ABSTRACT. We have developed an experimental platform for x-ray Thomson scattering (XRTS) at NIF to characterize plasma conditions in ICF indirectly-driven capsule implosions near stagnation [1,2]. This enabled us to investigate up to 30 times compressed ablator materials reaching pressures above 3 Gigabars, at conditions where the distance between the nuclei becomes comparable to the extent of the core shell bound states, which will eventually lead to their pressure ionization. In this talk we will present results from experiments with beryllium shells. We observe reduced elastic scattering for the most extreme conditions [2]. We interpret this reduction as the precursor of pressure ionization of the remaining K-shell electrons, that is, a strongly modified bound state. The beryllium charge state inferred from the data is considerable higher than standard models predict but agrees well with results from DFT simulations [2,3]. Accurate modelling of the K-shell occupation of light elements is not only imperative for creating predictive capabilities for ICF implosions but also for improving our understanding of giant planets and dwarf stars. Our experiments yield valuable benchmarks for this process and demonstrating a complex pathway of pressure ionization.

[1] D. Kraus et al., J. Phys. Conf. Ser. 717, 012067 (2016). [2] T. Döppner et al., Nature 618, 270 (2023). [3] M. Bethkenhagen et al., Phys. Rev. Res. 2, 023260 (2020).

*This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344 and supported by Laboratory Directed Research and Development (LDRD) Grants No. 18-ERD-033 & 24-ERD-044.

ABSTRACT. We have developed an experimental platform to study warm dense matter at the National Ignition Facility that uses colliding planar shocks to produce uniform plasma conditions and enable high-precision measurements of warm dense matter [1]. The Colliding Planar Shocks (CPS) platform currently uses simultaneous x-ray Thomson scattering and x-ray radiography to measure the density, electron temperature, and ionization state at pressures approaching 100 Mbar. The CPS platform creates a large volume of uniform plasma in the x-ray scattering volume, significantly improving the precision of the measurements necessary to test models for the equation of state and ionization potential depression in the warm dense matter regime. Here, we present the design of the CPS platform, compare hydrodynamic simulations to x-ray radiography and x-ray scattering data from initial experiments studying hydrocarbons, and propose future directions for the platform for laboratory astrophysics experiments.

[1] M. J. MacDonald et al., Phys. Plasmas 30, 062701 (2023).

ABSTRACT. Matter at extreme densities and temperatures displays a complex quantum behavior that is characterized by Coulomb interactions, thermal excitations, and partial ionization. Such warm dense matter (WDM) is ubiquitous throughout the universe and occurs in a host of astrophysical objects such as giant planet interiors and white dwarf atmospheres. A particularly intriguing application is given by inertial confinement fusion, where both the fuel capsule and the ablator have to traverse the WDM regime in a controlled way to reach ignition.

In practice, rigorously understanding WDM is highly challenging both from experimental measurements and numerical simulations [1]. On the one hand, interpreting and diagnosing experiments with WDM requires a suitable theoretical description. One the other hand, there is no single method that is capable of accurately describing the full range of relevant densities and temperatures, and the interpretation of experiments is, therefore, usually based on a number of de-facto uncontrolled approximations. The result is the vicious cycle of WDM diagnostics: making sense of experimental observations requires theoretical modeling, whereas theoretical models must be benchmarked against experiments to verify their inherent assumptions.

In this work, we outline a strategy to break this vicious cycle by combining the X-ray Thomson scattering (XRTS) technique [2] with new ab initio path integral Monte Carlo (PIMC) capabilities [3,4,5]. As a first step, we have proposed to interpret XRTS experiments in the imaginary-time (Laplace) domain, which allows for the model-free diagnostics of the temperature [6] and normalization [7]. Moreover, by switching to the imaginary-time, we can directly compare our quasi-exact PIMC calculations with the experimental measurement [5]. This opens up novel ways to diagnose the experimental conditions, as we have recently demonstrated for the case of strongly compressed beryllium at the National Ignition Facility.

Our results open up new possibilities for improved XRTS set-ups that are specifically designed to be sensitive to particular parameters of interest [8]. Moreover, the presented PIMC capabilities are important in their own right and will allow for a gamut of applications, including equation-of-state calculations and the estimation of structural properties and linear response functions.

[1] T. Dornheim et al., Phys. Plasmas 30, 032705 (2023) [2] S. Glenzer and R. Redmer, Rev. Mod. Phys. 81, 1625 (2009) [3] T. Dornheim et al., J. Phys. Chem. Lett. 15, 1305-1313 (2024) [4] T. Dornheim et al., arXiv:2403.01979 [5] T. Dornheim et al., arXiv:2402.19113 [6] T. Dornheim et al., Nature Commun. 13, 7911 (2022) [7] T. Dornheim et al., arXiv:2305.15305 [8] Th. Gawne et al., arXiv:2403.02776

ABSTRACT. The frontier of atomic physics lies in the dense plasma regime. At electron densities Ne ≳ 10^{25} cm^{−3} characteristic of stellar interiors and inertial fusion plasmas, atomic transition energies shift due to electrostatic interactions between the radiator and nearby charged particles. Though predicted by theory, experimentally isolating such line shifts and identifying the dependence on the thermodynamic state constitute a step change in understanding and will enable new spectroscopic diagnostics of dense plasmas. In plastic shells hosting a Cr tracer layer imploded at the OMEGA-60 laser facility, 1s−2p absorption lines from L-shell Cr ions present a decreasing red-shift as the stagnated shell releases from peak compression Ne ≈ 10^{25} cm^{−3}. The thermodynamic conditions and opacity of the Cr layer are constrained using a forward model of the measured spectrum. Under these constraints, Doppler and satellite contributions are insufficient to describe the magnitude of the red-shift. The case for the plasma polarization shift causing the residual shift is presented.

ABSTRACT. This talk will present opportunities for high energy density laboratory astrophysics experiments at LLNL’s Jupiter Laser Facility (JLF). The facility has just completed a 4-year long refurbishment and is welcoming users back through the LaserNetUS network. In addition to scientific discovery, JLF has historically served as a steppingstone to larger experiments at the NIF and OMEGA lasers. JLF supports multiple laser platforms: Titan, Janus TA1, and COMET. Titan’s two-beam system is composed of a nanosecond, kilojoule long-pulse beam and a short- pulse beam with 1 to 10 ps pulses and energies up to 300 J, depending on pulse duration, and these beams can be used together or independently. JLF’s Janus system has two independent beams, each of which can produce 1 kJ at 1.053 μm with pulse lengths from 1 to 20 ns. The system fires approximately every 30 minutes and offers frequency doubling, as well as a variety of pulse shapes. COMET’s flexible configuration, which was designed primarily to generate laboratory x-rays, offers uncompressed pulse lengths from 500 ps to 6 ns, compressed pulses down to 0.5 ps, and beam energies up to 10 J.

ABSTRACT. Shock front interaction with random density nonuniformities in the shocked material is a problem of interest in astrophysics and inertial confinement fusion (ICF). Astrophysical media are typically nonuniform, featuring density clumps and clouds of various scales. Many indirect- and direct-drive ICF target designs involve empty or DT-wicked plastic foams, which are strongly nonuniform on the foam cell scale. The shock interaction with the inhomogeneous density field generates turbulence in the shocked fluid, affecting the shock propagation. Numerical [1-6] and theoretical [7, 8] studies of this effect indicate a reduction of the shock density compression, the “undercompression” [2], compared to an instantly homogenized material of the same average density and equation of state (EOS). Such an effect could be observable in shock Hugoniot experiments with low-density CH foams, but the data accumulated since the 1970s is relatively scarce and inconclusive. We discuss the results of the empty CH foam Hugoniot measurements performed on the Nike krypton-fluoride laser facility at NRL. The Nike Hugoniot platform [9] combines a uniquely uniform laser drive (less than a 0.25% time-averaged laser drive intensity variation in the overlapping beams within a 400-um diameter flat-top focal spot) with high-resolution monochromatic X-ray streak imaging, enabling experiments in previously unexplored parameter ranges, with shock velocities and pressures up to 100 km/s and 9 Mbar, respectively. The observed trajectories of the shock front and the ablation piston deviated from straight lines, indicating steady shock propagation in the foam, by less than 1%. The Nike Hugoniot data obtained with 100 mg/cc DVB foams [9] supports the prediction of shock compression lower than that calculated from tabulated EOS, such as SESAME. However, more recent Nike data obtained with lower-density DVB foams, from 73 to 94 mg/cc, and with structured 3D-printed foams with densities from 64 to 144 mg/cc indicates higher levels of shock density compression. We discuss possible reasons for this discrepancy and the unresolved physics issues of shock interaction with a density inhomogeneity field. Work supported by U.S. DOE/NNSA. _________________________________ [1] L. Phillips, AIP Conf. Proc. 370, 459 (1996). [2] G. Hazak et al., Phys. Plasmas 5, 4357 (1998). [3] A. D. Kotelnikov and D. C. Montgomery, Phys. Fluids 10, 2037 (1998). [4] F. Philippe et al., Laser Part. Beams 22, 171 (2004). [5] D. Elbaz et al., Phys. Rev. E 85, 066307 (2012). [6] S. Davidovits et al., Phys. Rev. E 105, 065206 (2022) [7] C. Huete Ruiz de Lira, A. L. Velikovich, and J. G. Wouchuk, Phys. Rev. E 83, 056320 (2011). [8] A. L. Velikovich, C. Huete, and J. G. Wouchuk, Phys. Rev. E 85, 016301 (2012). [9] Y. Aglitskiy et al., Phys. Plasmas 25, 032705 (2018).

