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All sources NASA NTRS DOE OSTI

DOE OSTI2014

Coded aperture imaging for fluorescent x-rays

We employ a coded aperture pattern in front of a pixilated charge couple device detector to image fluorescent x-rays (6–25 KeV) from samples irradiated with synchrotron radiation. Coded apertures encode the angular direction of x-rays, and given a known source plane, allow for a large numerical aperture x-ray imaging system. The algorithm to develop and fabricate the free standing No-Two-Holes-Touching aperture pattern was developed. The algorithms to reconstruct the x-ray image from the recorded encoded pattern were developed by means of a ray tracing technique and confirmed by experiments on standard samples.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2018

X-ray spectrometer throughput model for (selected) flat Bragg crystal spectrometers on laser plasma facilities

At large laser faculties, such as OMEGA and the National Ignition Facility (NIF), x-ray spectrometers are provided by the facility to diagnose plasma conditions or monitor backlighters. Often the calibration of these spectrometers is unknown or out of date. In response to this situation, we present a simple ray trace method to calibrate flat crystal spectrometers using only basic information regarding the optical design of the spectrometer. This model is then used to output photometric throughput estimates, dispersion, solid angle, and spectral resolution estimates. This model is applied to the mono angle crystal spectrometer and Super Snout I at the NIF and the X-Ray Spectrometer at the OMEGA laser facility

47 OTHER INSTRUMENTATION↗

DOE OSTI2023

Iridescence from Total Internal Reflection at 3D Microscale Interfaces: Mechanistic Insights and Spectral Analysis

An experimental investigation and the optical modeling of the structural coloration produced from total internal reflection interference within 3D microstructures are described. Ray-tracing simulations coupled with color visualization and spectral analysis techniques are used to model, examine, and rationalize the iridescence generated for a range of microgeometries, including hemicylinders and truncated hemispheres, under varying illumination conditions. An approach to deconstruct the observed iridescence and complex far-field spectral features into its elementary components and systematically link them to ray trajectories that emanate from the illuminated microstructures is demonstrated. The results are compared with experiments, wherein microstructures are fabricated with methods such as chemical etching, multiphoton lithography, and grayscale lithography. Microstructure arrays patterned on surfaces with varying orientation and size lead to unique color-traveling optical effects and highlight opportunities for how total internal reflection interference can be used to create customizable reflective iridescence. The findings herein provide a robust conceptual framework for rationalizing this multibounce interference mechanism and establish approaches for characterizing and tailoring the optical and iridescent properties of microstructured surfaces.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Studies of the outer-off-midplane lower hybrid wave launch scenario for plasma start-up on the TST-2 spherical tokamak

Abstract Establishment of an efficient central solenoid (CS) free tokamak plasma start-up method may lead to an economical fusion reactor. CS-free start-up using lower hybrid (LH) waves has been studied on the TST-2 spherical tokamak. Plasma current of about a quarter of CS-driven discharges has been obtained fully non-inductively using the outer-midplane and top LH launchers. Recently, an outer-off-midplane LH launcher was developed to achieve higher plasma current by optimizing for core absorption and minimal fast electron losses. Using the (outer-)off-midplane launcher, fully non-inductive plasma current start-up up to about 8 kA was achieved. Coupled ray-tracing and Fokker–Planck simulation was performed on equilibria reconstructed with an extended MHD model. It was found that the experimentally observed plasma current was in reasonable agreement with the numerical simulation. The simulation predicted appreciable orbit losses for the off-midplane launcher driven discharge at the present parameters, which was consistent with the experimentally observed x-ray radiation characteristics. The simulation showed that the current density was saturated for the present off-midplane launcher discharges and higher density and higher LH power was necessary to achieve higher plasma current.

Physics↗

DOE OSTI2023

Spin Hall effect of radiofrequency waves in magnetized plasmas

In inhomogeneous media, electromagnetic-wave rays deviate from the trajectories predicted by the leading-order geometrical optics. This effect, called the spin Hall effect of light, is typically neglected in ray-tracing codes used for modeling waves in plasmas. Here, we demonstrate that the spin Hall effect can be significant for radiofrequency waves in toroidal magnetized plasmas whose parameters are in the ballpark of those used in fusion experiments. For example, an electron-cyclotron wave beam can deviate by as large as 10 wavelengths (~ 0.1 m) relative to the lowest-order ray trajectory in the poloidal direction. Finally, we calculate this displacement using gauge-invariant ray equations of extended geometrical optics, and we also compare our theoretical predictions with full-wave simulations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2024

Impact of flow-induced beam deflection on beam propagation in ignition scale hohlraums

