Paper  Title  Page 

TUP020  Recent Study in iSASE  393 


The Improved SelfAmplified Spontaneous Radiation (iSASE) scheme has potential to reduce SASE FEL bandwidth. This is achieved by repeatedly delaying the electrons with respect to the radiation pulse using phase shifters in the undulator break sections. It has been shown that the strength, locations and sequences of phase shifters are important to the iSASE performance. Particle swarm optimization algorithm is used to explore the phase shifters configuration space globally.  
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WEP076  Tapering Studies for TW Level Xray FELs with a Superconducting Undulator and Builtin Focusing  726 


Funding: U.S. Department of Energy DESC0009983. Tapering optimization schemes for TeraWatt (TW) level Xray Free Electron Lasers (FELs) are critically sensitive to the length of individual undulator and break sections. Break sections can be considerably shortened if the focusing quadrupole field is superimposed on the undulator field increasing the filling factor and the overall extraction efficiency of the tapered FEL. Furthermore, distributed focusing reduces the FODO length and allows one to use smaller beta functions. This reduces particle detrapping due to betatron motion from the radial tails of the electron beam. We present numerical calculations of the tapering optimization for such an undulator using the three dimensional time dependent code GENESIS. Time dependent simulations show that 8 keV photons can be produced with over 3 TW peak power in a 100m long undulator. We also analyze in detail the time dependent effects leading to power saturation in the taper region. The impact of the synchrotron sideband growth on particle detrapping and taper saturation is discussed. We show that the optimal taper profile obtained from time independent simulation does not yield the maximum extraction efficiency when multifrequency effects are included. A discussion of how to incorporate these effects in a revised model is presented. 

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