We report on record brightness from Ag x-ray emission obtained using a novel laser-produced plasma source. The reported K-shell conversion efficiency of nearly 1% with a radiant energy of X 0 . 6 kJ/sr from Ag ions is the highest presently recorded and is about twofold greater than more conventional metal-lined cavity targets. He-like Ag ions are the dominant radiators at X 22 . 7 keV, which contrast the x-ray sources from other pulse power facilities that produce K-shell x-rays from Auger processes in near-neutral ions driven by the nonthermal hot electrons produced in the Z-pinch implosion. The reported x-ray emission was produced from a 4-mm-diameter, 4-mm-long underdense silver nanowire target at 10 mg/cm3. The National Ignition Facility laser beams deposited X 1000 kJ of 3 omega light into the target with a X 400 TW, 2.5 ns square pulse. Finally, we show via comparisons of data with radiation-hydrodynamics simulations that flux-limited classical thermal energy transport models are inadequate in correctly modeling the behavior of these non-local thermodynamic equilibrium plasmas.

Optical components for laser beams with high peak and averaged powers are being developed worldwide using stimulated plasma scattering that occurs when plasmas interact with intense, coherent light. After decades of pursuit of pulse compressors, mirrors, and other plasma based components that can be created by stimulated scattering from electron density perturbations forming on ultra-short time scales (e.g., via Stimulated Raman Scattering), more recent work has produced optical components on longer time scales allowing ion motion as well [via Stimulated Brillouin Scattering (SBS)]. In the most recent work, ion wave plasma optics have had success in producing pulses of focusable coherent light with high energy and fluence by operating on ns time scales and now promise to enable numerous applications. Experiments have further shown that in some parameter regimes, even simple plasma response models can describe the output of such optics with sufficient accuracy that they can be used as engineering tools to design plasma optics for future applications, as is already being done to control power deposition in fusion targets. In addition, the development of more sophisticated models promises to enable still higher performance from SBS driven plasma optical components under a wider range of conditions. The present status and most promising directions for future development of ion wave plasma optic techniques are discussed here.

Beam combination via an ion wave plasma optic is discussed, including measurement of the power transfer (pump depletion and seed amplification) for several seed pulse durations and total pump energies, with accompanying simulation studies.

We propose a new approach to inertial confinement fusion (ICF) that could potentially lead to ignition and propagating thermonuclear burn at the National Ignition Facility (NIF). The proposal is based upon a combination of two concepts, referred to as polar direct drive and liquid deuterium–tritium wetted foam capsules. With this new concept, 2D radiation hydrodynamic simulations indicate that ICF ignition and propagating thermonuclear burn are possible with the laser power and energy capabilities available today on the NIF.

Polar direct drive neutron source experiments were performed at the National Ignition Facility showing substantial improvement in total neutron yield and efficiency of conversion of laser energy to fusion output. Plastic capsules 3–4 mm in diameter were filled with 1.5 mg/cc of deuterium–tritium (DT) fuel and imploded with laser beam pointing and defocus designed to compensate for polar asymmetry introduced by the facility beam entrance angles. Radiation-hydrodynamics simulations were employed to optimize the multi-dimensional laser and target parameter space, within facility and target fabrication constraints. Ensembles of 1D simulations tuned to match the outputs of early shots in the series were used to design subsequent shots in the series. This allowed the later shots to be designed based on empirically motivated sensitivities to laser and target input parameters, while eliminating the need to explicitly model phenomena such as hydrodynamic instabilities and nonlinear laser–plasma interactions. One experiment with a 3.0 mm diameter CH capsule produced 13.6 kJ (4.81 × 1015 DT neutrons) from a laser input below the NIF optics damage threshold at 585 kJ, 328 TW. Two experiments with 4.0 mm capsules produced 31.3 and 33.6 kJ of fusion output (1.11 × 1016 and 1.19 × 1016 DT neutrons) with 1.10 MJ, 390 TW and 1.26 MJ, 425 TW of laser input, respectively.

High fluence K-shell and L-shell x-ray sources are desired for various high energy density physics experiments. One efficient method for creating such a source is the laser heating of materials that are underdense to laser light. Nano-wire foams are an ideal choice for an underdense material and have average densities of 6-15 mg/cm 3 . The manufacture of robust Cu, Ag and Au nano-wire foams into millimeter scale targets is possible through a technique of freeze casting an aqueous suspension of nano-wires. Cylindrical targets with sizes between 2 to 4 mm have been shot on both the NIF and the Omega laser facilities. For example, x-ray conversion efficiencies (XRCE) from silver nano-wire foams have been measured to be ~1.0% when heated with ~400 TW of 3w laser light in a 2.5 ns square pulse from the NIF laser system. The XRCE from foam targets have been found to be ~2 times that observed in metal lined cylindrical cavity targets and ~5 times that observed in prepulsed metal foils. Experimental results and comparisons with simulations will be presented.

