DESY, Hamburg
The Free Electron Laser in Hamburg (FLASH) is a SASE FEL user facility and in addition serves as a prototype for the European XFEL. The recent upgrade of FLASH with a higher harmonic RF module opens a new possibility for ultra-short low charge operation. The advantage of small transverse emittance at low charges can be used only with strong, linearized bunch compression. At this report we consider simulations of the beam dynamics at low charges and estimate the expected properties of the radiation at FLASH and the European XFEL. We present first experimental results at FLASH.
DESY, Hamburg
The nonlinearities of the RF fields and the dispersion sections can be corrected with a higher harmonic RF module. In this paper we present an analytical solution for nonlinearity correction up to the third order in a multistage bunch compression and acceleration system without collective effects. A more general solution for a system with collective effects (space charge, wakefields, CSR effects) is found by iterative tracking procedure based on this analytical result. We apply the developed formalism to study two stage bunch compression in FLASH and three stage bunch compression in the European XFEL. Different charges are considered. Analytical estimations of RF tolerances are given.