• C. Gerth, F. Ludwig, Ch. Schmidt
  DESY, Hamburg

To exploit the short radiation pulses in pump-probe experiments at single-pass free-electron lasers (FELs), stabilization of the longitudinal profile and arrival time of the electron bunches is an essential prerequisite. Beam energy fluctuations, induced by the cavity field regulation in the accelerating modules, transform into an arrival time jitter in subsequent magnetic chicanes used for bunch compression due to the longitudinal dispersion. The development of beam based monitors is of particular importance for the validation and optimization of the cavity field regulation. In this paper we present bunch-resolved energy jitter measurements that have been recorded with a synchrotron radiation monitor at the Free-electron LASer in Hamburg (FLASH). The cavity field detectors of the accelerating module have been identified as the main source of the stochastical noise which corresponds to a beam energy jitter of 0.012%. The reduction of deterministic cavity field imperfections by applying an adaptive feedforward learning algorithm for the cavity field regulation is demonstrated.