PHOTON SCIENCE

PETRA III beamlines are supplied with light from various undulators tailored to the specific needs of the experiments [1]. Ten out of the 14 undulators are 2 m long planar devices with different period lengths (Fig. 1). The standard undulator (U29) is characterized by full energy tunability and a 1^st harmonic position at 3.5 keV (29 mm period length, K_max=2.2). Lower photon energies down to 2.4 keV are needed by certain X-ray spectroscopy techniques served by the spectroscopy undulator (U32) having a larger period length. A short period device (U23) is optimized for hard X-ray scattering experiments and provides tunability above the 3^rd harmonic. In the long straight section before the new octant, a longer version of U32 (5+5 m) with 12.5 mm minimum gap is installed with the possibility to double the undulator length at a later stage.

This series of standard undulators is complemented by two specialized devices, one for the very hard X-ray regime, the other for XUV techniques. X-rays up to 300 keV as needed for the High Energy Materials Science Beamline will be provided by a 4 m long in-vacuum undulator (U19) having a period length of 19 mm. A minimum gap of 7 mm can be realized for the initial operation phase of the machine. This undulator will mainly be operated at high harmonics and is tunable above the 5^th harmonic at 50 keV. The spectral characteristics are given in Figure 2.
In collaboration with BESSY, an APPLEII undulator (UE65, 65.6 mm period length) was built for the Variable Polarization XUV Beamline at PETRA III. In the circular mode, it covers an energy range from 245 eV to 2.5 keV in the 1^st harmonic and provides a high degree of polarization in the entire energy range [2].