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Backing - Inertial Confinement Fusion: X-rays heat ablator which expands and shocks the capsule compressing the fuel and causing fusion reaction; Mixing between the layers makes fusion harder; Simulations and models are used to visualize the instabilities that case the mixing.
Eruptive mass loss likely produces the energetic outbursts observed from some massive stars before they become core-collapse supernovae (SNe). The resulting dense circumstellar medium may also cause the subsequent SNe to be observed as Type IIn events. The leading hypothesis of the cause of these outbursts is the response of the envelope of the red supergiant (RSG) progenitor to energy deposition in the months to years prior to collapse. Early theoretical studies of this phenomenon were limited to 1D, leaving the 3D convective RSG structure unaddressed. Using FLASH's hydrodynamic capabilities, we explore the 3D outcomes by constructing convective RSG envelope models and depositing energies less than the envelope binding energies on timescales shorter than the envelope dynamical time deep within them. We confirm the 1D prediction of an outward-moving acoustic pulse steepening into a shock, unbinding the outermost parts of the envelope. However, we find that the initial 2–4 km s -1 convective motions seed the intrinsic convective instability associated with the high-entropy material deep in the envelope, enabling gas from deep within the envelope to escape and increasing the amount of ejected mass compared to an initially "quiescent" envelope. The 3D models reveal a rich density structure, with column densities varying by ≈10× along different lines of sight. Our work highlights that the 3D convective nature of RSG envelopes impacts our ability to reliably predict the outburst dynamics, the amount, and the spatial distribution of the ejected mass associated with deep energy deposition.
The double shell path to inertially confined volumetric thermonuclear burn relies on efficient kinetic energy transfer from an outer ablator shell to an inner shell containing DT fuel at implosion velocities near 250 km/s. In order to experimentally realize adequate compression, target imperfections and assembly features must be tightly controlled. Pulse shape and ablator material are critical design choices that impact all aspects of the implosion. In this article, we evaluate three designs: an Al ablator with single-shock radiation drive, a CH ablator with single-shock drive, and a CH ablator with reduced-adiabat 2-shock drive. All designs use the same W inner (pusher) shell overcoated with a glow discharge polymer tamper and filled with liquid-density DT. One-dimensional HYDRA simulations revealed that the plastic ablator design required the use of the 2-shock drive to match the performance of the Al design. Two-dimensional simulations resolving broadband surface roughness up to modes of several hundred placed only on the ablator showed plastic to greatly outperform Al. The plastic ablator designs did exhibit higher levels of inner shell instability growth when surface roughness was only placed at the pusher/tamper interface, which was mitigated with higher foam cushion densities. A unique and additional benefit of a plastic ablator is also discussed, where heating of the ablator by Au M-band radiation is predicted to rapidly expand the hemi-shell surfaces, closing the equatorial joint gap ahead of the first shock. Taken together, the properties of the plastic ablator for indirect-drive double shell implosions appear promising in removing several long-standing fabrication challenges.
Revolver and Double Shell Inertial Confinement Fusion capsule designs hope to achieve a robust volumetric thermonuclear burn via the use of a high-Z pusher shell filled with a cryogenic D–T fuel. Unfortunately, mix of the pusher material into the fuel (gas) may adversely impact the burn performance. Hydrodynamic instability of the metal/gas interface as the mix source is an obvious concern, but 1D effects may also be detrimental. Such effects include plasma diffusion at material interfaces, which has been the subject of numerous theoretical, computational, and experimental investigations. However, other 1D mix mechanisms may exist, which have yet to be thoroughly explored. In particular, plasma kinetic effects may drive the mix when a shock breaks out of the metal/gas interface. Using the state-of-the-art, hybrid (kinetic-ion/fluid electron), multi-ion Vlasov–Fokker–Planck code, iFP, we show herein that shock-driven kinetic effects can reconfigure the interface and the interfacial width subsequently grows diffusively. Finally, we consider any implications for high-Z pusher designs.