ABSTRACT. We present theoretical and simulation results for a novel laboratory platform capable of directly studying the electron cyclotron maser instability in the laboratory. Recent advances in observation [1,2], theory [3], and simulations [4,5] have fueled a renewed interest in the electron cyclotron maser instability as a mechanism for generating the brightest astrophysical radiation, including pulsar emissions and FRBs. This instability amplifies coherent electromagnetic radiation within magnetized plasmas due to an inverted Landau population. Distributions with horseshoe or ring-beam momentum shapes, distinctly influence maser dynamics and emission signatures [6,7]. Pair plasma beams in compact object magnetospheres are predicted to become maser unstable through various processes depending on specific conditions. The first laboratory realization of an electron-positron plasma beam [6] opens a new door to directly study beam-plasma instabilities in magnetic fields mimicking pulsars and magnetars. We propose two distinct laboratory platforms designed to generate maser-unstable plasmas relevant to diverse astrophysical scenarios. The first investigates the interaction of pair-plasma beams with a magnetic mirror, analogous to plasma infalling in a pulsar polar cap. The second platform utilizes betatron cooling, mimicking synchrotron cooling experienced by astrophysical beams. Our work offers, for the first time, the possibility of laboratory experiments directly capable of studying coherent radiation mechanisms relevant to FRBs under current experimental conditions, potentially leading to a deeper understanding of unexplained observations.

[1] The CHIME/FRB Collaboration, Nat. 587.7832 (2020): 54-58 [2] C. P. Hu, et al. Nat. 626.7999 (2024): 500-504 [3] W. Lu, and P. Kumar. MNRAS 477.2 (2018): 2470-2493 [4] B. D. Metzger, et al. MNRAS 485.3 (2019): 4091-4106 [5] P. J. Bilbao and L. O. Silva. Phys. Rev. Lett. 130.16 (2023): 165101 [6] D. C. Speirs, et al. Phys. Plasmas 17.5 (2010) [7] R. A. Cairns, et al. Phys. Plasmas 18.2 (2011) [6] C. D. Arrowsmith, et al. arXiv:2312.05244 (2023)

ABSTRACT. In this talk we will discuss recent experiments performed at the MAGPIE facility at Imperial College in which we use a combination of X-ray-drive, generated by imploding wire arrays, with multi-Tesla B-fields produced by the Z-pinch current [1], to form magnetized high-density plasmas for scaled modeling of astrophysical dynamics [2]. We will present investigations of the effects of magnetic fields on the development of turbulence in colliding, radiatively cooling plasma flows. We will also present results from a modified x-ray driven set-up complementary to described in [3], allowing introduction of differential rotation to free-boundary laboratory plasmas.

[1] J.W.D. Halliday, et al., “Investigating radiatively driven, magnetized plasmas with a university scale pulsed-power generator”, Physics of Plasmas, 29, 042107 (2022). [2] S.V. Lebedev, A. Frank, and D.D. Ryutov, “Exploring astrophysics-relevant magnetohydrodynamics with pulsed-power laboratory facilities”, Rev. Mod. Phys., 91, 025002 (2019). [3] V. Valenzuela-Villaseca et al., “Characterization of Quasi-Keplerian, Differentially Rotating, Free-Boundary Laboratory Plasmas”, Phys. Rev. Lett., 130, 195101 (2023).

ABSTRACT. The DART (Double Asteroid Redirection Test) recently demonstrated successful deflection of an asteroid with kinetic forces, but for larger and/or faster bodies a nuclear detonation may be able to provide a similar but thermonuclear deflection. This requires an understanding of how possibly novel asteroid material makeups behave with respect to a detonation, in particular as the height of burst is varied. An platform has been developed for NIF using an x-ray source that is hydrodynamically scaled from a nuclear detonation using one quad of beams (~10 kJ) incident into a small (2 mm diameter) Sn-doped CH capsule. Simulations of this x-ray source and recent experiments on Omega-EP and NIF will be presented.

ABSTRACT. Radiative cooling effects can strongly influence the structure of shocks formed by colliding supersonic plasma flows, leading to the growth of instabilities and turbulence. Here, we present experiments conducted at the MAGPIE pulsed-power generator (1.4 MA, 240 ns rise time) on colliding plasma flows produced from the ablation of solid targets using a wire array z-pinch as an x-ray source. A wide range of target geometries and materials have been considered for different experiments, exploring the interaction of flows in the presence of an ambient magnetic field supported by the current pulse flowing through the wire array. Ablating two parallel planar targets results in two counter-propagating, supersonic plasma flows which form a dense layer of shocked, stagnated plasma at the collision plane. This ‘stagnation layer’ is consistent with a 1D accretion shock model with γ≤1.2. By changing the position and orientation of the targets with respect to the ambient magnetic field, we can study the effect of magnetic field on the flow, while radiative cooling effects are explored by changing target material. Placing the planar surfaces at an angle to each other to form a wedge-shaped target opens the possibility of producing radiatively driven jets, where we can investigate factors such as the collimation of the jet in relation to the thermal properties of the plasma. Finally, to investigate inhomogeneous plasmas, the solid targets are replaced with 3D printed meshes to produce spatially modulated colliding plasma flows. The collision of modulated plasmas results in the formation of a turbulent layer which can be easily diagnosed using various laser-based diagnostics. This set of experiments aims to explore the effects of magnetic fields on the suppression of the structures formed within the plasma.

ABSTRACT. At high-energy-density conditions, a new realm of quantum behavior emerges including electron localization, structural complexity, and core-electron chemistry. Sodium (Na) behaves particularly unusual at these conditions because of its very high compressibility and lone valence electron. Normally a shiny ideal metal, Na transforms to a topological insulator at 200 GPa. This topologically insulating phase (hP4) is due to the valence electrons occupying interstitial positions of its crystalline lattice rather than the orbitals centered on ionic cores. Using lasers as high-pressure drivers, we report the structural and electronic properties of Na at the most extreme compressions yet studied. X-ray diffraction measurements to 480 GPa and 2000 K reveal unexpected new phases. Simultaneous reflectivity measurements suggest a dramatic drop in the conductivity of both the solid and fluid phases. These data together with ab initio evolutionary structure searches reveal a rich structural competitiveness than extends to greater than 300 GPa and thousands of degrees Kelvin. Recent experiments on ramp-compressed sodium at the National Ignition Facility will provide an experimental basis for understanding electron localization in traditionally simple metals at significant compressions.

Funding acknowledgement This material is based upon work supported by the Department of Energy National Nuclear Security Administration University of Rochester “National Inertial Confinement Fusion Program” under Award Number(s) DE-NA0004144, the U.S. Department of Energy, Office of Science, Fusion Energy Sciences funding the award entitled High Energy Density Quantum Matter under Award Number DE-SC0020340, the University of Rochester, and the New York State Energy Research and Development Authority. Partial funding for this research is provided by the Center for Matter at Atomic Pressures (CMAP), a National Science Foundation (NSF) Physics Frontiers Center, under Award PHY-2020249.

ABSTRACT. Superionic phases, in which protons diffuse like a liquid through stable lattices of heavier nuclei, have been observed experimentally and computationally in water and ammonia at high pressures, and have been predicted for a number of proton rich planetary materials. Here we describe a novel state of matter in the H-C-N-O chemical space: double superionicity. With density functional molecular dynamics and machine learning molecular dynamics simulations we show that hydrogen and one heavier species (either C or N) simultaneously diffuse at elevated temperature while the heaviest nuclei provide a stable sublattice until the entire material melts at yet higher temperature. We further demonstrate that proton superionicity is ubiquitous in planetary ices (focusing on H-C-N-O and N-H materials) at sufficiently high pressure and temperature. Superionic and doubly superionic phases may exist in the interiors of Uranus and Neptune and thus may influence their magnetic dynamo because of their high ionic conductivities.

