Theoretical Analysis of the Radiation Properties of Some Major X‐Ray Free Electron Lasers

Abstract

AbstractA theoretical analysis of the radiation in X‐ray free electron lasers (FELs) LCLS, PAL‐XFEL, SwissFEL, as well as SACLA, FLASH 2, and European XFEL is presented. Major losses in FELs are analytically accounted for and analyzed, using exact expressions for the Bessel factors in terms of the generalized Bessel functions. This allows distinguishing the contributions of key parameters and accounting for the losses individually for each harmonic, considering higher sensitivity of the electron‐photon interaction at higher harmonic wavelengths. The harmonic power evolution along FELs and the spectral width of the radiation lines is studied. The theoretical results are analyzed and are compared with the available experimental data for the FEL experiments. The harmonic generation and amplification in the FELs are modeled and studied with the harmonic lasing self‐seed (HLSS) with separate buncher and radiator, and the results are compared with those for SASE. The spectral properties of the radiation are analytically calculated and compared with the measured spectral characteristics. The advantages of HLSS versus SASE FEL are elucidated in the examples of FLASH2, European XFEL, and SwissFEL. The prospected radiation properties of LCLS‐II FEL are analyzed and the possibilities of using harmonics in this FEL are proposed.