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Kazem Ardaneh, Remi Meyer, Mostafa Hassan, Remo Giust, Chen Xie, Benoit Morel, Ismail Ouadghiri-Idrissi, Luca Furfaro, Luc Froehly, Arnaud Couairon, et al.
Abinash Manikandan, Sophie L. Sharpe, Kirk A. Flippo, Lars Pedersen, Eric Cervi, Gustav Blankenberg, S. Woodruff
Yutong He, Alexey Arefiev, Mario Manuel, Hui Chen, Christopher Ridgers
The linear Breit-Wheeler (LBW) process ($γ+γ\rightarrow e^{-}+e^{+}$) is a fundamental prediction of quantum electrodynamics, but yet to be observed under laboratory conditions using real photons. In recent years, a few experimental schemes utilizing high-intense ($\sim10^{22}$W/cm$^2$) laser-plasma interactions to observe the LBW process have been proposed. However, a high level of signal-to-noise-ratio are expected in these schemes, hindering the first-ever experimental detection of the LBW process by real photons. In this paper, we present a simple experimental setup which could enhance the expected positron signals by 2-3 orders of magnitude compared to previously proposed schemes, reaching the level of $10^{6}$MeV$^{-1}$str$^{-1}$. Moreover, such high positron signal is achieve in the direction opposite to the laser propagation, where a significantly quieter background is expected compared to the previously focused direction of laser propagation. The key to achieve this result is a newly discovered self-organized positron reorienting and pinching mechanism, enabled by the in-situ strong plasma fields from the laser-plasma interaction.
Xuanyu Chen, Bihao Xu, Bo Zeng, Ze Li, Zhaonian Zhang, Hanghang Ma, Guobo Zhang, Xiaohu Yang, Yan-Yun Ma, Jie Zhang
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 being 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.
Dongchi Cai, Zheng Gong, Guanqi Qiu, Deji Liu, Yinren Shou, Xueqing Yan
We develop a theoretical model for self-generated magnetic islands in relativistic laser-driven channels in near-critical-density plasmas. The islands arise from the nonlinear superposition of the quasi-static magnetic fields generated by the longitudinal channel current $j_x$ and the laser-front driven transverse current $j_y$. By deriving the critical conditions among laser depletion, transversely symmetric channel formation, and magnetic-island formation, we identify the laser-plasma parameter window in which the magnetic island structures can exist. Within this window, the balance between the laser ponderomotive force and the charge-separation force, expressed through an effec tive electron density $n_\mathrm{eff}$, determines the transverse island width $H$, whereas the mismatch between the laser group and phase velocities determines the longitudinal period $L$. Large-scale particle-in-cell simulations over a broad range of laser intensities and plasma densities validate the resulting scaling laws. The model turns the island geometry from a qualitative feature of the channel field into a predictable quantity, providing a basis for tailoring electron transport, particle acceleration, high-energy radiation, and novel fusion ignition schemes in relativistic laser-plasma interactions.
J. Y. Hua, X. F. Li, J. X. Wang, Y. X. Leng, Y. Tian, R. X. Li
The effect of stopping power on proton-boron fusion is investigated for a proton beam propagating through boron plasma. Due to the stopping power, the electron temperature of the boron target rises as the proton beam deposits energy. Consequently, a feedback mechanism becomes significant when the trailing part of the beam propagates into the preheated plasma. By coupling this phenomenon with the proton-boron fusion process, fusion yields are systematically investigated by varying the central energy of the proton beam, as well as the thickness and density of the boron target. It is found that, under the influence of stopping power, the optimal central energy for fusion deviates from the intrinsic 672 keV resonance and shifts to approximately 900 keV. Moreover, the present results are substantiated by particle-in-cell simulations, which provides a valuable reference for subsequent high-yield hydrogen-boron fusion.
