First Operational Results of the Waveguide BPM System for the TESLA Test Facility Free Electron Laser

For the beam based alignment procedure at the TESLA Test Facility Free Electron Laser (TTF FEL) a high precision beam position monitor (BPM) system has been developed and tested. The operation principle of the BPM is based on waveguides coupling through small slots to the beam field. Tests in laboratory as well as under beam conditions have proven the functionality of the design. Ten BPMs will be in operation for the next run of the TTF FEL starting in July 2000. This papers describes the system design and first measurements under beam at the TTF FEL.