Annular Source Research Articles

Optimizing the Size of a Moving Annular Hollow Laser Heat Source

The physical phenomenon of the annular hollow laser surface treatment process is complex, and the internal mechanism involves multiple disciplines and fields. In addition to the general parameters of laser beams, such as laser power and scanning speed, an annular hollow laser beam exhibits unique physical characteristics, including hollow ratio and hollow area. The selection of the inner and outer annular radii of the laser plays a critical role in the study of metal surface heat treatment. From the point of view of heat transfer, the entransy dissipation theory is introduced in the metal surface treatment process with an annular hollow heat source. Firstly, using the principle of the extreme value of the entransy dissipation rate, under a constant heat flux boundary condition, the entransy dissipation rate is obtained through the temperature field distribution in the calculation area by numerical simulation. Secondly, the selection of the inner and outer ring radii of the annular laser is explored, and the average temperature difference of the heating surface is minimized to reduce the thermal stresses of the material. This paper seeks new insights into the geometric parameters of the inner and outer radii of the annular heat source.

Design and optimization of the annular light source layout of the indoor visible light communication system

Design and optimization of the annular light source layout of the indoor visible light communication system

Picosecond laser-driven coded-source radiography with high resolution and contrast

The X-ray sources for Compton radiography of ICF experiments are generated by using intense picosecond lasers to irradiate wire targets. The wire diameter must be designed thin enough, for example ∼ 10 µm in many published works, to comply a high spatial resolution. This results in a low laser-target interception, which limits the photon yield. We investigated a technique of coded-source radiography based on laser-driven annular sources via Monte Carlo and PIC simulations. The annular X-ray source is formed by laser irradiating tube target in which the effect of electron recirculation plays an important role. We proved that this technique has an increased spatial resolution and contrast than that using the Gaussian source produced by wire targets. Therefore, the diameter of the backlighter target can be significantly increased to uplift laser-target interception without compromising on spatial resolution. This contributes towards a reconciliation between the spatial resolution and photon yield for Compton radiography. The results predict the possibility of improving source photon yield by several times in future experiments.

An analytical model and experimental validation of annular heat source during scanning electron beam treatment

In this investigation, the maximum depth of penetration and power density coefficient are calculated by simulating the motion trajectories of electrons in surface layer of 5CrNiMo steel using Monte Carlo method, and the number of electrons is 500,000 in simulation. Then tomographic calculation is used to determine the distribution of power density coefficient on the section perpendicular to electron incidence direction, and a Gaussian columnar heat source model that matches the properties of electron beam is established. Finally, a mobile annular heat source model of scanning electron beam is then derived, combining it with the real operating mode. The temperature field during surface modification is simulated by using the mobile annular heat source model, and the simulation findings are compared to experimental data. The findings of Monte Carlo simulation demonstrate that the power density coefficient is Gaussian distributed on the section perpendicular to the depth of electron incidence and the peak power density at the center of each section changes with depth. The thickness and microstructure of re-melting layer predicted from the temperature field simulation is very close to the one from experimental findings. In our investigation, on top of deriving a model for the heat source of a single beam spot, we have also solved the problem of mathematical representation of the beam spot when it is doing high-speed rotational and linear composite motions. The aforementioned findings demonstrate that our study can provide methodological references for the construction of heat source models for different materials during electron beam treatment.

Experimental measurements of X-rays emission cross sections induced by photons

Abstract The energy-dispersive X-ray fluorescence (ED-XRF) technique has been used for measurements of K α , K β , and total K X-rays emission cross sections induced by photons, as well as K-shell fluorescence yields for pure elements with 22 ⩽ Z ⩽ 49. These metals have been irradiated at 59.54 KeV excitation energy from an 241Am annular radioactive source. The characteristic K X-rays emitted by the targets have been detected with a Silicon drift detector (SDD); the net areas of the K α and K β spectral peaks have been determined using the fitting process of PYMCA software. The obtained experimental values of the K X-ray fluorescence cross sections and the K-shell fluorescence yields were compared to the theoretical calculated ones and also to the experimental results obtained from a different experimental setup using a point source. The obtained values were between (6.84 ± 0.55 b/at.) and (891.0 ± 67.5 b/at.) for pure metals form Scandium to Indium. Experimental values were in good agreement with theoretical values within limits of uncertainty, as well as with the data reported in the literature. Moreover, the experimental determination of K X-ray fluorescence cross-section of scandium (Sc) at 59.54 KeV has not been preceded as far as we know. The value obtained is (6.84 ± 0.55 b/at). This new result obtained maybe contribute to the enrichment of the available databases.

Determination of absorption and shielding parameters for Ba(ClO4)2.3H2O using experimental and theoretical methods

In this study, absorption and shielding parameters such as mass attenuation coefficient (MAC), linear attenuation coefficient (LAC), half-value layer (HVL), tenth-value layer (TVL), mean free path (MFP), radiation protection efficiency (RPE), total atomic cross-section (σt,a), molecular cross-section (σt,m), electronic cross sections (σt,e), effective atomic number (Zeff), effective electron density (Neff), molar extinction coefficient (ε), K-shell jump ratio (rK) and jump factor (JK) have been investigated experimentally around the K edge for Ba(ClO4)2.3H2O using EDXRF technique and the X-ray attenuation method. Initially, the targets used as secondary sources were excited by γ-rays of 59.54 keV energy emitted from a 5 Ci 241Am annular primary radioactive source. Then, HPGe detector with a resolution of 182 eV at 5.9 keV was used to count K X-rays emitted from these secondary source targets and absorbed by Ba(ClO4)2.3H2O. The experimental results obtained for various secondary photon energies were compared with the theoretical results obtained from programs such as WinXCOM, FFAST and Phy-X/PSD, and it was concluded that these experimental and theoretical results were quite compatible.

Study on the combustion, entrainment, and plume flow behaviors of annular pool fires.

Annular fire source is a common combustion form in fire accidents. Effects of Din/Dout (the ratio of inner to outer diameters of the floating-roof tank) on the flame morphology and plume entrainment mechanisms of annular pool fires were studied by numerical simulation. Results show, as Din/Dout increases, the area with low combustion intensity near the central axis of the pool surface gradually increases. Combined with the time-series HRR and the stoichiometric mixture fraction line of the fire plume, it reveals that the combustion of annular pool fire is dominated by non-premixed diffusion flame. The pressure near the pool outlet decreases with Din/Dout, while the plume turbulence presents an opposite trend. Based on the time-sequential plume flow and the gas-phase material distribution data, the flame merging mechanism of the annular pool fires is revealed. Furthermore, based on the similarity criterion, it verifies that the applicability of the above scaled simulation conclusions could also be extended to guide full-scale fires.

Three-dimensional annular heat source for the thermal simulation of coaxial laser metal deposition with wire

Coaxial laser metal deposition with wire (LMD-w) is an innovative additive manufacturing technology in which a wire is coaxially fed through the center of a hollow laser beam into a laser-induced melt pool. This special configuration results in a direction-independent process, which facilitates the manufacturing of thin-walled metal components at high deposition rates. However, laborious experimental test series must be conducted to adjust the process parameters so that the substrate and the part do not overheat. Therefore, models are needed to predict the resulting temperature field and melt pool dimensions efficiently. This paper proposes a finite element simulation model using an innovative heat source, which considers the unique intensity distribution of the annular laser spot. The heat source parameters were calibrated experimentally based on fusion lines obtained from metallographic cross sections of aluminum alloy samples (AA5078 wire and AA6082 substrate). Subsequently, the temperature distribution in the substrate plate was measured by means of thermocouples to validate the developed model. It was shown that the proposed heat source replicates the heat input accurately. With the presented model, essential features for process development, such as the temperature field and the melt pool dimensions, can be reliably predicted. The model contributes to a better understanding of the LMD-w process and facilitates an efficient process development in future research work as well as for industrial applications. Key words: thermal simulation, annular laser spot, heat source, laser metal deposition, coaxial wire feeding, directed energy deposition

K shell fluorescence parameters of some elements at 59.54 keV: Experimental and theoretical results

Kα, Kβ and total K X-ray fluorescence cross-sections, K shell fluorescence yields, Kβ/Kα X-ray intensity ratios, K shell level widths, K shell life times, K to L shell vacancy transfer probabilities, K shell jump ratios, Auger electrons emission ratios and excitation factors for some elements in the atomic number range 22 ≤ Z ≤ 48 have been investigated. A Si(Li) detector and Am-241 annular radioactive source were used in the measurements. The obtained experimental data were crosschecked with theoretically calculated results and other available experimental results from the literature. It was observed that there is a good agreement between them within experimental uncertainties.

