Accepted
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Abstract +
Exploited in radiation environments, including space, nuclear reactors and large accelerators, fibers would experience significant parameter change induced by the interaction with radiation, including radiation induced attenuation, radiation induced refractive index change, radiation induced lifetime change and radiation induced luminescence, which would then result in severe performance degradation of the fiber laser system. Here, the response characteristics of Yb-doped fiber lasers to gamma-ray radiation are investigated through both experiments and simulations. The performance variation of various fiber components after gamma radiation, including passive fiber, pump combiner, fiber Bragg grating and active fiber, is studied and compared with an accumulated total dose up to 1000 Gy. And, experiments show that, in a fiber laser system, the active fiber is the most sensitive part to gamma radiation, while various passive fiber components show negligible response. Then, impacts of cavity configuration parameters, such as pump scheme and active fiber length, on the response of fiber lasers are explored through series of radiation experiments. It’s shown that, compared to forward pump, backward pump scheme helpful to improve the radiation-resistant capability of fiber lasers. And, lasers with relatively shorter active fiber show smaller power drop when operated in radiation situations. Besides, corresponding simulations are carried out with the previously developed multi-physics thermal model considering hundred-watt level Yb-doped fiber lasers, demonstrating consistent results with the experiments. This research should be instructive for the design optimization of fiber laser systems operated in radiation environments.
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Abstract +
109Ag located on the path of the slow neutron capture process, and 79% of 109Ag is generated via the rapid neutron capture process.Meanwhile, the mass fraction of 109Ag in Ag-In-Cd control rods is 38.56%. Therefore, the neutron capture cross-section of 109Ag is crucial for both nuclear energy and nuclear astrophysics applications.In this work, a neutron capture cross-section measurement was performed using a 109Ag isotope target at the Back-n white neutron facility of the CSNS. Neutron capture cross-section in the 1-500 eV energy region were obtained by combining the time-of-flight method and the pulse-height weighting technique. The 109Ag resonance energy, neutron resonance width, and gamma resonance width parameters were extracted using the SAMMY code, which is based on R-matrix theory. The neutron resonance parameters extracted from this study at 139.4 eV are in agreement with the values in the JENDL-4.0 evaluation, while those at 169.9 eV and 328.1 eV agree with the JEFF-4.0 evaluation. Additionally, the result at 259.3 eV is consistent with the CENDL-3.2 evaluation.The datasets presented in this paper are openly available at https://www.doi.org/10.57760/sciencedb.j00213.00197 (Please use the private access link https://www.scidb.cn/s/RNfUnq to access the dataset during the peer review process)
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GeSn alloy, as a novel silicon-based optoelectronic material, demonstrates significant application potential in the field of infrared photonics due to its tunable bandgap properties and compatibility with silicon-based CMOS processes. Although the experimental performance of GeSn lasers under low-temperature conditions has been preliminarily validated, the optimization and practical application of this device still face challenges such as insufficient understanding of material properties. This paper addresses issues such as the unclear carrier dynamics mechanisms in GeSn alloy applications in infrared photonics. A theoretical model incorporating band parameters, non-equilibrium carrier transport, and radiative recombination have been proposed to systematically investigate the mechanism by which thermal excitation and phonon-assisted processes influence the direct-band spontaneous emission in GeSn alloys under variable temperature conditions. Results indicate that the carrier transfer process between the ΓCBM and LCBM energy bands of GeSn alloys exhibits significant composition dependence: for low-Sn-content GeSn alloys with Sn content below 10%, temperature-induced LCBM→ΓCBM electron transfer dominates, leading to an increase in direct band emission efficiency with rising temperature; whereas in high-Sn-content GeSn alloys with Sn content between 10% and 20%, the ΓCBM→LCBM electron escape process is more pronounced, resulting in a decrease in direct band emission efficiency with rising temperature. A modified Arrhenius modeling of the carrier dynamics competition further indicates that thermal excitation and phonon scattering synergistically regulate electron transfer between ΓCBM and LCBM. Analysis based on the modified Arrhenius model further demonstrates that both thermal excitation and phonon-assisted processes promote the injection and escape of electrons in the ΓCBM valley, serving as key factors in modulating the radiative recombination efficiency at the direct bandgap of GeSn alloys. The red shift of the peak position in the spontaneous emission spectrum of GeSn alloys primarily originates from the bandgap contraction effect; simultaneously, phonon-assisted processes reduce the dispersion of carrier energy distributions, leading to a pronounced narrowing effect in the direct band emission spectrum. Quantitative findings further elucidate the mechanism by which thermal excitation and phonon-assisted processes influence direct bandgap luminescence in GeSn alloys, offering theoretical guidance for performance regulation in infrared optoelectronic devices.
