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 TO04: ICF: Compression and Burn IIILive Streamed
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Chair: Alison Christopherson, LLNL Room: Ballroom 111 A |
Thursday, October 20, 2022 9:30AM - 9:42AM |
TO04.00001: Understanding Performance Variability in Mega-Joule Class Inertial Confinement Fusion Implosions Jim A Gaffney, Kelli D Humbird, Andrea L Kritcher, Michael K Kruse, Chris Weber, Eugene Kur, Bogdan Kustowski, Brian K Spears Recent high-yield experiments at the NIF have have made performance variability a key question for the ICF community; How reliably can we produce MJ-class yields? What drives the observed variability, and how can we reduce it? |
Thursday, October 20, 2022 9:42AM - 9:54AM |
TO04.00002: Mapping the ignition cliff with varying Lawson parameter on N210808-like implosions Alex B Zylstra, Andrea L Kritcher, Daniel T Casey, Joseph E Ralph, Arthur Pak, Laurent Divol, David J Schlossberg, Omar A Hurricane, Debra A Callahan, Otto L Landen, Alison R Christopherson, Pravesh K Patel, Paul T Springer, John D Lindl The NIF implosion experiment N210808 produced more than a MJ of fusion yield and surpassed Lawson's ignition criterion for the first time. Subsequent experiments attempting to reproduce N210808 experienced lower performance, between 400-750kJ, due to higher levels of degradations. These experiments provide a novel data set to empirically study the implosion performance versus several ignition metrics published in the literature, including generalized Lawson criteria, the ignition threshold factor (ITF), and other metrics. As expected these variable performance experiments are intermediate in metric values between previous high-performing implosions in the burning-plasma regime [Nature 601, 542 (2022)] and N210808, essentially mapping out the ignition cliff empirically and providing a novel data set to validate these ignition metrics. |
Thursday, October 20, 2022 9:54AM - 10:06AM |
TO04.00003: Observed dynamics of inertial confinement fusion implosions approaching unity gain at the National Ignition Facility Arthur Pak, Laurent Divol, Richard M Bionta, Benjamin Bachmann, Daniel T Casey, Eduard L Dewald, Tilo Doeppner, David N Fittinghoff, Edward P Hartouni, Matthias Hohenberger, Joe Holder, Andrea L Kritcher, Otto L Landen, Edward V Marley, Brian J MacGowan, Andrew G MacPhee, Alastair S Moore, Joseph E Ralph, David J Schlossberg, Riccardo Tommasini, Clement A Trosseille, Christopher V Young, Alex B Zylstra In indirect drive inertial confinement fusion experiments conducted with deuterium and tritium fuel, to achieve strong self-heating and energy gain (E_fusion ≥ E_laser_driver), the rate of heating from fusion product alpha particles must outpace all losses. The difference between heating and power losses and the duration over which this condition can be met, is important for setting the achievable energy production from such systems. Previous experiments have achieved a net power balance >0 near the minimum radius achieved by the implosion. Here, new experimental results will be presented where increased levels of alpha heating lead to increases the hot spot temperature, pressure and yield while the hot spot is expanding. This dynamic is a key signature associated with self-heating in the ignition regime and shown to be strongly correlated to the variability in fusion energy production, change in apparent hot spot size and areal density observed over a set of repeat implosions. Using the observed expansion dynamics together with analytic models and simulations the relative balance between heating and cooling will be examined. |
Thursday, October 20, 2022 10:06AM - 10:18AM |
TO04.00004: Theory for assessing yield amplification and ignition proximity in the presence of hotspot mixing Omar A Hurricane, Alison R Christopherson, Otto L Landen, Stephen A Maclaren, Paul T Springer It’s well known that the presence of high-Z mixing in a DT plasma increases Bremsstrahlung x-ray losses. The presence of mix, thus, increases the “ignition temperature” for the plasma. Therefore, mix has both an explicit and implicit impact on the inference of yield amplification and the ignition boundary. The explicit impact is a change to the thermodynamic variables such as plasma temperature and pressure as compared to what those variables would have been without mix. The implicit impact is that for a given thermodynamic state, the inferred yield amplification and ignition boundary for “clean” DT no longer applies. In this talk, we discuss how an existing theoretical framework [1] can be used to calculate a correction to yield amplification and the ignition boundary in the presence of mix. |
