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.
PSI, Villigen
DESY, Hamburg
The spectral and angular distribution of the radiation intensity by a single and individually radiating electron is in principle different from what expected from a high density electron beam. For a given wavelength, the beam particle density modifies via a charge form factor the angular and spectral distributions characterizing the radiation emission by a single electron. In particular, under high energy and high particle density conditions, the Transition Radiation (TR) energy spectrum by an electron beam is expected to be affected by the electron-transverse-density that, at very short wavelength even in the visible, in principle - can influence the number of photons emitted at a given wavelength and their angular distribution (brightness increase with density). The investigation of such a phenomenon is relevant to beam diagnostics and to understand the bunch collective effects influencing TR emission. The status of the experimental investigation of the beam-transverse-size effects in the Optical Transition Radiation (OTR) at SLS and, in perspective, at the SwissFEL will be presented and the main formal aspects of the model predicting them will be described.
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.