Artigos de revistas: "Relativist plasma"

1

MELROSE, D. B., M. E. GEDALIN, M. P. KENNETT e C. S. FLETCHER. "Dispersion in an intrinsically relativistic, one-dimensional, strongly magnetized pair plasma". Journal of Plasma Physics 62, n.º 2 (agosto de 1999): 233–48. http://dx.doi.org/10.1017/s0022377899007795.

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The properties of a relativistic plasma dispersion function (RPDF) for an intrinsically extremely relativist, strongly magnetized, one-dimensional, electron–positron plasma are discussed in detail. For a plasma with a mean Lorentz factor 〈γ〉 [Gt ] 1 in its rest frame, the RPDF has a large peak >〈γ〉 at a phase speed a fraction of order 1/〈γ〉 below the speed of light, and the asymptotic value (infinite phase speed) is 〈γ−3〉 ∼ 1/〈γ〉. These features are not particularly sensitive to the choice of distribution function. The RPDF is used to discuss the properties of waves in such plasmas. Particular points discussed are the implications of the RPDF for the maximum frequency for parallel Langmuir waves, and for the reconnection between the Langmuir mode and the Alfvén mode.

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Shapakidze, David, e George Machabeli. "Plasma Theory of Two Synchrotron Knots’ formation Discovered in the Crab Nebula". International Astronomical Union Colloquium 177 (2000): 505–6. http://dx.doi.org/10.1017/s0252921100060425.

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AbstractThe plasma mechanism of synchrotron knots’ formation discovered in the Crab Nebula at the distances 0″.65 (1016cm) and 3″.8 (6 × 1016cm) from the Crab pulsar is presented. The mechanism is based on exitation of cyclotron and Cherenkov-drift instabilities in the relativist s electron-positron plasma of the nebula. The higher luminosity of the knots is supposed due to the orientation of the direction of motion of the synchrotron radiation sources (Larmor circles) relative to the observer.

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NAKASHIMA, Ken-ichi, e Thomas E. COWAN. "Relativistic Plasma Physics. Relativistic Electron-Positron Pair Plasmas." Journal of Plasma and Fusion Research 78, n.º 6 (2002): 568–74. http://dx.doi.org/10.1585/jspf.78.568.

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Siddique, M., M. Jamil, A. Rasheed, F. Areeb, Asif Javed e P. Sumera. "Impact of Relativistic Electron Beam on Hole Acoustic Instability in Quantum Semiconductor Plasmas". Zeitschrift für Naturforschung A 73, n.º 2 (26 de janeiro de 2018): 135–41. http://dx.doi.org/10.1515/zna-2017-0275.

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AbstractWe studied the influence of the classical relativistic beam of electrons on the hole acoustic wave (HAW) instability exciting in the semiconductor quantum plasmas. We conducted this study by using the quantum-hydrodynamic model of dense plasmas, incorporating the quantum effects of semiconductor plasma species which include degeneracy pressure, exchange-correlation potential and Bohm potential. Analysis of the quantum characteristics of semiconductor plasma species along with relativistic effect of beam electrons on the dispersion relation of the HAW is given in detail qualitatively and quantitatively by plotting them numerically. It is worth mentioning that the relativistic electron beam (REB) stabilises the HAWs exciting in semiconductor (GaAs) degenerate plasma.

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Chen, Hui, e Frederico Fiuza. "Perspectives on relativistic electron–positron pair plasma experiments of astrophysical relevance using high-power lasers". Physics of Plasmas 30, n.º 2 (fevereiro de 2023): 020601. http://dx.doi.org/10.1063/5.0134819.

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The study of relativistic electron–positron pair plasmas is both of fundamental physics interest and important to understand the processes that shape the magnetic field dynamics, particle acceleration, and radiation emission in high-energy astrophysical environments. Although it is highly desirable to study relativistic pair plasmas in the laboratory, their generation and control constitutes a critical challenge. Significant experimental and theoretical progress has been made over recent years to explore the use of intense lasers to produce dense relativistic pair plasma in the laboratory and study the basic collective plasma processes associated with these systems. Important challenges remain in terms of improving the number of pairs, system size, and control over the charge neutrality required to establish laboratory platforms that can expand our understanding of relativistic pair plasma and help validate underlying models in conditions relevant to high-energy astrophysical phenomena. We highlight recent progress in this field, discuss the main challenges, and the exciting prospects for studying relativistic pair plasmas and astrophysics relevant instabilities in the laboratory in the near future.

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BINGHAM, R., R. A. CAIRNS e J. T. MENDONÇA. "Particle acceleration in plasmas by perpendicularly propagating waves". Journal of Plasma Physics 64, n.º 4 (outubro de 2000): 481–87. http://dx.doi.org/10.1017/s0022377800008722.

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The acceleration of particles to high energy by relativistic plasma waves has received a great deal of attention lately. Most of the particle-acceleration schemes using relativistic plasma waves rely either on intense terawatt or petawatt lasers or on electron beams as the driver of the acceleration wave. These laboratory experiments have attained accelerating fields as high as 1 GeV cm−1 with the electrons being accelerated to about 100 MeV in millimetre distances. In space and astrophysical plasmas, relativistic plasma waves can also be important for acceleration. A process that is common to both laboratory and space plasmas is the surfatron concept, which operates as a wave acceleration mechanism in a magnetized plasma. In this paper, we present test-particle results for the surfatron process.

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BALIKHIN, M., e M. GEDALIN. "Generalization of the Harris current sheet model for non-relativistic, relativistic and pair plasmas". Journal of Plasma Physics 74, n.º 6 (dezembro de 2008): 749–63. http://dx.doi.org/10.1017/s002237780800723x.

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AbstractReconnection is believed to be responsible for plasma acceleration in a large number of space and astrophysical objects. Onset of reconnection is usually related to instabilities of current sheet equilibria. Analytical self-consistent models of an equilibrium current sheet (Harris equilibrium) are known for non-relativistic plasmas and some special cases of relativistic plasmas. We develop a description of generalized Harris equilibria in collisionless non-relativistic and relativistic plasmas. Possible shapes of the magnetic field are analyzed.

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Pietrini, P., e J. H. Krolik. "Do Fluid Waves Propagate in Mildly Relativistic Thermal Pair Plasmas?" Symposium - International Astronomical Union 159 (1994): 357. http://dx.doi.org/10.1017/s0074180900175552.

