Search

Concentrated Solar Power (CSP) utilizing solar tower power plants exhibits significant potential for dispatchable sustainable power generation and fuel production, by concentrating up to hundred thousand focal spots of individual mirrors onto one surface. The irradiance on the receiver is a critical parameter for power plant operators, not only to prevent component-damaging temperature peaks and gradients but also to optimize the distribution of heliostat's focal spots. Therefore, recent approaches aim to exploit images of isolated focal spots on a Lambertian target, taken on a day-to-day basis in most commercial power plants, to achieve more accurate flux predictions. State-of-the-art methods for flux measurements require additional equipment and are mostly time-intensive. This study introduces a novel methodology to derive single heliostat irradiance profiles using simple digital camera images, employing an image-to-image neural network. The model we propose is capable of generating accurate, high-resolution flux distributions from single images. It uniquely accounts for the target surface's irregularities and reflectivity as well as background irradiation, factors critical for precise measurements of individual focal spots. By incorporating these factors, our methodology offers a new scaling approach for the measured flux density based on a calculated total flux, obviating the need for additional equipment such as flux gauges or moving bars. This enables effortless integration into the daily calibration routine in-situ using the camera-target method. This seamless integration not only supports existing flux prediction methodologies but also paves the way for future enhancements by potentially improving the accuracy of overall flux prediction. • Introduces a UNet-based approach for enhanced flux calculation in camera-target method in CSP plants using digital camera images. • Addresses traditional camera-target method limitations by accounting for background irradiation and surface irregularities. • Seamlessly integrates UNet architecture into existing heliostat calibration workflows in CSP plants. • Method enables calculation of absolute flux values without the need of flux gauges. [ABSTRACT FROM AUTHOR]

Highlights • Partially coherent vortex beam with periodical coherence properties is introduced theoretically and generated experimentally. • Intensity lattices with controllable beamlet can be formed through varying initial coherence width. • Partially coherent vortex beam with periodical coherence properties is useful for particle trapping and information transfer. Abstract We introduce a new kind of partially coherent vortex beam with periodical coherence properties, named optical coherence vortex lattices (OCVLs). With the help of the generalized Collins formula, we explore the propagation properties of the intensity and the complex degree of coherence of OCVLs focused by a thin lens. Compared to conventional partially coherent vortex beam, OCVLs display extraordinary propagation properties, i.e., a Gaussian beam spot evolves into multiple beam spots (i.e., intensity lattices) in the focal plane (i.e., in the far field). The intensity lattices with solid or hollow beamlets can be formed through manipulating the coherence width in the source plane. We also find that the topological charge of the OCVLs can be determined from the distribution of its complex degree of coherence in the focal plane. Furthermore, we report experimental generation of OCVLs. The OCVLs will be useful for particle trapping and information transfer. [ABSTRACT FROM AUTHOR]

As proton therapy is becoming an established treatment methodology for cancer patients, the number of proton centres is gradually growing worldwide. The economical effort for building these facilities is motivated by the clinical aspects, but might be also supported by the potential relevance for the research community. Experiments with high-energy protons are needed not only for medical physics applications, but represent also an essential part of activities dedicated to detector development, space research, radiation hardness tests, as well as of fundamental research in nuclear and particle physics. Here we present the characterization of the beam line installed in the experimental room of the Trento Proton Therapy Centre (Italy). Measurements of beam spot size and envelope, range verification and proton flux were performed in the energy range between 70 and 228 MeV. Methods for reducing the proton flux from typical treatments values of 10 6 –10 9 particles/s down to 10 1 –10 5 particles/s were also investigated. These data confirm that a proton beam produced in a clinical centre build by a commercial company can be exploited for a broad spectrum of experimental activities. The results presented here will be used as a reference for future experiments. [ABSTRACT FROM AUTHOR]

We demonstrate the influence on mode features with introducing typical intracavity perturbation and results of aberrated wavefront compensation in a folded-type unstable resonator used in high energy lasers. The mode properties and aberration coefficient with intracavity misalignment are achieved by iterative calculation and Zernike polynomial fitting. Experimental results for the relation of intracavity maladjustment and mode characteristics are further obtained in terms of S-H detection and model wavefront reconstruction. It indicates that intracavity phase perturbation has significant influence on out coupling beam properties, and the uniform and symmetry of the mode is rapidly disrupted even by a slight misalignment of the resonator mirrors. Meanwhile, the far-field beam patterns will obviously degrade with increasing the distance between the convex mirror and the phase perturbation position even if the equivalent disturbation is inputted into such the resonator. The closed-loop device for compensating intracavity low order aberration is successfully fabricated. Moreover, Zernike defocus aberration is also effectively controlled by precisely adjusting resonator length, and the beam quality is noticeably improved. [ABSTRACT FROM AUTHOR]

