Ray Tracing Study Research Articles

Monte–Carlo ray-tracing studies of multiplexed prismatic graphite analyzers for the cold-neutron triple-axis spectrometer at the High Flux Isotope Reactor

A modern cold triple-axis spectrometer to study quantum condensed matter systems is planned for the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. Here, we describe the conceptual principles and design of a secondary spectrometer using a multiplexed, prismatic analyzer system relying on graphite crystals and inspired by the successful implementation of the Continuous Angle Multiple Energy Analysis (CAMEA) spectrometers at the Paul Scherrer Institute. This project is currently known as MANTA for Multi-Analyzer Neutron Triple-Axis. We report Monte-Carlo ray-tracing simulations on a simple but realistic sample scattering kernel to further illustrate the prismatic analyzer concept’s workings, calibration, and performance. Then, we introduce a new statistical analysis approach based on the prismatic analyzer concept to improve the number of final energies measured on the spectrometer. We also study possible evolutions in the CAMEA design relevant for MANTA.

Ray-Tracing Study of Artificial Black Hole in Electromagnetic Field

Ray-Tracing Study of Artificial Black Hole in Electromagnetic Field

Peripheral visual field shifts after intraocular lens implantation.

To assess whether intraocular lens (IOL) implantation induces shifts in the peripheral visual field. Department of Ophthalmology, Leiden University Medical Center, Leiden, the Netherlands. Ray tracing study. Non-sequential ray tracing simulations were performed with phakic and pseudophakic versions of the same eye model to assess potential shifts in the visual field after IOL implantation. Two different IOL designs were evaluated and for each design 5 different axial positions and 7 different intrinsic powers were tested. The relation between the physical position of the light source and the location where the retina was illuminated was determined for each eye model. Subsequently, these relations were used to calculate whether the visual field shifts in pseudophakic eyes. The pseudophakic visual field shift was below 1 degree for central vision in all evaluated models. For peripheral vision, the light rays in the pseudophakic eyes were refracted to a more central retinal location compared to phakic eyes, resulting in a central shift of the peripheral visual field. The magnitude of the shift depended on the IOL design and its axial position, but could be as high as 5.4 degrees towards central vision. IOL implantation tends to have little effect on the central visual field but can induce an over 5 degrees shift in the peripheral visual field. Such a shift can affect the perception of peripheral visual complaints.

Design and evaluation of co-currently illuminated two-phase bubbly flow photochemical reactors

Current two-phase flow photochemical reactors are lacking energy efficiency required for industrial applicability. As an alternative, co-currently illuminated bubbly flow photochemical reactors are proposed. These have the advantage of running at higher absorbance values, thereby wasting less photons, improving cost efficiency, and decreasing gas holdup by separating gas and liquid residence time in the reactor. A mathematical model was used in the study in combination with photosensitized reactions, which yielded three coupled differential equations and four non-dimensional groups governing the reactor performance. A parameter study yielded an optimal operating point at a quantum photon balance (ϕtotρ) of 1, an absorbance (AS) of at least 1, a chemical quenching parameter (κA) of less than 0.1, and a sensitizer stability ratio (ϕS/fS) of less than 1. Optimal absorbance was determined via the use of a ray tracing study, yielding a theoretical optimal absorbance of 1.75 using 7 µM of rose bengal. The modelling results are experimentally validated, and the model was shown to be suitable across a wide range of operating conditions. Optimal absorbance was experimentally evaluated to match the modelling results, higher absorbance values lead to more local absorbance, throttling reactor performance. With high reagent concentrations, the reaction was found to be liquid side mass transfer limited. Guidelines are presented to design this novel type of reactor and ways to improve the reactor performance in scaled up versions. The reactor was compared against the current state-of-the-art reactors, yielding an improvement PSTY by 4.5 times and an increased reagent/sensitizer ratio by 100 times, both drastically decreasing operational cost of the reactor.

