Single shot, nondestructive monitor for longitudinal subpicosecond bunch profile measurements with femtosecond resolution

Abstract

Accurate knowledge of the charged particle bunch longitudinal (time) profile is important in the context of wakefield accelerators, Compton Light sources, x-ray SASE FELs and THz radiation sources. However, it is still a challenge to obtain this information for subpicosecond long bunches and microbunched beams with the required femtosecond (fs) resolution and nondestructively. Apart from determining the profile in a nondestructive manner, the ideal bunch diagnostic would enable extraction of all required information in a single shot, have a sufficiently high repetition rate to monitor each bunch, small footprint, good cost efficiency and reliability. In this paper we present the design of a longitudinal bunch profile monitor that can determine the charged particle bunch profile with femtosecond resolution, nondestructively and in a single shot via the spectral analysis of coherent Smith-Purcell radiation (cSPr). It is based on the simultaneous deployment of three gratings with different periodicities, each with its own set of detectors. The number of the frequency sampling points is equal to the number of the optical channels and the discrimination against background radiation is based on the different polarization properties of cSPr and background radiation. The rationales for the choices made to optimize the monitor operation will be presented and the criteria for determining the number of frequency sampling points will be discussed. The possible future developments of the monitor are also presented and discussed.