Laser Injection and Channel Guided Acceleration of Electrons in a Laser Wakefield Accelerator

Abstract

Summary form only given. Laser driven accelerators such as the laser wakefield accelerator (LWFA) have tremendous advantages over conventional radio-frequency accelerators because of the ultra-high acceleration gradients (>100 GV/m) provided by the large amplitude relativistic plasma waves that are excited by the intense ultra-short laser pulse. These ultra-high gradients were demonstrated in the last decade using a variation of the LWFA called the self-modulated LWFA (SM-LWFA). However, the high energy electrons generated in these schemes have an energy distribution that is essentially thermal in nature. The large energy spread is a consequence of the uncontrolled self-trapping and acceleration of background plasma electrons. Recent experimental results have made breakthroughs both in the first demonstration of controlled acceleration of optically injected electrons at the Naval Research Laboratory (NRL) and the first production of quasi-monoenergetic (~100 MeV) beams at several international institutes. An incorporation of the optical injection and an extended acceleration in a plasma channel can lead to stable and high-quality electron beams in the multi-GeV regime in a single stage. Staging of GeV LWFA's to generate substantially higher energy electrons is also being actively considered. The LWFA experiments at NRL have demonstrated high energy electron production in the optical injection scheme of high-density laser ionization and ponderomotive acceleration (HD-LIPA) and the first two-staged optically injected LWFA. Acceleration of optically injected electrons to >10 MeV was observed indicating an acceleration gradient of -10 GeV/m for the 1 mm acceleration distance. Further experiment to extend the acceleration distance to many centimeters for the demonstration of well controlled injection and acceleration to very high energies is in progress. The details of these injection-acceleration experiments will be presented