Cone Target Research Articles

Conical impact fragmentation test (CIFT)

Conical impact fragmentation tests (CIFT) were conducted to develop and demonstrate an experimental capability for uniformly inducing controlled fragmentation in structural metals. The setup involves a conical specimen impacting a mating conical target (similar in geometry to a funnel) at nominal velocities of 1–2 km/s. Three experiments were conducted as proof of concept to characterize the fragmentation behavior of 1018 steel. Photonic Doppler velocimetry probes on the free outer surface of the target cone allow for validating simulations that can indicate strain uniformity in the target cone. Overall, experimental results demonstrate CIFT to be a feasible method to evaluate fragmentation behavior. The conical geometry produces consistent and bounded strain rates that are maintained for at least 10 microseconds. Furthermore, when compared with other laboratory techniques, the CIFT technique is shown to be more ideal than sphere-on-plate impact (SPI) and more tunable than cylinder expansion (CYLEX), and so is a promising fragmentation characterization tool.

Effect of Lode angle incorporation into a fracture criterion in predicting the ballistic resistance of 2024-T351 aluminum alloy plates struck by cylindrical projectiles with different nose shapes

The aim of the present paper is to evaluate the effect of Lode angle incorporation into a fracture criterion when predicting the ballistic resistance of 2024-T351 aluminum alloy plates struck by cylindrical projectiles with different nose shapes through finite element (FE) simulations. To this end ballistic tests in the sub-ordnance impact velocity range were firstly conducted on 9.94 mm thick 2024-T351 aluminum alloy plates using cylindrical projectiles with blunt, hemispherical and ogival nose shapes, a nominal diameter of 12.66 mm, and a nominal mass of 50 g. Ballistic limit velocities (BLVs) for different projectile-target pairs considered were calculated using initial vs. residual velocity data obtained in the experiments. Subsequently FE simulations of the conducted experiments were performed with SIMULIA Abaqus software. In those simulations Johnson–Cook yield criterion with a modified strain hardening law was accompanied with either the Lode-independent Johnson–Cook (JC) fracture criterion or the Lode-dependent modified Mohr–Coulomb (MMC) fracture criterion to describe target material properties. Finally, the predicted ballistic resistance and fracture patterns of the targets were compared with those observed in the experiments. It was found that in the simulations with the Lode-independent JC fracture criterion the BLVs of the targets were overestimated by 18.0–35.1% depending on the projectile nose shape. In the simulations with MMC fracture criterion the BLVs predictions were substantially improved, so that the difference with the experimental results did not exceed 9.0%. Targets failure mechanisms obtained in the simulations with MMC fracture criterion also better match the experiments than those predicted with JC fracture criterion. In the simulations with MMC fracture criterion the targets impacted by the projectiles with blunt and hemispherical noses failed through shear plugging, whereas ogive-nosed projectiles caused ductile hole enlargement and target fragmentation due to its rear side radial fracture and bending of formed short petals with their eventual shear fracture. At the same time the simulations with JC fracture criterion predicted shear plugging for the blunt-nosed projectiles, very small conical plug ejection and target fragmentation due to discing for the hemispherical-nosed projectiles, and ductile hole enlargement for the ogive-nosed projectiles. A detailed analysis of the failure process revealed that in the case of the ogive-nosed and hemispherical-nosed projectiles, respectively, the ductile hole enlargement occurs during the initial stage of the impact and subsequent through-thickness fracture develops causing either fragmentation of the target or its shear plugging failure. The Lode-independent JC fracture criterion overestimates a material fracture strain under shear, thus leading to poor prediction of 2024-T351 aluminum alloy targets ballistic performance in the numerical simulations.

Incipient spallation of high purity copper under non-one-dimensional strain shock waves

