ANL, Argonne
An x-ray free-electron laser oscillator (XFELO)[1] promises to be an ideal hard x-ray source, particularly for applications requiring high spectral purity such as Moessbauer spectroscopy and inelastic scattering. Progress has been made in several areas of XFELO study: Performance of concrete XFELO cases with tunable, four-diamond crystal cavities[2] in the 9-20 keV range was calculated using the modified GINGER code[3]. We measured the reflectivity of the diamond crystal at 23.7 keV to be near the theoretical value and the thermal expansion coefficient below 100K to be small, indicating that the heat load will not adversely affect XFELO operation. A null feedback system has been implemented that stabilizes the crystal orientation to within 50 nr of the Rocking curve maximum, an encouraging first step towards achieving the <10 nr stability requirements. We are refining the conceptual design of an injector satisfying the XFELO requirements, starting from a thermionic cathode in a low-frequency rf cavity and followed by various beam filtering and manipulation stages. A 300-kV DC cathode assembly is under construction to demonstrate the production of ultralow-emittance beams.
[1] K.-J. Kim, Y. Shvyd’ko, and S. Reiche, PRL 100, 244802 (2008).
[2] K.-J. Kim and Y. Shvyd’ko, PRST-AB, 12, 030703 (2009).
[3] R.R. Lindberg and K.-J. Kim, submitted to PRST-AB.
ANL, Argonne
LBNL, Berkeley, California
Simulations of the x-ray free-electron laser (FEL) oscillator are presented that include transverse effects and realistic Bragg mirror properties with the two-dimensional FEL code GINGER. In the present cases considered, the radiation divergence is much narrower than the mirror acceptance, and the numerical algorithm can be simplified by ignoring the finite angular bandwidth of the mirror. In this regime GINGER shows that the saturated x-ray pulses have 109 photons and are nearly Fourier limited with peak powers in excess of 10 MW. We also include preliminary results for a four-mirror cavity that can be tuned in wavelength over a few percent, with future plans to incorporate the full transverse response of the Bragg mirrors into GINGER to more accurately model this tunable source.