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Francisco Ogando, Robert Earley, Wayne Meier, Rene Raffray, Patrick Sauvan, Jaime Marian, Susana Reyes, Conner Galloway
Xcimer Energy Corporation, Universidad Nacional de Educación a Distancia (UNED), Lawrence Livermore National Laboratory, University of California, University of California Los Angeles
T. Cordova, E. V. Marley, D. A. Chin, R. A. London, S. B. Hansen, S. M. Vinko, J. E. Pask, H. A. Scott, H. P. Le, D. Aberg, et al.
Warm dense matter remains a challenging regime to characterize experimentally and to model with predictive accuracy. Recent experimental platforms have been developed to generate, characterize, and diagnose uniform warm dense matter, enabling detailed comparisons with models. Here, we present experiments conducted at the OMEGA laser facility that compress and heat a buried layer target to warm dense matter conditions, where the targets are heated to temperatures of approximately 20 eV and compressed to densities of 25 g/cm^3. We probe the warm dense plasma using x-ray absorption spectroscopy, using the K-edge and bound-bound absorption features to constrain the temperature and charge state distribution of the plasma. We compare these measurements with two types of models: collisional-radiative models with detailed electronic structure and ad-hoc density effects, and a multi-ion model based on density functional theory in combination with excited-state projector augmented-wave potentials. Neither approach fully reproduces the observed data, We show that the broad structure and position of the K-edge region can be modeled using density functional theory in combination with excited-state projector augmented-wave potentials. The density functional theory results are contrasted with a collisional-radiative model approach that incorporates ad-hoc density effects, which show incomplete agreement with the experimental observations, highlighting a need for improved density-dependent atomic modeling in warm dense plasmas.
Lei Zhang, Feng Wang, Zanyang Guan, Yu Long Li, Xin Yulong, Xi Wang, Miao Li, Xinru Zhang, Huaquan Gan
China Academy of Engineering Physics, Chongqing University of Posts and Telecommunications, Guangdong University of Technology
The temporal evolution of shock wave velocity encodes critical physical information in inertial confinement fusion (ICF) experiments. Integrating a line-imaging velocity interferometer system for any reflector (VISAR) with compressed ultrafast photography (CUP), the resulting CUP-VISAR technique enables promising high spatiotemporal resolution two-dimensional (2D) measurement of continuous shock waves. However, reconstructing time-varying 2D fringe patterns from single-shot, highly underdetermined compressed sampling remains a formidable challenge. To improve reconstruction accuracy of continuous 2D shock wave velocity fields, this work proposes two technical enhancement strategies. First, a deep unfolding network reconstruction scheme for conventional CUP: adopting a hybrid data-and-model-driven approach, it deploys a trainable deep network as a denoiser to capture inherent spatiotemporal correlations in fringe patterns, markedly improving both fringe reconstruction efficiency and velocity field accuracy. Second, a novel integral-camera-based CUP architecture: unlike the conventional coded-aperture/streak-camera configuration, it acquires signals directly via an integral camera, with fringe reconstruction implemented by mixed integer programming guided by discrete phase-space constraints and interference fringe priors, simplifying system structure and enhancing noise robustness. Both schemes effectively improve compressed fringe reconstruction quality and reduce velocity field reconstruction errors, providing more accurate and reliable data support for ICF diagnostic analysis.
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.
Rishi Pillai, Debashish Sur, Severine Cambier, Adam Willoughby, Tracie Lowe, Youyang Zhao, Amanda Bye, Susana Reyes
Oak Ridge National Laboratory, XCIMER Energy Corporation
Vitalia A. Kuleshova, Artem V. Korzhimanov
Within the framework of a stationary model of relativistic self-focusing, it is shown that the addition of a thin layer of denser plasma on the propagation axis of a circularly polarized beam increases the axial magnetic field generated by it via the inverse Faraday effect by more than a factor of 10 compared to the case of a homogeneous plasma. The magnitude of the axial field in this case can exceed the magnetic field of the laser wave, which makes it possible, at radiation intensities $\sim 10^{26}$~W/cm$^2$ potentially achievable in the near future, to approach the level of teragauss quasi-stationary fields.
