Plasma channel generation for electron acceleration with a laser-induced density gradient

Abstract

Injection is a critical issue for the generation of a small-energy-spread, high-energy electron beam by using a laser wakefield accelerator (LWFA). By using a steep downward density gradient of plasma electrons at a gas target, a portion of the background electrons can be trapped locally in the laser wakefield, and they are accelerated by the field. To make a steep downward electron density gradient, we generated a pre-plasma using a 200-ps 800-mJ Nd:Glass laser, and we measured its electron density by using a Mach-Zehnder interferometer. Due to the shock structure of the plasma with a background neutral gas, a steep density gradient (∼ 8 × 1018 cm -3/20 μm) could be generated. In the near future, a 20-TW, 30-fs Ti:Sapphire laser will be sent to this pre-plasma to generate an electron beam. In this paper, some preliminary experimental results and an ongoing work are reported.