined analytically to study the salient characteristics of shock waves in such plasma. The nonlinear coefficient is found to have the lowest (highest) value when the negative ions move toward thermal equilibrium with a dip-shaped electron distribution (when both electrons and negative ions follow a dip-shaped distribution) for a particular value of relativistic factor, and it remains in an intermediate state when both electrons and negative ions follow a flat-topped distribution. On the other hand, the dissipative coefficient is found to decrease (increase) with increasing relativistic parameter (viscous parameter). A profound effect of the trapped state of both electrons and negative ions and the temperature ratio between positive ions and electrons (negative ions and electrons) on the structure of the shock wave is also seen. However, it has been noticed that the trapped parameter of electrons has a dominating control over the shock potential profile than the trapped parameter of negative ions.

Stimulated scattering instability in a relativistic plasma

Abstract: We study the stimulated scattering instabilities of an intense linearly polarized electromagnetic wave (EMW) in a relativistic plasma with degenerate electrons. Starting from a relativistic hydrodynamic model and the Maxwell's equations, we derive coupled nonlinear equations for low-frequency electron and ion plasma oscillations that are driven by the EMW's ponderomotive force. The nonlinear dispersion relations are then obtained from the coupled nonlinear equations which reveal stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS), and modulational instabilities (MIs) of EMWs. It is shown that the thermal pressure of ions and the relativistic degenerate pressure of electrons significantly modify the characteristics of SRS, SBS, and MIs.

Electron Acceleration by a Relativistic Electron Plasma Wave in Inverse-Free-Electron Laser Mechanism

Abstract: It has been revealed that a relativistic plasma wave, having an extremely large electric field, may be utilized for the acceleration of plasma particles. The large accelerating field gradient driven by a plasma wave is the basic motivation behind the acceleration mechanism. Such a plasma wave can be excited by a single laser in the form of wakefield in laser–plasma interactions. In this paper, we study the enhancement of electron acceleration by plasma wave in the presence of a wiggler magnetic field. Electrons trapped in the plasma wave are accelerated due to the additional resonance provided effectively by the wiggler field, which contributes in large energy gain of electrons during acceleration. The resonant enhancement of electron acceleration by the wiggler magnetic field has been validated by single particle simulations. The dependence of energy gain on plasma wave amplitude, initial electron energy, wiggler magnetic field strength has been investigated. Using the model, the involvement and importance of inverse free-electron laser mechanism in electron acceleration by the plasma wave was analyzed. A scaling law for electron energy optimization was proposed for future electron accelerator development.

Relativistic-amplitude electromagnetic waves—Beating the "magnetic" barrier

Abstract: The dispersion characteristics of a circularly polarized electromagnetic wave of arbitrary amplitude, propagating in a highly (thermally and kinematically) relativistic plasma, are shown to approach those of a linear wave in an unmagnetized, non-relativistic plasma. Further aided by high relativistic temperatures, the cut-off frequency tends to become negligibly small; as a result, waves with frequencies well below the nominal plasma and the cyclotron frequencies find the plasma to be essentially transparent. This relativistic phenomenon may greatly advance our ability to understand and model the dynamics of a large class of astrophysical and laser-produced high energy density systems.The dispersion characteristics of a circularly polarized electromagnetic wave of arbitrary amplitude, propagating in a highly (thermally and kinematically) relativistic plasma, are shown to approach those of a linear wave in an unmagnetized, non-relativistic plasma. Further aided by high relativistic temperatures, the cut-off frequency tends to become negligibly small; as a result, waves with frequencies well below the nominal plasma and the cyclotron frequencies find the plasma to be essentially transparent. This relativistic phenomenon may greatly advance our ability to understand and model the dynamics of a large class of astrophysical and laser-produced high energy density systems.

Oblique propagation of solitary waves in weakly relativistic magnetized plasma with kappa distributed electrons in the presence of negative ions

Abstract: The oblique propagation of nonlinear ion acoustic solitary waves (solitons) in magnetized collisionless and weakly relativistic plasma with positive and negative ions and super thermal electrons has been examined by using reduced perturbation method to obtain the Korteweg-de Vries equation that admits an obliquely propagating soliton solution. We have investigated the effects of plasma parameters like negative ion density, electrons temperature, angle between wave vector and magnetic field, ions velocity, and k (spectral index in kappa distribution) on the amplitude and width of solitary waves. It has been found out that four modes exist in our plasma model, but the analysis of the results showed that only two types of ion acoustic modes (fast and slow) exist in the plasma and in special cases only one mode could be propagated. The parameters of plasma for these two modes (or one mode) determine which one is rarefactive and which one is compressive. The main parameter is negative ions density (β) indicati...

