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DOE OSTI2010

High-accuracy X-ray detector calibration based on cryogenic radiometry

Cryogenic electrical substitution radiometers (ESRs) are absolute thermal detectors, based on the equivalence of electrical power and radiant power. Their core piece is a cavity absorber, which is typically made of copper to achieve a short response time. At higher photon energies, the use of copper prevents the operation of ESRs due to increasing transmittance. A new absorber design for hard X-rays has been developed at the laboratory of the Physikalisch-Technische Bundesanstalt (PTB) at the electron storage ring BESSY II. The Monte Carlo simulation code Geant4 was applied to optimize its absorptance for photon energies of up to 60 keV. The measurement of the radiant power of monochromatized synchrotron radiation was achieved with relative standard uncertainties of less than 0.2 %, covering the entire photon energy range of three beamlines from 50 eV to 60 keV. Monochromatized synchrotron radiation of high spectral purity is used to calibrate silicon photodiodes against the ESR for photon energies up to 60 keV with relative standard uncertainties below 0.3 %. For some silicon photodiodes, the photocurrent is not linear with the incident radiant power.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2013

Broad-band efficiency calibration of ITER bolometer prototypes using Pt absorbers on SiN membranes

The energy resolved efficiency of two bolometer detector prototypes for ITER with 4 channels each and absorber thicknesses of 4.5 μm and 12.5 μm, respectively, has been calibrated in a broad spectral range from 1.46 eV up to 25 keV. The calibration in the energy range above 3 eV was performed against previously calibrated silicon photodiodes using monochromatized synchrotron radiation provided by five different beamlines of Physikalische Technische Bundesanstalt at the electron storage rings BESSY II and Metrology Light Source in Berlin. For the measurements in the visible range, a setup was realised using monochromatized halogen lamp radiation and a calibrated laser power meter as reference. The measurements clearly demonstrate that the efficiency of the bolometer prototype detectors in the range from 50 eV up to ≈6 keV is close to unity; at a photon energy of 20 keV the bolometer with the thick absorber detects 80% of the photons, the one with the thin absorber about 50%. This indicates that the detectors will be well capable of measuring the plasma radiation expected from the standard ITER scenario. However, a minimum absorber thickness will be required for the high temperatures in the central plasma. At 11.56 keV, the sharp Pt-L{sub 3} absorption edge allowed to cross-check the absorber thickness by fitting the measured efficiency to the theoretically expected absorption of X-rays in a homogeneous Pt-layer. Furthermore, below 50 eV the efficiency first follows the losses due to reflectance expected for Pt, but below 10 eV it is reduced further by a factor of 2 for the thick absorber and a factor of 4 for the thin absorber. Most probably, the different histories in production, storage, and operation led to varying surface conditions and additional loss channels.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2010

The X-ray microscopy beamline UE46-PGM2 at BESSY

The Max Planck Institute for Metal Physics in Stuttgart and the Helmholtz Center Berlin operate a soft X-ray microscopy beamline at the storage ring BESSY II. A collimated PGM serves as monochromator for a scanning X-ray microscope and a full field X-ray microscope at the helical undulator UE46. The selection between both instruments is accomplished via two switchable focusing mirrors. The scanning microscope (SM) is based on the ALS STXM microscope and fabricated by the ACCEL company. The full field microscope (FFM) is currently in operation at the U41-SGM beamline and will be relocated to its final location this year.

43 PARTICLE ACCELERATORS↗

DOE OSTI2016

The EMIL project at BESSY II: Beamline design and performance

The Energy Materials In-Situ Laboratory Berlin (EMIL) at BESSY-II is currently under construction. Two canted undulators for soft- and hard X-rays will be installed into the BESSY II storage ring in one straight section, complex beamlines with more than twenty optical elements will be set up and a new laboratory building attached to BESSY II will host three endstations and a large UHV-transfer system connecting various HV- and UHV-deposition systems. The undulators, UE48 and U17, provide a broad energy spectrum of 80 - 10000 eV, of which the harder radiation (>700 eV) is provided by a cryogenic in-vacuum device. Three monochromators (two plane grating monochromators (PGM) and one LN{sub 2}-cooled double crystal monochromator (DCM)) disperse the radiation into separate pathways of 65 m length, while downstream of the monochromators split-mirror chambers distribute the photon beam to one (or simultaneously to two) of five upcoming endstations. Three of these endstations are designed for the full energy range with spatial overlap of the soft and hard foci, whereas one endstation (PEEM) uses only the soft and another one (PINK) only the hard branch, respectively.

