Recent Publications

Analysis of supercritical CO2 brayton cycle system for laser inertial confinement fusion concept reactors

Bingqian Zhang, Xinze Li, Ronghua Chen, Kui Zhang, Wenxi Tian

A polar-harmonic unified gas-kinetic scheme for magnetized ion dynamics from cyclotron kinetics to the Hall-Pedersen constitutive limit

Yixiao Wang, Zhigang Pu, Xing Ji, Kun Xu

Magnetized ion transport in weakly ionized plasmas ranges from gyroangle-dependent kinetics to Hall-Pedersen drift-diffusion as collisionality and magnetization vary. We develop a polar-harmonic unified gas-kinetic scheme (PH-UGKS) for the ion Vlasov-BGK equation in a uniform magnetic field. The scheme evolves the full ion distribution by coupling a conservative density update to exponential evolution of its nonequilibrium component. Exact collision-rotation integration in gyroangle Fourier space is combined with a time-averaged kinetic flux that incorporates spatial transport and electric acceleration, together with a compact Hall-Pedersen correction to the density flux. The scheme conserves ion number, and analysis establishes second-order temporal consistency and asymptotic preservation of the Hall-Pedersen density limit at fixed magnetization. Numerical tests reproduce ion Bernstein dispersion and Dory-Guest-Harris growth rates and resolve changes in the gyroharmonic spectrum as the collision-to-gyrofrequency ratio varies. The driven ion-flux response agrees with an independent characteristic-Volterra reference, including finite-frequency departures from the instantaneous Hall-Pedersen relation. In collisional tests, accurate responses are obtained with time steps far larger than both the collision time and the gyroperiod. Fixed-resolution density tests confirm convergence to the corresponding Hall-Pedersen discretization. The same kinetic formulation thus connects kinetic response and macroscopic transport without switching to a fluid solver or subcycling microscopic time scales.

High-charge, highly polarized positron beams generated from a laser-driven nanowire-array target

De-Sheng Zhang, Cui-Wen Zhang, Kun Xue, Feng Wan, Xue-Ren Hong, Jian-Xing Li, Bai-Song Xie

The generation of high-charge, highly polarized positron beams in the interaction of a linearly polarized laser pulse with a nanowire-array target is investigated. Here, laser-driven electrons emit high-energy photons through nonlinear Compton scattering (NCS), which subsequently produce electron--positron pairs through the nonlinear Breit--Wheeler (NBW) process. We model this interaction using two-dimensional spin-resolved quantum electrodynamics particle-in-cell (QED-PIC)} simulations. At positron birth, the sign of $S_z$ is statistically correlated with that of the local $B_z$. The spatiotemporal field structure arising from the laser--nanowire interaction strengthens the correlation between the birth spin sign and the direction of the subsequent transverse Lorentz impulse, thereby limiting cancellation between opposite-spin contributions at a given angle. The results show that the average polarization degree reaches $|\bar S_z|\approx0.46$, and the positron charge satisfying $|\bar S_z|>0.3$ is approximately $308\,\mathrm{nC}$. Parameter scans reveal that the high-polarization positron charge is maximized at intermediate target densities and nanowire periods. Such a source could enable polarization-sensitive studies of strong-field QED and spin-dependent phenomena in high-energy and materials physics.

AI Surrogate Modeling for Real-Time Tokamak Equilibrium Prediction: Benchmarking Neural Architectures and Validation on EXL-50U

Guoyang Shi, Zitong Zhang, Siqi Ding, Jianguo Chen, Yapeng Zhang, Jiayi Zhi, Hanyue Zhao, Tianyuan Liu

Fast and reliable plasma equilibrium prediction is essential for real-time tokamak operation and control, but conventional Grad-Shafranov (GS) solvers are often too costly for real-time deployment. We develop an AI surrogate framework and benchmark five architectures (MLP, CNN, FNO, Transformer, and KAN) on a numerical GS database with 100,000 IID and 10,000 OOD samples. Under a unified protocol, we evaluate accuracy, inference efficiency, model scaling, and robustness. We also establish device-level validation on the EXL-50U tokamak by linking numerical GS solutions, surrogate predictions, and the standard Shape Editor reference to assess simulation-to-device consistency. The surrogates achieve errors of $10^{-3}$-$10^{-2}$ relative to GS solutions, while the GS-to-device discrepancy remains at $10^{-3}$. Transformer gives the best IID accuracy, whereas CNN offers the best balance of accuracy, robustness, and speed, reaching 0.7 ms TensorRT latency. On unseen plasma geometries and parameter regimes, CNN and FNO show the strongest extrapolation stability, with 4%-5% relative $L_2$ error, while models with weaker inductive biases degrade more substantially. Scaling data and model capacity improves interpolation but not necessarily extrapolation, revealing a trade-off between capacity and OOD generalization. Overall, this work provides a systematic, device-consistent benchmark for AI-based GS prediction and practical guidance for selecting reliable surrogates for real-time plasma control and fusion applications.