Holistic Enlightening of Blackspots With Passive Tailorable Reflecting Surfaces for Efficient Urban mmWave Networks

Mitigating outage regions is of particular interest for emerging millimeter-wave (mmWave) and future sub-terahertz frequency cellular networks. Whereas smart radio environments based on metasurfaces constitute a key concept for 6G research, current networks cannot be served as new control procedures are required. Although small prototypes are already emerging, costs will be higher for the dense deployment of reconfigurable intelligent surfaces (RISs) than for passive reflectors. It is argued that passive reflectors can be used to effectively, cost-efficiently, and permanently boost connectivity in well-defined service areas. Leveraging the advantages of 3D printing and spray-painted conductive varnish, we introduce the Holistic Enlightening of bLackspots with passIve reflectOr moduleS (HELIOS) approach which is characterized by its scalability and parametrizability to meet the reflection requirements derived from sophisticated network planning. These slim reflectors meet the core criteria of ease of installation and minimal visual impact on the cityscape, which are imperative for market success. Our measurements-based comparison of prototypes against typical metal/aluminum reflectors shows at least equal reflectivity at a higher practicality of the proposed manufacturing process. The conducted simulation study validates the modular reflector pattern design process and finds a trade-off between the reflector efficiency and the minimum protrusion depth, which relates to the number of modules in the designated mounting area. An urban ray-tracing simulation-based case study further underlines the high applicability of the proposed approach, with the growth of the beyond line-of-sight (LOS) connectivity region being nearly twice as large for a site-tailored HELIOS configuration as for a simple reflector plate.

Effect of anatomical differences and intraocular lens design on negative dysphotopsia.

To assess the effect of ocular anatomy and intraocular lens (IOL) design on negative dysphotopsia (ND). Department of Ophthalmology, Leiden University Medical Center, Leiden, the Netherlands. Ray-tracing study based on clinical data. Ray-tracing simulations were performed to assess the effect of anatomical differences and differences in IOL design on the peripheral retinal illumination. To that end, eye models that incorporate clinically measured anatomical differences between eyes of patients with ND and eyes of pseudophakic controls were created. The anatomical differences included pupil size, pupil centration, and iris tilt. The simulations were performed with different IOL designs, including a simple biconvex IOL design and a more complex clinical IOL design with a convex-concave anterior surface. Both IOL designs were analyzed using a clear edge and a frosted edge. As ND is generally considered to be caused by a discontinuity in peripheral retinal illumination, this illumination profile was determined for each eye model and the severity of the discontinuity was compared between eye models. The peripheral retinal illumination consistently showed a more severe discontinuity in illumination with ND-specific anatomy. This difference was the least pronounced, 8%, with the frosted edge clinical IOL and the most pronounced, 18%, with the clear edge biconvex IOL. These results show that small differences in the ocular anatomy or IOL design affect the peripheral retinal illumination. Therewith, they can increase the severity of ND by up to 18%.

Development and Accuracy Assessment of a High-Precision Dual-Axis Pre-Commercial Solar Tracker for Concentrating Photovoltaic Modules

In recent decades, advances in the development of solar tracking systems (STSs) have led to concentrating solar technologies to increase their energy conversion efficiency. These systems, however, still have areas of opportunity or improving their performance and reducing their manufacturing costs. This paper presents the design, construction and evaluation of a high-precision dual-axis solar tracking system with a technology readiness level of 7–8. The system is controlled by a low-cost Arduino board in a closed-loop control using a micro-electromechanical solar sensor. Real-time tracking experiments were performed under a clear sky as well as during partly and mostly cloudy days. Solar tracking accuracy was evaluated in an operational environment using test procedures adapted from the International Electrotechnical Commission (IEC) 62817 standard. The total mean instantaneous solar tracking error on a clear day measured with a calibrated digital solar sensor was 0.37° and 0.52° with a developed pinhole projection system. Similarly, the total mean reported solar tracking accuracy achieved was 0.390° on a sunny day and 0.536° on a partially cloudy day. An annual power generation analysis considering a conventional photovoltaic (PV) panel system and a typical concentrator photovoltaic (CPV) module as payloads was also presented. Simulations showed an increase in the generation of up to 37.5% for a flat panel with dual-axis tracking versus a fixed panel. In the case of the CPV system, first, a ray tracing study was implemented to determine the misalignment coefficient, then the annual power generation was estimated. The developed STS allowed the CPV modules to reach at least 90% of their nominal energy conversion efficiency.