A. Mohapatra, E. C. Hansen, A. Reyes, A. F. A. Bott, E. G. Blackman, P. Tzeferacos
The origin of magnetic fields in turbulent astrophysical systems has long been a central problem in plasma astrophysics. Fluctuation dynamos are a class of field amplification mechanisms that occur in turbulent magnetohydrodynamics whereby stochastically forced motions of plasma at sufficiently high magnetic Reynolds numbers exponentially amplify magnetic energy. For steady forcing, such dynamos saturate with magnetic energies at a sizable fraction of the turbulent kinetic energy. Although fluctuation dynamo is widely studied within the framework of resistive magnetohydrodynamics (MHD) and driven-turbulence numerical simulations, this work explores the difference when the Hall term is included in the magneto-fluid's generalized Ohm's law. The inclusion is motivated in part by recent high energy-density plasma experiments studying fluctuation dynamo that are governed by an extended magnetohydrodynamics (xMHD) ansatz, which includes the Hall term. We first discuss the details of the Hall-MHD implementation in the FLASH code, the tool we use to model xMHD fluctuation dynamo. We then investigate the influence of the Hall term on the fluctuation dynamo in a three-dimensional periodic box, driven with stochastic forcing at the box scale. We compare cases with a Hall term of varying magnitude to no-Hall cases with respect to the magnetic field growth rate, saturation level, and magnetic field structure. The Hall-MHD fluctuation dynamo is found to saturate at lower magnetic energies and with fewer small-scale magnetic structures than the no-Hall cases. Both findings are consistent with the interpretation that the Hall term acts as an additional, non-linear transport term, akin to an enhanced turbulent diffusivity.
Zhi-Yu Lei, Zheng-Ming Sheng, Su-Ming Weng, Min Chen, Jie Zhang
Light amplification via Raman scattering in plasma has been severely constrained by stringent phase matching conditions and the need for plasma uniformity. To overcome these limitations, we propose a forward Raman amplification scheme that employs a positively chirped seed pulse co-propagating with a pump pulse in a nonuniform plasma with an upramp density profile. We demonstrate that the phase detuning induced by plasma nonuniformity can be dynamically compensated, enabling broadband amplification across the entire spectral bandwidth of the seed pulse. Concurrently, the chirped pulse duration undergoes continuous compression as a result of the spatially varying dispersion of the plasma. Our theoretical model, incorporating the detuning term and supported by particle-in-cell simulations, elucidates the compensation mechanism. It is shown that a chirped seed pulse with an initial bandwidth ~10% can be directly amplified by a factor of 1e7 to an intensity exceeding 1e17W/cm2 within a picosecond timescale in a steep density ramp. This scheme establishes a new foundation for advancing plasma-based light amplification toward practical applications.
Thomas Kluge, Uwe Hernandez Acosta, Klaus Steiniger, Ulrich Schramm, Thomas E. Cowan
We present an analytical and numerical study of how Doppler-induced spectral broadening in laser-heated plasmas degrades the coherence of small-angle x-ray scattering (SAXS) signals and show that the resulting loss of temporal coherence reduces the SAXS intensity. Applying this formalism to two benchmark geometries—single density steps (wires) and periodic gratings—we obtain analytic estimates. For gratings, finite coherence simultaneously lowers Bragg-peak heights and broadens their widths, whereas for isolated steps only the overall scaling with q is affected. We map the parameter space relevant to current self-amplified spontaneous emission (SASE) and self-seeded x-ray free electron lasers, revealing that Doppler effects remain manageable for the retrieval of geometry parameters (less than few 10% error) for SASE bandwidths but become the dominant error source in seeded configurations or above-keV temperatures. Practical consequences for density-gradient retrieval and interface-sharpness measurements are quantified. The results supply clear criteria for when Doppler broadening must be included in SAXS data analysis and offer a route to infer electron temperature directly from coherence-loss signatures.
A. Sam, F. Garcia-Rubio, S. Davidson, C. L. Ellison, J. Hamilton, R. Lau, N. Meezan, A. Reyes, P. Schmit, A. L. Velikovich
Magnetized liner inertial fusion (MagLIF) operates in a regime where anisotropic transport phenomena fundamentally influence implosion dynamics. In strongly magnetized plasmas, the viscous stress tensor becomes highly anisotropic, yet no prior work has incorporated or examined magnetized viscosity effects in MagLIF configurations. We present the first implementation of the full Braginskii magnetized viscosity tensor for arbitrary magnetic field orientations in the Pacific Fusion branch of FLASH. The implementation is verified through analytical comparisons, direct verification against Braginskii's original formulation, method of manufactured solutions, and against analytical shock solutions. Application to MagLIF-relevant configurations reveals that viscosity damps vortical structures, converts kinetic energy in those vortical structures into thermal energy, and mitigates the Rayleigh–Taylor instabilities. Simulations with seeded perturbations and alpha heating demonstrate higher fusion yields when viscosity is included. These results establish magnetized viscosity as a non-negligible physical mechanism in ignition-scale MagLIF configurations and provide a validated capability for predictive modeling of magnetized high-energy-density plasmas.
