Diagnostic Tools for the Undulator System of the Seeded HGHG-FEL at MAX-lab

Within a collaboration between MAX-lab and BESSY a one stage seeded HGHG-FEL has been set up at Maxlab. BESSY has built the undulator system consisting of a modulator, a radiator and an electromagnetic chicane. BESSY has also installed three types of diagnostic tools: optical fibres for a fast Cherenkov beam loss detection, optical fibres for absolute dose measurements via their radiation-induced attenuation and THz detectors for the characterization of electron bunch properties. During first injections with a laser driven rf-gun the Cherenkov fibres have delivered detailed spatial information on the beam losses inside the beamline. Over the last year the second system, based on powermeter measurements, has detected a total dose of 180Gy. The high sensitivity and low drift of this system has been demonstrated. A THz detector behind the last dipole magnet close to the beam dump provides information on the bunch compression and the laser induced energy modulation. We report on the measurements performed with these diagnostics tools