Tapered-wiggler free-electron laser optimization

Recent threshold analysis of free-electron lasers (FEL's) has indicated that the use of tapered wigglers may allow substantial single-pass electron energy extraction. This has led to a current experimental verification program in which the tapered wiggler is a critical element. This paper discusses the wiggler optimization for single-pass systems in the limit of low gain and extraction. The interaction of wiggler magnet and photon beam parameters is examined to identify configurations which produce maximum electron kinetic energy extraction for a given photon power. The analysis includes both permanent and electromagnet wigglers.