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Relativistic pair plasmas are implicated in the physics of the central regions of AGNs, and the observed variability of these sources can be related to the dynamics and changes in structure of these plasmas. To this respect a study of the behaviour of waves to which the pair plasma reacts as a fluid is quite relevant. We analyze the linear response to perturbations of a simple thermal mildly relativistic pair plasma system.

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9

CHAUDHARY, ROZINA, NODAR L. TSINTSADZE e P. K. SHUKLA. "Nonlinear propagation of intense electromagnetic waves in a hot electron–positron plasma". Journal of Plasma Physics 76, n.º 6 (17 de agosto de 2010): 875–86. http://dx.doi.org/10.1017/s0022377810000498.

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AbstractThe creation and annihilation of relativistically hot electron–positron (EP) pair plasmas in the presence of intense electromagnetic (EM) waves, which are not in thermal equilibrium, are studied by formulating a new plasma particle distribution functions, which are valid for both relativistic temperatures and relativistic amplitudes of the EM waves. It is found that intense EM waves in a collisionless EP plasma damp via nonlinear Landau damping. Accounting for the latter, we have obtained relativistic kinetic nonlinear Schrödinger equation (NLSE) with local and non-local nonlinearities. The NLSE depicts nonlinear Landau damping rates for intense EM waves. The damping rates are examined for dense and tenuous pair plasmas. Furthermore, we have studied the modulational instabilities of intense EM waves in the presence of nonlinear Landau damping. Our results reveal a new class of the modulational instability that is triggered by the inverse Landau damping in a relativistically hot EP plasma. Finally, we discuss localization of intense EM waves due to relativistic electron and positron mass increase in a hot pair plasma.

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10

MELROSE, D. B. "Generalized Trubnikov functions for unmagnetized plasmas". Journal of Plasma Physics 62, n.º 2 (agosto de 1999): 249–53. http://dx.doi.org/10.1017/s0022377899007898.

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A class of relativistic dispersion functions for unmagnetized thermal plasmas is defined by generalizing functions first defined by Trubnikov in 1958. Recursion relations are derived that allow one to generate explicit expressions for the class of functions in terms of the relativistic plasma dispersion function T(z, ρ) introduced by Godfrey et al. in 1975. These functions are relevant to the description of the response of a weakly mangetized, highly relativistic, thermal plasma.

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11

GARIEL, J., e Ph de GOTTAL. "TEST-PARTICLE MOTION IN A CLASSICAL RELATIVISTIC PLASMA". International Journal of Modern Physics D 03, n.º 01 (março de 1994): 187–90. http://dx.doi.org/10.1142/s0218271894000253.

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Starting from the covariant relativistic Balescu-Lenard (or Klinontovich-Silin) equation we derive a classical relativistic Fokker-Plank equation for a test-particle in a stable isotropic plasma with collective effects. The geometrical form of the diffusion tensor and friction 4-vector is given, and their behaviour is analyzed for various dynamical conditions: non relativistic and ultrarelativistic plasma. A H-theorem is proven. The main feature of the collective effects is that longitudinal oscillations of plasma appear, whereas transversal ones (Cerenkov effect) do not. A limit value of the critical velocity of the test-particle from which the plasm oscillations appear is found.

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Singh, Kuldeep, Amar Kakad, Bharati Kakad e Nareshpal Singh Saini. "Evolution of ion acoustic solitary waves in pulsar wind". Monthly Notices of the Royal Astronomical Society 500, n.º 2 (30 de outubro de 2020): 1612–20. http://dx.doi.org/10.1093/mnras/staa3379.

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ABSTRACT We have studied the evolution of ion acoustic solitary waves (IASWs) in pulsar wind. The pulsar wind is modelled by considering a weakly relativistic unmagnetized collisionless plasma comprised of relativistic ions and superthermal electrons and positrons. Through fluid simulations, we have demonstrated that the localized ion density perturbations generated in the polar wind plasma can evolve the relativistic IASW pulses. It is found that the concentration of positrons, relativistic factor, superthermality of electrons, and positrons have a significant influence on the dynamical evolution of IASW pulses. Our results may provide insight to understand the evolution of IASW pulses and their role in astrophysical plasmas, especially in the relativistic pulsar winds with supernova outflow, which is responsible for the production of superthermal particles and relativistic ions.

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13

Orefice, A. "Relativistic theory of absorption and emission of electron cyclotron waves in anisotropic plasmas". Journal of Plasma Physics 39, n.º 1 (fevereiro de 1988): 61–70. http://dx.doi.org/10.1017/s002237780001285x.

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The weakly relativistic theory of absorption and emission of electron cyclotron waves in hot magnetized plasmas is developed for a large class of anisotropic electron distribution functions. The results are expressed in terms of the weakly relativistic plasma dispersion functions, and therefore of the well-known plasma Z-function. The particular case of a loss-cone electron distribution function is presented as a simple example.

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14

STOCKEM, A., M. LAZAR, P. K. SHUKLA e A. SMOLYAKOV. "A comparative study of the filamentation and Weibel instabilities and their cumulative effect. II. Weakly relativistic beams". Journal of Plasma Physics 75, n.º 4 (agosto de 2009): 529–43. http://dx.doi.org/10.1017/s002237780800768x.

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AbstractCounterstreaming plasma systems with intrinsic temperature anisotropies are unstable against the excitation of Weibel-type instabilities, namely, filamentation and Weibel instabilities, and their cumulative effect. Here, the analysis is extended to counterstreaming plasmas with weakly relativistic bulk velocities, while the thermal velocities are still considered to be non-relativistic. Such plasma systems are relevant for fusion plasma experiments and the more violent astrophysical phenomena, such as jets in gamma-ray burst sources. Simple analytical forms of the dispersion relations are derived in the limit of a small transverse temperature or a large temperature anisotropy of the beams. The aperiodic growing solutions are plotted systematically for the representative cases chosen in Paper I (Lazar et al. 2009 J. Plasma Phys. 75, in press). In the limit of slow non-relativistic plasma flows, the numerical solutions fit well with those obtained in Paper I, but for weakly relativistic streams an important deviation is found.

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MENDONÇA, J. T., K. HIZANIDIS, D. J. FRANTZESKAKIS, L. OLIVEIRA e SILVA e J. L. VOMVORIDIS. "Covariant formulation of photon acceleration". Journal of Plasma Physics 58, n.º 4 (dezembro de 1997): 647–54. http://dx.doi.org/10.1017/s0022377897006168.