We demonstrate the influence on output coupling mode with introducing typical intracavity disturbation and results of aberrated mode compensation in a folded-type optical resonator used in high-energy lasers. The eigenmode profiles and relevant Zernike aberration with intracavity reflector misalignment are achieved by numerical calculation. Experimental result about the function of the reflector maladjustment and the mode features are described in terms of model reconstruction combined with Zernike annular polynomials. Results show that phase disturbation has significant influence on out-coupling beam property, and the uniform and symmetry of the mode are rapidly disrupted by a slight misalignment of the resonator reflectors. The influence on PSF profile in the far-field will be obviously different even if equivalent disturbation is inputted into the same cavity. The device of real-time controlling of the cavity reflector for compensating intracavity phase distortion is successfully constructed. In addition, Zernike defocus aberration is effectively controlled by precisely adjusting the resonator length. A high beam quality in the output coupling mode is realized, which is in good agreement with the analytical predictions. [ABSTRACT FROM AUTHOR]

Eigenmode of resonators with asymmetric circular mirrors based on misalignment passive positive-branch unstable resonator is investigated in the paper. To do so, we use iterative algorithm to simulate the effect of intracavity phase perturbation on eigenmode structure properties of the passive confocal unstable resonator. On this basis, further experiment of output beam properties on a misaligned passive unstable laser resonator has been performed by adopting Hartmann–Shack (H–S) method and Zernike modal wavefront reconstruction. Wavefront distribution and the first 35-order Zernike coefficient included in the wavefront are obtained. The results show that intracavity tilt perturbation notablely affects outcoupled beam intensity distribution, and will also increase some high-order aberrations of beam phase properties. However, low-order Zernike tilt aberration is the main component with phase-tilted perturbation is introduced into resonator cavity. Defocus, low-order astigmatism and coma aberration will all be brought with the augument of phase tilt aberration, which will obviously degrade output beam quality. When intracavity compensating elements are adopted for optical aberration correction, the correction of tilt aberration should be considered first. [ABSTRACT FROM AUTHOR]

Some representative factors of intracavity perturbation will obviously degrade output power and beam mode properties for crystal passive Q -modulated solid-state lasers. In this paper, eigenmode of resonators using general asymmetric circular mirrors in solid-state lasers is briefly discussed, moreover, experiment analysis of the output beam quality on a passive Q -switched zig-zag slab Nd:YAG laser has been presented by adopting Hartmann–Shack (H–S) method and Zernike mode reconstruction theory. In this way, the PV and RMS errors of the wavefront aberration, each order Zernike aberrations can be acquired accurately, distribution of circle energy in far-field and other beam evaluation factors can also be obtained by further calculation, so beam mode properties and quality can be analyzed comprehensively. Experimental results illuminate that wavefront aberration of the laser is concentrated in the frontal 10 ranks of Zernike aberration, mainly including the defocus Z 3 , the low-order astigmatism Z 5 , the coma aberration Z 6 and the spherical aberration Z 10 because of the crystal thermal effect and the intracavity phase perturbation. [ABSTRACT FROM AUTHOR]

Abstract: A program has been initiated to measure the energy dependence of selected high-yield fission products used in the analysis of nuclear test data. We present out initial work of neutron activation using a dual-fission chamber with quasi-monoenergetic neutrons and gamma-counting method. Quasi-monoenergetic neutrons of energies from 0.5 to 15MeV using the TUNL 10MV FM tandem to provide high-precision and self-consistent measurements of fission product yields (FPY). The final FPY results will be coupled with theoretical analysis to provide a more fundamental understanding of the fission process. To accomplish this goal, we have developed and tested a set of dual-fission ionization chambers to provide an accurate determination of the number of fissions occurring in a thick target located in the middle plane of the chamber assembly. Details of the fission chamber and its performance are presented along with neutron beam production and characterization. Also presented are studies on the background issues associated with room-return and off-energy neutron production. We show that the off-energy neutron contribution can be significant, but correctable, while room-return neutron background levels contribute less than to the fission signal. [Copyright &y& Elsevier]

Highlights: [•] A tool using low-cost collimated pyranometers has been developed to produce flux maps of heliostats at long range. [•] Flux maps created from Long-Range Heliostat Target were validated using BCS and Ray-Trace technology. [•] Long-Range Heliostat Target successfully produced flux map of single facets at a distance of over 1700m. [Copyright &y& Elsevier]

Abstract: Several optical arrangements using non-uniformly polarized fields are proposed for generating beams with spin and/or orbital angular momentum. By choosing adequately the input beam polarization and the characteristics of the different proposed set-ups we can control the overall angular momentum of the output beam at will. The orbital angular momentum is analyzed with the beam moments theory and the spin term is evaluated using the averaged s3 Stokes parameter. [Copyright &y& Elsevier]

