Energy Distribution Of Beam Research Articles

Vibration analysis of functionally graded saturated porous beams using radiative energy transfer method

An energy flow model based on the radiative energy transfer method (RETM) is established for the high-frequency response prediction of finite functionally graded saturated porous beams. The Timoshenko beam theory and the Biot thoery are applied to derive the motion governing equations of the beam. The response of the beam loaded by a high-frequency point force is described by vibrational energy density and intensity. The energy response of the beam is contributed by the rays emitted from the actual source set at load point and then reflected through the fictitious sources at the boundaries. Fictitious sources are determined by the energy balance equations at the boundaries. Numerical examples show that the energy distributions of the saturated porous beams are well predicted by the proposed approach.

Dose estimation using in-beam positron emission tomography: Demonstration for 11C and 15O ion beams

Ion therapy has been well established for many decades owing to sharp depth-dose gradient and high cell-killing capability of ions. However, monitoring of the incident ions is needed to reduce ion range uncertainty for effective tumor treatment. Positron-emitting ion beams, known as radioactive ion (RI) beams, can be used as the optimal clinical approach for simultaneously treating and monitoring the incident ions using positron emission tomography (PET) imaging. The low intensity of RI beams, which previously was the main difficulty of their clinical use, was recently addressed by the development of accelerator technology. Since the quantity of interest in ion therapy is the dose and a direct comparison of planned and delivered doses is highly desirable, we focused on predicting the depth dose from PET images for RI beams in this work for the first time. We developed a method for predicting the depth dose of polyenergetic ion beams of 11C and 15O from PET images of these ion beams. The depth dose in water was measured for mono- and polyenergetic ion beams. The monoenergetic ion beams had a momentum acceptance (MA) of ±0.25%, while the polyenergetic beams had an MA of ±2.5%. PET imaging was performed during and shortly after irradiation of a polymethylmethacrylate (PMMA) phantom with mono- and polyenergetic radioactive ion beams. The energy distribution of each polyenergetic ion beam was obtained from the measured momentum distribution of that beam. A set of depth dose and PET profiles in PMMA was constructed for several monoenergetic ion beams using measured data of a monoenergetic ion beam and the range-energy relation. To estimate the depth dose for each polyenergetic beam, a linear combination of weighted PET profiles of monoenergetic beams was iteratively fitted to the measured PET profile of the polyenergetic beam, and the resulting weights were combined with the corresponding monoenergetic depth doses to predict the depth dose distribution. Significance. The depth doses of the polyenergetic ion beams were predicted with mean relative errors of 2.20% and 1.95% for 11C and 15O ion beams, respectively. These errors represent the mean value of the differences between the predicted and measured values, normalized to the maximum measured value. The predicted distal fall-off positions at 80% of the Bragg peak were within 0.13 mm of the measured values for both ion beams. The applicability of the method was demonstrated for a head phantom irradiated with 11C ion beams using Monte Carlo simulation and the predicted distal fall-off positions at 80% of the Bragg peak was within 0.08 mm of the simulated values.

Effects of External Magnetic Field on Focusing and Energy Distribution of Primary Electrons in an Ion Source

The effect of the applied voltage and magnetic field on the defining slot in focusing and energy distribution of the primary filament electron beam was studied theoretically. In this work, SIMION 8.1 software was used to determine the best operational conditions for focusing and the distribution of the electron beam in the ion source system. Furthermore, the Larmor radius on the slot was calculated in two dimensions for different values of magnetic flux density. The results showed that the values of flux density and slot voltage play an effective role in improving the dimensions of beam spot andenergy distribution in the source. The dimensions of beam spot were reduced by about 71% at voltage value of slot 75 volt and flux density 780 G. In addition; the kinetic energy distribution for electrons were computed at different magnetic flux and obtaining a homogeneous beam energy. The results of this research support the calculations of plasma source designers.

Surface integrity analysis of Si3N4 under cryogenic assisted femtosecond laser ablation

Femtosecond laser is suitable to process Si3N4, but heat effect forming during machining process could degrade the performance of specimen. To reduce heat damage, in this study, the effects of cryogenic assisted laser machining on the surface quality and micro-structures of Si3N4 was investigated. The femtosecond laser was employed to ablate Si3N4 at various low temperatures, accompanied with comprehensive analysis of the surface roughness, material removal rate and SEM topography. To further illustrate the formation mechanism of surface structure, finite element analysis was conducted. Results indicated that while low temperature exerted negligible effects in single-layer ablation, multi-layer laser machining benefits from improved surface quality. Low temperature mitigated thermal effects and reduced the recast layer area, resulting in decreased surface roughness. The lowest surface roughness was obtained during the machining of the specimen at −60 °C of 1.072 μm, representing a 54.6 % reduction compared to ambient air machining. However, further decreasing the temperature below −60 °C led to an increase in surface roughness. This was attributed to the combined effects of Gaussian beam energy distribution and low temperature, resulting in incomplete ablation of the surface region between two scanning pitches, thereby decreasing surface quality. This research provides valuable insights into the cryogenic assisted femtosecond laser machining.

