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A comparative study of the dynamics of the electron beam-plasma system in two spatial dimensions is carried out by means of particle-in-cell (PIC) simulation and quasilinear theory. In the literature, the beam-plasma instability is usually studied with one-dimensional assumption. Among the few works that include higher-dimensional effects are two- and three-dimensional quasilinear theory and two-dimensional PIC simulations. However, no efforts were made to compare the theory and simulation side by side. The present paper carries out a detailed comparative study of two-dimensional simulation and quasilinear theory. It is found that the quasilinear theory quite adequately accounts for most important features associated with the simulation result. For instance, the particle diffusion time scale, the maximum wave intensity, dynamical development of the electron distribution function, and the change in the wave spectrum all agree quantitatively. However, certain nonlinear effects such as the Langmuir condensation phenomenon are not reproduced by the quasilinear theory. Nevertheless, the present paper verifies that the simple quasilinear theory is quite effective for the study of beam-plasma instability for the present choice of parameters. [ABSTRACT FROM AUTHOR]

The experimental study on the expanding plasma movement of low-density gold foam (~1% solid density) irradiated by a high power laser is reported in this paper. Experiments were conducted using the SG-III prototype laser. Compared to solid gold with 19.3 g/cc density, the velocities of X-ray emission fronts moving off the wall are much smaller for gold foam with 0.3 g/cc density. Theoretical analysis and MULTI 1D simulation results also show less plasma blow-off, and that the density contour movement velocities of gold foam are smaller than those of solid gold, agreeing with experimental results. These results indicate that foam walls have advantages in symmetry control and lowering plasma fill when used in ignition hohlraum. [ABSTRACT FROM AUTHOR]

This paper presents simulations of isolated 3D filaments in a slab geometry obtained using a newly developed 3D reduced fluid code, written using the BOUT++ framework. First, systematic scans were performed to investigate how the dynamics of a filament are affected by its amplitude, perpendicular size, and parallel extent. The perpendicular size of the filament was found to have a strong influence on its motions, as it determined the relative importance of parallel currents to polarization and viscous currents, whilst drift-wave instabilities were observed if the initial amplitude of the blob was increased sufficiently. Next, the 3D simulations were compared to 2D simulations using different parallel closures; namely, the sheath dissipation closure, which neglects parallel gradients, and the vorticity advection closure, which neglects the influence of parallel currents. The vorticity advection closure was found to not replicate the 3D perpendicular dynamics and overestimated the initial radial acceleration of all the filaments studied. In contrast, a more satisfactory comparison with the sheath dissipation closure was obtained, even in the presence of significant parallel gradients, where the closure is no longer valid. Specifically, it captured the contrasting dynamics of filaments with different perpendicular sizes that were observed in the 3D simulations which the vorticity advection closure failed to replicate. However, neither closure successfully replicated the Boltzmann spinning effects nor the associated poloidal drift of the blob that was observed in the 3D simulations. Although the sheath dissipation closure was concluded to be more successful in replicating the 3D dynamics, it is emphasized that the vorticity advection closure may still be relevant for situations where the parallel current is inhibited from closing through the sheath due to effects such as strong magnetic shear around X points or increased resistivity near the targets. [ABSTRACT FROM AUTHOR]

In this paper, we compare two recent models [N. A. Yampolsky and N. J. Fisch, Phys. Plasmas 16, 072104 (2009); D. Bénisti, D. J. Strozzi, L. Gremillet, and O. Morice, Phys. Rev. Lett. 103, 155002 (2009)] introduced to predict the nonlinear growth of stimulated Raman scattering in the kinetic regime, and providing moreover a nonlinear description of the collisionless, Landau-like, damping rate of the driven electron plasma wave. We first recall the general theoretical framework common to these two models, based on the derivation of the imaginary part of the electron susceptibility, χi, and then discuss in detail why the two approaches differ. By comparing the theoretical predictions for χi to those derived from test particle or Vlasov simulations, we moreover discuss the range of validity of the two models. [ABSTRACT FROM AUTHOR]

This paper deals with a two-dimensional simulation of electric wakefields generated by two color laser pulses propagating in homogeneous plasma, using VORPAL simulation code. The laser pulses are assumed to have a frequency difference equal to the plasma frequency. Simulation studies are performed for two similarly as well as oppositely polarized laser pulses and the respective amplitudes of the generated longitudinal wakefields for the two cases are compared. Enhancement of wake amplitude for the latter case is reported. This simulation study validates the analytical results presented by Jha et al. [Phys. Plasmas 20, 053102 (2013)]. [ABSTRACT FROM AUTHOR]

A direct Density Modulation Cathode (DMC) in magnetron is proposed in this paper. By removing the velocity modulation process, electron spokes corresponding to the dominant operating mode can be quickly formed when the DMC is used. Based on theoretical analysis, particle-in-cell simulations and experimental investigations are carried out for demonstration. The final results show that compared with conventional solid cathode and transparent cathode, the DMC can increase 68% and even 146% of relative microwave widths, respectively. [ABSTRACT FROM AUTHOR]

A positive slope in a velocity distribution function perpendicular to the ambient magnetic field, such as due to a loss cone or ring velocity distribution, can become a free energy source for the excitation of various plasma waves. Since there exists no analytic expression for integrals of Maxwellian ring velocity distribution functions, their linear properties have previously been studied using several approximations or modeled distributions. In this paper, a numerical method for analyzing the linear dispersion relation for Maxwellian ring-beam velocity distributions is developed. The obtained linear properties are confirmed by direct comparison with full particle simulation results. [ABSTRACT FROM AUTHOR]