Jiyuan Chen, Jihoon Kim, Roopendra Singh Rajawat, Gennady Shvets
Compact heavy ion accelerators have numerous applications, ranging from heavy ion fusion to carbon ion radiotherapy, and testing radiation-hardened electronics. The demand could be met by developing high-gradient traveling wave plasma accelerators of high-charge ($\simμ\mathrm{C}$) relativistic ion beams. We will discuss a novel ion acceleration regime -- Counter-propagating ionization Front Acceleration (CFA) -- utilizing counter-propagating Ionization Front (IF) and high-current Relativistic Electron Beam (REB). Theoretical modeling and 3D PIC simulations demonstrate the possibility of using typical REBs produced by induction voltage adders propagating through a gas-filled tube undergoing laser ionization to achieve acceleration gradients in excess of $\sim 250 {\rm MeV/m}$ while accelerating micro-Coulombs of ions over meters distance. A unique energy conversion mechanism -- from the REB to electromagnetic fields to the ions is discussed, as well as the limits on the accelerated ions charge and the degree of its neutralization, acceleration gradient, and ion energy spread.
S. Hilsabeck, S. Dannhoff, C. A. Walsh, M. Sherlock, G. D. Sutcliffe, E. R. Tubman
Experiments at the OMEGA EP laser facility were designed and executed to study plasma expansion into hohlraum-relevant gas fills (0.3-0.6 mg/cc of helium), providing a surrogate platform for investigating hohlraum wall blow-off, non-local transport, and magnetized plasma effects. We observe well-defined density features and filamentary structures as laser-driven copper plasma expands into a low-Z background gas. Shadowgraphy resolves sharp density features over time and reveals fine-scale filamentation in the laser spot region with characteristic transverse scales of 10-100 microns near the foil surface. Proton radiography provides sensitivity to path-integrated magnetic fields and density modulations throughout the bubble volume. We extract the bubble expansion as a function of time for two gas pressures, 350 psi (producing 0.3 mg/cc equivalent conditions) and 700 psi (0.6 mg/cc equivalent conditions), and compare the measured propagation to magnetohydrodynamic simulations performed with Gorgon and HYDRA. While the large-scale shape of the bubble is well reproduced by both codes, the time-dependent expansion rate shows significant discrepancies (20-50% faster) compared to experimental observations between 1 and 3 ns. This leads to increasingly larger differences in bubble sizes at later times. The optical measurements of bubble expansion and evolution of small-scale structures point to additional constraints required for Biermann-battery field generation, thermal transport, and instability growth in hohlraum-relevant plasmas, to ensure accurate, predictive modeling of gas-filled hohlraums.
CHRISTOS KARVOUNIS, Alexandros Skoulakis, Ioannis Tazes, Christos Vlachos, John Chatzakis, Evaggelos Kaselouris, Vasilis Menelaos Dimitriou, Nektarios Andrea Papadogiannis, Michael Tatarakis, Ioannis Fitilis
Hellenic Mediterranean University
This paper presents a detailed 2D resistive magnetohydrodynamic (MHD) study of a miniature deuterium-filled plasma focus (PF) device using the FLASH code. The simulations capture the full plasma evolution, from initial breakdown ("cold start") to pinch compression and disruption. A novel contribution is the implementation of a dynamic magnetic-field updating algorithm which tracks the evolving plasma sheath and self-consistently reconstructs the return-current path, including skin-effect corrections. To overcome limitations of optical probing diagnostics, an inhouse developed ray-tracing post-processing tool generates synthetic shadowgrams directly derived from the simulated plasma parameters validating the proposed modeling approach. Numerical results -including plasma density, velocity, current density, magnetic fields, and ion/electron temperatures -show strong agreement with experimental data from a 600 J (~80 kA) miniature PF device. This validation demonstrates the capability of FLASH to provide highfidelity physical insights into dense plasma focus dynamics.
