Ray-tracing Code Research Articles

Assessment of UAM and drone noise impact on the environment based on virtual flights

Drones and urban air mobility vehicles, which are mostly intended for urban operations, have attracted intensive research interest. Their environmental noise impact should not be ignored and should be a certification consideration. Numerical simulations can provide means to efficiently assess the noise impact on the complex urban environments, thanks to the advances in both software and hardware. In this study, virtual flights of the noise sources to mimic the drones and urban air mobilities are conducted to investigate the environmental impact by using the Gaussian beam tracing method implemented in an in-house solver Environmental Acoustic Ray Tracing Code, in which the dominant acoustic processes in outdoor applications are modelled. The solver also allows for modelling of sources with generic directivity patterns, which is beneficial for investigating the drone and urban air mobility noise produced by multiple rotors. Two examples of studying noise impact on building and realistic urban environment are conducted. The effects of the surface acoustic impedance, source type and flight path are investigated. By using the efficient simulation solver, the noise impact can be quickly assessed through virtual flights, providing a promising approach to assist the low-noise flight planning and noise certification.

Physically motivated X-ray obscurer models

Context. The nuclear obscurer of active galactic nuclei (AGN) is poorly understood in terms of its origin, geometry, and dynamics. Aims. We investigate whether physically motivated geometries emerging from hydro-radiative simulations can be differentiated with X-ray reflection spectroscopy. Methods. For two new geometries, the radiative fountain model and a warped disk, we release spectral models produced with the ray tracing code XARS. We contrast these models with spectra of three nearby AGN taken by NuSTAR and Swift/BAT. Results. Along heavily obscured sightlines, the models present different 4−20 keV continuum spectra. These can be differentiated by current observations. Spectral fits of the Circinus Galaxy favour the warped disk model over the radiative fountain, and clumpy or smooth torus models. Conclusions. The necessary reflector (NH ≥ 1025 cm2) suggests a hidden population of heavily Compton-thick AGN amongst local galaxies. X-ray reflection spectroscopy is a promising pathway to understand the nuclear obscurer in AGN.

Observation of synergy between lower hybrid waves at two frequencies in EAST

Synergistic effects between two frequencies of lower hybrid (LH) waves—operating at 2.45 and 4.6 GHz—were observed in experiment on EAST for the first time. At low density (ne,lin≈2.0×1019 m−3), simultaneous injection of a 65/35 mix of 2.45/4.6 GHz power achieved an lower hybrid current drive efficiency that was 25% higher than what should be expected from the linear combination of the two sources. The experiment was interpreted with time-dependent simulations, using the equilibrium and transport solver TRANSP, coupled with the ray-tracing code GENRAY and the Fokker–Planck solver CQL3D. For each discharge, profiles of current and hard x-rays from simulation and measurement agree within uncertainties. An examination of the electron distribution function indicates that the LH synergy is supported by the increased width of the LH resonance plateau in the simultaneous injection case compared to independent injection.

Ray-tracing analysis for cross-polarization scattering diagnostic on MAST-upgrade spherical tokamak.

A combined Doppler backscattering/cross-polarization scattering (DBS/CPS) system is being deployed on MAST-U for simultaneous measurements of local density turbulence, turbulence flows, and magnetic turbulence. In this design, CPS shares the probing beam with the DBS and uses a separate parallel-viewing receiver system. In this study, we utilize a modified GENRAY 3D ray-tracing code to simulate the propagation of the probing and scattered beams. The contributions of different scattering locations along the entire beam trajectories are considered, and the corresponding local B̃ wavenumbers are estimated using the wavevector matching criterion. The wavenumber ranges of the local B̃ that are detectable to the CPS system are explored for simulated L- and H-mode plasmas.

The Role of Adaptive Ray Tracing in Analyzing Black Hole Structure

Abstract The recent advent of the Event Horizon Telescope (EHT) has made direct imaging of supermassive black holes a reality. Simulated images of black holes produced via general relativistic ray tracing and radiative transfer provide a key counterpart to these observational efforts. Black hole images have a wide range of physically interesting image structures, ranging from extremely fine scales in their lensed “photon rings” to the very large scales in their relativistic jets. The multiscale nature of the black hole system is therefore suitable for a multiscale approach to generate simulated images that capture all key elements of the system. Here, we present a prescription for adaptive ray tracing, which enables efficient computation of extremely high-resolution images of black holes. Using the polarized ray-tracing code ipole, we image a combination of semianalytic and general relativistic magnetohydrodynamic (GRMHD) models, and we show that images can be reproduced with a mean squared error of less than 0.1% even after tracing 12× fewer rays. We then use adaptive ray tracing to explore the properties of the photon ring. We illustrate the behavior of individual subrings in GRMHD simulations, and we explore their signatures in interferometric visibilities.

