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The insulator–metal transition in liquid hydrogen is an important phenomenon to understand the interiors of gas giants, such as Jupiter and Saturn, as well as the physical and chemical behavior of materials at high pressures and temperatures. Here, the path toward an experimental approach is detailed based on spectrally resolved x-ray scattering, tailored to observe and characterize hydrogen metallization in dynamically compressed hydrocarbons in the regime of carbon–hydrogen phase separation. With the help of time-dependent density functional theory calculations and scattering spectra from undriven carbon samples collected at the European x-ray Free-Electron Laser Facility (EuXFEL), we demonstrate sufficient data quality for observing C–H demixing and investigating the presence of liquid metallic hydrogen in future experiments using the reprated drive laser systems at EuXFEL.

The successful characterization of high energy density (HED) phenomena in laboratories using pulsed power facilities and coherent light sources is possible only with numerical modeling for design, diagnostic development, and data interpretation. The persistence of electron correlation in HED matter is one of the greatest challenges for accurate numerical modeling and has hitherto impeded our ability to model HED phenomena across multiple length and time scales at sufficient accuracy. Standard methods from electronic structure theory capture electron correlation at high accuracy, but are limited to small scales due to their high computational cost. In this talk I will summarize our recent efforts on devising a data-driven and physics-informed workflow to tackle this challenge. Based on first-principles data we generate machine-learning surrogate models that replace traditional electronic-structure algorithms. Our surrogates both predict the electronic structure and yield thermo-magneto-elastic materials properties of matter under extreme conditions highly efficiently while maintaining their accuracy.

Part II of this special edition contains the remaining 11 papers arising from a Hooke discussion meeting held in March 2020 devoted to exploring the current status of inertial confinement fusion research worldwide and its application to electrical power generation in the future, via the development of an international inertial fusion energy programme. It builds upon increased coordination within Europe over the past decade by researchers supported by the EUROFusion Enabling Research grants, as well as collaborations that have arisen naturally with some of America's and Asia's leading researchers, both in the universities and national laboratories. The articles are devoted to informing an update to the European roadmap for an inertial fusion energy demonstration reactor, building upon the commonalities between the magnetic and inertial fusion communities' approaches to fusion energy. A number of studies devoted to understanding the physics barriers to ignition on current facilities are then presented. The special issue concludes with four state-of-the-art articles describing recent significant advances in fast ignition inertial fusion research. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 2)'.

The current driven electrothermal instability (ETI) forms when the material resistivity is temperature dependent, occurring in nearly all Z-pinch-like high energy density platforms. ETI growth for high-mass density materials is predominantly striation form which corresponds to magnetically perpendicular mode growth. The striation form is caused by a resistivity that increases with temperature, which is often the case for high-mass density materials. In contrast, low-density ETI growth is mainly filamentation form, magnetically aligned modes, because the resistivity tends to decrease with temperature. Simulating ETI is challenging due to the coupling of magnetic field transport to equation of state over a large region of state space spanning solids to plasmas. This dissertation presents a code-code verification study to effectively model the ETI. Specifically, this study provides verification cases which ensure the unit physics components essential to modeling ETI are accurate. This provides a way for fluid-based codes to simulate linear and nonlinear ETI. Additionally, the study provides a sensitivity analysis of nonlinear ETI to equation of state, vacuum resistivity, and vacuum density. Simulations of ETI typically use a collisional form of the resistivity as provided, e.g., in a Lee-More Desjarlais conductivity table. In regions of low-mass density, collision-less transport needs to be incorporated to properly simulate the filamentation form of ETI growth. Anomalous resistivity (AR) is an avenue by which these collision-less micro-turbulent effects can be incorporated into a collisional resistivity. AR directly changes the resistivity which will directly modify the linear growth rate of ETI, so a new linear growth rate is derived which includes AR's added dependency on current density. This linear growth rate is verified through a filamentation ETI simulation using an ion acoustic based AR model. Kinetically based simulations of vacuum contaminant plasmas provide

The successful characterization of high energy density (HED) phenomena in laboratories using pulsed power facilities and coherent light sources is possible only with numerical modeling for design, diagnostic development, and data interpretation. The persistence of electron correlation in HED matter is one of the greatest challenges for accurate numerical modeling and has hitherto impeded our ability to model HED phenomena across multiple length and time scales at sufficient accuracy. Standard methods from electronic structure theory capture electron correlation at high accuracy, but are limited to small scales due to their high computational cost. In this talk I will summarize our recent efforts on devising a data-driven and physics-informed workflow to tackle this challenge. Based on first-principles data we generate machine-learning surrogate models that replace traditional electronic-structure algorithms. Our surrogates both predict the electronic structure and yield thermo-magneto-elastic materials properties of matter under extreme conditions highly efficiently while maintaining their accuracy.

