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14th International Conference on Synchrotron Radiation Instrumentation, SRI 2021, Hamburg, Germany, 28 Mar 2022 - 1 Apr 2022; Journal of physics / Conference Series 2380(1), 012017 (2023). doi:10.1088/1742-6596/2380/1/012017, The use of circularly polarized soft X-rays at the FLASH-FEL at DESY will be a very versatile tool for investigation of dynamic properties in nanomagnetism. For that purpose, the development of a variable polarization undulator was started to provide an afterburner downstream of the FLASH2 SASE undulators. It will serve to produce circularly polarized light with a wavelength of 1.33 nm to 1.77 nm (890 eV - 700 eV) to investigate the L-edges of Fe, Co, and Ni. This wavelength range together with the future maximum beam energy of 1.35 GeV at FLASH leaves only a small and ambitious parameter window for the undulator if a noteworthy tunability range shall be provided.We report on design and development of an APPLE-III undulator with 17.5 mm period length operating at a minimum magnetic gap of 8 mm which will make use of a magnetic force compensation scheme. A short prototype has been built to verify and iterate both the mechanical and magnetic concept. Details on the keeper design, results of the magnetic measurements and the tuning concept will be presented., Published by IOP Publ., Bristol

13th International Conference on Synchrotron Radiation Instrumentation, SRI2018, Taipei, Taiwan, 10 Jun 2018 - 15 Jun 2018; AIP conference proceedings 2054(1), 030028 (2019). doi:10.1063/1.5084591, An undulator usually emits radiation at the energy of the fundamental wavelength and the higher harmonics at the same time. Likewise, monochromators with gratings or low-indexed crystals also transmit these higher harmonics with substantial efficiency. Most experiments, however, require a clean monochromatic spectrum and use mirrors or a detuning of the monochromator to suppress the higher harmonics in the spectrum. A quasi-periodic undulator is a well- established device which shifts the position of the higher harmonics to non-integer multiples of the fundamental and helps to improve the signal-to-background ratio in the measurement significantly.We have implemented a new alternative concept for suppression of higher harmonics which can be adapted on the fly during operation of the undulator. It is based on creating a distinct phase step in the center of the magnet structure which leads to a tailored distortion of the emitted spectrum. For that purpose, a permanent magnet phase shifter is embedded into the magnet structure of a planar hybrid undulator. We discuss the principle and technical implementation of this scheme, and present first experimental results., Published by AIP, Melville, NY

A record low horizontal emittance of 1 nm-rad was successfully obtained in PETRA III third generation synchrotron light source. A key system that allowed reaching such value includes 20 permanent magnet damping wigglers installed in two long straight sections. The wigglers radiate almost 1 MW at maximum current of hard X-ray radiation which issues a challenge for the design of SR absorbers and vacuum system components for the damping wiggler section. The paper describes in detail the design consideration, manufacturing and experimental performance of absorbers and vacuum system. The first experimental results of PETRA III damping wiggler section operation are presented.

The Petra III synchrotron radiation source was developed based on the Petra-II 6-GeV electron accelerator (DESY). After installing the system for radiation damping, the horizontal emittance of the electron beam of Petra III decreased from 5 nm rad to 1 nm rad, which is a record parameter for this class of installations. The system of radiation damping includes 20 permanent magnet wigglers installed in two straight sections, 50 m each. The total radiation power of the wigglers reaches 800 kW. The wigglers used in the radiation damping system of Petra III were developed in collaboration with DESY (Hamburg) and fabricated by the Budker Institute of Nuclear Physics. The wiggler length is 4.04 m, the gap between the poles is 24 mm, the maximum magnetic field is B = 1.52−1.56 T, and the period is λ = 20 cm. This paper describes the design features of the permanent magnet wigglers and the methods and results of adjustment of the wiggler operating parameters.

At the end of 2009, an extremely low horizontal emittance of 1 nm rad was achieved at the PETRA-III storage ring (Hamburg), a new third-generation SR source with an energy of 6 GeV, which offers new opportunities for SR experiments. Such an emittance was achieved through the efficient operation of a 4-m permanent magnet, with damping wigglers installed in long straight sections of the ring. The required final magnetic characteristics of the wigglers were achieved using the hardware and software package developed at the Budker Institute of Nuclear Physics (Novosibirsk). This paper briefly describes the magnetic measuring techniques, the equipment used and their parameters. A special section is devoted to the description of the programs for equipment control, data processing and presenting.