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We present a covariant theory of photon acceleration in time-varying plasmas. This is a ray-tracing model for frequency upshift of waves interacting with relativistic plasma perturbations, such as ionization fronts and plasma wakefields. This theory explores the formal analogy between a photon in a plasma and a relativistic particle with a finite rest mass. The covariant ray-tracing theory is applied to the case of photon acceleration by a modulated wakefield. Threshold criteria for transition to chaos are derived.

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CAO, LIHUA, TIEQIANG CHANG, WENWEI CHANG e ZONGWU YUE. "Relativistic electron heating in laser-produced plasmas". Journal of Plasma Physics 65, n.º 5 (junho de 2001): 353–63. http://dx.doi.org/10.1017/s0022377801001131.

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Two-dimensional multi-timescale fully electromagnetic relativistic particle simulation is used to investigate relativistic electron heating in laser-produced plasmas. When laser pulses with peak intensities 1019 W cm−2 and different durations (e.g. 118 fs and 442 fs) are incident on overdense plasma slabs with step-like density profiles, the dynamics of plasmas and Fourier frequency spectra from our particle simulations demonstrate distinctly different properties in hot-electron temperatures, absorption, relativistic electron heating, and so on. The particular motions of the critical surfaces are discussed. From the two examples simulated in this paper, it is concluded that the interactions between plasmas and laser pulses with the same intensities and different durations are dominated by different mechanisms, which can lead to dissimilar dynamics of plasmas, relativistic heating, and so on.

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17

Li, Han-Lin, Zhang-Hu Hu, Quan-Tang Zhao, Rui Cheng, Yong-Tao Zhao, Zi-Min Zhang, Xue-Chun Li e You-Nian Wang. "Simulation study of coupled two-stream and current filamentation instability excited by accelerator electron beams in plasmas". Physics of Plasmas 29, n.º 5 (maio de 2022): 052101. http://dx.doi.org/10.1063/5.0086500.

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A gas-discharge plasma device is simulated with COMSOL software, and the obtained plasma density profile is input into a two-dimensional particle-in-cell code, in which the transport of relativistic electron beams in the plasma with an actual density profile is investigated. The results show that the device can produce a wide range of high-density plasmas with the maximum density approaching [Formula: see text] m−3. With the relativistic electron beams produced from a linear electron accelerator, the gas-discharge plasma is shown to be an ideal medium for the investigation of coupled two-stream and current filamentation instability.

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18

WILLI, O., D. H. CAMPBELL, A. SCHIAVI, M. BORGHESI, M. GALIMBERTI, L. A. GIZZI, W. NAZAROV, A. J. MacKINNON, A. PUKHOV e J. MEYER-TER-VEHN. "Relativistic laser propagation through underdense and overdense plasmas". Laser and Particle Beams 19, n.º 1 (janeiro de 2001): 5–13. http://dx.doi.org/10.1017/s0263034601191019.

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Detailed investigations of the propagation of an ultraintense picosecond laser pulse through preformed plasmas have been carried out. An underdense plasma with peak density around 0.1nc was generated by exploding a thin foil target with an intense nanosecond laser pulse. The formation of plasma channels with an ultraintense laser pulse due to ponderomotive expulsion of elections and the subsequent Coulomb explosion were investigated. The laser transmission through underdense plasmas was measured for a picosecond pulse at intensities above 1019 W/cm2 with and without a plasma channel preformed with an ultraintense prepulse. The energy transmitted through the plasma increased from the few percent transmittance measured in absence of the preformed channel to almost 100% transmission with the channelling to main pulse delay at around 100 ps. The propagation of a relativistic laser pulse through overdense plasmas was also investigated. A well-characterized plasma with an electron density up to 8nc was generated by soft X-ray irradiation of a low-density foam target. The propagation of the laser pulse was observed via X-ray imaging and monitoring the energy transmission through the plasma. Evidence of collimated laser transport was obtained.

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19

Heidari, E. "Relativistic Laser-Plasma Interactions. Moving Solitary Waves in Plasma Channels and the Kinetic Dispersion Relation of Cherenkov Radiation". Ukrainian Journal of Physics 62, n.º 12 (dezembro de 2017): 1017–23. http://dx.doi.org/10.15407/ujpe62.12.1017.

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Hoshino, Masahiro. "Efficiency of nonthermal particle acceleration in magnetic reconnection". Physics of Plasmas 29, n.º 4 (abril de 2022): 042902. http://dx.doi.org/10.1063/5.0086316.

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The nonthermal particle acceleration during magnetic reconnection remains a fundamental topic in several astrophysical phenomena, such as solar flares, pulsar wind, and magnetars, for more than half a century, and one of the unresolved questions is its efficiency. Recently, nonthermal particle acceleration mechanisms during reconnection have been extensively studied by particle-in-cell simulations, yet it is an intriguing enigma as to how the magnetic field energy is divided into thermally heated plasmas and nonthermal particles. Here, we study both non-relativistic and relativistic magnetic reconnections using large-scale particle-in-cell simulation for a pair plasma and indicate that the production of the nonthermal particle becomes efficient with increasing the plasma temperature. In the relativistic hot plasma case, we determine that the heated plasmas by reconnection can be approximated by a kappa distribution function with the kappa index of approximately 3 or less (equivalent to 2 or less for the power-law index), and the nonthermal energy density of reconnection is approximately over [Formula: see text] of the total internal energy in the downstream exhaust.

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Treumann, R. A., R. Nakamura e W. Baumjohann. "Relativistic transformation of phase-space distributions". Annales Geophysicae 29, n.º 7 (19 de julho de 2011): 1259–65. http://dx.doi.org/10.5194/angeo-29-1259-2011.

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Abstract. We investigate the transformation of the distribution function in the relativistic case, a problem of interest in plasma when particles with high (relativistic) velocities come into play as for instance in radiation belt physics, in the electron-cyclotron maser radiation theory, in the vicinity of high-Mach number shocks where particles are accelerated to high speeds, and generally in solar and astrophysical plasmas. We show that the phase-space volume element is a Lorentz constant and construct the general particle distribution function from first principles. Application to thermal equilibrium lets us derive a modified version of the isotropic relativistic thermal distribution, the modified Jüttner distribution corrected for the Lorentz-invariant phase-space volume element. Finally, we discuss the relativistic modification of a number of plasma parameters.

