• V. Balandin, R. Brinkmann, W. Decking, N. Golubeva
  DESY, Hamburg

The post-linac collimation system should simultaneously fulfil several different functions. In first place, during routine operations, it should remove with high efficiency off-momentum and large amplitude halo particles, which could be lost inside undulator modules and become source of radiation-induced demagnetization of the undulator permanent magnets. The system also must protect the undulator modules and other downstream equipment against mis-steered and off-energy beams in the case of machine failure without being destroyed in the process. From beam dynamics point of view, the collimation section should be able to accept bunches with different energies (up to ± 1.5% from nominal energy) and transport them without deterioration not only of transverse, but also of longitudinal beam parameters. In this article we present the optics solution for the post-linac collimation system which fulfils all listed above requirements.

• V. Balandin, N. Golubeva
  DESY, Hamburg

The aim of the FLASH facility linac is to create electron bunches of small transverse emittance and high current for the FLASH free-electron laser at DESY. Available operational experience indicates that in order to optimize SASE signal at different wavelengths or to fine-tune the FEL wavelength, empirical adjustment of the machine parameters is required and, therefore, the sensitivity of the beamline to small changes in the beam energy and in the magnet settings becomes one of the important issues which affects the final performance. In this article the transverse optics of the FLASH beamline with low sensitivity to changes in beam energy and quadrupole settings is presented. This optics is in operation since spring 2006 and has shown a superior performance with respect to the previous setup of the transverse focusing.