Partial radiation damage has been observed over the previous five years of operation for a few of the PETRA III permanent magnet undulators at DESY. The degradation of the affected devices has been observed by a change in the energy tuning curves and the spectral properties of the undulator harmonics, and also by direct measurements of the peak field distribution of the magnet structure in the storage ring tunnel [1]. During the recent shutdown of the machine, two undulators were removed from the tunnel for repair. One of the devices (U29) has been retuned after flipping of all magnets of the hybrid structure. In addition to this temporary repair, one further magnet structure (U23) has been completely disassembled and refurbished by application of a rare earth diffusion process and a coating to the permanent magnets. We will report on the details of the refurbishment of these undulators which were both fully brought back to specifications and are meanwhile back in operation.

The 3$^{rd}$ generation low-emittance 6 GeV PETRA III facility has been substantially modified to add new beamlines. This extension project involved the complete removal and reconstruction of part of the storage ring with a double-bend achromat lattice as well as the construction of two new experimental halls. Making use of two long straight sections and a canted undulator scheme in the rebuilt arcs, up to ten new insertion device beamlines can be accommodated. In the current phase of the project, seven insertion device and one bending magnet beamline are being implemented.

DESY presently operates 14 independent insertion device (ID) beamlines at its 6 GeV storage ring PETRA III. Besides the 2 m long standard undulators U29 and U32, several special IDs of up to 5 m length have been installed to meet the experimental requests for high energy X-rays, elliptically polarized light, and a higher degree of coherence. Two additional half octants of the ring have recently been reconstructed, in order to extend the experimental capabilities at PETRA III. The straight sections also allow for installation of IDs of 2 m or 5 m length. This article gives an overview of the ID key parameters, the spectral properties and the brilliance of the current undulators installed at PETRA III. It also presents the characteristics of so me of the upcoming special IDs, like in-vacuum and short undulators.

At present, the storage ring DORIS III (4.5 GeV, 150 mA) serves as the main source for synchrotron radiation experiments at DESY. DORIS III is a second generation storage ring with a rather large emittance of 404 nmrad, thus producing high flux X-ray beams of comparatively low brilliance. In order to follow the increasing user request for high brilliance beams, DESY will rebuild the storage ring PETRA into a very low emittance synchrotron radiation source called PETRA III. PETRA (positron electron tandem ring accelerator) is a storage ring with 2.304 km circumference, which was built in 1976 as an e+ - e− collider. Currently PETRA is used as a pre-accelerator for the proton-lepton collider HERA. In parallel it also serves one undulator beamline in parasitic mode.

The structural and dynamical properties of molecular oxygen in submonolayer coverage adsorbed on Cu(100) were investigated by means of oxygen K-edge photoabsorption. The adsorption geometry of the O 2 molecules, as well as the disorder and anharmonic contributions to the pair distribution function for the first-nearest-neighbor O-Cu shell were quantitatively determined for well-defined sequential molecular states of physisorption and chemisorption

The Phase-1 of the VUV Free Electron Laser at the TESLA Test Facility finishes in fall 2002. Phase-2, an extension of Phase-1 towards shorter wavelengths is under construction and will be ready for operation in 2003. A radiation wavelength as low as 6 nm will be obtained by raising the electron energy to 1 GeV. There will be only minor changes to the undulator system. Compared to Phase-1, six instead of three undulator segments will be installed. The integrated focusing system will be replaced by an electromagnetic doublet structure. We report about the changes of the undulator, the undulator vacuum system, the separated quadrupoles including a stretched wire alignment systems and the modifications to the beam diagnostic system consisting of pick up monitors and wire scanners.

Radiation damage to undulator systems made of permanent magnet materials like NdFeB or SmCo is a critical issue in SASE projects. It is of even more interest in high-duty cycle machines using superconducting accelerators such as the TESLA Test Facility (TTF), which is a prototype for the future X-FEL at TESLA. This paper reports on experience on the undulator system of the VUV-FEL of TTF-1, which ended on May 6, 2002 after nearly 3 years of operation. The radiation exposure of the undulator system was recorded continuously and meticulously over the whole installation period in the TTF linac. Results of these dosage measurements as well as magnetic measurements after de-installation are reported. A comparison with magnetic field data taken prior to installation is given.

