ABSTRACT. Because it operates throughout the entire near- and mid-infrared spectral regions, the James Webb Space Telescope (JWST) is an ideal facility to use to study warm molecular gas within star-forming regions, including irradiated interfaces and photodissociation regions (PDRs) where molecules form and dissociate behind H-II regions, and behind shock fronts that exist within bow shocks of stellar jets and along the walls of evacuated cavities. The spectrometers on JWST produce data cubes that separate emission lines clearly from the continuum, and in the case of stellar jets, resolve velocity structures spatially within the flow. In this talk I will summarize some of the initial results from the large PDRs4All collaboration to study irradiated interfaces in the Orion Nebula, and PROJECT-J, a focused study of the collimation and excitation properties of a highly-obscured stellar jet. The rich data sets in these studies make it possible to trace the location of dozens of ions, atoms, and molecules and to calculate temperature and density maps using emission line ratios, especially with the complete set of rotational transitions of the H2 molecule now available with JWST. The infrared spectra show how complex hydrocarbons evolve within PDRs , and the mass loss rates inferred from molecular tracers imply that photons with energies < 13.6 eV may still drive enough photoevaporation to affect planet-formation lifetimes. Experiments involving radiation fronts, jets, and shock waves may lead to laboratory analogs of some of these phenomena and a way to test analytical theoretical formalisms.

ABSTRACT. Here we report on an experimental platform at the HiRadMat facility, within CERN’s accelerator complex aimed at recreating a laboratory analogue of ultra-relativistic blazar-induced pair jets propagating into the intergalactic tenuous plasma. A dense electron-positron pair beam is produced by irradiating a target with 440 GeV protons from the Super Proton Synchrotron. The pair yield and plasma extent are orders of magnitude larger than currently achievable at laser facilities, producing for the first time pair plasma conditions necessary for the study of relativistic kinetic plasma instabilities. In our experiment, the pair beams are remarkably stable as they propagate through 1-m of plasma. Linear theory predicts that the growth of kinetic instabilities is strongly suppressed when non-idealized beam conditions are assumed, such as the inclusion of a small transverse temperature, and particle-in-cell simulations suggest that beam divergences of a few percent are enough to significantly suppress the instability. An experimentally inferred growth rate, when scaled to blazar's jets, is comparable to the inverse-Compton cooling time of the pairs on the cosmic microwave background. Given that a cascade of GeV inverse-Compton scattered photons is not observed from blazar's jets, our results imply that such an absence must be the related to the presence of intervening magnetic fields in the intergalactic plasma of primordial origin.

ABSTRACT. Fast, axially collimated outflows, or “jets”, are ubiquitous in astrophysical environments. They flow from most classes of accreting compact objects including young stellar objects, neutron stars, and stellar mass black holes to supermassive black holes in the centers of galaxies. Such jets provide strong feedback effects to their surroundings, making them primary systems, for example, for understanding general relativity in black hole systems, their impact on galaxy formation as well as the non-thermal component in the overall cosmic energy flow.

Much progress has been made in astronomical observations and theoretical/computational modeling of astrophysical jets. But many fundamental challenges remain, including issues in jet generation, composition, transport, stability, and interactions. During the past decade, laboratory jet experiments have reached a level of maturity and have yielded interesting insights. Complimentary to magnetically driven laboratory jet experiments (e.g., MAGPIE, Caltech), the advent of high-energy-density (HED) laser facilities, such as NOVA, Gekko, LULI, OMEGA, and the NIF, has enabled experiments with kinetic/thermally driven to reproduce certain aspects of plasma jets in laboratory in the regimes directly relevant to astrophysical systems of interest. These laboratory jet experiments offer a unique opportunity of studying jet propagation, stability, and termination processes with in-situ measurements. Several key physical insights underpin the relevance of laboratory experiments for astrophysical jet studies include: first, when plasma dissipative processes such as viscosity and resistivity are insignificant, the nearly ideal plasma conditions are scale-free, allowing scaling studies of laboratory jets to astrophysical scales; second, when the (dimensionless) jet aspect ratio (length/radius) becomes large (> 10) and the jet lifetime is comparable or longer than the dynamic time (such as sound or Alfven wave crossing time), it becomes meaningful to investigate jet stability; and third, when the kinetic, thermal, radiative and magnetic energy components undergo exchanges, this provides valuable information on how to model such processes in astrophysical jets.

