Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Plasma Physics
Volume 66, Number 13
Monday–Friday, November 8–12, 2021; Pittsburgh, PA
Session CO04: ICF: Compression and Burn IOn Demand
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Chair: Radha Bahukutumbi, Laboratory for Laser Energetics - Rochester Room: Rooms 304-305 |
Monday, November 8, 2021 2:00PM - 2:12PM |
CO04.00001: Hotspot power balance in alpha-particle dominated ICF implosions Pravesh K Patel, Jay D Salmonson, Chris Weber, Ryan C Nora, Annie L Kritcher, Chris V Young, Omar A Hurricane, Paul T Springer, Arthur E Pak, Alex B Zylstra, James S Ross Recent advances in inertial confinement fusion (ICF) experiments on the National Ignition Facility (NIF) have led to a tripling of the fusion energy yield to 170 kJ. These experiments have entered a qualitatively new regime where the energy flow in the hotspot is dominated by alpha-particle self-heating. We report on analysis, based on experimental data and simulations, of the power balance in the hotspot which indicates that the static Lawson criterion is exceed at the time of maximum compression, i.e., the instantaneous alpha heating rate in the hotspot exceeds all power losses. To achieve ignition the remaining step required is to maintain a positive net heating rate in the hotspot during the expansion phase where PdV work performed by the hotspot gives rise to an additional energy loss term. |
Monday, November 8, 2021 2:12PM - 2:24PM |
CO04.00002: Evaluation of Ignition Metrics with xRage John L Kline, Sean M Finnegan, Brian J Albright, William S Daughton, Brian M Haines, Joshua P Sauppe, Joseph M Smidt There have been several metrics designed to track progress toward, and assess the proximity to, reaching thermonuclear ignition for ice layered inertial confinement fusion target designs. Most metrics use zero dimensional evaluations that examine the power balance between mechanisms that both heat and cool the central DT gas throughout a defined confinement time. These metrics are then compared with 1D radiation hydrodynamics codes to benchmark their ability to capture the ignition point. As a result, the 0D models are grounded by simulations. Two questions often arise in this work. The first is, "what is the definition of ignition?" The second is," are the results code dependent?" While one might expect different codes to produce similar results, variations of order 5-10% would not be surprising. This would have a significant effect on the required driver energy to drive a robust ignition target. All of the present work utilized codes that use Lagrangian computational methods. In this work, we cross check past results with the Eulerian adaptive mesh refinement radiation hydrodynamics code xRage and discuss the definition of ignition. |
Monday, November 8, 2021 2:24PM - 2:36PM |
CO04.00003: Hot Spot Dynamics in Ice-Layered Inertial Confinement Fusion Implosions Brian J Albright, William S Daughton, Sean M Finnegan, John L Kline, Brian M Haines, Joshua P Sauppe, Joseph M Smidt The mainline approach to achieving inertial confinement fusion (ICF) ignition in the laboratory involves the use of ice-layered implosions, where a hot spot is formed during the implosion from ablation of the inner layer of DT ice. The dynamics of the formation and evolution of the hot spot are complex and a recent study by the authors indicates the potential value of reexamining a few of the physics assumptions commonly made by the community. This paper will describe recent work on this problem, one which is central to understanding ICF capsule performance on the National Ignition Facility and to the prospects of achieving ignition. |
Monday, November 8, 2021 2:36PM - 2:48PM |
CO04.00004: A mechanism for reduced compression in indirectly-driven layered capsule implosions Brian M Haines High yield implosions on the National Ignition Facility rely on maintaining low entropy in the DT fuel, quantified by its adiabat, in order to efficiently couple energy to the hot spot through high compression of the fuel layer. We present very high resolution xRAGE [1] simulation results that show that jetting of |
Monday, November 8, 2021 2:48PM - 3:00PM |