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Mukhopadhyay, J., G. Pakira e A. Roy Chowdhury. "Nonlinear Wave Number Shift and Modulational Instability for Large Amplitude Waves in a Relativistic Magnetised Plasma". Australian Journal of Physics 45, n.º 6 (1992): 761. http://dx.doi.org/10.1071/ph920761.

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Properties of large amplitude waves in a relativistic magnetised plasma are studied using the method of reductive perturbation. The plasma under consideration consists of warm adiabatic ions and isothermal warm electrons, under the influence of a magnetic field. A onsideration of large amplitude waves demands study of the relativistic situation. In the present case we consider both the electrons and ions to be relativistic. A KdV equation is derived from which a nonlinear Schrodinger equation is deduced by further scaling. Lastly we derive an expression for nonlinear wave number shift, critical angle of propagation and the condition for modulational instability. Our analysis is applicable to both laboratory and space plasmas.

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Bacchini, Fabio. "RelSIM: A Relativistic Semi-implicit Method for Particle-in-cell Simulations". Astrophysical Journal Supplement Series 268, n.º 2 (1 de outubro de 2023): 60. http://dx.doi.org/10.3847/1538-4365/acefba.

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Abstract We present a novel Relativistic Semi-Implicit Method (RelSIM) for particle-in-cell (PIC) simulations of astrophysical plasmas, implemented in a code framework ready for production runs. While explicit PIC methods have gained widespread recognition in the astrophysical community as a reliable tool to simulate plasma phenomena, implicit methods have been seldom explored. This is partly due to the lack of a reliable relativistic implicit PIC formulation that is applicable to state-of-the-art simulations. We propose the RelSIM to fill this gap: our new method is relatively simple, being free of nonlinear iterations and only requiring a global linear solve of the field equations. With a set of one- and two-dimensional tests, we demonstrate that the RelSIM produces more accurate results with much smaller numerical errors in the total energy than standard explicit PIC, in particular when characteristic plasma scales (skin depth and plasma frequency) are heavily underresolved on the numerical grid. By construction, the RelSIM also performs much better than the relativistic implicit-moment method, originally proposed for semi-implicit PIC simulations in the relativistic regime. Our results are promising to conduct large-scale (in terms of duration and domain size) PIC simulations of astrophysical plasmas, potentially reaching physical regimes inaccessible by standard explicit PIC codes.

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HAAS, F. "Wave dispersion derived from the square-root Klein–Gordon–Poisson system". Journal of Plasma Physics 79, n.º 4 (7 de fevereiro de 2013): 371–76. http://dx.doi.org/10.1017/s0022377813000044.

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AbstractRecently, there has been great interest around quantum relativistic models for plasmas. In particular, striking advances have been obtained by means of the Klein–Gordon–Maxwell system, which provides a first-order approach to the relativistic regimes of quantum plasmas. The Klein–Gordon–Maxwell system provides a reliable model as long as the plasma spin dynamics is not a fundamental aspect, to be addressed using more refined (and heavier) models involving the Pauli–Schrödinger or Dirac equations. In this work, a further simplification is considered, tracing back to the early days of relativistic quantum theory. Namely, we revisit the square-root Klein–Gordon–Poisson system, where the positive branch of the relativistic energy–momentum relation is mapped to a quantum wave equation. The associated linear wave propagation is analyzed and compared with the results in the literature. We determine physical parameters where the simultaneous quantum and relativistic effects can be noticeable in weakly coupled electrostatic plasmas.

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Sadiq, Safeer, S. Mahmood e Q. Haque. "Nonlinear electron plasma waves in fully relativistic plasmas". Physica Scripta 95, n.º 10 (6 de outubro de 2020): 105608. http://dx.doi.org/10.1088/1402-4896/abbaf1.

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BINGHAM, R., L. O. SILVA, J. T. MENDONCA, P. K. SHUKLA, W. B. MORI e A. SERBETO. "PLASMA WAKES DRIVEN BY NEUTRINOS, PHOTONS AND ELECTRON BEAMS". International Journal of Modern Physics B 21, n.º 03n04 (10 de fevereiro de 2007): 343–50. http://dx.doi.org/10.1142/s0217979207042112.

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There is considerable interest in the propagation dynamics of intense electron and photon neutrino beams in a background dispersive medium such as dense plasmas, particularly in the search for a mechanism to explain the dynamics of type II supernovae. Neutrino interactions with matter are usually considered as single particle interactions. All the single particle mechanisms describing the dynamical properties of neutrino's in matter are analogous with the processes involving single electron interactions with a medium such as Compton scattering, and Cerenkov radiation etc. However, it is well known that beams of electrons moving through a plasma give rise to a new class of processes known as collective interactions such as two stream instabilities which result in either the absorption or generation of plasma waves. Intense photon beams also drive collective interactions such as modulational type instabilities. In both cases relativistic electron beams of electrons and photon beams can drive plasma wakefields in plasmas. Employing the relativistic kinetic equations for neutrinos interacting with dense plasmas via the weak force we explore collective plasma streaming instabilities driven by Neutrino electron and photon beams and demonstrate that all three types of particles can drive wakefields.

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Oks, Eugene. "Review of recent advances in the analytical theory of Stark broadening of spectral lines in plasmas: applications to laboratory discharges and astrophysical plasmas". Journal of Physics: Conference Series 2439, n.º 1 (1 de janeiro de 2023): 012009. http://dx.doi.org/10.1088/1742-6596/2439/1/012009.

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Abstract We present an overview of latest advances in the analytical theory of Stark broadening of spectral lines and their applications to various types of laboratory and astrophysical plasmas. They include: 1) in-depth study of intra-Stark spectroscopy in the x-ray range in relativistic laser-plasma interactions; 2) effect of diamagnetism on the number of observable hydrogen lines in plasmas; 3) influence of magnetic-field-caused modifications of trajectories of plasma electrons on the width of hydrogen/deuterium spectral lines: applications to white dwarfs; 4) Stark broadening of hydrogen/deuterium spectral lines by a relativistic electron beam: analytical results and applications to magnetic fusion; 5) counterintuitive dependence of the dynamical Stark width of hydrogenic spectral lines on the electron density.

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Romansky, V. I., A. M. Bykov e S. M. Osipov. "On electron acceleration by mildly-relativistic shocks: PIC simulations". Journal of Physics: Conference Series 2103, n.º 1 (1 de novembro de 2021): 012009. http://dx.doi.org/10.1088/1742-6596/2103/1/012009.

