First-, second-, and third-order achromatic bend systems for free-electron laser applications

The authors evaluated and compared several achromatic bend systems for the application of transporting a spent electron beam exiting the wiggler of a free-electron laser (FEL). For high-power, efficient FELs, the design of a postwiggler electron-beam transport system is challenging because of the large double-peaked momentum distribution caused by the laser. The optics systems had to be able to handle electron-beam power arbitrarily distributed between the two momentum peaks. This system included not only the achromatic bend but also the final transport that involved a beam distribution or rastering system targetting a beamstop. The salient features of 11 achromatic bend systems and the characteristics by which to choose one system over another are discussed.<>