INFN/LASA, Segrate (MI)
Fermilab, Batavia
DESY, Hamburg
The third harmonic cavities that will be used at the injector stage in the XFEL to linearize the rf curvature distortions and minimize beam tails in the bunch compressor are based on the rf structures developed at FNAL for the DESY FLASH linac. The design and fabrication procedures have been modified in order to match the slightly different interfaces of XFEL linac modules and the procedures followed by the industrial production of the main (1.3 GHz) XFEL cavities. A revision of the helium vessel design has been required to match the layout of the cryomodule strings, and a lighter version of the tuner has been designed (derived from the 1.3 GHz ILC blade tuner activities). The main changes introduced in the design of the XFEL cavities and the preliminary experience of the fabrication of three industrially produced and processed third harmonic rf structures are described here.
DESY, Hamburg
INFN/LASA, Segrate (MI)
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.
DESY Zeuthen, Zeuthen
INRNE, Sofia
DESY, Hamburg
YerPhI, Yerevan
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
INFN/LASA, Segrate (MI)
BESSY GmbH, Berlin
Uni HH, Hamburg
MEPhI, Moscow
Funding: This work was partly supported by the European Community, contracts RII3-CT-2004-506008 and 011935, and by the 'Impuls- und Vernetzungsfonds' of the Helmholtz Association, contract number VH-FZ-005.
The Photo Injector Test facility at DESY, Zeuthen site, (PITZ) was built to develop and optimize high brightness electron sources for Free Electron Lasers (FELs) like FLASH and the European XFEL. In the last shutdown a new RF gun cavity with improved water cooling was installed and conditioned. It is the first rf gun where the surface cleaning was done with dry ice technique instead of high pressure water rinsing and it showed a 10 times lower dark current emission than its precursor gun, even at cathode gradients as high as 60M V/m. In addition, a new photo cathode laser system was installed and will be available for operation in spring 2008. It will allow flat-top temporal laser shapes with 2ps rise/fall time. According to beam dynamics simulations this will further improve the beam quality reported at earlier conferences* and will lead to unprecedented low transverse projected emittance beams at a charge level of 1nC. This contribution will summarize the experimental results from the summer 2008 running period covering transverse projected emittance optimization, thermal emittance from the photocathode, longitudinal phase space and first transverse slice emittance measurements.
* L. Staykov et al., "Measurements of the Projected Normalized Transverse Emittance at PITZ", Proceedings of the FEL 2007, Novosibirsk, Russia, August 2007.