Vehicular VLC: A Ray Tracing Study Based on Measured Radiation Patterns of Commercial Taillights

In this letter, we investigate the performance of vehicular visible light communications based on the radiation patterns of different commercial taillights (TLs) using non-sequential ray tracing simulations. Our simulation results indicate a significant variation in the path loss compared with Lambertian model. Based on the ray tracing results, we propose a new path loss model as a function of the propagation distance considering the asymmetrical radiation pattern of TLs. We use this model to derive the attainable transmission distance. We further present the delay spread for various vehicular communication scenarios to demonstrate the effect of neighboring vehicles.

Multizonal Design Multifocal Intraocular Lens-Induced Astigmatism According to Orientation.

To evaluate the differences in intraocular lens (IOL)-induced astigmatism according to differences in orientation of a multizonal multifocal IOL, the Precizon Presbyopic NVA IOL (Ophtec BV). The clinical study reviewed 80 eyes from 40 patients with cataracts who underwent Precizon Presbyopic IOL implantation. Residual astigmatism, as measured by autorefraction and manifest refraction, was investigated using vector analysis of eyes implanted with vertical (90 ± 30 degrees) and horizontal (180 ± 30 degrees) orientations of the first near segment of the IOL. In the ray-tracing simulation study, pseudophakic eyes with the Precizon Presbyopic IOL were modeled. The modulation transfer function (MTF) of each case was compared with respect to the amount of corneal astigmatism of the model eyes and the orientation of the first near segment. The mean IOL-induced astigmatism measured by autorefraction was 0.68 ± 0.58 diopters (D) at 1 degree in the vertical orientation of the first near segment (n = 52) and 1.05 ± 0.81 D at 96 degrees in the horizontal orientation (n = 28). However, the mean IOL-induced astigmatism measured by manifest refraction was 0.14 ± 0.44 D at 171 degrees and 0.46 ± 0.40 D at 95 degrees. The MTF analysis showed that the highest MTF values were measured in eyes without corneal astigmatism in both the vertically and horizontally implanted IOLs. Autorefraction measurement indicates induction of with-the-rule astigmatism by the Precizon Presbyopic IOL when implanted vertically with respect to the first near segment, and against-the-rule astigmatism when implanted horizontally. However, this astigmatism is clinically insignificant according to manifest refraction and ray-tracing simulation. [J Refract Surg. 2020;36(11):740-748.].

Ray tracing study of ITER in-vessel lighting system

In-vessel lighting system is being developed for ITER. The diagnostic system is for inspecting and detecting eventual damages and defects of in-vessel components between discharges by illuminating the vacuum vessel with light sources. In this work, feasibility study of the in-vessel lighting system is performed using a ray tracing simulation. We installed sources and detectors in a ray tracing model using the field of views of wide-angle viewing systems and calculated the radiance profiles at detectors for different wall reflection scenarios. It was found that the wall is uniformly illuminated when the wall has a diffuse reflectance while the specular case has more brightness. We will discuss feasibility of the diagnostics system based on expected signal and noise levels.

Raytracing Study of Source Regions of Whistler Mode Wave Power Distribution Relative to the Plasmapause

