arXiv subjects

Zhongfeng Xu

Publications and source records attributed to Zhongfeng Xu.

7 recordsLinked to original sources

arXiv2026

Observation of stopping power reduction at strong ion-plasma coupling

Ion stopping in dense plasma is crucial for stellar evolution and fusion ignition. However, its behavior in the strong ion-plasma coupling regime beyond the linear limit has long remained elusive, due to formidable experimental challenges. Here we report the first experimental investigation of ion stopping at an unprecedented coupling parameter exceeding unity, achieved by sending laser-accelerated short-pulse and intense quasi-monoenergetic carbon ions ($\sim$583 keV/u, C$^{5+}$) into a uniform, long-lived, well-characterized dense plasma target ($T_e$ $\approx$ 17 eV, $n_e$ $\approx$ 4$\times$10$^{20}$ cm$^{-3}$). By simultaneously measuring ion energy loss and charge-state evolution, we eliminated key experimental ambiguities arising from charge-state determination. Our results clearly show a reduction in stopping power compared with predictions from standard linear dielectric response or binary collision models, and they agree well with the hybrid calculation of molecular dynamics with quantum corrections. The importance of nonlinear screening effects arising from many-body interactions and quantum effects due to the wave nature of electrons was demonstrated at strong coupling. This work establishes a definitive high-fidelity experimental benchmark for collisional dynamics in the strong-coupling regime. It offers critical insight for accurate modeling of energy transport in inertial confinement fusion and astrophysical plasmas.

physics.plasm-ph↗

arXiv2026

Intrinsic Instantaneous Coarse-to-Fine Recoverability in the Lorenz-96 System

In multiscale chaotic systems, a basic closure question is how much of the unresolved fine scales is instantaneously determined by the resolved coarse scales on the attractor. In a Fourier description, we formalize this by asking, given a target mode $k$ and a lower-mode cutoff $k_{\rm cut}<k$, how much of mode $k$ is determined by the retained modes $0,\ldots,k_{\rm cut}$. We quantify this relation by the correlation-ratio functional $R(k\mid k_{\rm cut})$, interpreted as conditional-mean explained variance, and use it to build a scale-resolved recoverability map $(k,k_{\rm cut})\mapsto R(k\mid k_{\rm cut})$, whose structure is sharply organized by the nonlinear dynamics. Applying the diagnostic to the Lorenz-96 system for forcings $F=8,16,32,64$, we find that the recoverability maps are strongly nonuniform: low modes remain weakly constrained by still coarser observations, while high modes exhibit finite-band partial slaving once the retained cutoff reaches the energetic intermediate modes. The growth of substantial recoverability is organized around the quadratic triad-access scale $k_{\rm cut}\approx\lceil k/2\rceil$, consistent with the Fourier coupling rule $p+q\equiv k\pmod N$, while remaining shifted by regime-dependent statistics. Increasing $F$ preserves this geometric organization but reduces its amplitude, indicating greater conditional freedom of the unresolved modes in more strongly driven regimes. The maps show that instantaneous deterministic closure varies systematically across scales as a property of the invariant measure: retained modes provide nontrivial deterministic information in some regions, while other regions are dominated by conditional residual variance.

nlin.CD↗

arXiv2025

Deformation and Stress Evolution during Laser Powder Bed Fusion of Semi-Crystalline Polyamide-12

Laser powder bed fusion (L-PBF) of semi-crystalline polymers such as polyamide-12 (PA12) has found increasing use in various industrial applications. However, achieving high dimensional accuracy remains a significant challenge. Despite the seemingly straightforward layer-by-layer manufacturing concept, the L-PBF process involves complex thermal histories and strongly coupled multiphysics, making the evolution of stress and deformation mechanisms still not fully understood. To address this, a comprehensive three-dimensional thermo-mechanical modeling framework is developed to simulate the L-PBF process of PA12. The model for the first time incorporates transient heat transfer, phase transformation induced volumetric shrinkage, thermoviscoelasticity, and a modified non-isothermal crystallization kinetics. To alleviate the computational burden of part-scale simulations, a dual-mesh strategy is employed to efficiently couple thermal and mechanical fields without compromising numerical accuracy, which also enables the framework to handle L-PBF simulations of arbitrarily complex three-dimensional geometries. Particular attention is paid to the role of mechanical and thermal boundary conditions. Specifically, the underlying powder bed is modeled as a fictitious viscous medium, providing support while permitting upward displacement. Additionally, a radiative heat loss boundary condition, which more closely approximates the actual physical process, is applied to the top powder surface. The incorporation of this radiation effect significantly enhances the crystallization rate and improves the agreement with experimentally measured warpage. The model is validated against experimental warpage data under various preheating temperatures. Furthermore, strain decoupling analysis for the first time reveals that displacement induced by phase transformation is approximately 10 times greater than that caused by thermal expansion, highlighting the dominant role of crystallizationinduced shrinkage in warpage formation. Numerical tests also indicate that warpage is highly sensitive to the preheating target temperature of the PA12 powder bed, while the temperature of the newly recoated powder within the tested range has a limited effect. This work provides a predictive modeling foundation for future optimization of polymer L-PBF processes at part-scale, particularly in controlling deformation and improving dimensional accuracy.

