Impact of space charge effects on ultrafast electron beam longitudinal profile diagnostics based on SPR

Accurate characterization of the longitudinal profile of ultrafast electron bunches is crucial for observing ultrafast dynamic processes in ultrafast electron diffraction (UED). Real-time monitoring of each ultrafast electron bunch's length would ideally provide a temporal basis for analyzing diffraction patterns. However, accurately and non-destructively measuring the longitudinal profile at the 10 femtoseconds level remains challenging. This paper investigates a method for monitoring the longitudinal profile of bunches using coherent Smith-Purcell radiation (cSPr). Space charge effects cause the elongation of electron bunches during flight, resulting in changes in the Smith-Purcell radiation spectrum. Therefore, the focus is on understanding the impact of space charge effects on the behavior of ultrafast electron bunches and their corresponding cSPr spectrum, with the aim of improving measurement accuracy.