LBNL, Berkeley, California
ANL, Argonne
The oscillator package within the GINGER FEL simulation code has now been extended to include angle-dependent reflectivity properties of Bragg crystals. Previously, the package was modified to include frequency-dependent reflectivity in order to model x-ray FEL oscillators[*] from start up from shot noise to saturation. We will present a summary of the algorithms used for modeling the crystal reflectivity and radiation propagation outside the undulator, discussing various numerical issues relevant to the domain of high Fresnel number and efficient Hankel transforms. We give some sample XFEL-O simulation results obtained with the angle-dependent reflectivity model, with particular attention directed to the longitudinal and transverse coherence of the radiation output.
[*] R.R. Lindberg et al., submitted to PRST-AB, 2010.
LBNL, Berkeley, California
UCB, Berkeley, California
ANL, Argonne
A concept for a tunable soft x-ray free electron laser (FEL) oscillator is proposed and studied numerically. It is based on the idea of echo enabled harmonic generation [1] and takes advantage of the oscillator’s ability to start up from spontaneous emission, thereby eliminating the need for optical lasers. In the proposed concept, harmonic tunability is accomplished through beam manipulations using magnetic chicanes and a tunable radiator while two FEL oscillators remain at a fixed frequency. An additional advantage of the proposed technique is the possibility to utilize multilayer x-ray mirrors with a high backward reflectivity of the order of 70%, allowing the initial beam manipulation to be accomplished at a short wavelength, close to the final soft x-ray output. The high repetition rate soft x-ray output is expected to have longitudinal coherence and a narrow bandwidth.
[1] G. Stupakov, PRL, 2009
ANL, Argonne
European XFEL GmbH, Hamburg
Free-electron lasers for hard x-rays can be constructed in oscillator (XFELO) configuration, providing ultra-high spectral purity and brightness [1]. The average brightness is expected to be several orders of magnitude higher than, and peak brightness comparable to that of SASE XFELs. XFELOs can enable revolutionary scientific opportunities as well as drastically improve experimental techniques developed at third-generation x-ray facilities. Low-loss x-ray crystal cavity and ultra-low-emittance electron beams are two major technical challenges in the realization of XFELOs. The requirements to x-ray cavity components are demanding: diamond crystals and curved grazing incidence mirrors must have near-perfect reflectivity, negligible wave-front distortions, and are subject to very tight tolerances on angular, spatial, and thermal stability under high heat load of the XFELO radiation. This paper gives an overview on the recent progress [2-4] and future plans in the R&D on the feasibility of x-ray cavities for XFELOs. The experimental and simulation studies results provide strong evidence for the feasibility of the x-ray cavities.
1. K-J. Kim, et al, PRL 100 (2008) 244802
2. Yu. Shvyd'ko, et al, Nature Phys. 6 (2010) 196
3. S. Stoupin, Yu. Shvyd'ko, PRL 104 (2010) 085901
4. S. Stoupin et al, Rev. Sci. Instr. 81 (2010) 055108