A design methodology of miniature photoacoustic cell based on beam energy distribution and acoustic resonator coupling

In photoacoustic spectroscopy, the photoacoustic cell plays the role of amplifying the photoacoustic signal, and the optimization of its parameters affects the sensitivity and dimensions of the whole system. However, none of the current optimization studies of photoacoustic cells have considered in depth the influence of beam waist radius, which limits the reduction of the size of photoacoustic cells. In this paper, based on the theory of photoacoustic spectroscopy, considering the inhomogeneity of the spatial distribution of the Gaussian beam energy and neglecting the loss of the beam in the acoustic resonator, a theoretical model of the effect of the beam waist radius on the cell constant of the first-order longitudinal resonant frequency is established. Six photoacoustic cells with different resonator radii were designed and measured for acetylene at five different beam waist radii. The relationship among beam waist radius, radius of acoustic resonator and cell constants shows that choosing a radius of resonator that matches the waist radius results in a more sensitive and smaller photoacoustic cell. The study provides a reference for the design of miniaturized photoacoustic cells with high sensitivity, thus promising to further improve the miniaturization of photoacoustic spectroscopy systems for more application scenarios.

Analytical solutions for quantum radiation reaction in high-intensity lasers

While the Landau-Lifshitz equation, which describes classical radiation reaction, can be solved exactly and analytically for a charged particle accelerated by a plane electromagnetic wave, no such solutions are available for quantum radiation reaction (the recoil arising from the successive, incoherent emission of hard photons). Yet upcoming experiments with ultrarelativistic electron beams and high-intensity lasers will explore the regime where both radiation-reaction and quantum effects are important. Here we present analytical solutions for the mean and variance of the energy distribution of an electron beam that collides with a pulsed plane electromagnetic wave, which are obtained by means of a perturbative expansion in the quantum parameter χ0. These solutions capture both the quantum reduction in the radiated power and the stochastic broadening, and are shown to be accurate across the range of experimentally relevant collision parameters, i.e., GeV-class electron beams and laser amplitudes a0≲200. Published by the American Physical Society 2024

Characterisation of neutron fields at the n-lab, a fast neutron facility at the University of Cape Town

The n-lab is a fast neutron facility based in the Department of Physics, University of Cape Town, offering collimated neutron beams produced by an MP 320 deuterium–tritium sealed tube neutron generator, and a 220 GBq americium–beryllium radioisotopic source. Characterisations of the spatial and energy distributions of the fast neutron beams were performed using an EJ-301 organic liquid scintillator detector and digital data acquisition system. Neutron energy spectra were obtained through unfolding analyses with MAXED, and a Monte Carlo approach to the propagation of uncertainties was implemented. Measurements of fluence and neutron emission rates were determined through the neutron activation of copper foils and subsequently used to validate the scaling of the unfolded neutron energy spectra.

Attosecond x-ray free-electron lasers utilizing an optical undulator in a self-selection regime

Accelerator-based x-ray free-electron lasers (XFELs) are the latest addition to the revolutionary tools of discovery for the 21st century. The two major components of an XFEL are an accelerator-produced electron beam and a magnetic undulator, which tend to be kilometer-scale long and expensive. A proof-of-principle demonstration of free-electron lasing at 27 nm using beams from compact laser wakefield accelerators was shown recently by using a magnetic undulator. However, scaling these concepts to x-ray wavelengths is far from straightforward as the requirements on the beam quality and jitters become much more stringent. Here, we present an ultracompact scheme to produce tens of attosecond x-ray pulses with several GW peak power utilizing a novel aspect of the FEL instability using a highly chirped, prebunched, and ultrabright tens of MeV electron beam from a plasma-based accelerator interacting with an optical undulator. The FEL resonant relation between the prebunched period and the energy selects resonant electrons automatically from the highly chirped beam which leads to a stable generation of attosecond x-ray pulses. Furthermore, two-color attosecond pulses with subfemtosecond separation can be produced by adjusting the energy distribution of the electron beam so that multiple FEL resonances occur at different locations within the beam. Such a tunable coherent attosecond x-ray sources may open up a new area of attosecond science enabled by x-ray attosecond pump/probe techniques. Published by the American Physical Society 2024

