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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Reduction of discretization error for ray tracing of MOC through a correction on collision probabilities

A new correction model for ray tracing of the method of characteristics is proposed in order to reduce discretization error. As the ray tracing parameters such as azimuthal angle division, polar angle division and ray separation are considered in this study. In the method of characteristics, region average scalar fluxes can be implicitly expressed by collision probabilities, although these collision probabilities are not directly treated in the ordinary calculation scheme. From this viewpoint, difference between a coarse ray tracing condition and a detailed one can be interpreted as the difference in the estimation of collision probabilities. In other words, the discretization error for ray tracing can be recognized as a consequence of inaccurate collision probabilities caused by coarse ray tracing. This discussion suggests that accurate region average scalar flux can be obtained through an appropriate correction on collision probabilities. In this paper, a correction model on collision probabilities is theoretically derived based on the neutron balance equation, and its validity is confirmed through typical single assembly calculations. The effectiveness of the present correction method is also discussed in this paper. It is confirmed that discretization error for ray tracing can be significantly reduced by the present correction method in a multi-assembly calculation, though the correction factor is estimated in single assembly geometry. (authors)

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2016

SU-F-T-555: Accurate Stereotactic Cone TMRs Converted from PDDs Scanned with Ray Trace

Purpose: To investigate whether the accuracy of TMRs for stereotactic cones converted from PDDs scanned with Ray Trace can be improved, when compared against the TMRs converted from the traditional PDDs. Methods: Ray Trace measurement in Sun Nuclear 3D Scanner is for accurate scan of small field PDDs. The system detects the center of field at two depths, for example, at 3 and 20 cm in our study, and then performs scan along the line passing the two centers. With both Ray Trace and the traditional method, PDDs for conical cones of 4, 5, 7.5, 10, 12.5, 15, and 17.5 mm diameter (jaws set to 5×5 cm) were obtained for 6X FFF and 10X FFF energies on a Varian Edge linac, using Edge detectors. The formalism of converting PDD to TMR given in Khan’s book (4th Edition, p.161) was applied. Sp values at dmax were obtained by measuring cone Scp and Sc. Continuous direct measurement of TMR by filling/draining water to/from the tank and spot measurement by moving the tank and detector were also performed with the same equipment, using 100 cm SDD. Results: For 6XFFF energy and all the cones, TMRs converted from Ray Trace were very close to the continuous and spot measurement, while TMRs converted from traditional PDDs had larger deviation. Along the central axis beyond dmax, 1.7% of TMR data points calculated from Ray Trace had more 3% deviation from measurement, with maximal deviation of 5.2%. Whereas, 34% of TMR points calculated from traditional PDDs had more than 3% deviation, with maximum of 5.7%. In this initial study, Ray Trace scans for 10XFFF beam were noisy, further measurement is warranted. Conclusion: The Ray Trace could improve the accuracy of PDDs measurement and the calculated TMRs for stereotactic cones, which was within 3% of the measured TMRs.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

Results from a synthetic model of the ITER XRCS-Core diagnostic based on high-fidelity x-ray ray tracing

A high-fidelity synthetic diagnostic has been developed for the ITER core x-ray crystal spectrometer diagnostic based on x-ray ray tracing. This synthetic diagnostic has been used to model expected performance of the diagnostic, to aid in diagnostic design, and to develop engineering tolerances. The synthetic model is based on x-ray ray tracing using the recently developed xicsrt ray tracing code and includes a fully three-dimensional representation of the diagnostic based on the computer aided design. The modeled components are: plasma geometry and emission profiles, highly oriented pyrolytic graphite pre-reflectors, spherically bent crystals, and pixelated x-ray detectors. Plasma emission profiles have been calculated for Xe 44+ , Xe 47+ , and Xe 51+ , based on an ITER operational scenario available through the Integrated Modelling & Analysis Suite database, and modeled within the ray tracing code as a volumetric x-ray source; the shape of the plasma source is determined by equilibrium geometry and an appropriate wavelength distribution to match the expected ion temperature profile. All individual components of the x-ray optical system have been modeled with high-fidelity producing a synthetic detector image that is expected to closely match what will be seen in the final as-built system. Particular care is taken to maintain preservation of photon statistics throughout the ray tracing allowing for quantitative estimates of diagnostic performance.