V. N. Goncharov, D. Cao, T. J. B. Collins, R. C. Shah, A. Shvydky
Pressure in the central hot-spot region plays a key role in determining ignition conditions in inertial confinement fusion implosions. This paper investigates the evolution of hot-spot pressure during the deceleration phase. Mass ablation from the inner shell surface increases the hot-spot size, causing the pressure phs to rise faster with hot-spot convergence than predicted by the adiabatic scaling ∼Rhs−5, where Rhs is the hot-spot radius. In contrast, radiation cooling reduces phs. By analyzing the balance between radiation and mass ablation, we relate the maximum phs, relative to the adiabatic scaling, to the hot-spot properties. Beyond the well-established role of bringing most of the fuel mass into the hot spot, mass ablation increases the peak pressure by approximately 60% relative to rigid-piston compression to the same final volume, an effect that has not been included in previous studies. In addition, in hydrodynamically scaled designs, where pressure and temperature are held constant, the pressure reduction due to radiation losses changes with the size as eΠ, where Π∼Rhs0.8. Therefore, neglecting radiation losses when scaling inertial confinement fusion performance to larger systems can lead to overly optimistic projections.
Yuanjie Huang, Guobin Fan
Ionization potential depression (IPD) plays an essential role in describing ionization in plasmas. Traditional models like Ecker–Kröll and Stewart–Pyatt relied on screening effects, yet they still fail to adequately interpret the spectroscopic data from the laser-irradiated plasmas. To bridge this gap, we introduce a novel IPD model and the concept of mechanical-electric coupling (MEC) in plasmas. MEC critically influences the electron diffusion, Debye screening, and the electron pressure. Unlike conventional approaches, our IPD model is derived from the downward shift in potential energy of ionized electrons instead of the screening effect. It aligns closely with the spectroscopy and measured IPD values. MEC and the IPD framework provide a foundation for an equation of state that matches the experimental observations. This study offers fresh insight into the plasma ionization and properties, offering a framework for predicting ionization balance and equation of state in dense, non-degenerate plasmas.
B. G. Repin, A. P. Orlov, M. Sh. Ibragimov, A. A. Agapov, P. B. Repin, A. V. Filippov, I. M. Markevtsev, S. Yu. Kornilov, P. I. Golyakov, D. S. Pokrovskiy, et al.
For several years, RFNC-VNIIEF has been conducting research on the generation of powerful soft x-ray (SXR) pulses during the stagnation of multi-wire cylindrical array systems powered by microsecond current pulses from both explosive and stationary current sources. In recent experiments generating the aluminum K-line using a helical explosive magnetic generator (EMG) with a 200 mm helix diameter, equipped with an explosive opening switch, the SXR pulse energy in the full spectrum reaches 70.4 kJ, and in the quantum energy range above 1 keV, it reaches 25.7 kJ, which is approximately 36% of the total radiation energy. The current pulse amplitude in the load is ∼5 MA, and the implosion time is ∼0.75–1 μs. The realized efficiency of the radiation generation with quantum energy above 1 keV is comparable with the best results obtained in the world's pulsed power installations with aluminum multi-wire loads. This paper presents the main results of the experimental studies conducted, as well as scaling calculations using the radiation magneto-hydrodynamic FLUX-rz and FLUX-3D codes to optimize the aluminum K-line generation for various load configurations powered by the helical EMG.