An X-ray diagnostic station will be installed for each of the XFEL undulator beamlines at TESLA. Primary purpose of the X-ray diagnostics is to provide an additional tool for alignment and commissioning of the numerous undulator cells along an XFEL beamline independently from electron-beam-based alignment procedures. Both methods will complement one another. The X-ray diagnostic station will be a sensitive instrument generating essential input for the undulator control system. The diagnostic station will be located about 120 m downstream from the last undulator cell. Total flux measurements will verify the XFEL's gain. Analysis of the spectral and spatial distribution of the spontaneous radiation of individual or several consecutive undulator segments will be used to optimize angle and position of the electron beam trajectory, to verify the magnetic gap, and to adjust the phase match between two undulator segments. The two latter purposes cannot be served by electron-beam-based alignment.

PETRA III is a new hard X-ray synchrotron radiation source, operating at 6 GeV with a beam current of up to 100 mA and extremely low horizontal emittance of 1 nm rad. Such low emittance is achieved by using two 100 m long damping wiggler sections which reduce the emittance by a factor of 4. Altogether the damping sections contain 20 wigglers of 4m length each. The emitted synchrotron radiation power produced by wigglers amounts to 420 kW at 100 mA beam current in total. In the new octant of PETRA III, there are 14 undulator beamlines, with a brilliance up to 1021 (s mrad2 mm2 0.1% BW)−1 which cover an energy range from 0.3 keV to more than 100 keV. The low emittance raises very high requirements to the field quality of the insertion devices. At first, it should not affect the positron beam trajectory. Secondly, the spectral properties of the radiation created, like the intensity of higher harmonics, should not be limited by the undulator field quality, but by the beam emittance effects in order to have some reserve for future machine upgrades or possible radiation demagnetization. This paper presents the current status of PETRA III insertion devices and describes intermediate commissioning results like impact of IDs on the positron beam orbit or photon beam and radiation problems.

Colloids of nanocrystalline tin dioxide containing 9.1 at. % and 16.7 at. % antimony have been prepared by the coprecipitation method. High-resolution transmission electron microscopy (TEM) images show crystalline particles in the 2–6 nm size regime. X-ray powder diffraction patterns of nanocrystalline powders obtained by drying the colloids and heating to 100 °C indicate the same rutile lattice structure known from bulk SnO2. On heating to 500 °C in air, the nanocrystalline powder shows a slight increase in particle size but especially a change in color from yellowish to bluish which is accompanied by the development of n-type conductivity. The coordination of antimony in the SnO2 nanocrystallites has been investigated by extended x-ray absorption fine structure measurements (EXAFS) at the Sb K-edge at 5 K while its valence state was determined by near edge x-ray absorption fine structure measurements (XANES) at the Sb L1 edge. The Sb higher neighbor shell distances in the doped material differ from the ...

Three management programmes to improve the reproductive performance of a dairy herd were compared in a prospective controlled field study on one commercial farm. A total of 542 cows were examined for endometritis 22 to 28 days postpartum and assigned to one of three treatment groups: in group 1 the cows with signs of endometritis were treated with an intrauterine infusion of 100 ml of a 2 per cent polycondensated m-cresolsulphuric acid formaldehyde solution; in group 2 the cows with signs of endometritis were treated with an intrauterine infusion of 125 ml of a 20 per cent eucalyptus compositum solution; and in group 3 all the cows were injected intramuscularly with 0.75 mg of tiaprost, an analogue of prostaglandin F2alpha (PGF2alpha) at two-week intervals, starting on day 43, until they were inseminated. Thirty-four per cent of the cows showed signs of endometritis. In group 3, oestrus detection efficiency was significantly higher than in groups 1 and 2 (P

We have performed Ni K-edge extended x-ray-absorption fine structure measurements on ${\mathrm{YNi}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ superconductor ${(T}_{c}\ensuremath{\sim}15.2$ K) in the temperature range 5--220 K. The results show that local structure is distorted from a perfect $I4/mmm$ crystalline structure expected from diffraction measurements below ${T}_{p}\ensuremath{\sim}60$ K. Two different Ni-Ni distances separated by $\ensuremath{\sim}0.09$ \AA{} may be extracted at 5 K. We argue that ${\mathrm{YNi}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ is inhomogeneous at the atomic length scale and discuss a possible reason for the observed distortions.