Abstract: X-ray lasers represent a powerful tool to explore matter under extreme conditions. A rigorous characterization of their output parameters is, therefore, of substantial importance for the purposes of the experiments being conducted at these sources. A profound knowledge of the spatial, temporal, spectral, statistical, coherence, and wavefront beam properties may protect us from an unwanted misinterpretation of the experimental data. We present an experimental technique of the spatial (transverse and longitudinal) characterization of the beam profile. Investigating ablative imprints in various materials, we evaluate the spatial properties of the incident beam, namely, the beam waist radius and position, the Rayleigh range, M 2 parameter, and divergence. In this paper, we recall briefly our recent work at the transverse beam profile reconstruction. A newly developed method of the longitudinal beam profile characterization is the main subject of this work. [Copyright &y& Elsevier]

Abstract: Dosimetry for Auger electron radiotherapy using monochromatic photon beams requires knowledge of beam characteristics. This study characterized a 35-keV photon beam generated at the LSU/CAMD synchrotron. Beam energy was measured by Compton spectroscopy and Si640c powder diffraction. Photon spatial distribution and virtual source position were measured using radiochromic film. Central-axis fluence was determined from Compton scattering measurements and application of the Klein–Nishina cross-section with percent polarization fit to results at 2–4 scattering angles. Broad-beam fluence was combined with MCNP5 Monte Carlo dose per fluence calculations to generate dose versus depth in a polymethylmethacrylate phantom, which was compared to ionization chamber and radiochromic film depth–dose measurements. For 22–41keV beams, diffraction-based and Compton-based energy measurements agreed to within −0.1±0.3 and 0.6±0.3keV, respectively, of monochromator calibrated energies. At 35keV and 0.66cm depth, dose uniformity over 80% of the 2.8cm×2.5cm beam varied from 105 to 78% of the central-axis value horizontally and from 90 to 100% vertically. Narrow-beam divergence yielded vertical and horizontal virtual source-to-surface distances of 3.8±0.2 and 15.7±1.0m, respectively. Incident fluence rates for a 35-keV beam (100mA ring current) ranged from 1.181±0.011×1011 to 3.053±0.004×1011 photonscm−2 s−1 with ≈100% polarization in the horizontal plane. Ion chamber and film dose measurements underestimated MCNP5-based dose by an average of 6.4±0.8 and 9.1±0.8%, respectively, over measured depths. These practical beam characterization methods should allow subsequent Monte Carlo dose calculations needed for planning future radiotherapy studies. Although simulated and measured depth–dose curves agree well in shape, improvement in absolute dose is desirable. [Copyright &y& Elsevier]

Abstract: Several global parameters are proposed to characterize the radial and azimuthal polarization content of non-uniformly totally polarized beams. Such figures of merit can be written and measured in terms of two Stokes parameters, and also from the data at the output of either a radial or an azimuthal dichroic polarizer, integrated throughout the beam profile. The measurability of the proposed parameters has also been experimentally checked. [Copyright &y& Elsevier]

Abstract: Several overall parameters are introduced to characterize the linear or circular polarization content of a non-uniformly totally polarized beam over the region of its wavefront where the irradiance is significant. These figures of merit are determined from the values of the Stokes parameters. The physical meaning of the proposed parameters is tested by computing some numerical examples, and their measurability is checked by considering non-uniformly totally polarized fields generated after propagation through uniaxial anisotropic materials. [Copyright &y& Elsevier]

As neutron radiography is even more in demand for industrial applications of aircraft, turbine blade, automobile, explosive igniters, etc, it is necessary to review the standards which are the most appropriate for preparing the procedures for setting up the QA system. Recently, Korea Of Lab Accreditation Scheme (KOLAS) was originated from ISO 17025. It is widely recognized by research peer groups for conducting valid tests. The neutron radiography facility (NRF) of High Flux Advanced Neutron Application Reactor (HANARO), which started ion 1996, is the preliminary stages of KOLAS. The HANARO NRF is not only characterized using ASTM standards E545-91/E803-91 to satisfy the requirements of KOLAS, but in the design phase of the tomography system. [Copyright &y& Elsevier]

SPIDER, the full-size prototype of the negative ion source for future ITER Heating and Current Drive, is equipped with a tomographic diagnostic to characterize the negative hydrogen (and deuterium) beam. The main goal of the tomographic system is the reconstruction of the beam emission pattern, which is proportional to the beam density, by assuming a uniform background gas, through the measurement of the beam emitted light along a sufficiently large number of lines-of-sight (LoSs), to study the beam homogeneity and divergence. Currently, 11 2D visible cameras observe the beam on a plane at a distance of 400 mm from the last grid of the accelerator, all around the beam; sensors of different sizes with different lenses are used, to maximize the resolution despite the limited number of points of view. The cameras are calibrated both in intensity and spatially and their fans of LoSs have been reconstructed. Once calibrated, the experimental data are compared with the simulated ones, simultaneously for all the cameras in order to have a complete profile of the extracted beam. Simultaneous Algebraic Reconstruction Technique (SART) algorithm as inversion technique is used to reconstruct for the first time the 2D beam emissivity profile, and it is applied to study the spatial uniformity of the beam as a function of the filter field and the extraction voltage. [ABSTRACT FROM AUTHOR]