Multilayer Targets Research Articles

Formation region effects in x-ray transition radiation from 1 to 6 GeV electrons in multilayer targets

The formation region effects in x-ray transition radiation have been experimentally investigated. The radiation was generated using 1–6 GeV electrons impinging on two multilayer targets with considerably different periods. The absolute yield of transition radiation was measured and the wide spectral peak in the range from 10 to 30 keV was observed. In the most part of the electron energy range the emission from the short-period radiator was expectedly suppressed, compared to the case of the long-period one. But for the electron energy of 1 GeV an opposite effect, though rather small, of the emission enhancement in the short-period radiator was observed. The conditions, under which this effect is much stronger, are derived and its possible practical value is outlined. The theory accounting for an arbitrary transversal shape of the electron beam and the finite size of the detector is developed. This theory describes rather well the experimental results.

Observation of resistive Weibel instability in intense laser plasma

AbstractWe observe experimentally periodic proton beam filamentation in laser-produced dense plasma using multilayered (CH–Al–CH) sandwich targets. The accelerated MeV proton beams from these targets exhibit periodic frozen filaments up to 5–10 µm as a result of resistive Weibel instabilities in the expanding plasma. The evolution of strong self-generated resistive magnetic fields at the targets interface is attributed to such plasma effects, which are supported, by our theory and simulations. We suggest that the resistive Weibel instability could be effectively employed to understand the evolution of magnetic fields in laser-generated plasma in the astrophysics scenario or the advanced fast igniter approach of the inertial confinement fusion.

Quasi-Cherenkov Mechanism of Radiation from Relativistic Electrons Flying near a Multilayer Prism Target

The angular characteristics of millimeter radiation generated by a 6.1-MeV electron beam flying near a multilayer prism target consisting of conducting plates separated by vacuum gaps and near a homogeneous Teflon prism have been studied experimentally. The angular distributions of radiation from both targets have been compared. It has been shown that the angular distribution for the Teflon prism is in good agreement with the classical theory of Cherenkov radiation, whereas the evolution of angular distributions for the multilayer target is inconsistent with known expressions with a fixed effective refractive index. Radiation from the multilayer target (quasi-Cherenkov radiation) should assumingly be described by a tensor refractive index.

Study on similarity law of non-proportionally scaled penetration/perforation test

Survivability and reliability assessment of components/key components on high-speed penetrating projectiles is a hot and difficult issue in the field of EPW development. Due to the cost limitation of prototype test, it is feasible to carry out non-proportionally scale experimental research by carrying prototype fuze components on scaled projectiles. Through the analysis of the process mechanism of a projectile penetrating concrete target, the analytic solution of rigid-body deceleration when the projectile penetrating the semi-infinite thick concrete target and the multi-layer thin concrete target are discussed respectively. From the point of view of similarity of rigid-body deceleration, the non-proportionally reduced-scale criterion of projectile is proposed when the traditional scaling scheme can not meet the requirements of similarity. The numerical results show that under the condition of penetrating semi-infinite thick concrete target, the rigid-body deceleration of the non-proportionally reduced-scale projectile can achieve the same conditions as which of the prototype projectile from the point of view of pulse width and amplitude; under the condition of penetrating multi-layered thin target, through reasonably setting the scale factor and adjusting the layout of the target plate and the initial velocity of the projectile. The pulse width and amplitude of the rigid-body deceleration in the reduced scale test can cover them in the prototype test. The rigid body deceleration characteristics obtained from scaled model test can provide reliable overload environment reference for missile projectile design.

Hepatic hemangioendothelioma: CT, MR, and FDG-PET-CT in 67 patients-a bi-institutional comprehensive cancer center review.

To evaluate the imaging features of hepatic epithelioid hemangioendothelioma (HEH) on multiphasic CT, MR, and FDG-PET-CT. Bi-institutional review identified 67 adults (mean age, 47years; 23 M/44 F) with pathologically proven HEH and pretreatment multiphasic CT (n = 67) and/or MR (n = 30) and/or FDG-PET-CT (n = 13). HEHs were multifocal in 88% (59/67). Mean size of the dominant mass was 4.1cm (range, 1.4-19cm). The tumors were located in the peripheral, subcapsular regions of the liver in 96% (64/67). Capsular retraction was present in 81% (54/67 cases) and tumors were coalescent in 61% (41/67). HEH demonstrated peripheral ring enhancement on arterial phase imaging in 33% (21/64) and target appearance on the portal venous phase in 69% (46/67). Persistent peripheral enhancement on the delayed phase was seen in 49% (31/63). On MR, multilayered target appearance was seen on the T2-weighted sequences in 67% (20/30) and on the diffusion-weighted sequences in 61% (11/18). Target appearance on hepatobiliary phase of MRI was seen in 57% (4/7). On pre-therapy FDG-PET-CT, increased FDG uptake above the background liver parenchyma was seen in 62% (8/13). HEHs typically manifest as multifocal, coalescent hepatic nodules in peripheral subcapsular location, with associated capsular retraction. Peripheral arterial ring enhancement and target appearance on portal venous phase are commonly seen on CT. Similarly, multilayered target appearance correlating with its histopathological composition is typically seen on multiple sequences of MR including T2-weighted, diffusion-weighted, and dynamic contrast-enhanced multiphasic MR. • Hepatic epithelioid hemangioendotheliomas manifest on CT and MR as multifocal, coalescent hepatic nodules in peripheral subcapsular location, with associated capsular retraction. • Enhancement pattern on contrast-enhanced CT and MR can vary but peripheral ring enhancement on arterial phase and target appearance on portal venous phase are commonly seen. • Retrospective two-center study showed that cross-sectional imaging may help in the diagnosis.

Ballistic performance of multi-metal systems

Ballistic resistance enhancement of armours and structures has been a prominent area of research over the years. Monolithic metallic plates have been the preferred choice for armours against high-velocity projectiles. High-strength steel is a popular choice for such systems. However, the high areal density deters in accommodating such systems in practical applications which require lightweight products. On the contrary, multi-metallic systems produced by the combination of low-density materials with similar or superior ballistic resistance as their monolithic counterparts have become attractive candidates in defence applications. However, only a limited number of comprehensive studies on the ballistic performance of multi-metal multi-layered targets are available in the literature. Moreover, these studies have drawn contradictory conclusions on the optimum arrangement of different layers and materials within the systems. In addition, existing knowledge in this area is scattered in the literature and there is a need to collate them to enhance the development of multi-metal multi-layered ballistic-resistant plate systems in order to be optimised for ballistic-related armour. This article aims to provide a comprehensive review of the effect of different metals, thickness, fracture mechanisms, feasibility of the connection types and the order of the metallic plates within targets on the ballistic performance.

Thickness of natural contaminant layers on metal surfaces and its effects on laser-driven ion acceleration

In the laser-driven ion acceleration studies, the naturally deposited contaminant layer on the target surface is thought to be a source of energetic ions and protons. Using ellipsometric measurements, we found that the thickness of the surface natural contaminant layer, which cannot be modified without external surface treatment, is on the order of a few nanometers. A conceptual approach is developed where “thick” and “thin” contaminant layer regimes of acceleration are identified and parameterized by the normalized thickness of the contaminant layer. These studies may also help in developing an ion acceleration concept using multilayered targets or through modifications of the target surface.

Design and Experiment of a Novel High-Impact MEMS Ceramic Sandwich Accelerometer for Multi-Layer Target Penetration

The output signal of traditional cantilever accelerometers usually overlapping and tailing during the high-velocity penetration process. And the sensitivity of traditional cantilever accelerometers cannot satisfy the application of multi-layer target penetration, that process contains large length-to-diameter ratios and high velocities. This paper proposes a novel high-impact Micro-Electro-Mechanical-System (MEMS) ceramic sandwich accelerometer (HMCSA) for the measurement of penetration-overload signals. Firstly, the HMCSA structure was designed and its structure-sensitive model was established. Then, the filling material in HMCSA was selected and the structure was simulated in ANSYS/LS-DYNA software. After that, the structure MEMS processing was introduced and the monitoring system was designed. Finally, the multi-layer target penetration process was simulated and HMCSA was tested in lab environment. The experiment verified that the design and manufacture of HMCSA was correct, and HMCSA can detect 30 000g acceleration.

Laboratory Observation of Radiative Shock Deceleration and Application to SN 1987A

Abstract The first laboratory evidence of a radiative shock (RS) decelerating during its free expansion phase in an optically thick medium is presented. A shock is generated in a multilayer solid target under the irradiation of a high-power laser at the GEKKO XII laser facility. The rear surface of the target is connected to a gas cell filled with Xe. Upon breakout, an RS, characterized by low Boltzmann number Bo ≪ 1 and Mihalas number R ≈ 10, is generated. Experimental results reveal that radiative losses through the radiative precursor cause the shock to lose energy and decelerate. A model is developed that describes the shock propagation as a function of time. The model is in agreement with both numerical simulations and experimental results. These results have tremendous consequences for astrophysical systems, such as SN 1987A, where radiative deceleration may play a role in the formation of the observed hotspots in the circumstellar ring.

Molecular dynamics simulations on shock response and spalling behaviors of semi-coherent {111} Cu-Al multilayers

Shock response and spalling behaviors of semi-coherent {111} Cu-Al multilayer are investigated by molecular dynamics simulations. Firstly, the influences of interfaces on shock wave propagation are studied. The simulations show that reflection-unloading happens when the shock wave propagates from Cu to Al and reflection-loading occurs when the shock wave propagates from Al to Cu. Strong discontinuities of stress components at the interfaces are revealed as well, the discontinuities are correlated to mismatches of Hugoniot curves and elastic-plastic properties of the two materials adjacent to the interfaces. Secondly, shock induced dislocation activities are studied. It is found that the stress barrier offered by the interface Cu-Al is smaller than that offered by Al-Cu. In fact, the resistance for dislocations to transmit through interfaces is determined by the coherency stresses, Koehler stresses and misfit dislocations at the interface. In addition, spalling fracture of Cu-Al multilayers after stress wave reflection at the free surface is studied. It is observed that ductile damage only nucleates in Al layer, rather than in Cu layers. This observation agrees well with the experimental results of Han (Acta Mater., 2014 (63) 150–161). Due to complex reflection and transmission of the stress waves at the interfaces, the profile of the free surface velocity histories of the multilayer target is quite different from that of the single-crystalline counterpart. In order to study thermal dissipation process during cavitation, analysis on thermal dissipation in the spalling damage zones is also provided in this paper. Moreover, contour plots and profiles of stress are illustrated to understand the spallation process of the multilayer target deeply. Tensile stress emerges in Al1 layer first, causing voids to nucleate; then the tensile stress wave attenuates rapidly and propagates to Cu1 and Cu2 layers. With the dissipation effect of damage and plastic deformation in the target, the tensile stress wave dissipates ultimately.

Advanced laser-driven ion sources and their applications in materials and nuclear science

The investigation of superintense laser-driven ion sources and their potential applications offers unique opportunities for multidisciplinary research. Plasma physics can be combined with materials and nuclear science, radiation detection and advanced laser technology, leading to novel research challenges of great fundamental and applicative interest. In this paper we present interesting and comprehensive results on nanostructured low density (near-critical) foam targets for TW and PW-class lasers, obtained in the framework of the European Research Council ENSURE project. Numerical simulations and experimental activities carried out at 100 s TW and PW-class laser facilities have shown that targets consisting of a solid foil coated with a nanostructured low-density (near-critical) foam can lead to an enhancement of the ion acceleration process. This stimulated a thorough numerical investigation of superintense laser-interaction with nanostructured near-critical plasmas. Thanks to a deep understanding of the foam growth process via the pulsed laser deposition technique and to the complementary capabilities of high-power impulse magnetron sputtering, advanced multi-layer targets based on near-critical films with carefully controlled properties (e.g. density gradients over few microns length scales) can now be manufactured, with applications outreaching the field of laser-driven ion acceleration. Additionally, comprehensive numerical and theoretical work has allowed the design of dedicated experiments and a realistic table-top apparatus for laser-driven materials irradiation, ion beam analysis and neutron generation, that exploit a double-layer target to reduce the requirements for the laser system.

