Radial Beam Research Articles

Energy flux density and angular momentum density of radial Pearcey-Gauss vortex array beams in the far field

The longitudinal and transverse energy flux density (EFD) and angular momentum density (AMD) of the radial Pearcey-Gauss vortex array beams are studied by using the vector angular spectrum representation and stationary phase method, where the influence of topological charge, initial phase index, noncanonical strength and the number of beamlet on far-field vectorial structures of the corresponding beam is emphasized. The results show that the topological charge of center optical vortex is always equal to initial phase index for different noncanonical strength. The longitudinal EFDs exhibit different structures by varying initial phase index and the number of beamlet. For an odd-N, the topological charge of center optical vortex can be determined by distinguishing the longitudinal EFD, however for an even-N the topological charge cannot be identified due to the equivalence of longitudinal EFD in the case of positive and negative initial phase index m. The AMD tends to split more branches from the positive and negative direction with increasing the absolute value of topological charge l, The inner structures of AMD are also affected by different beamlets while the zero value of AMD is always retained.

Study on Radial Sheet Beam Electron Optical System for Miniature Low-Voltage Traveling-Wave Tube

Angle log-periodic meander line microstrip radial sheet beam traveling-wave tube is one kind of novel minimized vacuum device with low beam voltage. To generate and focus the radial sheet electron beam, a novel radial divergent sheet beam electron optical system, including the tractable radial sheet electron beam gun and miniaturized and feasible radial small tunable periodic cusped magnetic focusing system, is proposed in this paper. The fan-shaped radial sheet beam is emitted from the cylindrical surface cathode, compressed in axial direction, and confined in azimuthal direction by the focusing electrode. Simulation results show that the total emission of the angular radial sheet beam gun is 51.2 mA with the dimensions of $0.26~\text {mm} \times 8$ ° under the voltage of 1.7 kV, and the fan-shaped radial sheet beam can totally pass through the fan-shaped drift tunnel under the magnetic field. The experimental results are good in agreement with the simulation results. The tested angular radial sheet beam transmission efficiency is >90% in an 18.8-mm-length beam tunnel with the fill factor of 50%.

The quality assessment of radial and tangential neutron radiography beamlines of TRR

To achieve a quality neutron radiographic image in a relatively short exposure time, the neutron radiography beam must be of good quality and relatively high neutron flux. Characterization of a neutron radiography beam, such as determination of the image quality and the neutron flux, is vital for producing quality radiographic images and also provides a means to compare the quality of different neutron radiography facilities. This paper provides a characterization of the radial and tangential neutron radiography beamlines at the Tehran research reactor. This work includes determination of the facilities category according to the American Society for Testing and Materials (ASTM) standards, and also uses the gold foils to determine the neutron beam flux. The radial neutron beam is a Category I neutron radiography facility, the highest possible quality level according to the ASTM. The tangential beam is a Category IV neutron radiography facility. Gold foil activation experiments show that the measured neutron flux for radial beamline with length-to-diameter ratio (L/D) =150 is 6.1× 106 n cm−2 s−1 and for tangential beamline with (L/D)=115 is 2.4× 104 n cm−2 s−1.

Finite element model approach of a cylindrical lithium ion battery cell with a focus on minimization of the computational effort and short circuit prediction

In this research, a parameterized beam-element-based mechanical modeling approach for cylindrical lithium ion batteries is developed. With the goal to use the cell model in entire vehicle crash simulations, focus of development is on minimizing the computational effort whilst simultaneously obtaining accurate mechanical behavior. The cylindrical cell shape is approximated by radial beams connected to each other in circumferential and longitudinal directions. The discrete beam formulation is used to define an anisotropic material behavior. An 18650 lithium ion cell model constructed in LS-Dyna is used to show the high degree of parameterization of the approach. A criterion which considers the positive pole deformation and the radial deformation of the cell is developed for short circuit prediction during simulation. An abuse testing program, consisting of radial crush, axial crush, and penetration is performed to evaluate the mechanical properties and internal short circuit behavior of a commercially available 18650 lithium cell. Additional 3-point-bending tests are performed to verify the approach objectively. By reducing the number of strength-related elements to 1600, a fast and accurate cell model can be created. Compared to typical cell models in technical literature, simulation time of a single cell load case can be reduced by approx. 90%.

