Development of longitudinal feedback system for a storage ring free electron laser

(TU-1-04) Presenting Author: Shigeru Koda

S. Koda, M. Hosaka, J. Yamazaki, M. Katoh and H. Hama(*)  

UVSOR, Insutitue for Molecular Science, (*)Laboratory of Nuclear Science, Tohoku University

Since an FEL micropulse is evolved through huge number of interactions with same electron bunch in storage ring free electron lasers, even a small detuning of the optical cavity limits significantly the evolution of the FEL. Therefore to maintain the best synchronism between the micropulse and the electron bunch is especially important to the oscillation stability. We have been developing a longitudinal feedback system for the UVSOR-FEL.

Based on detected temporal deviation of the micropulse with respect to the electron bunch, the system changes the storage ring rf frequency to control the effective length of the optical cavity. The temporal deviation is measured as a phase between higher harmonic components of revolution frequencies of the micropulse and the electron bunch. Resolution of the phase detection was about 0.5 deg, which corresponds to 5 ps in the domain of microtime. In a preliminary feedback experiment, the system was able to hold the micropulse on the centroid of the electron for a reasonably long time. The control accuracy of the temporal deviation was nearly equal to the resolution of the phase detection. We will report the latest progress of the feedback system in the conference