Xian Jiang, Shenming Xu, Dehua Zhang, Tao Tao, Jingfei Xin, Rui Yan, Hang Ding, Jian Zheng
University of Science and Technology of China, BYD Automobile Industry Co. Ltd
Two-dimensional two-mode couplings of the ablative Rayleigh-Taylor instability (ARTI) under inertial-confinement-fusion (ICF) relevant parameters are revisited via numerical simulations, with a focus on the regimes where the wavenumbers of the initial modes are close to the cutoff wavenumber. In the quasi-linear stage in which the generated modes approximately grow exponentially with time, both the self-growth of the generated mode (as if in the single-mode regime) and the driven-growth due to mode couplings are found to be important. A series of linearly unstable modes are found to be generated by coupling of two linearly stable initial modes, and then compete for the dominant mode according to a proposed criterion. A model including the contribution of both the self-growth and the driven-growth with an empirically modified coupling coefficient is proposed and shown to accurately predict the growth of the generated mode. The findings have implications for assessing the impact of ARTI in ICF designs.
Tomoyuki Johzaki, HIdeo Nagatomo, Yasuhiko Sentoku, Shinsuke Fujioka
The University of Osaka, Hiroshima University
The burn characteristics of multi-shock-compressed DT fuel under fast ignition conditions are investigated using two-dimensional burn simulations. In solid-sphere implosions, high fuel areal density can be achieved through multi-shock compression with reduced susceptibility to hydrodynamic instabilities. However, the resulting compressed-fuel density structure is highly nonuniform, consisting of a localized high-density core surrounded by a low-density fuel region that contains most of the fuel mass. In such a configuration, ignition can be initiated in the central high-density core, but the burn wave rapidly attenuates as it propagates into the surrounding low-density region, preventing self-sustained burn propagation. Consequently, the burn-up ratio is significantly lower than that of uniformly compressed fuel with comparable total fuel areal density. By examining the effects of implosion timing and artificially modified surrounding-density profiles, we show that the burn-up ratio is governed not only by the total fuel areal density, but also by the density structure around the ignition region. These results indicate that achieving a high burn-up ratio requires a sufficiently dense fuel region along the burn-wave propagation path, rather than a localized high-density core alone.
M. I. Nayeem, M. A. Malek
Khulna University, International University of Business Agriculture and Technology (IUBAT)
Dongxue Liu, Jiaqin Dong, Yunxing Liu, Zhiyu HE He, Wei Wang, Yuqiu Gu, Xiuguang Huang, Jian Zheng
China Academy of Engineering Physics Shanghai Institute of Laser Plasma, China University of Mining and Technology, University of Science and Technology of China
To quantify the sensitivity of diverse implosion designs to laser imprinting, we developed an equivalent perturbation model that maps laser imprinting as the initial target surface perturbation. By incorporating imperfections in target fabrication and thermal smoothing in the plasma, the model shows a reduced implosion sensitivity to laser imprinting, extending the analysis beyond geometric irradiation. The imprinting sensitivity threshold is defined as δh_{proxy}/δh{tar}(0)= 0.1, where δh_{proxy} is the imprinting amplitude and δh{tar}(0) is the initial target perturbation amplitude. Radiation-hydrodynamics simulations confirm that whenδh_{proxy}/δh{tar}(0)< 0.1, variations in nonlinear onset time and adiabat remain within 12\% of that with δh{tar}(0) alone. Moreover, the imprinting sensitivity is supported by OMEGA experiments. Overall, for linear perturbations of medium-to-high modes in direct-drive, the model enhances our physical understanding of how laser and target perturbations evolve and serves as a simplified tool to optimize implosion performance.
Gwilym T. Jones, David Goude, Ibrahim Gungen, David R. Sory, Philip Leichauer, Nicholas Hawker
First Light Fusion Ltd
Srinivasagopalan Madhavan, Aaditya Majalee, Vinayak Mishra, Rohit Shukla, Rishi Verma, Shashank Chaturvedi
Bhabha Atomic Research Centre
Jonathan D. Zuegel, Antonino Di Piazza, Karl M. Krushelnick, Daniele Margarone
University of Rochester, University of Michigan, The Extreme Light Infrastructure ERIC
The mini-conference on Multi-Petawatt Physics at New and Future Laser User Facilities, held at the 2024 Annual Meeting of the American Physical Society Division of Plasma Physics, updated worldwide progress at the frontier of multi-petawatt physics, including theoretical, computational, experimental, and technical advances.