AbstractA comprehensive numerical raytracing study of whistler mode wave power with the inclusion of finite background electron and ion temperature is performed in order to investigate wave power distribution in relation to the plasmapause. Both Landau damping and linear growth of whistler mode waves are taken into account using a bi‐Maxwellian hot electron distribution as well as an isotropic hot electron distribution. Isotropic and bi‐Maxwellian distributions yield similar results of statistical spatial wave power for frequencies below 500 Hz. The effect of finite background temperature of ∼1 eV for electrons and ions are secondary in terms of the spatial distribution of whistler mode waves relative to the plasmapause. Three primary equatorial source locations at L=2, Lpp and L=5, corresponding to within the plasmasphere, at the plasmapause and outside the plasmapause, are investigated for MLT values of 00, 06, 12, and 18. At each location, waves are launched with a range of initial wave normal angles (−70° to 20°). The simulated wave power distributions are compared with observations from the EMFISIS instrument on Van Allen Probe A. Correspondence between the simulated distribution and the observations requires a weighting of the source regions. Results suggest that the majority of whistler mode power in the plasmasphere is sourced from within the plasmasphere itself and near the plasmapause. Only at noon (MLT 12) is wave power sourced primarily from at and outside the plasmapause.

Magneto-gravity wave packet dynamics in strongly magnetized cores of evolved stars

ABSTRACT Magnetic fields are believed to be generated in the cores of massive main-sequence stars, and these may survive on to later stages of evolution. Observations of depressed dipole modes in red giant stars have been touted as evidence for these fields, but the predictions of existing magnetic theories have difficulty accommodating several aspects, including the need to return a fraction of wave energy from the core to the envelope, and the persistent gravity-like character of affected modes. In this work, we perform a Hamiltonian ray-tracing study investigating the dynamics of magneto-gravity waves in full spherical geometry, using realistic stellar models and magnetic field configurations. This technique applies in the limit where wavelengths are much shorter than scales of background variation. We conduct a comprehensive exploration of parameter space, examining the roles of wave frequency, spherical harmonic degree, wavevector polarization, incoming latitude, field strength, field radius, and evolutionary state. We demonstrate that even in the presence of a strong field, there exist trajectories where waves remain predominantly gravity-like in character, and these are able to undergo reflection out of the core, much like pure gravity waves. The remaining trajectories are ones where waves acquire significant Alfvén character, becoming trapped and eventually dissipated. Orientation effects, i.e. wavevector polarization and incoming latitude, are found to be crucial factors in determining the outcome (trapped versus reflected) of individual wave packets. The allowance for partial energy return from the core offers a solution to the conundrum faced by the magnetic hypothesis.

Coexistence of Lightning Generated Whistlers, Hiss and Lower Hybrid Noise Observed by e-POP (SWARM-E)–RRI

Whistler mode waves play a major role in regulating the lifetime of trapped electrons in the Earth’s radiation belts. Specifically, interaction with whistler mode hiss waves is one of the mechanisms that maintains the slot region between the inner and outer radiation belts. The generation mechanism of hiss is a topic still under debate with at least three prominent theories present in the literature. Lightning generated whistlers in their ducted or non-ducted modes are considered to be one of the possible sources of hiss. We present a study of new observations from the Radio Receiver Instrument (RRI) on the Enhanced Polar Outflow Probe (ePOP: also known as SWARM-E). RRI consists of two orthogonal dipole antennas, which enables polarization measurements, when the satellite boresight is parallel to the geomagnetic field. Here we present 105 ePOP - RRI events from 2014–2018, in which lightning whistlers(75) and hiss waves(39) were observed. In more than 50% of those whistler observations, hiss found to co-exist. Moreover, the whistler observations are correlated with observations of wave power at the lower-hybrid resonance. The observations and a whistler mode ray-tracing study suggest that multiple-hop lightning induced whistlers can be a source of hiss and plasma instabilities in the magnetosphere.