CO04.00005: Burning plasma analysis for indirect drive implosions at the National Ignition Facility Alison R Christopherson, Riccardo S Betti, Varchas Gopalaswamy, Samuel C Miller, Owen M Mannion, Duc M Cao, Jay D Salmonson, Denise E Hinkel, Omar A Hurricane In inertial confinement fusion, a spherical capsule of cryogenic DT is accelerated inward at a high velocity. The final fuel assembly consists of a relatively low density ``hot spot” (where the deuterium and tritium fuse) confined by a cold and dense shell. In the hot spot, one 3.5 MeV alpha particle is generated per fusion reaction which then deposits its energy back into the plasma, thereby increasing the temperature and the fusion reaction rate even more. This feedback process is called ``alpha heating,'' and ignition is a direct consequence of this thermal instability. On the path toward ignition, the onset of a burning-plasma regime occurs when the hot spot has received more heating from alpha particle deposition than it has from pure hydrodynamic compression. Progress toward the burning plasma regime is described by the parameter Qαhs =alpha energy deposited in hot spot/ PdV work delivered to the hot spot and it can be related to the measurable Lawson parameter χα~(ρR)0.61(Yield/Mstag)0.34 where ρR is the shell’s areal density, Yield is the neutron yield, and Mstag is the mass which has been has been stagnated by the large hot spot pressure. We discuss here how 2D asymmetries and uncertainties in the stagnated mass influence our ability to infer the burning plasma parameter in inertial fusion experiments on the National Ignition Facility. |
Monday, November 8, 2021 3:00PM - 3:12PM |
CO04.00006: Hot/Thick - The zero-coast path to increased areal-density at high velocity Daniel T Casey, Christopher V Young, Andrea L Kritcher, Alex B Zylstra, Kevin L Baker, Laurent Divol, David J Strozzi, Steven Ross, Edward P Hartouni, Patrick J Adrian, Brandon J Lahmann, Maria Gatu Johnson, Johan A Frenje, Debbie A Callahan, Omar A Hurricane Inertial confinement fusion (ICF) implosions must reach high hotspot energies (E) and high hotspot pressures (P) and a minimum requirement on the product E*P2 is required to achieve hotspot ignition. The size and scale of the facility and capsule required can be minimized using an implosion driven to high convergence to achieve high areal-density. However, previous attempts to increase convergence by lowering the adiabat have been severely limited by instabilities. We present a novel path to increasing areal-density that is instead achieved by thickening the ablator while simultaneously driving the increased capsule payload to comparable or higher velocity (>400 km/s) with a higher hohlraum radiation temperature (~315 eV). This results in a higher convergence implosion capable of being driven to peak compression (“zero-coast”). These design changes are calculated to have favorable stability in contrast to low adiabat designs because of stronger ablative stabilization and a lower inflight aspect ratio. A series of D3He gas-filled implosions were conducted and demonstrated symmetry control using cross-beam energy transfer. These implosions exhibit very high ~4.5 keV ion temperatures with evidence of increased hotspot E*P2 relative to close companions from other platforms. |
Monday, November 8, 2021 3:12PM - 3:24PM |
CO04.00007: High adiabat layered implosions driven in a frustraum Kevin L Baker, Peter A Amendt, James S Ross, Vladimir Smalyuk, Darwin Ho, Otto L Landen, John D Lindl, Derek Mariscal, Yuan Ping, Shahab Khan, David J Strozzi Frustraums enable large case-to-capsule ratio layered implosions with a reduced surface wall area relative to cylindrical hohlraums.1 These properties allow frustraums to drive large capsules, >1200 um inner radius, with high absorbed energy, >320 kJ. We report on the initial indirect-drive inertial confinement fusion experiments caried out in this frustraum campaign. Specifically, we discuss the symmetry of the tuning campaign and plot these results with empirical scalings2 derived for cylindrical hohlraums. We discuss experiments using delta lambda to control differences in drive between the pole and equator and present the performance results from the two layered implosions carried out in this campaign. |
Monday, November 8, 2021 3:24PM - 3:36PM |