C. D. Decker, C. J. Bruulsema, W. A. Farmer, J. Harte, D. P. Higginson, A. J. Kemp, W. Riedel, J. S. Ross, D. J. Strozzi, G. Zimmerman
We examine the validity of a multi-species 13-moment fluid approach to modeling hohlraum wall expansion occurring in inertial confinement fusion targets used at the National Ignition Facility. We compare our simulation to experiments conducted at the Omega laser facility [Pape et al., Phys. Rev. Lett. 124, 025003 (2020)], which produced counter-propagating gold–carbon plasmas, a phenomenon arising during hohlraum wall expansion. The two experiments we use to benchmark this fluid model produced counter-propagating gold–carbon plasmas in (1) vacuum and (2) a helium atmosphere. We find that simulations using this advanced fluid model replicate certain aspects of the vacuum experiment, such as material interpenetration, and distinct anisotropic gold and carbon ion temperatures are not captured with single-species lower-moment fluid models. However, our simulations underpredict the temperature of scarce gold ions that penetrate deep into the carbon—a phenomenon potentially requiring a kinetic treatment to model. When applied to the helium gas filled experiment, this advanced fluid model matches the amount of material mixing and gold stagnation point but overpredicts ion temperatures in the gold. Finally, we examine the applicability of single fluid models (as well as lower-order multi-species models) by comparing simulated plasma quantities vs the helium gas-fill density. As expected, we find the models converge as the helium gas density is increased. We find that for gas-fill densities larger than 0.6 mg/cm3 the single fluid model gives similar bulk plasma densities and temperatures as the multi-fluid 13-moment model. However, for gas-fill densities lower than 1.0 mg/cm3, simulations show substantial low-z material mixing in the gold—requiring multi-species modeling. Moreover, accurately modeling the low-z mixing to within 30% requires the full multi-species 13-moment fluid model.
Xinyu Xie, Fengyu Sun, Huai-Hang Song, Wei-Min Wang, Wenpeng Wang
Attosecond, collimated, bright, polarized $γ$-ray sources are in high demand across nuclear physics, astrophysics, and high-energy physics. However, realizing attosecond duration, high collimation, high brilliance, and high polarization simultaneously within a single isolated source remains an outstanding challenge, owing to the inherent trade-offs between beam trapping and radiative dynamics. Here, we propose a novel scheme to generate an isolated, collimated, high-brilliance, polarized attosecond $γ$-ray beam from conventional solid foils irradiated by a linearly polarized spatiotemporal optical vortex (STOV) laser pulse accessible in Lab. Three-dimensional spin-resolved particle-in-cell simulations reveal that this relativistic-intensity STOV pulse can trap and accelerate electrons at its spatiotemporal singularity, producing a compact isolated electron bunch. This electron bunch subsequently undergoes head-on collision with the reflected laser pulse, which generates isolated $γ$-ray beams through nonlinear Compton scattering. With a peak intensity of $7\times10^{21}$ W/cm$^2$, we observe an isolated collimated ($\sim1.5^{\circ}$) $γ$-ray beam with an average linear polarization of $>60\%$ and a duration of $\sim$500 attoseconds. This approach is feasible with current or upcoming laser facilities and robust against variations in laser and target parameters, highlighting the capability of spatiotemporal structured light field modulation to address outstanding problems in plasma physics.
Yao Guo, Dong Wu, Jie Zhang
Traditionally, fusion reactivity in thermonuclear plasmas has been calculated by assuming a local Maxwellian ion distribution. However, recent theoretical work [Phys. Rev. Lett. 135, 155101 (2025)] suggests that turbulence in plasmas can generate non-Maxwellian tail distributions, thereby enhancing reactivity. In this paper, we investigate this effect through numerical simulations of a sinusoidal shear flow. By comparing steady-state distributions obtained with the Bhatnagar-Gross-Krook (BGK) and Fokker-Planck (FP) collision operators, respectively, we demonstrate that the BGK model overestimates the reactivity enhancement while the FP operator gives a much more modest enhancement that is nearly halved under typical ICF parameters. Particle-in-cell (PIC) simulations incorporating nuclear reactions are also conducted, which reveal that the combined effects of preferential ion heating during shear flow dissipation and tail enhancement can even amplify the reactivity enhancement to be larger than the steady-state prediction.