Experiments examining the amount of specular reflection (or “glint”) within hohlraums containing different gas fill densities have recently been performed. Simulations of these experiments are presented that show using a single flux limiter cannot explain the decrease in glinted power with increasing gas fill density. The hypothesis that flow-induced beam deflection alters laser absorption is presented. A model is proposed that can be implemented into a ray tracing description of the laser commonly used in radiation hydrodynamic codes. It is shown that simulations using this model capture the trend with gas fill density improving agreement with measurements. This formulation is then applied to an ensemble of laser-driven inertial confinement fusion experiments performed at the National Ignition Facility. The proposed model shows little impact on the total x-ray drive on the capsule but a large impact on the resulting implosion symmetry.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1995

The X-ray telescope on board ASCA

The Advanced Satellite for Cosmology and Astrophysics (ASCA) instrument uses identical conical foil X-ray mirrors for its four telescopes. One of the major advantages of ASCA's telescopes is the first time ever use of X-ray imaging over a broad energy band and high throughput for conducting astronomical spectroscopy. Nested thin foil reflectors make possible a large effective area up to 10 keV, even under the tight weight restriction of the ASCA spacecraft. The expected characteristics of the ASCA mirrors are summarized based on ray tracings and pre-flight calibrations. The total effective area of four telescopes at 1 and 7 keV are approximately 1200 and 600 sq cm, respectively. The image size (half power diameter: HPD) is about 3 min. The field of view is 24 min and 16 min full width at half maximum for 1 and 7 keV, respectively. Observations of several X-ray sources from space during the performance verification phase have confirmed those performances as well as the alignment of the optical systems.

Serlemitsos, Peter J.↗

DOE OSTI2012

The Effects of the Scattering by Edge Plasma Density Fluctuations on Lower Hyybrid Wave Propagation

Scattering effects induced by edge density fluctuations on lower hybrid (LH) wave propagation are investigated. The scattering model used here is based on the work of Bonoli and Ott [Phys. Fluids 25 (1982) 361]. It utilizes an electromagnetic wave kinetic equation solved by a Monte Carlo technique. This scattering model has been implemented in GENRAY , a ray tracing code which explicitly simulates wave propagation, as well as collisionless and collisional damping processes, over the entire plasma discharge, including the scrape-off layer (SOL) that extends from the separatrix to the vessel wall. A numerical analysis of the LH wave trajectories and the power deposition profile with and without scattering is presented for Alcator CMod discharges. Comparisons between the measured hard x-ray emission on Alcator C-Mod and simulations of the data obtained from the synthetic diagnostic included in the GENRAY/CQL3D package are shown, with and without the combination of scattering and collisional damping. Implications of these results on LH current drive are discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2026

Gamma-ray signatures of 𝑟-process radioactivity from the collapse of magnetized white dwarfs

We predict the gamma-ray line emission from 𝑟-process nuclei synthesized in the ejecta of the accretion-induced collapse (AIC) of a magnetized, rapidly rotating white dwarf. Using ejecta from a two-dimensional general-relativistic neutrino-magnetohydrodynamic simulation, further evolved with a radiation-hydrodynamics code coupled to an in situ nuclear reaction network, we construct angle-dependent gamma-ray spectra in the 0.01–10 MeV band via composition-dependent ray tracing through the ejecta. The emission between ∼1 and 10 d is dominated by 132 I (𝑡 1/2 = 2.3 h), continuously replenished by the decay of its parent 132 Te (𝑡 1/2 = 3.2 d), with additional contributions from 131 I, 133 Xe, and 132 Te . At 𝑡 ≳ 20 d, 56 Co (from 56 Ni decay) becomes the primary emitter. The simultaneous presence of 𝑟 process and iron-peak gamma-ray lines is distinctive of AIC ejecta and absent in binary neutron star mergers, where iron-peak nuclei are generally not synthesized. Comparing with the 3⁢𝜎 continuum sensitivities of planned MeV gamma-ray telescopes (COSI, AMEGO-X, e-ASTROGAM, GRAMS, GammaTPC), we find the brightest 𝑟-process lines detectable to ∼10 Mpc by GammaTPC and GRAMS, with the signal approaching their sensitivity threshold at 30 Mpc. As a result, the 𝑟-process spectral features survive time integration over ∼30 d exposures, demonstrating robustness against the long observation times required by gamma-ray detectors.

