Computational Studies on Low Intensity Near Critical Density Laser Wakefield Acceleration for Medical Applications

Conventional laser wakefield acceleration requires high intensity lasers and plasma densities much lower than the laser critical density in order to both be stable against thermal plasma instabilities and to achieve electron trapping and acceleration. Here, we use particle-in-cell simulations to study laser wakefield acceleration near the critical density. We show that even at low intensities (<10¹⁵ W/cm²) nonlinear laser-plasma interactions excite both high and low phase velocity electron plasma waves through multi-wave coupling. The low phase velocity waves are able to initially trap and accelerate electron bunches so that higher phase velocity waves can further accelerate this bunch to energies of approximately 10 keV or greater. Theoretical studies using nonlinear optics formulations are also used to show the wave-wave excitation in the low intensity regime. These electron bunches of 10 keV are suitable for many applications, particularly medical and radiation therapy where doses of > 1 Gy are possible with improving fiber laser technology.