Recent Publications

Design of low-entropy compression experiment using uranium ion beam generated by the existing GSI accelerator SIS18

Naeem A Tahir, Z Major, S A Piriz, Paul Neumayer, Antonio Roberto Piriz, Vincent Bagnoud

In this paper, we present 2D hydrodynamic simulations of implosion of a multi-layered disc shaped target, that is driven by an intense uranium beam, which matches the parameters of the currently available beam at the GSI heavy ion synchrotron, SIS18. The purpose of these simulations is to assess the feasibility of a LAPLAS type implosion experiment, at the SIS18 accelerator facility. The target is comprised of a carbon sample that is enclosed in a tungsten ring. One face of the target is irradiated with the SIS18 beam, that has a circular focal spot, while the particle energy is 400 MeV/u. The thickness of the target is chosen in such a way that the beam is completely stopped in the tungsten region, whereas, it loses part of its energy in the carbon part, and escapes from the opposite face of the target. This means that the Bragg peak lies in the outer tungsten region, while it does not lie inside the carbon sample. In such a configuration, the higher pressure generated in the Bragg peak region due to higher energy deposition, can be utilized to achieve a higher compression in the sample, below the Bragg peak region. Our simulations show that with a suitable focal spot size, the carbon sample in that region can be transformed into the diamond phase.

Optimization of room-temperature targets for laser direct-drive fusion

QianLei Du, Fuyuan Wu, Rafael Ramis, Jie Zhang

Fusion ignition is a critical milestone toward the realization of fusion energy. For laser direct-drive fusion, the cryogenic deuterium-tritium (DT) targets encounter considerable fabrication and delivery challenges, such as the survival of cryogenic targets during the injection and flight in a reactor chamber. To mitigate the cryogenic bottlenecks, we explore the potential of room-temperature solid targets composed of low-Z elements and hydrogen isotopes via machine-learning optimization. In this work, a multi-fuel module is developed with the one-dimensional hydrodynamics code (MULTI-IFE) to simulate multiple room-temperature fuels. By optimizing the target structure and laser waveform parameters, a calculated fusion energy gain of 10.18 can be achieved with 2.35 MJ of laser energy, despite the additional radiative and conductive losses that may arise from the low-Z ions in the room-temperature target. A thicker target driven by a laser energy of 9.4 MJ is able to produce 109.7 MJ fusion energy with a maximum in-flight-aspect-ratio (IFAR) smaller than 17. During the fusion burning, tritium breeding via neutron–lithium reactions increases the fusion energy output for the LiBD₂T₂ target by 5.2%. This work provides a reference for the ongoing development of direct-drive repetition-rate laser fusion energy.

Beam filamentation instability drives deuterium-tritium fusion with polarized neutron emission

Guanqi Qiu, Deji Liu, Dongchi Cai, Ronghao Hu, Zheng Gong, Xueqing Yan

Filamentation instabilities are generally regarded as detrimental to fast-electron transport in fusion plasmas because they increase beam divergence and redistribute deposited energy. Here, we use two-dimensional particle-in-cell simulations coupled to a spin-dependent deuterium-tritium fusion module to investigate whether filamentation can instead transfer energy from counterstreaming electrons to prepolarized fusion ions. The simulations show that magnetic filaments, together with longitudinal inductive and transverse charge-separation electric fields, accelerate initially stationary deuterons and tritons to energies at which fusion reactions occur. Over the parameter range examined, the calculated neutron yield increases with the saturated magnetic-field energy. The model further predicts anisotropic, spin-resolved neutron emission. The direction of maximum neutron polarization is approximately perpendicular to the dominant deuterium-tritium collision direction and evolves with the angular distribution of the reacting ions. These results suggest that beam filamentation can couple relativistic-electron energy to fusion ions and that polarized neutron emission may provide a reaction-weighted signature of the underlying plasma dynamics.