Jun-Yi Lu, Kai Wang, Jinlong Jiao
The formation of ion-Weibel-mediated collisionless shocks (IW-CSs) in ultraintense-laser-produced counter-streaming plasmas is investigated using particle-in-cell simulations. Analysis of the underlying microphysics reveals that a shear-flow ion-Weibel instability generates magnetic fields, which isotropize the incoming flow and mediate shock formation. An analytical expression for the shearflow magnetic field is derived, and a scaling law relating the magnetic field amplitude to the laser intensity is established. The shock formation time and the required laser energy are reduced by three and two orders of magnitude, respectively, compared to high-power laser experiments, making it feasible to produce IW-CSs using existing multi-kilojoule, picosecond ultraintense laser facilities.
Yudong Pu, Chuankui Sun, Fengjun Ge, Jiwei Li, Tao Gong, Weiming Yang, Zhebin Wang, Qi Li, Kai Wang, Xiaobo Qi, et al.
The technique of indirect-drive cryogenic pure deuterium layered implosion is unique among published works in the research of inertial confinement fusion. After its feasibility was demonstrated recently, we proceeded to improve the implosion performance by using a 2-shock shaped pulse. The target design was evolved from an ignition target design with modifications compatible with current energy scale. The radiation uniformity was confirmed by the dual-axis keyhole targets and cryogenic gas-filled targets. The adiabat of the fuel was controlled by tuning shocks to emerge at the ice-gas interface. The implosion performance of the layered targets were then investigated. The pure deuterium layers of good quality were maintained for a few minutes. The lasers were fired during the survival time of such layer quality. The resulting neutron yield was 9.6×1010, and the hotspot pressure was 30Gbar. Radiative hydrodynamic simulations were carried out using as-shot target and laser parameters, and compared with the experimental measurements. The yield of clean was about 19%. The residual radiation non-uniformity alone cannot explain the observed performance degradation. The hydrodynamic instabilities seeded by ice roughness should play a role in decreasing the hotspot clean volume.
Xichen Zhou, Ning Kang, Huiya Liu, Jiyan Zhang, Ruirong Wang, Guoxiao Xu, Lin Yi, Jian Wang, Honghai An, Jun Xiong, et al.
For laser-driven inertial confinement fusion, implosion performance depends critically on the efficiency of laser energy coupling to mass ablation. Although recent experiments have confirmed that broadband lasers improve energy absorption efficiency by mitigating stimulated Brillouin scattering, evidence for a corresponding increase in mass ablation rate has remained absent. In this paper, we present the first experimental evidence that a broadband laser (0.6% fractional bandwidth) drives a higher mass ablation rate than a narrowband laser on planar titanium foils. Under matched laser intensity, the foil thickness that maximizes the Ti He‑α X-ray yield—the optimal thickness—shifts from ~10 μm for the narrowband case to ~15 μm for the broadband case. Simulations relating optimal thickness to mass ablation rate show that this shift corresponds to an approximately (50 ± 26)% enhancement in mass ablation rate. Analysis suggests that, in addition to the improved laser absorption, the greater nonlocal thermal transport induced by the enhanced hot electron yield from broadband lasers may contribute to this ablation enhancement. These findings provide evidence that a broadband laser can markedly enhance mass ablation, supporting its use as a practical route toward better implosion performance in inertial confinement fusion.
I. Cohen, I. Slabu, Q. Peysson, S. Dorard, Y. Abe, J. Béard, T. Moraine, S. N. Chen, A. Chessa, K. Iida, et al.
We have developed a compact passive energy-selector for MeV-range electrons produced by irradiating solid targets by ultra-intense short-pulse lasers. The device allows for generating electron beams with a variable energy spread over a broad range of energies, from tens of keV to tens of MeV. Here we have demonstrated its use by producing electrons from solid targets in the MeV range and with a ~10% bandwidth, thereby compensating the intrinsic broadband nature of the electrons produced from such source. Coupled with a pulsed magnetic field to further compensate the intrinsic large divergence of this source, it allows to produce a highly-collimated beam of narrow-band and ultra-fast electrons, suitable for a wide range of applications, e.g. radiation therapy or time-resolved electron probing.
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