ABSTRACT. Helium is strongly depleted in the atmospheres of gas giant planets relative to bulk solar compositions [1]. A proposed mechanism for this depletion is the phase separation from hydrogen, the main component of gas giant planets [2, 3]. While recent shock compression experiments support this hypothesis [4], the miscibility behavior of hydrogen with other important planetary components has yet to be experimentally explored at warm dense conditions. We combined static and dynamic compression to investigate the equation of state and reflectivity (an indicator of miscibility) of H2-Ne (Ne/H = 0.2) and H2-H2O (H20/H = 1:1) at the conditions of gas and ice giant interiors. Preliminary results on H2-Ne indicate miscibility at combined pressures and temperatures of up to 150 GPa and 20,000 K. H2 and H2O appear to form a mixed fluid state at ~350 GPa and ~10,000 K. Analyses of these systems are ongoing, and follow-up experiments will utilize different mixing ratios and probe a wider range of pressure-temperature conditions to further explore the phase relations of these mixtures.

This material is based upon work supported by the Department of Energy [National Nuclear Security Administration] University of Rochester “National Inertial Confinement Fusion Program” under Award Number DE-NA0004144.

[1] Niemann et al., Science 1996 [2] Stevenson, Phys.Rev. B 1975 [3] Wilson and Militzer, Phys. Rev. Lett. 2010 [4] Brygoo et al., Nature 2021

ABSTRACT. Recent experiments in shocked liquid deuterium [Fratanduono et al, Phys. Plasmas 26, 012710 (2019)] measured anomalously low sound speed near 200 GPa compared to theoretical models. The observed speed is shown to be consistent with a slowing of longitudinal compression waves that velocity-match to an electrostatic potential generated by the ion-acoustic plasma mode. This velocity resonance is expected to occur at electron degeneracies between approximately 2 and 4 (ratio of Fermi energy to thermal energy). The experimental evidence implies a reduction in adiabatic index compared to all theoretical models in this thermodynamic band. A reduced adiabatic index modifies our understanding of stellar structure, convective thresholds, and pulsation periods for astrophysical bodies such as brown, red, and white dwarf stars.

ABSTRACT. Matter under extreme densities and temperatures—often referred to as warm dense matter (WDM)— is pivotal for a number of cutting-edge technological applications such as the discovery and synthesis of novel materials and hot-electron chemistry. A particularly important and timely application is given by inertial confinement fusion, where the fuel capsule has to traverse the WDM regime in a controlled way towards ignition. Unfortunately, the theoretical understanding of such extreme states is rendered notoriously difficult by the complex interplay of a variety of physical effects (Coulomb coupling, thermal excitations, quantum degeneracy, etc.). In practice, density functional theory (DFT) constitutes the workhorse of WDM theory. In this work, we present our results on the dynamic structure factor and dynamic dielectric function of warm dense hydrogen computed from first principles using linear response time-dependent density functional theory. In addition, we discuss the relevance of the thermal exchange-correlation effects for the electronic structure in warm dense hydrogen [1-4].

REFERENCES

[1] Z. Moldabekov, M. Lokamani, J. Vorberger, A. Cangi, T. Dornheim, “Non-empirical Mixing Coefficient for Hybrid XC Functionals from Analysis of the XC Kernel”, J. Phys. Chem. Lett., 14, 1326-1333 (2023) [2] Z. Moldabekov, M. Böhme, J. Vorberger, D. Blaschke, T. Dornheim, “Ab Initio Static Exchange–Correlation Kernel across Jacob’s Ladder without Functional Derivatives”, J. Chem. Theory Comput., 19, 1286-1299 (2023) [3] Z. Moldabekov, M. Lokamani, J. Vorberger, A. Cangi, T. Dornheim, “Assessing the accuracy of hybrid exchange-correlation functionals for the density response of warm dense electrons”, J. Chem. Phys., 158, 094105 (2023) [4] Z. Moldabekov, M. Pavanello, M. Böhme, J. Vorberger, T. Dornheim, “Linear-response time-dependent density functional theory approach to warm dense matter with adiabatic exchange-correlation kernels”, Phys. Rev. Research 5, 023089 (2023) [5] Z. Moldabekov, S. Schwalbe, M. Böhme, J. Vorberger, X. Shao, M. Pavanello, F. Graziani, T. Dornheim, “Bound state breaking and the importance of thermal exchange-correlation effects in warm dense hydrogen”, J. Chem. Theory Comput., 20, 68-78 (2024)

ABSTRACT. Astronomical observations have confirmed the existence of ordered magnetic fields across a broad range of spatial and magnitude scales. From interstellar scales on the order of 10-5 G [1], to cosmic web filaments with an upper limit of 10-9 G [2]. These magnetic fields can be relevant in galactic dynamics [3], play an important role in stellar formation [4], and affect other physical processes such as cosmic ray acceleration [5] and thermal conduction [4]. The Biermann Battery mechanism paired with turbulent dynamo has been put forward as a potential mechanism for the generation, amplification, and sustainment of these observed fields [6, 1]. Recent planar experiments [7, 8] have successfully demonstrated turbulent dynamo in the laboratory for the first time. Theoretical work suggests that magnetic fields may be generated in inertial confinement fusion implosions [9], however diagnosing such systems remains a challenge. In contrast, cylindrical implosions retain the effects of convergence while allowing direct diagnostic access to the interior of the target by viewing down the axis of the system. Hydrodynamic instabilities within these implosions can grow due to the Rayleigh-Taylor (RT) [10, 11], and the Richtmyer-Meshkov (RM) [12, 13] instabilities, as well as the Bell-Plesset (BP) [14, 15] effect, and, at late times, turbulence may develop. Los Alamos National Laboratory has a long history of success studying instability growth in convergent systems using such platforms [16], yet the platform has not been designed for accessing physical regimes where Biermann battery can operate effectively, and magnetic resistivity does not diffuse the fields faster than the dynamically relevant time scales. Using the existing cylindrical implosion platform as a starting point for examining magnetic fields generated by the Biermann Battery mechanism, we present preliminary 2D FLASH simulations that indicate the viability of using this platform to study Biermann generated fields in a convergent geometry. We also analyze the potential growth of such fields due to the development of turbulence once the RT/RMI has left the linear stage.

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Work at Los Alamos National Laboratory used resources provided by Los Alamos National Laboratory, supported by the US Department of Energy (DOE) National Nuclear Security Administration (NNSA), operated by Triad National Security, LLC (Contract No. 89233218CNA000001). The Flash Center acknowledges support by the US DOE NNSA under Awards DE-NA0002724, DE-NA0003605, DE-NA0003842, DE-NA0003934, DE-NA0003856, DE-NA0004144, DE-NA0004147, and Subcontracts 536203 and 630138 with Los Alamos National Laboratory and B632670 with Lawrence Livermore National Laboratory; the National Science Foundation under Awards PHY-2033925 and PHY- 2308844; the US DOE Office of Science Fusion Energy Sciences under Award DE-SC0021990; and US DOE ARPA- E under Award DE-AR0001272.

ABSTRACT. Magnetic fields are pervasive on cosmological and galactic scales, and understanding their formation and evolution is essential to our understanding of modern cosmology. One of the predominant proposed mechanisms for the origin of these fields is via the thermoelectric Biermann battery effect, which describes the spontaneous generation of magnetic fields due to non-parallel density and temperature gradients in plasmas. Though the effect is difficult to observe directly in the intergalactic medium due to its relatively small magnitude and the large spatial scales along which measurements are made, rapid growth in the field of laboratory astrophysics in recent decades now allows us to use scaling relations to investigate these phenomena on laboratory scales. Using FLASH, a high-performance radiation-hydrodynamics code with extended magnetohydrodynamic terms, we collaborate with experimentalists at UCLA to model the generation of Biermann-driven fields in such a laboratory setting, using high repetition rate laser produced plasmas at a frequency of ~1 Hz. We validate the FLASH code at new spatiotemporal regimes, and use these newly validated capabilities to assist in the modeling and design of continuing laboratory astrophysics experiments which introduce a Nitrogen fill to the target chamber in order to facilitate shocks in the system, and to perform large scale simulations investigating the generation and subsequent amplification of seed fields and their impact on LSS.

ABSTRACT. A nova is a thermonuclear outburst on the surface of an accreting white dwarf [1]. At least a part of the accretion layer mostly composed of hydrogen, is ejected at high speeds of 200 to 5000 km/s, and shocks arise when a fast outflow encounters a slower outflow. They are very rich physical processes in novæ, as evidenced by their multi-wavelength radiation [2]. We can observe a highly absorbed X-ray radiation, which re-emerges in the UV-optical range. This indicates complex radiative shock structures that happen as a rather spherical wind crashes into a torus-shaped medium surrounding the binary system [2, 3]. It is crucial to validate a precise model of this shock structure because it plays a central role to explain dust formation or particle acceleration [4, 5].

