Relativistic Fluid Model Research Articles

Modulation instability of an intense laser beam in the hot magnetized electron-positron plasma in the quasi-neutral limit

The aim of the present study is to investigate the problem of modulation instability of an intense laser beam in the hot magnetized electron-positron plasma. Propagation of the intense circularly polarized laser beam along the external magnetic field is studied using a relativistic fluid model. A nonlinear equation describing the interaction of the laser pulse with the magnetized hot pair plasma is derived based on the quasi-neutral approximation, which is valid for the hot plasma. Also, the nonlinear dispersion equation for the hot plasma is obtained. The growth rate of the instability is calculated and its dependence on temperature and external magnetic field are considered.

ON LORENTZIAN QUASI-EINSTEIN MANIFOLDS

The notion of quasi-Einstein manifolds arose during the study of exact solutions of the Einstein field equations as well as during considerations of quasi-umbilical hypersurfaces. For instance, the Robertson-Walker spacetimes are quasi-Einstein manifolds. The object of the present paper is to study Lorentzian quasi-Einstein manifolds. Some basic geometric properties of such a manifold are obtained. The applications of Lorentzian quasi-Einstein manifolds to the general relativity and cosmology are investigated. Theories of gravitational collapse and models of Supernova explosions [5] are based on a relativistic fluid model for the star. In the theories of galaxy formation, relativistic fluid models have been used in order to describe the evolution of perturbations of the baryon and radiation components of the cosmic medium [32]. Theories of the structure and stability of neutron stars assume that the medium can be treated as a relativistic perfectly conducting magneto fluid. Theories of relativistic stars (which would be models for supermassive stars) are also based on relativistic fluid models. The problem of accretion onto a neutron star or a black hole is usually set in the framework of relativistic fluid models. Among others it is shown that a quasi-Einstein spacetime represents perfect fluid spacetime model in cosmology and consequently such a spacetime determines the final phase in the evolution of the universe. Finally the existence of such manifolds is ensured by several examples constructed from various well known geometric structures.

Ion-acoustic solitary waves in a fully relativistic ion-electron-positron plasma

A fully and coherent relativistic fluid model derived from the covariant formulation of relativistic fluid equations is used to study ion-acoustic solitary waves in a fully relativistic ion-electron-positron plasma. This approach has the characteristic to be consistent with the relativistic principle and consequently leads to a more general set of equations valid for fully relativistic plasmas with arbitrary Lorentz relativistic factor. Our results may be relevant to cosmic relativistic double- layers and relativistic plasma structures involving energetic plasma flows that may occur in space plasmas. Furthermore, they may complement and provide new insights into recently published results (G. Lu et al. in Astrophys. Space Sci., doi: 10.1007/s10509-010-0363-5 , 2010).

Weakly nonlinear kink-type solitary waves in a fully relativistic plasma

A fully and coherent relativistic fluid model derived from the covariant formulation of relativistic fluid equations is used to study small but finite amplitude solitary waves. This approach has the characteristic to be consistent with the relativistic principle and consequently leads to a more general set of equations valid for fully relativistic plasmas with arbitrary Lorentz relativistic factor. A kink-solitary wave solution is outlined. Due to electron relativistic effect, the localized structure may experience either a spreading or a compression. This latter phenomenon (compression) becomes less effective and less noticeable as the relativistic character of the ions becomes important. Our results may be relevant to cosmic relativistic double-layers and relativistic plasma structures that involve energetic plasma flows.

