UC Berkeley

Beam degradation is examined in a laser-plasma accelerator stage with a parabolic plasma channel when the laser pulse and/or the electron beam enters the channel off axis. Betatron oscillations in the beam become incoherent, resulting in a net increase of beam emittance through phase mixing. A quantitative model for transverse emittance growth due to misalignment in multistage accelerators, valid in the linear regime, is presented and compared with particle-in-cell simulations. The model is applied to a chain of laser-plasma accelerator stages, and tolerances are derived on the initial energy spread of the electron beam and misalignment in the multistage structure, with repercussions in high-energy physics applications of laser-plasma accelerators.