Magnetized liner inertial fusion (MagLIF) implosions on the Z accelerator have almost exclusively been driven by ∼100-ns rise time current pulses. The rise time is selected to be as short as achievable on Z partially to minimize the time during which deleterious implosion instabilities can develop. Modifying the shape of the current pulse could provide benefits for MagLIF, including more efficient compression of the fusion fuel and the magnetic flux inside the liner cavity. Quasi-isentropic compression of the liner prevents formation of shocks in the liner material and reduces the amount of entropy generation within the liner. This allows for more final compression of the liner and fuel assembly. We present results from one-dimensional (1D) radiation-magnetohydrodynamic (rad-MHD) simulations comparing thermonuclear fuel conditions in MagLIF implosions driven with two different current pulses: a ∼100-ns rise time, ∼21.5 MA peak current “short pulse” and a ∼200-ns rise time, ∼21.5 MA peak current “shockless” pulse. We also quantify and compare the instability development in three-dimensional (3D) MHD implosion simulations driven by these two different pulse shapes. Our 1D simulations indicate that the shocklessly compressed MagLIF implosion performs better than the short pulse driven implosion with a >50% higher thermonuclear neutron yield, and 3D simulations indicate comparable implosion instability development, suggesting that pulse shaping could enable improvements to MagLIF performance on Z without compromising implosion stability.
ABSTRACT We report on the results of a simulation-based study of colliding magnetized plasma flows. Our set-up mimics pulsed power laboratory astrophysical experiments but, with an appropriate frame change, is relevant to astrophysical jets with internal velocity variations. We track the evolution of the interaction region where the two flows collide. Cooling via radiative losses is included in the calculation. We systematically vary plasma beta (βm) in the flows, the strength of the cooling (Λ0), and the exponent (α) of temperature dependence of the cooling function. We find that for strong magnetic fields a counter-propagating jet called a ‘spine’ is driven by pressure from shocked toroidal fields. The spines eventually become unstable and break apart. We demonstrate how formation and evolution of the spines depend on initial flow parameters and provide a simple analytical model that captures the basic features of the flow.
In this work we present a comprehensive investigation of state-of-the-art closure models employed to represent interphase momentum, thermal, and work exchange between the gas and particulate phases for Euler–Lagrange (EL) simulations in shock-driven flows. A complete list of closures for the force, torque, heat transfer, and work exchange models is provided. In particular, the present work includes a stochastic closure for the particle-to-particle variation in the quasi-steady force and a deterministic closure for particle-to-particle variation in the added mass force in an EL framework. These variations arise due to the presence of neighboring particles and particle–particle interactions. To investigate the importance of each closure term, we carry out fully three-dimensional simulations for a planar shock propagating over a random bed of inert particles. The primary goal is to evaluate the role of each closure term on the gas dynamic features (such as transmitted and reflected shock locations) and particle curtain features (such as upstream and downstream curtain locations). To this end, thirteen cases are considered, with each case progressively including a closure model with the goal to identify and quantify its contribution to the simulated dynamics. We show that the volume fraction dependence of the mean force models plays an important role in generating wave-like instabilities that lead to concentration bands. In addition, fluctuations in quasi-steady and added mass forces primarily decrease the internal instabilities that tend to enhance local volume fraction variations. Particle rotation is primarily due to inter-particle collisions, is generally weak, and does not play an important role in the translational dynamics for the present configuration. Inter-phase heat transfer has a strong effect on gas phase temperature, slows down the transmitted and reflected shocks, and decreases the width of the curtain. Furthermore, the absence of a work-coupling model fails to conserve the total energy, greatly under-predicts the gas temperature which in turn affects the particle dynamics.
The first Discovery Science shot day with the NIF DDCyl campaign demonstrated that Rayleigh-Taylor instability growth during the deceleration phase is scale-invariant for targets that varied in radial dimension and implosion time-scale by a factor of three. Smaller cylindrical implosions at the OMEGA laser facility were compared to the larger cylinders fielded in our first NIF outing. Both sets of targets had an initial m = 20 sinusoidal perturbation machined on the inner surface of an embedded aluminum marker layer, with the amplitude larger by the same factor of three for the NIF-scale targets. We observed growth factors of 14 at late time (t=λ = 7:7 ns, where λ = 1 for OMEGA and λ = 3 for NIF). These used a high density (300 mg/cm³) CH foam core, providing a very long period of deceleration before the rebounding shock hit the incoming spike tips, but the final convergence was only CR≈ 2:25. For our second shot day with this campaign, we are attempting to increase the convergence ratio to CR≥ 5 before reshock, while still measuring instability growth during the convergence/deceleration phase. As discussed in previous reports, the best way to increase convergence before reshock is to lower the density of the central foam. The preshot designs called for the use of a 30 mg/cm³ CH foam, though the as-built foams are closer to 40-42 mg/cm³, which is predicted to result in a final CR≈ 5:1 before reshock. Other than the lower foam density, the target design is identical to those used previously.
