The effects of preformed plasmas on the directionality of the relativistic electron beam

The preformed plasmas increase laser energy coupling to plasmas and help to generate the relativistic electrons (kinetic energy " 0.511 MeV), which are important to many of the laser plasma applications, such as laser produced positron--electron pairs. However, utilization of the preformed plasmas to generate and control the relativistic electrons is yet to be achieved because the detailed conditions of preformed plasmas under which electrons gain energy and change characteristics, such as the directionality and divergence.;This thesis reports the detailed conditions of preformed plasmas under which the relativistic electrons become directional along the laser propagation. The study was done in two separate experiments on the Titan laser at Lawrence Livermore National Laboratory by simultaneously measuring the density of preformed plasmas and the relativistic electron spectra. A hydro-dynamic simulation, HYDRA, was used to investigate the details of plasma conditions. It was found that the plasma scalelength (plasma density decay length) larger than 3 mum resulted in directional electron beams along the laser propagation, and producing such conditions were dependent on target materials and configurations. These findings suggests strong possibilities of controlling the directionality of energetic electrons for laser plasma applications.