Characterization of plasma wake excitation and particle trapping in the nonlinear bubble regime

We investigate the excitation of nonlinear wake (bubble) formation by an ultra-short ($k_pL \sim 2$), intense ($e A_{\rm laser}/mc^2 > 2$) laser pulse interacting with an underdense plasma. A detailed analysis of particle orbits in the wakefield is performed by using reduced analytical models and numerical simulations performed with the 2D cylindrical, envelope, ponderomotive, hybrid PIC/fluid code {\small INF\&RNO}, recently developed at LBNL. In particular we study the requirements for injection and/or trapping of background plasma electrons in the nonlinear wake. Characterization of the phase-space properties of the injected particle bunch will also be discussed.