• M. Hüning, M. Schmitz
  DESY, Hamburg

The Linac II at DESY consists of a 6A/150kV DC electron gun, a 400 MeV primary electron linac, a 800 MW positron converter, and a 450 MeV secondary electron/positron linac. The Particle Intensity Accumulator (PIA) is also considered part of the injector complex accumulating and damping the 50 Hz beam pulses from the linac and transferring them with a rate of 6.25 Hz or 3.125 Hz into the Synchrotron DESY II. The typical positrons rates are 6·10¹⁰/s. DESY II and Linac II will serve as injectors for the two synchrotron light facilities PETRA III and DORIS. Since PETRA III will operate in top-up mode, Linac availability of 98-99% are required. DORIS requires positrons for operation. Therefore during top-up mode positrons are required for both rings. In order to maintain its reliability over the operation time of the new facility PETRA III, the major components of the linac were renovated. Some components were redesigned taking into account experience from 30 years of operation.

• E. Vogel, W. Decking, M. Dohlus, M.G. Hoffmann, M. Hüning, J. Iversen, K. Jensch, G. Kreps, T. Limberg, A. Matheisen, W.-D. Möller, K. Rehlich, A. Schmidt, J.K. Sekutowicz, W. Singer
  DESY, Hamburg
• A. Bosotti, P. Pierini, D. Sertore
  INFN/LASA, Segrate (MI)
• H.T. Edwards, E.R. Harms, T.N. Khabiboulline
  Fermilab, Batavia

Ultra short bunches with high peak current are required for the creation of high brilliance coherent light in the VUV and X-ray range in undulators. At the Free Electron Laser in Hamburg (FLASH) and the European X-ray free electron laser (XFEL) they are obtained by a two stage bunch compression scheme based on acceleration off the rf field crest and transverse magnetic chicanes. The deviation of the rf field's sine shape from a straight line leads to long bunch tails and reduces the peak current. This effect can be eliminated by adding a third harmonic rf system. The paper gives an overview on the actual status of the beam dynamical examinations and as well on the development of the third harmonic sub-systems like modules, cavities and radio frequency systems for FLASH and the XFEL.