In this talk, we will present some of recent experiments by our team on OMEGA facilities, highlight and discuss our understanding of the underlying physics and remaining issues. These experiments have been instrumental in defining the exciting scientific issues that are attainable with laboratory experiments gaining the physical insight into the jet generation, instability, and interactions, scoping out the possible parameter spaces that are unique to be achieved in large HED facility, such as the NIF, and finally enabling the establishment of the physical scaling from laboratory experiments to astrophysical environments.

This work was supported in part by the U.S. Department of Energy NNSA MIT Center-of-Excellence under Contract DENA0003868, the U.S. Department of Energy, Office of Science and NNSA, HEDLP under Contract DE-NA0004129, and NLUF under Contract DE-NA0003938.

ABSTRACT. Plasma jets are commonly observed in the universe. They originate from most classes of accreting systems, for instance, star forming systems, accreting neutron stars, and even black holes. The light resulting from their interaction with surrounding interstellar medium and molecular clouds provides important insights about these astrophysical objects and their systems of origin. Despite this wealth of information and sophisticated simulations developed to model these jets, a consensus has yet to be reached to describe them in their entirety. In particular, their high collimation and apparent stability continue to be subjects for debate. To better understand these objects and to validate the simulated results, plasma jets were produced at OMEGA 60 laser facility in a controlled environment.

In this experimental campaign, laser beams were employed to ablate the inner surface of a half-sphere target. The expanding plasma plumes collided at the center of the half-sphere, resulting in the formation of a cylindrical jet. These jets had a high velocity nearing 1500 km/s and a large aspect ratio (~34) making them relevant for studies of young stellar objects. Various radiative and magnetic conditions were studied by varying the material of the target (low and high atomic number) and by imposing an external magnetic field with a MIFEDS. In this presentation, the results of this experiment, obtained from a set of diagnostics, will be compared to FLASH4 magnetohydrodynamic simulations.

This work was supported in part by the U.S. DOE, LLE and NLUF.

ABSTRACT. Of all the astrophysical outflows emmited from objects, Herbig-Haro (HH) stellar jets are among the most energetic (Bally 2016). The recent development of laboratory astrophysics using high-power laser facilities makes it possible to study such astrophysical phenomena in the laboratory (Foster et al. 2005). In this work we investigate the role these Herbig-Haro jets play in triggering new star formations in dense media. To do so, a high-energy-density experiment was performed at the LULI2000 laser facility. A plastic ball was compressed by a fast titanium jet produced with a nanosecond laser. In addition, simulations were made on the 3D radiative hydrodynamics code TROLL (CEA-DAM) for a greater detail analysis of the ball compression and the jet characteristics. Using scaling laws, we discuss the similarity between the stellar, the experiment and the numerical jets. Simulations of the diagnostics (radiative emissions, X-ray and density gradient) were also performed. The agreement between the experiment and the 3D simulation has enabled an in-depth numerical study of the propagation of the jet in media of different densities, or of the deflection of the jet in the case of an off-axis impact with the ball.

ABSTRACT. The acceleration of energetic charged particles by collisionless shock waves is an ubiquitous phenomenon in astrophysical environment. By coupling high-power lasers with strong magnetic fields, we have been able to generate and characterize magnetized collisionless shocks [1]. Further, we showed that these could accelerate particles in the shock-surfing (SSA) governed, non-relativistic regime [2]. We will here review recent results obtained at the Vulcan TAW laser facility, in which we used higher-energy lasers to generate faster shocks. This, coupled to a shock-shock collision scheme that allows to exploit a phase-locking acceleration mechanism [3,4], allowed us to accelerate particles to higher energy, in a regime which simulations suggest is drift-shock acceleration (DSA). We will also discuss the potential of multi-PW lasers, e.g. Apollon (France) [5] or ELI (Czech Rep., Romania), to generate near- relativistic shocks in the laboratory, by producing a fast enough piston driven into a magnetized ambient plasma.