However, internal shocks are buried deep within the ejecta which prevents direct observations : the physics of the structure must be infered. Every alternative approach that can provide direct insight into one of these objects is of primary importance. In this context, we have recently developed a new research program: the CIRENE project (Chocs Internes Radiatifs dans les Ejectas de NovaE). Its main objective is to improve the modeling and the understanding of radiative accretion shocks occurring in novæ ejectas by coupling theoretical, numerical and experimental studies. Recent theoretical and numerical works [6, 7] have demonstrated that the double-shock structure can be simulated. In this poster, we will present the first radiative hydrodynamics simulations of the double shock structure, performed with the RAMSES code [8] and we will compare these results to an improved version of the theoretical 1D model of [9]. These simulations will highlight the cooling processes as well as the instabilities that can develop in this structure and thus provide a better understanding of the formation of the thin cold central layer. Moreover, thanks to many works on the scalability of radiation hydrodynamics flow [10], we have proved that adapted scaling laws can be applied to reproduce these phenomena in a laboratory with powerful lasers [7]. To this end, we propose in this poster a target design for the LULI2000 laser facility in order to observe the double-shock structure for the very first time. We will also present in the poster the numerous 1D and 2D simulations of the experiment we conducted with the Troll code to optimize the target characteristics. These experiments will allow us to validate the classical model of internal radiative shocks.

REFERENCES [1] Warner, B. – Cataclysmic variable stars – Camb. Astrophys. Ser., Vol. 28 (1995) [2] Chomiuk, L. et al. – New insights into classical novæ – ARAA 59: 391-444 (2021) [3] Aydi, E. et al. – Early spectral evolution of classical novæ: consistent evidence for multiple distinct outflows – ApJ 905: 62-94 (2020) [4] Metzger, B. D. et al. – Gamma-ray novæ as probes of relativistic particle acceleration at non-relativistic shocks – MNRAS 450: 3739-2748 (2015) [5] Derdzinski, A. M. et al. – Radiative shocks create environments for dust formation in classical novæ – MNRAS 469: 1314-1329 (2017) [6] Del Valle, M. V. et al. – Adiabatic-radiative shock systems in YSO jets and novae outflows – A&A ,660, A104 (2022) [7] Dollerschell et al., 2024, in prep [8] Teyssier, R. – Cosmological hydrodynamics with adaptative mesh refinement, a new high-resolution code called RAMSES – A&A 385: 337-364 (2002) [9] Metzger, B. D. et al. – Shocks in nova outflows, I. Thermal emission – MNRAS 442: 713-731 (2014) [10] Falize, É. et al.– Similarity properties and scaling laws of radiation hydrodynamic flows in laboratory astrophysics – ApJ 730: 96-102 (2011)

ABSTRACT. During violent astrophysical phenomena very energetic particles can be accelerated, these are the cosmic rays. Shocks in particular are likely to be accelerating structures for cosmic rays via processes such as those presented by Fermi in 1949 [1]. Due to the impossibility of in situ measurements, laboratory astrophysics experiments are necessary to study the acceleration processes of cosmic rays [2]. One way to do laboratory astrophysics is to use high power lasers like the National Ignition Facility (NIF) in the United States of America or LMJ in France, i.e. megajoule class laser facilities. In particular to obtain high Mach number shocks high power lasers must be used [3]. There will be shots at the NIF to study for the first time in the laboratory non-thermal ion populations generated by magnetized high-Mach-number quasi-parallel (magnetic field parallel to the shock velocity) collisionless shocks. To prepare and analyse this experiment hydrodynamic simulations with the code FLASH [4] have been performed. The collisional shock characteristics are required as input for kinetic plasma simulations that can model the development of the collisionless shock and the associated particle acceleration. The analysis of the FLASH simulation results will be presented, and the transition towards the kinetic simulations will be discussed. Shots on the OMEGA laser facility were also performed (October 2023) to prepare the experiment on NIF. To understand the results of those shots, additional FLASH simulations were run. The analysis of these additional simulations will be presented, as well as the scaling of the collisional shock velocity as a function of the main laser and target parameters.

[1] E. Fermi, Physical Review, vol 75, no. 8, April (1949) [2] F. Fiuza et al., Nature Physics, vol. 16, no. 9, (2020) [3] D.B. Schaeffer et al, Physics of Plasma, vol. 24, no. 12 (2017) [4] B. Fryxell et al., Astrophys. J. Suppl.Ser., vol 131, no. 1 (2000)

ABSTRACT. Mosaic crystals, with their high integrated reflectivities, are widely-employed in spectrometers used to diagnose high energy density systems. X-ray Thomson scattering (XRTS) has emerged as a powerful diagnostic tool of these systems, providing direct access to important properties such as the temperature via detailed balance. However, the measured XRTS spectrum is broadened by the spectrometer instrument function (IF), and without careful consideration of the IF one risks misdiagnosing system conditions. Here, we consider in detail the IF of mosaic crystals and how the broadening varies across the spectrometer. Notably, we find a strong asymmetry in the shape of the IF towards higher energies, suggesting temperatures inferred via detailed balance can be overestimated if an approximate symmetric IF is used.

ABSTRACT. Streaked Optical Pyrometer (SOP) measures the temporally and spatially resolved brightness temperature of a dynamically compressed material by assuming it radiates like a blackbody. On laser facilities such as OMEGA and OMEGA EP at Laboratory for Laser Energetics, the measurement duration is typically several tens of nanosecond, with time resolution <100 ps. Today, typical SOP can measure temperature above ~4000 K. As temperature decreases, the number of photons emitted by the target drops precipitously, resulting in signals buried in detector noises. In this work, we present a statistical model that allows SOP data reduction with high temporal and spatial resolution at temperatures where the traditional analysis method fails, extending the capability of SOP to measure temperatures of relatively cold targets.

ABSTRACT. Rotating bipolar outflows are commonly observed in the Young Stellar Object (YSO) phase of early star formation, and are thought to be influenced by complex magnetic field structures. Yet, the conditions of the launch region for these flows remain unclear due to limited resolution in observations. We employ a scalable laboratory experiment of a pulsed-power-driven cylindrical wire array in order to generate radially collapsing flows that transition into bipolar outflows. By introducing tunable current path elements around the wire array, we enable the ratio of axial to azimuthal magnetic field ($B_z/B_\theta$) to be varied by minor changes in the 3D-printed load design. This allows us to add rotation in the flows by introducing $B_z$ or by pushing the radial plasma streams off-axis as they merge. Our experiment is driven by a ~1 MA, 200 ns rise current pulse on the COBRA Marx driver, and is diagnosed with optical Thomson scattering, interferometry, inductive probes, and gated UV or optical imaging. We calculate scaling parameters for our system using velocity, electron temperature, magnetic field and density measurements, and compare our outcomes to simulations from the PERSEUS extended-MHD code.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

ABSTRACT. With the emergence of High Energy Density (HED) physics, scientists can now replicate extreme stellar conditions within controlled laboratory environments on Earth. This advancement enables the in-depth study of astrophysical phenomena and addresses national security concerns. These experiments demand precise knowledge of the areal density of the targets. However, the traditional validation method, Rutherford BackScattering (RBS), necessitates destructive measures to achieve the required precision and offers limited probing depth. Consequently, it can only be applied to surrogate targets. General Atomics has pioneered a laboratory-based AutoEdge method, ensuring x-ray transmission measurements with synchrotron-like precision and accuracy. This innovative approach operates continuously, supporting 24/7 target production for real targets intended for large-scale HED facilities like the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) and the Z Facility at Sandia National Laboratories (SNL). By utilizing the x-ray opacity database, also known as the mass attenuation coefficient database, nondestructive determination of areal density from x-ray transmission becomes possible.

While routinely achieving a 1% precision in areal density, there exists a potential ~5% systematic error contingent upon the x-ray opacity database employed for data conversion. Although the x-ray opacity of elements was extensively studied from the 1920s to the 1980s, widely used tabulated x-ray databases like NIST-XCOM (Hubbell), NIST-FFAST (Chantler), CXRO (Henke), SNL (Biggs), and LLNL (McMaster) demonstrate consistency only ~ ±10 percent, occasionally worse, even for common elements. These discrepancies, largely unknown, significantly impact the interpretation of High Energy Density (HED) experiments. For instance, anomalies in Solar opacity must be referenced to room temperature behavior. Since areal density computation relies on x-ray transmission using an opacity database, it is akin to measuring length with an inaccurate meter stick. Every measurement made using this flawed reference will be proportionally incorrect. To address this database inconsistency, we opted to employ the AutoEdge method in reverse, analyzing free-standing single-element metal foils with accurately determined areal density via gravimetric methods. We developed a methodology to refine the x-ray opacity database within the photon energy range of 3 to 17 keV. In this process, we contributed to the 'International Initiative on X-ray Fundamental Parameters' (IIFP), a collaboration led by NIST, CEA, and PTB. Our work on Ni, Fe, and Au has been completed, demonstrating an agreement of ~1% with gravimetric measurements. Additionally, we established a 1% consistency between AutoEdge and RBS measurements for Fe foils and a 1% consistency between AutoEdge and synchrotron measurements for Ni.

