SOME ASPECTS OF LASER-PLASMA INTERACTION FOR ELECTRON ACCELERATION

Abstract

This thesis focuses on investigation of laser-plasma interaction relevant to electron acceleration to high energies. This work explores various ideas for producing an energetic and good quality electron beam from laser wakefield acceleration (LWFA) in plasmas. In LWFA, a high-intensity laser pulse excites a plasma wave, which propagates behind the laser pulse with the equal speed of the laser group velocity. For efficient accelerations, electrons should be injected into the wakefield. Thus, the wakefield evolution and electron injection both are quite important aspects in LWFA. In order to draw the maximum output from the wakefield structure, which is called wakefield bubble in case of high-intensity laser, the basic understanding behind the factors controlling electron injection into wake structure must be very clear. This thesis work focus toward controlling the electron beam quality by understanding the factors affecting bubble wake evolution. The dependence of beam energy and the beam quality on the shape of the bubble is the main motivation behind this investigation. Particle-in-cell (PIC) simulations are conducted to study the bubble dynamics for optimum electron accelerations. A good quality electron bunch with pC to nC charge are obtained with current laser-plasma parameters. During LWFA, generation of wakefield results in variation of refractive index that may distort the laser pulse shape. Thus, the laser pulse shape may be a significant factor to control the electron beam parameters in LWFA. Various shapes such as q-Gaussian laser pulse and flattened-Gaussian laser pulse have been taken into account to observe the laser pulse effect on electron beam parameters in LWFA. The implications of laser pulse shape was shown to control and optimize the bunch charge as well as the bunch energy. Our insights into the acceleration process might be quite supportive in the future optimization of electron beam stability and quality. The electron bunch generated by LWFA could be used to obtain femtosecond x-rays and subsequent applications in medical sciences.