Status of the 3rd Harmonic Systems for FLASH and XFEL in Summer 2008

Ultra short bunches with high peak current are required for the creation of high brilliance coherent light in the VUV and x-ray range in undulators. At the Free Electron Laser in Hamburg (FLASH) and the European x-ray free electron laser (XFEL) they are obtained by a two stage bunch compression scheme based on acceleration off the rf field crest and transverse magnetic chicanes. The deviation of the rf field’s sine shape from a straight line leads to long bunch tails and reduces the peak current. This effect can be eliminated by adding a third harmonic rf system [1, 2, 3]. This paper gives an overview on the actual status of the beam dynamical examinations, as well as on the development of the third harmonic sub-systems like modules, cavities and radio frequency systems for FLASH and the XFEL. For an basic overview on the activities we refer to [3].