Resonantly driven laser‐plasma electron accelerators

Abstract

A method for generating large‐amplitude nonlinear plasma waves, which utilizes an optimized train of independently adjustable, intense laser pulses, is analyzed in 1‐D both theoretically and numerically (using both Maxwell‐fluid and particle‐in‐cell codes). Optimal pulse widths and interpulse spacings are computed for pulses with either square or finite‐risetime sine shapes. A resonant region of the plasma wave phase space is found where the plasma wave is driven by the laser most efficiently. The width of this region, and thus the optimal finite‐risetime laser pulse width, was found to decrease with increasing plasma density and plasma wave amplitude, while the nonlinear plasma wavelength, and thus the optimal interpulse spacing, was found to increase. Also investigated are the resonance sensitivities to variations in the laser and plasma parameters. Non‐linear Landau damping of the wave by trapped background electrons is found to be important. Resonant excitation by this method is shown to more advantageous for electron acceleration than either the single pulse wakefield or the plasma beatwave concepts, because comparable plasma wave amplitudes may be generated at lower plasma densities, thus reducing electron‐phase detuning, or at lower laser intensities, thus reducing laser‐plasma instabilities. Practical experimental methods for producing the required pulse trains are discussed. © 1995 American Institute of Physics.