Enhanced H permeation barrier via sispersed He-irradiation-induced defects in Al 2 O 3 /FeAl coatings

Yulin Wei, Deng Shunjie, Meidie Wu, Ping Peng, Qingjie Zhang, Min Liu

The service performance of tritium permeation barriers (TPB) under He irradiation damage is critical to the safe operation of fusion reactors. In this study, He irradiation, annealing, and deuterium (D, H isotope) permeation experiments were performed on Al2O3/FeAl coatings. Systematic characterizations, combined with DFT calculations, were employed to elucidate the mechanisms of He irradiation resistance and irradiation defect-enhanced H permeation barrier. The pronounced crystallographic orientation anisotropy in certain Al2O3 regions may contribute to the formation of high-density grain boundary networks. After irradiation-annealing treatment, the dispersed He distribution may be associated with these anisotropic regions, contributing to the reduced irradiation hardening response. Furthermore, the intrinsic H permeation resistance of Al2O3 originates from the strong orbital hybridization between H and lattice O/Al atoms, while He implantation-induced lattice distortion enhances the H-lattice bonding strength. This enables highly dispersed He-defect clusters to form abundant H-trapping sites, which deflect the H migration path and elevate the H diffusion energy barrier. Consequently, within the temperature range of 500-650 °C, the D permeation resistance of irradiated coatings outperforms that of unirradiated counterparts. At 500 °C, the D permeation reduction factor (PRF) of the irradiated coating reaches as high as 3300, representing an 83% enhancement compared with the unirradiated sample. Under the He irradiation, annealing, and D2 permeation conditions investigated in this study, the coating exhibits certain potential for TPB applications. However, its long-term reliability under the complex service conditions of a fusion blanket remains to be further validated.

Tunable high-charge relativistic electron beams via direct laser acceleration in hohlraum-preheated foam targets

Ziyao Wang, Jieru Ren, Zhigang Deng, Wenqing Wei, Wei Qi, Olga N. Rosmej, Nikolay E. Andreev, Sergey Yu. Gus'kov, Rafael Yakhin, Yifang Gao, et al.

Direct laser acceleration (DLA) in near-critical-density (NCD) plasmas can efficiently generate high-charge relativistic electron beams, yet beam parameters depend critically on precise plasma state manipulation. Solid-ablation NCD plasmas evolve rapidly, posing severe controllability challenges. We produce NCD plasma via indirectly heating foam targets with ns laser driven hohlraum soft X-ray. Electrons are generated through irradiating the plasma with another picosecond laser. Tuning the laser pulse delay $τ$ enables control of plasma profiles and beam parameters. Experiments show that when the foam is heated ($τ$ = 6 ns, 9 ns), the beam exhibits $T \sim 13$ MeV effective temperature, $E_k \sim 80$ MeV cutoff energy, and hundreds of nC/sr charge for $E_k > 7.5$ MeV. These values are significantly higher than those from solid-foil ($T$ $\sim$ 2.7 MeV, $E_k$ $\sim$ 20 MeV, $Q$ $\sim$ 9 nC/sr) and cold-foam ($T$ $\sim$ 12 MeV, $E_k$ $\sim$ 50 MeV, $Q$ $\sim$ 5 nC/sr) interactions. At a longer delay of $τ$ = 15 ns, the charge increases further while the temperature decreases, and at a shorter delay of $τ$ = 3 ns, both temperature and charge are lower. 3D PIC simulations link these observations to the interplay between the microstructure of the cold foam and the evolving plasma density profile at different delay times, which together determine the beam charge, effective temperature, and divergence. The finding provides a routine to generate and tailor the relativistic electron beams, which is essential for designing laser-driven electron sources for high energy density physics and photonuclear reaction applications.

