Showing papers on "Relativistic plasma published in 2023"

Perspectives on relativistic electron–positron pair plasma experiments of astrophysical relevance using high-power lasers

Abstract: 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.

Comment on “Wave-breaking amplitudes of relativistic upper-hybrid oscillations in a cold magnetized plasma” [Phys. Plasmas 23, 064503 (2016)]

Abstract: First Page

On the quadruple Beltrami fields in thermally relativistic electron-positron-ion plasma

Abstract: A thermally relativistic electron-positron-ion (EPI) plasma self-organizes into a quadruple Beltrami (QB) field. The QB field, which is the combination of four Beltrami fields, is described by four scale parameters. These scale parameters are often either real or both real and complex in nature. The values of the scale parameters are determined by Beltrami parameters, relativistic temperatures, and the densities of plasma species. It is demonstrated that all the scale parameters become real at higher relativistic temperatures and ion densities, which naturally lead to paramagnetic structures. It is also shown that the scale separation in the QB state provides the possibility of field and flow generation in such thermally relativistic plasmas. The present study may have implications for space, astrophysical and laboratory plasmas.

Formation of population inversions in relativistic plasmas through nonresonant interactions with Alfv\'en waves

Abstract: We solve the full quasilinear kinetic equation governing nonresonant interactions of Alfv\'en waves with relativistic plasmas. This work was motivated by the need to determine the energy available for the synchrotron maser in the context of Fast Radio Bursts (FRBs). This interaction can result in plasma heating and the formation of population inversions necessary for the maser. We find that population inversions containing $\sim 1-10\%$ of the distribution's energy form in the relativistic regime, providing an explanation for the formation of the inversion in the environment expected near FRBs.

Effect of an external magnetic field on the self-focusing of a cosh-Gaussian laser beam in plasma under the relativistic-ponderomotive effect

Abstract: This work presents an analytical and numerical study of the relativistic-ponderomotive effect on self-focusing of an intense cosh-Gaussian laser beam in a collisionless magnetized plasma by considering an external magnetic field in the direction of propagation of the laser beam. The nonlinear differential equation for the beam width parameter/intensity of a cosh-Gaussian laser beam in a magnetized plasma is obtained by Wentzel–Kramers–Brillouin (WKB) and paraxial-ray approximations. The self-focusing of the cosh-Gaussian beam at different values of the magnetic field parameter is investigated. The results have also been compared to relativistic nonlinearity. The results show that the self-focusing effect of cosh-Gaussian beam in magnetized plasma becomes stronger, when relativistic and ponderomotive nonlinearities acts together. In addition, the self-trapping of cosh-Gaussian beam in magnetized plasma has also been studied. Numerical results are presented for the well-established laser and plasma parameters.

Formation of population inversions in relativistic plasmas through nonresonant interactions with Alfvén waves

Abstract: We solve the full quasilinear kinetic equation governing nonresonant interactions of Alfv\'en waves with relativistic plasmas. This work was motivated by the need to determine the energy available for the synchrotron maser in the context of Fast Radio Bursts (FRBs). This interaction can result in plasma heating and the formation of population inversions necessary for the maser. We find that population inversions containing $\sim 1-10\%$ of the distribution's energy form in the relativistic regime, providing an explanation for the formation of the inversion in the environment expected near FRBs.

Perspectives on laser-plasma physics in the relativistic transparency regime

Abstract: Abstract With the advent of multi-petawatt lasers, the relativistic transparency regime of laser-plasma interactions becomes readily accessible for near-solid density targets. Initially opaque targets that undergo relativistic self-induced transparency (RSIT) have already shown to result in promising particle acceleration and radiation generation mechanisms, as well as relativistic optical and photonics phenomena that modify the spatial, temporal, spectral and polarization properties of the laser pulse itself. At the maximum laser intensities currently available, this opaque-to-RSIT transition regime can be achieved through ultrafast ionization, heating and expansion of initially ultrathin foil targets. Here, we review findings from our programme of work exploring this regime experimentally and numerically, including changes to the laser energy absorption, mechanisms for laser-driven particle acceleration and the generation of a relativistic plasma aperture. New physics induced by this aperture, such as the production of intense light with higher order spatial modes and higher harmonics, and spatially-structured and temporally-varying polarization states, is summarized. Prospects for exploring the physics of the RSIT regime with higher intensity and high repetition rate lasers, including expected new phenomena such as high-field effects and the application of new techniques such as machine learning, are also discussed; outlining directions for the future development of this promising laser-plasma interaction regime.

