Plasma beatwave accelerator based on a nonlinear bistability of relativistic plasma waves

Summary form only given. Plasma beatwave is one of the originally proposed schemes for making a plasma-based accelerator. Its traditional implementation assumes that the plasma wave is a linear oscillator driven by the ponderomotive force of the two lasers detuned by the plasma frequency. We demonstrate how the off-resonance excitation of the plasma wave and the relativistic dependence of the plasma frequency on its amplitude can be used to observe the nonlinear bistability of the plasma wave. The relativistic threshold for observing the nonlinear bistability is derived and confirmed using particle in cell simulations. One of the surprising results is the realization that a very long laser beatwave pulse slightly detuned from the nonrelativistic plasma wave resonance can excite plasma waves behind the pulse if the peak pulse amplitude exceeds the threshold. Specific examples of laser and plasma parameters relevant to high-gradient plasma accelerators given. Also, excitation of plasma wakes by a strongly modulated (for example, by an FEL interaction) electron beam is considered, and the possibility of developing a combined accelerator/fs-injector is discussed.