The AutoEdge method has become integral to the characterization of all opacity targets utilized in the US national program, including both ZAPP and Discovery Science targets. This enhanced metrology capability has paved the way for the engineering of new target types, such as SiO2 targets up to 15 μm in thickness, and mixed SiO2 and MgO targets for solar opacity research. These targets, whose areal densities cannot be accurately determined by RBS, have been successfully characterized using the joint application of AutoEdge and photolithography-based target fabrication. This innovative approach recently facilitated benchmarking between the NIF and Z experimental platforms. Shot data from these experiments not only substantiated the anomalous increases in x-ray opacity for iron and oxygen under solar convection zone conditions but also contributed significantly to resolving the long-standing solar opacity problem.

ABSTRACT. Accreting black holes in X-ray binaries and active galactic nuclei constitute some of the most luminous objects in the universe. Model fits to reflection spectra from a number of such systems have predicted unreasonably high Fe abundances, inconsistent with predictions from stellar evolutionary theory. This has revealed a need for increased scrutiny of the models. The Z machine at Sandia National Labs has a unique capability to probe the relevant physics. The photoionized expanding foil experimental platform uses the copious X-ray radiation from the Z-pinch to achieve temperature, density, and photoionization conditions found in black hole accretion disks. It provides a means to benchmark astrophysical photoionized plasma codes (such as XSTAR) by measuring high-resolution absorption and emission spectra, which can be used to test the underlying atomic physics in the models. To provide a more thorough interpretation of the data, we have begun using radiation hydrodynamics simulations to address questions of density and temperature gradients, effective mixing of the foil layers, and expansion effects, which can affect the spectroscopic analysis and data-model comparisons. (POSTER PRESENTATION)

ABSTRACT. Using intense femtosecond laser pulses one can drive materials to Warm Dense Matter (WDM) conditions. WDM exists at temperatures ~0.1-1eV and densities ~0.1-10g/cc, placing it outside condensed matter or plasma conditions; thus its material properties are hard to predict with either theory. Understanding the properties of WDM is important for many areas of physics including planetary astrophysics and fusion ignition. In particular, the electrical conductivity of WDM is a vital parameter for modeling magnetic fields produced by planetary dynamos [1].

I will present experimental results using terahertz (THz) spectroscopy to measure the electrical conductivity of Warm Dense Nickel (WD-Ni). We use single-shot THz time-domain spectroscopy to measure changes in the THz transmission of nickel heated to the WDM regime. These changes are used to infer the electrical conductivity. THz pulses are ideal probes of conductivity because THz fields oscillate slowly compared to the timescale of electron-electron and electron-ion interactions. In addition, THz pulses provide picosecond resolution and thus can probe transient states of matter. The recent development of single-shot THz detection techniques has enabled THz measurements of materials irreversibly driven to extreme conditions [2, 3]. We observe an approximately four-fold decrease in the electrical conductivity of nickel when heated to the WDM regime. These results are an important first step towards understanding the Earth’s dynamo, where nickel is an abundant element.

[1] R. P. Drake, Phys. Plasmas 16(5), 055501 (2009). [2] B. K. Ofori-Okai, Rev. Sci. Instrum. 89(10), 10D109 (2019) [3] B. K. Ofori-Okai, Phys. Plasmas (In press 2024)

ABSTRACT. Induced Compton scattering (CS) is a quantum nonlinear interaction between an intense electromagnetic field and a rarefied plasma. Although induced CS is considered to occur in radiation fields with high brightness temperature such as pulsars in nature [1], the principle of induced CS has not been proven experimentally. Therefore, we conducted a proof-of-principle experiment on induced CS using an ultra-intense laser [2] and measured the scattered spectra from the plasma and the laser. As a result, we observed a nonlinear redshift [3], which is considered to be caused by induced CS. We also performed particle-in-cell simulations in which induced CS is not included and found that the experimental results are not explained by classical plasma physics.

[1] S. J. Tanaka et al. Prog. Theor. Exp. Phys. 123E01 (24pp) (2013) [2] S. J. Tanaka et al. Prog. Theor. Exp. Phys. 063J01 (8pp) (2020) [3] S. J. Tanaka et al. Prog. Theor. Exp. Phys. 074E01 (14pp) (2015)

ABSTRACT. A compact high-flux, short-pulse neutron source would have applications from nuclear astrophysics to cancer therapy. Laser-driven neutron sources can achieve fluxes much higher than spallation and reactor neutron sources by reducing the volume and time in which the neutron-producing reactions occur by orders of magnitude. We report progress towards an efficient laser-driven neutron source in experiments with a cryogenic deuterium jet on the Texas Petawatt laser. Neutrons were produced both by laser-accelerated multi-MeV deuterons colliding with Be or mixed metallic catchers and by d(d, n)3He fusion reactions within the jet. We observed deuteron yields of 10^13/shot in quasi-Maxwellian distributions carrying ∼ 8 − 10% of the input laser energy. We obtained neutron yields greater than 10^10/shot and found indications of a deuteron-deuteron fusion neutron source with high peak flux (> 10^22 cm^−2 s^−1). The estimated fusion neutron yield in our experiment is one order of magnitude higher than any previous laser-induced dd fusion reaction. Though many technical challenges will have to be overcome to convert this proof-of-principle experiment into a consistent ultra-high flux neutron source, the neutron fluxes achieved here suggest laser-driven neutron sources can support laboratory study of the rapid neutron-capture process, which is otherwise thought to occur only in astrophysical sites such as core-collapse supernova, and binary neutron star mergers. Moving forward, we are preparing an experiment for late 2023 to reproduce the high neutron flux and measure for the first time a multi-neutron capture process with 103Rh and 197Au as nuclear waiting materials.

ABSTRACT. Neutron stars are generally separated into two regions a thin, partially solid, crust and a liquid, inner core. The crust is about 10% of the star’s radius and about 1% of its mass. The behavior of the inner core is an open question. The crust acts as a heat blanket for the star and mediates its cooling, but understanding its behavior provides information about the core. Specifically, there is a relationship between the surface temperature of the star and the temperature at the boundary between the crust and the core, which modeling suggests is isothermal. As one goes deeper into a neutron star crust, the energy transport is radiation dominated before becoming electron dominated in the degenerate material at higher densities. The behavior of the plasma near the transition from radiation dominated to electron dominated heat transport is important for determining the temperature at the crust-core boundary. These high-energy-density conditions have not been explored in transition elements, which are present in neutron star crusts.

This work presents results of capsule implosion experiments at the Omega-60 laser facility that generate radiative shocks in nickel at extreme temperatures and densities. 60 lasers implode a thin shell capsule with an outer layer of plastic and a layer nickel on the interior surface. 1D simulation results suggest that this produces densities greater than 100 g cm-3 and temperatures over 1 keV at average ionization greater than 20. Simulations suggest the conditions in the experiment are near the radiation/electron-dominated conduction boundary in neutron stars with iron-like crusts and surface temperatures near 100 eV. These conditions result in strongly coupled ions with an ion-ion coupling parameter of about 10. The results show spectroscopic measurements and self-emission images of these implosions. The spectroscopic measurements cover the several keV range and capture the k-shell emission from nickel. The self-emission images use molybdenum and nickel filters to only image the emission from the nickel during the implosion.

The work of H. J. L. is based upon work supported by the National Science Foundation MPS-Ascend Postdoctoral Research Fellowship under Grant No. 2138109. This work is funded by the NNSA Stockpile Stewardship Academic Alliances under grant number DE-NA0004100. The experiment was conducted at the Omega Laser Facility at the University of Rochester’s Laboratory for Laser Energetics with the facility time through the National Laser Users’ Facility (NLUF) Program supported by DOE/NNSA.

ABSTRACT. Astrophysical jets develop over a range of scale lengths and source energies with many having common features that suggest universal mechanisms may be responsible for jet formation and stability. To probe these mechanisms, a novel experiment resembling a planar plasma gun has been developed to produce magnetically driven high-energy-density (HED) plasma jets on the 1 MA, 220 ns rise time COBRA generator. The experimental setup consists of two concentric planar brass electrodes which inject gas directly into vacuum through a central gas line and azimuthally continuous slit. Because there is no ablation phase of a solid target, magnetized jets develop earlier in the current pulse and can be driven longer without depleting their mass source and disrupting. A permanent ring magnet can be housed within the central electrode to provide an initial poloidal magnetic field which links the two electrodes. In this way, the experiment captures the basic dynamics of a central engine-disk system. Specifically, the winding of poloidal field lines due to disk rotation. The resulting free-boundary, high-aspect ratio (>50:1) plasma jets remain stable for hundreds of nanoseconds, achieve lengths >5 cm, and strongly resemble naturally occurring astrophysical jets. Here, we present the design of the experiment and measurements obtained using Thomson scattering, B-dot probes, Faraday rotation, laser interferometry, and self-emission imaging. We demonstrate that jet parameters reasonably scale to their astrophysical counterparts. The experimental results are used to benchmark 3D PERSEUS XMHD simulations with the goal of quantifying the injection and transport of relative canonical helicity.