[1] W. Yao, et al. “Detailed characterization of laboratory magnetized super-critical collisionless shock and of the associated proton energization”, Matter and Radiation at Extremes 7, 014402 (2022) [2] W. Yao, et al. "Laboratory evidence for proton energization by collisionless shock surfing". Nature Physics, 17(10):1177–1182, 2021. [3] W. Yao, et al., “Investigating particle acceleration dynamics in interpenetrating magnetized collisionless super-critical shocks”. Journal of Plasma Physics 89(1), 915890101 (2023) [4] A. Fazzini et al., “Particle energization in colliding subcritical collisionless shocks investigated in the laboratory”, A&A 665, A87 (2022) [5] K. Burdonov et al. “Characterization and performance of the Apollon Short-Focal-Area facility following its commissioning at 1 PW level”, Matter and Radiation at Extremes 6 (2021)

ABSTRACT. Several multi-petawatt laser facilities are coming online around the world including ZEUS at the University of Michigan and ELI-Beamlines in the Czech Republic that will push forward the energetic frontier of plasma physics with expected laser intensities exceeding 10^23 W/cm^2. One of the most exciting applications of the laser systems at these facilities will be to the study of extreme astrophysical processes. Standard laboratory astrophysics configurations, for example two-beam magnetic reconnection, performed on these facilities will see much stronger fields than has previously been demonstrated. Diagnosing the experiments performed in this regime will be challenging and will likely require novel measurement techniques. In addition, the interactions will be so energetic that strong-field quantum electrodynamics (SFQED) processes including non-linear Compton scattering and non-linear Breit-Wheeler pair creation will become important to the dynamics of the interactions. These SFQED processes are not only important to laser-plasma interactions but appear in the simulations and models used by the extreme astrophysics community for various astrophysical systems including pulsars and magnetars. The validation of models used for these processes is one of the primary goals of these multi-petawatt facilities and will therefore form another area for the plasma physics community to connect with the astrophysics community. In this talk I will discuss work that I have performed to build toward laboratory astrophysics on multi-petawatt laser facilities and my outlook on what these facilities will allow us to study.

This work was supported by the National Science Foundation (NSF Award No. 1751462) and Czech Science Foundation (NSF-GACR collaborative Grant No. 2206059 and NSF Grant No. 2108075). The OSIRIS Consortium (UCLA and IST) provided access to the OSIRIS 4.0 framework (NSF ACI-1339893).

ABSTRACT. We investigate the growth of Kelvin–Helmholtz instability (KHI) and the emergence of vortices in laser produced plasmas through numerical simulations. By irradiating two flat targets, placed at a slight distance from each other, with intense lasers, supersonic plasma from the rear side of each target is generated, leading to counter-streaming flows between the targets. The collision of these flows results in the observation of filamentary structures via proton backlight imaging, indicating the excitation of electric and/or magnetic fields within the shock-compressed plasma. We have done radiation hydrodynamic simulations and high-resolution hydrodynamic simulations to analyze our experimental setup. We observed the growth of KHI at the contact discontinuities, attributed to the curved contact discontinuity and shear flows. This instability growth induces turbulence in the shocked plasma and the excitation of electric and/or magnetic fields. We have been implementing data science and machine learning to reconstruct the vector three-dimensional turbulent electromagnetic fields.

ABSTRACT. Understanding the conditions conducive to particle acceleration at collisionless, non-relativistic shocks is important for the origin of cosmic rays. We use hybrid (kinetic ions—fluid electrons) and full particle-in-cell kinetic simulations to investigate particle acceleration and magnetic field amplification at non-relativistic, weakly magnetized, quasi-perpendicular shocks. So far, no self-consistent kinetic simulation has reported non-thermal tails at quasi-perpendicular shocks. Unlike 2D simulations, 3D runs show that protons develop a non-thermal tail spontaneously (i.e., from the thermal bath and without pre-existing magnetic turbulence). They are rapidly accelerated via shock drift acceleration up to a maximum energy determined by their escape upstream. We discuss the implications of our results for the phenomenology of heliospheric shocks, supernova remnants and radio supernovae.