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Abstract Radio observations revealed a presence of relativistic supernovae - a class of objects intermediate between the regular supernovae and gamma-ray bursts. The typical Lorentz-factors of plasma flows in relativistic radio-bright supernovae were estimated to be about 1.5. Mildly relativistic shocks in electron-ion plasmas are known to efficiently accelerate radio-emitting electrons if the shock is subluminous. The inclination angle of the velocity of subluminous shock to the ambient magnetic field should be below a critical angle which depends on the Mach number and the plasma magnetization parameter. In this paper we present particle-in-cell modeling of electron acceleration by mildly-relativistic collisionless shock of different obliquity in a plasma with ratio of the magnetic energy to the bulk kinetic energy σ ≈ 0.004 which is of interest for the relativistic supernovae modeling. It was shown earlier that a development of the ion scale Bell-type instability in electron-ion relativistic shock may have a strong influence on the electron injection and acceleration. In the time period of about 1500 ω p i − 1 (ωpi is the ion plasma frequency) after the shock initialization the magnetic field fluctuations generated by Bell’s instability may significantly decreases number of accelerated electrons even in a sub-luminous shock. We study here the evolution of the electron spectra of subluminous shocks of different obliquity. This is important to for modeling of synchrothron spectra from relativistic supernovae.

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Kuramitsu, Yasuhiro, Yosuke Matsumoto e Takanobu Amano. "Nonlinear evolution of the Weibel instability with relativistic laser pulses". Physics of Plasmas 30, n.º 3 (março de 2023): 032109. http://dx.doi.org/10.1063/5.0138855.

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The Weibel instability is investigated using relativistic intense short laser pulses. A relativistic short laser pulse can generate a sub-relativistic high-density collisionless plasma. By irradiating double parallel planar targets with two relativistic laser pulses, sub-relativistic collisionless counterstreaming plasmas are created. Since the growth rate of the Weibel instability is proportional to the plasma density and velocity, the spatial and temporal scales of the Weibel instability can be much smaller than that from nanosecond large laser facilities. Recent theoretical and numerical studies have revealed that astrophysical collisionless shocks in sub-relativistic regimes in the absence and presence of an ambient magnetic field play essential roles in cosmic ray acceleration. With experimental verification in mind, we discuss the possible experimental models on the Weibel instability with intense short laser pulses. In order to show the experimental feasibility, we perform 2D particle-in-cell simulations in the absence of an external magnetic field as the first step and discuss the optimum conditions to realize the nonlinear evolutions of the Weibel instability in laboratories.

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LIU, SAN-QIU, e XIAO-CHANG CHEN. "Dispersion relation of transverse oscillation in relativistic plasmas with non-extensive distribution". Journal of Plasma Physics 77, n.º 5 (15 de fevereiro de 2011): 653–62. http://dx.doi.org/10.1017/s0022377811000043.

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AbstractThe generalized dispersion equation for superluminal transverse oscillation in an unmagnetized, collisionless, isotropic and relativistic plasma with non-extensive q-distribution is derived. The analytical dispersion relation is obtained in an ultra-relativistic regime, which is related to q-parameter and temperature. In the limit q → 1, the result based on the relativistic Maxwellian distribution is recovered. Using the numerical method, we obtain the full dispersion curve that cannot be given by an analytic method. It is shown that the numerical solution is in good agreement with the analytical result in the long-wavelength and short-wavelength region for ultra-relativistic plasmas.

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Robinson, P. A. "Electron cyclotron waves: dispersion and accessibility conditions in isotropic and anisotropic plasmas". Journal of Plasma Physics 35, n.º 2 (abril de 1986): 187–207. http://dx.doi.org/10.1017/s0022377800011272.

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Dispersion and accessibility conditions for electron cyclotron waves are investigated for arbitrary weakly relativistic plasmas and for specific isotropic and loss-cone distributions. The transition between the cold plasma and vacuum dispersion relations is investigated as a function of temperature and density. The behaviour of mode structure (including mode coupling), cut-offs and resonances are also examined. Generalizations are obtained of earlier results which indicate that access by extraordinary waves to regions nearthe cyclotron layer from the low-field side is easier in weakly relativistic plasmas than predicted by cold plasma theory because of a reduction in the cut-off frequency of the fast extraordinary mode. This effect is found to be more pronounced in loss-cone distributions than in isotropic distributions, permitting access at temperatures considerably lower than those predicted in the isotropic case. Extra loss-cone modes are found to appear near the cyclotron frequency in loss-cone plasmas which also exhibit instabilities near the cyclotron harmonics.

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32

Nunotani, Keiichiro, e Zensho Yoshida. "Clebsch representation of relativistic plasma and generalized enstrophy". Physics of Plasmas 29, n.º 5 (maio de 2022): 052905. http://dx.doi.org/10.1063/5.0084281.

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The theory of relativistic plasmas is attracting interest as a model of high-energy astronomical objects. The topological constraints, built in the governing equations, play an essential role in characterizing the structures of plasmas. Among various invariants of ideal models, the circulation is one of the most fundamental quantities, being included in other invariants like the helicity. The conventional enstrophy, known to be constant in a two-dimensional flow, can be generalized, by invoking Clebsch variables, to the topological charge of a three-dimensional fluid element, which essentially measures circulations. Since the relativistic effect imparts space-time coupling into the metric, such invariants must be modified. The non-relativistic generalized enstrophy is no longer conserved in a relativistic plasma, implying that the conservation of circulation is violated. In this work, we extend the generalized enstrophy to a Lorentz covariant form. We formulate the Clebsch representation in relativity using the principle of least action and derive a relativistically modified generalized enstrophy that is conserved in the relativistic model.

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33

Hamilton, Russell J., Frederick K. Lamb e M. Coleman Miller. "Disk-Accreting Magnetic Neutron Stars as High-Energy Particle Accelerators". International Astronomical Union Colloquium 142 (1994): 837–39. http://dx.doi.org/10.1017/s0252921100078180.