Solving the infrared reflections contribution by inversion of synthetic diagnostics: First results on WEST

Infrared (IR) diagnostics are used to measure plasma-facing components (PFC) surface temperature in fusion devices. However, the interpretation of such images is complex in all-reflective environments because of unknown emissivity and multiple reflections issues. In order to assess these challenges an iterative inversion method based on a fast photonic model, the radiosity method, has been developed. This method is applied to two different direct models based on different geometries, Sec-Tore and RADIOS, in order to estimate temperatures from experimental-like data simulated with a Monte Carlo ray-tracing code with diffuse reflective surfaces or specularly reflective surfaces. RADIOS allows retrieving temperature on colder targets (lower than 200°C) with errors of 33% and the peak temperatures with errors of 6%.

Modelling effects of edge density fluctuations on electron-cyclotron current drive used for neoclassical tearing mode stabilization

In this work we study the undesired effects of electron density fluctuations (in the form of blob structures which may exist in the edge region of tokamak plasmas) to the electron-cyclotron wave propagation and current drive in connection to the efficiency of neoclassical tearing mode stabilization. Our model involves the evaluation of the driven current in the presence of density perturbations, by using a combination of a wave solver based on the transfer matrix and electromagnetic homogenization methods for the propagation part prior to and inside the region of these structures (where standard asymptotic propagation methods may not be valid due to the short-wavelength limit breakdown), with a ray tracing code including island geometry effects and current drive computation for the propagation past the perturbed region. The computed driven current is input into the modified Rutherford equation in order to estimate the consequences of the wave deformation (driven by the density fluctuations) to the mode stabilization.

Ray-tracing simulation of gravitational lensing using a gradient-index model

We present a method for modeling gravitational lensing as gradient-index lenses in the ray-tracing software CODE V. When applied to gravitational lensing by the Sun, these models yield results in agreement with theoretical and experimental results. The extension of this type of model to “lumpy” astronomical objects whose lensing behavior is difficult to predict with traditional methods is discussed.

Numerical simulation of very high harmonic fast waves for an off-axis current drive in a China fusion engineering test reactor by the GENRAY code

Recent studies have shown that helicon waves may be an attractive option for driving an efficient off-axis current drive in order to supplement bootstrap current for steady state operation in fusion reactors. Based on the China fusion engineering test reactor parameters, the helicon wave trajectories, profiles of driven current and current driven efficiency are calculated with the ray-tracing code GENRAY. Both the peak position and the peak value of driven current profiles are dependent on the wave frequency. In the frequency range of 1.6 GHz–2.0 GHz, the peak value increases with the increase of frequency, and the peak position has a slight change (concentrate around ρ= 0.75). High electron temperature and low electron density seem to be favorable for the helicon wave absorption. A driving current of I/P > 70 kA MW−1 at the off-axis position of ρ < 0.7 can be obtained with the electron temperature at the plasma center, T e(0) < 25.4 keV and the electron density at the plasma center, n e(0) ∼ 0.7 × 7.8 × 1019m−3–0.8 × 7.8 × 1019m−3. The current drive efficiency decreases with the increase of the electron density. Peak positon of the driven current profile is insensitive to the parallel refractive index n ∥. It is found that the poloidal launch angle has some effect on the peak positon and its value.

X-ray spectrometer simulation code with a detailed support of mosaic crystals

We present a newly developed ray tracing code called mmpxrt, dedicated to study and design X-ray crystal optics, with a special focus on mosaic crystal spectrometers. Its main advantage over other currently available ray tracing codes is that it includes a detailed and benchmarked algorithm to treat mosaic crystals, especially HOPG and HAPG (Highly Oriented/Annealed Pyrolitic Graphite). The code is primarily designed to study crystal spectrometers, therefore their implementation is very straightforward and includes the automated evaluation of their performance. It can, however, be used universally to study other Bragg crystal based instruments, such as monochromators, mirrors, and analyzers. The code is publicly available, written in Python3 and is distributed as a Python library with test cases and user manual included. Program summaryProgram title: mmpxrtCPC Library link to program files:https://dx.doi.org/10.17632/dkpbzvtz3b.1Developer’s repository link:https://gitlab.hzdr.de/smid55/mmpxrtLicensing provisions: MITProgramming language: Python 3Nature of problem: Mosaic crystals are commonly used for X-ray spectroscopy and similar applications. However, the complicated structure of such crystals makes their function non-trivial and often counter-intuitive, therefore a proper simulation tool is needed to design and understand such instruments.Solution method: We have developed a Monte-Carlo X-ray ray tracing code which simulates the setup of given spectrometer, analyzes the results and provides the performance of the spectrometer.