Nuclear reactions↗

DOE OSTI2012

X-Ray Emission Spectrometer Design with Single-Shot Pump-Probe and Resonant Excitation Capabilities

Core-level spectroscopy in the soft X-ray regime is a powerful tool for the study of chemical bonding processes. The ultrafast, ultrabright X-ray pulses generated by the Linac Coherent Light Source (LCLS) allow these reactions to be studied in greater detail than ever before. In this study, we investigated a conceptual design of a spectrometer for the LCLS with imaging in the non-dispersive direction. This would allow single-shot collection of X-ray emission spectroscopy (XES) measurements with varying laser pump X-ray probe delay or a variation of incoming X-ray energy over the illuminated area of the sample. Ray-tracing simulations were used to demonstrate how the components of the spectrometer affect its performance, allowing a determination of the optimal final design. These simulations showed that the spectrometer's non-dispersive focusing is extremely sensitive to the size of the sample footprint; the spectrometer is not able to image a footprint width larger than one millimeter with the required resolution. This is compatible with a single shot scheme that maps out the laser pump X-ray probe delay in the non-dispersive direction as well as resonant XES applications at normal incidence. However, the current capabilities of the Soft X-Ray (SXR) beamline at the LCLS do not produce the required energy range in a small enough sample footprint, hindering the single shot resonant XES application at SXR for chemical dynamics studies at surfaces. If an upgraded or future beamline at LCLS is developed with lower monochromator energy dispersion the width can be made small enough at the required energy range to be imaged by this spectrometer design.

43 PARTICLE ACCELERATORS↗

NASA NTRS1993

Propagation of high frequency jet noise using geometric acoustics

Spherical directivity of noise radiated from a convecting quadrupole source embedded in an arbitrary spreading jet is obtained by ray-tracing methods of geometrical acoustics. The six propagation equations are solved in their general form in a rectangular coordinate system. The noise directivity in the far field is calculated by applying an iteration scheme that finds the required radiation angles at the source resulting in propagation through a given observer point. Factors influencing the zone of silence are investigated. The caustics of geometrical acoustics and the exact locations where it forms is demonstrated by studying the variation in ray tube area obtained from transport equation. For a ring source convecting along the center-axis of an axisymmetric jet, the polar directivity of the radiated noise is obtained by an integration with respect to azimuthal directivity of compact quadrupole sources distributed on the ring. The Doppler factor is shown to vary slightly from point to point on the ring. Finally the scaling of the directivity pattern with power -3 of Doppler factor is investigated and compared with experimental data.

Khavaran, A.↗

NASA NTRS1993

Propagation of high frequency jet noise using geometric acoustics

Khavaran, A.↗

NASA NTRS2022

Electromagnetic signatures from supermassive binary black holes approaching merger

We present fully relativistic predictions for the electromagnetic emission produced by accretion disks surrounding spinning and nonspinning supermassive binary black holes on the verge of merging. We use the code Bothros to post-process data from 3D General Relativistic Magnetohydrodynamic (GRMHD) simulations via ray-tracing calculations. These simulations model the dynamics of a circumbinary disk and the mini-disks that form around two equal-mass black holes orbiting each other at an initial separation of 20 gravitational radii, and evolve the system for more than 10 orbits in the inspiral regime. We model the emission as the sum of thermal blackbody radiation emitted by an optically thick accretion disk and a power-law spectrum extending to hard X-rays emitted by a hot optically thin corona. We generate time-dependent spectra, images, and light curves at various frequencies to investigate intrinsic periodic signals in the emission, as well as the effects of the black hole spin. We find that prograde black hole spin makes mini-disks brighter since the smaller ISCO angular momentum demands more dissipation before matter plunges to the horizon. However, compared to mini-disks in larger separation binaries with spinning black holes, our mini-disks are less luminous: unlike those systems, their mass accretion rate is lower than in the circumbinary disk, and they radiate with lower efficiency because their inflow times are shorter. Compared to a single black hole system matched in mass and accretion rate, these binaries have spectra noticeably weaker and softer in the UV. Finally, we discuss the implications of our findings for the potential observability of these systems.

Eduardo M. Gutiérrez↗

DOE OSTI2019

A real-time phase-space beam emittance monitoring system

An electron beam position and angle monitoring system, ps-BPM, has been shown to be able to measure the electron source position and angle at a single location in a beamline at a synchrotron source. This system uses a monochromator to prepare a photon beam whose energy is at that of the K -edge of an absorber filter. The divergence of the beam from the source gives an energy range that will encompass the K -edge of the filter. A measurement of the centre of the monochromatic beam and the K -edge location through the absorber filter gives the position and angle of the electron source. Here, it is shown that this system is also capable of measuring the source size and divergence at the same time. This capability is validated by measurement as the beam size in the storage ring was changed and by ray-tracing simulations. The system operates by measuring the photon beam spatial distribution as well as a K -edge filtered beam distribution. These additional measurements result in the ability to also determine the electron source size and divergence.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS1991

X-ray optics. II - A technique for high resolution spectroscopy

A novel combination of optical elements and properties is combined to achieve high-spectral resolution using grazing incidence optics of modest quality. Analysis and ray tracing of examples show that using radial groove gratings at high blaze angles in the manner of an echelle spectrograph can provide high spectral resolution. This arrangement is compared to the conventional in-plane designs to show that the off-plane is superior in nearly every respect. Cross dispersion can be provided by the energy resolution of a CCD detector. Additional resolution can be squeezed from the system by strategic placement of gratings to take advantage of the azimuthal response of a Wolter X-ray optic.

