The PETRA IV project aims at upgrading PETRA III into an ultralow-emittance synchrotron radiation source.

We present the first observation of self-amplified spontaneous emission (SASE) in a free-electron laser (FEL) in the vacuum ultraviolet regime at 109 nm wavelength (11 eV). The observed free-electron laser gain (approximately 3000) and the radiation characteristics, such as dependency on bunch charge, angular distribution, spectral width, and intensity fluctuations, are all consistent with the present models for SASE FELs.

PETRA, currently operating as a proton and positron injector for HERA, has been modified to serve also as a synchrotron radiation source in 1995. Running at 12 GeV with currents up to 60 mA the machine will be a unique source. The PETRA injector optic will be changed locally to suit the requirements of an undulator beam. In addition a new low emittance optic has been examined both theoretically and experimentally. The undulator with a period length of 33" and a maximum field of 0.59 T at a gap of 14" has been installed in the straight section North East. The photon energy range up to 200 keV can be covered using the lst, 3rd and 5th harmonics. At 12 GeV, 60 mA and using the low emittance optic a photon brilliance in excess of IO'* photons/(s O.l%BW 0.1 mrad' mm2) will be obtained. To allow for compatibility between injector and synchrotron radiation operation a keyhole shaped vacuum chamber, with both a wide and narrow aperture for the two operational modes respectively has been constructed. The photon beam travels along a 120 m long beamline until it reaches the experimental hall. The beamline includes elements of the beam position control system and the safety system needed to avoid damage to machine components due to the high power undulator beam.

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At the 12 GeV storage ring PETRA, the ®rst synchrotron radiation beamline uses a 4 m-long undulator. The beamline, with a length of 130 m between source and sample, delivers hard X-ray photons usable up to 300 keV. The photon beam has a total power of 7 kW. Combined with the high brilliance, the powerful beam is very critical for all beamline components. Copper, located at a distance of 26 m, hit by the full undulator beam, melts within 20 ms. Different monitors are described for stable, safe and reliable operation of beam and experiments.