Long-Pulse, high-current free electron laser with no external focusing

A 2-μ sec-duration electron beam from an induction linac is used to drive a free electron laser (FEL). Experiments using a helical wiggler without any external focusing have made possible an unambiguous study of the FEL radiation. Power levels of 2–4 MW have been measured at ∼ 30 GHz, corresponding to an interaction efficiency of 1.5–3%.