Longitudinal diagnostics of ultra-short relativistic electron bunches based on coherent undulator radiation*

Time resolved diagnostics of current profile in relativistic electron bunch is a challenging task. It is particular challenging to diagnose ultra-short electron bunches produced in plasma wakefield accelerators. The bunch length is on the order of a femtosecond, which cannot be measured with existing techniques. We report development of the longitudinal time resolved diagnostics based on coherent undulator radiation. Coherent undulator radiation results in the signal, which power spectral density is proportional to the one of the bunch current profile. Measurement of the power spectral density of coherent radiation is simplified in case of undulator radiation since different frequencies are emitted at different angles and they are directly measured on a single detector downstream. The temporal profile of the electron bunch current is reconstructed from the spectral data. Here we report start-to-end analysis of the proposed diagnostics and demonstrate its feasibility for diagnosing ultrashort LWFA bunches.