The development of lasers in which the active medium is a relativistic stream of free electrons has evoked much interest. The prospect of operating these continuously tunable, high gain devices at high efficiencies by appropriately tapering the wiggler field parameters has significantly increased the interest in these devices. Variable parameter wiggler free electron laser have been previously considered for operation in the amplifier configuration and also in the micro-pulse, low gain operation in the oscillator configuration. The present analysis extends the range of application to the case of intense, long pulsed electron beams in which the self-consistently derived space charge potential arising from the axial bunching of the particles in the beat wave is not negligible. Also included in this analysis are arbitrarily relativistic beams i.e., no ultra-relativistic beam approximation. We have obtained theoretical expressions for the nonlinear efficiency and present a comparison of these results with a fully nonlinear simulation.
Prepared in collaboration with Berkeley Research Associates, Springfield, VA. Supersedes AD-A187 997.