Formation of modified layers on the outer surface of cylindrical samples from E110 alloy under the influence of radial argon ions beam in the mode of multilayered films ion mixing

Results of experiments of modified layers formation on the long-length cladding tubes from E1 10 alloy (Zr – 1 % Nb) are presented in this paper. Samples were modified by surface polishing by radial Ar+ beam with wide-range energy spectrum, series of films from alloying elements deposition and their subsequent processing in the ion mixing mode. The concentration of implanted atoms is 1–5 at. %, with a maximum penetration depth of 1–2 μm

Effect of ion polishing on corrosion resistance of the cladding of fuel elements from E110 alloy in the steam water environment

The method of modification of the outer surface of the cladding of fuel elements from E110 Zr alloy by means of irradiation with a radial beam of Ar+ ions with a broad energy spectrum is proposed. It is shown that the use of ion beam treatment at the final stage of the cladding production can improve the surface quality owing to removal of a large part of surface defects after mechanical polishing. The kinetics of the growth of oxide films on ion-beam-treated (cleaning or polishing by Ar+ ions) tubular Zr alloy specimens in a steam environment (350, 375, and 400°C up to 3000 h) was investigated. Monoclinic zirconia layer formation is found to occur on the specimen surface oxidized at 350°C in water and steam environments. Oxidation of the fragments of the alloy fuel-element cladding in steam under pressure contributes to the formation of a thicker and more friable oxide film in comparison with the oxidation in water.

Structuring light under different polarization states within micrometer domains: exact analysis from the Maxwell equations.

We show the possibility of arbitrary longitudinal spatial modeling of non-diffracting light beams over micrometric regions. The resulting beams, which are highly non-paraxial, possess subwavelength spots and can acquire multiple intensity peaks at predefined locations over regions that are few times larger than the wavelength. The formulation we present here provides exact solutions to the Maxwell's equations where the linear, radial, and azimuthal beam polarizations are all considered. Modeling the longitudinal intensity pattern at small scale can address many challenges in three-dimensional optical trapping and micromanipulation.

Legitimacies of the growth of oxide films on ion-modified samples from the alloy E110 at high-temperature oxidation

The possibility to obtain barrier layers during the surface modification by ion-plasma to decrease the oxidation and hydrogenation rate of fuel claddings from zirconium alloys at various operation conditions is studied in this paper. Fuel claddings from the alloy E110 obtained on the outer surface of fuel elements after ion polishing are determined on the basis of calculations and experiments performed: the average ion energy in a beam is 3-4 keV, the ion current is 0.4-0.7 mA cm-2, and the total irradiation dose is 5×1018 ion cm-2. Cleaning and polishing of samples from the alloy E110 were carried out on the installation ILUR-03 by a radial beam of argon ions with a wide energy spectrum. Thin films (up to 100 nm) of alloying elements – Fe, Al, Mo, Y, Mg, and Cr were obtained on the polished surface by magnetron deposition and then implanted into the near-surface layer under the influence of a radial beam of argon ions. Study of the element composition of cleaned and modified near-surface layers was performed by X-ray microanalysis. A part of the samples was preliminarily autoclaved in distilled water at the temperature of 350 °C and the pressure of 17 MPa for 500 h to obtain a protective layer from an oxide film enriched by implanted elements. It is shown that alloying elements are mostly located at the oxide-metal boundary and in the oxide.

Biomimetic surface structuring using cylindrical vector femtosecond laser beams

We report on a new, single-step and scalable method to fabricate highly ordered, multi-directional and complex surface structures that mimic the unique morphological features of certain species found in nature. Biomimetic surface structuring was realized by exploiting the unique and versatile angular profile and the electric field symmetry of cylindrical vector (CV) femtosecond (fs) laser beams. It is shown that, highly controllable, periodic structures exhibiting sizes at nano-, micro- and dual- micro/nano scales can be directly written on Ni upon line and large area scanning with radial and azimuthal polarization beams. Depending on the irradiation conditions, new complex multi-directional nanostructures, inspired by the Shark’s skin morphology, as well as superhydrophobic dual-scale structures mimicking the Lotus’ leaf water repellent properties can be attained. It is concluded that the versatility and features variations of structures formed is by far superior to those obtained via laser processing with linearly polarized beams. More important, by exploiting the capabilities offered by fs CV fields, the present technique can be further extended to fabricate even more complex and unconventional structures. We believe that our approach provides a new concept in laser materials processing, which can be further exploited for expanding the breadth and novelty of applications.

Topological features of vector vortex beams perturbed with uniformly polarized light

Optical singularities manifesting at the center of vector vortex beams are unstable, since their topological charge is higher than the lowest value permitted by Maxwell’s equations. Inspired by conceptually similar phenomena occurring in the polarization pattern characterizing the skylight, we show how perturbations that break the symmetry of radially symmetric vector beams lead to the formation of a pair of fundamental and stable singularities, i.e. points of circular polarization. We prepare a superposition of a radial (or azimuthal) vector beam and a uniformly linearly polarized Gaussian beam; by varying the amplitudes of the two fields, we control the formation of pairs of these singular points and their spatial separation. We complete this study by applying the same analysis to vector vortex beams with higher topological charges, and by investigating the features that arise when increasing the intensity of the Gaussian term. Our results can find application in the context of singularimetry, where weak fields are measured by considering them as perturbations of unstable optical beams.

Analyzing the average intensity distribution and beam width evolution of phase-locked partially coherent radial flat-topped array laser beams in oceanic turbulence

In this research, an analytical expression for cross-spectral density matrix elements (and consequently, average intensity) of partially coherent flat-topped (PCFT) radial array laser beams in weak oceanic turbulence are derived based on the extended Huygens–Fresnel principle and the previously developed knowledge of the propagation of a partially coherent beam in atmosphere. Mean-squared beam width is calculated analytically using average intensity formula. The simulation is done by considering the effects of source parameters (such as the radius of the array setup’s circle and effective width of spectral degree of coherence) and turbulent ocean factors (such as the rate of dissipation of the turbulent kinetic energy per unit mass of fluid and relative strength of temperature-salinity fluctuations, Kolmogorov micro-scale, and the rate of dissipation of the mean squared temperature) in detail. It is found that when salinity fluctuations in the ocean dominate temperature fluctuations, the average intensity of the PCFT array beam becomes more broad and the array beam profile conversion process to a single wider Gaussian beam profile will occur at a faster rate. For the same turbulent conditions and the same initial beam width, the divergence of a flat-topped array beam is less than the Gaussian array beam. The simulation and calculation results are shown by graphs.

高斯阵列光束自耦合特性的实验研究

Based on the generalized Huygens-Fresnel principle and the modified von Karman spectrum model, the analytic expressions for intensity distribution of radial Gaussian array beams after incoherent combination that propagation in the atmospheric turbulence were derived. And the self-coupling characteristics of array beams was analyzed numerically with the change of transmission distance and the radial radius. Finally self-coupling characteristics of array beam of different radial radius with the change of the transmission distance had been measured by using a beam analyzer. The experimental results show that when Gaussian array beams propagate in atmospheric turbulence horizontaly, array beam will combine a beam from a certain distance with the increasing of transmission distance. And the average intensity of the combined beam is like-Gaussian distribution; under the same transmission conditions, the smaller the radial radius, the better the self-coupling characteristics of the array beams is.

Monte Carlo Simulation for Designing Collimator of the Neutron Radiography Facility in Malaysia

Neutron collimator is the most important component in a neutron radiography facility set-up, which defines the neutron beam characteristic at the object plane. The neutron radiography facility in Malaysia was built at one of the radial beam ports of TRIGA MARK II PUSPATI research reactor (RTP). At present, the facility has low thermal neutron intensity at the sample position, which leads to long irradiation times; it gives many limitations for the industrial applications. The collimator used for this facility is based on step divergent collimator type. The aim of this research is to design the best geometry and to choose materials for thermal neutron collimator so as to obtain a uniform beam, high L/D ratio and a maximum thermal neutron flux at the object plane. In order to achieve this aim new collimator geometry has been designed to improve the existing radiography facility by using Monte-Carlo simulation codes of SIMRES and MCNPX. The new design results are compared with those of the existing facility. Our simulation result may be of help in the design of new collimator for neutron radiography facility.

