Yan-Yun Ma

The direct-drive inertial confinement fusion schemes like the double-cone ignition (DCI) scheme can efficiently utilize the laser energy, while it faces significant challenges in uniform implosion and achieving high areal density of the fuel. This is because of the P2 asymmetry driven by the laser and the high-mode Rayleigh–Taylor instability (RTI) growth. We propose an efficient optimization approach by integrating multiple algorithms and physical models to address these limitations. Based on two-dimensional (2D) radiation hydrodynamics simulations, a scaling law for the areal density is derived, incorporating laser parameters, target structure, and instability factors, all of which have significant effects on the areal density. The particle swarm optimization algorithm is employed to optimize the irradiation positions and spot radius of the two-ring laser, improving the uniformity of laser intensity distribution on the target surface and thus reducing the P2 asymmetry. Combining one-dimensional simulations with the RTI growth theory, a quantitative predictive model for P2 asymmetry and a qualitative predictive model for high-mode RTI are established, significantly reducing computational costs. Finally, the outputs of the predictive models are used as input parameters to perform Bayesian optimization for iteratively optimizing laser profile and target structure. The areal density of the DCI in 2D simulations increases from 0.156 to 0.274 g cm − 2 with 2 × 16 kJ drive lasers. This method provides a new paradigm for the experimental design of DCI and polar direct-drive scheme.

The double-cone ignition (DCI) scheme is a promising approach to inertial confinement fusion. In this scheme, the fuel compression is guided in gold cones, and it is separated with the ignition process, which significantly reduces the ignition threshold. However, maintaining the structural integrity of the cone under intense dynamic loading during the compression phase remains a key challenge for successful ignition. In this paper, the loading response of the gold cone subjected to both laser ablation and fuel impact in the DCI compression phase is investigated using radiation-hydrodynamics simulations. Results show that the critical loading on the cone is mainly localized near the cone tip, where fuel impact dominates the dynamic stability of the cone because its peak pressure is substantially higher than the laser ablation pressure. The failure of the gold cone primarily arises from the interaction of rarefaction waves inside the material, which are generated upon reflection of shock waves at the free surface. Accordingly, the critical thickness conditions for avoiding spallation failure of the gold cone prior to ignition under various driving energies are derived. The theoretical thickness deviates from that of the simulations by less than 10%. These results provide a valuable reference for designing cone structures in the DCI scheme and for evaluating structural stability in high-energy-density physics experiments.

To improve the modeling of laser ablation of structured high-Z materials, we extended the hybrid ablation-expansion framework of Hudec et al (Physics of Plasmas 30, 042704, 2023) to Ta 2 O 5 foam targets, with a key improvement of the explicit coupling of radiation energy from the macroscopic radiation hydrodynamic module into the pore-scale ablation-expansion model. The material thermodynamic properties and radiation–matter interaction are described using tabulated equations of state and opacities. The model is recalibrated using updated Ta 2 O 5 equation-of-state and opacity tables and is quantitatively benchmarked against published x-ray self-emission measurements. It is found that the foam microstructure modifies laser coupling in a non-monotonic manner. The effects of foam density and laser intensity on the laser absorption efficiency (LAE) and x-ray conversion efficiency (XCE) are investigated. The LAE exhibits a non-monotonic dependence on the foam density, reaching its maximum at a foam density of ρ ― = 35   mg ⋅ cm − 3 under a laser intensity of I = 10 15   W ⋅ cm − 2 . The XCE also varies non-monotonically with the foam density, but its maximum is shifted to 40   mg ⋅ cm − 3 . This offset indicates that XCE is not controlled by laser absorption alone; it is also affected by the density-weighted radiation generation and optical-depth-limited radiation escape. In addition, the XCE decreases with increasing laser intensity, suggesting enhanced radiation losses and reduced conversion efficiency at higher drive conditions. Higher laser intensity, however, produces a larger total x-ray energy output. A maximum XCE of 24.8% is achieved at 40   mg ⋅ cm − 3 and 10 15   W ⋅ cm − 2 . The hybrid model provides a physically consistent description of laser–Ta 2 O 5 foam interaction and an effective simulation tool for laser ablation of high-Z foam materials in inertial confinement fusion research.