A new spallation experimental method by using conical target is proposed. Based on the analysis of wave propagation, the basic principle of spallation experiment of conical target is discussed. Then incipient spallation of high purity (HP) copper under non-one-dimensional strain shock wave is studied experimentally by using a gas gun setup. The damage distribution characteristics and micro-mechanism of conical HP copper target are analyzed. The intrinsic relationship between the characteristics of free surface velocity profiles and damage evolution is explored. The results indicate that 1) continuous damage zones including different damage states appear in the conical HP copper target with initial spallation from the bottom of cone to the top of cone along the direction parallel to the cone surface, which is attributed to the spatial evolution of the amplitude and duration time of tensile stress in the conical target; 2) quantitative statistical analysis of damage inside conical HP copper target reveals that the nucleation and early growth of micro-voids are random, while the coalescence of micro-voids has significant localization characteristics; 3) the normal free surface particle velocity profiles with typical pull-back spallation signals at different locations of conical HP copper target are measured by multi-channel photon Doppler velocimetry. Comparing with the damage distribution characteristics, it is revealed that the spallation strength based on pull-back velocity is independent of damage, and is the critical nucleation stress of micro-voids. But the slope and amplitude of pull-back rebound velocity depend on damage evolution process, which relates to the change of damage evolution rate and stress relaxation caused by damage degree respectively.

Influences of Target Configurations on the Trigger Characteristics of Laser-Triggered Vacuum Switch

Working performances of laser-triggered vacuum switch (LTVS) mainly rely on the interactions of laser with target materials. Influences from target configuration, which is one of key factors in the interactions, are neglected so far. The trigger performances of LTVS with different target configurations are studied in this paper. Relevant influence factors about target configurations are discussed briefly based on theoretical analysis about the trigger process. The test prototype is established based on detachable vacuum chamber. The trigger characteristics of LTVS with different target structures, target depths, and laser focal positions are compared. The relationships between target configurations and trigger performances of LTVS are analyzed and discussed. The preferred targets in LTVS are suggested while considering its lifetime. The test results prove that the conical target shows the best trigger performances compared to other targets. Due to the enlarged laser irradiated area and shortened plasma moving distance, the delay time of LTVS reduces with the decrease in conical target angle and the increase in target depth, while the delay time is controlled within 32 ns. Benefited from laser reflection and plasma collision, the trigger performances of conical targets can be enhanced by focusing laser on the target side surface. In particular, the 90° conical target with 1.5 mm depth is suggested to be employed in LTVS products.

Three‐dimensional reconstruction of space rotating target based on narrow‐band radar networks

The micro-motion of space target is an important signature for classification and recognition, which has received great attention. Based on the micro-Doppler signals from narrow-band radar networks, this study proposes a three-dimensional reconstruction method of space rotating target. First, the rotational plane projection model and the three-dimensional structure construction model are built based on the micro-Doppler analysis of rotating targets. Then, the rotational axis of the target is accurately estimated by exploiting the relationship of micro-Doppler features of sub-radars in the radar networks. Finally, under the constraint of the physical shape of a cone target, the target with arbitrary number scatters can be reconstructed by setting a cost function. Experiments verify the validity and accuracy of the proposed method.

Radiometric Characterization of a Water-Based Conical Blackbody Calibration Target for Millimeter-Wave Remote Sensing

In this paper, we present the design and radiometric characterization of a water-based conical blackbody calibration target to be applied as a precise reference source in laboratories and for the accurate calibration of ground-based microwave instruments. The concept of aqueous blackbody targets circumvents the conflict between the electromagnetic and thermal properties of traditional calibration target designs. The temperature controllable target consists of a conical low loss plastic shell, which has been manufactured using a stereolithography three-dimensional printer to define the water–air interface. An advanced exponential profile of the shell is used to compensate the comparatively high refractive index of water and to obtain a high emissivity. Simulations and active measurements of the coherent backscattering S11 have been performed verifying its excellent electromagnetic properties. Furthermore, radiometric measurements at 110 GHz demonstrate the outstanding thermal performance at various target temperatures between 10 and 60 °C. The differences between the brightness temperature and the water temperature are measured to be less than 40 mK and therefore significantly smaller in comparison to traditional calibration targets. In addition, the measured baseline ripples in the spectra caused by the water-based calibration target are small compared to established blackbody concepts.

