MULTISTAGING IN FREE-SPACE LASER PARTICLE ACCELERATORS

One important issue with regard to acceleration of electrons in free s pace using intense laser beams is the phase slippage of the electrons relative to the electromagnetic field. This arises from a phase veloci ty mismatch between the electron and light wave. Left uncontrolled thi s slippage can result in degradation of the e-beam characteristics (e. g., emittance) and dispersion of the electron bunches. By a method sim ilar to microwave accelerators, multistaging offers a means to control the e-beam evolution by tuning each successive stage. The phase of th e electron bunches relative to the laser field at the entrance of each section determines the acceleration and/or focusing that ensues in th at section; therefore, the entrance phase is a natural tuning paramete r. It is shown that by controlling the entrance phase it is possible t o preserve the e-beam quality, both transverse (emittance) and longitu dinal (bunching, energy spread). Calculations of the longitudinal and transverse beam dynamics are performed to determine the evolution of a finite-emittance e beam from stage to stage. By this method the condi tions on entrance phase that allow successful e-beam trapping are foun d. It is also shown that conditions that assure e-beam trapping automa tically preserve the overall beam quality.