ABSTRACT. Design and analysis of high energy density (HED) experiments utilizing high power lasers usually rely on radiation hydrodynamics simulations. There are some laser-plasma interaction regimes, however, where plasma possesses long mean-free-path properties, such as magnetic field generation via the Biermann battery mechanism, strongly driven magnetic reconnection, or formation of magnetized collisionless shocks via ablated plume-ambient plasma interaction. Thus, first-principle kinetic simulations or extended fluid models may be necessary for better understanding of the HED physics. In our work, we present the benchmarking and the first results obtained with laser energy deposition module implemented in the particle-in-cell code PSC. The simulation results are tested against the radiation hydrodynamic simulations with the FLASH code and analytical estimates. We also discuss possible kinetic effects that are to be expected from laser target ablation in the HED regime.

ABSTRACT. Resonant inelastic x-ray scattering (RIXS) is a powerful spectroscopic technique capable of providing direct access to the electronic structure (and dynamics) of atoms, molecules, and solids. However, RIXS is a photon hungry technique that requires access to an energetic and highly monochromatic x-ray source. To date, these requirements have hindered its application to the study of matter at extreme conditions, including matter driven by laser shock compression, which, in turn, has limited our ability to study the evolution of electronic structure in matter at high density. Here I will discuss how high-resolution RIXS measurements can be enabled by using the stochastic nature of the full self-amplified spontaneous emission FEL pulse via a newly developed dynamic kernel deconvolution method with a neural surrogate. Using this approach, we can discriminate between the valence electronic structures of Fe in pure Fe and in Fe2O3, and measure the temperature in warm-dense Fe compounds via the M-shell ionization signature in RIXS directly.

ABSTRACT. Heat transport throughout high-energy-density systems and across interfaces is an important process with many unresolved aspects. In particular, thermal conductivity in warm dense matter has extensive theoretical predictions but lacks experimental benchmarking [1]. We use Fresnel Diffractive Radiography [2-4] to measure the interface evolution in an isochorically-heated plastic-coated tungsten wire. After pressure equilibration, the interface is hydrodynamically stable and its evolution is driven primarily through thermal conduction, which modifies the temperature and density profiles. We find experimental evidence of a significant, enduring heat barrier between the warm dense tungsten and its surrounding plastic. This temperature jump is characteristically similar to temperature jumps resulting from interfacial thermal resistance [5], indicating that the phenomenon can play a significant role at these extreme conditions. The restricted heat flow may be of particular importance for inertial confinement fusion experiments, where instability-prone material interfaces play a large role in determining capsule implosion performance [6]. [1] T. G. White et al. Phil. Trans. Roy. Soc. A 381, 20220223 (2023). [2] C. H. Allen et al. Appl. Opt. 61, 1987 (2022). [3] M. Oliver et al. Rev. Sci. Inst. 93, 093502 (2022). [4] M. O. Schoelmerich et al. Rev. Sci. Inst. 94, 013104 (2023). [5] J. Chen et al. Rev. Mod. Phys. 94, 025002 (2022). [6] B. Hammel et al. High Ener. Dens. Phys. 6, 2, 171 (2010)

ABSTRACT. Determining transport properties like viscosity under extreme conditions remains challenging, yet critical for applications like inertial confinement fusion and modeling planetary interiors. We present a new experimental implementation to infer viscosity at extreme pressures and temperatures by leveraging rippled shock waves in laser-driven experiments. The experiments utilize OMEGA EP beams to drive a multi-megabar shock into a fused silica target with pre-imposed sinusoidal interface modulations. This perturbation is transferred to the shock front, initiating damped oscillatory motion. We demonstrate that a combination of line-imaging velocity interferometry and streaked optical pyrometry enables measurements of continuous temporal evolution of the rippled shock from a single laser shot. We also compare the measurements with two-dimensional hydrodynamic simulations which qualitatively reproduce the observed dynamics and provide insights into the experiment's hydrodynamics. Further quantitative analysis based on analytical rippled shock theory will allow determining viscosity of shock-compressed material.

ABSTRACT. I would like to submit this abstract for an oral presentation.

When a high-intensity laser is incident on a solid target, the preferential and rapid heating of electrons over the ions creates a highly non-equilibrium state. These highly transient, high-energy-density plasmas are a precursor to equilibrated warm dense matter (WDM). We have developed a high-resolution (∼50 meV) X-ray scattering platform to be used with free-electron lasers that is capable of measuring changes to the quasi-elastic Rayleigh peak. Governed by Doppler broadening, the peak’s width corresponds to a direct measurement of the ions’ velocity distribution. This acts as a model-independent ion temperature measurement for the plasma. Combining this temperature measurement with the Bragg peak diffraction allows us to use the Debye-Waller relationships to uniquely determine the Debye temperature and ultimately the inter-atomic bond strength of the thin metallic samples.