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Inductively coupled plasma (ICP) generators involve complex interactions between electromagnetic, thermal, and chemical processes, making direct diagnostics difficult. To clarify these coupling mechanisms, a two-dimensional axisymmetric model of an argon ICP torch operating at kilopascal pressure was developed using COMSOL Multiphysics under both local thermodynamic equilibrium (LTE) and nonequilibrium (NLTE) assumptions. A two-dimensional axisymmetric magnetohydrodynamic (MHD) model was established, incorporating electromagnetic induction, convective–radiative heat transfer, and a seven-reaction argon plasma chemistry mechanism. The LTE model assumes a uniform temperature for all species, while the NLTE model independently solves for the electron temperature (Te) and gas temperature (Tg), thereby accounting for incomplete energy exchange between electrons and heavy particles.At a discharge power of 1000 W and working pressure of 10 kPa, the LTE model predicts a peak temperature of approximately 8200 K, concentrated around the induction coils. In contrast, the NLTE model yields a maximum gas temperature of about 5990 K, with the hot zone shifted downstream. The NLTE model reveals a clear two-temperature structure: Te peaks near the coil wall (~0.93 eV) while Tg reaches its maximum downstream, indicating a pronounced thermal non equilibrium state where electrons are preferentially heated by the induced field. The calculated skin depth (~11.3 mm) coincides with the region of strongest electromagnetic energy deposition.Species analysis shows that the plasma core is dominated by ground-state argon (Ar) (>99%), while excited argon (Ar*) and argon ions (Ar+) increase notably near the coil region, confirming that excitation and ionization processes are localized within the skin layer. Furthermore, comparison between 5 kPa and 10 kPa cases demonstrates that as pressure decreases, the difference between Te and Tg widens, reflecting enhanced thermal non-equilibrium due to reduced collisional coupling.Overall, the results highlight that LTE and NLTE assumptions lead to markedly different predictions of temperature and energy coupling at kilopascal pressures. The NLTE model captures delayed energy transfer and spatial temperature decoupling more realistically, providing new insights into the electromagnetic– thermal–flow interactions of ICP discharges and offering a modeling reference for ICPbased high-enthalpy plasma wind tunnel design and related aerospace applications.
, , Received Date: 2025-09-09
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, , Received Date: 2025-08-29
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With the technological advantages of high thrust, high specific impulse, long life, variable specific impulse, and high efficiency, the variable specific impulse magnetoplasma rocket engine has become the essential advanced propulsion system for the deep space exploration and manned space flight in the future. In the variable specific impulse magnetoplasma rocket engine, the ion cyclotron resonance heating stage is linked with the helicon plasma source. The operation status of the helicon plasma source has a direct influence on the ion heating process in the ion cyclotron resonance heating stage. It is of great significance for the testing and the optimization of the engine performance to reveal the influence of the ionization process on the ion heating process. In this paper, a multi-fluid model in which the ion cyclotron resonance heating stage is linked with the helicon plasma source is developed. The numerical simulations with different input currents of helicon plasma source and different pressures are performed to analyze the effect of the operation status in the helicon plasma source on the ion energy density in the ion cyclotron resonance heating stage. The results show that the discharge mode of the helicon plasma source gradually changes with the increase of the input current and that the plasma density jump appears while the ion temperature remains basically unchanged. With the plasma density jump and nearly identical ion temperature the ion energy density jump also appears in the simulation domain. Similar to the results of the simulation under different input currents of the helicon plasma source, the plasma density and the ion energy density also jump when the pressure increases. However, the ion temperature decreases due to the discrepancy between the input frequency and the resonance frequency. With the numerical model and the input conditions of this study, the ionization process in the helicon plasma source is decoupled with the ion heating process in the ion cyclotron resonance heating stage. The energy gain of a single ion in the ion cyclotron resonance heating stage does not change with the operation status of the helicon plasma source, thereby accounting for the ability of the engine to work in multi mode.