A. J. Kemp, T. Chapman, L. Divol, D. P. Higginson, E. Kur, N. Lemos, S. MacLaren, P. Michel, D. J. Strozzi, G. B. Zimmerman
Lawrence Livermore National Laboratory
We report progress modeling stimulated Brillouin scatter (SBS) at the National Ignition Facility (NIF). For indirect-drive, ignition-relevant hohlraum experiments, backward SBS light is a long-standing concern due to its potential for damaging laser optics as well as affecting the symmetry of the x-ray field that drives capsule implosions. To model SBS, we use maps of underdense plasma conditions, i.e., temperatures, densities, materials, charge states, and flows, from hydrodynamics simulations of the hohlraum to run backscatter simulations with the code pF3D [Berger et al., Phys. Plasmas 26, 012709 (2019)]; the latter calculates propagation of incident- and backscattered light of a NIF quad in the paraxial approximation. For the inner cone quads, in designs that utilize significant wavelength detuning, i.e., those that use cross-beam energy transfer to control implosion symmetry, this approach typically has overestimated both the peak power and the duration of SBS measured in experiments. In this work, we discuss how multi-species hydrodynamics simulations can lead to better agreement with experiments through changes to the simulated plasma conditions and the resulting SBS growth rates. Specifically, we discuss SBS reflectivity in the 23° and 30° inner cone quads, compare simulated spectra to FABS measured ones, and discuss how the time history of the backscattered light is related to the absorption/refraction of the incoming light off density features in the hohlraum plasma.
Hannah M. Bellenbaum, Dave A. Chapman, Maximilian P. Böhme, Thomas Gawne, Sebastian Schwalbe, Willow M. Martin, Michael Bussmann, Dirk O. Gericke, Uwe Hernandez Acosta, Jan Vorberger, et al.
Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Center for Advanced Systems Understanding (CASUS), Stanford University, Universität Rostock, First Light Fusion Ltd.
X-ray Thomson scattering (XRTS) is a common diagnostic used in the warm dense matter (WDM) regime to estimate plasma parameters like density, temperature, and charge state. Experimental analysis typically relies on a forward model to obtain estimates for these parameters, as the measured spectrum is a convolution of the dynamic structure factor (DSF) and the source-instrument function. The Chihara decomposition, where the spectrum is separated into contributions from bound and free electrons, is commonly used to estimate DSFs in the WDM regime, as it allows for the fast calculation of DSFs and therefore can easily be applied in a large-scale parameter optimization. Due to the limited availability of XRTS codes, we present “x-ray diagnostics, analysis, verification, and exploration”, a code designed to quickly estimate DSFs using the Chihara decomposition and analyze experimental spectra. The code is validated by re-analyzing an experiment with isochorically heated beryllium at the OMEGA Laser Facility. In addition, we demonstrate the applicability of the code to plan experiments and predict scattering spectra through the coupling to a ray-tracing code. Finally, the importance of accounting for the energy-dependence of spectrometer instrument functions is demonstrated by comparing ray-tracing simulations to the standard convolution for strongly compressed beryllium experiments at the National Ignition Facility, similar to previously published results.
D. Patel, R. Betti, V. Gopalaswamy, A. Lees, D. Cao, R. C. Shah
University of Rochester
A fundamental question in inertial confinement fusion is how implosion performance, and therefore ignition thresholds and fusion gain, evolve with target size. In laser-driven direct drive fusion, the scaling of laser-drive performance with size is critical to this evolution and to extrapolating results from the 30-kJ OMEGA laser-fusion experiments to ignition-class facilities such as the National Ignition Facility. Beyond the well-known adverse effects of cross-beam energy transfer (CBET) on drive performance, here we demonstrate that effects related to the non-scaling physics of thermal conduction and electron–ion energy equilibration exert an influence on drive behavior with scale that equals or surpasses that of CBET. We find that a significant portion of the lost implosion performance with increasing scale is due to the loss of shell implosion velocity. Furthermore, we show that while modest modifications to hydro-scaled designs can recover most of the lost implosion velocity, a full hydro-equivalent performance extrapolation is difficult to achieve without CBET mitigation or subcooling below the triple point of DT.
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