This work was supported by the DOE Office of Science grant No. DE-SC0023238.

ABSTRACT. The structure of oblique shocks formed by colliding plasma flows can be influenced by factors such as radiative cooling. Here, we present experiments conducted at the MAGPIE pulsed-power generator (1.4 MA, 240 ns rise time) on colliding plasma flows produced from the ablation of solid targets using a wire array z-pinch as an x-ray source. The experiments use two planar wedge targets placed at an angle to each other such that a jet is formed where the two ablated plasma flows collide. The experiment aims to study the oblique shock where the flow is redirected. In this experiment, the targets are placed outside the return current structure so that there is no background magnetic field from the z pinch. By using different materials for each of the targets (silicon and carbon), we can investigate the effect of radiative cooling on the flow, and how it changes the structure of the shocks at the edges of the jet, as well as the boundary where the two materials collide. We present interferometry and Thomson scattering measurements to characterise this, as well as comparison with simulations using the radiation transport and MHD code Chimera.

ABSTRACT. The mechanisms by which non-thermal particles are accelerated, commonly observed in solar winds, supernova remnants, and gamma ray bursts, is a topic of intense study. When shocks are present the primary acceleration mechanism is first-order Fermi, which accelerates particles as they cross a shock. While the primary acceleration mechanism for non-thermal particles is first-order Fermi, second-order Fermi acceleration can also contribute, utilizing magnetic mirrors for particle energization. Despite being less efficient, the ubiquitous nature of magnetized turbulence in the universe necessitates the consideration of second order Fermi acceleration. Another acceleration mechanism is the lower-hybrid drift instability, arising from gradients of both density and magnetic field, which produces lower-hybrid waves. The lower-hybrid wave generates an electric field, which if co-propagating with the particle will lead to acceleration. With the combination of high-powered laser systems and particle accelerators it is possible to use magneto-hydrodynamical (MHD) scaling to study the mechanisms behind cosmic ray acceleration in the laboratory. In this work we combine experimental results and high-fidelity three-dimensional simulations to estimate the efficiency of ion acceleration in a weakly magnetized interaction region. We validated the FLASH MHD code with experimental results, using OSIRIS particle-in-cell (PIC) code to verify the initial formation of the interaction region, showing good agreement between codes and experimental results. The study revealed that the plasma conditions in the experiment are conducive to the lower-hybrid drift instability, yielding an increase in energy between 200 keV and 1,200 keV.

ABSTRACT. The transport of magnetic flux and energy in collisional, magnetized, high energy density plasma experiments are governed by an extended magnetohydrodynamics (xMHD) ansatz, which includes the Hall-MHD term in the generalized Ohm’s law. In this presentation, we discuss the details of the Hall-MHD implementation in the FLASH code, utilizing driven turbulence simulations. FLASH is a publicly available, high-performance computing, multiphysics simulation code, developed by the Flash Center for Computational Science. We investigate the role of the Hall effect in magnetic field generation by studying three-dimensional simulations of the Hall-MHD equations subjected to stochastic drive for a given Mach number. We focus on examining the impact of the Hall effect on the efficiency of the dynamo process across various values of the Hall parameter. By incorporating the Hall effect into the simulations, we explore how it influences the generation and evolution of magnetic fields. Furthermore, we examine energy transfer rates among spatial scales and observe the changes due to the Hall effect in the direct energy cascade at scales relative to the Hall effect. Through detailed analysis, these findings enhance our understanding of the interplay between the Hall effect and magnetohydrodynamics and contribute to the broader knowledge of magnetic field generation and energy transport in high energy density plasmas. The implications of this work extend to various applications, including astrophysics and laboratory plasma experiments, where the Hall effect significantly influences the behavior and dynamics of magnetized systems.

The Flash Center for Computational Science acknowledges support by the U.S DOE NNSA under Awards DE-NA0003856 and DE-NA0003842, DE-NA0004147, DE-NA0004144, and Subcontracts 536203 and 630138 with LANL and B632670 with LLNL. Support from the U.S. DOE ARPA-E under Award DE-AR0001272 and U.S. DOE Office of Science, Fusion Energy Sciences under Award DE-SC0021990 is also acknowledged.

ABSTRACT. THz time domain spectroscopy (TDS) measurements of dc conductivity at high energy densities (HED) will help constrain models of planetary interiors, especially planetary dynamos which are necessary to sustain life. Such measurements are within reach at the Laboratory for Laser Energetics thanks to collaborations with the Zhang Terahertz Research Group in the Institute of Optics. It has been shown that THz TDS provides a reliable method to constrain the dc conductivity of materials at extreme conditions [1]. This project develops the experimental design for THz TDS measurements on Omega. Results of a recent, spectrally integrated reflectivity measurement of high intensity THz on Si, carried out on Omega EP, are also presented.

[1] Z. Chen, C.B. Curry and et al. “Ultrafast Multi-Cycle Terahertz Measurements of the Electrical Conductivity in Strongly Excited Solids.” Nature Communications, 12, 1638 (2021).

ABSTRACT. We examine numerically the processes of magnetic field generation in relativistic femtosecond laser-solid interactions. Our study is motivated by a recent experiment at LOA, whereby the B fields induced in a thin (~20 μm) solid foil by a ∼1019 Wcm−2, ∼30 fs laser pulse were diagnosed via electron deflectometry. In contrast to a previous experiment[1], the ~100 MeV-range probe beam was produced by an auxiliary laser-wakefield accelerator, and injected into the solid foil through its rear (non-irradiated) surface. The mean angular deflection and root-mean-square (rms) spread of the beam electrons after exiting the irradiated foil surface showed nontrivial dependencies on delay time and transverse position with respect to the driving laser pulse. We compare these measurements with the results of 2D collisional particle-in-cell simulations run under conditions as close as possible to the actual ones. Notably, we take into account the 2D preplasma created by the laser’s pedestal and describe self-consistently the interaction of the probe electrons with the induced plasma fields. Two main B-field generation mechanisms are found to account for the observed electron deflections: (i) the collisionless current filamentation instability[2], which excites strong (~103 T), kinetic-scale fields around the laser spot[3]; (ii) the fountain-like motion of the fast electrons near the plasma-vacuum boundaries, which leads to azimuthal B fields surrounding the laser spot up to ~100 μm radii[4,5]. Our synthetic deflectometry maps reproduce qualitatively the experimental data as regards both the mean and rms deflections. To shed further light on the simulation results, we proceed with a quasistatic approach which enables the respective effects of the small- and large-scale field components to be isolated as a function of the location and time of probing. Finally, to illuminate the conditions under which these B-field components are generated and evolve, we proceed with a series of plane-wave simulations for laser intensities ranging from 1✕1018 Wcm-2 to 5✕1020 Wcm-2 under normal or oblique incidence. For increasing laser intensity, we observe an exponential increase in the maximum amplitude reached by both field components during the interaction. The two front-side field components are found to be of comparable magnitude and enhanced at oblique incidence.

P.S. Please not that I am submitting for an oral presentation. There is no section to declare it during submission, so I would like to declare it here.

References [1] G. Raj et al., Phys. Rev. Res. 2, 023123 (2020). [2] A. Bret, L. Gremillet, and M. Dieckmann, Phys. Plasmas 17, 12050 (2010). [3] J. C. Adam et al., Phys. Rev. Lett. 97, 205006 (2006). [4] G. Sarri et al., Phys. Rev. Lett. 109, 205002 (2012). [5] W. Schumaker et al., Phys. Rev. Lett. 110, 015003 (2013)

ABSTRACT. Radiative hydrodynamics models the coupling between the dynamics of a hypersonic hot plasma and the radiation it produces or external radiation. Almost every numerical codes use simplified models, that are in most cases either limited or wrong. To accurately model the photon transport the HADES 2D code was specifically developed [2, 3, 4]. Such a code is indispensable for studying astrophysical objects, in which optically intermediate regions are still poorly modeled, yet commonly encountered within such phenomena.

This code couples the hydrodynamics with the M1-multigroup model for radiation transfer [1], to accurately represent the spectral behavior of light, involving the partitioning of the electromagnetic spectrum into groups [5]. Nevertheless, simulating radiative hydrodynamics flows remains highly time-consuming, constraining our capacity to conduct comprehensive numerical studies within this field.

The most expensive part of the M1-multigroup simulations is the calculation of the closure relation, relating the radiative pressure to the radiative energy and the radiative flux, via the Eddington factor. This is due to the lack of an analytical solution. Consequently, two methods exist:

- one accurate yet costly, relying on expensive search algorithms implemented in HADES [4],

- another quicker but incorrect, utilizing the analytical grey case closure relation for each group, implemented in HERACLES [6].

