Effect of energy spread on micro-bunching from shot noise in SASE FELs

The motion of NeNe electrons moving along a helical undulator and interacting with each other through Lienard–Wiechert fields is considered. The numerical solution for initially mono-energetic electrons shows the emergence and growth of micro-bunching. For the case of initially non-mono-energetic electrons, calculations show that the presence of energy spread results in partial suppression of the micro-bunching. The calculations also show that the initial energy spread would shift the micro-bunching maximum to deeper positions within the undulator. Analytical treatment of equations of motion demonstrates that the micro-bunching fall and shift is mainly due to the random motion of the interacting electrons.

Research highlights
► The effect of energy spread on micro-bunching is studied by Lienard–Wiechert field.
► It is claimed that micro-bunching from shot noise produces a plasma poly-crystal.
► The evolution of phase space of non-mono-energetic electron beam is plotted.