Analysis of chaotic behaviour in a Raman FEL

To compare with the experiment of Raman FEL carried out at JAERI, extensive data of the simulation have been compiled and behaviours of particle orbits in the phase space relative to rf field were studied in detail to get a phenomenological understanding of the effects of beam space charge on FEL performance. Although an ordinary Hamiltonian analysis cannot rigorously be applied to the Raman FEL due to its dissipative character, it is found that the orbits in the phase space become chaotic on going up in beam intensity. The effect of the tapering on the behaviour of the orbits was also discussed.