The Richtmyer-Meshkov Instability of Thermal, Isotope, and Species Interfaces in a five-moment multi-fluid plasma

K. C. Tapinou, V. Wheatley, D. Bond, Ingo Jahn

The Richtmyer-Meshkov instability (RMI) results from the impulsive acceleration of a density interface where either it or the acceleration is perturbed. Density interfaces may arise due to a change in gas species, isotope, temperature or a combination of these. We computationally investigate the effect of interface type on the plasma RMI, which is relevant for a range of applications, including inertial confinement fusion. We simulate the evolution of single-mode perturbed thermal, species and isotope interfaces in an ideal ion-electron plasma using the multi-fluid plasma (MFP) model. We find that in the MFP model, the evolution of different types of interface differ significantly, in contrast to single-fluid models where they behave similarly if the Atwood number is matched. The thermal and species interfaces produce the most severe response to shock acceleration, experiencing the secondary instabilities and enhanced primary mode growth. The isotope interface evolution is restrained in comparison to the former cases, resembling the response predicted by single-fluid models. The determining factor in the severity of the MFP RMI is the density ratio across the initial interface in the electron fluid, which is unity for an isotope interface. We observe that as the density ratio across the electron interface decreases, so do the magnitudes of the self-generated fields and consequently the severity of the growth amplification. Generally, the evolution of the RMI with different types of interface becomes more similar as the level of coupling between the ion and electron fluids is increased, characterised by reducing the plasma non-dimensional skin depth

Imaging ablator-fuel mix of hot spot in inertial confinement fusion via resonant X-ray absorption using an X-ray free electron laser

Lingen Huang, Long Yang, Alejandro Laso Garcia, Oliver S. Humphries, Michal Šmíd, Mikhail Mishchenko, Victorien Bouffetier, Carsten Baehtz, Erik Brambrink, Samuele D. Di Dio Cafiso, et al.

A novel diagnostic is proposed for active probing of doped inertial confinement fusion (ICF) spherical shells, enabling direct measurements of mix and burn dynamics at next-generation implosion facilities via resonant absorption imaging with an X-ray free-electron laser (XFEL). The charge-state-sensitive imaging of embedded dopants provides spatiotemporally resolved constraints on ionization, opacity, and material mix seeded by hydrodynamic instabilities in stagnated plasmas. Proof-of-principle experiments demonstrating resonant XFEL probing of hot spot in coated copper wires driven by an ultra-short relativistic laser pulse, have established the feasibility of this approach. Furthermore, atomic and radiation-hydrodynamic simulations, combined with synthetic resonant X-ray absorption imaging, extend the diagnostic concept to laser-driven direct-drive ICF shells with copper-doped ablators and radiation-driven indirect-drive shells with tungsten-doped ablators. This unique approach, combining a laser-driven implosion facility with a high-brightness XFEL, could enable precise measurements of fusion-relevant hot dense plasmas at multi-keV temperatures, provide stringent benchmarks for radiation-hydrodynamics models, and advance the realization of inertial fusion energy.

Compressional heating above 1 keV on the LM26 magnetized target fusion machine

S. J. Howard, D. Krotez, P. Carle, J. Sanchez Rojo, R. Underwood, A. Froese, M. Reynolds, N. Sirmas, K. Conquergood, K. Epp, et al.

The LM26 device has achieved a peak electron temperature of $T_e = 1180 \pm 65$ eV as measured by filtered X-ray diodes, supported by adjacent Thomson scattering measurements of $T_e = 1090 \pm 40$ eV, with a deuterium ion temperature of $T_i = 459 \pm 33$ eV as inferred from neutron yield. LM26 compresses a spherical tokamak plasma inside an initially 1.76 m diameter solid lithium liner imploded by theta-pinch coils. Radial compression by a factor of 2.75 increases $T_e$ over fivefold, while $T_i$ increases as much as twofold. The integrated observation of magnetic flux compression, electron heating, ion heating, and neutron production in a magnetized plasma compressed by a large lithium liner is an important milestone for magnetized target fusion

Multi-MA fusion accelerator performance insensitivity to electrode contamination

Anonymous

An improved high-precision meshfree method for 2-D 3-T radiation diffusion equations by reducing strong nonlinearity

