Optimum trapping condition for laser wakefield acceleration of electrons in an inhomogenious plasma

Summary form only given. Extraordinary ability of space-charge waves in plasmas to accelerate charged particles at gradients that are orders of magnitude greater than in current accelerators has been well documented. Controlling and understanding the injection of background plasma electrons into a plasma wave is critical to the design of plasma-based accelerators. Self trapping is an important source of electrons in laser wakefield accelerator experiments. In an inhomogeneous plasma density, we propose to investigate the optimum trapping condition of thermal electrons in a nonlinear electron plasma wave of arbitrary phase velocity is investigated. It is known that the electrons velocity depends on the laser intensity and the phase velocity of the wake wave is correlated to the density gradient. Thus, by using a model based on single-particle dynamics, electron trapping condition for downward density ramp profile of the plasma is calculated. In our simulations, it is found that for very steep plasma density ramp, the trapping of the plasma electrons start early in comparison to slight density ramp. Consequently, the accelerated bunch has less energy spread and the beam quality is found to be good with improvement in charge of the accelerated electron bunch. Implications for experimental and numerical investigations of laser wakefield accelerations of the electrons are discussed for this studies.