The design of two color interferometer system for the 3-dimensional analysis of plasma density evolution on KSTAR

A 5-channel two color interferometer (TCI) system has been designed on KSTAR. TCI system is designed for tangential beam paths, which will combine with two existing interferometer systems of vertical and radial beam paths, so that it will provide 3-dimensional measurement of electron density evolution. TCI system uses wavelengths of 10.6μm by a CO2 laser and 0.633μm by a HeNe laser. The system compensates the vibrational noise by using two colors and avoids refraction by short wavelengths. The main purpose of the TCI is to generate routine measurement of the line integrated plasma density for the real time density control on KSTAR. The 5-channels will provide profile data for the density. Time resolution of the system is expected to be 500kHz or higher in order to measure 3-dimensional density fluctuations for ELMs and other MHD activities including TAE modes. The system is planned to be working on KSTAR 2016 campaign with 1–2 channels.

Study of the Symmetrical Microstrip Angular Log-Periodic Meander-Line Traveling-Wave Tube

The symmetrical microstrip angular log-periodic meander-line (ALPML) slow-wave structure (SWS), which is suitable for Ka-band low-voltage traveling-wave tubes, is described in this paper. The dispersion characteristics and coupling impendence of this kind of SWS are achieved by simulation. A radial uniform magnetic field of 0.4 T is developed using radially magnetized permanent magnets to focus the radial sheet electron beam. To exploit the potentialities of the symmetrical ALPML SWS, the beam–wave interaction is carried out with a radial convergent and a divergent sheet electron beam. For the radial divergent electron beam with a voltage of 791 V and a current of 0.3 A, an output power over 60 W with an electron efficiency of 26% at 30 GHz is achieved from particle-in-cell simulation. The effects of misalignments and phase mismatches are carried out at the end.

Analyzing the propagation behavior of coherence and polarization degrees of a phase-locked partially coherent radial flat-topped array laser beam in underwater turbulence

In this research, based on an analytical expression for cross-spectral density (CSD) matrix elements, coherence and polarization properties of phase-locked partially coherent flat-topped (PCFT) radial array laser beams propagating through weak oceanic turbulence are analyzed. Spectral degrees of coherence and polarization are analytically calculated using CSD matrix elements. Also, the effective width of spatial degree of coherence (EWSDC) is calculated numerically. The simulation is done by considering the effects of source parameters (such as radius of the array setup's circle, effective width of the spectral degree of coherence, and wavelength) and turbulent ocean factors (such as the rate of dissipation of the turbulent kinetic energy per unit mass of fluid and relative strength of temperature and salinity fluctuations, Kolmogorov micro-scale, and rate of dissipation of the mean squared temperature) in detail. Results indicate that any change in the amount of turbulence factors that increase the turbulence power reduces the EWSDC significantly and causes the reduction in the degree of polarization, and occurs at shorter propagation distances but with smaller magnitudes. In addition, being valid for all conditions, the degradation rate of the EWSDC of Gaussian array beams are more in comparison with the PCFT ones. The simulation and calculation results are shown by graphs.

SU-G-TeP2-03: Comparison of Standard Dosimetry Protocol in Japan and AAPM TG-51 Addendum in Order to Establish Optimal Dosimetry for FFF Beam

Purpose: Japan Standard Dosimetry of Absorbed dose to water in external beam radiotherapy (JSDP12) is widely used to measure radiation dose in radiotherapy. However, JSDP12 does not take flattening-filter-free (FFF) beam into consideration. In addition, JSDP12 applied TPR20,10 for dose quality index for photon beam. The purpose of this study is to compare JSDP12 with AAPM TG-51 addendum in order to establish optimal dosimetry procedure for FFF beam. Method: We evaluated the ion-recombination factor (ks) and the correction factor of radial beam profile (Prp) in FFF beam dosimetry. The ks was introduced by 2 voltages method and verified by Jaffe's plot. The Prp was given by both film measurement and calculation of treatment planning system, and compared them. Next, we compared the dose quality indexes (kQ) between TPR20,10 method and PDD(10)x method. Finally we considered optimal dosimetry protocol for FFF photon beam using JSDP12 with referring TG-51 addendum protocols. The FFF photon beams of 6 MV (6X-FFF) and 10 MV (10X-FFF) from TrueBeam were investigated in this study. Results: The ks for 6X-FFF and 10X-FFF beams were 1.005 and 1.010, respectively. The Prp of 0.6 cc ionization chamber for 6X-FFF and 10X-FFF beams (Film, TPS) were (1.004, 1.008) and (1.005, 1.008), respectively. The kQ for 6X-FFF and 10X-FFF beams (JSDP12, TG-51 addendum) were (0.9950, 0.9947) and (0.9851, 0.9845), respectively. The most effective factor for uncertainty in FFF photon beam measurement was Prp for JSDP12 formalism. Total dosimetric differences between JSDP12 and TG-51 addendum for 6X-FFF and 10X-FFF were -0.47% and -0.73%, respectively. Conclusion: The total dosimetric difference between JSDP12 and TG-51 addendum was within 1%. The introduction of kQ given by JSDP is feasible for FFF photon beam dosimetry. However, we think Prp should be considered for optimal dosimetry procedure even if JSDP12 is used for FFF photon beam dosimetry.