CO04.00008: Reaching significant yield amplification at high adiabat on the National Ignition Facility with a 2-shock CH implosion design Steve A MacLaren, Laurent P Masse, Kevin L Baker, Stephane Laffite Implosions with high fuel entropy, or adiabat (defined as the ratio of the DT fuel layer pressure to the Fermi degenerate pressure) at the National Ignition Facility have historically resulted in the highest ratios of measured to simulated yield. For example the recent adiabat 4.3 high yield “Big Foot” experiment[1] achieved 45% of the yield predicted by 1D simulation, while the 2-shock CH cryo-layered implosion[2] achieved >90% of 1D simulated yield, albeit at minimal yield amplification. Here we describe a series of upcoming experiments at the NIF to test the performance of 2-shock CH implosions at a scale (1150 µm fuel outer radius) large enough to generate significant yield amplification. Initial experiments will test 2-shock CH at an adiabat of 5.5 and a yield amplification of 5, and follow-on experiments will reduce the implosion adiabat to 4.1 for a yield amplification of 20. The strategy for achieving a symmetric implosion of such a large CH capsule will be described, as well as the proximity to the ignition threshold for the two different adiabat designs. |
Monday, November 8, 2021 3:36PM - 3:48PM |
CO04.00009: Improving Performance and Understanding of Direct-Drive Inertial Fusion Implosions Using Statistical Modeling of Experimental Data Riccardo Betti, Varchas Gopalaswamy, Aarne Lees, Dhrumir Patel, Connor A Williams, James P Knauer, Duc M Cao, P. B Radha, Sean P Regan, Wolfgang R Theobald, Cliff A Thomas Statistical modeling of experimental and simulation databases [1] has enabled the development of an accurate predictive capability for OMEGA DT layered implosions leading to new target designs and record fusion yields. Neutron yields are currently predicted with 10% accuracy. Improvements to the model formulation [2] have revealed specific dependencies of the yield on adiabat, in-flight aspect ratio, ion-temperature asymmetries, laser beam size, and age of DT fill. This enables corrections of the yield predictions to account for laser mispointing, target offset and age of fill. Statistical modeling has identified that the multiple-pulse driver (MPD) configuration of the OMEGA laser [smoothing by spectral dispersion (SSD)-ON during the initial picket and SSD-OFF during the main drive] results in yield enhancement due to reduction in laser beam size when the driver changes from SSD-ON to SSD-OFF. While the highest yields have been achieved with large size targets, the model indicates that similar yields are possible on smaller targets with appropriate pulse shape modifications. The statistical model has been extended to predictions of areal density but with less accuracy due to large shot to shot variations. Results from statistical analysis and initial MPD campaign are presented. |
Monday, November 8, 2021 3:48PM - 4:00PM |
CO04.00010: Laser-Direct-Drive Cryogenic Implosion Performance on OMEGA Versus Target and Laser-Spot Radius Cliff A Thomas, Wolfgang R Theobald, James P Knauer, Christian Stoeckl, Timothy J Collins, Valeri N Goncharov, Riccardo Betti, Edward M Campbell, Kenneth Anderson, K. A Bauer, Duc M Cao, Stephen Craxton, Dana H Edgell, Reuben Epstein, Chad Forrest, Vladimir Y Glebov, Varchas Gopalaswamy, Igor Igumenshchev, Steven T Ivancic, Douglas W Jacobs-Perkins, Roger T Janezic, Tirtha R Joshi, Joe Kwiatkowski, Aarne Lees, Owen M Mannion, Frederic J Marshall, Michael Michalko, Zaarah L Mohamed, Dhrumir P Patel, Jonathan L Peebles, P. B Radha, Sean P Regan, Hans Rinderknecht, Michael J Rosenberg, Siddharth Sampat, Thomas C Sangster, Rahul C Shah, Kevin L Baker, Andrea L Kritcher, Max Tabak, Mark C Herrmann, Alison R Christopherson Advances in statistical modeling of laser-direct-drive (LDD) implosions have led to record fusion yields on the OMEGA laser.[1,2] Experiments on the NIF have shown Si dopant and wavelength detuning can mitigate hot-electron preheat and cross-beam energy transfer (CBET).[3,4] Applying these concepts to ignition-scale LDD requires an understanding of performance as a function of physical size (using scale factor S = Rt/RW, the ratio of target radius to a fiducial OMEGA target radius) and the beam-to-target radius (defined as R = Rb/Rt). We show the measured fusion yield Y and areal density ρR increase with capsule size as S5.0±0.2 and S1.6±0.2, respectively, in excess of simple 1-D expectations (Y~S4.3, and ρR~S1.0). Neutron production also increases with beam to target radius as R3.5±0.5, with benefits that saturate at R~1. Both results imply that target and relative beam size mitigate sources of degradation and improve confinement. DRACO simulations including nonlocal transport and CBET[5] show these trends are expected when laser imperfections (e.g., speckles, port geometry) are a primary source of perturbations in 2/3-D. To test this hypothesis, we have also performed implosions with improved stability, and find higher yields and areal densities. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856. [1] V. Gopalaswamy et al., Nature 565, 581 (2019). [2] A. Lees, Bull. Am. Phys. Soc. 65, TI01.00005 (2020). [3] A. A. Solodov et al., Phys. Plasmas 27, 052706 (2020). [4] J. A. Marozas et al., Phys. Rev. Lett. 120, 085001 (2018). [5] P. B. Radha et al., Phys. Plasmas 12, 032702 (2005). |