, , Received Date: 2025-07-29
Abstract +
Rotating spokes, as one of the low-frequency, long-wavelength instabilities, are commonly observed in the ${\boldsymbol{E}} \times {\boldsymbol{B}}$ plasma discharge devices, such as the magnetrons and Hall thrusters. In Hall thrusters, the rotating spokes, which are located in the discharge channel and rotate in the azimuthal direction, feature the bright luminous regions. The space potential will be distorted by the instability of rotating spokes, thereby increasing the possibility for electrons to reach the anode and enhancing their drift along the equipotential lines. However, the excitation mechanism of the rotating spoke and its influencing factors remain ambiguous. In order to address this problem, we conduct numerical simulations and linear stability analysis to investigate the effects of the magnetic field gradient on the driving mechanism and mode characteristics of the rotating spoke instability. In this work, a particle-fluid two-dimensional hybrid model in the axial-azimuthal plane is employed to numerically study the effect of axial magnetic field gradient in the discharge channel on the rotating spoke. The numerical simulation results are analyzed using a dispersion relation derived from fluid theory, which combines the effects of plasma density and the magnetic field gradient. The output profiles of ion density, potential, and electric field from the numerical simulation serve as input parameters for the dispersion relation used in the linear stability analysis. The simulation results show that the frequency and propagation velocity of the $m = 1$ rotating spoke slightly increase as the magnetic field gradient in the discharge channel decreases. However, changing the magnetic field gradient in the discharge channel does not affect the propagation direction nor intrinsic characteristics of the rotating spoke. More specifically, when the value of ${\alpha _1}$increases from 1.1 to 1.7, which means a decrease of the magnetic field gradient in the discharge channel, the mode frequency rises from 6.2 kHz to 7.5 kHz, remaining within the frequency range of the rotating spoke instability. At the same time, the phase velocity also increases form 1013 m/s to 1225 m/s, which is consistent with the propagation velocity of the rotating spoke instability, and the rotating spoke instability still propagates along the ${\boldsymbol{E}} \times {\boldsymbol{B}}$ direction. Dispersion relation analysis indicates that the rotating spoke arises from an azimuthal drift instability which is located near downstream region of the thruster exit, and it is excited by the plasma density and magnetic field gradient effects. The axial position of the azimuthal drift instability, responsible for the rotating spoke formation, is slightly modulated by density profile variations caused by the change of magnetic field in the discharge channel. However, it remains near the downstream region of the thruster exit. The results indicate that the rotating spoke does not originate from ionization instabilities, and changing the magnetic field distribution in the discharge channel does not affect its propagation direction nor mode number. The research results provide theoretical support for explaining the excitation mechanism and key influencing factors of rotating spoke.
, , Received Date: 2025-11-17
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, , Received Date: 2025-08-04
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Ferrite (α-Fe), as a fundamental phase of steel materials, plays a decisive role in determining their macroscopic mechanical behaviors through its microscopic properties, particularly in engineering applications involving resistance to plastic deformation and fracture, fatigue resistance, wear resistance, and low-temperature toughness. Therefore, alloying elements are commonly introduced to improve the performance of steel via mechanisms such as grain refinement strengthening and precipitation strengthening. However, in these strengthening mechanisms, the effects of doped alloying elements on the stability, electronic structure, and mechanical properties of ferrite itself have not been thoroughly investigated. In this study, orthogonal experimental design and first-principles calculations are employed to investigate the effects of ternary alloy doping with M (Mn, Ti, Mo) on the stabilities, electronic structures, and mechanical properties of a ferrite-based supercell model Fe16-x-y-zMnxTiyMoz (x, y, or z = 0, 1, or 2), aiming to provide both theoretical insight and experimental reference for improving the comprehensive performance of ferrite-based steels by modifying the properties of the matrix phase. The results of the formation enthalpy (Hform) calculations indicate that all solid solutions have negative formation enthalpies, suggesting that they can form spontaneously. Among them, Ti doping is the most favorable for solid solution formation, followed by Mn, with Mo being the least favorable. The Fe13Ti1Mo2 configuration is the easiest to form spontaneously. The cohesive energy (Ecoh) results demonstrate that all solid solutions exhibit structural stabilities. Fe13Ti1Mo2 has the largest (most negative) cohesive energy of –477.96 eV, indicating that it possesses the highest structural stability. The contribution of Mo doping to stability enhancement is the greatest, followed by Ti, while the influence of Mn is the smallest. Electronic structure calculations reveal that M doping consistently reduces the density of states (DOS) at the Fermi level for Fe16-x-y-zMnxTiyMoz. The lowest DOS at the Fermi level is found to be 4.294 in Fe13Ti1Mo2, indicating enhanced hybridization and overlap between Mn 3d, Ti 3d, Mo 4d, and Fe 3d states. This strong hybridization leads to a decrease in the Fermi level and contributes to the high stability of the Fe13Ti1Mo2 phase. Mechanical property calculations indicate that M doping reduces the Young’s modulus (E) and Vickers hardness (HV) of the solid solutions. However, the K values (K = GH/BH) are all greater than 1.75, and Poisson’s ratios (ν) exceed 0.26, implying that while stiffness and hardness decrease, the ductility of the materials is improved. This study provides valuable guidance for designing ductile and tough ferrite-based steel materials.
