Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Plasma Physics
Volume 67, Number 15
Monday–Friday, October 17–21, 2022; Spokane, Washington
Session JO04: ICF: Compression and Burn IILive Streamed
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Chair: Duc Cao, U. Rochester/LLE Room: Ballroom 111 A |
Tuesday, October 18, 2022 2:00PM - 2:12PM |
JO04.00001: Experimental Benchmarking and Stability Analysis of Double Shell Implosions on the National Ignition Facility Harry F Robey, Eric N Loomis, Ryan F Sacks, Paul A Keiter, David Stark, Elizabeth C Merritt Double-shell ICF implosions are being performed on NIF as an alternative to the more widely investigated case of single-shell implosions. Double shells offer a complementary approach to achieving ignition in that they operate at lower convergence ratios and potentially ignite at lower temperatures. Due to the multiple interfaces, however, double shells can suffer from interfacial instability growth that will degrade performance. In this talk, we report results from integrated hohlraum simulations using the radiation-hydrodynamics code HYDRA [1]. The simulations are first compared with data from NIF double-shell experiments, which were performed to quantify both the high-energy (Au L-shell) preheat environment and the implosion trajectory and timing. The performance of these experimentally benchmarked simulations is then assessed, and this tuned implosion is used to quantify the degradation due to surface roughness on the multiple interfaces of a double shell. Both lower-resolution full-sphere and more highly resolved wedge capsule-only simulations are used to quantify the degradations due to interfacial instability. Mitigation strategies to reduce these degradations are discussed. |
Tuesday, October 18, 2022 2:12PM - 2:24PM |
JO04.00002: First tungsten-based double shell implosions on the National Ignition Facility Eric N Loomis, David J Stark, David S Montgomery, Joshua P Sauppe, Harry F Robey, R. F Sacks, Tom Byvank, Patrick Donovan, Saba Goodarzi, Brian M Haines, Paul A Keiter, Sasi Palaniyappan, Elizabeth C Merritt, David D Meyerhofer, Zaarah Mohamed, Alexander M Rasmus, Irina Sagert, Derek W Schmidt, Hongwei Xu Inertial Confinement Fusion Double Shell implosions rely on the efficient transfer of kinetic energy from an outer (ablator) shell to an inner shell to compress and heat its central DT fuel. Due to imperfections associated with the target and laser, ideal transfer of energy is never achieved; however, design choices and target advancements can reduce these losses. Reaching the ignition and burn with double shells at MJ-scale laser facilities requires the use of dense, high-Z metal inner shells due to their ability to undergo efficient shell collisions while maintaining compressibility and high work rate on the DT plasma. The ability of heavy metal shells to withstand imperfections, such as engineering features and low-mode asymmetries from the incoming ablator and hohlraum, has not previously been measured. |
Tuesday, October 18, 2022 2:24PM - 2:36PM |
JO04.00003: Simulation of Single Mode perturbations on Double Shell Implosions on the National Ignition Facility (NIF) Ryan F Sacks, Harry F Robey, Eric N Loomis, Paul A Keiter, Elizabeth C Merritt The LANL double shell platform on the National Ignition facility is a target design that is intended to produce a robust yield by trading relaxed fuel conditions for target complexity [1]. The reliance on kinetic energy transfer from an outer ablator (shell) layer to an inner shell to compress the fuel brings the necessity of investigating shape transfer between shells. This can take a number of different forms including the outer shells imprinting on inner shells as the target implodes, or through the shock’s passage (and reverberation) from one shell to the next. Understanding the amount of transfer, how individual perturbations grow, and the dominant mechanism is an important part in understanding limitations on acceptable initial perturbations. |
Tuesday, October 18, 2022 2:36PM - 2:48PM |
JO04.00004: Characterizing instability mitigation and preheat effects in gradient inner shells for double shell designs David Stark, Eric N Loomis, Sasi Palaniyappan, Nomita Vazirani, Harry F Robey, Brian M Haines, Alexander M Rasmus, Joshua P Sauppe, Ryan F Sacks While double shell designs offer many advantages for inertial confinement fusion (ICF) implosions, they are susceptible to hydrodynamic instabilities at their interfaces. We employ the Eulerian radiation-hydrodynamics code xRAGE to explore alternative inner shell density profiles – using gradients comprised of beryllium and tungsten – and to specifically characterize their stability and impact on performance. First, we examine the preheat expansion of the different inner shells using a drive that has been constrained by measured preheat; we measure the density