Liu, S. Decking, W. Feng, G. Geloni, G. Kocharyan, V. Serkez, S. Zagorodnov, I. JACoW Geneva, Switzerland 978-3-95450-179-3 10.18429/JACoW-FEL2017-TUP004 English 259-262 TUP004 ion FEL simulation undulator electron Contribution to a conference proceedings 2018 2018-02 https://doi.org/10.18429/JACoW-FEL2017-TUP004 http://jacow.org/fel2017/papers/tup004.pdf For the implementation of Hard X-ray Self-Seeding (HXRSS) at European XFEL, short electron-beam bunches (FWHM ≤ 50 fs) are preferred to mitigate spatio-temperal coupling effect and to fit to the seeding bump width. Therefore, operations with low charges (< 250 pC) are preferred. Longitudinal phase-space optimization has been performed for the 100 pC case by flattening the current distribution. Start-to-end simulations show that, with the optimized distribution, for the photon energy of 14.4 keV, the HXRSS output power, pulse energy and spectral intensity can be increased by a factor of approximately 2 as compared to the nominal working point.