Multistaging and e-beam trapping in laser particle accelerators

Any practical laser particle acceleration (LPA) scheme will necessarily require a series of acceleration sections arranged in tandem. The phase of the electrons with respect to the laser field can be readjusted at the beginning of each stage, thereby determining that stage's contribution to the acceleration and/or focusing of the e-beam. Multistaging, in fact, offers a natural way to control the e-beam/laser interaction by tuning each successive stage to achieve a high acceleration gradient while preserving or enhancing the quality of the e-beam (e.g., emittance and energy spread). The stage-to-stage evolution of the beam can be treated somewhat independently of specific details in each accelerator section. Therefore, the laser/e-beam interaction within the sections is treated using a generic approach. The basic conditions for beam trapping are established for a multistaged system. Calculations of the longitudinal and transverse beam dynamics are performed to determine the evolution of a finite-emittance e-beam through successive stages. It is found that maintaining the e-beam quality requires only that the trapping condition be satisfied