ABSTRACT. Shock-bubble interactions occur in a wide range of astrophysical flows and can be studied directly in scaled laboratory experiments. We present new simulation results using the xRAGE radiation-hydrodynamic code which examine the role of heat and radiation transport in high energy density (HED) void collapse experiments performed at SLAC National Accelerator Laboratory. The experiments and simulations involved a 300-400 GPa shock generated by laser ablation of a polystyrene-like target containing an artificial void. We show that our simulations are largely insensitive to radiation model, indicating that radiation transport does not yet play an important role at “low” HED pressures. We also show that the dominant effect of heat conduction on experimental observables is to alter the properties of secondary shocks that reverberate between the ablation front, sharp impedance gradients, and the primary shock front. In particular, we show that this relationship is simple and monotonic. These results suggest that it may be possible to infer transport properties such as heat conductivity from shock characteristics that are measurable by direct imaging in these experiments.

ABSTRACT. The high intensity high contrast short pulse laser is a unique tool for generation of the high temperature (~ 10 keV) solid density highly charged plasma in an extreme condition. The understanding the dynamics and ionization physics of the plasma is very important because the plasmas provide a platform for transforming electromagnetic laser fields into quasi-electrostatic fields for the high energy particle accelerations. For high efficient acceleration of the charged particles, obtaining highly charged ion states is crucial. However, the way to achieve the condition is not simple because the ionization physics is strongly related to the dynamics of the non-LTE plasma which is rapidly heated up within a femtosecond time scale. In our previous study, we clarified experimentally/theoretically/computationally the transition of dynamics and ionization mechanism of the silver (Z=47) plasma depending on the target thickness formed by the 5x1021 Wcm-2, 12 J, 45 fs laser pulses with relatively good intrinsic contrast condition. For the optically thick target case, the collisional ionized silver ions in a resistively heated up to ~ 10keV plasma are accelerated by the sheath field at the back side of the target (Au+40 13MeV/u), while in the optically thin plasma the laser field ionized silver ions are accelerated by Hole boring mechanism at the front side of the target and sheath field at the back side of the targets (Au+45, 25 MeV/u). We recently extend the study of the dynamics and ionization mechanisms to heavier ion plasms, such as gold (Z=79) with 3x1021 Wcm-2, 10 J, 45 fs, plasma mirror cleaned laser pulses. The purpose of using plasma mirror cleaned laser pulse is to inject the laser energy in the gold plasma before the plasma cools down by radiation. We simultaneously invent X-ray diagnostic for the temperature measurement. For the optically thick target, the observed temperature of ~ 10 keV level is consistent with the PIC simulation and the analytical calculation by assuming that the plasma is resistively heated up. The average charge states of gold plasmas estimated by the shift of the spectral lines (corresponds to M to L shells transitions) with the help of atomic code GRASP reasonably matches to the observed temperature. We have demonstrated that a short pulse high intensity laser can heat up high-Z targets to extreme conditions by controlling the laser pulse temporal profile. The comprehensive understanding of laser-driven heavy ion acceleration dynamics paves the way to controlling the production of highly charged high-energy heavy-ion beams with PW class high-intensity short-pulse lasers. The ability to accelerate high charge state heavy ions over such small spatial and temporal scales is a significant step toward the realization of a next-generation compact heavy-ion accelerator, enabling exploration at the frontier of nuclear physics and nuclear astrophysics.

ABSTRACT. Laser-plasma electron accelerators using the already available ps lasers at HED facilities [1] provide a new method of charged particle radiography of HED conditions [2 ]. Relativistic electrons are far more penetrating than laser-generated protons and provide contrasting electric and magnetic field measurements. This is crucial for measuring fields in high-Z conditions of interest, such as hohlraums [3]. The <1 ps probe time of the electrons also allows for very precise probing of specific times of HED conditions. This talk will report measurements of fields in laser driven foils with pulse lengths ranging from 0.1-2.5 ns and foil materials ranging from plastic to gold. These results provide insight into the expansion of laser-driven plasmas in hohlraum relevant conditions as well as insight into the laser-plasma accelerator itself.