Design of a new turbulent dynamo experiment on the OMEGA-EP

Turbulent dynamos that exponentially amplify initially small, seed magnetic fields are crucial in magnetizing the Galaxy and beyond. Until now, the ideal environment for turbulent dynamos to grow has been difficult to recreate. In a new approach, we leverage the long pulse capability of the OMEGA-EP laser to recreate the highly conductive and inviscid (Rem∼5500, Prm≳1) growth environment of the turbulent dynamo within the magnetized plasma jet ablated from a simple cone target of CH plastic. In 3-D FLASH simulations of our scheme, we find that the ideal dynamo environment is a typically ∼1 mm3, ≳1.5 keV hot spot where the laser beams intersect to produce maximum direct heating of the jet plasma. The dynamo environment is maintained from the onset of steady flows through the ∼10 ns length of the laser pulse. For a plasma vorticity of 0.3–3.0 ns–1 and a dynamo active over ∼5 ns, the magnetic energy increases on an exponential trajectory by more than a decade. Fourier analysis reveals that the dynamo progressively saturates up to EB/EK∼20% from small scales k≳30 cm−1 to large in the time it is sustained. We find robust agreement between the evolution of magnetic energy spectra extracted from the FLASH physics simulation and that derived from synthetic sheath-accelerated proton deflectometry images, thereby demonstrating that the dynamo activity can be quantified in a real experiment.

Space Precession Target Classification Based on Radar High-Resolution Range Profiles

Precession is a common micromotion form of space targets, introducing additional micro-Doppler (m-D) modulation into the radar echo. Effective classification of space targets is of great significance for further micromotion parameter extraction and identification. Feature extraction is a key step during the classification process, largely influencing the final classification performance. This paper presents two methods for classifying different types of space precession targets from the HRRPs. We first establish the precession model of space targets and analyze the scattering characteristics and then compute electromagnetic data of the cone target, cone-cylinder target, and cone-cylinder-flare target. Experimental results demonstrate that the support vector machine (SVM) using histograms of oriented gradient (HOG) features achieves a good result, whereas the deep convolutional neural network (DCNN) obtains a higher classification accuracy. DCNN combines the feature extractor and the classifier itself to automatically mine the high-level signatures of HRRPs through a training process. Besides, the efficiency of the two classification processes are compared using the same dataset.

Peculiarities of Cherenkov radiation from a charge moving through a dielectric cone

Radiation generated by a charge moving in a vacuum channel through a dielectric cone is analyzed. The size of the conical target is assumed to be much greater than the wavelengths under consideration. We calculate the wave field outside the target using Stratton-Chu formulas (``aperture integrals''). This work focuses mainly on investigation of the electromagnetic field in the far-field area (Fraunhofer area). We calculate representative radiation patterns and show that typically the maximal radiation is generated in the direction of one of the refracted rays. However, in the specific case where the refracted ray is parallel to the symmetry axis, the maximal radiation is observed at some small (but nonzero) angle with respect to this axis. The maximum radiation in this case is much more intensive compared to all other situations. This phenomenon can be referred to as the ``Cherenkov spotlight.''

Enhancement of proton collimation and acceleration by an ultra-intense laser interacting with a cone target followed by a beam collimator

A special method is proposed of a laser-induced cavity pressure acceleration scheme for collimating, accelerating and guiding protons, using a single-cone target with a beam collimator through a target normal sheath acceleration mechanism. In addition, the problems involved are studied by using two-dimensional particle-in-cell simulations. The results show that the proton beam can be collimated, accelerated and guided effectively through this type of target. Theoretically, a formula is derived for the combined electric field of accelerating protons. Compared with a proton beam without a beam collimator, the proton beam density and cut-off energy of protons in the type II are increased by 3.3 times and 10% respectively. Detailed analysis shows that the enhancement is mainly due to the compact and strong sheath electrostatic field, and that the beam collimator plays a role in focusing energy. In addition, the simulation results show that the divergence angle of the proton beam in type II is less than 1.67 times that of type I. The more prominent point is that the proton number of type II is 2.2 times higher than that of type I. This kind of target has important applications in many fields, such as fast ion ignition in inertial fusion, high energy physics and proton therapy.

Translational Motion Compensation of Space Micromotion Targets Using Regression Network

The high-speed translational motion of space targets will cause the micro-Doppler to shift, tilt, and fold, which brings great difficulty to the extraction of micromotion features. Translational motion must be compensated in advance to extract the authentic characteristics of micro-Doppler curves. To solve the problem of translational motion compensation, an estimation method of translational parameters based on deep learning theory is proposed. A polynomial model describing translational motion is constructed firstly by analyzing its dynamic principle. Meanwhile, the parametric characterization of micromotion signal is deduced by taking the cone target as an example. On this basis, two regression networks that can estimate acceleration and velocity respectively from the time-frequency graph are built using transfer learning. The translational motion compensation is accomplished with high accuracy and low computation complexity. The proposed method can also achieve satisfactory results in the presence of high intensity noise and discontinuous scattering points. Finally, the effectiveness and robustness of the proposed method are validated by simulations.

