PETRA III - Status of the Storage Ring

The project status for the reconstruction of the 2304 m long existing storage ring PETRA II into a third generation low emittance synchrotron radiation source is presented. To reach the design emittance of 1 nmrad at an energy of 6 GeV together with a beam current of at least 100 mA and a supply of 14 straight sections for the installation of undulators, several fundamental measures are foreseen. For the emittance of 1 nmrad a FODO lattice in seven arcs together with damping wiggler sections in two long straights are envisaged. One eighth of the ring gets new magnets arranged to DBA cells to provide space and the required optics for the undulators. A complete new separately supported vacuum system reduces drastically movements of beam position monitors and magnetic elements due to synchrotron radiation heat load. This is an important precondition for the orbit stabilization system. To beat multi bunch instabilities in order to get a high beam current a powerful wideband feedback system will be established. The planned topping up mode guarantees stable beam current and therefore stable thermal conditions for the experiments.