The accelerating gradients in conventional linear accelerators are currently limited to ~100 MV/m. Plasma-based accelerators have the ability to sustain accelerating gradients which are several orders of magnitude greater than that obtained in conventional accelerators. Due to the rapid development of laser technology the laser-plasma-based accelerators are of great interest now. Over the past decade, successful experiments on laser wakefield acceleration of electrons in the plasma have confirmed the relevance of this acceleration. Evidently, the large accelerating gradients in the laser plasma accelerators allow to reduce the size and to cut the cost of accelerators. Another important advantage of the laser-plasma accelerators is that they can produce short electron bunches with high energy. The formation of electron bunches with small energy spread was demonstrated at intense laser–plasma interactions. Electron self-injection in the wake-bubble, generated by an intense laser pulse in underdense plasma, has been studied. With newly available compact laser technology one can produce 100 PW-class laser pulses with a single-cycle duration on the femtosecond timescale. With a fs intense laser one can produce a coherent X-ray pulse. Prof. T. Tajima suggested utilizing these coherent X-rays to drive the acceleration of particles. When such X-rays are injected into a crystal they interact with a metallic-density electron plasma and ideally suit for laser wakefield acceleration. In numerical simulation of authors, performed according to idea of Prof. T.Tajima, on wakefield excitation by a X-ray laser pulse in a metallic-density electron plasma the accelerating gradient of several TV/m has been obtained. It is important to form bunch with small energy spread and small size. The purpose of this paper is to show by the numerical simulation that some precursor-laser-pulse, moved before the main laser pulse, controls properties of the self-injected electron bunch and provides at certain conditions small energy spread and small size of self-injected and accelerated electron bunch.
Optimization of electron bunch quality using a chirped laser pulse in laser wakefield acceleration