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This paper reports about aspects of design, manufacturing, and commissioning of the 12 FLASH2 variable gap undulator segments. The accuracy of gap drive and encoder systems was tested by magnetic measurements; changes in the phase error proved to be a highly sensitive probe to verify a reproducibility of 1 μm. After magnetic tuning of the IDs, the remaining gap dependence in the field integrals could be successfully compensated by corrector coils. Inconsiderate handling of components during assembling necessitated an elaborate demagnetisation process before the tuning could start., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

In the new octant of PETRA~III, there are 14 undulator beamlines covering photon energy range from 0.3keV to 150keV. There are also 80m of damping wigglers in order to achieve a low emittance of 1nmrad. Some of these devices, operating at PETRAIII since 2008, accumulated total radiation doses of about 100kGy. Visible corrosion at the magnet structures of some permanent magnet undulators setting in after a few years and a high dose rate measured regularly by thermoluminescent dosimeters (TLDs) gave reason to inspect the magnetic field of all insertion devices in the PETRA tunnel. This paper presents details of the magnetic field degradation caused by radiation damage to the undulator magnets. For some undulators changes in the spectral properties of the generated light were observed. It was measured with different taper settings in order to partly compensate the nonuniform demagnetization along the structure. The results are compared with the data from the sFLASH undulators and measurements of special 3 pole "sacrificial" undulator, installed in FLASH. Its magnetic field is periodically remeasured and shows field amplitude decrease of 1% per 16kGy accumulated dose., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

A seeded free-electron laser (FEL) experiment at VUV wavelengths, called sFLASH, is being prepared at the existing SASE FEL user facility FLASH. Seed pulses at wavelengths around 35 nm from high harmonic generation (HHG) will interact with the electron beam in sFLASH undulators upstream of the existing SASE undulator section. In this paper the tuning results and performance of the sFLASH undulators are presented., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan