Electron transport in solids at keV energies: Improved Monte Carlo simulation of backscattering and absorption phenomena.

High-energy photon beams in the multi-MeV range are essential for applications such as medical and industrial imaging, material science, and non-destructive testing (NDT) of large and highly attenuating objects. Laser-plasma accelerators overcome the limitations of conventional gamma ray sources, by generating smaller and much shorter electron bunches, resulting in high-energy Bremsstrahlung radiation that improves the spatial and temporal resolution in gamma-ray imaging. This study presents the development and commissioning of a gamma irradiation station at the 100 TW laser beam output of ELI-NP, designed for industrial imaging applications. Laser pulses with energies of 1.4 - 2 J were focused to a 21 μm ×24 μm spot size on supersonic gas jets of low-density Argon and Helium-Nitrogen mixture (3-6 x1018 part/cm3), generating electrons with energies up to 220 MeV and bunch charge of (311±29) pC via the Wakefield acceleration mechanism. These electrons produced Bremsstrahlung gamma rays upon interaction with a 2-mm-thick Aluminum target, enabling gamma ray imaging of various objects with a resolution of about 0.1 mm/px. We also report here, for the first time experimentally, the electron bunch charge density dependency on laser pulse duration, offering insights for optimizing future gamma-ray sources.

This study presents a comprehensive comparative investigation of nanosecond laser-induced shock waves (LISWs) generated on an aluminum target under air and water confinement regimes. The spatiotemporal evolution of shock waves (SWs) was systematically characterized using the optical beam deflection technique with subnanosecond temporal resolution. LISW propagation exhibited significantly enhanced dynamics, achieving velocities of 2.5km/s and pressures of 35MPa in a confined medium. These values correspond to 1.67-fold and 2.69-fold increases in velocity and pressure, respectively, relative to air confinement conditions (1.5km/s, 13MPa) under identical fluence conditions. These experimental results demonstrate that enhancements in SW dynamics are attributed to water's superior plasma confinement capability and higher energy coupling efficiency. Theoretical modeling of SW expansion exhibited excellent agreement with the experimental data, validating the observed confinement effects. Furthermore, morphological analysis reveals that water confinement produces more uniform ablation craters with reduced thermal effects and significantly improved ablation efficiency compared to air environments. Specifically, water confinement yields 58% greater ablation at equivalent fluences, demonstrating its advantages for precision material processing. These findings will provide critical insights for optimizing laser-based material processing techniques, particularly for applications requiring controlled SW propagation and enhanced material removal efficiency.

We explore the wettability modulation induced on alumina (Al2O3) targets by femtosecond laser texturing to demonstrate the stable and durable hydrophilic character of the surface. Specifically, we identify a suitable operational regime to tailor micro-nanostructures onto Al2O3 plates and accurately assess the ablation threshold in our experimental conditions. A periodic geometry with triangular patterns of various groove depths, ranging from 3.2 ± 0.1 to 17.1 ± 0.1 µm, was optimized for establishing a long-term wetting response. The latter was monitored on daily basis over a time interval exceeding 40 days by collecting the contact angle measurements of samples with and without a post-process thermal annealing, adopted to stabilize the surface wettability soon after the laser treatment. The results show that deeper grooves significantly enhance and maintain the hydrophilic character, particularly in samples without post-process thermal annealing, where superhydrophilicity (θ < 5°) is demonstrated to persist the entire time throughout the test. These findings disclose the potential for an effective fine-tuning of the alumina wettability, thus opening up the possibility of specific applications requiring long-term control of surface-liquid interactions, such as biomedical implants, and orthopedic and dental prostheses.

In this study aluminum and Moon regolith (substitute) materials were irradiated at HIT medical facility with protons, helium and carbon ions, at energy 430 MeV/u. The ambient doses equivalent — H*(10) values were measured with different equipment at different angles relative to the target(s) and compared with simulations done using Monte Carlo code — FLUKA. The measured doses showed a good agreement with FLUKA simulations; different aspects of the measured radiation fields, as well as of the used measurement equipment are discussed.

A method for obtaining a beam of charged hadrons in the momentum range of 2–13 GeV/c has been implemented at the SPASCHARM facility of the U-70 accelerator complex for methodological studies. A scheme for obtaining such a beam has been demonstrated using a crystal deflector placed in the vacuum chamber of the U-70 strong focusing accelerator to extract primary protons onto an external aluminum target. It has been shown that this method allows for obtaining beams of charged particles in the specified momentum range for methodological studies.

A hybrid plasma resulting from a combination of a stationary microwave electron cyclotron resonance (with magnetic field) discharge, and a pulsed laser ablation plasma was used to deposit aluminum nitride (AlN) thin films. The hybrid plasma was created at a working pressure of 8 × 10−2 Pa in nitrogen atmosphere. The use of the hybrid plasma allowed efficient laser ablation at low working pressures. Different samples were grown varying the laser power density deposited on the aluminum target. The variation of this power produced ions with different mean kinetic energy (Ek) in the laser ablation plasma. The values of the mean kinetic ion energy were determined using a Langmuir planar probe and were used as the working parameter. The composition of the AlN thin films was measured using the XPS technique. These measurements showed that most of the bonds between Al and N corresponded to that of the AlN compound and their amount increases with Ek. The bandgap of the samples was determined as a function of Ek and was observed to vary between 5.4 and 6 eV. Nano indentation measurements showed a variation of the hardness between 23 and 30 GPa as a function of Ek. The wear rate and friction coefficient were evaluated on samples deposited under different values of Ek, using a reciprocating tribometer.

In this article, we compare laser prepulse interactions with flat and periodic 1D grating aluminum targets. We describe the cases of normal and oblique radiation incidence. The choice of an appropriate radiation incidence angle and target geometry reduces back-reflection and increases the performance of laser-driven experiments due to more uniform target heating. We studied preplasma generation in front of the targets and described its temporal evolution for different angles of radiation incidence. The electron density has a symmetric periodic distribution in front of grating targets and an irregular distribution in front of flat targets. It varies from 0.3×1022cm−3 to 3.5×1022cm−3 for grating targets, and from 1×1022cm−3 to 2.5×1022cm−3 for flat targets. The generation of overcritical density regions occurs before the end of the prepulse stage. We developed a semi-analytical model based on the effective refractive index and Bloch wave approximation to describe changes in reflectivity during the simulations. During the preplasma expansion, the reflectivity varies from 0.1 to 0.8. The numerical simulation results align well with the analytically predicted behavior of the preplasma–target ensemble. Grating targets are more suitable for experiments compared with flat ones. The most convenient angle of radiation incidence is about 15°.

Laser-driven shock wave dynamics in aluminum target

Magnetic field generation and amplification techniques are widely used due to their applications in various fields, including laboratory astrophysics and inertial confinement fusion. Microtube Implosion (MTI) is a scheme that amplifies a seed magnetic field by several orders of magnitude through the ultraintense irradiation of solid targets with a laser. In this study, we conducted 2D EPOCH simulations to investigate the ability of a tetrafoil (TF) target to generate a magnetic field in the absence of a seed magnetic field. The results show that the TF target generates magnetic field intensities comparable to a hollow cylindrical aluminum target undergoing MTI with a 10 kT seed. Furthermore, the configuration of the TF can be used to control the direction of the magnetic fields produced. The combined TF and microtube target sustained a higher magnetic field and flux compared to both the microtube and TF targets, without the need for a seed magnetic field.

Scaled equations for ogive-nose rods into aluminum targets

Effects of focusing geometries and detection methods on laser-induced breakdown spectroscopy of an aluminum target

On the effect of projectile material on damage induced to aluminum target under hypervelocity impact

Research of the different impact velocity influences on the efficacy of Penetration with Enhanced Lateral Efficiency (PELE) ammunition was performed using numerical simulations, where several conclusions were drawn. Namely, the average mass of fragments decreases as impact velocity rises. The mass of the residual projectile drops as impact velocity rises. At higher impact velocities, the casing and core of the projectile fracture more, and more fragments are formed. At higher impact velocities, the dispersion of fragments is greater, and bigger holes in the target are present. The fragment velocity rises linearly with the increase of impact velocity. Research on different target material influences on terminal ballistics of PELE is also conducted, where one target material from experimental research was also compared with numerical simulation. Several conclusions were made. Namely, the harder the target, the more fragments are created. The radial velocity of fragments is higher behind the steel target than behind the aluminum one. The aluminum target fragments the most and gives the highest residual velocity of the projectile. The highest fragmentation of the projectile jacket was recorded for the case of the hardest target (Nanos-BA). Nanos-BA steel target deformed the least upon impact, has the smallest hole, and gives the smallest number of fragments (from the target itself). The Nanos-BA steel target produces the largest number of fragments from the projectile jacket.

The OMEGA EP laser at the Laboratory for Laser Energetics was used to investigate high-power, relativistically intense laser interactions with near-critical density plasmas produced using low-density CH foam targets. A proton probe beam diagnostic, sensitive to the quasi-static electric and magnetic fields in the target, measured plasma-generated field structures along the foam interface with an aluminum target holder. Many discrete field structure sites were observed, suggesting filamentation of the electron beam during propagation through the plasma and magnetic field generation enhancement at plasma interfaces. Particle-in-cell simulations of the interaction were also performed, showing similar effects.

This study compares the properties of aluminum targets manufactured through casting, rolling, and extrusion processes, examining thin films produced via DC magnetron sputtering using each target. Despite minimal differences in density, electrical conductivity, and resistivity among the targets, the extrusion target exhibited higher internal deformation energy than the casting and rolling targets. Thin films fabricated from each target showed similar grain sizes and deposition rates. However, thin films produced using the extrusion target demonstrated a higher frequency of hillock formations and displayed resistivity values approximately 1.5 µΩ-cm higher than those produced with other targets.

Abstract The measurement of the 2D-angular correlation of electron positron annihilation radiation (ACAR) provides unique information about the bulk electronic structure of single crystals. We set up a new prototype for 2D-ACAR measurements using two 24 × 24 (26.8 mm × 26.8 mm) pixelated lutetium-yttrium oxyorthosilicate scintillation (LYSO) crystals in combination with a glass light guide and 8 × 8 (24 mm × 24 mm) multi pixel photon counters. Compared to conventional Anger-cameras, typically comprising large NaI(Tl) scintillators read out with photomultiplier arrays, a larger implementation of our prototype would drastically improve resolution and count rate by taking advantage of the small pixel size of the scintillator, its much higher attenuation coefficient for 511 keV γ-quanta and faster digital readout. With our prototype we achieved a detection efficiency of around five times higher compared to NaI(Tl) used in our Anger cameras, leading to a 25 times higher coincidence count rate in ACAR measurements. A spatial resolution of 1 mm was obtained, which is limited by the pixel size of the scintillator. We demonstrate the high performance of the setup by (i) imaging the local distribution of 22Na in a proton-irradiated aluminum target and (ii) determining the Fermi energy of Cu from 2D-ACAR spectra recorded for a polycrystalline copper sample.

This study presents an automated docking block placement system developed for regular and emergency repairs of large ships and naval vessels. Traditional methods involve manually arranging heavy concrete docking blocks using cranes or forklifts, which can take several days and pose significant safety risks because of the heavy materials involved. The proposed system integrates an unmanned crane with a six-degree-of-freedom (6-DOF) robotic platform and a mobile robot-based 3D precision positioning system to automate block relocation. The use of a 3D laser tracker mounted on the mobile robot is the key to the system, which, when combined with environmental sensors such as LiDAR and RTK-GPS, provides millimeter-level positional feedback. To address the lack of clear reference points in conventional docking blocks, a precisely machined aluminum target block was attached to each block. An algorithm employing Density-Based Spatial Clustering of Applications with Noise (DBSCAN), KD-Tree, and Random Sample Consensus (RANSAC) techniques was used to detect and classify the vertex of the target block from the 3D point cloud data. The experimental results demonstrated a positional measurement error within 0.5 mm at an 8 m distance. This novel system reduces the setup time, enhances worker safety, and increases the overall efficiency and capacity of dry dock maintenance operations.

The numerical simulation of the velocity decay characteristics of multilayer spherical fragments under bombardment loading is carried out by using LS-DYNA, and the distribution law of the velocity decay characteristics of multilayer spherical fragments is obtained. The ballistic limit (V50) of the multilayer spherical fragment on a 4mm 2024 aluminum target at 90° angle of attack is also obtained by ballistic test. Based on the consistency between the numerical simulation and the test results, the influence of the quality of the multilayer spherical fragment on V50 is analyzed. The air resistance coefficient is calculated with the numerical simulation results by constructing a rag flight distance calculation model. The maximum error between the calculated results and the test results is about 2%, and the theoretical calculated values are in good agreement with the numerical simulation and test results. Under the condition of the same initial velocity, the attenuation coefficient of the spherical fragment in long-distance flight is constant. The aerodynamic drag coefficient is related to the initial velocity of the fragment, which is linearly related to the initial velocity in the range of the design concern of the combat unit (1.2-2.2km/s).

Direct current (DC) reactive magnetron discharge in Ar + O2 mixtures with an aluminum (Al) target was investigated. Electrical measurements of the discharge voltage and current along with the deposition rate trends observed with varying the oxygen flow rate indicated the presence of hysteresis, typical to when using a DC power supply. The transition between metallic and oxide (compound) modes was analyzed in more detail by measuring the mass-resolved fluxes of positively and negatively charged ions together with the optical emission spectra of plasma. The dependence of constituent ion fluxes (Ar+, Ar2+, Al+, O+, O2+, O−, and O2−) on the reactive oxygen gas flow rate was revealed, indicating the transition (in 1.2–1.8 sccm O2 flow range) from a metallic regime to a poisoned regime. The optical diagnostics indicated a nonlinear hysteresis loop pattern of dependence for various constituents (ions and neutrals) of the magnetron discharge plasma. The comparison between the particle and optical measurements, though exhibiting a pronounced correlation, demonstrated individual features of both methods, which need to be taken into account when interpreting the results. The hysteresis patterns were further discussed by comparing the experimental data with the calculation results from the Berg model. An approach of adapting the model results to the case of a power-regulated magnetron power supply is expressed.