Estimating the size of X-ray lamppost coronae in active galactic nuclei

Aims. We report estimates of the X-ray coronal size of active galactic nuclei in the lamppost geometry. In this commonly adopted scenario, the corona is assumed for simplicity to be a point-like X-ray source located on the axis of the accretion disc. However, the corona must intercept a number of optical/UV seed photons from the disc consistent with the observed X-ray flux, which constrains its size. Methods. We employ a relativistic ray-tracing code, originally developed by Dovčiak and Done, that calculates the size of a Comptonizing lamppost corona illuminated by a standard thin disc. We assume that the disc extends down to the innermost stable circular orbit of a non-spinning or a maximally spinning black hole. We apply this method to a sample of 20 Seyfert 1 galaxies using simultaneous optical/UV and X-ray archival data from XMM-Newton. Results. At least for the sources accreting below the Eddington limit, we find that a Comptonizing lamppost corona can generally exist, but with constraints on its size and height above the event horizon of the black hole depending on the spin. For a maximally spinning black hole, a solution can almost always be found at any height, while for a non-spinning black hole the height must generally be higher than 5 gravitational radii. This is because, for a given luminosity, a higher spin implies more seed photons illuminating the corona, which is due to a larger and hotter inner disc area. The maximal spin solution is favoured, as it predicts an X-ray photon index in better agreement with the observations.

Radiative heat load distribution on the EU-DEMO first wall due to mitigated disruptions

Abstract The EU-DEMO First Wall (FW) will be a relatively thin structure. In order not to damage this layer, heat loads distributed onto the wall should be carefully controlled. In the case of transient events, as for example plasma disruptions, the steady-state heat load limit ( ∼ 1 - 2 M W / m 2 ) can be largely exceeded for a timespan sufficiently long to cause damages. Therefore, when the control system detects an upcoming disruption, Shattered Pellet Injection (SPI) or Massive Gas Injection (MGI) mitigation techniques can be employed to inject impurities and switch off the plasma safely. In the present work, the Monte-Carlo ray-tracing code CHERAB is used to compute the radiative heat load distribution on the EU-DEMO Plasma Facing Components (PFCs) due to a mitigated plasma disruption. By applying ad-hoc techniques to improve the quality of the Monte Carlo calculation, we obtain a peak radiative load of ∼ 490 M W / m 2 on the PFCs, which is ∼ 25 % lower than previous estimates.

Using Teleseismic P-Wave Arrivals to Calibrate the Clock Drift of Autonomous Underwater Hydrophones

ABSTRACT Networks of autonomous underwater hydrophones (AUHs) are successfully employed for monitoring the low-level seismicity of mid-oceanic ridges by detecting hydroacoustic phases known as T waves. For a precise localization of a seismic event from T-wave arrival times, all AUHs must be synchronized. To this effect, at the beginning of the experiment, all instrument clocks are set to GPS time, which serves as a common reference. However, during the experiment, the instrument clock often deviates from GPS time, and, because the amount of deviation differs from one instrument to another, the synchronization of the AUHs deteriorates, as the experiment progresses in time. Just after the instrument recovery, the time difference (called “skew”) between the instrument and the GPS clocks is measured. Assuming that the skew varies linearly with time, the correction of a time series for the clock drift is a straightforward procedure. When the final skew cannot be determined, correcting for the clock drift is not possible, and any event localization becomes problematic. In this article, we demonstrate that the clock-drift rate (assumed to be time-independent) can be successfully estimated from arrival times of teleseismic P waves, commonly recorded by AUHs. Using a ray-tracing code, and accounting for the uncertainties in event hypocenter locations, origin times, and the Earth seismic-velocity model, confidence intervals of the estimated drift rates are deduced. The validity of the approach is tested on data from two AUHs with known clock drifts. Our results show that a reliable estimation is possible for skews as small as 4 s per two years (corresponding to a drift rate of about 5.5 ms·day−1). This method can also be applied to correct data of other recording instruments subject to internal-clock drift, such as ocean-bottom seismometers, when the skew is unknown.