Matter exposed to extreme conditions (strong electro-magnetic fields, high temperatures, and high pressures) creates high energy density (HED) phenomena which is an archetypal manifestation of a complex system. The successful characterization of these phenomena in laboratories using pulsed power facilities and coherent light sources is possible only with numerical modeling for design, diagnostic development, and data interpretation. The persistence of electron correlation in HED matter is one of the greatest challenges for accurate numerical modeling and has hitherto impeded our ability to model HED phenomena across multiple length and time scales at sufficient accuracy. Standard methods from electronic structure theory capture electron correlation at high accuracy, but are limited to small scales due to their high computational cost. In this talk I will summarize our recent efforts towards devising digital twins of HED phenomena. Based on first-principles data we generate machine-learning surrogate models that replace traditional electronic-structure algorithms. Our surrogates both predict the electronic structure and yield thermo-magneto-elastic materials properties of matter under extreme conditions highly efficiently while maintaining their accuracy.

The successful characterization of high energy density (HED) phenomena in laboratories using pulsed power facilities and coherent light sources is possible only with numerical modeling for design, diagnostic development, and data interpretation. The persistence of electron correlation in HED matter is one of the greatest challenges for accurate numerical modeling and has hitherto impeded our ability to model HED phenomena across multiple length and time scales at sufficient accuracy. Standard methods from electronic structure theory capture electron correlation at high accuracy, but are limited to small scales due to their high computational cost. In this talk I will summarize our recent efforts on devising a data-driven and physics-informed workflow to tackle this challenge. Based on first-principles data we generate machine-learning surrogate models that replace traditional electronic-structure algorithms. Our surrogates both predict the electronic structure and yield thermo-magneto-elastic materials properties of matter under extreme conditions highly efficiently while maintaining their accuracy.

Wire X-pinches have been comprehensively studied for nearly four decades as a fast (~1 ns Full-Width Half-Max: FWHM), small (~1\textmu m) X-ray source in pulsed-power experiments. Room for improvement to this array remains though, including reducing variability in source timing, size, quantity, and flux, and the presence of strong electron beam emission post-pinch that tends to doubly expose any acquired radiograph. Many of these limitations can be reduced by optimal mass-matching of the target X to the current driver in use and a reliable cross-point geometry.Addressing these two parameters, we developed a new X-pinch, and tested in on the 200kA, 150ns rise-time GenASIS driver at UC San Diego. This new X is cut from thin metallic foils using a precision laser-cutting facility which can fabricate virtually any cross-sectional mass or crosspoint configuration. The first laser-cut foil X-pinch (LCXP) experiments used Ta, and demonstrated comparable evolution and equal or superior X-ray source parameters to comparably massed W wire X-pinches (WXPs), despite markedly different initial geometry (ie a square or trapezoidal crosspoint cross-section). Subsequent Cu LCXP experiments showed that the X-ray pulse from these targets was confined to a ~2ns period in contrast with the resolvable second pulse of hard X-ray electron beam emission common in WXPs. However, spectroscopic data showed evidence of a beam source co-located with the $\geq$10% solid density, ~1keV hot pinch source. Another promising X-pinch configuration (developed at Cornell University), the hybrid X-pinch (HXP), which consists of two conical electrodes 1-3mm apart bridged by a thin wire or capillary, demonstrated predominantly single source X-pinches and less hard X-ray emission than found in WXPs. To compare all three aforementioned X-pinch configurations–wire, hybrid, and laser-cut foils–we conducted an in-depth performance study of these X’s on the GenASIS driver, representing the first time all three c