Filtered diode array spectrometers are routinely employed to infer the temporal evolution of spectral power from x-ray sources, but uniquely extracting spectral content from a finite set of broad, spectrally overlapping channel spectral sensitivities is decidedly nontrivial in these under-determined systems. We present the use of genetic algorithms to reconstruct a probabilistic spectral intensity distribution and compare to the traditional approach most commonly found in the literature. Unlike many of the previously published models, spectral reconstructions from this approach are neither limited by basis functional forms nor do they require a priori spectral knowledge. While the original intent of such measurements was to diagnose the temporal evolution of spectral power from quasi-blackbody radiation sources-where the exact details of spectral content were not thought to be crucial-we demonstrate that this new technique can greatly enhance the utility of the diagnostic by providing more physical spectra and improved robustness to hardware configuration for even strongly non-Planckian distributions.

Submitted for the DPP19 Meeting of The American Physical Society Ion Wave Plasma Optic Concepts for NIF and Other Lasers 1 ROBERT KIRKWOOD, P. L. POOLE, T. D. CHAPMAN, S. C. WILKS, P. MICHEL, L. DIVOL, Lawrence Livermore Natl Lab, N. J. FISCH, Princeton, P. NORREYS, Oxford, W. ROZMUS, University of Alberta, J. BUDE, B. E. BLUE, B. M. VAN WONTERGHEM, Lawrence Livermore Natl Lab — Recent demonstrations at NIF of plasma optics produced with ion waves driven by Cross Beam Energy Transfer (CBET) [1,2,3] have motivated work to develop concepts for similar optics to enhance laser performance at NIF and other laser facilities. The success of CBET models based on the linear response of ion waves in plasmas with minimal inverse Bremsstrahlung absorption [3,4], now motivates their use to design new plasma optics to produce beams with high performance in other respects, including: a beam combiner transferring energy to a beam with reduced focal spot size, a short pulse amplifier that transfers the power from many 1 ns beams to a single beam with <0.1 ns duration, and a pulse compressor that uses a plasma combined pump with >40 kJ in 1ns compressed to a duration of 10 to 100 ps in a second stage of interaction in a ̃15 cm plasma. The challenges associated with designing and fielding such optics at NIF and elsewhere, as well as the requirements plasma optics place on new or upgraded facilities will be discussed to identify the most promising concepts. [1] P. Poole in preparation [2] R. K. Kirkwood et al Nat. Phys. 14 , 80 (2018). [3] R. K. Kirkwood et al Phys. of Plas. 25 056701 (2018). [4] A Colaitis et al Physics of Plasmas 25, 033114 (2018) 1Work performed under the auspices of the U.S. DoE by Lawrence Livermore National Lab under Contract DE-AC52-07NA27344 Robert Kirkwood Lawrence Livermore Natl Lab Date submitted: 03 Jul 2019 Electronic form version 1.4

Sentinel is a 16-channel, filtered x-ray diode array spectrometer that has been developed to measure ∼1 keV-20 keV x-ray emission generated by the National Ignition Facility (NIF) laser. Unlike the large, fixed-port versions of this diagnostic that currently exist on the NIF (known as Dante), Sentinel is a Diagnostic Instrument Manipulator compatible such that it can be fielded along the polar or equatorial lines-of-sight-an essential new capability for characterizing the often anisotropic x-ray emission from laser-driven sources. We present the diagnostic design along with preliminary diode calibrations and performance results. The novel, small-form-factor x-ray diode design allows for ≳5×-25× increased channel areal density over that of Dante, simultaneously enabling improved diagnostic robustness and fidelity of spectral reconstructions. While the Sentinel diagnostic is anticipated to improve line-of-sight spectral characterization of x-ray sources for a wide variety of programs on the NIF, the compact and portable design is also attractive to small- and mid-scale facilities with limited diagnostic real estate.