An X-ray ray tracing simulation code for mono- and polycapillaries: Description, advances and application

Polycapillary optics, consisting of bundles of narrow hollow glass channels, are regularly used in the field of (micro-)X-ray fluorescence (XRF) spectroscopy to focus X-rays down to a microscopic spot while increasing the flux density of the beam on the sample. Polycapillaries guide X-ray photons through multiple total reflection events, similar to how light is guided within optic fibers. Although the use of polycapillaries in XRF spectroscopy allows for fairly straightforward qualitative elemental analysis, fundamental parameter (FP) based quantification remains difficult due to the energy dependent photon transmission efficiency, focal size, acceptance, etc. of these optics.In order to predict the polycapillary and input beam parameter dependent beam forming properties, a multithreaded Monte Carlo based polycapillary X-ray ray tracing code is presented. Apart from supporting photon ray tracing in ‘ideal’ straight, conical and ellipsoidal shaped polycapillary optics, it also allows for the simulation of photon propagation through arbitrarily shaped optics to account for small deviations from the ideal shape, as is often the case in real world examples. The current code allows for the simulation of so-called ‘leak events’, where the probability of a photon traveling through a capillary wall is taken into account, and also includes support for photon beam polarization effects.The simulated results show good agreement with experimental results obtained at the BM26A beamline of the European Synchrotron Radiation Facility (ESRF, Grenoble, France). The (poly)capillary X-ray ray tracing simulation code, called ‘polycap’, developed in the C language and with bindings for Python, is released under the GPLv3 license. The code is expected to assist in the quantification of (poly)capillary based X-ray fluorescence spectroscopy and may yield additional insight into the manufacturing and development of polycapillary optics.

Resonant-line radiative transfer within power-law density profiles

ABSTRACT Star-forming regions in galaxies are surrounded by vast reservoirs of gas capable of both emitting and absorbing Lyman α (Lyα) radiation. Observations of Lyα emitters and spatially extended Lyα haloes indeed provide insights into the formation and evolution of galaxies. However, due to the complexity of resonant scattering, only a few analytic solutions are known in the literature. We discuss several idealized but physically motivated scenarios to extend the existing formalism to new analytic solutions, enabling quantitative predictions about the transport and diffusion of Lyα photons. This includes a closed form solution for the radiation field and derived quantities including the emergent flux, peak locations, energy density, average internal spectrum, number of scatters, outward force multiplier, trapping time, and characteristic radius. To verify our predictions, we employ a robust gridless Monte Carlo radiative transfer (GMCRT) method, which is straightforward to incorporate into existing ray tracing codes but requires modifications to opacity-based calculations, including dynamical core-skipping acceleration schemes. We primarily focus on power-law density and emissivity profiles, however both the analytic and numerical methods can be generalized to other cases. Such studies provide additional intuition and understanding regarding the connection between the physical environments and observational signatures of galaxies throughout the Universe.

Helicon wave heating and current drive in toroidal plasmas

Investigation of helicon wave heating and current drive (CD) in toroidal plasma has been carried out with the ray-tracing code GENRAY. The wave trajectories, profiles of power deposition and driven-currents are presented. It is shown that increasing the poloidal launch angle does not change the absorption rate of the wave, but moves the peak of the wave deposition toward the plasma core. Wave frequencies in the range of our interest (460 MHz ∼ 480 MHz) do not change the absorption of the wave. Under low parameter plasmas, we find that both the peak position and magnitude of the wave power deposition are dependent on the launched parallel refractive index n||. With increasing the refractive index, the driving efficiency first increases and then decreases. The parallel refractive index figure of merit for mid-plane launching in HL-2M configuration is 3.2. With high plasma parameters, both the position and magnitude of the driving current are weakly dependent on n||. The magnitude of the driven current is determined by both the absorption rate and the value of ξe, which is related to n||. It is also demonstrated that driven current increases with increase of the core plasma temperature and decrease of the core plasma density. The plasma ohmic current seems do not significantly affect the helicon CD efficiency, but moves the driven current toward the plasma core region and narrows the width of the driven current profile. In addition, the preliminary calculations including scrape-off-layer (SOL) suggest that the power absorption rate loss in SOL is about 5%–20%. These results provide a reference and theoretical basis for the design and construction of HL-2M helicon wave system.

