Microbunching and beam break-up in DUV-FEL accelerator

We present the results of electron beam longitudinal modulation studies in the DUV-FEL accelerator. For bunch length determination we used the "zero-phasing" method, based on a measurement of the chirped electron bunch energy spectra. The measurements revealed a spiky structure in the longitudinal phase space. A model based on space charge effect is considered to explain of the obtained phenomena. The analysis of the energy spectra has shown a sensitivity of the structure to the electron beam peak current, energy and longitudinal non-uniformity of the RF gun drive laser. Analytical calculations have demonstrated a qualitative agreement with experimental observations. Several experiments have been made to compare with theory; measured results are reviewed in this paper. The obtained effect is briefly discussed in relation to high brightness accelerators.