Optical guiding and beat wave phase velocity control in the plasma beat wave accelerator

Abstract

Relativistic optical guiding allows two colinear short pulse radiation beams, provided they are of sufficiently high power, to propagate through a plasma without diffracting. By further accounting for finite radial beam geometry, it is possible for the phase velocity of the radiation beat (ponderomotive) wave to equal the speed of light. Provided the plasma wave phase velocity remains equal to the beat wave phase velocity, then phase detuning between the accelerated electrons and the plasma wave is no longer a limiting factor in determining the maximum energy gain in the plasma heat wave accelerator. As the plasma wave grows to sufficiently large amplitudes, however, it strongly affects the diffractive properties of the radiation beams. In particular, a large amplitude plasma wave will break up an initially uniform radiation beam into periodic beamlet segments, of length less than or equal to half a plasma wavelength, which remain optically guided as they propagate. In the plasma beat wave accelerator, for an optimal choice of the mismatch between the radiation beat frequency and the ambient plasma frequency, then the resonantly driven plasma wave may lead to enhanced focusing of the radiation beams.