An Experiment on Free Electron Laser Efficiency Enhancement with a Variable Wiggler

Abstract

The demonstration of a tunable, visible wavelength, high power high efficiency laser beam is the ultimate goal of a free electron laser program. However, the current theoretical and experimental data base is so limited that it cannot support the demonstration of the long range program goals in one step. Rather, it requires the evolutionary demonstration of one or more intermediate levels of performance. In particular, it is necessary to verify experimentally the theoretical predictions of high efficiencies for free electron lasers operating in the trapped electron regime with adiabatically tapered magnetic wiggler fields and to determine the influence of operating parameters. An experiment designed to achieve this goal is outlined in this paper. A fraction of the beam electrons is trapped in the ponderomotive well formed by the wiggler and an external EM signal that is to be amplified. The wiggler amplitude and/or wavelength is then modified to extract energy from the trapped electrons. The theory of operation is sufficiently well developed at this time to permit the design of the experimental hardware required. In addition, the experiment has been designed for maximum flexibility to provide for experimental optimization and design variations which may be predicted by more elaborate analytical and numerical models currently under development.