Yi Liu, Qiuyan Xu, Zhiyong Liu, Jiye Yang

The 2-D 3-T radiation diffusion equations are a typical strongly nonlinear partial differential equations widely applied in inertial confinement fusion, astrophysical radiative shock simulations and so on. Conventional numerical methods for such radiation equations take radiation temperature as the unknown variable, which suffer from poor iterative convergence and low numerical precision under strong nonlinear conditions. To overcome this difficulty, we propose a novel framework based on the radial basis function meshfree method, which takes radiative energy density as the primary unknown variables. Three time discretization schemes, namely the fully implicit scheme, backward differentiation formula scheme, and Crank-Nicolson scheme, are comprehensively evaluated, and the simplified Newton iteration is adopted for nonlinear solving. Numerical benchmarks verify that the framework based on radiative energy density yields better nonlinear convergence and numerical precision compared with the conventional formulation based on radiation temperature. We further conduct numerical experiments without analytical solutions, which confirm that the proposed method enables long-time simulations and performs favorably for multi-material problems.

Experimental observations of microturbulence-suppressed parallel heat conduction in a weakly collisional, high-\b{eta} plasma

T. A. Vincent, P. Ariyathilaka, L. Creaser, C. Danson, R. Davies, D. Lamb, J. Meinecke, C. A. J. Palmer, S. Pitt, H. Poole, et al.

Classical theories of heat conduction in magnetized plasma predict that thermal transport, mediated by Coulomb collisions of electrons, occurs predominantly along magnetic field lines. Recent theoretical and computational studies challenge this description for weakly collisional, magnetized plasmas in which thermal pressure dominates magnetic pressure (so-called high-\b{eta} plasmas). Such plasmas, which include the intracluster medium of galaxy clusters and inertial-confinement-fusion hot spots, are thought to be susceptible to kinetic-scale microinstabilities that can suppress parallel heat conduction. Revised theories of heat conduction accounting for these instabilities have been proposed, but experimental data with which to benchmark them are lacking. Here, we report experiments at the Orion laser facility in which the temporal evolution of temperature of a high-\b{eta}, weakly collisional plasma is sensitive primarily to the thermal conductivity along its initially quasi-laminar magnetic field. We characterize the temperature, density and magnetic field using x-ray spectroscopy and imaging, and proton imaging. Once stochastic magnetic fluctuations develop, the measured temperature evolution requires suppression of thermal conduction by at least an order of magnitude relative to classical predictions, providing the first laboratory evidence linking magnetic microturbulence with suppression of heat conduction in a high-\b{eta} plasma.

Spectral diagnosis of quantum turbulence beyond the Ehrenfest time

Leonardo P. G. De Assis

Dense quantum plasmas in white dwarfs, planetary interiors, and inertial fusion targets pose a major challenge: beyond the Ehrenfest time, classical chaos diagnostics lose meaning, yet identifying intrinsic turbulence and testing the universal scrambling bound λ≤2πkBT/ℏ remain vital. We hypothesize that in fully developed turbulence, the phase-space Liouvillian behaves as a large complex random matrix belonging to the Gaussian unitary ensemble (GUE) class. The central diagnostic, the connected spectral form factor (SFF) of the Liouvillian's normal operator, takes the parameter-free GUE form: Kconn(τ)=τ for 0<τ≤1 and Kconn(τ)=1 for τ>1. We show how this SFF can be extracted from temporal correlations in the dynamic structure factor measured by x-ray Thomson scattering, and outline a numerical implementation using the kernel polynomial method. The synthetic GUE and Poisson benchmarks validate the numerical pipeline, and the quantum Zakharov equations surrogate displays GUE-like local spectral statistics in the post-Ehrenfest regime. Crucially, the connected SFF does not display a resolved universal ramp under the tested parameters. We, therefore, present the connected SFF as an exploratory, highly sensitive diagnostic of long-range universality, demonstrating the framework's capacity to distinguish partial spectral mixing from full random-matrix rigidity in physical surrogates.

