Variable wiggler free electron laser experiment and theory

The Free Electron Laser (FEL) efficiency can be dramatically enhanced by adiabatically tapering the wiggler field amplitude and/or wavelength. The beam electrons are trapped in the ponderomotive potential well (“bucket”) formed by the wiggler field and the input e.m. signal. By tapering the wiggler, the phase velocity of the bucket can be decreased in a controlled manner. The electrons that are initially trapped can remain trapped and therefore its mean energy decreased if the motion is sufficiently adiabatic. The extracted electron energy goes into radiation providing the amplification of the laser signal. In this paper, we discuss the details of an amplifier experiment in progress at TRW to demonstrate this schere. In addition, the theoretical formulation and simulations being developed to predict and interpret the performance of such a device is presented.