Optimization-Based Discontinuous Observation Strategy for Micro-Doppler Signature Extraction of Space Cone Targets

In order to obtain relatively complete micro-Doppler (m-D) signatures of space precession cone targets, at least one precession period of dwell time is always required. In practice, most of the space cone targets do precession with a relativity low frequency (i.e., 0.5-1 Hz), which means second-level dwell time is necessary. However, second-level dwell time is prohibitive in terms of radar resource consumption, especially as radar has to face the challenges of multi-targets and multi-tasks. To tackle this problem, we conduct m-D signature extraction based on a discontinuous-observation-based strategy named multi-short-dwell observation (MSDO). Specifically, by incorporating the time-frequency information, the extraction Cramer-Rao bounds give reliable bounds for the performance of the m-D signature extraction. Therefore, they are derived and used as optimization criterions for optimizing the time parameters involved in the MSDO. A cost function is established to minimize the time resource occupation ratio such that the extraction precision requirement is met. The m-D signature extraction is implemented based on the optimized MSDO parameters in which the real sinusoid estimator and the least square estimator are adopted. The simulation results illuminate the effectiveness of the proposed method.

Brightness Temperature Calculation and Uncertainty Propagation for Conical Microwave Blackbody Targets

We discuss the analytical derivation of the absolute brightness temperature uncertainty of a hollow conical blackbody source for radiometer calibration. We introduce a Monte Carlo uncertainty propagation analysis method to quantify uncertainty contributions from nonideal emissivity, physical temperature, and antenna pattern, which are the three major factors contributing to the uncertainty of the brightness temperature radiation from the source. The low reflectance of the hollow conical geometry depends on multiple bounces on the absorber surface. To quantify total brightness temperature over a nonuniform temperature surface, each individual bounce must be considered. We derive a recursive analytical relationship to quantify this multiple-bounce effect as a function of a view angle. The resulting effective blackbody brightness temperature uncertainty is a function of frequency, temperature, antenna pattern, measurement distance, and the measurement environment. We also propagate the uncertainty to the antenna flange of a radiometer viewing the conical blackbody. This includes additional effects, such as spillover, illumination efficiency, and antenna efficiency. We demonstrate the propagation method with an example case. We use fictional input values to investigate the response of the uncertainty to input variables and distance. We find that as the distance between antenna and blackbody increases, the uncertainty due to spillover dominates, but at close distances, the dominant uncertainty contributor is linked to the physical temperature of the absorber.

Reprint of "Ion beam sputter coating in combination with sol-gel dip coating of Al alloy tube inner walls for corrosion and biological protection"

Aluminium alloy AlCuMg is an alloy with high mechanical strength and fracture toughness, but it suffers from poor corrosion resistance and friction behaviour. With a combined process of sol-gel deposition of zirconium oxide and a top coating of diamond-like carbon formed by ion beam sputtering with a movable conical sputter target inside the tube, the inner walls of AlMgCu tubes were homogeneously coated with a duplex coating with high resistance against corrosion in chloride solution. When Ag was added to the carbon sputter target, a DLC coating that contained Ag was obtained. Microbial tests showed that the coating is effective against pathogenic E. coli bacteria.

Numerical analysis of pulsed magnetic field diffusion dynamics in gold cone target

Strong magnetic fields from a few hundred to a thousand tesla have been produced in a laboratory by using high-intensity laser beams. This strong magnetic field in a laboratory becomes a powerful tool to perform experiments in the fields such as laboratory astrophysics and nuclear fusion research. The diffusion dynamics of a pulsed magnetic field in a target is a key phenomenon for experiments with the laser-produced magnetic field. Here, we have developed a two-dimensional (2D) electromagnetic dynamics simulation code with consideration of inductive heating to simulate spatiotemporally resolved 2D profiles of the applied magnetic field in a target. The application of an external kilo-tesla-level magnetic field to a gold-cone-attached target is a promising scheme for the enhancement of heating efficiency of the fast-ignition inertial confinement fusion scheme. Our simulation revealed that the magnetic field heats the gold cone due to the inductive heating and penetrates the gold cone during its pulse duration. The developed simulation code is generally useful for designing and analyzing experiments using a strong magnetic field.