In the experimental campaigns of the double-cone ignition (DCI) scheme, gold cones were employed because of the well-established fabrication techniques. However, the intense M-band radiation from interaction between imploding laser irradiation and the gold cones could cause preheating and high- Z mixing problems of the colliding plasma. Here we propose tungsten as an alternative substitute and evaluate its performance under DCI-relevant extreme conditions. The results show that under extreme high pressures ( > 10 4 GPa), the dynamical responses of tungsten and gold cones are comparable. Nevertheless, tungsten exhibits distinctly different radiative behaviors, with a notably lower laser-to-radiation conversion, lower M-band yield, a softer radiation spectrum, and reduced penetration into the ablating CH shells. These characteristics therefore lead to a substantially lower radiation ablation rate. Full-process 2D simulations further confirm that tungsten cones effectively suppress high- Z mixing and produce a cleaner, denser fuel assembly. This study demonstrates that radiative properties govern material behaviors in high-energy-density regimes, and verifies that the tungsten cones could be a viable substitute for gold in DCI, providing a theoretical basis for material selection in similar systems.

The turbulent dynamo is the most plausible mechanism for generating strong magnetic fields in space. Recent laser-driven plasma experiments now reproduce relevant astrophysical conditions in the laboratory, enabling direct studies of this process. Using the FLASH code, we perform magnetohydrodynamic simulations of a turbulent dynamo in both two dimensions (2D) and three dimensions (3D) and conduct a scale decomposition analysis. While 2D simulations reproduce most basic plasma parameters, they exhibit an upscale energy transfer due to the vorticity conservation, absent in 3D, that renders 2D results unreliable at later evolutionary stages. Among energy transfer terms, the magnetic field line stretching term ⟨T2,l⟩ most efficiently converts kinetic to magnetic energy. Its solenoidal component T2s dominates the dilatational part T2d. The joint probability density function of R and Q, the second and third invariants of the velocity gradient tensor, shows that large T2s values occur where both Q and R are low, while small T2s appears where Q and R are large. The (R,Q) plane is divided into six regions corresponding to distinct topological structures and turbulent dynamo efficiencies. The most efficient region corresponds to (Q<0 and R<0) region or (D<0) region, where D is the discriminant of the velocity gradient tensor's eigenpolynomial. These numerical findings are supported by a simple analytical derivation. Our analysis identifies the most efficient turbulent dynamo topology in the (R,Q) plane, offering new insights into the underlying mechanism.

High-Z elements, such as silicon (Si), are usually doped in the outer ablator in direct-drive inertial confinement fusion (ICF) to smooth the laser non-uniformity. However, their specific effects on the implosion performance are not well understood. In this article, the direct-drive implosions of targets with varying Si doping ratios (0%, 6.25%, 12.5%) are studied through 2D radiation hydrodynamic simulations, in which the non-local electron transport is considered. As the doping ratio increases, the inward electron heat flux is reduced, while the radiation temperature is enhanced. This leads to a 9.3% and 18.6% increase in the preheat fuel temperature for the two doped targets. Besides, the maximum perturbation amplitude is also decreased by 39.5% and 66.3%. Consequently, the stagnation hot spot pressure rises by 8.35\% and 9.09\%, and the stagnation areal density increases by 10.3% and 13.8%, respectively. These findings indicate that high-Z dopant can improve implosion performance through significant suppression of hydrodynamic instability, with the trade-off of enhanced preheating. Therefore, appropriately increasing the doping concentration may improve implosion performance. Above findings advance the understanding of high-Z dopant effects in direct-drive implosions and offer valuable insights for the design of ICF targets.