Mesoscopic simulation of molten pool heat transfer and fluid flow with moving annular laser via lattice Boltzmann method

Using the lattice Boltzmann method (LBM), a double distribution LB model for annular heat sources based on the variation of thermal conductivity and thermal diffusivity with temperature to study annular laser-material interaction is developed. The model is verified with the enthalpy-based method, and good agreement is obtained. The inner and outer annular radii can regulate convective heat transfer to affect the flow pattern and the depth of the molten pool. The temperature field, velocity vector field and average Nusselt number under different inner and outer annular radii are analyzed. The ratio of Marangoni number to Rayleigh number is proposed for the comparative analysis of natural convection and Marangoni convection intensities in the molten pool. The simulation results reveal that smaller inner and outer annular radii lead to smaller Nuavg, and the inhibition of convection inside of molten pool leads to a deeper molten pool. In the scope of present work, the outer annular radius to make the temperature field of the molten pool more uniform is in the range of 2.0–2.5 mm. The inner annular radius to make the molten pool deeper is in the range of 1.5–2.0 mm.

Investigation of molten pool and heat transfer mechanisms after moving annular laser incidence metal by lattice Boltzmann method

Using the lattice Boltzmann method (LBM), a double distribution LB model for annular heat sources based on the variation of thermal conductivity and thermal diffusivity with temperature to study annular laser-material interaction is developed. Firstly, the model is verified with the simulation results of the enthalpy-based method, and good agreement is obtained. Secondly, the prediction results are compared between models with the difference in consideration of the temperature-related thermal conductivity. Furthermore, the unique controllable parameters (inner annular radius and outer annular radius) of the annular laser not only affect the flow pattern and molten pool depth, but can also regulate convective heat transfer. Thus, the flow patterns of the melt and the depth of the molten pool are analyzed with different inner and outer annular radii. The simulation results reveal that the outer annular radius of 3.0 to 3.5 mm and the inner annular radius of 2.0 to 2.5 mm can achieve deeper molten pool and more uniform temperature distribution in the scope of present work.

Cross-Section Measurement of In-coherent Scattering from Annular 241Am Gamma Ray Source

Compton scattering of gamma- rays has been carried out with the aluminum target at a fixed angle of 650± 2.50. 241Am gamma ray source, having 59.57 KeV energy and a long half-life of 432.2 years has been used to carry out the scattering. The strength of the source is 1000 mCi and it has an annular geometry. Scintillation detector NaI (Tl) of type 708 having a crystal size 1 3^"/4 × 2^" connected to a Multichannel Analyzer (MCA) has been used for this study. MCA was calibrated using 133Ba, and 137Cs sources through ACCUSPEC software. The data accumulated was used to estimate the energy of the backscattered peak of the said sources and compared with their respective theoretical value. Spectrums were accumulated directly from 241Am and the shift in the photo-peak of 241Am with the aluminum scatterer. Data was used to calculate the scattering cross-section and compared with its theoretical value using Kline and Nishina’s equation. A good agreement is found in theoretical and experimental values.

Droplet spatter suppression in laser lap welding of galvanized sheets using additional coaxial annular laser source

This study is to prevent droplet spatter in laser welding of galvanized sheets. Three-dimensional welding simulation model is also established and analyzed to reveal the relationship between keyhole oscillation and flow behavior. It is found major reason for droplet spatter is the impact force of the reflux and eddy of the metal pool toward the keyhole. Keyhole oscillates seriously and reflux impact causes energy exchange discontinuity, making the keyhole opening intermittent closed in traditional Gaussian laser source alone. While certain output proportion of coaxial annular and Gaussian laser source could considerably improve impact resistance on the reflux and suppress droplet spatter obviously. Weld appearance is relatively beautiful and harmonious, with few undercuts, collapses and humps.

