As the electron beam passes between the copper colored magnets, it changes directions. The poles of the magnets alternate, so the electron beam is forced to wiggle up and down. Any wiggling electric charge emits electromagnetic radiation. The type of electromagnetic radiation produced depends on how quickly the charge wiggles.
Slower wiggles can make radio waves or microwaves, while faster wiggles can make x-rays.
The FEL's electron beam will produce infrared light and a future upgrade will allow it to produce ultraviolet light. This page is maintained by Steve Gagnon .