A one-dimensional steady-state model for stimulated Raman backscatter (SRS) and stimulated Brillouin backscatter (SBS) processes in laser-irradiated plasmas is presented. Based on a novel “predictor-corrector” method, the model is capable to deal with broadband scattered light and inhomogeneous plasmas, exhibiting robustness and high efficiency. Influences of the electron density and temperature on the linear gains of both SRS and SBS are investigated, which indicates that the SRS gain is more sensitive to the electron density and temperature than that of the SBS. For the low-density case, the SBS dominates the scattering process, while the SRS exhibits much higher reflectivity in the high-density case. The nonlinear saturation mechanisms and competition between SRS and SBS are included in our model by a phenomenological method. The typical anti-correlation between SRS and SBS versus electron density is reproduced in the model. Calculations of the reflectivities are qualitatively in agreement with the typical results of experiments and simulations.

We study the influence of finite-emittance electron bunches in the bubble regime of laser-driven wakefield acceleration onto the microscopic structure of the bunch itself. Using resilient backpropagation (Rprop) to find the equilibrium structure, we observe that for realistic and already observed emittances the previously found crystalline structures remain intact and are only widened marginally. Higher emittances lead to larger electron displacements within the crystal and finally its breaking.

The nonlinear evolution of electron Weibel instability in a symmetric, counterstream, unmagnetized electron–positron e−/e+ plasmas is studied by a 2D particle-in-cell (PIC) method. The magnetic field is produced and amplified by the Weibel instability, which extracts energy from the plasma anisotropy. A weakly relativistic drift velocity of 0.5c is considered for two counterstreaming e−/e+ plasma flows. Simulations show that in a homogeneous e−/e+ plasma distribution, the magnetic field amplifies exponentially in the linear regime and rapidly decays after saturation. However, in the case of inhomogeneous e−/e+ plasma distribution, the magnetic field re-amplifies at post-saturation. We also find that the amount of magnetic field amplification at post-saturation depends on the strength of the density inhomogeneity of the upstream plasma distribution. The temperature calculation shows that the finite thermal anisotropy exists in the case of an inhomogeneous plasma distribution which leads to the second-stage magnetic field amplification after the first saturation. Such density inhomogeneities are present in a variety of astrophysical sources: for example, in supernova remnants and gamma-ray bursts. Therefore, the present analysis is very useful in understanding these astrophysical sources, where anisotropic density fluctuations are very common in the downstream region of the relativistic shocks and the widely distributed magnetic field.

This article presents a preliminary study of the longitudinal self-compression of ultra-intense Gaussian laser pulse in a magnetized plasma, when relativistic nonlinearity is active. This study has been carried out in 1D geometry under a nonlinear Schrodinger equation and higher-order paraxial (nonparaxial) approximation. The nonlinear differential equations for self-compression and self-focusing have been derived and solved by the analytical and numerical methods. The dielectric function and the eikonal have been expanded up to the fourth power of r (radial distance). The effect of initial parameters, namely incident laser intensity, magnetic field, and initial pulse duration on the compression of a relativistic Gaussian laser pulse have been explored. The results are compared with paraxial-ray approximation. It is found that the compression of pulse and pulse intensity of the compressed pulse is significantly enhanced in the nonparaxial region. It is observed that the compression of the high-intensity laser pulse depends on the intensity of laser beam (a0), magnetic field (ωc), and initial pulse width (τ0). The preliminary results show that the pulse is more compressed by increasing the values of a0, ωc, and τ0.

This paper presents the results of comprehensive studies of the efficiency of a pulsed electron beam transmission through a mixture of gases: nitrogen (83%), carbon dioxide (14%), and oxygen (2.6%) in the presence of ash and water vapor. The studied concentrations correspond to the concentrations of nitrogen, oxygen, and carbon dioxide in flue gas. The pressure and concentration of water vapor and ash in the drift chamber varied (375, 560, and 750 Torr; humidity 15 ± 5% and 50 ± 15%). The charge dissipation of a pulsed electron beam in the gas mixture in the presence of ash and water vapor was investigated, as well as the effect of the concentration of water vapor and ash on the geometric profile of the pulsed electron beam.

In this paper, self-focusing of finite Airy–Gaussian (AiG) laser beams in collisionless plasma has been investigated. The source of nonlinearity considered herein is relativistic. Based on the Wentzel–Kramers–Brillouin (WKB) and paraxial-ray approximations, the nonlinear coupled differential equations for beam-width parameters in transverse dimensions of AiG beams have been established. The effect of beam's modulation parameter and linear absorption coefficient on the self-focusing/defocusing of the beams is specifically considered. It is found that self-focusing/defocusing of finite AiG beams depends on the range of modulation parameter. The extent of self-focusing is found to decrease with increase in absorption.

A recently published scheme for inertial fusion based on instantaneous heating of an uncompressed fuel is criticized. It is shown that efficient fusion and “time-like” fusion burn propagation cannot be realized due to the low nuclear reaction cross-sections. The suggested use of nanospheres inside the volume of the target to support the fast heating of the fuel is also questioned.