Systematic measurements of M X‐ray components X‐ray fluorescence cross‐sections for the elements with 77 ≤ Z ≤ 92 by employing laboratory source based energy dispersive X‐ray fluorescence setup

AbstractThe differential X‐ray fluorescence (XRF) cross‐sections for (Mξ2, Mξ1, Mδ1), (Mδ2, Mα1,2 M5‐O3), (Mβ, M4‐O2,3), (Mγ, Mm2, M3‐N4, M5‐O2,3), (Mm1, M3‐N6,7, M3‐O4,5) and (Mm2, M2‐N6) group of M X‐rays components have been measured for the elements with 77 ≤ Z ≤ 92 following photoionization by Mn K X‐rays (EKαβ = 5.96 keV) obtained from 55Fe radioisotope. The measurements were performed in annular source geometry at 126° emission angle using a low‐energy Ge (LEGe) detector. The measured cross‐section values are compared with theoretical values calculated using available sets of Mi (i = 1–5) photoionization cross‐sections, radiative emission rates (Fij), Coster‐Kronig (fij), and fluorescence (ωi) yields. The measured XRF cross‐sections for the (Mξ2, Mξ1, Mδ1), (Mm1, M3‐N6,7) and (Mm2, M2‐N6) groups of X‐rays agree with the theoretical values within the experimental errors. The (Mβ, M4‐O2,3) group of X‐rays exhibit agreement with theoretical values within experimental uncertainty for all the elements under investigation except 79Au and 80Hg. The XRF cross‐section for the (Mδ2, Mα1,2) group of X‐rays are in general higher by ~20% for the elements with Z = 77–83 and exhibit agreement for the 90Th and 92U elements. For the (Mγ, Mm2, M3‐N4) X‐ray group, the measured values are generally higher than the theoretical values, but the deviations are within experimental uncertainties. The large deviation in measured XRF cross‐section for different M X‐ray components from the theoretical ones are attributed to (i) poor separation of M X‐ray components (ii) contribution of self‐resonant Raman scattering (RRS) process and (iii) self‐fluorescence of M5 subshell by Mi subshell X‐rays (i = 1–3).

Analysis of dual-phase-lag heat conduction in a two-dimensional slab heated by a moving annular laser pulse

The controlled scan of a laser beam is at the core of the technology used for the micromachining of metals. To improve the laser micromachining of metal surfaces and reduce the thermal stress caused by the difference in temperature obtained in the process, a moving annular pulse laser heat source is introduced in present work. A mathematical model based on the dual-phase-lag (DPL) model is formulated to simulate the temperature response in a finite two-dimensional slab heated by the moving annular pulse laser heat source. Green's function approach and the superposition method are used to develop an analytical solution for the temperature field, and influences of the ratio of the thermalization time to the relaxation time of heat flux vector on the slab temperature distribution are investigated. The laser parameters that comprise the inner and outer radii are also examined to determine the induced temperature characteristics and advantages of the novel heat source.

Tabletop integral imaging 3D display system based on annular point light source

When the viewers sitting around the table observe 3D images, the viewing direction is generally oblique and the viewpoints should be distributed as annular. In this paper, a tabletop integral imaging (II) three-dimensional (3D) display system based on annular point light sources is demonstrated, which can present 3D images to multiple viewers in a standard annular viewing area with oblique viewing direction. The proposed system consists of annular point light sources, a Fresnel lens, a lens array, a two-dimensional (2D) display panel, and a diffuser screen. Each point light source illuminates the Fresnel lens to form parallel light and then illuminates the lens array and the display panel. A viewing sub-area is generated at the position of the diffuser screen, in which the 3D images can be viewed. Multiple viewing sub-areas are created in a way of time-division multiplexing to form a 360° annular viewing area. Compared with the previous tabletop 3D display, the viewing area can be concentrated at an oblique angle near the tabletop. The experimental results demonstrate the feasibility of the tabletop II 3D display system.