High-energy-density plasma jet generated by laser-cone interaction

The generation of high-energy-density (HED) plasma jet from a laser ablating thin cone target is studied theoretically and by numerical simulations. Theoretical analysis and 1D simulations show that a maximum kinetic energy conversion efficiency (CE) of 26% can be achieved when nearly 80% of the foil is ablated by laser. A HED plasma jet is generated when an intense laser (∼1015 W/cm2) irradiates the cone target, inducing a great enhancement of energy density compared to that of the planar target, which is attributed to the cumulative effect of the cone shape and the new generation mechanism of jet, i.e., laser directly accelerating the cone wall onto the axis. The characteristic of jet is influenced by the cone geometry, i.e., thickness and cone angle. It is found that a cone with a half opening angle around 70° and the optimized thickness (∼5 μm) can induce a jet with a high CE and long duration, whose peak energy density can reach 3.5 × 1015 erg/cm3. The results can be beneficial for laser-driven novel neutron sources and other fusion related experiments, where HED plasma jet can be applied.

The laser radar Doppler spectrum of moving conical target in its spaced orbit observed by ground-based station

Utilizing the characteristics of laser Doppler spectrum of rotating conical target in target coordinate system and combining with a hypothetical spaced orbit data and transformed relationships between space target, ground-based observation and geocentric coordinate system, the model on the laser radar Doppler spectrum of moving conical target in its orbit observed by ground-based station is presented in this paper. Three applied cases are detaily calculated and analyzed that the lidar normalized power of moving conical target observed by ground-based station is changed with the time of orbit and the Doppler frequency shift in different dimensions and roughness of conical target and different ground-based observed directions. The calculated results are shown that the dimension and roughness of orbited conical target and different ground-based observed directions have influnce on their laser Doppler spectrum. The rules of the lidar normalized power changed with the time of orbit and the Doppler frequency shift is periodically fluctuated for any spaced conical targets. As the rotation speed is constant, the dimension of conic target is bigger, Doppler frequency shift is higher. The roughess of the conic surface is bigger, the fluctuatations of lidar normalized power changed with the time of orbit and the Doppler frequency shift is strongger. So our works are based on further developed to theoretically study on all kinds of spased complex targets in their orbits and furth given a technological support for laser radar observing spased complex targets with micro-motion and distinguishing true/false targets in their orbits on gound-based station.

Splitter target for controlling magnetic reconnection in relativistic laser plasma interactions

The utilization of a conical target irradiated by a high power laser is proposed to study fast magnetic reconnection in relativistic plasma interactions. Such target, placed in front of the near critical density gas jet, splits the laser pulse, forming two parallel laser pulses in the 2D case and a donut shaped pulse in the 3D case. The magnetic annihilation and reconnection occur in the density downramp region of the subsequent gas jet. The magnetic field energy is converted into the particle kinetic energy. As a result, a backward accelerated electron beam is obtained as a signature of reconnection. The above mechanisms are demonstrated using particle-in-cell simulations in both 2D and 3D cases. Facilitating the synchronization of two laser beams, the proposed approach can be used in designing the corresponding experiments on studying fundamental problems of relativistic plasma physics.

Ion beam sputter coating in combination with sol-gel dip coating of Al alloy tube inner walls for corrosion and biological protection

Aluminium alloy AlCuMg is an alloy with high mechanical strength and fracture toughness, but it suffers from poor corrosion resistance and friction behaviour. With a combined process of sol-gel deposition of zirconium oxide and a top coating of diamond-like carbon formed by ion beam sputtering with a movable conical sputter target inside the tube, the inner walls of AlMgCu tubes were homogeneously coated with a duplex coating with high resistance against corrosion in chloride solution. When Ag was added to the carbon sputter target, a DLC coating that contained Ag was obtained. Microbial tests showed that the coating is effective against pathogenic E. coli bacteria.

Parameters estimation of precession cone target based on micro-Doppler spectrum

The micro-Doppler (m-D) provides valuable information for the motion parameters extraction and the target recognition of space targets. To address the issue of estimating the motion parameters of precession warhead targets, a new method based on the m-D spectrum of the top and the bottom of the cone is proposed in this paper. In this method, the m-D features of the cone target are firstly extracted by calculating the first-order moments of the time-frequency distribution of the echo signal. Then, the motion parameters of the target are roughly estimated by the Fourier transformation of the m-D curve. Based on the rough estimation, the search method is employed to estimate the motion parameters of the cone target precisely. The validity of the proposed method is verified by the analysis data.