gradient length scale seen prior to shell collision as a function of initial profile, as this will impact stability. We next perform a mode study to determine the sensitivity of different density gradients to each mode and to quantify feedthrough to the fuel-inner shell boundary. This motivates exploring alternative shell dimensions to exploit improved stability of the implosion, and a preliminary study is presented. Certain engineering features – such as the joint in the outer hemispherical shells – also can imprint onto the inner shell, and we measure the impact of this on the various inner shell profiles. Finally, a complementary graded layer campaign at OMEGA is discussed, and future directions – including observable metrics – are given. |
Tuesday, October 18, 2022 2:48PM - 3:12PM |
JO04.00005: Coupling Computationally Expensive Radiation-Hydrodynamic Simulations with Machine Learning for Graded Inner Shell Design Optimization in Double Shell Capsules Nomita Vazirani High energy density experiments rely heavily on predictive physics simulations in the design process. Specifically, in inertial confinement fusion (ICF), predictive physics simulations, such as in the radiation-hydrodynamics code xRAGE, are computationally expensive, limiting the design process and ability to find an optimal design. Machine learning provides an opportunity to leverage expensive simulation data and alleviate the limitations on computational time and resources in the search for an optimal design. Machine learning makes use of limited expensive simulation data to identify regions of the design space with high predicted performance as well as regions with high uncertainty, which upon exploration may lead to unexpected designs with great potential. This dissertation focuses on the application of Bayesian optimization to design optimization for ICF experiments conducted by the double shell campaign at Los Alamos National Lab (LANL). The double shell campaign is interested in implementing graded inner shell layers to their capsule geometry. Graded inner shell layers are expected to improve stability in the implosions with fewer sharp density jumps, but at the cost of lower yields, in comparison to the nominal bilayer inner shell targets. This work explores minimizing hydrodynamic instability and maximizing yield for the graded inner shell targets by building and coupling a multi-fidelity Bayesian optimization framework with multi-dimensional xRAGE simulations for an improved design process. |
Tuesday, October 18, 2022 3:12PM - 3:24PM |
JO04.00006: First measurements of mix in a metal shell fusion implosion using charged particle radiochemistry at the NIF Steve A MacLaren, Eduard L Dewald, David A Martinez, Narek Gharibyan, Peter J Bedrossian, Robert D Hoffman, Robert E Tipton, Jesse E Pino, Alexander Vazsonyi, Darwin D Ho, George B Zimmerman, Corie A Horwood, Elvin R Monzon, Cohl V Houldin-Hatala, Weston Montgomery, Edward P Hartouni, Hongwei Xu, Casey Kong, Neal Rice A primary objective for LLNL's Pushered Single Shell (PSS) campaign is to study the effect of metal-gas mix on fusion implosions. PSS implosions result in enhanced shell areal density by means of a graded density region near the capsule inner surface. The gradient is accomplished via a gradual inrease in the concentration of either a Cr or Mo dopant in the Be ablator, minimizing instability that would otherwise tend to destroy an ablator with a step-change in density. Recent PSS experiments have recorded the first demonstration of an independent radiochemical measurement of metal-fuel mix in a fusion implosion. The mix at the ablator-DT interface generates radio-isotopes of either Mn (for Cr dopant) or Tc (for Mo dopant) through charged-particle interactions, a process that is very sensitive to the amount and distribution of the fuel-ablator mix. Radiochemical analysis of solid-capture debris has successfully isolated and counted key Cr and Mn isotopes, the ratio of which is proportional to the mix. Post-shot simulations of the implosion run with a benchmarked model for the mix and that calculate the isotopic production will be compared with data. |
Tuesday, October 18, 2022 3:24PM - 3:36PM |
JO04.00007: Efficacy of an Anti-Mix Layer on Implosions of the Pushered Single Shell Platform Alexander R Vazsonyi, Eduard L Dewald, Jesse E Pino, Steve A MacLaren, Darwin D Ho, David A Martinez, Robert E Tipton, Vladimir Smalyuk The Pushered Single Shell (PSS) campaign at the National Ignition Facility aims to study the efficacy of a mid -Z pusher on enhancing radiation trapping and core tamping of a burning fusion plasma. To achieve this goal, the capsule design includes a beryllium shell doped with a varying concentration of chromium, the mid-Z material, surrounding a deuterium-tritium gas. However, the presence of the chromium presents a challenge, as mixing of this material into the central hot spot tends to reduce core temperatures and yields due to increased bremsstrahlung radiation. To remedy this, an additional beryllium “anti-mix” layer is placed interior to the chromium, preventing substantial intrusion of the chromium into the core plasma. |
