NONLINEAR MACROSCOPIC EQUATIONS FOR PULSE EVOLUTION IN A HIGH-GAIN COMPTON FEL

The non-linear stage of the interaction between electron and light pul ses is considered of a high-gain FEL. It is shown that the non-linear oscillations of the radiation intensity can be described analogously t o the bouncing motion of a particle in a time-dependent, anharmonic po tential. In case the electrons all have the same energy and bunching f actor, the potential is constant in the steady state region of the lig ht pulse. In this region, analytical solutions are in good agreement w ith the full solution. Using the same approximation also in the traili ng edge of the light pulse, it is shown that the model provides a surp risingly good description of the physics involved.