Light propagation in a neutron detector based on 6Li glass scintillator particles in an organic matrix

Composite materials consisting of 6Li scintillator particles in an organic matrix can enable thermal neutron detectors with excellent rejection of gamma-ray backgrounds. The efficiency of transporting scintillation light through such a composite is critical to the detector performance. This optical raytracing study of a composite thermal neutron detector quantifies the various sources of scintillation light loss and identifies favorable photomultiplier tube (PMT) readout schemes. The composite material consisted of scintillator cubes within an organic matrix shaped as a right cylinder. The cylinder surface was surrounded by an optical reflector, and the light was detected by PMTs attached to the cylinder end faces. A reflector in direct contact with the composite caused 53% loss of scintillation light. This loss was reduced 8-fold by creating an air gap between the composite and the reflector to allow a fraction of the scintillation light to propagate by total internal reflection. Replacing a liquid mineral oil matrix with a solid acrylic matrix decreased the light transport efficiency by only ∼10% for the benefit of creating an all-solid-state device. The light propagation loss was found to scale exponentially with the distance between the scintillation event and the PMT along the cylinder main axis. This enabled a PMT readout scheme that corrects for light propagation loss on an event-by-event basis and achieved a 4.0% energy resolution that approached Poisson-limited performance. These results demonstrate that composite materials can enable practical thermal neutron detectors for a wide range of nuclear non-proliferation and safeguard applications.

Radiation characteristics of water droplets in a fire-inspired environment: A Monte Carlo ray tracing study

The effects of radiation of water mists in a fire-inspired environment are numerically investigated for different complexities of radiative media in a three-dimensional cubic enclosure. A Monte Carlo ray tracing (MCRT) method is employed to solve the radiative transfer equation (RTE). The anisotropic scattering behaviors of water mists are modeled by a combination of the Mie theory and the Henyey-Greestein relation. A tabulation method considering the size and wavelength dependencies is established for water droplets, to reduce the computational cost associated with the evaluation of the nongray spectral properties of water mists. Validation and verification of the coupled MCRT solver are performed using a one-dimensional slab with gray gas in comparison with the analytical solutions. Parametric studies are then performed using a three-dimensional cubic box to examine radiation of two monodispersed and one polydispersed water mist systems. The tabulation method can reduce the computational cost by a factor of one hundred. Results obtained without any scattering model better conform with results obtained from the anisotropic model than the isotropic scattering model, when a highly directional emissive source is applied. For isotropic emissive sources, isotropic and anisotropic scattering models predict comparable results. The addition of different volume fractions of soot shows that soot may have a negative impact on the effectiveness of water mists in absorbing radiation when its volume fraction exceeds certain threshold.

Diffraction gratings metrology and ray-tracing results for an XUV Raman spectrometer at FLASH.

The extreme-ultraviolet double-stage imaging Raman spectrometer is a permanent experimental endstation at the plane-grating monochromator beamline branch PG1 at FLASH at DESY in Hamburg, Germany. This unique instrument covers the photon energy range from 20 to 200 eV with high energy resolution of about 2 to 20 meV (design values) featuring an efficient elastic line suppression as well as effective stray light rejection. Such a design enables studies of low-energy excitations like, for example, phonons in solids close to the vicinity of the elastic line. The Raman spectrometer effectively operates with four reflective off-axial parabolic mirrors and two plane-grating units. The optics quality and their precise alignment are crucial to guarantee best performance of the instrument. Here, results on a comprehensive investigation of the quality of the spectrometer diffraction gratings are presented. The gratings have been characterized by ex situ metrology at the BESSY-II Optics Laboratory, employing slope measuring deflectometry and interferometry as well as atomic force microscopy studies. The efficiency of these key optical elements has been measured at the at-wavelength metrology laboratory using the reflectometer at the BESSY-II Optics beamline. Also, the metrology results are discussed with respect to the expected resolving power of the instrument by including them in ray-tracing studies of the instrument.

A Comparison of Indoor MIMO Measurements and Ray-Tracing at 24 and 2.55 GHz

Colocated $4\times 4$ multiple-input multiple-output measurements at 2.55 and 24 GHz are presented for two university buildings consisting of classrooms and offices. Link gain in hallways and connected laboratories looks similar at the two frequencies when the effect of lower effective receive antenna aperture with increasing frequency is removed. Non-line-of-sight (NLOS) propagation through a wall or around hallway corners exhibits approximately 5–20 dB (11 dB on average) greater loss beyond the 20 dB aperture loss at 24 GHz compared to that at 2.55 GHz. Fixed directional antennas increase path loss (PL) by an average of 13 dB when misaligned. Capacity for normalized signal-to-noise ratio is very similar in the two bands and is close to that for the optimal independent identically distributed case, indicating sufficient multipath for spatial multiplexing at 24 GHz. A ray-tracing study suggests that material loss must increase from 2.55 to 24 GHz to correctly predict the higher PL at 24 GHz in severely obstructed scenarios, indicating a need for future material characterization in high microwave bands. The results suggest that 24 GHz is a viable option to replace medium-range (10–30 m) NLOS wireless services currently operating at 2.4 GHz.

