Impact of beam energy modulation on rf zero-phasing microbunch measurements

Temporal profile of a simple bunch distribution may be obtained by measuring the horizontal density profile of an energy-chirped electron beam at a dispersive region using the rf zero-phasing technique. For an energy-modulated beam, the horizontal profile obtained by this technique is also modulated with an enhanced amplitude. We study the microbunching experiment at the NSLS source development laboratory and show that the horizontal modulation observed by the rf zero-phasing technique can be explained by the space–charge-induced energy modulation in the accelerator.