Cash, Webster C., Jr.↗

DOE OSTI2016

Collimating Montel mirror as part of a multi-crystal analyzer system for resonant inelastic X-ray scattering

Advances in resonant inelastic X-ray scattering (RIXS) have come in lockstep with improvements in energy resolution. Currently, the best energy resolution at the Ir L 3 -edge stands at ~25 meV, which is achieved using a diced Si(844) spherical crystal analyzer. However, spherical analyzers are limited by their intrinsic reflection width. A novel analyzer system using multiple flat crystals provides a promising way to overcome this limitation. For the present design, an energy resolution at or below 10 meV was selected. Recognizing that the angular acceptance of flat crystals is severely limited, a collimating element is essential to achieve the necessary solid-angle acceptance. For this purpose, a laterally graded, parabolic, multilayer Montel mirror was designed for use at the Ir L 3 -absorption edge. It provides an acceptance larger than 10 mrad, collimating the reflected X-ray beam to smaller than 100 µrad, in both vertical and horizontal directions. The performance of this mirror was studied at beamline 27-ID at the Advanced Photon Source. X-rays from a diamond (111) monochromator illuminated a scattering source of diameter 5 µm, generating an incident beam on the mirror with a well determined divergence of 40 mrad. A flat Si(111) crystal after the mirror served as the divergence analyzer. From X-ray measurements, ray-tracing simulations and optical metrology results, it was established that the Montel mirror satisfied the specifications of angular acceptance and collimation quality necessary for a high-resolution RIXS multi-crystal analyzer system.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

NASA NTRS1986

Theoretical analysis of segmented Wolter/LSM X-ray telescope systems

The Segmented Wolter I/LSM X-ray Telescope, which consists of a Wolter I Telescope with a tilted, off-axis convex spherical Layered Synthetic Microstructure (LSM) optics placed near the primary focus to accommodate multiple off-axis detectors, has been analyzed. The Skylab ATM Experiment S056 Wolter I telescope and the Stanford/MSFC nested Wolter-Schwarzschild x-ray telescope have been considered as the primary optics. A ray trace analysis has been performed to calculate the RMS blur circle radius, point spread function (PSF), the meridional and sagittal line functions (LST), and the full width half maximum (PWHM) of the PSF to study the spatial resolution of the system. The effects on resolution of defocussing the image plane, tilting and decentrating of the multilayer (LSM) optics have also been investigated to give the mounting and alignment tolerances of the LSM optic. Comparison has been made between the performance of the segmented Wolter/LSM optical system and that of the Spectral Slicing X-ray Telescope (SSXRT) systems.

Shealy, D. L.↗

DOE OSTI2015

ALGORITHMS AND PROGRAMS FOR STRONG GRAVITATIONAL LENSING IN KERR SPACE-TIME INCLUDING POLARIZATION

Active galactic nuclei (AGNs) and quasars are important astrophysical objects to understand. Recently, microlensing observations have constrained the size of the quasar X-ray emission region to be of the order of 10 gravitational radii of the central supermassive black hole. For distances within a few gravitational radii, light paths are strongly bent by the strong gravity field of the central black hole. If the central black hole has nonzero angular momentum (spin), then a photon’s polarization plane will be rotated by the gravitational Faraday effect. The observed X-ray flux and polarization will then be influenced significantly by the strong gravity field near the source. Consequently, linear gravitational lensing theory is inadequate for such extreme circumstances. We present simple algorithms computing the strong lensing effects of Kerr black holes, including the effects on polarization. Our algorithms are realized in a program “KERTAP” in two versions: MATLAB and Python. The key ingredients of KERTAP are a graphic user interface, a backward ray-tracing algorithm, a polarization propagator dealing with gravitational Faraday rotation, and algorithms computing observables such as flux magnification and polarization angles. Our algorithms can be easily realized in other programming languages such as FORTRAN, C, and C++. The MATLAB version of KERTAP is parallelized using the MATLAB Parallel Computing Toolbox and the Distributed Computing Server. The Python code was sped up using Cython and supports full implementation of MPI using the “mpi4py” package. As an example, we investigate the inclination angle dependence of the observed polarization and the strong lensing magnification of AGN X-ray emission. We conclude that it is possible to perform complex numerical-relativity related computations using interpreted languages such as MATLAB and Python.

79 ASTRONOMY AND ASTROPHYSICS↗