Electron bunch compression using a laser-plasma compressor

A new scheme for the compression of electron bunches is proposed. This scheme uses a plasma wave generated by a high intensity laser pulse to compress an electron bunch produced by a typical rf photogun. In the scheme, the electron bunch is injected into a plasma channel in front of the high intensity laser pulse. The laser pulse generates a plasma wave which ``sweeps up'' the electron bunch resulting in both compression and acceleration. The electron bunch will eventually overtake the laser pulse so that, afterwards, the electrons travel in front of the plasma wave. The scheme differs from previous schemes using a plasma wave to accelerate and compress electron bunches by sacrificing part of the acceleration to get a lower final energy spread and decrease the sensitivity to jitter in the synchronization between laser and electrons. Using a hybrid model, combining particle tracking for the electrons and a relativistic fluid model for the plasma, the scheme is investigated. The model is used to study the effects of the size of the injected bunches, the initial energy spread, and jitter in the laser-bunch synchronization. Also, one of the ways to vary the compression ratio of the scheme is explored by varying the plasma density. From these simulations, it can be concluded that the proposed scheme can compress bunches from an initial size of picoseconds to below one hundred femtoseconds with an energy spread below 0.2%. The scheme can also be adjusted to still produce these bunches in the presence of synchronization jitter up to 1 ps (for the parameters chosen).

Comparaison des patients caucasiens et non caucasiens au cours de la maladie de Takayasu : étude rétrospective monocentrique de 82 cas

The main features of codes for inertial confinement fusion studies are outlined, and a few recent simulation results are presented. The two-dimensional Lagrangian fluid code DUED is used to study target evolution, including beam-driven compression, hydrodynamic stability, hot spot formation, ignition and burn. An electro-magnetic particle-in-cell (PIC) code is applied to the study of ultraintense laser–plasma interaction and generation of fast electron jets. A relativistic 3D collisionless fluid model addresses relativistic electron beam propagation in a dense plasma.

Ions motion effects on the full unstable spectrum in relativistic electron beam plasma interaction

A relativistic fluid model is implemented to assess the role of the ions motion in the linear phase of relativistic beam plasma electromagnetic instabilities. The all unstable wave vector spectrum is investigated, allowing us to assess how ion motions modify the competition between every possible instability. Beam densities up to the plasma one are considered. Due to the fluid approach, the temperatures must remain small, i.e., nonrelativistic. In the cold limit, ions motion affect the most unstable mode when the beam gamma factor γb≳αM∕mZi, α being the beam to plasma density ratio, Zi the ion charge, M their mass, and m the electrons. The return current plays an important role by prompting Buneman-type instabilities which remain in the nonrelativistic regime up to high beam densities. Nonrelativistic temperatures only slightly affect these conclusions, except in the diluted beam regime where they can stabilize the Buneman modes.

Relativistic Fluid Dynamics: Physics for Many Different Scales.

The relativistic fluid is a highly successful model used to describe the dynamics of many-particle, relativistic systems. It takes as input basic physics from microscopic scales and yields as output predictions of bulk, macroscopic motion. By inverting the process, an understanding of bulk features can lead to insight into physics on the microscopic scale. Relativistic fluids have been used to model systems as “small” as heavy ions in collisions, and as large as the Universe itself, with “intermediate” sized objects like neutron stars being considered along the way. The purpose of this review is to discuss the mathematical and theoretical physics underpinnings of the relativistic (multiple) fluid model. We focus on the variational principle approach championed by Brandon Carter and his collaborators, in which a crucial element is to distinguish the momenta that are conjugate to the particle number density currents. This approach differs from the “standard” text-book derivation of the equations of motion from the divergence of the stress-energy tensor in that one explicitly obtains the relativistic Euler equation as an “integrability” condition on the relativistic vorticity. We discuss the conservation laws and the equations of motion in detail, and provide a number of (in our opinion) interesting and relevant applications of the general theory.

On the effects of geometry on guided electromagnetic waves

The method of moving (Cartan) coframes is used to analyze the influence of geometry on the behavior of electromagnetic fields in confining guides and the effect of such fields on their ultra-relativistic sources. Such issues are of relevance to a number of topical problems in accelerator science where the need to control the motion of high current-density micro-meter size bunches of relativistic radiating charge remains a technical and theoretical challenge. By dimensionally reducing the exterior equations for the sources and fields on spacetime using symmetries exhibited by the confining guides one achieves a unifying view that offers natural perturbative approaches for dealing with smooth non-uniform and curved guides. The issue of the back-reaction of radiation fields on the sources is approached in terms of a simple charged relativistic fluid model. .