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AbstractInteraction of an accretion disk with the magnetic field of a neutron star produces large electromotive forces, which drive large conduction currents in the disk-magnetosphere-star circuit. Here we argue that such large conduction currents will cause microscopic and macroscopic instabilities in the magnetosphere. If the minimum plasma density in the magnetosphere is relatively low (≲109 cm−3 ), current-driven micro-instabilities may cause relativistic double layers to form, producing voltage differences in excess of 1012 V and accelerating charged particles to very high energies. If instead the plasma density is higher (≳ 109 cm−3 ), twisting of the stellar magnetic field is likely to cause magnetic field reconnection. This reconnection will be relativistic, accelerating plasma in the magnetosphere to relativistic speeds and a small fraction of particles to very high energies. Interaction of these high-energy particles with X-rays, γ-rays, and accreting plasma may produce detectable high-energy radiation.Subject headings: acceleration of particles — accretion, accretion disks — gamma rays: theory — plasmas — radiation mechanisms: nonthermal — stars: neutron

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34

Zhang, Chaojie, Yipeng Wu, Mitchell Sinclair, Audrey Farrell, Kenneth A. Marsh, Jianfei Hua, Irina Petrushina et al. "Electron Weibel instability induced magnetic fields in optical-field ionized plasmas". Physics of Plasmas 29, n.º 6 (junho de 2022): 062102. http://dx.doi.org/10.1063/5.0089814.

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Generation and amplification of magnetic fields in plasmas is a long-standing topic that is of great interest to both plasma and space physics. The electron Weibel instability is a well-known mechanism responsible for self-generating magnetic fields in plasmas with temperature anisotropy and has been extensively investigated in both theory and simulations, yet experimental verification of this instability has been challenging. Recently, we demonstrated a new experimental platform that enables controlled initialization of highly nonthermal and/or anisotropic plasma electron velocity distributions via optical-field ionization. Using an external electron probe bunch from a linear accelerator, the onset, saturation, and decay of the self-generated magnetic fields due to electron Weibel instability were measured for the first time to our knowledge. In this paper, we will first present experimental results on time-resolved measurements of the Weibel magnetic fields in non-relativistic plasmas produced by Ti:Sapphire laser pulses (0.8 μm) and then discuss the feasibility of extending the study to a quasi-relativistic regime by using intense CO2 (e.g., 9.2 μm) lasers to produce much hotter plasmas.

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35

Zhang, Chaojie, Yipeng Wu, Mitchell Sinclair, Audrey Farrell, Kenneth A. Marsh, Jianfei Hua, Irina Petrushina et al. "Electron Weibel instability induced magnetic fields in optical-field ionized plasmas". Physics of Plasmas 29, n.º 6 (junho de 2022): 062102. http://dx.doi.org/10.1063/5.0089814.

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Generation and amplification of magnetic fields in plasmas is a long-standing topic that is of great interest to both plasma and space physics. The electron Weibel instability is a well-known mechanism responsible for self-generating magnetic fields in plasmas with temperature anisotropy and has been extensively investigated in both theory and simulations, yet experimental verification of this instability has been challenging. Recently, we demonstrated a new experimental platform that enables controlled initialization of highly nonthermal and/or anisotropic plasma electron velocity distributions via optical-field ionization. Using an external electron probe bunch from a linear accelerator, the onset, saturation, and decay of the self-generated magnetic fields due to electron Weibel instability were measured for the first time to our knowledge. In this paper, we will first present experimental results on time-resolved measurements of the Weibel magnetic fields in non-relativistic plasmas produced by Ti:Sapphire laser pulses (0.8 μm) and then discuss the feasibility of extending the study to a quasi-relativistic regime by using intense CO2 (e.g., 9.2 μm) lasers to produce much hotter plasmas.

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36

Takahashi, M. "Accreting Plasmas in Black Hole Magnetospheres". Symposium - International Astronomical Union 195 (2000): 233–40. http://dx.doi.org/10.1017/s0074180900162977.

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We present a fully relativistic study on the standing shock formation for magnetohydrodynamical plasmas in a stationary and axisymmetric black hole magnetosphere. We express all the postshock physical quantities in terms of the relativistic compression ratio. Then, the downstream state of a shocked plasma is determined by the upstream state of the accretion. We also discuss the dragging-effects of the rotating black hole on the shock conditions.

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37

Mościbrodzka, M. "Linear and circular polarization of a 1D relativistic jet model". Astronomy & Astrophysics 623 (março de 2019): A152. http://dx.doi.org/10.1051/0004-6361/201834503.

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Context. Polarimetric observations of black holes allow us to probe structures of magnetic fields and plasmas in strong gravity. Aims. We present a study of the polarimetric properties of a synchrotron spectrum emitted from a relativistic jet using a low-dimensional model. Methods. A novel numerical scheme is used to integrate relativistic polarized radiative transfer equations in a slab geometry where the plasma conditions change along the integration path. Results. We find that the simple model of a non-uniform jet can recover basic observational characteristics of some astrophysical sources with a relativistic jet, such as extremely high rotation measures. Our models incorporate a time-dependent component. A small fluctuation in density or temperature of the plasma along the jet produces significant amounts of fluctuations not only in the fractional linear and circular polarizations, but also in the jet internal rotation measures. Conclusions. The low-dimensional models presented here are developed within the same computational framework as the complex three-dimensional general relativistic magnetohydrodynamics simulations of black hole disks and jets, and they offer guidance when interpreting the results from more complex polarization models. The models presented here are scalable to stationary and transient polarized radio emissions produced by relativistic plasma ejected from around compact objects, in both stellar-mass and supermassive black hole systems.

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38

Paul, S. N., B. Chakraborty e L. Debnath. "Study of nonlinear wave processes in plasmas using the formalism of a special Lorntz transformation for a space-independent fram". International Journal of Mathematics and Mathematical Sciences 8, n.º 3 (1985): 599–614. http://dx.doi.org/10.1155/s0161171285000655.

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A study is made of nonlinear waves in plasmas using the formalism of a special Lorentz transformation for a space-independent frame,S′. This special transformation is used to transform the space-time dependent equations in a cold, relativistic, magnetized plasma to theS′frame. Then the transformed equations are employed to derive the expressions for the Lagrangian and the Hamiltonian in theS′frame. The Lagrengian and the Hamiltonian for a strong circularly polarized laser beam have also been obtained in theS′frame. The exact form of the nonlinear dispersion relation is derived for circularly polarized waves. Then the results for the frequency and the wave number shifts of these waves in a cold, magnetized relativistic plasma are obtained with some Discussion on the nature of the frequency shifts. Finally, numerical results are presented for the radiation of Nd-glass laser in dense plasmas.

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39

Jha, Alok Kumar Singh, Mayank Dimri, Dishu Dawra e Man Mohan. "A Study of the Atomic Processes of Highly Charged Ions Embedded in Dense Plasma". Atoms 11, n.º 12 (15 de dezembro de 2023): 158. http://dx.doi.org/10.3390/atoms11120158.