Thursday, October 20, 2022 10:18AM - 10:30AM |
TO04.00005: Hot spot mass ablation and enthalpy in ice-layered inertial fusion implosions Brian J Albright, William S Daughton, Sean M Finnegan, John L Kline, Brian M Haines, Joshua P Sauppe, Joseph M Smidt In layered implosions, most of the fuel in the central hot spot comes from mass ablation from the inner layer of DT ice. This ablation is associated with an enthalpy contribution to the hot spot energy that plays a key role in setting the conditions for thermonuclear ignition. A recent study of this problem indicates that prior studies of hot spot ignition have underestimated by a factor of 2-4 the rate of mass ablation, leading to a corresponding, systematic underestimate of the energy needed to ignite a hot spot [1]. In this presentation, an improved model of mass ablation will be shown that is in excellent agreement with radiation hydrodynamics simulations. Implications of the use of this improved model on setting the conditions for ignition will be discussed. |
Thursday, October 20, 2022 10:30AM - 10:42AM |
TO04.00006: Influence of mass ablation on the ignition threshold in layered fusion capsules William S Daughton, Brian J Albright, Sean M Finnegan, Brian M Haines, John L Kline, Joshua P Sauppe, Joseph M Smidt The ignition physics for layered fusion capsules involves a complex interplay between the dynamically forming hot spot and the dense surrounding fuel. Recent analysis has demonstrated [1] that the mass ablation rate into the hot spot depends sensitively upon the temperature of the dense fuel. This produces an enthalpy flux into the hot spot which plays a critical role in controlling the hot spot temperature and the ignition threshold. In this presentation, we demonstrate that net influence of mass ablation on the ignition threshold is regulated by a dimensionless parameter which depends upon the temperature of the dense fuel. As a consequence, the ignition threshold is sensitive to any mechanism that heats the dense fuel, such as neutrons or radiation emitted from the hot spot. These predictions are confirmed using radiation hydrodynamic simulations for a series of capsules near ignition conditions. These results may have relevance for understanding the variable performance of recent experiments and for guiding new capsule designs toward higher fusion yields. |
Thursday, October 20, 2022 10:42AM - 10:54AM |
TO04.00007: Exploration of Non-Maxwellian Effects of Alpha Heating on Neutron Spectra Using the Vlasov-Fokker Planck code iFP Benjamin Reichelt, Luis Chacon, Steven Anderson, William T Taitano, Brett Keenan, Brian M Haines, Maria Gatu Johnson, Neel Kabadi, Edward P Hartouni, Brian Appelbe, Aidan C Crilly, Chikang Li In nuclear fusion reactions, a set amount of energy is liberated and distributed amongst the products in a manner dictated by kinematics, momenta and energies of the fusion reactants. Within a plasma, the reactants take on a distribution of velocities, affecting the width and peak location of the neutron energy spectra produced in both DT and DD fusion reactions. For a Maxwellian plasma, the relationship between neutron-energy peak location and peak width forms a concave-down curve. Even for nonuniform plasmas, any observed neutron spectra from a plasma well-described by hydrodynamics must be an average of points along the curve and thus lie below the curve. However, recent work in analyzing the neutron spectra of high yield NIF shots has revealed that the DT neutron data lie significantly above the curve when alpha heating is considerable. In this work, the Los Alamos developed kinetic code iFP is utilized to explore the effect of alpha heating on neutron spectra. With the help of iFP’s fully kinetic burn model and neutron spectrum calculator, the effect of small angle coulombic alpha collisions on neutron spectra is investigated as a potential source of the anomaly. |
Thursday, October 20, 2022 10:54AM - 11:06AM |
