Test particle injection in the relativistic plasma waves excited by two co-propagating laser beams

The authors report on a series of experiments aimed at the demonstration of controlled acceleration of externally injected test particles (electrons) by a relativistic plasma wave. The plasma wave is excited resonantly by beating two co-propagating laser beams at the plasma frequency. The first part of the paper describes the electron linear accelerator and the beam transport system, as well as the particle detection system. The electron macropulse energy spectrum and beam emittance are measured and are shown to be consistent with the requirements of the experiment. The electron beam is passed through a Θ-pinch plasma. Although Raman scattering of the incident CO/sub 2/ laser has shown the plasma to be reproducible in density to within 15% from one shot to the next at peak compression, direct evidence of localized density inhomogeneities due to trapped magnetic fields is found via the deflection of the injected electron beam