Production and measurement of MeV proton microbeams in atmospheric environment based on glass capillary

<sec>Traditionally, ion microbeam is produced by focusing or/and collimating to reduce the beam size to submicron level. The traditional setup for producing the microbeam consists of an expensive focusing and collimating system with a large space, based on electromagnetic fields. Meanwhile, the microbeam obtained through pure collimation of metal micro-tubes is limited by the fabrication processing, i.e. the size of beam spot is largely limited to a few microns and its manufacture is not as simple as that of a glass capillary. Inspired by early studies of the guiding effect, the use of inexpensive and easy-to-make glass capillaries as the tool for ion external microbeam production has become a new direction.</sec><sec>In this work, we use a glass capillary with an open outlet (108 μm in diameter), which serves as a vacuum differential and collimating component, to produce a 2.5 MeV-proton microbeam directly from the linear accelerator into the atmosphere for measurements. We measure the beam spot diameter and energy distribution of the microbeam as a function of the tilt angle of the capillary. We also conduct calculations and ion trajectory analysis on the scattering process of 2.5 MeV protons on the inner walls.</sec><sec>The measurement results show that when the tilt angle is around 0°, there are a direct transmission part that maintains the initial incident energy, and a scattering part with the energy loss in the microbeam. It is found that the proportion of directly transmitted protons and the beam spot size are highest near zero tilt angle. As the tilt angle increases, the beam spot diameter decreases; when the tilt angle is greater than the geometric angle, all the microbeams come from the scattering with the energy loss. The simulation combined with the ion trajectory analysis based on the scattering process can explain the experimental results. It is found that the large angle scattering determines the entire external microbeam spot, and the central region of the beam spot is composed of directly penetrating ions, whose size is determined by the geometric shape of the glass capillary, i.e. the outlet diameter and aspect ratio.</sec><sec>The natural advantage of producing external micobeames easily and inexpensively through glass capillaries is their relative safety and stable operation, and the last but not least point is to simply locate the microbeams on the sample without complex diagnostic tools. The microbeams are expected to be widely used in fields such as radiation biology, medicine, and materials.</sec>

Trajectory planning of deep-cutting laser profiling of superabrasive profile grinding wheels

The low profiling efficiency is the key barrier to the industrial application of laser dressing technology for profile grinding wheels. In this paper, the trajectory planning method of deep-cutting laser profiling was proposed for the first time, the theoretical model of the energy distribution of the Gaussian laser beam on the surface of the profile grinding wheel was established, and the effect of this method on improving the profiling efficiency of superabrasive profile grinding wheel was systematically studied. Through comparative experiments, it was confirmed that the trajectory planning method could effectively improve the profiling efficiency of the V-shaped grinding wheel, and it was found that the smaller the tip angle, the greater the efficiency improvement. The change of grain size will lead to the change of grain removal method, which will affect the profiling efficiency of V-shaped grinding wheel, but it has little influence on the profiling accuracy. The V-tip arc radius of the diamond grinding wheel with a particle size of 20–180 μm after laser profiling could be controlled between 10 and 20 μm, which was difficult to achieve by mechanical or electrical dressing method. The trajectory planning method could also significantly improve the profiling efficiency of convex/concave arc-shaped grinding wheels, and the greater the arc radius or chord-to-diameter ratio of the grinding wheel, the greater the efficiency improvement. Even though convex/concave arc-shaped grinding wheels were the same size, their profiling efficiency and material removal efficiency were quite different. For grinding wheels with different arc radii or chord-to-diameter ratios, different process strategies should be selected during laser profiling to ensure a comprehensive balance between efficiency, accuracy and quality.

Terahertz magneto-optical metadevice for active spin-selective beam steering and energy distribution with nonreciprocal isolation

Active beam steering and energy distribution have important applications for terahertz (THz) communication, radar, and imaging. However, the spin-conjugated mirror symmetry of a passive Pancharatnam–Berry (PB) metasurface limits the active energy distribution. Here, we prepared a low dispersion, low loss, and high magneto-optical coefficient La:YIG single crystal, ±45∘ Faraday rotation angle that can be actively tuned by a weak magnetic field in broadband THz range at room temperature. Based on this functional material, a THz magneto-optical (MO) spin-modulated metadevice has been demonstrated, which is integrated with a La:YIG, an anisotropic metasurface, and a PB metasurface layer. The spin-conjugated mirror symmetry is broken by the MO chirality effect and photonic spin Hall effect in this metadevice so that spin-selective beam steering within the range of ±27∘−±41∘ is dynamically manipulated by external magnetic fields and power distribution can be tuned with the max modulation depth of 91.6%. More importantly, the MO crystal introduces nonreciprocal phase shift between two spin states so that the device not only achieves active THz beam steering but also provides isolation for reflected waves with the max isolation of 23 dB. This mechanism of THz nonreciprocal spin beam steering provides multiple functions for THz point-to-point networking communication, anti-shielding, anti-interference, and power distribution.