TO04.00008: Optimizing Shock Timing for Improved Compression and Reduced Adiabat in High-Yield, Burning-Plasma Experiments on the National Ignition Facility Matthias Hohenberger, Daniel S Clark, Christopher V Young, Joseph E Ralph, Arthur Pak, Andrea L Kritcher, Daniel T Casey, Benjamin Bachmann, Alex B Zylstra, Edward P Hartouni, David J Schlossberg, Alastair S Moore, Shahab F Khan, Katya Newman, Omar A Hurricane, Michael Stadermann, Tom Braun, Otto L Landen Laser-indirect—drive inertial confinement fusion (ICF) experiments at the National Ignition Facility (NIF) have demonstrated a burning plasma [1] and are approaching the ignition regime with demonstrated yields exceeding a MJ [2]. In these experiments, increasing the compression is thought to be one method of obtaining higher amounts of fusion energy production. Based on the current, best-performing implosion, N210808, with a total yield of 1.3 MJ, we have performed experiments with modified pulse shapes for optimized shock timing. The goal is to reduce the adiabat and increase compression by ~10% with respect to the baseline experiment, while also maintaining moderate levels of ablation-front instability growth and fuel-ablator Atwood number. We will report on simulations and a first series of experiments studying performance metrics with the updated pulse shape design, as well as the viability of this approach for a robust, high-yield ICF platform. This work was performed under the auspices of the U.S. Department of Energy by LLNS, LLC, under Contract No. DE-AC52- 07NA27344. LLNL-ABS-836763. |
Thursday, October 20, 2022 11:06AM - 11:18AM |
TO04.00009: Frustraum 1100 campaign on the National Ignition Facility Kevin L Baker, Peter A Amendt, David Mariscal, Darwin D Ho, James S Ross, Denise E Hinkel, Vladimir Smalyuk, Otto L Landen, John D Lindl, David J Strozzi, Jose L Milovich The frustraum 1100 campaign aims to reduce the hohlraum losses by approximately 15% relative to previous cylindrical implosions in order to couple more energy into the capsule while still providing symmetry control.1 These reduced hohlraum losses translate effectively into an equivalent increase in laser energy, ~300 kJ, which can then be used to drive hydroscaled implosions with greater robustness, reduced coast times or thicker ice layers to increase burn efficiency. We will present the results from an initial set of experiments conducted in a frustraum2 hohlraum. These experiments implemented an energy walkup using a VISAR platform to measure shock strength and symmetry and radiography and self-emission platforms to measure inflight and stagnated shape. The experiments looked at azimuthal smoothing of outer beam intensity to reduce gold bubble motion and provided an initial look at P2 symmetry control in the platform by applying a wavelength offset between cones of beams to control the level of cross-beam energy transfer between the cones. |
Thursday, October 20, 2022 11:18AM - 11:30AM |
TO04.00010: Controlling sources of low mode asymmetry in ignition experiments at the National Ignition Facility(NIF) Brian J MacGowan, Daniel T Casey, Otto L Landen, Christopher V Young, Jose L Milovich, Matthias Hohenberger, Eduard L Dewald, Jean-Michel Di Nicola, Edward P Hartouni, Haibo Huang, Casey Kong, Alastair S Moore, Abbas Nikroo, Ryan C Nora, Arthur Pak, Travis S Petersen, Joseph E Ralph, Jim D Sater, David J Schlossberg, Kevin Sequoia, Michael Stadermann, Bruno Van Wonterghem, Steven T Yang, Alex B Zylstra Low mode 3D drive and capsule asymmetries (l = 1 and 2) are important degradation mechanisms for high yield NIF indirect drive implosions. Sources of asymmetry include laser power, capsule ablator thickness and composition, laser/target positioning errors, drive losses from target diagnostic windows, and Cross Beam Energy Transfer (CBET). The resultant mode-1 asymmetries are seen on NIF implosions as high bulk imploded hotspot velocities (~ 100km/s), measured by comparison of neutron time of flight measurements on several lines of sight. The expected asymmetry inferred from the laser diagnostics and target characterization, has been compared with hotspot velocity and shape measurements on multiple implosions to calibrate sensitivity of the implosions to asymmetry and identify systematic trends in the facility and target performance that may be mitigated. Modifications to the configuration of the diagnostics windows has reduced their mode-1 and 2 impact on recent DT shots. Capsule thickness variations and misalignment are characterized pre shot and can be mitigated by power adjustments of order +/- 1% to specific groups of laser beams. |
Thursday, October 20, 2022 11:30AM - 11:42AM |