In spite of their technical use and relevance the structural properties of diesel engine exhaust gas catalysts are not yet understood on an atomic scale. This study investigates structural changes during aging of Pt/V2O5/TiO2 based catalysts in order to get insight into the mutual interaction of the active constituents. X-ray photoelectron spectrometry, secondary ion mass spectrometry and X-ray absorption fine structure measurements were used to characterize the chemical composition and the electronic and geometric structure of the catalyst's surface and bulk. In the freshly prepared catalyst the interaction among the active species turns out to be moderate, i.e. vanadium is present in a distorted 5+ state. TiO2, as expected, is present as in the precursor and Pt is found to form monometallic clusters of about 16 A diameter without any significant interaction with the other metal species. Particularly, no alloying is observed. Upon aging of the catalyst vanadium is reduced to 4+ and preferentially orders in a VO2 structure although other minor phases may also be present. This is accompanied by a partial transformation of TiO2 from the initial anatase to rutile. Like V, Pt undergoes a strong modification upon aging: Pt is partly oxidized but still forms metal particles with a slightly smaller size.

Thiolcapped CdTe nanocrystals (18 A diameter) are investigated by extended x-ray absorption fine structure (EXAFS) measurements between 8 and 290 K at the Cd and Te K-edge. The different coordination sites of Cd in the particle core and at the surface are identified and are consistent with a CdTe particle core which is covered by a Cd–SR surface layer (R=organic rest). We are able to study individually changes of the properties of the interior and the surface of the nanoparticle with respect to bulk material. Structure and dynamics of the CdTe nanocrystals are mainly altered by the requirement of heteroepitaxial growth at the interface between the CdTe core and the Cd–SR shell. As a consequence, bond lengths and Debye temperatures of particle core and surface show a tendency to accommodate in thiolcapped CdTe nanocrystals. The trends in bond lengths variation observed in the experiment can be reproduced by calculations of the strain distribution induced by the lattice mismatch in a simplified isotropic mo...

The local structure around the Cu atoms in rare earth (RE) doped (La,Sr) 2 CuO 4 has been studied by means of measuring the X-ray absorption fine structure (XAFS) at the Cu K-edge. On the local scale the tilting angle of the oxygen octahedra surrounding a Cu atom depends on the Sr and RE content. No anomalies indicating charge modulation in this system have been found.

Using magnetic circular X-ray dichroism (MCXD), Co/Ni, Cu/Co and Cu/Ni bilayers and Co/Cu/Ni and Ni/Cu/Co trilayers grown on a Cu(001) substrate were investigated. The Co layers were about 2 monolayers (ML) and the Ni layers were between 1.5 and 4.5 ML thick. It was observed that, for Co/Ni bilayers, the entire system has only one Curie temperature, T c . After having been covered by 2-7 ML Cu, Ni and Co films exhibit a significantly lower Tc. For trilayers, different Curie temperatures were determined for Ni and Co when separated by a 2-6 ML Cu spacer. The coupling of Ni and Co layers was found to be both ferromagnetic and antiferromagnetic, depending on the spacer thickness and the order of the layers.

The coverage dependence of surface structures and vibrations of ClNi(100) have been investigated by means of Cl K-edge SEXAFS (surface extended X-ray absorption fine structure) spectroscopy. In the 0.25 ML phase, Cl was found to locate on the fourfold hollow site with little or no surface reconstructions, this being similar to the c(2 × 2) phase with 0.50 ML Cl. The ClNi bond distance was determined to be 2.31 ± 0.02 A for 0.25 ML, which is slightly shorter than that of 2.35 ± 0.02 A for 0.50 ML. The temperature dependence of the SEXAFS spectra was analyzed to yield the second- and third-order cumulants which provide harmonic and anharmonic force constants. The ClNi chemical bond was consequently found to be stiffer and less anharmonic in the 0.25 ML state than in the 0.50 ML state, this corresponding to a slightly shorter bond distance at a lower coverage. Such a trend is discussed in terms of charge transfer from substrate to adsorbate and the repulsive interaction between adsorbates.

