M. Hagelstein

Characterization of nanocrystalline γ-Fe2O3 with synchrotron radiation techniques

A variety of synchrotron radiation techniques like soft X-ray magnetic circular dichroism, near-edge as well as extended X-ray absorption fine structure, and synchrotron radiation X-ray diffraction have been used to characterise the crystal and electronic structure as well as the magnetic properties of superparamagnetic nanocrystalline samples with the nominal composition γ-Fe2O3. The results are compared with data from bulk reference samples like Fe3O4, Fe3—δO4, α-Fe2O3, and FeO.

The X-ray-fluorescence facility at ANKA, Karlsruhe: Minimum detection limits and micro probe capabilities

Abstract At the recently constructed synchrotron radiation facility ANKA at Karlsruhe, Germany, a beamline partially dedicated to X-ray fluorescence has been constructed where TXRF and micro probe SRXRF experiments can be performed. The beam line with its retractable double multilayer monochromator is described. First measurements on reference samples allow a preliminary characterization of beam line parameters like exploitable energy range and the energy resolution as well as the sensitivity of the set-up in means of minimum detection limits.

Instrumentation development for ESRF beamlines

Abstract We report on instrumentation developments concerning a subset of ESRF beamlines: BL6 & 26 (linear, circular dichroism); BL8 (energy dispersive XAFS); BL18 (multipurpose energy scanned XAFS studies). We review in more detail the instrumentation of BL6 & 26 which are now under commissioning. A 1 4 wave plate was successfully used at 2.8 keV in the direct undulator beam. High-quality CMXD spectra have already been recorded in the fluorescence detection mode.

Curved Crystal Transmission Optics for Energy-Dispersive X-ray Absorption Spectroscopy.

The development of a curved crystal monochromator of the Laue type for energy-dispersive X-ray absorption spectroscopy is presented. The quality of the X-ray absorption spectra at high photon energies is compared with spectra measured with silicon crystals in the more frequently used Bragg geometry. In the Bragg case, an asymmetric broadening of the reflectivity profile leads to strong distortions of the near-edge fine structure and to a reduction in spectral resolution. The reflectivity profiles of fiat and curved crystals for Laue and Bragg geometry have been calculated using dynamical theory and are compared with experimental data. The new optics have been used for in situ time-resolved X-ray absorption spectroscopy. An example of the application of the technique for the characterization of a Pd catalyst is given. The X-ray absorption fine structure at the Pd K-edge has been measured during the activation and during the heterogeneous catalytic oxidation of carbon monoxide.

Nanosecond-resolved XMCD on ID24 at the ESRF to investigate the element-selective dynamics of magnetization switching of Gd–Co amorphous thin film

The one-bunch filling mode of the ESRF is combined with a microcoil to generate a pulsed-magnetic-field pump phased with respect to the probe that is given by the bunch of photons emitted each turn (357 kHz). Nanosecond-resolved X-ray magnetic circular dichroism (XMCD) is carried out. Besides the microcoil, the two other key-elements are the energy-dispersive XAS spectrometer, which yields parallel data acquisition, and the diamond-based quarter-wave plate, which tunes the helicity of the photon alternatively left and right.

Training and Magnetic Field Measurements of the ANKA Superconducting Undulator

In this contribution we report the results of the training and of the local field measurements performed in a liquid helium bath of the ANKA superconducting undulator. The period length is 15 mm and the coils are 1.5 m long. The key specifications of the system are an undulator parameter K higher than 2 (for a magnetic gap of 5 mm) and a phase error smaller than 3.5 degrees. The superconducting undulator is planned to be installed in the ANKA storage ring by the beginning of 2011 to be the light source of the new beamline NANO for high resolution X-ray diffraction..

Quarter-Wave Plates and X-ray Magnetic Circular Dichroism on ID24 at the ESRF

The first XMCD measurements carried out on the ID24 energy-dispersive XAS beamline at the ESRF are reported. Circular-polarized X-rays are obtained using perfect diamond crystals as quarter-wave plates. The very small source divergence allows circular polarizations close to unity to be obtained.

An exchangeable Bragg/Laue polychromator for energy-dispersive XAFS

An original design for a cooled exchangeable polychromator for energy-dispersive XAFS (X-ray absorption fine structure) working either in the transmission configuration (Laue case) or in the reflection configuration (Bragg case) is presented. It enables the acquisition of X-ray absorption spectra between 5 and 25 keV with a spot size on the sample that can reach to less than 20 microm FWHM for some energies. Only 1 h is needed to exchange both benders in operative mode. Parallel transmission spectra with a bandpass between 5 and 10% can be obtained in the full energy range. The dispersive optics and mechanics of ID24 (ESRF, Grenoble, France) have been designed to obtain XAFS spectra in less than 1 s and, in some cases, in the millisecond range.

The New Conduction-Cooled Superconducting Undulator for ANKA

Babcock Noell GmbH (BNG) is completing the fabrication of a 1.5 m long superconducting insertion device for the Karlsruhe Institute of Technology (KIT). The unit is planned to be installed in the ANKA storage ring at the end of 2010 to become the light source of the new beamline NANO for high resolution X-ray diffraction. The period length of the device is 15 mm for a total of 100.5 full periods plus an additional matching period at each end. The key specifications of the system are: a K value higher than 2 for a magnetic gap of 5 mm, the capability of withstanding a 4 W beam heat load and a phase error smaller than 3.5 degrees. The superconducting coils have been qualified by means of a vertical test in liquid helium at CERN and are ready to be installed in the cryostat. This paper describes the main features of the system.

CASPER- A magnetic measurement facility for superconducting undulators

For a given gap and a given period length superconductive cold-bore undulators have a higher field strength compared to permanent magnet undulators. The measurement of the field and the field quality in the cold bore is demanding since the position of the Hall-probes have to be precise within a few microns over a distance of one to two meters. At the Forschungszentrum Karlsruhe two measuring facilities are under construction which allow to measure short mock-ups and undulators with a length of up to two meters. In this paper the two devices called CASPER (ChAracterization Setup for Phase Error Reduction) are described.