SUPPRESSION OF MODE-BEATING IN A SATURATED HOLE-COUPLED FEL OSCILLATOR

In a hole-coupled resonator, either empty or loaded with a linear FEL gain medium, the phenomenon of mode-degeneracy and mode-beating have been studied. When the magnitudes of the eigenvalues, derived from a linear analysis, are equal for two or more dominant eigenmodes, the system cannot achieve a stable beam-profile. We investigate this phenomenon when a saturated FEL is presented within the cavity, thus introducing nonlinearity. We use a three-dimensional FEL oscillator code, based on the amplifier code TDA, and show that mode-beating is suppressed in the nonlinear saturated regime. We suggest a simple, qualitative model for the mechanism responsible for this suppression.