Beam loss monitors for FEL using optical fiber

Beam losses and beam profiles at particle accelerators can be determined by measuring the ionizing radiation outside the vacuum chamber. The next generations of free electron lasers require novel solutions for beam loss monitor and radiation detection systems. A new concept at the Free-Electron-Laser Hamburg (FLASH) and Photo Injector Test Facility Zeuthen (PITZ) was developed and put into operation. The concept based on optical fibers used as radiation detection sensor. Slow beam loss monitors determine the total ionization dose at selected positions or along the beam line and undulator sections in a response time of a few milliseconds by measuring the radiation-induced attenuation of the fiber. Fast beam loss monitors detect the Cerenkov light generated by relativistic electrons or gamma rays penetrating radiation hard fiber. The new beam loss position and beam profile monitor systems utilize this effect. The time response is below milliseconds with a time resolution of nanoseconds. These monitors provide a technique to improve the beam performance and trace the stability of the over all setting parameters. This paper presents the new diagnostic methods and the operation experience of the systems with a focus on the fast beam loss monitor systems.