PERFORMANCE STUDY OF HIGH BANDWIDTH PICKUPS INSTALLED AT FLASH AND ELBE FOR FEMTOSECOND-PRECISION ARRIVAL TIME MONITORS

At today’s free-electron lasers, high-resolution electron bunch arrival time measurements have become increasingly more important in fast feedback systems for a timing jitter reduction down to the femtosecond level as well as for time-resolved pump-probe experiments. This is fulfilled by arrival time monitors which employ an electro-optical detectionschemebymeansofsynchronisedultrashortlaserpulses. Even more, at FLASH and the European XFEL the measurement has to cover a wide range of bunch charges from 1nC down to 20pC with equally sub-10fs resolution. To meet these requirements, recently a high bandwidth pickup electrode with a cut-off frequency above 40GHz has been developed. These pickups are installed at the macro-pulsed SRF accelerator of the free-electron laser FLASH and at the macro-pulsed continuous wave SRF accelerator ELBE. In this paper we present an evaluation of the pickup performance by direct signal measurements with high bandwidth oscilloscopes and by use of the electro-optical arrival time monitor.