NON-WIGGLER-AVERAGED THEORY OF SHORT-WAVELENGTH FREE-ELECTRON LASERS

Short wavelength free-electron lasers are studied using a 3D nonlinear simulation using a superposition of Gauss-Hermite modes. The differen tial equations governing each mode are solved along with the 3D Lorent z force equations (no wiggler average is used) for an ensemble of elec trons. This permits the self-consistent modeling of (1) beam injection , (2) emittance growth, (3) wiggler imperfections and (4) beatatron os cillations. Simulations are performed for a 1.4 (A)ngstrom FEL. Result s indicate that beam emittance is the crucial limiting factor requirin g Delta gamma(z)/gamma(0) less than or equal to 0.01%. The radiation i s sufficiently guided that no severe degradation is found in the effic iency for moderate levels of wiggler fluctuations.