Bunching evolution within the electron beam of a SASE FEL

Abstract

Evolution of bunching factor in different sections of an electron beam moving along an undulator is investigated. An averaging code is developed to calculate the average value of bunching in two different modes. In the first mode, the magnitude of bunching factor is averaged. In the second mode, the average of bunching factor is calculated taking into account its complex nature. The first averaging shows that all sections have similar trend of evolution; but, the result is completely different for the second averaging. The difference is attributed to the inherent phase cancellation present in the second mode of averaging.