, , Received Date: 2025-09-08
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Crystallization of ions in aqueous micro-droplet or nano-droplet on solid surfaces is ubiquitous, with applications ranging from inkjet printing to pesticide spraying. The substrates involved are typically nonpolar. Yet, the atomistic mechanism of crystallization within sessile droplets on such nonpolar substrates is still unclear. Here, we employ molecular dynamics simulations to investigate the crystallization of sodium chloride inside an aqueous nano-droplet on a nonpolar face-centered-cubic (111) surface. Crystallization occurs inside the droplet rather than at the liquid-gas or solid-liquid interface, when the concentration of the sodium chloride in the droplet exceeds 3.76 mol/kg. The phenomenon originates from the spatial distributions of water molecules and ions: a dense interfacial water layer forms at the solid-liquid interface, whereas ions accumulate in the droplet interior, increasing the local concentration. The ion-water hydration caused by the electrostatic interaction is dominant in ion-solid interaction. The spatial confinement provided by the solid, rather than the physical properties of the solid, enriches ions inside the nano-droplet, thereby triggering the crystallization. We further apply this mechanism to the separated aqueous sodium chloride nanodroplets, in which the gas phase destroys the continuous spatial distribution of ions in the droplet. Analogous crystallization is observed in the sessile droplets of potassium chloride solution on nonpolar solid surfaces, indicating the generality of crystallization in nano-droplets. These findings provide atomic-scale guidance for controlling crystallization in nano-droplets related to microelectronics, inkjet printing, and related technologies.
Reactivity enhancement with hybrid discharge mode enabled by microstructure-induced field distortion
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To investigate the enhancement mechanism of atmospheric-pressure oxygen pulsed discharge in a parallel-plate dielectric barrier discharge (DBD) with microstructures fabricated on the dielectric surface of the highvoltage electrode, this paper systematically analyzes the electron transport processes, the formation and evolution of electric fields, and the spatial distribution of particles using a two-dimensional fluid model. The introduction of microstructures induces significant electric field distortion, generating a strong transverse electric field that locally confines and focuses electrons beneath the micro-structured region, leading to the formation of a stable corona-mode discharge. Simultaneously, the reduced local discharge gap near the microstructure enhances the longitudinal electric field, resulting in a temporal asynchrony between the corona discharge under the microstructure and the parallel-plate discharge in the adjacent flat regions. As the geometric dimensions of the microstructures increase, a secondary discharge is triggered, further modulating the overall discharge behavior. Under conditions where the corona discharge is suppressed due to higher protrusions, the secondary discharge effectively compensates by increasing both the high-energy electron fraction and the spatially averaged density of reactive oxygen atoms. Simulation results reveal that the corona discharge and the secondary discharge significantly elevate electron density, electron temperature, and the proportion of highenergy electrons, thereby intensifying the discharge activity. These findings provide deep insight into the micro-mechanisms of microstructure-induced discharge enhancement and offer valuable guidance for the design of highly efficient plasma devices with tailored geometric features.
