Optical Synchronization and Electron Bunch Diagnostic at ELBE

The recent upgrade of the ELBE accelerator included the installation of a new beamline section which will be used to compress the electron bunches to a duration of 100 fs at a charge of 1 nC. Two THz sources based on coherent transition or diffraction radiation und and an undulator source making use of the compressed bunches. In addition an Xray source based on Thomson backscattering, combining high power lasers with the relativistic electrons, is currently in commissioning phase and will deliver narrow bandwidth and tunable pulses.
To enable time resolved experiments on a 100 fs scale an optical synchronization system has been installed. It is based on a low noise fiber laser oscillator as optical reference. The signal is distributed to the remote stations via singlemode fibers. Drifts introduced by temperature variations and mechanical stress are measured by a balanced optical cross-correlator detection scheme and compensated with fast actuators. A stability of better than 30 fs over several hours has been demonstrated.
Based on the optical synchronization system a bunch arrival time monitor (BAM) has been set up. It is modulating the laser pulse train with a pickup signal from the electric field surrounding the electron bunch. The arrival time information is mapped into an amplitude modulation which can be detected by fast readout electronics. This technique enables arrival time measurements with a few femtosecond resolution.
The talk will give an overview on the ELBE upgrade and in particular on the installation of the synchronization system. First results of the arrival time measurements for both injectors (DC gun, SRF gun) are discussed.