TO04.00011: Increasing the areal density of N210808 implosion with thicker ablators Annie L Kritcher, Alex B Zylstra, Kelli D Humbird, Chris Weber, Arthur Pak, Debbie A Callahan, Omar A Hurricane, Daniel T Casey, Daniel S Clark, Alison R Christopherson, Laurent Divol, Denise E Hinkel, Bogdan Kustowski, Otto L Landen, Steve A MacLaren, Katya Newman, Joseph E Ralph, David J Schlossberg, Christopher V Young On August 8, 2021, ignition was finally demonstrated in the laboratory [1-3] on the National Ignition Facility (NIF) in Northern California in the HYBRID-E platform [4-5]. The experiment, N210808, produced a fusion yield of 1.37 MJ from 1.9 MJ of laser energy and has crossed the tipping-point of thermodynamic instability according to several ignition metrics. High areal densities are required to trap the fusion products (alpha particles) for “self” heating of the plasma to reach the conditions for ignition and propagating burn. N210808 burned about 2% of the initial DT fuel and showed variability to unintentional perturbations from changing capsule quality and odd mode asymmetries in follow-on experiments. |
Thursday, October 20, 2022 11:42AM - 11:54AM |
TO04.00012: The impact of ablator-fuel mixing in ignition-class ICF implosions on NIF Chris Weber, Benjamin Bachmann, Laurent Divol, Jim A Gaffney, Andrea L Kritcher, Andrew G MacPhee, Steve A MacLaren, Edward V Marley, Arthur Pak ICF implosion experiments on NIF that attempted to repeat the 1.3 MJ experiment from August 2021 have underperformed and sometimes observed increased levels of ablator material mixing with the DT. Capsules are hydrodynamically unstable at many interfaces (hot-spot/fuel, fuel/ablator, undoped/doped-ablator, and ablation front), and these can degrade the implosion in different ways. Through 1D and 2D radiation-hydrodynamics models, we show how these different sources of mixing can degrade performance and their expected experimental signatures. In comparison with the data, this allows us to identify the origin of this mix, which can help focus mitigation efforts. We also discuss how this design can be made more robust to these different instability types. |
Thursday, October 20, 2022 11:54AM - 12:06PM |
TO04.00013: Progress towards fielding Boron-Carbide Ablators on the National Ignition Facility Ryan C Nora, Suzanne J Ali, John H Bae, Leonardus B Bayu Aji, Richard J Briggs, Peter M Celliers, Tilo Doeppner, Alison Engwall, Denise E Hinkel, Sergei O Kucheyev, Paul B Mirkarimi, Swanee Shin, Gregory V Taylor Boron Carbide (B4C) is a promising ablator material for inertial confinement fusion at the National Ignition Facility (NIF). B4C is an amorphous material with a density of 2.52g/cm^3, making it dense enough to be suitable for short drive pulses like High-Density-Carbon (HDC, 3.2g/cm^3) but without fabrication defects such as grain interstitials and voids. Additionally, B4C's low-melting temperature allows for implosion experiments to be fielded at adiabats lower than those achievable for HDC implosions. This presentation will outline the advancements made by target fabrication at Lawrence Livermore, experimental tests completed on the OMEGA laser, and progress in capsule and hohlraum modeling in preparation for spherical implosions at the NIF. |
Thursday, October 20, 2022 12:06PM - 12:18PM |
TO04.00014: Diagnosing the impact of low-mode asymmetries in ignition experiments at the National Ignition Facility Daniel T Casey, Brian J MacGowan, Omar A Hurricane, Otto L Landen, Ryan C Nora, Steven W Haan, Andrea L Kritcher, Alex B Zylstra, Joseph E Ralph, Eduard L Dewald, Matthias Hohenberger, Arthur Pak, Edward P Hartouni, Richard M Bionta, Kelly D Hahn, David J Schlossberg, Alastair S Moore Ignition via inertial confinement fusion (ICF) requires implosions to achieve high hotspot energies and pressures that are inertially confined by a dense shell of DT fuel. This requires high inflight shell velocity, good energy coupling between the hotspot and imploding shell, and high areal-density at peak compression. Three-dimensional (3D) asymmetries seeded by imperfections in the drive symmetry or target [MacGowan et al., HEDP 40 100944 (2021)] can grow during an implosion and damage both the coupling of energy to the hotspot and confinement of that energy. Recent high-yield experiments at the NIF have shown evidence that low-mode asymmetries are a key degradation mechanism and contribute to shot to shot variability. Experimental and theoretical evidence show experimental signatures of asymmetry (e.g. the observed hotspot velocity, and areal density asymmetry) change with increasing implosion yield given the same initial seed. Likewise, the level of performance degradation as inferred by the observables also changes. Understanding how these asymmetries respond to differences in performance helps untangle how they impact variability and performance at high yield. |
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