Femtosecond level electron bunch diagnostic at quasi-cw SRF accelerators: test facility ELBE

Superconducting radiofrequency (SRF) accelerator technology allows to accelerate electron bunches not only in considerably longer bunch trains than is possible by normal conducting accelerator technology, but also in principle enables a mode of operation that can circumvent any macropulse scheme and provides relativistic electron bunches with real repetition rates scaling from the kHz to GHz regime [1, 2, 3, 4]. In this proceedings we discuss different approaches foreseen for online electron bunch diagnostic at the new femtosecond electron beamline of the superconducting cw RF accelerator ELBE [11]. In medium term we believe the concepts tested at the femtosecond beamline at ELBE are off great importance for various energy recovvery linac accelerators (ERL) coming online in the next few years [2, 4] as well as facilities like the European X-FEL [5] and FLASH [6] when operated in long bunchtrain mode of operation.