Double-shell targets offer significant advantages in ignition margins and energy gain. We conducted theoretical studies and radiation hydrodynamic simulations to achieve efficient implosion of the double-shell targets driven by Z-pinch dynamic hohlraum (ZPDH). Theoretical models incorporating the ablator ablation, target implosion, and shell collisions are developed. The final implosion velocity can be theoretically predicted based on the given target and radiation drive parameters. The theoretical predictions exhibit a good agreement with the results from radiation hydrodynamic simulations, with deviations within 10%. Then, an optimal target structure using the random walk algorithm is designed. It is found that a target with a 3 mm radius can be ignited and yields energy of 165 MJ under a 285.6 eV radiation-driven source produced by ZPDH with a 50 MA load current. These findings provide valuable insights for designing double- or multi-shell targets in inertial confinement fusion.

Optimizing extreme ultraviolet (EUV) conversion efficiency (CE) is a core yet challenging requirement for laser-produced plasma sources. This study demonstrates the specific effects of laser- and tin target conditions on hydrodynamic and radiation properties of the light source, leading to a laser–target co-optimization scheme toward achieving optimal CE. For laser–droplet interactions, peak CE at 4-μm laser wavelength stems from modified laser penetration depth and balanced in-band radiation emissivity and opacity. However, geometric losses and strong reflections of laser energy prevent global CE optimization. The rarefied and spatially extended target induced by the pre-pulse can expand the laser–target interaction region and enhance laser absorption, leading to a substantial improvement in CE. Moreover, shaped-target morphology critically modulates laser ablation dynamics and in-band radiation. Symmetric and uniform optimized targets can be achieved by adjusting the delay time of the dual-pulse, which can mitigate the in-band radiation emission anisotropy. Eventually, it is found that the stable and homogeneous heating of optimized targets can maximize the CE to 7.1% under 4-μm laser irradiation. This study demonstrates a promising approach to improve the light performance through mid-infrared laser driving and target morphology selection.

In the direct drive inertial confinement fusion (ICF) scheme, a rippled interface between the ablator and the deuterium–tritium ice fuel can feed out and form perturbation seeds for the ablative Rayleigh–Taylor instability, with undesirable effects. However, the evolution of this instability remains insufficiently studied, and the effects of high-Z dopant on this instability remain unclear. In this paper, we develop a theoretical model to calculate the feedout seeds and describe this instability. Our theory suggests that the feedout seeds are determined by the ablation pressure and the adiabatic index, while the subsequent growth depends mainly on the ablation velocity. Two-dimensional radiation hydrodynamic simulations confirm our theory. It is shown that targets with high-Z dopant in the outer ablator exhibit more severe feedout seeds, because of their higher ionization compared with undoped targets. The X-ray pre-ablation in high-Z doped targets significantly suppresses subsequent growth, leading to suppression of short-wavelength perturbations. However, for long-wavelength perturbations, this suppression is weakened, resulting in increased instability in high-Z doped targets. The results are helpful for understanding the inner-interface-initiated instability and the influence of high-Z dopant on it, providing valuable insights for target design and instability control in ICF.

This study investigates the quantum stochasticity effects (QSE) in the interaction between a laser-wakefield accelerated electron beam (γe≈2000) and ultra-intense laser pulses (I =1021–1023 W/cm2). Quantum electrodynamics-particle in cell simulations reveal three distinct manifestations of QSE: angular and spectral distributions of the electron beam, asymmetric photon divergence patterns, and double-peak positron distributions. Evolution of photon divergence angles with laser intensity indicates efficient energy transfer to high-energy photons within 1–3 laser periods, preceding quantum-dominated positron production. These effects induce significant modifications in both the angular and spectral evolution of the electron beam, concurrently generating characteristic photon divergence patterns via nonlinear Breit–Wheeler processes. Substantial alterations in electron beam dynamics are observed, with QSE inducing notable variations in high-energy photon divergence angles through pair production mechanisms. The identified characteristic signals offer critical empirical data for the development of advanced laser wakefield acceleration-driven all-optical radiation sources and optimization of lepton pair production methodologies.