Polarization-Conditioned Fourier-enhanced DeepONet for Electric Field Reconstruction from EFISH Measurements

Zhijian Yang, Edwin Setiadi Sugeng, Yaqi Zhang, Anbang Sun, Tat Loon Chng

Electric-field-induced second-harmonic generation (EFISH) is an established laser diagnostic for quantifying electric fields in plasmas, yet ensuring field accuracy remains challenging given the coherent, path-integrated nature of the signal. We address this via machine learning, developing a Polarization-Conditioned Fourier-enhanced Deep Operator Network (PC-FDON) -- a unified operator-learning model that reconstructs field profiles from EFISH measurements across both polarizations and various optical parameters. Its architecture incorporates three advances: (i) a Fourier-enhanced branch providing inductive bias for the Gouy phase shift and wave-vector mismatch; (ii) a polarization-conditioning branch encoding signal polarization via Feature-wise Linear Modulation (FiLM) and gated units, enabling one model to handle both polarizations; and (iii) a physics-informed loss enforcing self-consistency with the governing EFISH equation. Trained on data spanning multiple function families, polarization states, and phase-mismatch values, PC-FDON achieves promising reconstruction under noise-free, incomplete, and noisy inputs, with generalizability comparable to our previous polarization-specific model. Pointwise epistemic uncertainty estimates via Monte Carlo dropout reflect model confidence and enable out-of-distribution (OOD) detection through a location-dependent exceedance fraction metric. Validation is performed on realistic electrode configurations under both polarizations and varying Rayleigh ranges, including a simulated surface dielectric barrier discharge where the framework correctly flags OOD inputs, and experimental data showing good agreement with simulations. The architecture -- spectral inductive bias, conditional modulation, and dataset-specific uncertainty -- shows strong potential for broader application beyond plasma diagnostics.

Polarization-resolved attosecond gamma-ray emission from few-cycle laser interactions with cone targets

De-Sheng Zhang, Cui-Wen Zhang, Xue-Ren Hong, Feng Wan, Jian-Xing Li, Bai-Song Xie

Linearly polarized attosecond $γ$-ray pulses in the MeV range are generated from a cone target irradiated by a single few-cycle laser pulse. Electron layers are periodically extracted from the cone walls and subsequently accelerated. Their interaction with the counter-propagating reflected attosecond field produces high-energy photons through nonlinear Compton scattering (NCS), forming attosecond $γ$-ray pulses. We model this interaction using two-dimensional quantum electrodynamics particle-in-cell (QED-PIC) simulations that resolve electron spin and photon polarization during emission. The results show a shortest equivalent duration of $300\,\mathrm{as}$, with a corresponding linear polarization degree of 0.78. The photon spectrum extends to $6\,\mathrm{MeV}$, and the linear polarization degree in the high-energy range reaches 0.88. The linear polarization degree remains high when photons from both emission directions are collected over wide momentum-angle ranges. Scans over the cone opening angle and the coupled laser-plasma parameters reveal tradeoffs among photon number, mean photon energy, and polarization. Such highly polarized attosecond $γ$-ray pulses could be used to investigate ultrafast nuclear dynamics and polarization-dependent processes in strong-field quantum electrodynamics.

Numerical simulation of CuCr vacuum arc considering stepwise ionization and radiation energy loss

Hongjian Wang, Lijun Wang, Xiangyu Wang, Jieli Chen, Xinyang Qi, Zhongji Han

The charge state distribution and energy radiation within the multi-species vacuum arc have always been a major research focus. In this paper, a magnetohydrodynamic method is employed to consider the comprehensive ionization–recombination processes of the plasma within the copper–chromium (CuCr) vacuum arc, including both direct and stepwise ionization. Radiation energy loss is also introduced to investigate the internal species distribution more accurately. Simulation results show that for the high-current subsonic vacuum arc, stepwise ionization is significantly stronger than direct ionization, resulting in the dominance of double-charged ions, and the introduction of the radiation model leads to a reduction in electron temperature. Conversely, for the low-current supersonic arc, the effect of stepwise ionization is practically negligible. As the current increases, the average charge state rises, and the ionization length of the high charge state ions shortens accordingly. Comparisons reveal that the simulation results are in good agreement with the experimental and theoretical analyses conducted by other researchers.

A multi-mass-point model for drive asymmetry of double-shell capsules

Xinrui Chen, Guanqiong Wang, Xindong Li, Wu Wen, Lulu Li, Xiaoguang Wang, Yuanbo Lu, Lixia Huang, Xiangting Yu, Delong Xiao

Drive asymmetry is one of the main sources that degrade the implosion performance of double-shell capsules in inertial confinement fusion. In this paper a multi-mass-point theoretical model under the time-invariant radiation source is proposed to investigate the transfer of drive asymmetry in double-shell capsules and its impact on the fusion performance. In this model, the capsule is divided into independent azimuthal slices by ignoring the azimuthal motion and then assembled to investigate the effect of drive asymmetry. Each slice is described by different models according to the characteristics of different stages. The theoretical predictions exhibit good agreement with the results from radiation hydrodynamic code MULTI. It is found that the radiation asymmetry generates the asymmetry of the ablated mass and velocity in the outer shell during ablation. Then, the outer shell asymmetry is transferred to the inner shell through the acceleration process due to the shell collision. This method can calculate how drive asymmetry develops, propagates, and affects fusion yield during the implosion process of double-shell capsules, while simultaneously providing scaling laws for the relationship between capsule parameters and the transfer of drive asymmetry.