Experiments on the 1-MA, 220-ns COBRA generator at Cornell University were conducted to provide detailed measurements of structured cylindrical gas-puff z pinches. In the experiments, a 7 cm diameter triple-nozzle gas valve assembly with concentric outer and inner annular nozzles and a central gas jet initialize the z-pinch load with various working gases, radial density profiles, and externally applied axial magnetic fields. Planar laser-induced fluorescence provides a measure of the initial neutral gas density of the load, while three-frame laser shearing interferometry and multi-frame extreme ultraviolet (XUV) cameras reveal the formation and propagation of a magneto-Rayleigh–Taylor (MRT) unstable shock layer. Implosion trajectories are compared to simple, experimentally informed models and found to be in good agreement. Differences in the structure of the accelerating plasma sheath and evolution of the MRT instability are observed for different gas species and axial magnetic field strengths, correlating with differences in pinch uniformity and x-ray emission. Here, the average instability growth is compared to linear MRT theory predictions using the instantaneous acceleration of the best-fit implosion models and characteristic instability wavelength, with the effective Atwood number and seed perturbation size as fit parameters. For high density argon center jets, ionization prior to the arrival of the imploding plasma sheath suggests a heating mechanism consistent with photoionization by XUV self-emission.
Fuel–ablator mix has been established as a major performance degrading effect in the burning plasma regime of recent inertial confinement fusion (ICF) experiments. As such, the study of fuel–ablator mix with experiments and simulations can provide valuable insight for our understanding of these experiments and establish a path for even higher yields and increased robustness. Here we present a novel high-yield experimental ICF design that is motivated by recent experiments measuring ice–ablator mix with a CH ablator instead of a high-density carbon (HDC) ablator. Here we review these experiments in more detail and describe the modeling assumptions and parameters used to obtain agreement with the data from implosion and burn simulations with mix. Using this mix model calibrated a posteriori to the experimental data, we design an implosion that uses a CH ablator that is predicted to achieve better performance than a recent experiment that achieved net target gain of 1.5 in HDC. Because hydrodynamic instabilities are greatly reduced with this new design, we also expect a high reproducibility at the same implosion adiabat as current record yield experiments.
Dark matter could have a small electromagnetic charge, provided the charge-to-mass ratio is much less than that of electrons or protons. This candidate, commonly known as millicharged dark matter (mDM), would form a plasma and interact with the interstellar medium and electromagnetic fields within galaxies. In general, understanding the dynamics of mDM requires consideration of collective plasma effects. It has been proposed that mDM can be accelerated in supernova remnants, forming a dark cosmic ray population that would leave distinct experimental signatures. In this work, we study a microphysical model where mDM is shocked by a supernova remnant and isotropized in the frame of the expanding fluid. We find that for | q χ / m χ | ≳ 10 – 13 e / MeV , the isotropization length for electromagnetic plasma instabilities is much shorter than the size of the supernova remnant. This is a necessary, though not sufficient, first step for formation of a Fermi-accelerated mDM component, and determining the size of this component requires further study. Finally, we discuss additional implications of mDM interactions in supernova remnants.