Determination of L-shell fluorescence parameters of thallium in thallium compounds

The Li (i = l, α, β, and γ) production cross-sections, L-shell average fluorescence yields, and Coster-Kronig vacancy transfer factors for L3 subshell X-rays of thallium in some thallium compounds were determined using Energy Dispersive X-ray Fluorescence spectrometer. The compounds were excited by 59.5 keV gamma-rays from an Americium-241 annular radioactive source, and the L X-rays emitted by the compounds were counted using an ultra-low energy germanium detector with a resolution of 150 eV at 5.9 keV. The production cross-sections, average fluorescence yields, and Coster-Kronig vacancy transfer factors of thallium in these compounds were compared with theoretical calculations and available experimental values of the pure thallium.

Effect of solid and annular laser heat sources on thermal cycle and solid phase transformation in rail steel manufactured by laser directed energy deposition

The service performance of U75V rail steel depends entirely on its laser-deposited microstructure, as coarse martensite has a damaging effect on wheel-rail contact behaviors. In this study, the formation mechanism of the microstructure in the rail steel was investigated based on simulated temperature fields in both solid and annular laser heat source models. U75V rail steel with pearlite was first fabricated via laser additive manufacturing with the annular laser beam and had a microstructure superior to that of the commercial U75V rail steel produced using the traditional slow-cooling heat treatment. This overcomes the long-perceived limitation that high-carbon steel can only form martensite through laser additive manufacturing. Active design of the grain size and the microstructure of U75V rail steel were proposed by controlling the cooling rate in two stages of solid phase transformation. The primary stage extended from the melting temperature to Ar1 and the secondary stage extended from Ar1 to the valley temperature. Granular pearlite in the annular laser beam-deposited sample shows considerably finer grains than the tempered martensite of the solid laser beam-deposited counterpart; therefore, the impact toughness of the sample can be increased by approximately 150%. The high cooling rate in the primary stage aids grain refinement in the annular laser beam-deposited sample, while the high valley temperature of the thermal cycle combined with the low cooling rate in the secondary stage leads to the formation of pearlite, instead of twin martensite.

Measurement of Total Electronic Cross-Section, Total Atomic Cross-Section, Effective Atomic Numbers, Effective Electron Densities and Kerma for Some Br Compounds

The aim of this study is to calculate the experimental and theoretical the mass attenuation coefficient some Br compounds by using transmission method. Also using these values were determined the total electronic section, total atomic section, effective atomic number, effective electron density and Kerma. We performed the calculations of these values in attenuation by using direct excitation experimental geometry. The total attenuation cross sections of some halogene Br compounds were measured in a narrow beam good geometry using a high resolution Si(Li) detector in the energy with γ photons at 59.543 keV from Am-241 annular source. Theoretical mass attenuation coefficient values were computed from the XCOM data programme, based on mixture rule method. This study provide new insight into the literature since the values of effective atomic number, electron density and Kerma for some Br compounds have not been determined before. According to the results shown in mass attenuation coefficient, Zeff and Neff of Br compounds are closely associated with chemical structure. This research were undertaken to explore how Bromine compounds is gamma ray shielding material.

Characterization of the influence of the sample thickness upon the background in energy dispersive x-ray fluorescence (EDXRF)

The influence of sample thickness to the background region in energy dispersive x-ray fluorescence (EDXRF) system was investigated. The investigated spectrum was from 4.09 keV to 79.03 keV and was divided into 8 regions. Some of these regions include contributions by photons from tails of fluorescent lines. HgO samples with thicknesses from 0.010 to 0.335 cm were prepared. The samples were excited by 59.54 keV gamma rays from a 5 Ci Am241 annular radioactive source in an energy dispersive x-ray fluorescence system. The scattered and emitted photons were counted by a high purity germanium (HPGe) detector. The results showed that the background intensity increases with the sample thickness and further enhancement in results in no further increase in the background intensity. The determined saturation (experimental) and critical (theoretical) thickness values considering the low and high energy tail regions of Compton scattering peak were compatible.