Calibration and characterization of a highly efficient spectrometer in von Hamos geometry for 7-10 keV x-rays

MOSARIX: Multi-crystal spectrometer in the tender x-ray range at SOLEIL synchrotron

We have built and commissioned a novel standalone multi-crystal x-ray spectrometer (MOSARIX) in the von Hamos configuration based on highly annealed pyrolytic graphite crystals. The spectrometer is optimized for the energy range of 2-5 keV, but this range can be extended up to 20 keV by using higher reflection orders. With its nine crystals and a Pilatus detector, MOSARIX achieves exceptional detection efficiency with good resolving power (better than 4000), opening the door to study small cross section phenomena and perform fast in situ measurements. The spectrometer operates under a He atmosphere, which provides a flexible sample environment for measurements in gas, liquid, and solid phases.

High-resolution x-ray spectrometer for x-ray absorption fine structure spectroscopy

Two extended x-ray absorption fine structure flat crystal x-ray spectrometers (EFX's) were designed and built for high-resolution x-ray spectroscopy over a large energy range with flexible, on-shot energy dispersion calibration capabilities. The EFX uses a flat silicon [111] crystal in the reflection geometry as the energy dispersive optic covering the energy range of 6.3-11.4 keV and achieving a spectral resolution of 4.5 eV with a source size of 50 μm at 7.2 keV. A shot-to-shot configurable calibration filter pack and Bayesian inference routine were used to constrain the energy dispersion relation to within ±3 eV. The EFX was primarily designed for x-ray absorption fine structure (XAFS) spectroscopy and provides significant improvement to the Laboratory for Laser Energetics' OMEGA-60 XAFS experimental platform. The EFX is capable of performing extended XAFS measurements of multiple absorption edges simultaneously on metal alloys and x-ray absorption near-edge spectroscopy to measure the electron structure of compressed 3d transition metals.

Laboratory-scale X-ray absorption spectroscopy of 3d transition metals in inorganic thin films

In this paper we present laboratory-scale X-ray absorption spectroscopy applied to the research of nanometer-scale thin films. We demonstrate the Cu K edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) of CuI and CuO thin films grown with atomic layer deposition. Film thicknesses in the investigated samples ranged from 12 to 248 nm. Even from the thinnest films, XANES spectra can be obtained in 5-20 minutes and EXAFS in 1-4 days. In order to prove the capability of laboratory-based XAS for in situ measurements on thin films, we demonstrate an experiment on in situ oxidation of a 248 nm thick CuI film at a temperature of 240 °C. These methods have important implications for novel and enhanced possibilities for inorganic thin film research.

Transport of an intense proton beam from a cone-structured target through plastic foam with unique proton source modeling

Laser-accelerated proton beams are applicable to several research areas within high-energy density science, including warm dense matter generation, proton radiography, and inertial confinement fusion, which all involve transport of the beam through matter. We report on experimental measurements of intense proton beam transport through plastic foam blocks. The intense proton beam was accelerated by the 10ps, 700J OMEGA EP laser irradiating a curved foil target, and focused by an attached hollow cone. The protons then entered the foam block of density 0.38g/cm^{3} and thickness 0.55 or 1.00mm. At the rear of the foam block, a Cu layer revealed the cross section of the intense beam via proton- and hot electron-induced Cu-K_{α} emission. Images of x-ray emission show a bright spot on the rear Cu film indicative of a forward-directed beam without major breakup. 2D fluid-PIC simulations of the transport were conducted using a unique multi-injection source model incorporating energy-dependent beam divergence. Along with postprocessed calculations of the Cu-K_{α} emission profile, simulations showed that protons retain their ballistic transport through the foam and are able to heat the foam up to several keV in temperature. The total experimental emission profile for the 1.0mm foam agrees qualitatively with the simulated profile, suggesting that the protons indeed retain their beamlike qualities.

Shock Ignition Laser-Plasma Interactions in Ignition-Scale Plasmas

We use a subignition scale laser, the 30 kJ Omega, and a novel shallow-cone target to study laser-plasma interactions at the ablation-plasma density scale lengths and laser intensities anticipated for direct drive shock-ignition implosions at National Ignition Facility scale. Our results show that, under these conditions, the dominant instability is convective stimulated Raman scatter with experimental evidence of two plasmon decay (TPD) only when the density scale length is reduced. Particle-in-cell simulations indicate this is due to TPD being shifted to lower densities, removing the experimental back-scatter signature and reducing the hot-electron temperature. The experimental laser energy-coupling to hot electrons was found to be 1%-2.5%, with electron temperatures between 35 and 45 keV. Radiation-hydrodynamics simulations employing these hot-electron characteristics indicate that they should not preheat the fuel in MJ-scale shock ignition experiments.

A von Hamos spectrometer based on highly annealed pyrolytic graphite crystal in tender x-ray domain

We have built an x-ray spectrometer in a von Hamos configuration based on a highly annealed pyrolytic graphite crystal. The spectrometer is designed to measure x-ray emission in the range of 2-5 keV. A spectral resolution E/ΔE of 4000 was achieved by recording the elastic peak of photons issued from the GALAXIES beamline at the SOLEIL synchrotron radiation facility.

200-mm segmented cylindrical figured crystal for von Hamos x-ray spectrometer

A von Hamos Bragg crystal spectrometer at 1C beamline of Pohang Accelerator Laboratory for x-ray emission spectroscopy (XES) is described. Diced Si crystals of different orientations ([111], [110], [100], and [311]) are glued onto a planoconcave glass substrate having 250/500 mm radius of curvature. To enhance the spectrometer efficiency, the length of the crystal analyzer is kept 200 mm. The emission spectra of Cu foil and Fe foil and elastic scattering from Al foil are measured using the von Hamos geometry in which curved crystals disperse the x-rays. Spectrometer efficiency and energy resolution are measured at various x-ray photon energies. X-rays are incident at 6.54 keV, 9.00 keV, 9.205 keV, and 11.51 keV for Si(440), Si(444), Si(800), and Si(933) crystal analyzers, respectively. The cylindrical figured analyzer is placed near 80° with respect to the sample, which gives better energy resolution. The spectrometer efficiency of the Si(444) crystal analyzer increases by ∼2 times when the length of the analyzer is increased from 100 mm to 200 mm. Furthermore, to measure Fe Kα₁, Kα₂, and K_β simultaneously, we made a mixed crystal analyzer in which alternative strips of Si[111] and Si[110] are glued onto one preshaped cylindrical substrate. The enhanced efficiency and simultaneous measurement of K_α and K_β emission lines will give an edge over in situ and time-resolved x-ray emission spectroscopy studies. The information extracted with a high efficiency spectrometer from low intensity XES emission lines will be useful for the in situ elemental characterization in catalytic reactions.

A laboratory spectrometer for high throughput X-ray emission spectroscopy in catalysis research

We have built a laboratory spectrometer for X-ray emission spectroscopy. The instrument is employed in catalysis research. The key component is a von Hamos full cylinder optic with Highly Annealed Pyrolytic Graphite (HAPG) as a dispersive element. With this very efficient optic, the spectrometer subtends an effective solid angle of detection of around 1 msr, allowing for the analysis of dilute samples. The resolving power of the spectrometer is approximately E/ΔE = 4000, with an energy range of ∼2.3 keV-10 keV. The instrument and its characteristics are described herein. Further, a comparison with a prototype spectrometer, based on the same principle, shows the substantial improvement in the spectral resolution and energy range for the present setup. The paper concludes with a discussion of sample handling. A compilation of HAPG fundamentals and related publications are given in a brief Appendix.