To mitigate these challenges, we’ve pioneered an inventive approach intertwining neural networks with simplified models. This innovative method dramatically reduces the computation time, while maintaining an acceptable precision, revolutionizing the efficiency of these calculations within M1-multigroup simulations.

To affirm the efficiency of our approach, we conducted validation simulations, beginning with the renowned benchmark simulation of a 1D radiative shock, wherein we used up to five groups. Additionally, we undertook a radial test, to assess the efficiency of our method in a 2D situation. We wish to present this exciting method to the HEDLA conference, through a poster presentation.

References

[1] Dubroca, B. and Feugeas, J.-L., 1999, CRAS - Series I - Mathematics, vol. 329, p. 915-920 [2] Michaut, C., Nguyen, H.C. and Di Menza, L., 2011, ASS, vol. 336, p. 175–181 [3] Michaut, C., Di Menza, L., Nguyen, H.C., Bouquet, S.E. and Mancini, M., 2017, HEDP, vol. 22, p. 77-89 [4] Nguyen, H.C., 2011, Simulation de modèles hydrodynamiques et de transfert radiatif intervenant dans la description d’écoulements astrophysiques, PhD thesis, Paris 11 [5] Turpault, R., 2005, JQSRT, vol. 94, p. 357-371 [6] Vaytet, N.M.H., Audit, E., Dubroca, B. and Delahaye, F., 2011, JQSRT, vol. 112, p. 1323-1335

ABSTRACT. Laser-driven, counter-streaming plasmas are susceptible to filamentation due to the nonlinear Ion-Weibel instability [1]. Such behavior is hypothesized to be a source of some large magnetic fields in astrophysical plasmas [2]. Experiments conducted on the OMEGA laser facility leveraged novel optical Thomson scattering techniques to measure these filaments and their associated B-fields by examining local intensity fluctuations in ion acoustic waves [2]. This project incorporates analysis of the electron plasma wave (EPW) measurements. The EPW data shows large, rapid fluctuations in plasma density. By measuring the density fluctuations, we can infer the size and growth rate of the filaments.

Additionally, we can leverage our measurements of plasma parameters such as density, temperature, and flow velocity to infer the strength of the B-field in two ways. First, by assuming cylindrical current filaments, allowing us to use Ampere’s law to calculate the field [2]. Second, by assuming the thermal pressure in the filaments is balanced by magnetic pressure, with the total pressure only varying in a smooth, non-oscillatory manner. These field estimates, on the order of a hundred Tesla, are then compared to results of 2-D and 3-D PIC simulations.

[1] C. Bruulsema , W. Rozmus , G. F. Swadling , S. Glenzer , H. S. Park, J.S. Ross, F. Fiuza , Phys. Plasmas 27, 052104 (2020) [2] G.F. Swadling, C. Bruulsema , F. Fiuza , D. P. Higginson, C.M. Huntington, H S. Park, B. B. Pollock, W. Rozmus , H. G. Rinderknecht , J. Katz, A. Birkel and J. S. Ross, Phys. Rev. Let. 124, 215001 (2020) rettich@ualberta.ca bruulsema1@llnl.gov anna.grassi@polytechnique.edu frederico.fiuza@tecnico.ulisboa.pt amild@lle.rochester.edu wrozmus@ualberta.ca swadling1@llnl.gov

ABSTRACT. The double shell campaign for inertial confinement fusion uses a low-Z ablator and a high-Z inner shell that encloses the deuterium-tritium fuel. During a double shell implosion, the ablator collides with the inner shell, setting it in motion. The inner shell then compresses the fuel to high densities and pressures, enabling volumetric ignition. Due to its high density, the inner shell is prone to the formation of fluid instabilities, particularly on the outer surface of the inner shell, which can significantly degrade capsule performance. Mitigation strategies have been suggested to reduce the growth of instabilities. However, the latter are challenging to image in a spherically converging system, making it potentially non-trivial to quantify whether instability growth is sufficiently suppressed or not. The double cylinder experimental platform is composed of two concentric cylinders to mimic the double shell setup. However, due to their geometry, double cylinders provide the capability to directly measure instability growth by viewing down the cylinder axis, allowing quantification of possible mitigation schemes for fluid instabilities. A key challenge for the double cylinders is ensuring that the inner cylinder stays sufficiently uniform in the axial direction during the implosion for imaging to be effective.  Here, we will give an overview of current and future design ideas, and we will present results from recent double cylinder experiments at the National Ignition Facility.

ABSTRACT. Large-scale High-Energy Density (HED) facilities provide a unique platform for astrophysicists to conduct controlled laboratory experiments, replicating extreme conditions found in white dwarf stars and solar interiors. General Atomics (GA) has been at the forefront of this endeavor, researching and developing cutting-edge material science processes. This involves producing freestanding thick oxide and metal foils with precise areal densities required for experiments at facilities such as the National Ignition Facility (NIF) and the Z Facility. The top two contributors to solar opacity are (1) oxygen (2) iron. The effect of Fe has been extensively studied since 2004 using Fe/Mg comix targets (and contrast against Ni/Mg targets) where GA contributed photolithography-based target production and x-ray transmission-based metrology known as AutoEdge, the effect of oxygen is unknown due to the lack of HED targets with sufficient oxygen areal density. In this work, we have created thick oxide targets to enable the experimental investigation of the oxygen contribution on NIF and Z. Addressing the challenge of obtaining high-density oxygen, we utilize SiO2 to immobilize a significant amount of oxygen, while using the broadening of Si k-shell emission line as a local plasma condition sensor. Improved plasma condition determination is achieved with Mg k-shell emission lines when MgO is incorporated into SiO2, either as a discrete layer or in composite form. The high areal density required, typically 3 µm to 6 µm of SiO2 deposition, leads to high stress buildup, resulting in issues like delamination and cracking. Stress management becomes an integral aspect of our coating design, especially for mixed oxides where the stress build-up is significantly worse. The oxide thickness is one order of magnitude beyond the probing depth of Rutherford Backscattering Spectrometry (RBS) method, necessitating the deployment of AutoEdge which also has the side benefit of being non-destructive. (RBS degrades & destroys the tamping layer made of parylene.) Preliminary data from Z (the ZAPP program at Sandia) and NIF (the Discovery Science program at LLNL) suggest that oxygen contributes anomalously to x-ray opacity under higher HED conditions, which along with iron, contributes significantly to the surplus needed to resolve the solar opacity problem. Through the Sun as a model system for stellar evolution, we gained a deeper understand of the fundamental building block of our universe.

ABSTRACT. (Abstract submission for poster)

Understanding the thermal conductivity of materials found in the cores of large rocky planets can help us predict planetary evolution and understand the mechanisms necessary for the existence of organic life. However, significant variations in scientific modeling and a scarcity of experimental measurements limit our understanding of materials at these temperatures and pressures. Here we use our isochoric heating platform[1] developed for the OMEGA 60 Laser System to measure the thermal conductivity of iron alloys at planetary interior conditions. By heating a buried 5 μm high-concentration iron alloy wire encased in 10 μm of borosilicate glass to the conditions close to those found in the interiors of large Earth-like planets, we generate an interface that mimics the core-mantle boundary. After pressure equilibration, the shape of the density profile across the interface evolves primarily through thermal conductivity. The profile is measured using diffraction-enhanced X-ray radiography with a spatial resolution on the order of 1 μm[1,2,3], which enables the accurate extraction of the thermal conductivity scale length.

ABSTRACT. I'd like to present a poster on the following:

When a high-intensity laser beam hits a solid target, preferential and rapid heating of one part over the other results in a highly non-equilibrium state1;2. These temporary, high-energy-density plasmas pave the way for warm dense matter (WDM) and allow us to test quantum mechanical ideas concerning electron-ion interactions in this state. Using a high-resolution (~50meV) X-ray scattering platform3 designed for use with free-electron lasers, we are capable of measuring changes to the quasi-elastic Rayleigh peak. The peak’s full-width half max directly reflects the ions’ velocity distribution, which correlates to a model-independent ion temperature measurement of the plasma and is determined by Doppler broadening. We have measured the time evolution of the ion temperature over the first ~20ps for a metallic thin films after irradiation, during which the ions are acceleratedly heated to electronvolt temperatures. Using the ion’s temperature progression, we are able to determine the electron-ion equilibration rates in the warm dense regime. We investigate the behavior of electron-ion equilibration rates across the solid-liquid phase boundary for gold, and expect to see similar behavior in other metals.

This work was funded in part by the U.S. Department of Energy, National Nuclear Security Administration (NNSA) under Award No. DE-NA0004039. Use of the Linac Coherent Light Source (LCLS), SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. The MEC instrument is supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences under contract No. DE-AC02-76SF00515.