Temperature and angle dependent surface extended X-ray absorption fine structure (SEXAFS) measurements are reported for c(2 × 2)ClNi(100). A complete dynamic analysis including SEXAFS Debye-Waller factor and mean cubic relative displacement is presented for nearest neighbour (n.n.) and for the first time next nearest neighbour (n.n.n.) ClNi coordinations and compared with the data available on c(2 × 2)SNi(100). The ClNi bonding to the second layer Ni atoms seems to be stronger than for SNi. Einstein temperatures for the first and second ClNi coordinations suggest that in the present system vibrations associated with longer out-of-plane bonds are more anharmonic than the shorter and relatively stronger in-plane bonds.

Initiating the gain process in a free-electron laser (FEL) from an external highly coherent source of radiation is a promising way to improve the pulse properties such as temporal coherence and synchronization performance in time-resolved pump-probe experiments at FEL facilities, but this so-called "seeding" suffers from the lack of adequate sources at short wavelengths. We report on the first successful seeding at a wavelength as short as 38.2 nm, resulting in GW-level, coherent FEL radiation pulses at this wavelength as well as significant second harmonic emission at 19.1 nm. The external seed pulses are about 1 order of magnitude shorter compared to previous experiments allowing an ultimate time resolution for the investigation of dynamic processes enabling breakthroughs in ultrafast science with FELs. The seeding pulse is the 21st harmonic of an 800-nm, 15-fs (rms) laser pulse generated in an argon medium. Methods for finding the overlap of seed pulses with electron bunches in spatial, longitudinal, and spectral dimensions are discussed and results are presented. The experiment was conducted at FLASH, the FEL user facility at DESY in Hamburg, Germany. (Less)

We report near-edge x-ray-absorption fine-structure (NEXAFS) and magnetic circular x-ray dichroism (MCXD) measurements of 4-ML Ni films grown on Cu(100). The films were exposed to oxygen which then adsorbed in different adsorption states. The changes in the density of states as probed at the Ni ${\mathit{L}}_{2,3}$ edges, the oxygen K edge, as well as the magnetic response of the sample are investigated simultaneously for the various adsorption states that range from ${\mathrm{O}}_{2}$/Ni at 38 K to an ultrathin film of NiO. The NEXAFS spectra provide a characterization of the changes in the different nickel 3d, 4sp, and oxygen 2p density of states above the Fermi level. These states dominate the interaction of the oxygen and nickel atoms and can be studied separately using the element specificity of x-ray absorption. We find that 0.5 ML of atomic oxygen suppresses the magnetization corresponding to one layer of Ni, and for 1.5 ML no ferromagnetic response from a 4-ML film at 38 K could be detected. \textcopyright{} 1996 The American Physical Society.

We report magnetic circular X-ray dichroism (MCXD) measurements of ultrathin Ni films grown on Cu(100). The Curie temperature of the films is determined by means of a.c. MXCD susceptibility, a technique that allows T c to be probed precisely and unambiguously. Furthermore, the interaction of submonolayer oxygen with the films, adsorbed in physisorbed molecular and atomic states, is studied. The decrease in the magnetic response of the sample is investigated systematically for various adsorption states of increasing chemisorption strength. The oxygen induced changes in the MCXD difference and in the absorption features measured with linear polarized light provide a better characterization of the electronic states involved in the MCXD response. The magnetism of the Ni films is already influenced by O 2 molecules in a physisorbed state, a c(2 × 2) overlayer of atomic oxygen is found to neutralize the magnetism of two layers of an ultrathin Ni film.

An overview for a dynamical SEXAFS analysis for several systems is presented in terms of effective pair potentials. Model potentials of Madelung type are found to describe well the adsorption of N, ...

Values for the magnetic moments of 3d transition metals have been calculated from magnetic circular X-ray dichroism measurements using sum rules. In this work we reveal that these calculations are sensitive to a damping effect resulting from a decrease in photon penetration at the L3.2 peaks. Known as saturation effects, we present a simple correction to compensate for this phenomenon. We also show that the magnetic moments, as determined using sum rules, are relatively insensitive to the step function fitted to the absorption spectra. The magnetic moments derived from our data differ from the known ground-state moments. The corresponding collective factors appear to be transferable between cobalt and nickel.

