Speaker
Description
We perform analysis of a typical practical case of FLASH operation with the number of radiation modes in the range pulse M ~ 4 ... 8. Standard tuning procedure (for maximum pulse energy at full undulator length) results in visible energy chirp along the electron bunch such that spectrum bandwidth is increased to about 1% fwhm, visibly wider than natural FEL bandwidth. These features were taken in the current consideration. Simulation results with numerical simulation code FAST are illustrated for the radiation wavelength 18 nm, 13.5 nm and 8 nm. As it was predicted earlier, maximum value for the degree of transverse coherence at FLASH1 is in the range of 0.8, and it is a bit better for the case of FLASH2. Actual value is dependent on the stage of amplification process, and can be visibly lower in the deep post saturation regime. Several experiments on measurements of the degree of transverse coherence have been performed at FLASH1 and FLASH2 so far, and we believe that the results presented here will be useful for analysis of experimental data. From our side we compare simulation results with coherence characteristics measured with statistical methods*, and find good agreement.
Footnotes
- E.A. Schneidmiller and M.V. Yurkov, Coherence properties of the radiation from FLASH, Journal of Modern Optics, Special Issue Short Wavelength Free Electron Lasers and their Interactions with Matter 2015, pp.1-5, DOI:10.1080/09500340.2015.1066456.
** E.A. Schneidmiller and M.V. Yurkov, Coherence Properties of the Radiation from X-ray Free Electron Lasers, CERN Yellow Reports: School Proceedings, Vol. 1, 2018, 539-596; DOI: http://dx.doi.org/10.23730/CYRSP-2018-001.539