A computational modeling capability is created and available to the fusion community to understand and design lower-cost and innovative fusion concepts. The approach uses high- fidelity kinetic, moment-kinetic, and moment models and includes sophisticated plasma- boundary interactions. A majority of fusion-relevant simulations are performed with magnetohydrodynamic models and hybrid particle-in-cell codes, with limited-fidelity electron and kinetic physics. However, in fusion configurations like Z-pinches, field-reversed- configurations, plasma jet magneto-inertial fusion, spinning mirrors, and others, kinetic effects (both electron and ions) are critical to understand the physics and design scaling into the highly kinetic regime of a burning fusion plasma. Furthermore, as present fusion machines move towards a burning plasma regime, liquid-metal blankets are needed to handle first-wall heat- flux, reduce erosion, and eventually for energy conversion and fuel breeding. The work performed under this ARPA-E BETHE Capability Team advances the state-of-the-art in modeling and understanding plasma dynamics in fusion devices and its coupling with liquid-metal dynamics. These are critical areas of research for fusion energy to become realizable. To address these complex problems, we have leveraged and extended computational capabilities through the code, Gkeyll (developed jointly with Princeton Plasma Physics Laboratory and academic partners), for kinetic and moment modeling of fusion plasmas. The Concept Teams supported by this Capability Team include the Wisconsin High-field Axisymmetric Mirror (WHAM), Centrifugal Mirror Experiment (CFME), Plasma-Jet Magneto- Inertial Fusion (PJMIF), and solid and liquid wall plasma-material interaction studies relevant to a number of fusion concepts including Zap Energy’s Z-pinch. This software is open-source and available to the fusion community as a high-fidelity tool for the design of lower-cost fusion experiments. 3D gyrokinetic simulations of WHAM are now possible for long enough time scales to understand the evolution of interchange instabilities. 3D multi-fluid simulations of CMFE at higher Mach numbers are now possible for detailed design iterations with the goal of stability. The state-of-the-art in understanding shock formation and shock mitigation regimes in merging liners for PJMIF have been furthered by our kinetic simulations. Our novel models and frameworks studying plasma-material interaction by incorporating wall emission for various solid wall materials of relevance to pulsed and steady fusion concepts have advanced the state-of-the-art in our understanding of particle fluxes, heat fluxes, and other quantities at cathodes and anodes. The results from this work may explain discrepancies between experimental and theoretical predictions of achieved current densities in pulsed concepts such as Z-pinches. Another significant contribution of this Capability Team is the development and deployment of a novel experimental platform, LEX (Liquid Electrode eXperiment), at Virginia Tech to understand liquid metal free-surface response to electromagnetic pulses. The novel experiments along with model validation quantified the effect of different materials and sizes of liquid metal droplets on the radiative power balance of fusion plasmas for pulsed concepts. Furthermore, these experiments provided mitigation strategies for violent liquid metal response for high current pulses as would be expected in fusion regimes.
The following slides summarize the effect that AMR has on results obtained using the inviscid version of xRAGE, i.e., when solving the Euler equations. The simulations are 2D and were done in the context of the ModCons experiments, where a shock travels from a heavy material (PAI of density 1.45 g/cm 3 ) to a light material (foam of density 0.1 g/cm 3 ). The shock is initialized using the 1D shock relations and is sustained by a freeze region during the entire simulation (0 ≤ t ≤ 6 ns). The initial perturbation has a wavelength of λ = 100 µm and an initial amplitude of a 0 = 10 µm. Five cases are considered: four with AMR with decreasing resolutions (from 1 µm to 1/8 µm at the interface) and one without AMR with 1/8 µm resolution in the entire domain.
Mesoscale imperfections, such as pores and voids, can strongly modify the properties and the mechanical response of materials under extreme conditions. Tracking the material response and microstructure evolution during void collapse is crucial for understanding its performance. In particular, imperfections in the ablator materials, such as voids, can limit the efficiency of the fusion reaction and ultimately hinder ignition. To characterize how voids influence the response of materials during dynamic loading and seed hydrodynamic instabilities, we, in this paper, have developed a tailored fabrication procedure for designer targets with voids at specific locations. Our procedure uses SU-8 as a proxy for the ablator materials and hollow silica microspheres as a proxy for voids and pores. By using photolithography to design the targets’ geometry, we demonstrate precise and highly reproducible placement of a single void within the sample, which is key for a detailed understanding of its behavior under shock compression. This fabrication technique will benefit high-repetition rate experiments at x-ray and laser facilities. Insight from shock compression experiments will provide benchmarks for the next generation of microphysics modeling.