Monday, November 8, 2021 4:00PM - 4:12PM |
CO04.00011: Systematic Trends of Hot-Spot Flow Velocity in Laser-Direct-Drive Implosions on OMEGA Sean P Regan, Owen M Mannion, Chad Forrest, Hannah McClow, Zaarah L Mohamed, Adam Kalb, Joe Kwiatkowski, James P Knauer, Christian Stoeckl, Rahul C Shah, Vladimir Y Glebov, Wolfgang R Theobald, Kristen Churnetski, Riccardo S Betti, Varchas Gopalaswamy, Hans Rinderknecht, Igor Igumenshchev, Radha Bahukutumbi, Valeri N Goncharov, Dana H Edgell, Joe Katz, David Turnbull, Dustin H Froula, Mark J Bonino, David R Harding, Mike Campbell, Claudia M Shuldberg, Rain W Luo, Martin Hoppe, Arnaud Colaitis DT cryogenic targets and DT gas-filled, spherical plastic or glass targets are imploded on the OMEGA Laser System using laser-direct-drive inertial confinement fusion. The hot-spot flow velocity is diagnosed using multiple neutron time-of-flight detectors arranged along four quasi-orthogonal diagnostic lines of sight.[1] A systematic study of the magnitude and direction of the mode-1 asymmetry observed at stagnation[2] will be presented and possible seeds of mode-1 asymmetry from inaccuracies in beam pointing, beam-to-beam energy/power imbalance, inaccuracies in target positioning, laser–plasma interactions,[3] and target asymmetries will be discussed. It is shown that beam mispointing leads to a significant mode l = 1 illumination nonuniformity being the dominate cause for the hot-spot flow. With improved beam pointing, inaccuracies in target positioning and laser-plasma interactions are the leading causes for the hot-spot flow. [1] O. M. Mannion et al., Rev. Sci. Instrum. 92, 033529 (2021). [2] O. M. Mannion et al., Phys. Plasmas 28, 042701 (2020). [3] D. H. Edgell et al., “Nonuniform Absorption and Scattered Light in Direct-Drive Implosions Driven by Polarization Smoothing,” to be published in Physical Review Letters. |
Monday, November 8, 2021 4:12PM - 4:24PM |
CO04.00012: Mix, Temperature and Compression of Statistical Model Optimized Cryogenic Implosions Rahul C Shah, Duc M Cao, Riccardo Betti, Reuben Epstein, Varchas Gopalaswamy, Michael J Rosenberg, Wolfgang R Theobald, Sean P Regan, Petr L Volegov, Benjamin Bachmann We report on the x-ray continuum inferred mix, temperature and compression of direct-drive DT cryogenic layered implosions on OMEGA that were optimized with a statistical model.[1] The x-ray measurement is obtained from a new four-channel, differentially filtered pinhole imager recorded on calibrated image plate, from which an electron temperature and absolute yield are determined. The mix analysis is based on a ratio of measured x-ray and neutron yields.[2] The influence of nonequilibration of electrons and ions in the hot spot is interpreted from a database of 2‑D radiation-hydrodynamic simulations. Within limits of a few percent by atom CD (imposed by the nonequilibrium conditions), we do not find indications of hot-spot mix over the range of typically accessed implosions for highest ignition-relevant performance. The bremsstrahlung temperature and line-integrated amplitude are also spatially resolved and compared to an identical analysis of the 2-D simulation (accounting for beam geometry, laser imprint, and cryogenic layer roughness). The results suggest that our current models do not yet explain the limitations on hot-spot compression. [1] V. Gopalaswamy et al., Nature 565, 581 (2019). [2] T. Ma et al., Phys. Rev. Lett. 111, 085004 (2013). |
Monday, November 8, 2021 4:24PM - 4:36PM |