Determining the composition of radio plasma via circular polarization: the prospects of the Cygnus A hot spots.

Abstract: The composition of the relativistic plasma produced in active galactic nuclei and ejected via powerful jets into the interstellar/intergalactic medium is still a major unsettled issue. It might be a positron-electron plasma in case the plasma was created by pair production in the intense photon fields near accreting super-massive black holes. Alternatively, it might be an electron-proton plasma in case magnetic fields lift and accelerate the thermal gas of accretion discs into relativistic jets as the recent detection of $\gamma$-rays from blazars indicates. Despite various attempts to unambiguously establish the composition of the relativistic jets, this remains a major unknown. Here, we propose a way to settle the question via sensitive measurements of circular polarization (CP) in the radio emission of the hot spots of bright radio galaxies like Cygnus A. The CP of synchrotron emission is determined by the circular motions of the radiating relativistic leptons. In case of charge symmetric energy spectra of a electron-positron plasma, it should be exactly zero. In case of an electron-proton plasma the electrons imprint their gyration onto the CP and we expect the hot spots of Cygnus A to exhibit a fractional CP at a level of $10^{-3}\,( u/\mbox{GHz})^{-{1}/{2}}$, which is challenging to measure, but not completely unfeasible.

Lorentz invariant `potential magnetic field' and magnetic flux conservation in an ideal relativistic plasma

Abstract: A family of Lorentz invariant scalar functions of the magnetic field is defined in an ideal relativistic plasma. These invariants are advected by the plasma fluid motion and play the role of the potential magnetic field introduced by Hide in (Ann. Geophys., vol. 1, 1983, 59) along the lines of Ertel’s theorem. From these invariants we recover the Cauchy conditions for the magnetic field components in the mapping from Eulerian to Lagrangian variables. In addition, the adopted procedure allows us to formulate, in a Lorentz invariant form, the Alfven theorem for the conservation of the magnetic flux through a surface comoving with the plasma.

Relativistic magnetic reconnection in application to gamma-ray astrophysics

Abstract: Cosmic sources of gamma-ray radiation in the GeV range are often characterized by violent variability, in particular this concerns blazars, gamma-ray bursts, and the pulsar wind nebula Crab. Such gamma-ray emission requires a very efficient particle acceleration mechanism. If the environment, in which such emission is produced, is relativistically magnetized (i.e., that magnetic energy density dominates even the rest-mass energy density of matter), then the most natural mechanism of energy dissipation and particle acceleration is relativistic magnetic reconnection. Basic research into this mechanism is performed by means of kinetic numerical simulations of various configurations of collisionless relativistic plasma with the use of the particle-in-cell algorithm. Such technique allows to investigate the details of particle acceleration mechanism, including radiative energy losses, and to calculate the temporal, spatial, spectral and angular distributions of synchrotron and inverse Compton radiation. The results of these simulations indicate that the effective variability time scale of the observed radiation can be much shorter than the light-crossing time scale of the simulated domain.

Self-focusing of q-Gaussian laser beam in relativistic plasma using exponential density based transition

Abstract: We have investigated self-focusing of a q-Gaussian laser beam in a relativistic plasma channel using exponential density based transition. The present paper is devoted to the importance of using a ramp density profile in decreasing the beam width parameter considerably. The preference of ramp type plays a better role in guiding the high intensity laser pulses to several Rayleigh lengths. Our results obtained from numerical analysis show that laser self-focusing can be controlled by varying laser intensity parameter, q-values and suitable density ramp parameter. We have derived the nonlinear differential equation for the beam width parameter using WKB and Paraxial ray approximation and solved it numerically using the Runge Kutta method to study the nature of self-focusing and defocusing. It is observed that self-focusing of q-Gaussian laser beam can be increased with increasing laser intensity parameter. Moreover, in case of q-Gaussian laser beam, it is easier to focus lower q-values using suitable type of plasma density ramp.