Pa 30—the likely remnant of the Galactic Type Iax supernova of 1181 AD—displays an unusual, firework-like morphology, consisting of radial filaments extending from a common center, where a white dwarf (WD) currently drives a very fast wind (speed ≳10 4 km s −1 ). We propose the filaments arose from the Rayleigh–Taylor-unstable nature of the interface between the circumstellar medium (CSM) and the shocked wind launched by the natal WD; the filaments then elongated intact due to the Kelvin–Helmholtz-stable nature of the large initial density contrast between the wind and CSM, supplemented by the slowly declining wind density profile (relative to homologously expanding ejecta). To support this interpretation, we present two-dimensional hydrodynamical simulations and derive the filament properties, including their speed, density, and temperature, all of which are consistent with observations. We suggest the filaments elongate until the wind and CSM densities become comparable at the contact discontinuity, which occurs within 1–10 yr, and then truncate because the Rayleigh–Taylor instability (RTI) halts. The subsequent Kelvin–Helmholtz instability growth timescale across the current width of the filaments is longer than the age of Pa 30, so they remain intact. The filament-less central region in Pa 30 is therefore more likely a consequence of the finite timescale over which the RTI operates, rather than a wind termination shock. In general, firework-like filaments may form in other systems, provided there is a sufficiently large density contrast between the ejecta and its surroundings.
A high-order method for Eulerian simulation of material undergoing large elastic–plastic deformation is developed. Thermodynamically consistent hyperelastic constitutive relations are assumed, facilitating the treatment of solids, liquids, and gases in a unified manner. Here, the method enables the simulation of multi-material interactions using a diffuse interface approach. Numerical capturing of material interfaces, shock waves, contact surfaces, and elastic-plastic strain discontinuities using high-order compact-difference schemes is assisted by Localized Artificial Diffusivity (LAD). In the new setting involving elastic–plastic deformation, the previously established terms for the artificial properties are verified to effectively regularize normal shocks. Additional LAD terms are introduced to the elastic and plastic kinematic equations to regularize shear shocks and other strain discontinuities, improving solution stability. Other important features of the method that improve robustness include the numerical treatment of compatibility terms in the kinematic equations, and the treatment of rotation. Particular emphasis is focused toward new advancements of the methods for plastic-deformation integration and the associated strain hardening of the material, including rate-dependent plasticity. The method is demonstrated on a variety of test problems, including 1-D impacts, a variant of the Shu-Osher problem, a Taylor impact, and a Richtmyer-Meshkov instability between two elastic–plastic solids with strain hardening.
The staged Z-pinch is a potential high-energy gain fusion concept where a high atomic number liner implodes on a deuterium target using a pulsed multi-MA current source. Over the past several years this concept has been studied on 0.5–1.0 MA facilities using Ar and Kr gas puffs injected at R = 1.2 cm. Neutron yield up to (2.5 ± 0.34) x 10 10 was measured, Ruskov et al (2023 IEEE Trans. Plasma Sci. 51 3310–6). Here, in this study, we present experimental results from the 4 MA, 110 ns current rise time Double-EAGLE facility at L3Harris (currently, Fisica Inc.) where a larger radius nozzle created gas density profiles peaked at R = 2.5 cm. Modeling with the MACH2 and FLASH codes indicates that the larger radius allows stronger acceleration of the liner plasma and generation of shock waves that preheat a target plasma layer next to the liner to temperatures $T_i >$1 keV. The resulting counter thermal pressure on the liner plasma limits the growth of the Magneto-Rayleigh–Taylor (MRT) instability at the liner-vacuum boundary and the implosion proceeds in a relatively stable manner. Near bang time the enormous target plasma thermal pressure smoothens the MRT perturbations developed during the earlier implosion stages. Time integrated x-ray pinhole images with cutoff energy of 100 eV confirm that a long (∼3 cm), stable and uniform high energy density plasma column is formed in the final implosion stage. Consistent neutron yield in the 10 10 –10 11 range was measured for both Ar and Kr liners imploding on a deuterium target.
In this paper, we introduce SuperLite, an open-source Monte Carlo radiation transport code designed to produce synthetic spectra for astrophysical transient phenomena affected by circumstellar interaction. SuperLite utilizes Monte Carlo methods for semi-implicit, semirelativistic radiation transport in high-velocity shocked outflows, employing multigroup structured opacity calculations. The code enables rapid post-processing of hydrodynamic profiles to generate high-quality spectra that can be compared with observations of transient events, including superluminous supernovae, pulsational pair-instability supernovae, and other peculiar transients. We present the methods employed in SuperLite and compare the code's performance to that of other radiative transport codes, such as SuperNu and CMFGEN. We show that SuperLite has successfully passed standard Monte Carlo radiation transport tests and can reproduce spectra of typical supernovae of Type Ia, Type IIP, and Type IIn.