Single-laser scheme for reaching strong field QED regime via direct laser acceleration

Robert Babjak, Marija Vranić

We investigate a single-laser scheme for reaching the strong-field QED regime based on direct laser acceleration (DLA) of electrons followed by their head-on collision with the same laser pulse reflected from an overdense foil. In this configuration, electrons are first accelerated inside an underdense plasma by a relativistic laser pulse and subsequently interact with the reflected laser field, emitting high-energy photons via nonlinear Compton scattering which are transformed into electron–positron pairs through the nonlinear Breit–Wheeler process. Using analytical scalings supported by quasi-3D particle-in-cell simulations including QED effects, we demonstrate that a laser pulse with power as low as 2 PW is sufficient to reach the quantum regime characterized by χe > 1. For higher powers, we observe a rapid nonlinear increase in the number of generated positrons, reaching more than 2 nC for a 10 PW laser pulse with energy of approximately 1.1 kJ. A semi-analytical model is employed to estimate the positron yield, showing good agreement with simulation results. We further study the influence of laser depletion and the positioning of the reflecting foil on the efficiency of pair production. The presented scheme provides a platform for probing strong-field QED effects using currently available multi-petawatt laser systems.

X-ray spectroscopy of hot dense plasmas using LLNL's upgraded Titan 2$ω$ short-pulse laser

A. J. Fairchild, D. T. Bishel, T. Cordova, H. Flores-Alimboyoguen, M. F. Gu, P. Hamilton, N. Hell, M. J. MacDonald, E. W. Magee, R. C. Mancini, et al.

We are developing an experimental platform at Lawrence Livermore National Laboratory's Jupiter Laser Facility to characterize X-ray emission from highly charged ions in the high-density ($n_e > 10^{23}$ cm$^{-3}$), high-temperature ($T_e \sim 1$ keV) regime, leveraging the recently upgraded frequency-doubled short-pulse Titan laser. These measurements will provide experimental benchmarks for high electron density effects on atomic structure, including Stark broadening, ionization potential depression, density-dependent line shifts, and suppression of dielectronic recombination, effects that are relevant to spectral modeling packages used by both the high-energy-density and astrophysics communities. Here, we describe the current status of the platform and present results from first experiments using the upgraded frequency-doubling capability, including calibrated K-shell spectra acquired from five time-integrated X-ray channels. Comparisons with MERL line shape calculations and with spectra recorded at AWE's Orion Laser Facility indicate that the upgraded Titan laser reliably produces the necessary plasma conditions, establishing a foundation for systematic benchmarking of high-density atomic physics in future campaigns.

Proton probing measurements of filamentary electromagnetic structure in laser ablation of solids

J. L. Peebles, P. V. Heuer, D. H. Barnak, Y. V. Zhang, J. R. Davies

Proton radiography of laser direct-drive spherical implosions has shown anomalous structures that correspond to strong electric or magnetic fields extending throughout the corona. These fields have the ability to affect laser–target interactions and act as an energy sink. To better understand these fields, simplified experiments were conducted in planar geometry on the OMEGA extended performance laser at the Laboratory for Laser Energetics. Field structure was measured using dual-axis proton radiography for experiments that varied target material, target size, pulse shape, and intensity. Proton radiographs were analyzed and quantitatively demonstrate that the growth of these features is dominated by incident laser energy and target Z. The data are consistent with a secondary, electrostatic instability established by the expansion-driven Weibel instability as the primary driver for these fields in these interactions.

Laser-driven production of the medical radioisotope 11C: Paving the route toward preclinical-dose generation

D. L. Balabanski, A. S. Cucoaneș, V. Horný, J. F. Ong, S. Popa, V. A. Popescu, P. Tomassini, D. Ursescu

High-power laser systems have the potential to provide a compact and decentralized complementary technology to conventional cyclotrons for the production of medical radioisotopes. Within the Dr. Laser project at Extreme Light Infrastructure - Nuclear Physics, we focus on the production of 11C, a key positron-emitting radionuclide that can be incorporated into a wide range of molecules without altering their biological functionality. This work presents a comprehensive simulation framework for optimizing the entire laser-driven radioisotope production chain. The framework integrates hydrodynamic and particle-in-cell simulations for secondary ion generation from sub-micron liquid targets, as well as nuclear activation calculations for natural and enriched boron. The article also discusses optical techniques for beam focusing and the 11C extraction from target materials, such as boron nitride, boron oxide, and sodium borohydride. The simulation results indicate that current 100-TW-class, 10-Hz laser systems can achieve end-of-irradiation activities of 50–100 MBq. After processing, these activities are expected around 10–20 MBq, which is sufficient for preclinical research studies. Our simulations also show that a system based on 100 TW laser and sub-micron liquid-sheet targets is able to provide stable Target Normal Sheath Acceleration conditions, well suited for efficient laser-driven 11C production.

