Relativistic phase fluctuations of beat wave accelerators and wakeless triple solitons

Abstract

The coupled wave equations for two incident laser beams, their cascade beams, and a relativistic electron plasma wave are numerically analyzed to show phase fluctuations of the acceleration field. It is found that the phase fluctuations are induced by the relativistic nonlinear shift of the plasma frequency together with the electromagnetic pump wave depletion. When the phase fluctuations become significant, the accelerated particle energy is reduced strongly. The triple-soliton concept, which is proposed to overcome the above difficulties, is also numerically investigated. In particular, effects of the relativistic nonlinearity and the frequency mismatch are discussed. The numerical analysis clarified that the appropriate initial frequency mismatch cancels the relativistic nonlinearity, as indicated by McKinstrie and DuBois [Phys. Rev. Lett. 57, 2022 (1986)] and the triple-soliton propagates for a long distance.