66 research outputs found
Design and advancement status of the Beam Expander Testing X-ray facility (BEaTriX)
The BEaTriX (Beam Expander Testing X-ray facility) project is an X-ray
apparatus under construction at INAF/OAB to generate a broad (200 x 60 mm2),
uniform and low-divergent X-ray beam within a small lab (6 x 15 m2). BEaTriX
will consist of an X-ray source in the focus a grazing incidence paraboloidal
mirror to obtain a parallel beam, followed by a crystal monochromation system
and by an asymmetrically-cut diffracting crystal to perform the beam expansion
to the desired size. Once completed, BEaTriX will be used to directly perform
the quality control of focusing modules of large X-ray optics such as those for
the ATHENA X-ray observatory, based on either Silicon Pore Optics (baseline) or
Slumped Glass Optics (alternative), and will thereby enable a direct quality
control of angular resolution and effective area on a number of mirror modules
in a short time, in full X-ray illumination and without being affected by the
finite distance of the X-ray source. However, since the individual mirror
modules for ATHENA will have an optical quality of 3-4 arcsec HEW or better,
BEaTriX is required to produce a broad beam with divergence below 1-2 arcsec,
and sufficient flux to quickly characterize the PSF of the module without being
significantly affected by statistical uncertainties. Therefore, the optical
components of BEaTriX have to be selected and/or manufactured with excellent
optical properties in order to guarantee the final performance of the system.
In this paper we report the final design of the facility and a detailed
performance simulation.Comment: Accepted paper, pre-print version. The finally published manuscript
can be downloaded from http://dx.doi.org/10.1117/12.223895
Electronic and magnetic excitations in the "half-stuffed" Cu--O planes of BaCuOCl measured by resonant inelastic x-ray scattering
We use resonant inelastic x-ray scattering (RIXS) at the Cu L edge to
measure the charge and spin excitations in the "half-stuffed" Cu--O planes of
the cuprate antiferromagnet BaCuOCl. The RIXS line shape
reveals distinct contributions to the excitations from the two
structurally inequivalent Cu sites, which have different out-of-plane
coordinations. The low-energy response exhibits magnetic excitations. We find a
spin-wave branch whose dispersion follows the symmetry of a CuO sublattice,
similar to the case of the "fully-stuffed" planes of tetragonal CuO (T-CuO).
Its bandwidth is closer to that of a typical cuprate material, such as
SrCuOCl, than it is to that of T-CuO. We interpret this result as
arising from the absence of the effective four-spin inter-sublattice
interactions that act to reduce the bandwidth in T-CuO.Comment: 10 pages, 8 figure
A degrading Bouc\u2013Wen model for the hysteresis of reinforced concrete structural elements
This paper presents a smooth hysteresis model for reinforced concrete (RC) structural elements based on the differential equation of the Bouc?Wen model. Stiffness degradation and strength degradation are defined by introducing a damage index that includes both dissipated energy and maximum displacement. The pinching effect acts directly on the stiffness of the system and is controlled by an activation energy. The degrading functions are connected to the actual processes with which the damage occurs, thereby giving each parameter a physical meaning. The simple formulation of the model allows a straightforward identification of the best-fitting parameters and an easy interpretation of the results. Applications to the cyclic behaviour of RC structural elements demonstrate that the model is well capable of describing complex hysteretic behaviours involving degradation and pinching effects
Decoupling carrier concentration and electron-phonon coupling in oxide heterostructures observed with resonant inelastic x-ray scattering
We report the observation of multiple phonon satellite features in ultra thin
superlattices of form SrIrO/SrTiO using resonant inelastic x-ray
scattering. As the values of and vary the energy loss spectra show a
systematic evolution in the relative intensity of the phonon satellites. Using
a closed-form solution for the cross section, we extract the variation in the
electron-phonon coupling strength as a function of and . Combined with
the negligible carrier doping into the SrTiO layers, these results indicate
that tuning of the electron-phonon coupling can be effectively decoupled from
doping. This work showcases both a feasible method to extract the
electron-phonon coupling in superlattices and unveils a potential route for
tuning this coupling which is often associated with superconductivity in
SrTiO-based systems.Comment: 4 pages, 5 figure
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Analysis of the EMCCD point-source response using x-rays
Electron Multiplying Charge Coupled Devices, EMCCD are used as x-ray detectors. The NSLS-II Soft Inelastic x-ray Scattering (SIX) beam line has two EMCCDs for x-ray detection in the spectrometer arm. The spectrometer with high resolving power disperses x-rays vertically. The x-ray vertical position on the sensor plane is related to its energy. This allows for very accurate x-ray energy measurements through x-ray coordinates. X-rays interact with silicon and create a number of electron–hole pairs proportional to the x-ray energy. Electrons drift and diffuse toward pixel gates and are collected there. The diffused electrons form a charge cloud distributed over several neighboring pixels. This charge sharing enables coordinate measurements with accuracy better than the pixel pitch. The charge distribution shape has to be taken into account to achieve ultimate accuracy in coordinate measurements. In this paper, we present a method of the charge distribution shape analysis and demonstrate its applications.
The drift and diffusion of electrons from the point of generation to pixel gates results in the bell-shaped electron cloud usually approximated by Gaussian shape. The number of electrons collected under a pixel is proportional to the shape function integral. These electron packets get transferred to the sense node of the output amplifier. The transfer process could introduce distortions to the original charge distribution. For example, during transfers, electrons in the packet could be exposed to traps if they are present in the sensor. The trapping and later the release processes distort the apparent shape of the charge distribution. Therefore, deviations of the charge distribution shape from the originally symmetrical form can indicate the presence of trap centers in the sensor and can be used for sensor diagnostics
Performance Testing of a Large-Format Reflection Grating Prototype for a Suborbital Rocket Payload
The soft X-ray grating spectrometer on board the Off-plane Grating Rocket
Experiment (OGRE) hopes to achieve the highest resolution soft X-ray spectrum
of an astrophysical object when it is launched via suborbital rocket. Paramount
to the success of the spectrometer are the performance of the reflection
gratings populating its reflection grating assembly. To test current grating
fabrication capabilities, a grating prototype for the payload was fabricated
via electron-beam lithography at The Pennsylvania State University's Materials
Research Institute and was subsequently tested for performance at Max Planck
Institute for Extraterrestrial Physics' PANTER X-ray Test Facility. Bayesian
modeling of the resulting data via Markov chain Monte Carlo (MCMC) sampling
indicated that the grating achieved the OGRE single-grating resolution
requirement of at the 94% confidence level.
The resulting posterior probability distribution suggests that this
confidence level is likely a conservative estimate though, since only a finite
parameter space was sampled and the model could not constrain the upper
bound of to less than infinity. Raytrace simulations of the system found
that the observed data can be reproduced with a grating performing at
. It is therefore postulated that the behavior of the obtained
posterior probability distribution can be explained by a finite
measurement limit of the system and not a finite limit on . Implications
of these results and improvements to the test setup are discussed.Comment: 25 pages, 16 figures, preprint of an article accepted for publication
in the Journal of Astronomical Instrumentation \copyright 2020 [copyright
World Scientific Publishing Company]
[https://www.worldscientific.com/worldscinet/jai
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