Wire X-pinches have been comprehensively studied for nearly four decades as a fast (~1 ns Full-Width Half-Max: FWHM), small (~1\textmu m) X-ray source in pulsed-power experiments. Room for improvement to this array remains though, including reducing variability in source timing, size, quantity, and flux, and the presence of strong electron beam emission post-pinch that tends to doubly expose any acquired radiograph. Many of these limitations can be reduced by optimal mass-matching of the target X to the current driver in use and a reliable cross-point geometry.Addressing these two parameters, we developed a new X-pinch, and tested in on the 200kA, 150ns rise-time GenASIS driver at UC San Diego. This new X is cut from thin metallic foils using a precision laser-cutting facility which can fabricate virtually any cross-sectional mass or crosspoint configuration. The first laser-cut foil X-pinch (LCXP) experiments used Ta, and demonstrated comparable evolution and equal or superior X-ray source parameters to comparably massed W wire X-pinches (WXPs), despite markedly different initial geometry (ie a square or trapezoidal crosspoint cross-section). Subsequent Cu LCXP experiments showed that the X-ray pulse from these targets was confined to a ~2ns period in contrast with the resolvable second pulse of hard X-ray electron beam emission common in WXPs. However, spectroscopic data showed evidence of a beam source co-located with the $\geq$10% solid density, ~1keV hot pinch source. Another promising X-pinch configuration (developed at Cornell University), the hybrid X-pinch (HXP), which consists of two conical electrodes 1-3mm apart bridged by a thin wire or capillary, demonstrated predominantly single source X-pinches and less hard X-ray emission than found in WXPs. To compare all three aforementioned X-pinch configurations–wire, hybrid, and laser-cut foils–we conducted an in-depth performance study of these X’s on the GenASIS driver, representing the first time all three c

We report on the generation and characterization of submillimetric Argon gas jets with peak density higher than 10^21 atoms/cm3 from capillary nozzles of varying throat diameter in the range of 50-450 μm. The use of gas jet targets to generate a suitably dense, reliable, and reproducible interaction medium is particularly important in the broad field of laser-plasma interactions, in areas such as high energy density physics (HEDP), plasma waveguides, electron/ion acceleration and x-ray generation. Here, it is essential to place those targets in the laser focus with subwavelength accuracy and have control over the gas flow using a sonic or supersonic nozzle to provide the desired interaction density. The use of a sonic or supersonic gas flow provides a Gaussian like or plateau neutral density profile. By changing the gas pressure and temperature, one can change the initial neutral density and by using a combination of gases, one can obtain plasmas with multiple ions species, which is needed to localize electrons injection for innovative laser-plasma accelerator schemes. In this thesis, we present a study of the specific characteristics of gas jets produced by micron-sized nozzles in the context of laser-plasma physics. The study is based on experimental work on gas jets of varying sizes and parameters such as backing pressure and temperature. The thesis is organized as follows: Chapter 1 examines the motivation for generating such high density gas jets in the context of laser wakefield acceleration and the flow physics of supersonic gas jets. Chapter 2 presents the work in manufacturing the nozzles and characterizing the gas jets produced from the straight capillary nozzles using interferometry methods to measure the density profiles and Rayleigh Scattering to identify clusters in the target. Chapter 3 explores the possible applications of the gas jets in terms of generating gas targets in atmospheric conditions, producing icy filament targets by cooling and demonstr

In order to understand the transport of fast electrons within solid density targets driven by an optical high power laser, wehave numerically investigated the dynamics and structure of strong self-generated magnetic fields in such experiments.Here we present a systematic study of the bulk magnetic field generation due to the ponderomotive current, Weibel-likeinstability and resistivity gradient between two solid layers. Using particle-in-cell simulations, we observe the effect ofvarying the laser and target parameters, including laser intensity, focal size, incident angle, preplasma scale length, targetthickness and material and experimental geometry. The simulation results suggest that the strongest magnetic field isgenerated with laser incident angles and preplasma scale lengths that maximize laser absorption efficiency. The recentcommissioning of experimental platforms equipped with both optical high power laser and X-ray free electron laser(XFEL), such as European XFEL-HED, LCLS-MEC and SACLA beamlines, provides unprecedented opportunities toprobe the self-generated bulk magnetic field by X-ray polarimetry via Faraday rotation with simultaneous high spatialand temporal resolution. We expect that this systematic numerical investigation will pave the way to design and optimizenear future experimental setups to probe the magnetic fields in such experimental platforms

A number of laser facilities coming on–line all over the world promise the capability of high–power laser experiments with shot repetition rates between 1 and 10 Hz. Target availability and technical issues related to the interaction environment could become a bottleneck for the exploitation of such facilities. In this paper, we report on target needs for three different classes of experiments: dynamic compression physics, electron transport and isochoric heating and laser–driven particle and radiation sources. We also review some of the most challenging issues in target fabrication and high repetition rate operation. Finally, we discuss current target supply strategies and future perspectives to establish a sustainable target provision infrastructure for advanced laser facilities.