43 PARTICLE ACCELERATORS↗

DOE OSTI2016

Multi-MHz time-of-flight electronic bandstructure imaging of graphene on Ir(111)

In the quest for detailed spectroscopic insight into the electronic structure at solid surfaces in a large momentum range, we have developed an advanced experimental approach. It combines the 3D detection scheme of a time-of-flight momentum microscope with an optimized filling pattern of the BESSY II storage ring. Here, comprehensive data sets covering the full surface Brillouin zone have been used to study faint substrate-film hybridization effects in the electronic structure of graphene on Ir(111), revealed by a pronounced linear dichroism in angular distribution. The method paves the way to 3D electronic bandmapping with unprecedented data recording efficiency.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2010

Resonant and Near-Threshold Photoionization Cross Sections of Fe{sup 14+}

Photoionization (PI) of Fe{sup 14+} in the range from 450 to 1100 eV was measured at the BESSY II storage ring using an electron beam ion trap achieving high target-ion area densities of 10{sup 10} cm{sup -2}. Photoabsorption by this ion is observed in astrophysical spectra and plasmas, but until now cross sections and resonance energies could only be provided by calculations. We reach a resolving power E/{Delta}E of at least 6500, outstanding in the present energy range, which enables benchmarking and improving the most advanced theories for PI of ions in high charge states.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2010

Status of the Metrology Light Source

The Physikalisch-Technische Bundesanstalt (PTB), the German national metrology institute, has set up the low-energy electron storage ring Metrology Light Source (MLS) in close cooperation with the Helmholtz-Zentrum Berlin (HZB, formerly BESSY). This new storage ring has been in regular user operation since April 2008 and is dedicated to synchrotron-radiation-based metrology and technological developments in the far-IR/THz, IR, UV, VUV and EUV spectral range. The MLS has a double-bend-achromate lattice structure, injection is from a 105 MeV racetrack microtron. The electron energy can be ramped to any value from 105 MeV up to 630 MeV and the electron beam current covers the range from one stored electron (1 pA) up to 200 mA. The MLS is the first electron storage ring optimized for the generation of coherent synchrotron radiation, based on an electron bunch shortening mode. In this mode, MLS delivers coherent radiation in the far-IR/THz spectral range with enhanced intensity as compared to the normal mode of operation. Several beamlines are in operation or in construction, including one undulator beamline, bending magnet beamlines for the calibration of radiation sources and detectors and for reflectometry, an EUV metrology beamline and three IR/THz beamlines.

43 PARTICLE ACCELERATORS↗

DOE OSTI2016

EPU correction scheme study at the CLS

The Canadian Light Source (CLS) Quantum Materials Spectroscopy Center (QMSC) beamline will employ a novel double period (55 mm, 180 mm) elliptically polarizing undulator (EPU) to produce photons of arbitrary polarization in the soft X-ray regime. The long period and high field of the 180 mm period EPU will have a strong dynamic focusing effect on the storage ring electron beam. We have considered two partial correction schemes, a 4 m long planar array of BESSY-II style current strips, and soft iron L-shims. In this paper we briefly consider the implementation of these correction schemes.

43 PARTICLE ACCELERATORS↗

DOE OSTI2010

New Developments in Femtosecond Soft X-ray Spectroscopy

Recent instrumentation developments in X-ray spectroscopy for ultra-fast time-resolved measurements with soft X-rays done in HZB Berlin during the last years are described. The significant performance improvements achieved this way are based on Fresnel diffraction from structures being fabricated on a surface of a total externally reflecting mirror. The first type of this spectrometer, an off-axis reflection zone plate, has been implemented at the BESSY Femtoslicing setup and shows on the order of 20 times higher flux in the focal plane compared to the classical grating monochromator beamline. It has proven to serve very precise experiments with a time resolution down to 100 fs on magnetic materials after optical laser pulse excitation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2010

Compensation of Beam Line Polarizing Effects at UE112 of BESSY II

Reflections in synchrotron radiation beam lines tend to change the state of polarization of the radiation. This effect is more pronounced for steep angle of incidence, i.e. at low photon energy (say below 100 eV) beam lines. The APPLE II undulator UE112 at BESSY has all four magnetic rows shiftable and thus generates any state of polarization. To provide any intended polarization state at the sample we perform polarization measurements based on simple and fast linear polarization analysis that together with calculations of the undulator radiation predicts undulator settings that cancel beam line polarization effects.

43 PARTICLE ACCELERATORS↗

DOE OSTI2010

Heydemann Algorithm for Energy Scale Linearisation

Many monochromators rely on quadrature encoders for positioning optical elements like gratings or mirrors. In most cases the required accuracy is significantly higher than the pitch of the encoders and an interpolation scheme becomes necessary. The accuracy of this procedure can be significantly enhanced, if signal errors in the detection systems are compensated. We report on the implementation of this technique at the BESSY monochromators and the impact on spectroscopic data.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2010

Fully automated, fixed exit, in vacuum double-multilayer monochromator for synchrotron-based hard X-ray micro-imaging applications

We present a double multilayer monochromator (DMM) design which has been realized for the BAMline(BESSY-II light source, Germany) as well as in an updated version for the TopoTomo beamline (ANKA light source. Germany)[1-4]. The latter contains two pairs of multilayer stripes in order to avoid absorption edges of the coating material. For both DMMs, the second multilayer offers a meridional bending option for beam compression to increase the available photon flux density. Each multilayer mirror is equipped with a vertical stage for height adjustments allowing for compensation of varying incoming beam heights and giving a certain flexibility choosing the offset. The second multilayer can be moved in the beam direction in order to cover the full energy range available. Furthermore, a white beam option is available.