Quantum effects in plasmas

M. Bonitz, H. Kählert, D. Krimans, C. Makait, P. Hamann, J. Vorberger, Zh. Moldabekov, S. X. Hu, V. V. Karasiev, D. Kraus, et al.

The year 2025 has been designated by UNESCO as the International Year of Quantum Science and Technology. One hundred and twenty-five years ago, Max Planck's discovery of radiation quanta started the quantum era, and 100 years ago, quantum mechanics was developed by Schrödinger, Heisenberg, Bohr, Pauli, Dirac, Born, Fermi, and many others. By now, quantum mechanics is the theoretical foundation of most fields of physics and chemistry, and it is the basis for modern nanotechnology. How about plasma physics? How important are quantum effects in plasmas? In what experiments are quantum effects observed, and where do they govern the behavior of plasmas? How can these effects be treated theoretically and via computer simulations? Starting with a brief historical overview, we discuss the broad parameter range that is the characteristic of plasmas and outline where quantum effects are relevant. This is the case primarily for warm dense matter and inertial fusion plasmas. We provide an overview of the theoretical quantum methods that are available for these dense plasmas and how their respective advantages can be combined in order to achieve predictive capability. The key is a downfolding approach that is based on first-principles simulations.

Moments in time: Numerical analysis of a method for time-resolved neutron spectroscopy

C. B. Stuart, B. Appelbe, A. J. Crilly, C. Forrest, A. DeVault, M. Gatu Johnson, B. J. Lahmann, D. Schlossberg, S. P. Regan, G. Gregori

Time-resolved neutron information is essential for understanding the dynamics of inertial confinement fusion (ICF) implosions, providing key indicators that distinguish igniting from non-igniting plasmas and revealing the underlying causes of shot-to-shot performance variations. The moments method framework offers a practical pathway to extract such temporally resolved quantities using only a small number of neutron time-of-flight detectors. For example, one only needs four detectors to extract the burn-averaged rate of change of ion temperature, a well-defined physically useful quantity. In this work, we evaluate and validate the moments method across several levels of complexity. We first employ a controlled toy model to test the foundational assumptions and mathematical structure of the approach. We then demonstrate that the method generalizes to realistic one-dimensional simulation data of direct drive implosions with a 25 kJ laser driver that include time-dependent ion temperature evolution and hydrodynamic burn dynamics. Together, these results establish the moments method as an experimentally accessible and robust tool for extracting unique and independent information such as the burn-averaged rates of change of fluid velocity and ion temperature with time from neutron time-of-flight measurements, broadening the diagnostic capability of existing neutron detector systems. Fielding this diagnostic on ICF campaigns would improve our understanding of failure modes, helping to determine causes for improved or reduced performance during implosions, informing future target and laser drive design.

Effect of small magnetic fields on stimulated Raman scattering in the kinetic regime

Roman P. Lee, Benjamin Winjum, S.J. Spencer, Simon Bolaños, Mathieu Bailly-Grandvaux, Mario J.-E. Manuel, Frank S. Tsung, Farhat Beg, Warren B. Mori