Analysis of multilayered homogeneous dielectric targets by using time‐domain physical optics method

An improved time-domain physical optics (TDPO) method is proposed to simulate multilayered dielectric structures, in which the characteristic matrix theory of multilayered medium is implemented. In order to accurately calculate the total reflection coefficient on the surface of the multilayered medium, a series of two-dimensional characteristic matrices are established. Based on the characteristic matrices, the total reflection coefficient can be directly derived, instead of summing up the multiple reflected and refracted waves, which is insensitive to the number of the number of the layers and the polarization of the incident wave. Numerical examples are given to validate effectiveness of the proposed TDPO method. It states that this method has much higher computational efficiency, without the loss of accuracy.

Formation of inelastic scattered background photoelectrons, X-ray photoelectron spectroscopy from multilayer inhomogeneous surface

In this work, a new method of background subtraction in XPS is suggested considering multiple inelastic scattering in a multilayer inhomogeneous target. The method is based on solution of the problem of multiple inelastic photoelectron scattering in a multilayer plane-parallel target. For a overlayer/substrate system, formulae for subtraction of background generated by multiple inelastic photoelectron scattering are found. It is shown that backgroundы of a spectral line of photoelectrons emitted from the overlayer and emitted from the substrate and inelastically scattered in the overlayer differ significantly.

Research on layer-counting experimental simulation system for projectile penetrating multi-layered targets

In order to achieve accurate damage to the multi-layer target by the ammunition, the projectile needs to accurately measure the number of layers that have passed through during the penetration. An experimental system for projectile penetrating the multi-layer target based on the discharge effect of piezoelectric ceramic under shock wave was designed and the penetration experiments were carried out. The experimental results show that the system can obtain the output signals of the piezoelectric ceramic when the projectile penetrates the multi-layer target and accurately calculate the number of penetrating layers. Moreover, the acquisition of signals and the calculation of penetration layers are visual and without delay. The higher the penetration speed of the projectile, the less energy is consumed by the single-layer target plate. By adjusting the load resistance, the peak value and duration of the output signals can be controlled to achieve accurate perception of low overload signals.

Long-term evolution of spherical shell with boron carbide layer after explosive compression

Predictive simulation of the long-term response of multilayer targets with ceramics layers to shock compression demands appropriate material models. Because ceramics are complex brittle materials, which tend to lose their strength under heavy loads, such simulation requires the failure models well-proven for a wide range of strains and strain rates. Standard plate impact experiments provide the main data utilized for developing and validating the mechanical models of material response to shock compression. However, apart from the fact that such experimental data are inherently one-dimensional, they can be insufficient to verify the failure model at relatively low strain rates typical for long unloading waves. Here, we present the experimental results for explosive compression of a spherical multilayer shell initiated by a single detonator. The explosive-coated shell consists of the nested spherical layers: the outer made of boron carbide and the inner of lead. X-ray images showing the evolution of those layers after detonation are then compared with simulation results. Propagation of the compression wave through the layers resulting in ceramics damage is analyzed in detail. We demonstrate that the failure model of boron carbide should be adjusted for compressions below 10 GPa to achieve a good agreement with our experimental images. Such an improved failure model provides the predictive simulation of long-term dynamics of targets after unloading, and it has almost no effect on wave profiles after plate impact.

Investigation on Dynamics Characteristic of Multilayer Steel Plate Impacted by Projectile

The paper describes a work focused on the process of perforation of multilayer advanced high strength steel (AHSS). A numerical investigation has been carried out to analyze in details the perforation process subjected to normal impact by different nose shapes of projectiles. The perforation process has been simulated by the application of 3D analysis using IMPACT dynamic FE program suite. The comparison on failure modes depending on the projectile nose shape have been studied and evaluated. An appropriate constitutive relation was applied to describe the material behaviour of the multilayer target plate. The study covered different failure modes of perforated advanced high strength steel (AHSS) sheet according to different level of impact velocity ranging from 22 m/s to 78 m/s. The blunt projectile impact towards multilayer target plate leads to generation of plug formation and fragmentation while hemispherical projectile impact shows almost similar petals formation between first, second and third layer.

