ABSTRACT
Large-amplitude plasma wave is known to accelerate electrons to high energies. The electron energy gain mainly depends on plasma wave amplitude. In this paper, we investigate the excitation of large-amplitude plasma waves by laser beat-wave in an inhomogeneous plasma. The idea behind this work is to employ linear and radial plasma density profiles to enhance the plasma wave amplitude. PIC simulations are used to validate the numerical solution of the nonlinear wave equation in cylindrical dimensions through the finite difference method. Furthermore, the effects of the quadratic-radial plasma density profiles and magnetic field on the plasma wave excitation are investigated. The study shows that compared to the linear density profile of plasma, the plasma wave amplitude in the case of a linear-radial density profile is far more pronounced. For the linear-radial density profile, the plasma wave amplitude remains steady over greater distances of propagation compared to the linear density profile, resulting in reduced immediate damping effects. It can also be seen that the plasma wave amplitude is higher for the quadratic-radial than for the linear-radial density profiles. The effect of a longitudinal magnetic field on plasma wave amplitude is investigated. It can be seen that the plasma wave amplitude is increased by applying a magnetic field. This study may provide a way to enhance the plasma wave field for accelerating the electrons in laser-plasma accelerators.
ABSTRACT
A new scheme for injection and acceleration of electrons in wakefield accelerators is suggested based on the co-action of a laser pulse and an electron beam. This synergy leads to stronger wakefield generation and higher energy gain in the bubble regime. The strong deformation of the whole bubble leads to electron self-injection at lower laser powers and lower plasma densities. To predict the practical ranges of electron beam and laser pulse parameters an interpretive model is proposed. The effects of altering the initial electron beam position on self-trapping of plasma electrons are studied. It is observed that an ultra-short (25 fs), high charge (340 pC), 1 GeV electron bunch is produced by injection of a 280 pC electron beam in the decelerating phase of the 75 TW laser driven wakefield.
ABSTRACT
Metamaterials in which plasmas are included have significant properties that may not be found in ordinary metamaterials. The permittivity function of these engineered materials can be rapidly manipulated by applying external electric and magnetic field or changing the gas pressure, temperature, and collisional frequency. We investigate the conditions necessary for the existence of Dyakonov surface waves (DSWs) propagating along the interface of a plasma metamaterial (PMM) and an isotropic dielectric material in the terahertz region. We assume the PMM to be a multilayer structure that consists of plasma and background isotropic material alternately. The influence of considering the plasma collisional loss in the DSW dispersion curve is studied. We demonstrate that the angular regions in which the DSW propagation is allowed can be tuned and significantly expanded. We also show that the large birefringence represented by the PMM allows DSWs to exist within large angular existence domains and levels of localization similar to plasmons, thus making these surface waves available for practical applications.