We report Magnetic Circular X-ray Dichroism (MCXD) measurements of ultrathin monolayers (ML) and bulk-like Co films grown on a Cu(100) surface. No increase is observed in the orbital magnetic moment of the Co atoms for the ultrathin films in contrast to expectations due to symmetry lowering on the surface. We developed a new ac field modulated MCXD-susceptibility technique permitting accurate measurements of the critical temperature T c . At about 1.8 ML, T c suddenly increases by more than 150 K when the film structure changes from hetero-to homoepitaxial growth.

We present soft X-ray magnetic circular X-ray dichroism (MCXD) measurements at the Ni L edges of thin Ni films on Cu(100) with a thickness between 1 and 7 monolayers. The data were measured around the L 3 edge covering the whole temperature range up to the critical temperature. Furthermore, measurements around both the L 3 and L 2 edges were performed at low temperatures. The temperature variation of the MCXD signal and the critical temperatures of the films as a function of their thickness are discussed and compared to results of other studies

FLASH has been a user facility since 2005, delivering radiation in the wavelength range between 7 and 47 nm using the SASE principle. After the present upgrade, the wavelength range is extended to 4.45 nm. With the third harmonic accelerating module in place to linearize the longitudinal phase space, the stability and reproducibility of the machine is substantially improved. The user requests for beam time by far exceeds the time available. In order to increase user beam time and to improve the radiation properties delivered to users, a major extension of the user facility called FLASH II has been proposed by DESY in collaboration with the HZB. FLASH II is a seeded FEL in the parameter range of FLASH. As logical continuation, the seeding with HHG which started with sFLASH will result in direct seeding. Because in the foreseeable future there will probably not be HHG seed lasers available at high repetition rates down to wavelengths of 4 nm, a cascaded HGHG scheme is proposed to produce short wavelengths. After a first design report, the project now enters its technical design phase. During this time, the FLASH beam parameters after the present upgrade 2009/2010 will be characterized and the present design will be re-evaluated and adjusted. In addition, start-to-end simulations will complete the simulations which have been performed so far, including a design of the extraction area.

Helmholtzzentrum Berlin has built an APPLE II undulator for the storage ring PETRA III. The device has a total length of 5m and a minimum gap of 11mm. The high magnetic forces in particular in the inclined mode have been analyzed by means of finite element methods (FEM). Specific mechanic components such as flexible joints have been optimized to cope with the gap‐ and shift‐dependent 3D‐forces and a sophisticated control and drive system has been implemented. After completion of the device, detailed laser interferometer measurements for all operation modes have been performed. The data are compared to the FEM simulations.

When Raman spectra are excited in the near-infrared range, the probability of fluorescence of the sample or its impurities, obstructing the Raman spectrum, is reduced considerably. The ν 4 decrease of the intensity can be compensated by using FT-spectrometers and spherical cuvettes. Noise is reduced by eliminating the exciting line (reduction to about 10 −12 ) with only small reduction of the intensity of the Raman lines. With no extra time necessary the ‘Stokes’- and ‘anti-Stokes’ Raman lines can be recorded in order to determine the temperature of the sample. Examples shown include colored samples, polymers and micro Raman spectra of bio material.

We report Magnetic Circular X-ray Dichroism (MCXD) measurements of Ni, Co and Fe overlayers on a Cu(100) surface. These films grow pseudomorphically and were characterized in situ. MCXD measurements as function of the X-ray incidence angle allow saturation effects to be removed before applying the MCXD sum rules for the determination of magnetic moments. By applying the MCXD sum rules to thick overlayers we obtain values for the magnetic moments that differ from those for the bulk. A comparison of the present set of data to others in the literature indicates that the origin for this discrepancy appears to be linked to the different crystal structure of these overlayers on various substrates.

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.

A 4 m long hard X‐ray wiggler has been built and installed in the DORIS III storage ring at DESY. The device replaces an old wiggler especially designed for angiography studies. Future use of this beamline at the HARWI straight section has been dedicated to hard X‐ray scattering and diffraction experiments for material science and geological investigations. The required energy range is from 30 keV to about 200 keV with emphasis on the ∼100 keV spectral range. The magnet configuration corresponds to a hybrid structure with additional side magnets to achieve a 2 T peak field for the specified period length of 110 mm. The wiggler position in the storage ring has been moved 8 m upstream into the next cell which allowed for reduction of the minimum magnetic wiggler gap to 14 mm.