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Abstract +
Achieving a balance between low density, high strength, and good ductility remains a major challenge in the development of structural materials. Ti-based bulk metallic glasses (BMGs) have attracted considerable attention due to their exceptionally high specific strength; however, the intrinsic strength–plasticity trade-off has hindered their practical applications. Based on a quasicrystal-derived structural heredity and minor-element microalloying, this work realizes a synergistic enhancement of specific strength and plasticity in Ti-based BMGs. The resulting ((Ti40Zr40Ni20)72Be28)97Al3 BMGs exhibits an ultrahigh specific strength of 5.34 × 105 N·m·kg-1, setting a new record for Ti-based BMGs, together with a plastic strain of 13%, breaking the conventional strength–plasticity limitation of BMGs. Structural analyses reveal that Al microalloying effectively inherits and modulates the short-range order originating from the quasicrystalline structure, thereby achieving the observed synergistic enhancement in both strength and plasticity. This work provides new insights into composition design and lightweight structural applications of Ti-based BMGs.
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Abstract +
The finite - difference time - domain (FDTD) modeling of targets with infinitely thin graphene sheets poses a challenge due to the existence of surface current and the inability of longitudinal discretization. When analyzing the electromagnetic properties of targets via FDTD method, spatial discretization of the target is essential. In the case of macroscopic electromagnetic targets that incorporate ‘infinitely thin’ graphene interfaces, this interface cannot be longitudinally partitioned. Moreover, a surface current exists on the interface, rendering the conventional calculation methods for the tangential electric field on the interface inapplicable. To address this issue, we put forward a novel Equivalent Source Current (ESC) approach. The proposed method enables the graphene sheet to retain a two - dimensional structure and be positioned on the surface of the Yee cell during the spatial discretization of the FDTD method(Fig.2). Subsequently, the surface current on the graphene sheet is approximated as a source volume current. Then, the active Maxwell's equations are discretized at the tangential electric - field nodes on the graphene surface(Fig.2, Fig.3), thereby obtaining a modified formula for the electric - field. By introducing intermediate variables and integrating the Shift Operator (SO) method, which is employed to handle issues related to dispersive media, to process the correction formula, an FDTD iterative formula for calculating the tangential electric field at the graphene interface is deduced. This ultimately enables the FDTD calculations for targets with ‘infinitely thin’ graphene sheets. Excellent agreement between our FDTD results and analytical solutions in several numerical examples validates the proposed method. The methodological framework proposed in this study can be generalized and applied to the ‘zero-thickness’ dispersive interfaces with surface current distributions (such as metallic films and two-dimensional transition metal sulfides). This allows for a convenient numerical analysis of the electromagnetic properties of structures incorporating conductive dispersive interfaces.
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Abstract +
Proton radiography is an effective technique for diagnosing field distributions in plasmas. However, due to the complexity of electromagnetic field structures, reconstructing electromagnetic fields from proton radiographs is extremely challenging and often requires some simplified symmetry assumptions about the fields. Here, we present a machine learning approach to reconstruct three-dimensional (3D) magnetic field distributions from complex proton radiographs without relying on such assumptions.
To enable this, we construct the target 3D magnetic fields by linearly superposing multiple elementary magnetic structures generated from the Weibel instability. Each element is characterized by eight parameters—structural parameters (a, b, B0), spatial coordinates (x0, y0, z0), and rotation angles (θ, ϕ)—resulting in 80 degrees of freedom in total. Parameters were uniformly sampled within ±25% of their baseline values, and a dataset of 50,000 magnetic field–proton radiograph pairs was generated through forward simulation using GEANT4. All proton radiographs reside in the caustic regime, exhibiting multiple asymmetric caustics and significant flux concentrations.
A lightweight three-layer convolutional neural network (CNN) was designed for the reconstruction task. The network consists of an input layer, three convolutional modules (the first two following a ”convolution–batch normalization–max pooling” cascaded structure, and the third is simplified to a single convolutional layer), a flattening layer, a dropout layer, and an output layer. Bayesian optimization was applied to determine the optimal hyperparameters. The model was trained on 40000 samples, with 5000 samples for validation and 5000 for testing.
On the test set, the CNN achieves a mean absolute percentage error (MAPE) of 8.5% in predicting the 80 magnetic parameters, below the 12.9% random-guessing threshold. Prediction errors for most parameters follow near-zero-mean Gaussian distributions, with relative standard deviations under 6%. The reconstructed fields show high spatial agreement with the reference fields, and corresponding proton images match the originals with a cosine similarity of 0.89.