Optical Design of a Novel Two-Stage Dish Applied to Thermochemical Water/CO2 Splitting with the Concept of Rotary Secondary Mirror

In this paper, a novel two-stage dish concentrator (TSD) with a rotary secondary mirror (SM) is presented for solar thermal water/CO2 splitting. An in-house code for ray-tracing simulation of the concentrator was developed and validated. Among all feasible geometries, a hyperboloid with an upper sheet is the most popular option and is widely used as a secondary reflector, which is mainly discussed here. All para-hyperboloid geometric combinations can be categorized into three typical patterns (φ1 &lt; π/2, φ1 = π/2, φ1 &gt; π/2, φ1 = field angle of PM). The initial designs of the TSD, respective to different off-axis levels for each combination, were first designed. Then a new mathematical model was introduced to reshape the SM to reach optimal truncated designs. Finally, a new concept of an off-axis primary mirror (PM) combined with the truncated SM was evaluated by using the in-house ray-tracing code. The results include the optical efficiency, concentration ratio and intercepted radiant flux. The best solutions with the highest optical efficiency fall in the range π/2 ≤ φ1 ≤ (π − arcsin 0.8) rads and 0.4 ≤ NA2 ≤ 0.6 (NA2 = sin φ2, φ2 = field angle of SM), which vary with the concentration ratio and inclination angle.

A tool to minimize the need of Monte Carlo ray tracing code for 3D finite volume modelling of a standard parabolic trough collector receiver under a realistic solar flux profile

AbstractThe energy collection element of a parabolic trough collector includes a selective coated metallic receiver tube inside an evacuated glass tube. Perpendicularly incident sun light on the parabolic trough mirror aperture is concentrated on the receiver tube highly nonuniformly along its circular direction. This solar energy is collected as thermal energy circulating a suitable heat transfer fluid (HTF) through the tube. This conjugate heat transfer phenomenon under nonuniform heat flux boundary condition is computationally studied applying 3D finite volume (FV) modelling technique of computational fluid dynamics coupled with Monte Carlo ray tracing (MCRT) optical data. The MCRT model simulates the actual flux profile around the receiver tube. Apart from a FV model, this coupled study requires expertise in, and access to, a suitable MCRT code. A combination of polynomial correlations and user‐defined function (UDF) is introduced in this article in order to minimize the need of MCRT codes from subsequent FV modelling of the receiver tube of the Luz Solar 2 (LS2) collector. The correlations are developed from a verified 3D MCRT model, which is equivalent to the local irradiation data as a function of receiver circular location. The UDF includes two algorithms: one to develop solar flux profile from the correlations around the receiver, and the other to calculate heat loss from the receiver. Interpreting the UDF into ANSYS Fluent, a 3D FV model of the LS2 receiver is developed and validated with experimental results. The effectiveness of the UDF as an alternative to MCRT code is verified. The FV model is capable to investigate the heat transfer characteristics of the LS2 collector receiver at different solar irradiation level, optical properties of the collector components, glass tube conditions, HTFs, inserts or swirl generators, collector length, and internal diameter of the tube.

Oblique and vertical incidence ionogram simulations with the presence of Es layer

The methodology making available an analysis of high frequency (HF) wave propagation in ionosphere with the presence of sporadic E layer (Es) is presented. A numerical ray tracing code is exploited to estimate the ray-paths through ionosphere comprising E, Es, F1 and F2 layers. A number of vertical and oblique sounding ionograms were emulated in the frame of NIM-RT propagation model. Fairly good resemblance between measured and simulated ionograms with the presence of Es layer was achieved. Numerical modelling provides an assessment of a number of parameters defining Es layer features including virtual height of the layer and its transparency.

Assessing the impact of non‐ideal optical factors on optimized solar dish collector system with mirror rearrangement

An optimized solar dish collector (OPSDC) system was proposed in our previous work, which can achieve excellent the optical efficiency and flux uniformity under ideal optics. On this basis, the impacts of the non-ideal optical factors on the optical performance of OPSDC system with a cylindrical and conical receiver are studied in detail and compared with the conventional solar dish collector (COSDC) system in this paper. Where the non-ideal optical factors considered are relatively comprehensive, including the mirror slope error, tracking error, installation error of the mirror and receiver, and receiver's absorptivity degeneration. An optical model with the non-ideal optical factors is built in detail by the ray tracing method, and the corresponding ray tracing codes are developed and verified by literatures and optical software OptisWorks 2012. The results show that the OPSDC system not only has a significantly smaller peak local concentration ratio (LCR) and non-uniformity factor than the COSDC system under the same non-ideal optical factor, but also has excellent optical performance. This means that OPSDC system can effectively avoid the heat absorber generating high-temperature hot spots, thus significantly improving its working reliability and service lifetime. In addition, the tracking error, installation error of the receiver and mirror all lead to the increase of the peak LCR and non-uniform factor, while the mirror slope error and absorber's absorptivity degeneration are conducive to reducing the peak LCR and non-uniform factor. This work can provide a reference for error control of COSDC system and OPSDC system in manufacturing, installation and operation.