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The study of atomic spectroscopy and collision processes in a dense plasma environment has gained a considerable interest in the past few years due to its several applications in various branches of physics. The multiconfiguration Dirac-Fock (MCDF) method and relativistic configuration interaction (RCI) technique incorporating the uniform electron gas model (UEGM) and analytical plasma screening (APS) potentials have been employed for characterizing the interactions among the charged particles in plasma. The bound and continuum state wavefunctions are determined using the aforementioned potentials within a relativistic Dirac-Coulomb atomic structure framework. The present approach is applied for the calculation of electronic structures, radiative properties, electron impact excitation cross sections and photoionization cross sections of many electron systems confined in a plasma environment. The present study not only extends our knowledge of the plasma-screening effect but also opens the door for the modelling and diagnostics of astrophysical and laboratory plasmas.

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40

LONTANO, M., M. BORGHESI, S. V. BULANOV, T. Z. ESIRKEPOV, D. FARINA, N. NAUMOVA, K. NISHIHARA et al. "Nondrifting relativistic electromagnetic solitons in plasmas". Laser and Particle Beams 21, n.º 4 (outubro de 2003): 541–44. http://dx.doi.org/10.1017/s0263034603214105.

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Low-frequency, relativistic, subcycle solitary waves are found in two-dimensional and three-dimensional particle-in-cell (PIC) numerical simulations, as a result of the interaction of ultrashort, high-intensity laser pulses with plasmas. Moreover, nondrifting, subcycle relativistic electromagnetic solitons have been obtained as solutions of the hydrodynamic equations for an electron–ion warm plasma, by assuming the quasi-neutrality character of the plasma response. In addition, the formation of long-living macroscopic soliton-like structures has been experimentally observed by means of the proton imaging diagnostics. Several common features result from these investigations, as, for example, the quasi-neutral plasma response to the soliton radiation, in the long-term evolution of the system, which leads to the almost complete expulsion of the plasma from the region where the electromagnetic radiation is concentrated, even at subrelativistic field intensity. The results of the theoretical investigations are reviewed with special attention to these similarities.

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41

Mace, R. L. "A dielectric tensor for a uniform magnetoplasma with a generalized Lorentzian distribution". Journal of Plasma Physics 55, n.º 3 (junho de 1996): 415–29. http://dx.doi.org/10.1017/s0022377800018961.

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It is demonstrated that the dielectric tensor for a non-relativistic magnetized plasma whose particle velocity distributions can be modelled by isotropic kappa, or generalized Lorentzian, distributions admits an expression similar to that obtained by Trubnikov for a relativistic plasma. The kappa distribution is a useful distribution for modelling space plasmas containing significant numbers of superthermal particles, i.e. those that have energies in excess of the thermal energy. The dielectric tensor is valid for arbitrary wavevectors, and is shown to reproduce the known limiting case of wave propagation parallel to the magnetic field. Even in this limiting case, the results obtained represent a generalization of previous results to arbitrary real values of the index K, the parameter that shapes the superthermal tail on the distribution. The expression for the dielectric tensor might be useful as a starting point for numerical studies of waves and instabilities in plasmas containing superthermal particles.

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42

Korzhimanov, Artem V. "Generation of Cold Magnetized Relativistic Plasmas at the Rear of Thin Foils Irradiated by Ultra-High-Intensity Laser Pulses". Applied Sciences 11, n.º 24 (16 de dezembro de 2021): 11966. http://dx.doi.org/10.3390/app112411966.

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A scheme to generate magnetized relativistic plasmas in a laboratory setting is proposed. It is based on the interaction of ultra-high-intensity sub-picosecond laser pulses with few-micron-thick foils or films. By means of Particle-In-Cell simulations, it is shown that energetic electrons produced by the laser and evacuated at the rear of the target trigger an expansion of the target, building up a strong azimuthal magnetic field. It is shown that in the expanding plasma sheath, a ratio of the magnetic pressure and the electron rest-mass energy density exceeds unity, whereas the plasma pressure is lower than the magnetic pressure and the electron gyroradius is lower than the plasma dimension. This scheme can be utilized to study astrophysical extreme phenomena such as relativistic magnetic reconnection in laboratory.

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43

Shukla, P. K., e L. Stenflo. "Nonlinear Propagation of Pulsar Radiation". International Astronomical Union Colloquium 160 (1996): 171–74. http://dx.doi.org/10.1017/s0252921100041361.

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AbstractThe nonlinear propagation of pulsar radiation in an electronpositron plasma is considered. Accounting for the pulsar radiation ponderomotive force, the relativistic mass variation, and the plasma magnetization, we obtain a pair of nonlinear equations which exhibit coupling of pulsar radiation with the background plasma slow motions in magnetized plasmas. The modulational/filamentation instability as well as the localization of pulsar radiation are investigated. We conclude that our investigation is relevant to the microstructures in the pulsar magnetosphere.

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44

Saberian, E., A. Esfandyari-Kalejahi e M. Akbari-Moghanjoughi. "Propagation of ion-acoustic solitary waves in a relativistic electron-positron-ion plasma". Canadian Journal of Physics 89, n.º 3 (março de 2011): 299–309. http://dx.doi.org/10.1139/p11-024.

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The propagation of large amplitude ion-acoustic solitary waves (IASWs) in a fully relativistic plasma consisting of cold ions and ultra-relativistic hot electrons and positrons is investigated using the Sagdeev pseudopotential method in a relativistic hydrodynamics model. The effects of streaming speed of the plasma fluid, thermal energy, positron density, and positron temperature on large amplitude IASWs are studied by analysis of the pseudopotential structure. It is found that in regions in which the streaming speed of the plasma fluid is larger than that of the solitary wave, by increasing the streaming speed of the plasma fluid, the depth and width of the potential well increase, resulting in narrower solitons with larger amplitude. This behavior is opposite to the case where the streaming speed of the plasma fluid is less than that of the solitary wave. On the other hand, an increase in the thermal energy results in wider solitons with smaller amplitude, because the depth and width of the potential well decrease in that case. Additionally, the maximum soliton amplitude increases and the width becomes narrower as a result of an increase in positron density. It is shown that varying the positron temperature does not have a considerable effect on the width and amplitude of IASWs. The existence of stationary soliton-like arbitary amplitude waves is also predicted in fully relativistic electron-positron-ion (EPI) plasmas. The effects of streaming speed of the plasma fluid, thermal energy, positron density, and positron temperature on these kinds of solitons are the same for large amplitude IASWs.

