Simulation of density channel guiding in capillary discharge experiments and laser wakefield accelerators

Laser-driven accelerators require guiding of the laser pulse over many Rayleigh lengths. Plasma channels such as those produced by a capillary discharge have been shown experimentally to be capable of guiding intense laser pulses over distances as long as 6 cm. Simulations of laser propagation in these channels show that the laser pulse radius undergoes oscillations about the matched radius at the expected frequency. The pulse may be distorted by several effects, including laser-generated ionization. Experiments to date have been at relatively high densities (10¹⁸ - 10¹⁹ cm^-3). For standard laser wakefield accelerator applications, the channel density is likely to be substantially lower. As expected, simulations in this lower density regime show lower accelerating gradients, larger laser spot sizes, and higher wakefield phase velocities and dephasing-limited energy gain.