Dependence of the electron beam parameters on the stability of laser propagation in a laser wakefield accelerator

Characteristics of electron beams produced by the laser wakefield acceleration are presented. The dependence of the electron beam parameters on the laser focal spot size is investigated. The experimental result shows the generation of quasimonoenergetic electron beam although the laser spot size was several times larger than the plasma wavelength. Stable electron beam generation at large laser spots was owing to the stable laser propagation in plasma channels. At a small laser spot, the beam quality is poor and this is attributed to the the filamentation instability of the laser beam.