Longitudinal wake of a suddenly accelerated electron bunch
We consider the longitudinal wake of an electron bunch that is suddenly accelerated. This wake approximates the edge-radiation wake of an electron exiting a bending magnet, the wake of an electron accelerated in a high-field gradient, and the wake of forward transition radiation. The on-axis wake is large within the radiation formation zone, where it provides resistive impedance that decelerates the bunch electrons. A comparison with the computed wake downstream of a bending magnet yields good agreement. For schemes in which a bunch produced by laser-plasma acceleration drives a VUV or xray FEL, the wake causes large energy losses that may spoil the FEL process.