Tuesday, October 18, 2022 3:36PM - 3:48PM |
JO04.00008: MCNP Analysis of Double Shell NIF-ARC Radiography David D Meyerhofer, Tom Byvank, Paul A Keiter, Irina Sagert, David A Martinez, David S Montgomery, Eric N Loomis Double shell capsule implosions are radiographed using the Advanced Radiographic Capability at the National Ignition Facility. The ultimate goal is to reconstruct the shape and density profile of the compressed inner shell. The Monte Carlo N-Particle (MCNP®) code is used to model these radiographs, using input from radiation-hydrodynamics simulations. This presentation will compare MCNP simulations with experimental observations. |
Tuesday, October 18, 2022 3:48PM - 4:00PM |
JO04.00009: Initial shape measurements of the inner shell of a Double Shell implosion with high-energy x-rays Paul A Keiter, Eric N Loomis, Joshua P Sauppe, Irina Sagert, David D Meyerhofer, Tom Byvank, Scott Vonhoff, Cohl Houldin Hatala, Riccardo Tommasini, David Alessi, Matt Prantil, Tom Lanier, Weston Montgomery, Daniel H Kalantar, David A Martinez, Saba Goodarzi Double shell capsules provide a complementary and alternative path to the single shell inertial confinement fusion (ICF) approach. Generically, a double shell capsule consists of an outer shell, a medium between the shells and a high-Z inner shell filled with DT fuel. Double shell targets rely on effectively transferring the kinetic energy of the outer shell to the inner shell to compress the DT fuel. To measure the shape of the inner shell surface pushing against the DT, high energy x-rays are required. We will present initial results from experiments on the National Ignition Facility (NIF) utilizing the Advanced Radiographic Capability (ARC) measuring the shape of the inner shell. |
Tuesday, October 18, 2022 4:00PM - 4:12PM |
JO04.00010: Assessment of Radiation Trapping in Inertial Confinement Fusion Implosion Experiments Based on Characteristic Quantities of Simple Models Reuben Epstein, Valeri N Goncharov, Suxing Hu, Duc Cao, Alexander Shvydky, Timothy J Collins, Patrick m McKenty The “volume-burn” approach to inertial confinement fusion utilizes a “pushered” shell to minimize the escape of thermal energy from the hot spot prior to ignition. Single-shell pushered implosions utilize an opaque high-Z inner shell lining to “trap” the radiation that would otherwise escape the core, cooling the fuel below the temperature required for ignition. We explore the physics of radiation trapping by means of existing analytic physical models and numerical radiation-hydrodynamic simulations, presenting simple metrics for the effectiveness of radiation trapping, not only in igniting implosions, but also in near-term experiments intended to demonstrate radiation-trapping effects. The Marshak wave model is extended to allow for converging geometry and simple hydrodynamic motion of the stagnating shell and is used to demonstrate relationships among the thermal energy of the fuel, the reduction of radiative flux escaping the fuel, and properties of the opaque shell surrounding the fuel that determine its effectiveness as a radiation trap. Implications of this model for future directions will also be presented. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856. |
Tuesday, October 18, 2022 4:12PM - 4:24PM |
JO04.00011: Radiation Trapping and Hot-Spot Energy Balance in High-Z Pusher Implosions Alexander Shvydky, Reuben Epstein, Daniel J Haberberger, Suxing Hu, Andrei V Maximov, Valeri N Goncharov, Joseph M Smidt Single-,[1] double-,[2] and triple-shell[3] inertial confinement fusion target designs offer an alternative (to cryogenic layer implosions) pathway to ignition. They use a high-Z layer (metal pusher) on the inside of the innermost shell that effectively traps the radiation from the hot spot and lowers the temperature required to achieve ignition conditions. It also improves the hot-spot compression because of the increase in the shell density. In this talk, we use the radiation-hydrodynamic code LILAC to analyze energy balance between the compression work and thermal-conduction and radiation losses in the DT hot spot of CH single-shell implosions with a high-Z inner layer. The code employs a straight line (Sn) model to accurately treat the radiation transport in both the optically thin hot spot and the optically thick high-Z layer around it. The studies will be used to design a low convergence ratio, high-adiabat implosion to experimentally study the hot-spot radiation trapping on the OMEGA Laser System. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856. [1] E. L. Dewald et al., Phys. Plasmas 15, 072706 (2008).