A non-tracking concentrating collector for solar thermal applications

We report the development of a solar thermal collector module based on our proposed design (Ratismith et.al., 2014) of a large acceptance-angle multiple-parabolic trough which surrounds a standard evacuated cylindrical tube containing a planar absorber plate. The concentrator accepts diffuse solar radiation with an intercept factor of near 100% and so is suitable particularly for tropical climates. The module incorporates a novel direct metal-to-water contact resulting in an improved efficiency of heat transfer to the working liquid. Comparison with the performance characteristics, principally power output and temperatures attained, of a commercially-available non-concentrating assembly of evacuated absorber tubes is made. The experimental results, obtained by testing under typical conditions of solar irradiation throughout the day in Bangkok, indicate that the improvement over a non-concentrating collector, suggested theoretically on the basis of ray-tracing studies, is attained in practice. The superior performance of the concentrating collector indicates its suitability both for residential and industrial applications.

Ray Tracing Study on Top ECCD Launch in KSTAR

The current drive efficiency of electron cyclotron (EC) wave is typically low compared with other RF and neutral beam heating system in tokamak. It is known that EC current drive by outboard launch suffers from low current drive efficiency due to electron trapping. However, the heating and current drive by EC wave is being regarded as a strong candidate for DEMO reactor due to the simplicity of the launcher, none of its interaction with plasma, and no coupling issue at the plasma edge. Also, off-axis heating and current drive by EC wave plays an important role of steady state operation optimization. To enhance the current drive efficiency in DEMO-relevant operation condition having high density and high temperature, the top launch of EC wave is recently proposed in FNSF design [2]. In FNSF, a top launch makes use of a large toroidal component to the launch direction adjusting the vertical launch angle so that the rays propagate nearly parallel to the resonance layer increasing of Doppler shift with higher n||. The results shows a high dimensional efficiency for a broad ECCD profile peaked off axis. In KSTAR, the possibility of efficient off-axis ECCD using top launch is investigated using the ray tracing code, GENRAY [3] for the operating EC frequencies (105 GHz or 140 GHz, and 170 GHz). The high current drive efficiency is found by adjusting the toroidal magnetic field and the radial pivot position of the final launcher mirror for fundamental O-mode and second harmonic X-mode. A large Doppler shift is not quite sure in the typical plasma profile in KSTAR, but the simulation results show high current drive efficiency. This paper presents ray tracing results for many cases with the wave trajectories and damping of EC by scanning the launching angle for specific launcher pivot positions and toroidal magnetic field, and two equilibriums of the KSTAR.

Influence of spatial curvature of a liquid jet on the rainbow positions: Ray tracing and experimental study

Rainbow refractometry is largely used in optical metrology of particles thanks to its advantages of being non-intrusive, precise and fast. Many authors have contributed to its development and the application in the characterization of liquid jets/droplets. The researches reported in the literature are mainly for the spherical droplets or the liquid jets which can be considered as a cylinder of constant section. However, the section of a real liquid jet, even in the simplest configuration, varies with distance from the exit. The influence of the spatial curvature of the jets must, therefore, be taken into account. In this paper, we report experimental measurements of the shifts of the rainbow positions in the horizontal and vertical directions of a liquid jet and the theoretical investigation with the vectorial complex ray model. It is shown that the shifts of rainbow positions are very sensitive to the spatial curvature of the jets. This work is hoped to provide a new approach to characterizing the structure and the instability of liquid jets.