Effects of fusion-relevant gas atmospheres and pressures on hydrogen isotope characterization for fuel-retention diagnostics by LIBS

Hao Sun, Zhenhua Hu, Jian Wu, Ying Zhou, Xinyu Guo, Huace Wu, Fang Ding, Hai-Shan Zhou, Xingwen Li, Jiangang Li

Fuel retention in plasma-facing components (PFCs) affects the operational efficiency and safety of fusion devices. However, detection of retained fuel by Laser-Induced Breakdown Spectroscopy (LIBS) remains challenging because the Hα and Dα Balmer lines commonly used for hydrogen-isotope identification are separated by only about 0.18 nm, making their discrimination highly sensitive to fusion-relevant ambient conditions. In this study, LIBS was employed to systematically investigate Hα/Dα discrimination on real EAST-exposed graphite tiles under various simulated ambient conditions. Depth-resolved measurements showed that the second laser pulse generally provided a more favorable Hα/Dα emission ratio and improved fitting quality, with the noise-normalized RMS residual decreasing from 3.6 to 1.26 compared with the first pulse. Meanwhile, time-resolved plume analysis helped explain the role of ambient environments in governing spectral broadening and isotope discrimination. At 100 Pa, the initial plume-height expansion rates within 200 ns were 15.6, 14.2, and 8.0 km/s in He, air, and Ar, respectively, revealing pronounced gas-dependent differences in plasma expansion. Combined spectral and plume analyses showed that vacuum provided high spectral resolution but suffered from a relatively short plasma lifetime. Within the investigated ambient parameters, a helium atmosphere at a moderate pressure of 100 Pa offered the most favorable balance between plasma lifetime and spectral resolution. In contrast, higher pressures or denser gases tended to enhance Stark broadening, leading to more severe peak overlap and a narrower effective discrimination window. The effective discrimination window was evaluated using the resolution factor Rs, with Rs ≈ 1.5 taken as a reference for baseline separation. These findings provide practical guidance for LIBS-based fuel retention diagnostics under EAST-relevant conditions.

Temporal instability in repetitive nanosecond-pulse spark discharges: Periodic behavior and parameter dependence

Le Feng, Yizhou Jiao, Jiahe Zhu, Zheng Tang, Qiaogen Zhang

Temporal fluctuations in repetitive nanosecond-pulse spark discharges are critical for maintaining discharge-parameter consistency and ensuring reliable pulse-power output. Here, statistical and frequency-domain analyses are used to examine periodic peak fluctuations and to clarify the roles of repetition rate, switch-gap parameters, and electric-field nonuniformity in shaping discharge periodicity. The results show that, under specific gap conditions, increasing the repetition rate drives the characteristic cycle toward a longer-period structure at first, after which the periodic feature progressively weakens until it becomes indistinct. For different gap configurations, increasing gas pressure while shortening the gap preserves a discernible periodic structure in the peak sequence even at higher repetition rates, whereas increasing the electrode curvature radius markedly suppresses periodic fluctuations. These trends are interpreted using a residual-species model that relates the inter-pulse decay of residual charged species to the measured peak-voltage fluctuation through the discharge–inception relation, thereby providing a consistent explanation for the observed repetition-rate-dependent peak stratification. Based on the identified evolution of peak stratification with repetition rate, p-d distribution, and electrode curvature radius, design-oriented suggestions are further outlined for mitigating temporal fluctuations by optimizing the p-d combination and electrode geometry.

