Generation of maximum photon flux at the optimum plasma density in the laser-driven betatron oscillation

Abstract

The plasma density effect on x-ray characteristics from betatron oscillation in a laser wakefield accelerator was studied via two-dimensional particle-in-cell simulations. Inside an ion cavity, accelerated electrons with betatron oscillatory motion produce synchrotron radiation. As the plasma density increases, both bunch charge and betatron oscillation amplitude increase in the laser unmodulated regime and decrease again in the laser modulated regime. The multicavitation and weaker field from the laser modulation result in a smaller bunch charge and a decrease in oscillation amplitude in the modulated regime. The photon flux and critical energy in the wiggler regime, where the ion cavity acts as a wiggler, can be optimized and controlled through plasma density. In this work, the mechanism of the optimum ratio of laser pulse duration to plasma wavelength for maximum photon flux was investigated.