We report on the performance of high x-ray fluence Kr K-shell sources that are being developed for high energy density experiments. These targets are 4.1 mm in diameter 4.4 mm tall hollow epoxy tubes having a 40 μm thick wall holding 1.5 atm of Kr gas. For these shots, the National Ignition Facility laser delivered a nominally constant total energy of ≈750 kJ of 351 nm (3ω) light at the three power levels [e.g., ≈120 (low), ≈145 (medium), and ≈210 TW (high)]. The Kr K-shell (Ephoton = 8–20 keV) x-ray radiant intensity and radiant energy (kJ/sr) of these sources were found to increase as a function of laser power but began to plateau at the highest laser power. The Kr K-shell radiant energy increased from ≈1 kJ/sr at ≈120 TW to ≈2 kJ/sr at ≈210 TW. Radiation hydrodynamics simulations predict radiant energies to be always higher than these measurements. The increase in K-shell emission is attributed to its strong dependence on the electron temperature. Electron temperature distributions were inferred from measured Heα and Lyα line emission through the use of a genetic algorithm and Scram modeling. The inferred temperatures from the experiment are 20% to 30% higher than those predicted from modeling.

Supersonic flows with high Mach number are ubiquitous in astrophysics. High-powered lasers also have the ability to drive high Mach number, radiating shock waves in laboratory plasmas, and recent experiments along these lines have made it possible to recreate analogs of high Mach-number astrophysical flows under controlled conditions. Streak cameras such as the Rochester optical streak system (ROSS) are particularly helpful in diagnosing such experiments, because they acquire spatially resolved measurements of the radiating gas continuously over a large time interval, making it easy to observe how any shock waves and ablation fronts present in the system evolve with time. This paper summarizes new ROSS observations of a laboratory analog of the collision of a stellar wind with an ablating planetary atmosphere embedded within a magnetosphere. We find good agreement between the observed ROSS data and numerical models obtained with the FLASH code, but only when the effects of optical depth are properly taken into account.

Combining laser beams in a plasma is enabled by seeded stimulated Brillouin scattering which allows cross-beam energy transfer (CBET) to occur and re-distributes the energy between beams that cross with different incident angles and small differences in wavelength [Kirkwood et al. Phys. Plasmas 4, 1800 (1997)]. Indirect-drive implosions at the National Ignition Facility (NIF) [Haynam et al. Appl. Opt. 46, 3276–3303 (2007)] have controlled drive symmetry by using plasma amplifiers to transfer energy between beams [Kirkwood et al., Plasma Phys. Controlled Fusion 55, 103001 (2013); Lindl et al., Phys. Plasmas 21, 020501 (2014); and Hurricane et al. Nature 506, 343–348 (2014)]. In this work, we show that the existing models are well enough validated by experiments to allow a design of a plasma beam combiner that, once optimized, is expected to produce a pulse of light in a single beam with the energy greatly enhanced over existing sources. The scheme combines up to 61 NIF beams with 120 kJ of available energy into a single f/20 beam with a 1 ns pulse duration and a 351 nm wavelength by both resonant and off-resonance CBET. Initial experiments are also described that have already succeeded in producing a 4 kJ, 1 ns pulse in a single beam by combination of up to eight incident pump beams containing <1.1 kJ/beam, which are maintained near resonance for CBET in a plasma that is formed by 60 pre-heating beams [Kirkwood et al., Nat. Phys. 14, 80 (2018)].

This paper shows results from experiments diagnosing the development of the Rayleigh–Taylor instability with two-dimensional initial conditions at an embedded, decelerating interface. Experiments are performed at the Omega Laser and use ∼5 kJ of energy to create a planar blast wave in a dense, plastic layer that is followed by a lower density foam layer. The single-mode interface has a wavelength of 50 μm and amplitude of 2.5 μm. Some targets are supplemented with additional modes. The interface is shocked then decelerated by the foam layer. This initially produces the Richtmyer–Meshkov instability followed and then dominated by Rayleigh–Taylor growth that quickly evolves into the nonlinear regime. The experimental conditions are scaled to be hydrodynamically similar to SN1987A in order to study the instabilities that are believed to occur at the He/H interface during the blast-wave-driven explosion phase of the star. Simulations of the experiment were performed using the FLASH hydrodynamics code.

Extreme optical fluences, much beyond the damage threshold of conventional optics, are of interest for a range of high-energy-density physics applications. Nonlinear interactions of multiple beams in plasmas have the potential to produce optics that operate at much higher intensity and fluence than is possible in solids. In inertial confinement fusion experiments indirectly driven with lasers, many beams overlap in the plasma inside a hohlraum, and cross-beam energy transfer by Brillouin scattering has been employed to redistribute energy between laser beams within the target. Here, we show that in a hot, under-dense plasma the energy of many input beams can be combined into a single well-collimated beam. The emerging beam has an energy of 4 kJ (over 1 ns) that is more than triple that of any incident beam, and a fluence that is more than double. Because the optic produced is plasma, and is diffractive, it is inherently capable of generating higher fluences in a single beam than solid-state refractive or reflective optics.