1)J. L. Shaw et al., “Microcoulomb (0.7 ± 0.40.2 μC) laser plasma accelerator on OMEGA EP,” Scientific Reports, vol. 11, no. 1, pp. 1–9, 2021.

2)Bruhaug, G., Freeman, M.S., Rinderknecht, H.G. et al. Single-shot electron radiography using a laser–plasma accelerator. Sci Rep 13, 2227 (2023).

3)C. A. Walsh, J. D. Sadler, and J. R. Davies, “Updated magnetized transport coefficients: Impact on laser-plasmas with self-generated or applied magnetic fields,” Nuclear Fusion, vol. 61, no. 11, 2021.

ABSTRACT. Nanowire (NW) arrays are of wires with a few hundred nm in diameter and 2-10 µm in length aligned vertically on a bulk surface. is a promising nano-structured target for laser-plasma experiment. A previous study shows that nanowire array targets can absorb a higher laser energy than a flat foil target, efficiently creating volumetric ultra-high energy density states [1,2], which is of astrophysical interests. However, energy absorption and transport mechanisms in the laser-NW array interaction are still unclear. Here, we report an experiment on SACLA x-ray free electron laser (XFEL) facility to evaluate the energy absorption and transport in the nanowire arrays. The NW arrays we used in this experiment were fabricated by AAO template method. Cu wires with 2 µm lengths were grown on a 10 µm thick Cu substrate. The wire diameter and the density of the NW array were 200-300 nm and 16%, respectively. As a reference target, we employed 10-µm thickness Cu foils. The NW arrays and solid targets irradiated with an ultrahigh-intensity laser were probed with an XFEL beam with a photon energy of 8.92 keV for x-ray transmission imaging [3]. We observed temporal evolution of the heated region in the NW array by changing the delay time of the ultra high-intensity laser and the XFEL. The optical laser at a wavelength of 800 nm produced a 30 fs pulse with a 0.8 J beam energy in 15-20 µm spot diameter (FWHM). Fast electrons and electron-induced x-rays were measured with an electron spectrometer, an Bragg crystal spectrometer and a Cu Kα imager. Details of the measurements and interpretation of the data will be discussed.

ABSTRACT. Short-pulse intense lasers have potentials to model extreme astrophysical environments in laboratories. Although ex-situ measurements of distribution functions using electron spectrometer and Thomson parabola are standard diagnostics in the intense laser experiments, the diagnostics to measure the interaction region of laser and plasma are limited. We have been developing the diagnostics of the interaction between intense laser and plasma using scattered intense laser. We performed experiments to observe the spatial distributions and spectra of the scattered main laser beam interacting with gas-like target using optical imaging and spatially resolved spectrometer, respectively. The observed light has a polarization that is consistent with the main laser beam indicating the observed light originates from the main laser. The image reflects the spatial distribution of electron and focusing laser beam. The spectrum has a periodic structure in the wavelength. Comparing the results with numerical simulations, the periodic structure can be the Bernstein wave resonant feature and one can estimate magnetic field from the periodic spectrum.

ABSTRACT. Stars form in turbulent clouds of molecular hydrogen, where shocks in the compressible turbulence drive local density enhancements that can lead to local gravitational decoupling from the cloud and star formation. Key star formation metrics, such as the star formation rate or the mass distribution of the resulting stellar population, are therefore tied to the density distribution of the turbulence. This density distribution, in turn, is sensitive to the way the turbulence is driven, where a turbulent driving parameter links the density variance to the level of turbulence as measured by the turbulent Mach number. Here we describe progress on experiments to infer the turbulent driving parameter for turbulence forced by shocks, as is often the case for star forming clouds. Compressible turbulence is generated in a shock tube at the National Ignition Facility (NIF) by sending a shock through a foam with pre-fabricated density non-uniformity. Radiography and line-imaging VISAR, along with secondary diagnostics, are used to diagnose the experiments. An initial analysis of the experiments infers the shock-forced turbulence has a highly compressive driving parameter.

This work was performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344.