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New X-ray free-electron laser architecture for generating high fluxes of longitudinally coherent 50 keV photons

Materials science needs to study dynamic properties of high-Z materials lead to a unique and challenging set of requirements for future X-ray free-electron lasers (XFELs), with single-pulse fluxes of up to 1012 50 keV X-rays that are both transversely and longitudinally coherent. These parameters cannot be met through an extension of the beam and FEL technologies used at existing and currently planned X-ray FEL facilities. We describe a novel technique to achieve higher fluxes by reducing the transverse beam emittance of high bunch charges and another to achieve longitudinal coherency by pre-modulating the electron beam current before it reaches the undulator. These techniques are investigated numerically and analytically, and also hold potential for increasing performance and decreasing cost of soft X-ray FELs.