Abstract
The research center DESY in Germany is one of the leading accelerator centers worldwide. At the facilities located in Hamburg more than 3000 scientists from all over the world do research with photons and in the field of particle physics. Since 1992 the 6-km-long HERA storage ring was used for high energy collisions of electrons/positrons and protons. It consists of two rings. The one for the 27.5 GeV electrons/positrons uses normal conducting magnets. The other one bends the up to 920 GeV protons with superconducting magnets. Data taking at HERA has been terminated only recently. Synchrotron light for 36 experimental stations is generated by the 4.5 GeV storage ring DORIS. The 2.3 km long storage ring PETRA is presently rebuilt into PETRA III, one of the most brilliant X-ray sources worldwide, to start user operation in 2009. Therefore the vacuum system is completely replaced. The construction of the European X-ray Free Electron Laser XFEL, a new international research facility, just has started next to DESY. Its extremely intense X-ray laser flashes with tunable wavelengths down to 0.1 nm will open up completely new experimental possibilities for nearly all fields of natural sciences. The basic process adopted to generate the X-ray pulses is SASE (Self-Amplified Spontaneous Emission). Therefore electron bunches are brought to high energy of about 20 GeV through a superconducting linear accelerator, and conveyed to up to 250 m long undulators where the X-rays are generated. The beam vacuum system of this 3.4 km long straight facility contains sections operated at room temperature as well as at 2 K in the areas of the superconducting accelerating structures. In addition to standard UHV requirements the vacuum system needs to preserve the particle cleanliness of the superconducting cavity surfaces. Further challenges are the undulator vacuum chambers filling more than 750 m with extreme requirements to the surface quality. Unique research opportunities worldwide are offered already now by the 250 m long free-electron laser FLASH, the prototype for the XFEL, which is under operation since several years as a user facility. The vacuum systems of the various DESY accelerator facilities will be discussed in this paper in more detail.
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