physics.med-ph↗

arXiv2025

A high-resolution prediction dataset for solar energy across China (2015-2060)

A high spatiotemporal resolution and accurate middle-to-long-term prediction data is essential to support China's dual-carbon targets under global warming scenarios. In this study, we simulated hourly solar radiation at a 10 km* 10 km resolution in January, April, July, and October at five-year intervals from 2015 to 2060 across China using the WRF-Chem model driven by bias-corrected CMIP datasets and future emission inventories. We further calculated the monthly photovoltaic power potentials based on an improved assessment model. Results indicate that the WRF-Chem model can reproduce the spatiotemporal evolution of solar radiation with small simulation errors. GHI in 2030 and 2060 over China are characterized by a pronounced west-to-east gradient. The interannual fluctuations of GHI from 2015 to 2060 over China's major PV power generation bases are small, and the interannual variability of GHI is mainly dominated by TCC and the influence of AOD is limited. National averaged PV power generation in China shows a significant growth trend and increases from 68.7 TWh in 2015 to 129.7 TWh in 2060, which is approximately twice the 2015 value. The dataset will provide an important scientific basis for renewable energy planning and grid security under China's dual-carbon strategy.

physics.ao-ph↗

arXiv2023

Charge equilibration of Laser-accelerated Carbon Ions in Foam Target

The charge equilibration of laser-accelerated carbon ion beams in 2 mg/cm3 foam target was investigated experimentally. The ions were generated through target normal sheath acceleration mechanism in laser-foil interaction scheme. This allows to get the equilibrium charge state in wide energy range near Bragg peak within a single shot. By using foam, the charge equilibration measurement in density regime between gas and solid state was firstly reached out experimentally. It was found that the theoretical predictions with tabulated cross section data for gas target greatly underestimated the charge states. The experimental data are in close agreement with both semi-empirical formula as well as rate equation predictions based on ion-solid interactions. The important role of target density effects that increase the ionization probability and decrease the electron capture probability through frequent multi-collisions in foam are demonstrated. The double electron processes are shown to have little influence on the average charge states. The findings are essential for high energy density physics research where the foams are widely used, and have impacts on a broad range of applications in medical, biological and material fields. The method also provides a new approach to investigate the interaction mechanism of swift heavy ions in matter by taking advantage of the laser-accelerated short-pulse wide-energy range ions.

physics.atom-ph↗

arXiv2023

Energy loss enhancement of very intense proton beams in dense matter due to the beam-density effect

Thoroughly understanding the transport and energy loss of intense ion beams in dense matter is essential for high-energy-density physics and inertial confinement fusion. Here, we report a stopping power experiment with a high-intensity laser-driven proton beam in cold, dense matter. The measured energy loss is one order of magnitude higher than the expectation of individual particle stopping models. We attribute this finding to the proximity of beam ions to each other, which is usually insignificant for relatively-low-current beams from classical accelerators. The ionization of the cold target by the intense ion beam is important for the stopping power calculation and has been considered using proper ionization cross section data. Final theoretical values agree well with the experimental results. Additionally, we extend the stopping power calculation for intense ion beams to plasma scenario based on Ohm's law. Both the proximity- and the Ohmic effect can enhance the energy loss of intense beams in dense matter, which are also summarized as the beam-density effect. This finding is useful for the stopping power estimation of intense beams and significant to fast ignition fusion driven by intense ion beams.

physics.plasm-ph↗

arXiv2022

Target density effects on charge tansfer of laser-accelerated carbon ions in dense plasma

We report on charge state measurements of laser-accelerated carbon ions in the energy range of several MeV penetrating a dense partially ionized plasma. The plasma was generated by irradiation of a foam target with laser-induced hohlraum radiation in the soft X-ray regime. We used the tri-cellulose acetate (C$_{9}$H$_{16}$O$_{8}$) foam of 2 mg/cm$^{-3}$ density, and $1$-mm interaction length as target material. This kind of plasma is advantageous for high-precision measurements, due to good uniformity and long lifetime compared to the ion pulse length and the interaction duration. The plasma parameters were diagnosed to be T$_{e}$=17 eV and n$_{e}$=4 $\times$ 10$^{20}$ cm$^{-3}$. The average charge states passing through the plasma were observed to be higher than those predicted by the commonly-used semiempirical formula. Through solving the rate equations, we attribute the enhancement to the target density effects which will increase the ionization rates on one hand and reduce the electron capture rates on the other hand. In previsous measurement with partially ionized plasma from gas discharge and z-pinch to laser direct irradiation, no target density effects were ever demonstrated. For the first time, we were able to experimentally prove that target density effects start to play a significant role in plasma near the critical density of Nd-Glass laser radiation. The finding is important for heavy ion beam driven high energy density physics and fast ignitions.

physics.plasm-ph↗