Evolution characteristics and influencing factors of coronal plasma in vacuum electrical explosion of wires

Yiming Zhao, Jian Wu, Zhongyang Zheng, Zhiyuan Jiang, Wei Wang, Zhenyu Wang

Addressing the difficulty of diagnosing low-density coronal plasma during the vacuum electrical explosion of wires, this study developed a high-sensitivity laser dispersion interferometry diagnostic system with nanosecond temporal resolution. The system achieved a line-integrated electron-density detection sensitivity of 6.7 × 1013 cm−2. Combined with Mach–Zehnder interferometry, laser shadowgraphy, and streak imaging, the system was used to investigate the spatiotemporal evolution characteristics and influencing factors of coronal plasma during wire electrical explosions. These results show that, in terms of radial evolution, the coronal plasma exhibits pronounced radial dilution during outward expansion. For a 30 μm Ag wire, the peak electron density decreased from 8.5 × 1016 at 4 mm to 0.7 × 1016 cm−2 at 15 mm, while the corona-front velocity decreased from 93.0 ± 4.7 to 69.8 ± 3.5 km/s. In terms of load-material effects, the coronal plasma density shows a clear material dependence. For 20 μm Al, Ag, and W wires measured at a radial position of 15 mm, the peak electron densities were 1.72 × 1016, 1.11 × 1016, and 0.80 × 1016 cm−2, respectively. Combined with the deposited-energy analysis, the deposited energy of Al and Ag is relatively high compared with their atomization enthalpies, leading to more sufficient wire vaporization and therefore higher electron densities, whereas W produces the lowest electron density because its much higher atomization enthalpy limits wire-core ablation. In terms of load-diameter effects, the coronal plasma density shows a weak diameter dependence. For Ag wires with diameters of 20–50 μm, the peak electron density varied only slightly, ranging from 1.02 × 1016 to 1.25 × 1016 cm−2. These results provide experimental evidence for understanding the formation and evolution mechanisms of coronal plasma during wire electrical explosions and provide experimental constraints for magnetohydrodynamic model validation and load-design optimization.

A unified Bayesian framework for multi-diagnostic inversion in Z-pinch experiments

Bowen Zhu, Zhiyin Deng, Jian Wu, Wei Wang, Yiming Zhao, Zhongyang Zheng

We present a unified Bayesian inversion framework for multi-diagnostic plasma analysis, demonstrated here on Z-pinch experiments. A shared Bayesian neural network (BNN) core couples with interchangeable physics-based forward models, so that one variational inference engine serves all diagnostics with built-in uncertainty quantification. Two modules are developed. (i) A two-angle Thomson scattering (TS) module that enforces a single self-consistent plasma state across viewing angles by modeling the full dynamic structure factor convolved with pre-characterized instrumental functions—unlike conventional analyses that treat each angle independently. (ii) A joint interferometry and Faraday rotation module that simultaneously constrains phase and magnetic field, replacing the standard sequential workflow in which phase-unwrapping errors propagate uncorrected into field estimates; a hybrid semi-global matching plus BNN approach resolves phase-branch ambiguities where conventional algorithms fail. On synthetic data with realistically modeled noise, the TS module achieves overall coefficient of determination R2>0.98 for ne, Te, Ti, and ion velocity, and satisfactory reconstruction of the electron velocity, which is inherently harder to infer. The interferometry module achieves phase mean absolute error (MAE) <0.14 rad over a ∼5π rad dynamic range and path-averaged magnetic-field MAE <7.2 T against ∼40 T peak values. The framework is validated on a Z-pinch experiment, yielding spatially resolved ne, Te, Ti, and flow velocities with full uncertainty quantification.

Comparative analysis of multi-physical models for nanosecond pulsed diffuse discharges

Yulin Guo, Baohong Guo, Yaqi Zhang, Anbang Sun

Nanosecond pulsed diffuse discharges under extreme overvoltages exhibit unique properties for various technological applications. In this work, the applicability of different numerical frameworks—including the 2D/3D drift-diffusion fluid model, stochastic Monte Carlo photoionization, and particle-in-cell with Monte Carlo Collisions (PIC-MCC)—is comprehensively evaluated and compared with experimental observations. Experimental results reveal distinct morphological transitions in diffuse discharges across varying pressures (200 mbar to 1 atm). Laser Thomson scattering measurements are performed to obtain spatially resolved electron density profiles at 200 mbar, providing a rigorous benchmark for the simulations. The study demonstrates that while the Helmholtz photoionization approximation accurately captures the global characteristics of diffuse discharges, the Monte Carlo photoionization model reveals significant stochastic fluctuations at the discharge head, particularly at low background ionization levels. A comparative analysis of coordinate systems shows that while 2D Cartesian models fail to replicate the correct electric field enhancement of pin-plane geometries, 3D Cartesian simulations offer superior agreement with experimental discharge widths and morphology compared to 2D axisymmetric models, primarily by reducing artificial numerical diffusion. Furthermore, the PIC-MCC model predicts electron densities near the pin electrode that are two orders of magnitude higher than fluid model predictions, highlighting the influence of non-local effects and stochastic fluctuations in the high-field inception region. These findings provide critical guidelines for selecting appropriate computational models to optimize diffuse discharge systems.