Response to “Comment on ‘Wave-breaking amplitudes of relativistic upper-hybrid oscillations in a cold magnetized plasma,’ ” [Phys. Plasmas 30, 024701 (2023)]

Abstract: First Page

Nonlinear evolution of the Weibel instability with relativistic laser pulses

Abstract: 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.

Suppression of Bremsstrahlung losses from relativistic plasma with energy cutoff

Abstract: We study the effects of redistributing superthermal electrons on Bremsstrahlung radiation from hot relativistic plasma. We consider thermal and nonthermal distribution of electrons with an energy cutoff in the phase space and explore the impact of the energy cutoff on Bremsstrahlung losses. We discover that the redistribution of the superthermal electrons into lower energies reduces radiative losses, which is in contrast to nonrelativistic plasma. Finally, we discuss the possible relevance of our results for open magnetic field line configurations and prospects of the aneutronic fusion based on proton-Boron11 (p-B11) fuel.

Self-generated magnetic field induced by Karpman–Washimi ponderomotive force in relativistic electron plasmas

Abstract: The relativistic effects on nonstationary Karpman–Washimi ponderomotive magnetization are investigated in relativistic electron plasmas. The magnetization M p and radiation power [Formula: see text] are obtained as functions of the relativistic parameter α, scaled wave frequency [Formula: see text], and wave number [Formula: see text]. It is shown that the ponderomotive force is more likely to induce a low-frequency and small-scale magnetic field. In addition, the results indicate that the magnetization and radiation power are suppressed by the relativistic effects in the ultrarelativistic case but enhanced in the moderately and weakly relativistic cases, especially in the moderately relativistic regime.

Spin effects on the relativistic strong EM wave modes in magnetized plasma

Abstract: Based on the relativistic hydrodynamic model of EM wave–spin plasmas interaction, the spin effects on the relativistic strong EM modes in magnetized plasma are investigated. The dispersion relations of the EM wave propagating parallel and perpendicular to the external magnetic field are obtained. Results show that the strong EM wave modes are affected by the time component of four-spin as well as the increase of electron effective mass. Especially in the case of EM wave propagating parallel to the external magnetic field, the time component of four-spin amplifies the influence of spin effects on the low-frequency modes obviously.

Relativistic toroidal light solitons in plasma

Abstract: In the laser–plasma interaction, relativistic soliton formation is an interesting nonlinear phenomenon and important light mode convection in plasmas. Here, it is shown by three-dimensional particle-in-cell simulations that relativistic toroidal solitons, composed of intense light self-consistently trapped in toroidal plasma cavities, can be produced by azimuthally-polarized relativistic laser pulses in a near-critical underdense plasma.

The Morphology and Dynamics of Relativistic Jets with Relativistic Equation of State

Abstract: We study the effect of plasma composition on the dynamics and morphology of relativistic astrophysical jets. Our work is based on a relativistic total variation diminishing simulation code. We use a relativistic equation of state in the simulation code that accounts for the thermodynamics of a multispecies plasma, which is a mixture of electrons, positrons, and protons. To study the effect of plasma composition, we consider various jet models. These models are characterized by the same injection parameters, same jet kinetic luminosity, and the same Mach numbers. The evolution of these models shows that the plasma composition affects the propagation speed of the jet head, the structure of the jet head, and the morphology, despite fixing the initial parameters. We conclude that electron-positron jets are the slowest and show more pronounced turbulent structures in comparison to other plasma compositions. The area and locations of the hot-spots also depend on the composition of the jet plasma. Our results also show that boosting mechanisms are an important aspect of multi-dimensional simulations, which are also influenced by the change in composition.

The Morphology and Dynamics of Relativistic Jets with Relativistic Equation of State

Abstract: We study the effect of plasma composition on the dynamics and morphology of the relativistic astrophysical jets. Our work is based on a relativistic total variation diminishing (TVD) simulation code. We use a relativistic equation of state in the simulation code which accounts for the thermodynamics of a multispecies plasma which is a mixture of electrons, positrons, and protons. To study the effect of plasma composition we consider various jet models. These models are characterized by the same injection parameters, same jet kinetic luminosity, and the same Mach numbers. The evolution of these models shows that the plasma composition affects the jet head propagation speed, the structure of the jet head, and the morphology despite fixing the initial parameters. We conclude that the electron-positron jets are the slowest and show more pronounced turbulent structures in comparison to other plasma compositions. The area and locations of the hot-spots also depend on the composition of jet plasma. Our results also show that boosting mechanisms are also an important aspect of multi-dimensional simulations which are also influenced by the change in composition.