Neutron spectrum measurements at a radial beam port of the NUR research reactor using a Bonner spheres spectrometer

This paper describes the measurement campaign held around the neutron radiography (NR) facility of the Algerian 1MW NUR research reactor.The main objective of this work is to characterize accurately the neutron beam provided at one of the radial channels of the NUR research reactor taking benefit of the acquired CRNA Bonner spheres spectrometer (BSS). The specific objective was to improve the image quality of the NR facility. The spectrometric system in use is based on a central spherical 3He thermal neutron proportional counter combined with high density polyethylene spheres of different diameters ranging from 3 to 12in. This counting system has good gamma ray discrimination and is able to cover an energy range from thermal to 20MeV. The measurements were performed at the sample distance of 0.6m from the beam port and at a height of 1.2m from the facility floor. During the BSS measurements, the reactor was operating at low power (100W) to avoid large dead times, pulse pileup and high level radiation exposures, in particular, during spheres handling.Thereafter, the neutron spectrum at the sample position was unfolded by means of GRAVEL and MAXED computer codes. The thermal, epithermal and fast neutron fluxes, the total neutron flux, the mean energy and the Cadmium ratio (RCd) were provided. A sensitivity analysis was performed taking into account various defaults spectra and ultimately a different response functions in the unfolding procedure. Overall, from the obtained results it reveals, unexpectedly, that the measured neutron spectrum at the sample position of the neutron radiography of the NUR reactor is being harder with a predominance of fast neutrons (>100keV) by about 60%. Finally, those results were compared to previous and more recent measurements obtained by activation foils detectors. The agreement was fairly good highlighting thereby the consistency of our findings.

Aperture averaging in multiple-input single-output free-space optical systems using partially coherent radial array beams.

Multiple-input single-output (MISO) techniques are employed in free-space optical (FSO) links to mitigate the degrading effects of atmospheric turbulence. In this paper, for the MISO FSO system, a partially coherent radial array and a finite-sized receiver aperture are used at the transmitter and the receiver, respectively. Using the extended Huygens-Fresnel principle, we formulate the average power and the power correlation at the finite-sized slow detector in weak atmospheric turbulence. System performance indicators such as the power scintillation index and the aperture averaging factor are determined. Effects of the source size, ring radius, receiver aperture radius, link distance, and structure constant and the degree of source coherence are analyzed on the performance of the MISO FSO system. In the limiting cases, the numerical results are found to be the same when compared to the existing coherent and partially coherent Gaussian beam scintillation indices.

Bit error rate analysis of MISO FSO systems

Multiple-input single-output (MISO) systems are employed in free space optical (FSO) links to mitigate the degrading effects of atmospheric turbulence. In this paper, we consider a MISO FSO system with practical transmitter and receiver configuration that consists of radial laser array with Gaussian beams and a Gaussian receiver aperture function. We have employed our previously derived formulation of the power scintillation in which Huygens–Fresnel principle was employed. Therefore, we choose system parameters within the range of validity of the wave structure functions. Using the on-off keying modulation and the log-normal probability distribution function, we quantify the average bit error rate (〈BER〉) of laser array beams in weak turbulence. It is observed that the radial array beams at the transmitter are more advantageous than the single Gaussian beam. However, increasing the number of array beamlets to more than three seems to have negligible effects on 〈BER〉 . It is further observed that 〈BER〉 decreases when the source size, the ring radius and the receiver aperture radius increase.