47 OTHER INSTRUMENTATION↗
NASA NTRS1988

Ray tracing optical analysis of offset solar collector for space station solar dynamic system

OFFSET, a detailed ray tracing computer code, was developed at NASA Lewis Research Center to model the offset solar collector for the Space Station solar dynamic electric power system. This model traces rays from 50 points on the face of the Sun to 10 points on each of the 456 collector facets. The triangular facets are modeled with spherical, parabolic, or toroidal reflective surface contour and surface slope errors. The rays are then traced through the receiver aperture to the walls of the receiver. Images of the collector and of the Sun within the receiver produced by this code provide insight into the collector receiver interface. Flux distribution on the receiver walls, plotted by this code, is improved by a combination of changes to aperture location and receiver tilt angle. Power loss by spillage at the receiver aperture is computed and is considerably reduced by using toroidal facets.

Jefferies, Kent S.↗
NASA NTRS1988

Ray tracing optical analysis of offset solar collector for Space Station solar dynamic system

OFFSET, a detailed ray tracing computer code, was developed at NASA Lewis Research Center to model the offset solar collector for the Space Station solar dynamic electric power system. This model traces rays from 50 points on the face of the sun to 10 points on each of the 456 collector facets. The triangular facets are modeled with spherical, parabolic, or toroidal reflective surface contour and surface slope errors. The rays are then traced through the receiver aperture to the walls of the receiver. Images of the collector and of the sun within the receiver produced by this code provide insight into the collector receiver interface. Flux distribution on the receiver walls, plotted by this code, is improved by a combination of changes to aperture location and receiver tilt angle. Power loss by spillage at the receiver aperture is computed and is considerably reduced by using toroidal facets.

Jefferies, Kent S.↗
DOE OSTI2025

A three-dimensional laser ray-tracing methodology for radiation-hydrodynamics simulations

We report on a methodology for performing laser ray-tracing in three spatial dimensions for radiation-hydrodynamics simulation codes. Our method, which is an extension of that developed in Haines et al., Comput. Fluids 201, 104478 (2020), utilizes an automatically generated separate mesh for the laser ray-tracing from the radiation-hydrodynamics mesh. This enables the laser mesh to be tailored to minimize ray noise with significantly fewer rays than would be required when the ray-tracing is performed on the radiation-hydrodynamics mesh, primarily by allowing the use of high-aspect-ratio cells that are not suitable for hydrodynamics solvers. For a planar target, we show that our method provides a ≈ 100× reduction in computational expense to achieve a fixed level of ray noise relative to ray-tracing directly on the radiation-hydrodynamics mesh. The relatively low ray requirement also enables efficient computation of cross-beam energy transfer. Each cell in the logically cubic laser mesh is a non-convex dodecahedron with triangular sides, and numerical integration of the ray trajectories and inverse bremsstrahlung is performed by mapping each cell to the unit cube. We will describe our methodology in detail as well as its implementation in the xRAGE radiation-hydrodynamics code, discuss performance, and present the results from applying the methodology to test problems with analytic solutions for laser ray-tracing through a quadratic density gradient with an analytic solution as well as for a laser-driven heat front. In 3D radiation-hydrodynamics simulations of laser-driven experiments performed on the National Ignition Facility, laser ray-tracing with our methodology uses less than 1% of total computational time while introducing acceptably low levels of ray noise.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1980

Ray tracing of Jovian kilometric radiation

Results of computer ray tracing of Jovian kilometric radiation from 56.2 kHz to 1 MHz in a model Jovian magnetosphere with an Io torus are presented. Ray tracing calculations indicate that the Io torus presents a propagation barrier to the radiation and that the Jovian kilometric radiation must be generated in the L-O mode from a source near Jupiter on field lines passing through the Io torus. One effect of the Io torus is to refract the rays away from the magnetic equator forming a shadow zone at radial distances beyond the torus. In general, at radial distances greater than 10 Jovian radii, as the wave frequency increases (greater than 200 kHz) so does the magnetic latitude of the shadow zone. These and other features of the ray tracing calculations are in good qualitative agreement with the observations from the plasma wave receiver and planetary radio astronomy experiment on board both Voyagers 1 and 2.

