Free Electron Laser - Return Line
Only a small percentage of the beam's energy is converted into laser light by the wiggler magnet. In order to improve the Free Electron Laser's efficiency, the 'spent' beam is guided back to the linear accelerator portion of the machine where the electrons are once again sent through the cryomodule. The cryomodule isn't used to accelerate the electrons on this second trip, though. The electrons are intentionally sent through the cryomodule 'out of phase' so that their energy can be extracted and given to the 'fresh' beam that is passing through the cryomodule at the same moment. This energy recycling program allows the Free Electron Laser to operate very efficiently.