The transformation of the TESLA test facility into the VUV FEL user facility at DESY

After the end of the very successful operation of the TESLA Test Facility in November 2002, the modification of TTF into a VUV FEL user facility took place during the years 2003 and 2004. The injector complex was completely modified. By the beginning of this year 5 cryomodules were installed and the vacuum system was closed. For bunch length measurements there is a special S-band structure driven by a SLAC 5045 Klystron and an Electro-Optical-Sampling Experiment. Six undulator modules of 30 m total length have also been installed. Until May 2004 the five cryogenic modules and their rf power input couplers were conditioned up to full rf power. In one cavity of the first module an accelerating gradient of 35 MV/m with beam could be demonstrated. The last module (No.5) can be reliably operated at an average gradient of 25 MV/m. So far, beam has been sent only through the first module and through the first bunch compressor. First emittance measurements show values around 3 pmm mrad. In the second half of this year completion of installation of technical components like power supplies, beam diagnostic elements etc. took place prior to full commissioning of the entire machine which started in the beginning of September. (orig.)