BEAM DYNAMIC STUDIES FOR THE GENERATION OF SHORT SASE

Many users at FLASH work on pump-probe experiments, where time resolution is determined by the duration of the SASE pulses. Therefore users have expressed the strong wish for shorter XUV pulses. The shortest possible pulse is a single longitudinal optical mode of the SASE radiation. The most direct way to realize this at FLASH would be to reduce the electron bunch length to only a few μm at the entrance of the undulator section. A bunch charge of 20 pC is sufficient for the generation of such short bunches. Such a small bunch charge reduces space charge in the injector area drastically and thus makes it possible to shorten the bunch duration directly at the photo-cathode [1]. This in turn helps to overcome technical limitations of the bunch compression due to RF induced non-linearities and minimizes collective effects during the compression process. Beam dynamic studies are being performed to optimize the parameters of the photo injector laser, of the accelerating modules, and of the bunch compression. This includes particle tracking starting from the cathode through the accelerating modules with the ASTRA code and through the dipole chicanes using CSRtrack. The expected SASE pulses are being simulated with the Genesis code.