Standing Ultrashort Relativistic Solitons in Overdense Plasmas

By using a one-dimensional self-consistent relativistic fluid model, an investigation is made numerically on relativistic electromagnetic solitons with a high intensity in cold overdense plasmas with an electrons' initial velocity opposite to the laser propagating direction. Two types of standing solitons with zero group velocity are found at the given electrons' initial velocities. One is single-humped with a weakly relativistic intensity; the another is multi-humped with a strong relativistic amplitude. The properties of these two types of solitons are presented in detail.

Ion dynamics effect in forming relativistic solitons in plasmas

By using one-dimensional self-consistent relativistic fluid model, moving relativistic electromagnetic solitons with high intensity in electron-ion plasmas where the ion dynamics is taken into account are investigated numerically. It is demonstrated that two types of relativistic solitons with a precisely defined group velocity can occur in underdense and overdense plasmas with a given different background density. One is single-humped with weak scalar and vector potential amplitude; the other is multi-humped with high one. For these two types of solitons, the eigenvalue spectra of the group velocity versus the background density are found. The existence of soliton solutions is investigated in plasmas with a different background density, and the properties of these solitons are presented in detail.

Charged sphere of shear-free fluids with $$\frac{\partial}{\rho} \partial r \leq 0$$

The Einstein-Maxwell equations for non-static charged shear-free spherically symmetric perfect fluid distribution reduce to a second-order non-linear differential equation in the radial parameter. Several solutions of this equation have been obtained in earlier work without considering the general requirement for physical relevance of the solutions. Generally physically acceptable relativistic fluid models demand that the solutions satisfy the reality conditions ρ ≥ 0, p ≥ 0, ρr ≤ 0, etc. throughout the fluid model. In this article the expression for density gradient ρ x (or ρr) has been utilized to produce charged shear-free relativistic fluid models with non-positive density gradient (NDG)ρr ≤ 0. Eventually, we have found that none of the Riccati solutions have NDG including Vaidya metric. Also, the solutions with NDG neither possess Lie-symmetries nor Painleve property. Further, it is observed that the solutions with NDG have no uncharged analogue.

Electron acceleration in combined intense laser fields and self-consistent quasistatic fields in plasma

The acceleration of plasma electron in intense laser-plasma interaction is investigated analytically and numerically, where the conjunct effect of laser fields and self-consistent spontaneous fields (including quasistatic electric field Esl, azimuthal quasistatic magnetic field Bsθ and the axial one Bsz) is completely considered for the first time. An analytical relativistic electron fluid model using test-particle method has been developed to give an explicit analysis about the effects of each quasistatic fields. The ponderomotive accelerating and scattering effects on electrons are partly offset by Esl, furthermore, Bsθ pinches and Bsz collimates electrons along the laser axis. The dependences of energy gain and scattering angle of electron on its initial radial position, plasma density, and laser intensity are, respectively, studied. The qualities of the relativistic electron beam (REB), such as energy spread, beam divergence, and emitting (scattering) angle, generated by both circularly polarized (CP) and linearly polarized (LP) lasers are studied. Results show CP laser is of clear advantage comparing to LP laser for it can generate a better REB in collimation and stabilization.

Fluid and kinetic simulation of inertial confinement fusion plasmas

The main features of codes for inertial confinement fusion studies are outlined, and a few recent simulation results are presented. The two-dimensional Lagrangian fluid code DUED is used to study target evolution, including beam-driven compression, hydrodynamic stability, hot spot formation, ignition and burn. An electro-magnetic particle-in-cell (PIC) code is applied to the study of ultraintense laser–plasma interaction and generation of fast electron jets. A relativistic 3D collisionless fluid model addresses relativistic electron beam propagation in a dense plasma.