43 PARTICLE ACCELERATORS↗

DOE OSTI2010

A KB-Focusing Mirror Pair for a VUV-Raman Spectrometer at FLASH - Mirror Metrology and Ray Tracing Results

A plane mirror and two strongly curved plane elliptical mirrors comprising the refocusing system downstream the plane grating monochromator at FLASH in DESY have been characterized with the Nanometer Optical Component Measuring Machine at the BESSY-II Optics Laboratory of the Helmholtz Zentrum Berlin. Based on the measurement results the two elliptical cylinders were optimized by deterministic surface finishing technology (Ion Beam Finishing). The expected focusing performance was verified by ray tracings after each ion beam finish iteration using the measured topography results.

43 PARTICLE ACCELERATORS↗

DOE OSTI2010

Full Hemisphere Fermi Surface Mapping Using A Novel Toroidal Electron Spectrometer

An overview is provided of a next-generation toroidal angle-resolving photoemission spectrometer, currently in operation at BESSY II. The instrument features exceptional multi-detection in energy and angle, facilitating rapid full-hemisphere photoemission measurements. The instrument is ideal for band structure and Fermi Surface (FS) mapping using Angle Resolved Photoemission Spectroscopy (ARPES). Recent full-hemisphere FS measurements of a prototypical material, copper, reveal previously unseen fine structure due to lifetime broadening, demonstrating the high angular resolution and dense {kappa}-space sampling capabilities of the instrument.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2010

Multitone harmonic-balance simulations of an x-ray transition-edge sensor characterized at BESSY II

We present multitone harmonic-balance (MTHB) simulations of a Ti-Au x-ray transition-edge sensor (TES) microcalorimeter in a 5x5 pixel spectrometer array. The dynamic response of the TES microcalorimeter under simulation has been extremely well characterized at the BESSY II Synchrotron Radiation Facility in Berlin. We compare our simulated results directly with these measurements, and show that the MTHB algorithm is able to simulate to great accuracy the dynamic behavior of the TES, even when saturated by 6 keV photons. In this paper, we provide a detailed account of the MTHB simulations, and discuss the impact of this work on future missions such as the International X-ray Observatory.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2010

Quantitative studies on inner interfaces in conical metal joints using hard x-ray inline phase contrast radiography

Quantitative investigation of micrometer and submicrometer gaps between joining metal surfaces is applied to conical plug-socket connections in dental titanium implants. Microgaps of widths well beyond the resolving power of industrial x-ray systems are imaged by synchrotron phase contrast radiography. Furthermore, by using an analytical model for the relatively simple sample geometry and applying it to numerical forward simulations of the optical Fresnel propagation, we show that quantitative measurements of the microgap width down to 0.1 {mu}m are possible. Image data recorded at the BAMline (BESSY-II light source, Germany) are presented, with the resolving power of the imaging system being 4 {mu}m in absorption mode and {approx}14 {mu}m in phase contrast mode (z{sub 2}=0.74 m). Thus, phase contrast radiography, combined with numerical forward simulations, is capable of measuring the widths of gaps that are two orders of magnitude thinner than the conventional detection limit.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2011

TXM-NEXAFS of TiO{sub 2}-Based Nanostructures

In this work, electronic properties of individual TiO{sub x}-pristine nanoribbons (NR) prepared by hydrothermal treatment of anatase TiO{sub 2} micro-particles were studied using the HZB transmission x-ray microscope (TXM) at the BESSY II undulator beamline U41-FSGM. NEXAFS is ideally suited to study TiO{sub 2}-based materials because both the O K-edge and Ti L-edge features are very sensitive to the local bonding environment, providing diagnostic information about the crystal structures and oxidation states of various forms of titanium oxides and sub-oxides. TXM-NEXAFS combines full-field x-ray microscopy with spectroscopy, allowing the study of the electronic structure of individual nanostructures with spatial resolution better than 25 nm and a spectral resolution of up to E/{Delta}E = 10000. The typical image field in TXM-NEXAFS measurements is about 10 {mu}mx10 {mu}m, which is large compared to the individual nanoparticle. Therefore, one image stack already contains statistically significant data. In addition, the directional electric field vector (E-bar) of the x-rays can be used as a 'search tool' for the direction of chemical bonds of the atom selected by its absorption edge.

36 MATERIALS SCIENCE↗

DOE OSTI2012

Femtosecond laser-induced modification of potassium-magnesium silicate glasses: An analysis of structural changes by near edge x-ray absorption spectroscopy

The effects of femtosecond laser pulse irradiation on the glass structure of alkaline silicate glasses were investigated by x-ray absorption near edge structure spectroscopy using the beamline of the Physikalisch-Technische Bundesanstalt at the electron synchrotron BESSY II in Berlin (Germany) by analyzing the magnesium K-edge absorption peak for different laser fluences. The application of fluences above the material modification threshold (2.1 J/cm{sup 2}) leads to a characteristic shift of {approx}1.0 eV in the K-edge revealing a reduced ({approx}3%) mean magnesium bond length to the ligated oxygen ions (Mg-O) along with a reduced average coordination number of the Mg ions.

36 MATERIALS SCIENCE↗