A compact radio-frequency ion source for high brightness and low energy spread negative oxygen ion beam production.

A high brightness and low energy spread (∆E) ion source is essential to the production of a high-quality primary ion beam applied in secondary ion mass spectrometry (SIMS). A compact 13.56MHz radio-frequency (RF) ion source with an external planar spiral antenna has been developed as a candidate ion source for the production of negative oxygen ion beams for SIMS application. This ion source is designed with a three-and-a-half-turn water-cooled planar antenna for RF power coupling, a multi-cusp magnetic field for effective plasma confinement, and a three-electrode extraction system. The experimental results show that more than 50 µA negative oxygen ion beams have been extracted, which consist of 56% O-, 25% O2-, and 19% O3-. The ion energy distribution of the negative oxygen ion beam exhibits a Gaussian distribution with a minimum ∆E of 6.3eV. The brightness of the O- beam is estimated to be 82.4Am-2 Sr-1V-1. The simulation, design, and experimental study results of this RF ion source will be presented in this paper.

Process and corrosion property of laser-chemical hybrid polishing of TC4 alloy

In order to reduce the adverse effects of recast layer and heat-affected zone during laser polishing of titanium alloys, a novel laser-chemical hybrid polishing method was proposed. The surface of TC4 alloy in phosphoric acid solution was irradiated by nanosecond laser for polishing experiments. White light interferometer was used to measure the surface roughness at different number of laser scanning times. The surface composition was analyzed by XPS. The results showed that the surface roughness of the substrate was reduced from 304 nm to 59 nm, and the corrosion resistance of the polished substrate were significantly improved compared with the original substrate. Local electrochemical effects occur on the substrate surface due to thermal difference caused by uneven energy distribution of the laser beam on the substrate. Under the continuous irradiation of the laser, further corrosion under the electrochemical effect gradually reduced the surface roughness of the substrate. After laser-chemical hybrid polishing, the surface roughness of the titanium alloy substrate was reduced, and no recast layer and heat-affected zone were found on the surface of the substrate.

A Calibration Method for Large-Footprint Full-Waveform Airborne Laser Altimeter without a Calibration Field

The geometrical measurement precision of laser spots is affected by the deviation between the parameters of the laser altimeter and the laboratory measurement results, and the inversion accuracy of surface object height is also limited. The measurement parameters and the load state can be obtained by calibration of the laser altimeter system. Usually, ground detectors are deployed to calibrate the measurement parameters of the laser altimeter, including the divergence angle and the energy distribution of the laser beam. A calibration method for a laser footprint spot without a calibration field was proposed in this paper, focused on the airborne large-footprint laser altimeter system. The geometric parameters of the laser spot were calibrated through the laser echo waveforms of a specific terrain. The experimental results show that geometric calibration of the large-footprint laser altimeter can be achieved in the area of the step surface. The divergence angle of the laser beams obtained from the six experimental areas is 4.604 ± 0.359 mRad, and the consistency of the energy distribution from each laser spot reaches 92.67%. A new method of on-orbit calibration and verification is provided for the satellite laser altimeter system.

Low-energy protons shallow spread-out Bragg peak imaging with a lithium fluoride crystal

The 35 MeV proton beam produced by a modular linear accelerator was used to irradiate at grazing incidence a LiF crystal through a spinning Mylar multi-sector range modulation wheel and a Pyrex range shifter. Starting from a measured pristine depth dose curve, these energy-modulation devices were designed to plan a test shallow spread-out Bragg peak in water. The irradiation of the LiF crystal produced in its lattice a volume distribution of color centers, which could be visualized in a fluorescence microscope as a fluorescent image under blue-light illumination. Since the intensity of this fluorescent image was proportional point-by-point to the absorbed energy, it was elaborated to obtain an experimental depth dose curve in the LiF crystal, from which the proton beam energy distribution was estimated. This latter was finally used to evaluate the corresponding spread-out Bragg peak that would be obtained in water and compare it to the designed one.