Damage of multi-layer spaced metallic target plates impacted by radial layered PELE

Abstract Three different kinds of PELE (the penetrator with lateral efficiency) were launched by ballistic artillery to impact the multi-layer spaced metal target plates. The impact velocities of the projectiles were measured by the velocity measuring system. The damage degree and process of each layer of target plate impacted by the three kinds of projectiles were analyzed. The experimental results show that all the three kinds of projectiles have the effect of expanding holes on the multi-layer spaced metal target plates. For the normal structure PELE(without layered) with tungsten alloy jacket and the radial layered PELE with tungsten alloy jacket, the diameters of holes on the second layer of plates are 3.36 times and 3.76 times of the diameter of the projectile, respectively. For radial layered PELE with W/Zr-based amorphous composite jacket, due to the large number of tungsten wires dispersed after the impact, the diameter of the holes on the four-layer spaced plates can reach 2.4 times, 3.04 times, 5.36 times and 2.68 times of the diameter of the projectile. Besides, the normal structure PELE with tungsten alloy jacket and the radial layered PELE whit tungsten alloy jacket formed a large number of fragments impact marks on the third target plate. Although the number of fragments penetrating the third target plate is not as large as that of the normal structure PELE, the area of dispersion of fragments impact craters on the third target plate is larger by the radial layered PELE. The radial layered PELE with W/Zr-based amorphous composite jacket released a lot of heat energy due to the impact of the matrix material, and formed a large area of ablation marks on the last three target plates.

SPH-based method to simulate penetrating impact mechanics into ballistic gelatin: Toward an understanding of the perforation of human tissue

This study aims to investigate the penetration of a projectile into a human tissue surrogate using meshless-based numerical method (SPH method). The ballistic gelatin being considered in the literature as a biofidelic human tissue simulant, 10% Ballistic Gelatin (BG) is impacted by a steel rigid sphere, and penetration time history as well as velocity are investigated, and compared to existing results of the literature. In addition, due to the paucity of experimental results to validate the numerical model, validation data are extended to analytical comparisons, giving interesting results for the analysis of the perforation of biological tissues by a projectile. Discussion of the simulations are also conducted based on existing results on 20% ballistic gelatin, coupling both 10% and 20% BG for an investigation of a multi-layered target, in order to approach the multi-layered behavior of the human body.

Simulation of Jet Penetrating Concrete Target Process

Jet penetrate concrete target is an extremely complicated mechanical problem. Based on explicit dynamic analysis program AUTODYN, the numerical model to simulate the process of jet penetrating multi-layer target (perforating gun, casing and concrete target) is established with Lagrange method. The large deformation, high strain rate dynamic processes of penetrating multilayer targets by jet was studied in this work. Numerical results show consistent agreements with experimental results, the errors of penetration depth and diameter are 4.27% and 5.26%, respectively. The dynamic response of the penetration process was discussed, including the shock wave and velocity at collision point of the tunnel. The simulation model and Lagrange algorithm used in this research were proved to be reasonable and feasible. This approach can provide a guidance for effectiveness evaluation of oil perforating charge.

Single-Shot Multi-Frame Imaging of Cylindrical Shock Waves in a Multi-Layered Assembly

We demonstrate single-shot multi-frame imaging of quasi-2D cylindrically converging shock waves as they propagate through a multi-layer target sample assembly. We visualize the shock with sequences of up to 16 images, using a Fabry-Perot cavity to generate a pulse train that can be used in various imaging configurations. We employ multi-frame shadowgraph and dark-field imaging to measure the amplitude and phase of the light transmitted through the shocked target. Single-shot multi-frame imaging tracks geometric distortion and additional features in our images that were not previously resolvable in this experimental geometry. Analysis of our images, in combination with simulations, shows that the additional image features are formed by a coupled wave structure resulting from interface effects in our targets. This technique presents a new capability for tabletop imaging of shock waves that can be extended to experiments at large-scale facilities.