• E. Prat, C. Gerth, K.E. Hacker
  DESY, Hamburg

At the Free Electron Laser in Hamburg (FLASH), when the electron beam is accelerated some degrees off-crest in the first accelerator module as during SASE operation, a correlation between the longitudinal position and the beam energy is induced. Between the second and the third dipole of the first bunch compressor (BC2), the horizontal beam position correlates linearly with the beam energy. With additional vertical dispersion, the beam is tilted in the x-y plane in this region, thereby increasing the projected vertical emittance. A systematic study of how vertical dispersion tilts the beam at the BC2 and causes an increase of the vertical emittance is presented here. The dispersion is generated by applying vertical trajectory bumps through the first accelerator module.

• C. Behrens, C. Gerth, I. Zagorodnov
  DESY, Hamburg

The free-electron laser (FEL) user facility FLASH at DESY operates a high-gain FEL and provides radiation in the vacuum-ultraviolet and soft X-ray regime. In order to improve the capability and performance of the facility, FLASH will be upgraded with a third-harmonic (3.9 GHz) RF system to linearise the longitudinal phase space in front of the bunch compressors. For the study of the phase space linearisation, a new diagnostic and matching section located directly in front of the undulators which are used for the generation of SASE (self-amplified spontaneous emission) was designed. This section makes it possible to determine sliced beam parameters with high longitudinal resolution. In this paper, we describe the design considerations for this diagnostic section and demonstrate the expected performance by means of particle tracking simulations.