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45

Sen, Sonu, Meenu Asthana Varshney e Dinesh Varshney. "Relativistic Propagation of Linearly/Circularly Polarized Laser Radiation in Plasmas". ISRN Optics 2013 (2 de setembro de 2013): 1–8. http://dx.doi.org/10.1155/2013/642617.

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Paraxial theory of relativistic self-focusing of Gaussian laser beams in plasmas for arbitrary magnitude of intensity of the beam has been presented in this paper. The nonlinearity in the dielectric constant arises on account of relativistic variation of mass. An appropriate expression for the nonlinear dielectric constant has been used to study laser beam propagation for linearly/circularly polarized wave. The variation of beamwidth parameter with distance of propagation, self-trapping condition, and critical power has been evaluated. The saturating nature of nonlinearity yields two values of critical power of the beam ( and ) for self-focusing. When the beam diverges. When the beam first converges then diverges and so on. When the beam first diverges and then converges and so on. Numerical estimates are made for linearly/circularly polarized wave applicable for typical values of relativistic laser-plasma interaction process in underdense and overdense plasmas. Since the relativistic mechanism is instantaneous, this theory is applicable to understanding of self-focusing of laser pulses.

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Ivanov, A. Yu, P. A. Andreev e L. S. Kuz'menkov. "Balance equations in semi-relativistic quantum hydrodynamics". International Journal of Modern Physics B 28, n.º 21 (24 de junho de 2014): 1450132. http://dx.doi.org/10.1142/s021797921450132x.

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Method of the quantum hydrodynamics has been applied in quantum plasmas studies. As the first step in our consideration, derivation of classical semi-relativistic (i.e., described by the Darwin Lagrangian on microscopic level) hydrodynamical equations is given after a brief review of method development. It provides better distinguishing between classic and quantum semi-relativistic effects. Derivation of the classical equations is interesting since it is made by a natural, but not very widespread method. This derivation contains explicit averaging of the microscopic dynamics. Derivation of corresponding quantum hydrodynamic equations is presented further. Equations are obtained in the five-momentum approximation including the continuity equation, Euler and energy balance equations. It is shown that relativistic corrections lead to presence of new quantum terms in expressions for a force field, a work field etc. The semi-relativistic generalization of the quantum Bohm potential is obtained. Quantum part of the energy current, which is an analog of the quantum Bohm potential for the energy evolution equation, is derived. The Langmuir wave dispersion in semi-relativistic quantum plasmas, corresponding to the Darwin Lagrangian, is also considered to demonstrate contribution of semi-relativistic effects on basic plasma phenomenon.

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47

Orefice, A. "Resonant interaction of electron cyclotron waves with a plasma containing arbitrarily drifting suprathermal electrons". Journal of Plasma Physics 34, n.º 2 (outubro de 1985): 319–26. http://dx.doi.org/10.1017/s0022377800002890.

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A relativistic treatment of the plasma dispersion functions and of the dielectric tensor for electron cyclotron electromagnetic waves is given for non-thermal plasmas where the electron distribution function can be represented as a combination of Maxwellians with arbitrary drifts along the magnetic field.

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48

Shukla, Padma Kant, e Bengt Eliasson. "Localization of intense electromagnetic waves in plasmas". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 366, n.º 1871 (24 de janeiro de 2008): 1757–69. http://dx.doi.org/10.1098/rsta.2007.2184.

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We present theoretical and numerical studies of the interaction between relativistically intense laser light and a two-temperature plasma consisting of one relativistically hot and one cold component of electrons. Such plasmas are frequently encountered in intense laser–plasma experiments where collisionless heating via Raman instabilities leads to a high-energetic tail in the electron distribution function. The electromagnetic waves (EMWs) are governed by the Maxwell equations, and the plasma is governed by the relativistic Vlasov and hydrodynamic equations. Owing to the interaction between the laser light and the plasma, we can have trapping of electrons in the intense wakefield of the laser pulse and the formation of relativistic electron holes (REHs) in which laser light is trapped. Such electron holes are characterized by a non-Maxwellian distribution of electrons where we have trapped and free electron populations. We present a model for the interaction between laser light and REHs, and computer simulations that show the stability and dynamics of the coupled electron hole and EMW envelopes.

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BORGHESI, M., D. H. CAMPBELL, A. SCHIAVI, O. WILLI, M. GALIMBERTI, L. A. GIZZI, A. J. MACKINNON et al. "Propagation issues and energetic particle production in laser–plasma interactions at intensities exceeding 1019 W/cm2". Laser and Particle Beams 20, n.º 1 (janeiro de 2002): 31–38. http://dx.doi.org/10.1017/s0263034602201044.

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A series of experiments recently carried out at the Rutherford Appleton Laboratory investigated various aspects of the laser–plasma interaction in the relativistic intensity regime. The propagation of laser pulses through preformed plasmas was studied at intensities exceeding 1019 W/cm2. The transmission of laser energy through long-scale underdense plasmas showed to be inefficient unless a plasma channel is preformed ahead of the main laser pulse. The study of the interaction with overdense plasmas yielded indication of collimated energy transport through the plasma. The production of fast particles during the interaction with solid density targets was also investigated. The measurements revealed the presence of a small-sized directional source of multi-megaelectron volt protons, which was not observed when a plasma was preformed at the back of the solid target. The properties of the source are promising in view of its use in radiographic imaging of dense matter, and preliminary tests were carried out.

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Caditz, D. M., e S. Tsuruta. "Relativistic Adiabatic Shocks in Accretion Flows". Symposium - International Astronomical Union 195 (2000): 381–84. http://dx.doi.org/10.1017/s0074180900163193.

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Accretion flows onto compact astronomical sources are likely to be supersonic, and shock waves may therefore be common in such flows. Plasma passing through a shock front will be compressed and heated according to the jump conditions across the shock discontinuity. Shocks in accretion flows may therefore have important consequences for the flow structure and emission characteristics. The equations governing adiabatic (nonradiative) shocks in relativistic plasmas are presented including the effects of radiation pressure and energy density, and pair equilibria in the postshock flow. We find that postshock states for accretion flows within cool, optically thick, accretion-driven sources such as AGN become radiation- or pair-dominated, and the postshock plasma will likely become optically thin before returning to steady-state conditions.

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