Analysis of atmospheric turbulence and vibration impact on the performance of satellite–ground laser communication beam

AbstractWith satellite laser communication, advantages can be achieved in high communication rate, precise beam pointing, high confidentiality, and light‐small terminal. Satellite–ground (SG) laser links also play a crucial role as trunk links. However, the SG link is influenced by atmospheric turbulence and platform vibration, these two factors will cause unstable link tracking. This paper focuses on the viewpoint of beam energy transmission, using the low‐frequency harmonic phase compensating method to establish the random phase screen. On the basis of this model, the laser beam energy distribution and the spot mass positioning error are analyzed considering turbulence taking vibration which is not considered in previous studies. The simulation results show that the spot mass center (SMC) is impressionable in strong turbulence under platform vibration, but in a weak turbulent environment, SMC is insensitive to vibration when turbulence and vibration are at the same noise level.

The NCT-WES directional neutron spectrometer: validation of the response with monoenergetic neutron fields

A directional neutron spectrometer named NCT-WES (Neutron Capture Therapy Wide Energy Spectrometer) was developed for quality assurance of the therapeutic neutron beam in Neutron Capture Therapy (NCT). NCT-WES operates as a “parallelized” Bonner spheres spectrometer, embedding six semiconductor-based thermal neutron detectors in a collimated cylindrical moderator. With the objective of validating the simulation model used to derive its response matrix, irradiations in reference monoenergetic fields were performed at National Physical Laboratory (UK). As the energy distributions of neutron beams in NCT extend from keV to a few MeV, monoenergetic fields in this domain were chosen, namely 71.5 keV, 144.2 keV, 565.1 keV, 841.9 keV and 1200.4 keV. The results of the experiment confirm the correctness of the NCT-WES simulation model, within an overall uncertainty lower than ± 2%.

Numerical studies of a layered lithium-boron target for laser-driven aneutronic fusion reactions

This paper explores a novel target design for laser-driven, aneutronic, proton-boron and proton-lithium fusion reactions consisting of a stack of boron and lithium foils. In contrast to a homogeneous target, this multi-layer setup provides additional fusion channels in the different materials. The composition of the layers is chosen in descending order of the fusion reactions' thresholds, facilitating the fusion of protons that penetrate further into the material despite their energy losses due to electronic and nuclear stopping power. We employ a combination of Fluka simulations and additional numerical computations to evaluate thousands of target configurations. Four different beam energy distributions are considered: two Gaussian distributions with 6~MeV and 10~MeV mean energies, respectively, a Maxwell-Boltzmann distribution and a power law distribution. We explore the production of energy in a range of layer thicknesses motivated by the proton ranges based on ionization losses. The configuration which maximizes the produced energy for each beam type is reported. The production of fusion energy ranges from hundreds to thousands of millijoules for proton bunches of $10^{15}$ having mean energies between 2-10 MeV.

Preparing Phase 4 of the n_TOF/CERN facility

After CERN’s Long Shutdown 2, the n_TOF facility infrastructure was largely upgraded. The biggest change is the installation of a new lead spallation target, the performance of which needs to be carefully examined. During Summer 2021, the facility’s two flight paths were characterised in terms of neutron beam energy distribution, profile and resolution. In this work, the characterisation of the facility is described and the first results are given.

Electron beam energy slicing performance in laser wakefield acceleration

The first stage of electron acceleration, the plasma cathode, is a key part of LWFA. Output parameters of this stage such as beam charge, mean energy, energy spread, and emittance can be varied in a rather broad range depending on laser pulse and gas target conditions. These parameters are usually evaluated via particle-in-cell (PIC) simulations. However, if an essential improvement of the beam quality could be further performed with a conventional beamline, the selection of an acceleration regime, including laser pulse and gas target characteristics, should be done taking into account not only PIC simulations but also beam transport simulations. Here is shown that improvements of electron beam quality via energy slicing using magneto-optics (MO) may become an important step in developing full-optical electron accelerators and radiation devices. Since the typical energy of electrons presently achieves sub-GeV in a single acceleration stage, the elaboration of slicing techniques for quasi-mono-energetic, high density LWFA beams is of particular interest. Depending on the efficiency of beam slicing the reverse problem of initial beam energy distribution and, therefore, a proper acceleration regime can be solved. An efficient slicing may allow operation with broader beam energy spreads, higher charges, and getting better stability in contrast to narrower beam energy spreads requiring far more precise control over laser and gas target parameters. Even though this technique has been used in classical particle accelerators, its limitations have not been well studied in LWFA with their less stable beams. MO slicing is explored numerically with use of realistic LWFA electron beams obtained from 3D PIC simulations at various target parameters.