Pfeiffer, SvenSvenPfeifferSchmidt, Jan-ChristianJan-ChristianSchmidtBock, Marie KristinMarie KristinBockSchlarb, HolgerHolgerSchlarbJałmużna, WojciechWojciechJałmużnaLichtenberg, GerwaldGerwaldLichtenbergWerner, HerbertHerbertWerner2023-02-082023-02-082012-05Contributions to the proceedings: 26-28 (2011)http://hdl.handle.net/11420/14761The key for pump-probe and seeding experiments at Free Electron Lasers such as FLASH is a femto-second precise regulation of the bunch arrival time and compression. To achieve this beam based requirements, both for a single bunch and within a bunch train, it is necessary to combine field and beam based feedback loops. We present in this paper an advancement of the currently implemented beam based feedback system at FLASH. The principle of beam based modulation of the RF set point can be superimposed by a direct feedback loop with a beam optimized controller. Recent measurements of the achieved bunch arrival time jitter reduction to 20 fs have shown the performance gain by this direct feedback method [1]. The combination of both approaches will be presented and possible advantages are discussed. Copyright © 2012 by IEEE.enTechnikIngenieurwissenschaftenConference PaperOther