Results from one- and two-dimensional particle-in-cell simulations – both of nonlinear electron plasma waves (EPWs) and of self-consistent stimulated Raman scattering (SRS) – are shown that explore effects of small magnetic fields ( omega Subscript c Baseline divided by omega Subscript p Baseline much less than 1 ω c / ω p ≪ 1 $\omega _c / \omega _p \ll 1$ ) oriented perpendicular to the direction of laser propagation on SRS across a range of laser intensities of relevance to inertial fusion energy. The magnetic field effect is strongly intensity dependent. The magnetic field raises the threshold for kinetic inflation and can suppress SRS entirely at intensities just above the unmagnetised threshold. At intermediate intensities, it reduces time-averaged reflectivity by factors of approximately two to three in one dimension. Far above threshold the suppressive effect largely disappears, and the reflectivity becomes comparable to, or modestly greater than, its unmagnetised value. Nevertheless, the instability retains distinct signatures in the presence of the magnetic field. The magnetic field promotes the detrapping of resonant electrons, enhances EPW damping, limits distribution-function flattening and the associated nonlinear frequency shift, and thereby produces a more regular recurrence of SRS bursts. Multi-dimensional effects weaken the contrast in EPW damping through transverse localisation and wavefront effects, but preserve the same qualitative intensity dependence and changes in recurrence behaviour. These results delimit the regime in which small transverse magnetic fields mitigate kinetic SRS and show that time-averaged reflectivity alone does not fully characterise their influence on the instability.

Modulated deuteron spectra observed with the magnetic recoil neutron spectrometer at the National Ignition Facility

Bao Nguyen, Yousef Lawrence, Christopher Wink, Timothy Mark Johnson, Niels Vanderloo, Benjamin Reichelt, Amber Hennessy, Daniel Thomas Casey, Dave Schlossberg, Nathan Masters, et al.

The Magnetic Recoil Spectrometer (MRS) at the National Ignition Facility is used to measure the neutron spectrum from deuterium–tritium-fuelled inertial confinement fusion implosions via neutron–deuteron elastic scattering and magnetic dispersion of recoil deuterons. From the MRS-determined neutron spectrum, the yield ( upper Y Subscript n Y n $Y_n$ ), apparent ion temperature ( upper T Subscript i T i $T_i$ ) and areal density ( rho upper R ρ R $\rho R$ ) are determined. However, anomalous energy modulations in recoil deuterons have been observed in several high-yield indirect drive experiments ( upper Y Subscript n Baseline tilde 10 Superscript 16 Baseline minus 10 Superscript 18 Y n ∼ 10 16 − 10 18 $Y_n\sim 10^{16}{-}10^{18}$ ). These observations raise concerns about their potential impact on the MRS-inferred performance metrics. Analytic calculations and particle-in-cell simulations are used to examine the possible beam–plasma instabilities, which indicate the two-stream instability as a plausible mechanism behind energy modulations. Based on a statistical analysis of synthetic deuteron spectra, the modulation-induced errors are found to be within the errors of the determined upper Y Subscript n Y n $Y_n$ , upper T Subscript i T i $T_i$ and rho upper R ρ R $\rho R$ values and thus do not have a significant impact on the MRS measurement.

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

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

Experimental demonstration of broadband-laser suppression of cross-beam energy transfer

Guoxiao Xu, Xiaoran Li, Ning Kang, Huiya Liu, Liang Hao, Zhiyuan Li, Guowei Yang, Honghai An, Xichen Zhou, Jian Wang, et al.

In direct-drive inertial confinement fusion (ICF), cross-beam energy transfer (CBET) redirects a significant fraction of the incident laser energy out of the plasma. We report the experimental demonstration that broadband lasers reduce CBET-enhanced reflected-light return, performed at the low-coherence Kunwu laser facility with two crossed beams of 0.6% bandwidth and up to 550J at $\sim$2.6$\times$10$^{14}$ W/cm$^{2}$. A coupled ray-tracing model shows that the strong CBET amplification of narrowband reflected light is much weaker under broadband illumination. In symmetric incidence condition of two orthogonal beams, the total fractional scattered energy decreases from 7.57% to 4.64%; in asymmetric incidence condition, which separates stimulated Brillouin scattering (SBS) from specular reflection, the SBS fraction decreases from 3.75% to 0.46% and the specular-reflection fraction decreases from approximately 2.2% to 1.3%. These results establish broadband lasers as an effective, experimentally validated approach to reducing energy escape through CBET-enhanced reflection in direct-drive ICF.