Green, J. L.↗
DOE OSTI2015

Simulation of radiation damping in rings, using stepwise ray-tracing methods

The ray-tracing code Zgoubi computes particle trajectories in arbitrary magnetic and/or electric field maps or analytical field models. It includes a built-in fitting procedure, spin tracking many Monte Carlo processes. The accuracy of the integration method makes it an efficient tool for multi-turn tracking in periodic machines. Energy loss by synchrotron radiation, based on Monte Carlo techniques, had been introduced in Zgoubi in the early 2000s for studies regarding the linear collider beam delivery system. However, only recently has this Monte Carlo tool been used for systematic beam dynamics and spin diffusion studies in rings, including eRHIC electron-ion collider project at the Brookhaven National Laboratory. Some beam dynamics aspects of this recent use of Zgoubi capabilities, including considerations of accuracy as well as further benchmarking in the presence of synchrotron radiation in rings, are reported here.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

Simulation of Radiation Damping in Rings using Stepwise Ray-Tracing Methods

The ray-tracing code Zgoubi has been subject to benchmarking regarding synchrotron radiation damping in rings, in the past months. This work is reported here. It has been performed in view in particular of further spin diffusion simulations benchmarking, and application to electron beam polarization transmission in e-RHIC.

43 PARTICLE ACCELERATORS↗
NASA NTRS1971

Ray tracing program with options for diffraction gratings

Diffraction theory, developed in vectorial form and coded into ray tracing routines, permits tracing rays of any wavelength through surfaces that are plane, spherical, conical, or aspheric polynomial. Ruled diffraction gratings may run in either X-direction or Y-direction, where Z is optical axis.

Howell, B. J.↗
NASA NTRS1984

Three dimensional ray tracing of the Jovian magnetosphere in the low frequency range

Ray tracing studies of Jovian low frequency emissions were studied. A comprehensive three-dimensional ray tracing computer code for examination of model Jovian decametric (DAM) emission was developed. The improvements to the computer code are outlined and described. The results of the ray tracings of Jovian emissions will be presented in summary form.

Menietti, J. D.↗
NASA NTRS1993

AXAF FITS standard for ray trace interchange

A standard data format for the archival and transport of x-ray events generated by ray trace models is described. Upon review and acceptance by the Advanced X-ray Astrophysics Facility (AXAF) Software Systems Working Group (SSWG), this standard shall become the official AXAF data format for ray trace events. The Flexible Image Transport System (FITS) is well suited for the purposes of the standard and was selected to be the basis of the standard. FITS is both flexible and efficient and is also widely used within the astronomical community for storage and transfer of data. In addition, software to read and write FITS format files are widely available. In selecting quantities to be included within the ray trace standard, the AXAF Mission Support team, Science Instruments team, and the other contractor teams were surveyed. From the results of this survey, the following requirements were established: (1) for the scientific needs, each photon should have associated with it: position, direction, energy, and statistical weight; the standard must also accommodate path length (relative phase), and polarization. (2) a unique photon identifier is necessary for bookkeeping purposes; (3) a log of individuals, organizations, and software packages that have modified the data must be maintained in order to create an audit trail; (4) a mechanism for extensions to the basic kernel should be provided; and (5) the ray trace standard should integrate with future AXAF data product standards.

Hsieh, Paul F.↗
DOE OSTI2019

Rapid simulation of X-ray scatter measurements for threat detection via GPU-based ray-tracing