[2] D. S. Montgomery et al., Phys. Plasmas 25, 092706 (2018).
[3] K. Molvig et al., Phys. Rev. Lett. 116, 255003 (2016).
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Tuesday, October 18, 2022 4:24PM - 4:36PM |
JO04.00012: Synthetic Radiograph Data for Double Shell Implosions Zaarah L Mohamed, Eric N Loomis Double shell implosions seek to achieve volumetric burn as an alternative to hot-spot ignition inertial confinement fusion. These experiments typically involve targets that include a volume of liquid DT surrounded by W, Be, foam, and Al shells, which are shot in an indirect drive configuration at the National Ignition Facility. Shell velocities and energy transferred between shells are vital diagnostic quantities for these implosions, as efficient transfer of kinetic energy/momentum between shells minimizes the time for growth of hydrodynamic instabilities, reducing their eventual impact on burn performance. |
Tuesday, October 18, 2022 4:36PM - 4:48PM |
JO04.00013: Ablative Energetics for High Gain Direct Drive on the National Ignition Facility Mark J Schmitt, Brett S Scheiner, Rick E Olson, Derek W Schmidt, Lynn Kot, Michael J Rosenberg, Stephen Craxton We present results from 1.1 MJ direct drive simulations and experiments on NIF where a large 5 mm diameter CH capsule directly driven at a low surface intensity of 250 TW/cm2 produces high hydro-efficiency with very low coupling to either laser plasma instabilities (including cross-beam energy transfer (CBET)) and hot electrons. Even though the large capsule is driven using fully defocused (~32 mm) laser beams to achieve the largest laser spots, the laser beam spot to capsule diameter ratio remains small (~0.4). Having laser spots sizes smaller than the capsule diameter eliminates the need for CBET mitigation and increases the absorption of laser energy by the capsule above 95% as confirmed by scattered light diagnostics. By nesting a 1/3 size mid-Z Cr capsule concentrically inside the CH capsule, we can diagnose the residual kinetic energy in outer shell after laser turn-off (which occurs prior to the inter-shell collision) by measure the implosion trajectory of the inner shell using x-ray backlighting. Simulations using full laser drive over-predict the implosion convergence speed of both outer and inner shells. Artificially reducing the laser drive power (by ~25%) to non-physically force a match to the experimental outer shell implosion trajectory results in an inner shell implosion trajectory that is too slow. Only by removing 17% of the laser drive energy and re-depositing this energy as thermal energy into the outer half of the ablator shell can one simultaneously match both trajectories. We hypothesize that ablation pressure is being lost to tangentially directed hydrodynamic forces acting on a rippled ablation front. The impact for wetted-foam ignition designs is assessed. |
Tuesday, October 18, 2022 4:48PM - 5:00PM |
JO04.00014: Evaluation of the Effects of Laser Beam Zooming In OMEGA Next, Wetted-foam Target Designs Patrick m McKenty, John A Marozas, Timothy J Collins, William T Trickey, Duc Cao, Jonathan Carrol-Nellenbeck, Valeri N Goncharov Indirect-drive–ignition experiments at the National Ignition Facility (NIF) are laying the groundwork for the revitalization of interest in inertial fusion energy (IFE) concepts for the implementation of laser-fusion platforms for commercial power production. Recent results on the NIF have produced 1.3 MJ of fusion output that has the community poised to reach the decades-long goal of achieving ignition in the laboratory. As part of an overall laser-direct-Drive IFE platform, the University of Rochester’s Laboratory for Laser Energetics has begun investigating advanced, broadband laser designs,[1] target fabrication, and ignition target designs. In the area of target design, several different ablator materials are being investigated to optimize the laser drive. We will detail our efforts using wetted-foam ablators to produce ignition designs. In addition to 1-D LILAC scoping studies, results from 2-D DRACO simulations will ascertain the effects of nonuniformities due to finite beams geometries and various levels of laser-beam zooming afforded by the advanced laser system designs currently under study. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856. [1] E. M. Campbell et al., Phil. Trans. R. Soc. A 379, 2020011 (2020).
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