This study demonstrates that our CNN-based proton radiography reconstruction method can effectively reconstruct complex 3D magnetic fields without symmetry assumptions or manual parameter tuning, offering a novel tool for diagnosing electromagnetic fields in high-intensity laser-plasma interactions. Future work may incorporate multi-angle proton radiography and transfer learning from experimental data to enhance the method’s practicality and robustness.
To enable this, we construct the target 3D magnetic fields by linearly superposing multiple elementary magnetic structures generated from the Weibel instability. Each element is characterized by eight parameters—structural parameters (a, b, B0), spatial coordinates (x0, y0, z0), and rotation angles (θ, ϕ)—resulting in 80 degrees of freedom in total. Parameters were uniformly sampled within ±25% of their baseline values, and a dataset of 50,000 magnetic field–proton radiograph pairs was generated through forward simulation using GEANT4. All proton radiographs reside in the caustic regime, exhibiting multiple asymmetric caustics and significant flux concentrations.
A lightweight three-layer convolutional neural network (CNN) was designed for the reconstruction task. The network consists of an input layer, three convolutional modules (the first two following a ”convolution–batch normalization–max pooling” cascaded structure, and the third is simplified to a single convolutional layer), a flattening layer, a dropout layer, and an output layer. Bayesian optimization was applied to determine the optimal hyperparameters. The model was trained on 40000 samples, with 5000 samples for validation and 5000 for testing.
On the test set, the CNN achieves a mean absolute percentage error (MAPE) of 8.5% in predicting the 80 magnetic parameters, below the 12.9% random-guessing threshold. Prediction errors for most parameters follow near-zero-mean Gaussian distributions, with relative standard deviations under 6%. The reconstructed fields show high spatial agreement with the reference fields, and corresponding proton images match the originals with a cosine similarity of 0.89.
This study demonstrates that our CNN-based proton radiography reconstruction method can effectively reconstruct complex 3D magnetic fields without symmetry assumptions or manual parameter tuning, offering a novel tool for diagnosing electromagnetic fields in high-intensity laser-plasma interactions. Future work may incorporate multi-angle proton radiography and transfer learning from experimental data to enhance the method’s practicality and robustness.
, , Received Date: 2025-07-22
Abstract +
AlCoCrFeNi high-entropy alloys have consistently attracted attention due to their outstanding strength-to-ductility ratio. However, the substantial content of expensive cobalt in these alloys has somewhat limited their engineering applications. Consequently, there is an urgent need to design and develop high-performance, low-cost cobalt-free high-entropy alloys. AlCrFeNi alloys exhibit microstructures and properties similar to AlCoCrFeNi alloys. Simultaneously, the absence of Co significantly reduces costs and markedly improves casting performance. These alloys represent a potential structural material for harsh environments, demonstrating promising engineering applications. In order to explore the phase modulation mechanism of Nb element on AlCrFeNi alloy, this study combines experiments with first principles calculations to systematically investigate the effects of Nb on the microstructure, mechanical properties and wear resistance of AlCrFeNi alloy. The research results show that the AlCrFeNiNb0.4 high-entropy alloy has the best mechanical properties and wear resistance.The doping of Nb changes the wear mechanism of the AlCrFeNi alloy and improves the wear resistance of the alloy. This is attributed to the phase modulation effect of Nb on AlCrFeNi alloy. On the one hand, it induces the precipitation of Laves phase, which has high hardness, and on the other hand, it solidly dissolves in the BCC and B2 phases of the alloy, significantly improving the mechanical properties of the two phases. In addition, Nb doping refines the microstructure of the AlCrFeNi alloy, which leads to an increase in the phase interface density, thus enhancing the hardness, yield strength and wear resistance of the alloy. First principles calculations show that the Nb atoms change the electronic structures of the BCC and B2 phases in the AlCrFeNi alloy, thereby enhancing the stability of the two phases and confirming the solid solution strengthening effect of Nb on the two phases. The Nb atoms form strong antibonds with most of the atoms in the two phases, which further explains the nature of the generation of a large number of Laves phases in the microstructure of the alloy after Nb doping.
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