Scatter-based X-ray imaging has increased in prominence in areas ranging from cancer diagnostics to threat detection in aviation security, due largely to the development of new algorithms and components over the last decade. However, system design and algorithm development are often hindered by an inability to generate a sucient amount of accurate data. To further the development of scatter-based systems, we created a rapid X-ray scatter simulation tool built with a GPU-centric, parallel ray-tracing framework (NVIDIA OptiX). This tool models a full range of X-ray imaging components and describes 3D objects formed with heterogeneous media using polygon meshes. The scatter simulation algorithm we used is similar to the previously-described hybrid approach; however, instead of employing Monte Carlo techniques, we developed a purely analytical algorithm to sample the distribution of single-scatter events throughout the region of interest. The contribution of scattered photons to the measured signal is then calculated using the first-Born approximation. Here, the accuracy of the implemented pipeline has been validated by comparing simulated against experimental data obtained with a laboratory X-ray scattering system and phantoms of varied materials. Using a single desktop computer with an NVIDIA GTX 770 GPU, we show that the scatter signal generated by an incident fan beam and recorded by a 125 125 element detector array can be simulated in on the order of a few to tens of minutes (depending on the object extent and complexity). As a point of comparison, simulations performed via CPU-based Monte Carlo tools, such as GEANT4 (i.e., the gold standard), can take up to tens of hours to achieve comparable results.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Real and complex valued geometrical optics inverse ray-tracing for inline field calculations

In this work, a 3-D ray based model for computing laser fields in dissipative and amplifying media is presented. The eikonal equation is solved using inverse ray-tracing on a dedicated nonstructured 3-D mesh. Inverse ray-tracing opens the possibility of using Complex Geometrical Optics (CGO), for which we propose a propagation formalism in a finite element mesh. Divergent fields at caustics are corrected using an etalon integral method for fold-type caustics. This method is successfully applied in dissipative media by modifying the ray-ordering and root selection rules, thereby allowing one to reconstruct the field in the entire caustic region. In addition, we demonstrate how caustics in the CGO framework can disappear entirely for sufficiently dissipative media, making the complex ray approach valid in the entire medium. CGO is shown to offer a more precise modeling of laser refraction and absorption in a dissipative medium when compared to Geometrical Optics (GO). In the framework of Inertial Confinement Fusion (ICF), this occurs mostly at intermediate temperatures or at high temperatures close to the critical density. Additionally, GO is invalid at low temperatures if an approximated expression of the permittivity is used. The inverse ray-tracing algorithm for GO and CGO is implemented in the IFRIIT code, in the framework of a dielectric permittivity described in 3-D using a piecewise linear approximation in tetrahedrons. Fields computed using GO and CGO are compared to results from the electromagnetic wave solver LPSE. Excellent agreement is obtained in 1-D linear and nonlinear permittivity profiles. Good agreement is also obtained for ICF-like Gaussian density profiles in 2-D. Finally, we demonstrate how the model reproduces Gaussian beam diffraction using CGO. The IFRIIT code will be interfaced inline to 3-D radiative hydrodynamic codes to describe the nonlinear laser plasma interaction in ICF and high-energy-density plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1992

Combining ray-trace and diffraction analysis: A design example

An example is presented of using a combined ray trace and diffraction modeling code to simulate effects of objective-lens tilt in an optical data storage device. In some cases, neither ray-trace analysis nor diffraction analysis can give an adequate description of an optical system. The designer that is faced with the problem of analyzing such a system is forced to use a ray-trace program to determine aberrations in the exit pupil and then introduce aberration coefficients into a diffraction model that simulate the propagation. This approach was found rather awkward, especially if complicated aberrations are present. Our approach is to integrate a diffraction analysis and a ray-trace description of an optical path into one program. Our design is taken from a data storage application, where we must analyze the effects of objective-lens tilt.

Milster, Tom D.↗
DOE OSTI2023

Analytical Meridional, Non-Paraxial Ray Tracing

We present an analytical method for non-paraxial, meridional ray tracing through a system of basic geometric surfaces derivable from a generalized ellipse; i.e. the most general ray tracing method for a 2-dimensional system comprised of elliptical, circular, and linear surfaces. This work is meant as a non-small angle generalization of standard ray tracing for geometric optics.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1973

Light ray tracing through a leaf cross section

A light ray, incident at about 5 deg to the normal, is geometrically plotted through the drawing of the cross section of a soybean leaf using Fresnel's equations and Snell's law. The optical mediums of the leaf considered for ray tracing are: air, cell sap, chloroplast, and cell wall. The ray is also drawn through the same leaf cross section with cell wall and air as the only optical mediums. The values of the reflection and transmission found from the ray tracing tests agree closely with the experimental results obtained using a Beckman Dk-2A Spectroreflector.

Kumar, R.↗