[1] E. Bevillon et al., Phys. Rev. B. 89(11), 115117 (2014) [2] T. G. White et al., Phys. Rev. B. 90(1), 014305 (2014) [3] E. E. McBride et al., Rev. Sci. Instrum. 89(10), 10F104 (2018)

ABSTRACT. The development of chirped-pulse-amplification (CPA)[1] has made it possible to realize a new type of ion source called laser ion acceleration, where the ions are accelerated by plasma generated when a target irradiated by an intense laser. Laser ion acceleration is a useful method for simulating cosmic ray acceleration in space, and its acceleration mechanism is actively being researched. Furthermore, the ability of laser ion acceleration to miniaturize accelerators is expected to lead to applications in various fields, including medicine and nuclear physics. However, ions with energy levels as high as actual cosmic rays have not yet been generated, and they have not reached the energy levels required for applications. This is the current situation, and the generation of high-energy ions remains a challenge in laser ion acceleration[2]. Generally, as the target thickness decreases, the energy of the accelerated ions increases, but on the other hand, there is a problem that a thin target is easily destroyed by prepulses and pedestals before the laser intensity reaches its peak[3]. To solve this problem, we developed a large-area suspended graphene (LSG) target[4]. LSG is the thinnest target in the world that can be adjusted in thickness with 1 nm accuracy. In addition, it shows very high resistance to laser prepulses and pedestals from previous ion acceleration experiments, where energetic protons and carbons are generated by irradiation of an ultra-intense laser without plasma mirror[5]. Therefore, LSG is considered to be a suitable target for laser ion acceleration. Previous studies have focused on demonstrating ion acceleration by irradiating the thinnest target with an intense laser. In this study, the aim is to optimize laser ion acceleration using LSG. As a means to achieve this, parameters such as the F-number and intensity of the laser, as well as the thickness of LSG, are scanned to increase ion energy through particle-in-cell (PIC) simulation. As a result, optimal parameter conditions for acceleration were identified, leading to the successful generation of highly energetic ions at that condition.

REFERENCES [1] P.Maine, D.Strickland, P.Bado, M.Pessot and G.Mourou, IEEE J. Quantum Electron., vol. QE-24, pp. 398-403 (1988) [2] A. Macchi, M. Borghesi and M. Passoni, Rev. Mod. Phys. 85, 751 (2013) [3] J. Schreiber, P.R. Bolton, and K. Parodi, Rev. Sci. Instrum. 87, 071101 (2016) [4] N. Khasanah et al., High Power Laser Science and Engineering 5, e18 (2017) [5] Y. Kuramitsu et al., Sci. Rep. 12, 2346 (2022)

ABSTRACT. Collisionless shocks are ubiquitous in many astrophysical systems. While we have a wealth of data from satellite measurements, many questions can best be explored in a laboratory setting. Experiments at the Omega Laser Facility (Shaeffer et al 2017, 2019) demonstrated the creation of a high-Mach-number collisionless shock but were limited to a small, magnetized volume. The Z Machine at Sandia National Laboratories can produce a large, magnetized plasma and fast, laser-driven piston by utilizing an exploding wire array and the Z-Beamlet high-powered laser. This would allow previous experiments to be extended to much larger magnetized volumes, enabling collisionless shocks to evolve over much longer time and length scales and undergo processes like shock reformation. This study shows FLASH simulation results of proposed experiments on The Z Machine to study collisionless shocks. We show the dynamics of a laser-driven piston expanding into a large, magnetized plasma.

ABSTRACT. We present results from X-ray imaging of high-aspect-ratio magnetic reconnection experiments driven at the National Ignition Facility. Two parallel, self-magnetized, elongated laser-driven plumes are produced by tiling 40 laser beams. A magnetic reconnection layer is formed by the collision of the plumes. A gated X-ray framing pinhole camera with micro-channel plate (MCP) detector produces multiple images through various filters of the formation and evolution of both the plumes and current sheet. As the diagnostics integrates plasma self-emission along the line of sight, 2-dimensional electron temperature maps ⟨T_e ⟩_Y are constructed by taking the ratio of intensity of these images obtained with different filters. The plumes have a characteristic temperature ⟨T_e ⟩_Y=180±30 eV, 2 ns after the initial laser irradiation and exhibit a slow cooling up to 4 ns. The reconnection layer forms at 3 ns with a temperature ⟨T_e ⟩_Y=280±50 eV as the result of the collision of the plumes. The error bars of the plumes and current sheet temperatures separate at 4 ns, showing the heating of the current sheet from colder inflows. Using a semi-analytical model, we find that the observed heating of the current sheet is produced by electron-ion drag, rather than the conversion of magnetic to kinetic energy, in these experiments.

ABSTRACT. Thomson scattering diagnostics are powerful approaches to obtain reliable, non-intrusive measurements of electron temperature (Te) and density (ne) without assumptions of the plasma state of equilibrium. Current methods for analyzing Thomson scattering spectra, such as the χ2 method, are computationally expensive, hindering real-time Te and ne measurements. We present a new machine learning model to derive Te and ne from Thomson scattering spectra in both the non-collective (α ≪ 1) and collective (α > 1) regimes. The model uses a transfer learning technique by first training a base model with 10,000 synthetic spectral distributions. Then additional hidden layers are added and trained with experimental data. We find that the calculation time of the neural network is faster compared with the Thomson scattering fitting algorithm in the open source PlasmaPy Python package, and we compare their accuracies too.

ABSTRACT. Collisionless shocks are common in astrophysical plasmas and are known to be important for the magnetic field amplification and acceleration of both high energy electrons and protons. While diffusive shock acceleration is well established, particle injection into the nonthermal tail remains an important puzzle. In this work we present the results of large-scale one-dimensional particle-in-cell simulations of magnetized, non-relativistic, collisionless shocks to discuss how the properties of the injected particles depend on the plasma parameters, namely the Alfvénic Mach numbers and the orientation of the ambient magnetic field with respect to the shock normal. Quasi-parallel and quasi-perpendicular shocks are analyzed. We discuss the shock structure and the injection efficiency into a non thermal power-law-like energy tail, finding that quasiparallel shocks with high Mach number are the most efficient. We analyze the dominant modes excited upstream and discuss their role in controlling electron heating and nonthermal particle energization.

ABSTRACT. X-ray radiation interacts with matter in a variety of astrophysical systems throughout our Universe including accretion disk phenomena, supernova remnants, and photoionization fronts. The photoionization front plays an essential role in understanding the evolution of the early Universe. A photoionization (PI) front marks the region within a gas or plasma where the process of photoionization predominantly occurs. PI fronts formed as the first stars heated and ionized surrounding gasses. After the Cosmic “Dark Ages”, radiation from the first stars reionized the Universe after hot matter from the Big Bang cooled and recombined. We aim to study the evolution of PI fronts in a scaled laboratory experiment by creating an x-ray source that is incident on a neutral gas. Characterization of the x-ray course is key to understanding the formation and evolution of the PI front. We show preliminary data analysis of x-ray emission from laser-irradiated copper foils conducted using soft x-ray images and DANTE data on Omega-60. This data serves to characterize the most effective driver for future experiments investigating photoionization fronts.

This work is funded by the U.S. Department of Energy NNSA Center of Excellence under cooperative agreement number DE-NA0003869.

ABSTRACT. Massive stars are commonly found in binary systems or multiple star systems. When the evolved primary star in a close binary system expands and engulfs its companion, the two stars share a temporary common envelope (CE). CE evolution is a transient yet critical process in binary star evolution and lead to either a merger of the primary core and the companion or the ejection of the shared envelope. Jet feedback from accretion onto the companion during a CE evolution is speculated to affect the orbital evolution and envelope unbinding process. Previous simulations demonstrate that jets are choked quickly after the plunge-in phase and efficiently transfer their energy to the envelope thereafter, which leads to increased percentage of envelope unbinding [1]. In this study we investigate the dynamical interaction between jets and stellar envelopes and propose a laboratory-scale, laser-driven plasma experiment to mimic the interaction in a controlled environment. The experiment is designed using FLASH, the radiation-magneto-hydrodynamics code developed at the Flash Center for Computational Science. These simulations can inform and reveal in detail the energy transformations and instability development during jet-envelope interactions, guiding future laboratory astrophysics experiments.

The Flash Center acknowledges support by the U.S DOE NNSA under Awards DE NA0004144, DE NA0004147, and Subcontracts 536203 and 630138 with LANL and B632670 with LLNL. Support from the U.S. DOE ARPA E under Award DE AR0001272 and U.S. DOE Office of Science, Fusion Energy Sciences under Award DE SC0021990 is also acknowledged. We acknowledge support from the National Science Foundation under Award PHY 2308844.

REFERENCES [1] Zou, Chamandy, et al., “Jets from main sequence and white dwarf companions during common envelope evolution”, Monthly Notices of the Royal Astronomical Society, 514, (2022)