Thesis (Ph. D.)--University of Rochester. Department of Mechanical Engineering, 2015., The creation of stable, straight channels in dense plasma with high intensity laser beams is of interest to a number of applications in laser-produced plasma science. This includes the generation of MeV to GeV electron beams in laser wakefield accelerators (LWFA), coherent and brilliant X-ray generation from electron betatron radiation, and fast ignition of inertial confinement fusion targets (FI ICF). This thesis studies the creation of channels through dense preformed plasma on the OMEGA EP laser system. A new optical probing method was developed to image the channeling process. The experiments show that the channel bores faster than the ponderomotive hole boring velocity of Wilks et al. predicted by a balance of light pressure at the channel front. In the wake of the channeling pulse, a shock-driven parabolic density profile exists in the radial direction, allowing for the guiding of a subsequent high intensity pulse to an embedded steep gradient. A structure of this type is beneficial to the applications mentioned above. The results of this study can be extended to an integrated FI experiment on OMEGA, planned for the upcoming year. Current laser systems are able to create high energy density (HED) systems where the radiation-pressure in the laser field totally overwhelms the thermal pressure of the material. In this radiation-pressure dominated regime, the radiation-pressure, 2I/c, where I is the intensity of the radiation field and c the speed of light, is orders of magnitude greater than the thermal pressure, nkBT, where n is the material density and kBT is the specific energy of the system. This radiation-pressure driven flow modifies the plasma density in the region of the laser. This work presents measurements of a channel or density cavitation bored into an inhomogeneous HED plasma. A high-energy chirped-pulse amplification (CPA) laser beam (> I ∼ 1018 W/cm2) was used to drive a radiation-pre

Thesis (Ph. D.)--University of Rochester. Dept. of Mechanical Engineering, 2008., An experimental investigation of shock wave induced heating and compression in planar targets relevant to direct-drive inertial confinement fusion (ICF) was conducted on the OMEGA laser system. A physical understanding of shock wave heating, radiative heating, and heating by energetic electrons in direct-drive ICF is necessary because the achievement of energy gain requires accurate control of the pressure in the main fuel layer. The shock wave provides the dominant heating mechanism. Plasma conditions of a direct-drive shock wave heated and compressed planar plastic target were diagnosed using non-collective, spectrally resolved x-ray scattering and time-resolved x-ray absorption spectroscopy. In the non-collective x-ray scattering experiment, the spatially averaged electron temperature (Te) and average ionization (Z) of the shock wave heated target were inferred from the spectral line shape of the Rayleigh (elastic) and Compton (inelastic) components. Local plasma conditions during shock wave heating and compression as well as the timing of heat front penetration were diagnosed with time-resolved Al 1s-2p absorption spectroscopy of planar plastic foils with a buried layer of Al. The measured Al 1s-2p spectra were analyzed with an atomic physics code PrismSPECT to infer Te and the mass density (ρ) assuming uniform plasma conditions. The experimental results for a variety of square and shaped laser pulse drives were compared with the 1-D hydrodynamics code LILAC using a flux-limited (f = 0.06 and f = 0.1) and a nonlocal thermal transport model. The accuracy of the electron temperatures inferred from the absorption spectroscopy experiment was sufficient to validate the electron thermal transport model in LILAC. The LILAC simulation using the nonlocal model or f = 0.06 accurately predicts the shock wave heating and timing of heat front penetration for square and shaped laser pulses while the shock is transiting the foil. The measured shock wave heating inferred from t

Thesis (Ph. D.)--University of Rochester. Department of Physics and Astronomy, 2021., Much of modern physics has been built on studying phenomena in isolated systems. These seemingly simple mechanisms, when applied to larger collection of system, become more complicated. The tools used to understand these systems were developed primarily at conditions relevant to the surface of the Earth and therefore comparison to experiments have been readily available. A similar addition of complexity exists when transitioning to extreme thermodynamic states. In these conditions, temperatures in the tens of thousands to many millions of Kelvin and densities from miligrams per cubic centimeter to kilograms per cubic centimeter, there exists complex collective behaviour that leads a wealth of interesting new phenomena not present in isolated atomic interaction or under standard thermodynamic conditions. These phenomena no doubt are critical to the evolution of astrophysical bodies, such as planets and stars. The modeling efforts have largely outpaced the experimental capabilities with regards to these systems at high energy density (HED, equivalently high pressure) and the laboratory landscape is moving towards measurements that are challenging to analyze independent of advanced modeling techniques. This work aims to present a systematic method for designing, executing, and analyzing HED experiments that enforces a self-consistent picture of the physics present in the system. This is done by creating a Bayesian inference framework, similar to those that exist in other fields of physics, that uses all relevant experimental data to constrain the integrated physicals model used to understand the experiments. The ultimate goal is to move away from 'benchmarking' techniques and towards proper statistical constraint of the models used to describe physics under extreme conditions.