CO04.00013: Studies of kinetic effects in shock-driven implosions using a comprehensive set of x-ray and nuclear diagnostics at OMEGA Patrick J Adrian, Johan A Frenje, Benjamin Bachmann, Vladimir Y Glebov, Maria Gatu Johnson, Neel Kabadi, Justin H Kunimune, Chikang Li, Sean P Regan, Fredrick H Seguin, Christian Stoeckl, Graeme Sutcliffe, Jacob A Pearcy, Richard Petrasso In thin-glass, shock-driven implosions, a strong shock propagates through the plasma during the early phase of implosion. This strong shock heats the low-density material causing the ions’ mean-free path to be larger than the hydrodynamic length scale. Previous studies demonstrated substantial yield degradation as the fill pressure was decreased. Radiation-hydrodynamic simulations using empirically-tuned ion kinetic models [M. J. Rosenberg et al. PRL 2014] and simulations solving the Vlasov-Fokker-Plank equations for the ions [O. Larroche et al. PoP 2016] reproduce the yield-degradation trend. Both simulation methods predict the dominant mechanism responsible for the yield degradation is kinetic ion-diffusion, which interchanges D3He gas with the glass shell. We report on a set of x-ray measurements from a series of implosions with varied D3He gas fill. The measurements show increased x-ray emission as the D3He gas-fill pressure decreases. In addition, x-ray images in multiple energy bands show a transition from a shell-like emission to a center-like emission structure as the gas-fill pressure decreases. Both observations support the prediction of a partial interchange between the glass and D3He due to the long mean-free paths. These x-ray measurements provide an additional constraint for the kinetic modeling of ICF implosions. Results are compared to iFP, xRage, and ARES simulation codes. |
Monday, November 8, 2021 4:36PM - 4:48PM |
CO04.00014: National Ignition Facility Polar-Drive Exploding-Pusher Experiments Improving Performance via Imprint Mitigation John A Marozas, Michael J Rosenberg, Patrick m McKenty, Timothy J Collins, Valeri N Goncharov, Sean P Regan, Edward M Campbell, Laurent Divol, Gregory E Kemp, Charles B Yeamans Exploding pushers (XP’s) produced the highest polar-direct-drive (PDD) DT yield (~1.1x1016) on the National Ignition Facility (NIF) using a ~1.1-MJ pulse illuminating a ~4-mm-diam, 25-mm CH target. Development continues to improve DT yield with an ultimate goal >2x1016. These NIF PDD-XP targets provide a high-yield neutron source as well as a platform to develop predictive inertial confinement fusion modeling using the 2-D code DRACO. Recent NIF PDD-XP experiments focused on a smaller 3.4-mm-diam target using a DD fill as a surrogate target to keep the illumination intensity similar to the 4-mm-diam targets while increasing shot throughput with its modest facility impact. Shell morphology was improved as predicted by DRACO but the yield was not affected unless the deleterious imprint was included. In addition, the NIF PDD-XP experiments across the larger target diameters (>3 mm) with either DT or DD fills have indicated sensitivity to imprint. Potential yield degradation sources guided the design of subsequent experiments at 3.4-mm scale to assess the impact of imprint mitigation via pulse-shape control as one method to improve performance while improving predictive code capability. The 3.4-mm-scale target results are presented here. |
Monday, November 8, 2021 4:48PM - 5:00PM |
CO04.00015: Examining the Role of Cross-Beam Energy Transfer in National Ignition Facility Direct-Drive Exploding-Pusher Experiments Patrick m McKenty, John A Marozas, Michael J Rosenberg, Timothy J Collins, Laurent Divol, Gregory E Kemp, Charles B Yeamans Direct-drive exploding-pusher experiments at the National Ignition Facility (NIF) have been shown to comprise a robust target platform producing a wide range of yields, from 1 ´ 1012 up to current levels of 1 ´ 1016. Inherent in these polar-drive implosions is the presence of cross-beam energy transfer (CBET), which has been shown to alter and degrade absorption of the incoming laser beams. Mitigation strategies are currently underway on several fronts, including capsule contouring, dedicated phase plates, wavelength detuning, and pulse shaping. However, comparisons of experimental data, at a constant target diameter, indicate improving differences in target shape as the laser energy is increased. Understanding this trend is imperative in our pursuit of remedying CBET in not only these high-yield experiments but also in eventual direct-drive–ignition designs. This observation could be influenced by several factors, particularly including CBET and thermal conduction. This presentation will numerically examine the underlying physics that determines shape for several NIF implosions, attempting to understand the relevant mechanisms behind the experimental trend. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856. |
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