After reconstruction, 8 straight sections will be available for installation of undulators in PETRA III at DESY. Five of these straights will be split up into two parts separated by a 5mrad bend giving space for totally 13 undulators of 2m or 5m length. Additionally, one long straight section will be available to accommodate a 20m long device. A common development of planar undulators for both, the PETRA III and the XFEL project has been started recently. First devices, which will be available in the near future, are expected to meet the more demanding requirements regarding specification and performance of either project. Besides, a quasi‐periodic undulator with shifted higher harmonics and an APPLE2 device generating circular polarized light in the VUV region are in the design phase.

Within the reconstruction of the PETRA booster ring at DESY towards a third generation light source after 2007, damping wigglers will be installed to reduce the emittance to a value of 1 nmrad. Two damping sections in the long straights of PETRA have been assigned to accommodate 20 wigglers in total. The wigglers will be permanent magnet devices with a fixed gap which are surrounded by an iron enclosure to reduce the leakage flux. Each wiggler will provide a damping integral of 4 T2m per segment and generate a synchrotron radiation power of 42 kW. A short one period long prototype has recently been built to prove the magnetic design and study the correction scheme for tuning the pole strength. The wiggler segments will be followed by an SR absorber protecting the downstream quadrupole and successive wiggler segment. The accumulated on-axis power of about 200 kW will be taken up by the final absorber at the damping section end.

Published online 16 November 2005 Groupe SERA; Many scientific disciplines ranging from physics, chemistry and biology to material sciences, geophysics and medical diagnostics need a powerful X-ray source with pulse lengths in the femtosecond range [1-4]. This would allow, for example, time-resolved observation of chemical reactions with atomic resolution. Such radiation of extreme intensity, and tunable over a wide range of wavelengths, can be accomplished using high-gain free-electron lasers (FEL) [5-10]. Here we present results of the first successful operation of an FEL at a wavelength of 32 nm, with ultra-short pulses (25 fs FWHM), a peak power at the Gigawatt level, and a high degree of transverse and longitudinal coherence. The experimental data are in full agreement with theory. This is the shortest wavelength achieved with an FEL to date and an important milestone towards a user facility designed for wavelengths down to 6 nm. With a peak brilliance exceeding the state-of-the-art of synchrotron radiation sources [4] by seven orders of magnitude, this device opens a new field of experiments, and it paves the way towards sources with even shorter wavelengths, such as the Linac Coherent Light Source [3] at Stanford, USA, and the European X-ray Free Electron Laser Facility [4] in Hamburg, Germany.

DESY in Hamburg, Germany, has decided to reconstruct its 2.304 km long storage ring PETRA II into a third generation synchrotron radiation source starting 2007. The synchrotron source will operate at 6 GeV particle energy, 100 mA current and an emittance of 1 nmrad. In the first phase thirteen independent undulator beamlines will be available for user experiments.

Beginning in 2007, the present PETRA storage ring at DESY will be reconstructed towards a dedicated third generation light source operating at 6 GeV. An emittance down to 1 nmrad can be achieved by means of damping wigglers. We propose a compact permanent magnet wiggler with fixed gap which will be installed in the long straight sections of PETRA. The paper discusses the magnetic design, field distribution, and optical properties. A damping integral ID ∼ 1.25 T2m per meter wiggler will be reached. The totally required wiggler length of about 80 m will be split into 5 m long segments, each followed by an absorber. The development of these damping wigglers will have a strong spin‐off for the ones planned in the damping rings of the TESLA linear collider.

The adsorption of 0.5 monolayer of atomic nitrogen on a Cu(100) surface has been studied by means of temperature- and angle-dependent surface-extended x-ray-absorption fine-structure (SEXAFS) measurements. The c (2×2) surface structure on the Cu(100) surface was obtained both by (i) adsorption of iongun-activated nitrogen at room temperature and by (ii) thermal dissociation of NH 3 adsorbed at 50 K. The measured data were directly analyzed by means of Fourier-filtering techniques and were also compared to multiple-scattering calculations. It can be shown that for both preparation methods the nitrogen adsorbs in a fourfold hollow site with a vertical distance of 0.4 A towards the topmost Cu layer which undergoes an outward relaxation of 4% with respect to the bulk value