Fluid interpretation of Cardassian expansion

A fluid interpretation of Cardassian expansion is developed. Here, the Friedmann equation takes the form $H^2 = g(\rho_M)$ where $\rho_M$ contains only matter and radiation (no vacuum). The function $g(\rhom)$ returns to the usual $8\pi\rhom/(3 m_{pl}^2)$ during the early history of the universe, but takes a different form that drives an accelerated expansion after a redshift $z \sim 1$. One possible interpretation of this function (and of the right hand side of Einstein's equations) is that it describes a fluid with total energy density $\rho_{tot} = {3 m_{pl}^2 \over 8 \pi} g(\rhom) = \rhom + \rho_K$ containing not only matter density (mass times number density) but also interaction terms $\rho_K$. These interaction terms give rise to an effective negative pressure which drives cosmological acceleration. These interactions may be due to interacting dark matter, e.g. with a fifth force between particles $F \sim r^{\alpha -1}$. Such interactions may be intrinsically four dimensional or may result from higher dimensional physics. A fully relativistic fluid model is developed here, with conservation of energy, momentum, and particle number. A modified Poisson's equation is derived. A study of fluctuations in the early universe is presented, although a fully relativistic treatment of the perturbations including gauge choice is as yet incomplete.

Interaction of a relativistic soliton with a nonuniform plasma.

By using a relativistic fluid model, a nonlinear theory for the propagation of an intense laser pulse in an inhomogeneous cold plasma is developed. Assuming that the radiation spot size is larger than the plasma wavelength, we derive an envelope equation for the momentum of the electron fluid, taking into account relativistic electron mass variation and finite amplitude electron density perturbations that are driven by the relativistic ponderomotive force of light. Localized solutions of the envelope equation are discussed from an energy integral containing an effective potential. Numerical results for envelope solitons are obtained in a quasistationary approximation. The dependency of these localized solutions on the amplitude and the group velocity of the laser pulse is discussed. Also derived is an equation that governs the dynamics of the pulse center.

Stochastic electron gas theory of coherence in laser-driven synchrotron radiation

The transition from coherent to incoherent laser-driven synchrotron radiation is studied within the framework of a stochastic electron gas model. The fundamental difference between this approach and a relativistic fluid model resides in the fact that, for any number of incoherently phased point electrons, the 4-current contains Fourier components at arbitrarily short wavelengths, whereas the fluid model introduces an unphysical cutoff scale.

Fast ignitor: Fluid dynamics of channel formation and laser beam propagation

The concept of fast ignitor is intimately connected with the fundamental phenomenon of ultra-intense light beam propagation through dense matter in which kinetic effects combine with radiation pressure dominated hydrodynamics to form a complex scenario of extremely non-linear physics. In this paper, the fluid dynamic aspect of channel formation in a highly over-dense plasma is studied and possible attenuation mechanisms of the propagating pulse are evaluated in one dimension. Under the assumption that mass ablation reaches a quasistationary state, the radiation-assisted ablation pressure, the speed of the bow shock, and the density steepening around the critical point are determined self-consistently from the ID fluid conservation relations and the electromagnetic wave equation. Due to ponderomotive profile steepening, the ablation pressure is reduced by 40% in the subsonic region and is dominated by the radiation pressure in the supersonic domain. Channel lengths are calculated for various intensities and pellet compression ratios. Likewise, the nonlinear propagation of a superintense electromagnetic wave in an underdense plasma channel is investigated for the ID case with the help of a relativistic fluid model.

Relativistic arbitrary-amplitude electrostatic solitons in a plasma.

A relativistic fluid model of a plasma in the case of a general polytropic process is considered. A "trajectory-boundary" method of analysis of electrostatic solitons is proposed as an alternative to the formalism of the Sagdeev pseudopotential, and is generalized to obtain an existence domain for compressive relativistic solitons in a two-component plasma.

Shear-free, irrotational, geodesic, anisotropic fluid cosmologies

General relativistic anisotropic fluid models whose fluid flow lines form a shear-free, irrotational, geodesic timelike congruence are examined. These models are of Petrov type D, and are assumed to have zero heat flux and an anisotropic stress tensor that possesses two distinct non-zero eigenvalues. Some general results concerning the form of the metric and the stress tensor for these models are established. Furthermore, if the energy density and the isotropic pressure, as measured by a co-moving observer, satisfy an equation of state of the form , with , then these spacetimes admit a foliation by spacelike hypersurfaces of constant Ricci scalar. In addition, models for which both the energy density and the anisotropic pressures only depend on time are investigated; both spatially homogeneous and spatially inhomogeneous models are found. A classification of these models is undertaken. Also, a particular class of anisotropic fluid models which are simple generalizations of the homogeneous isotropic cosmological models is studied.