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 NO04: ICF: Compression and Burn IIOn Demand
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Chair: Ryan Nora, Lawrence Livermore National Laboratory Room: Rooms 304-305 |
Wednesday, November 10, 2021 9:30AM - 9:42AM |
NO04.00001: Ablative energetics of large-capsule low-intensity direct drive implosions at the National Ignition Facility Mark J Schmitt, Brett S Scheiner, Derek Schmidt, Lynn Kot, Brett Keenan, Michael J Rosenberg, Patrick m McKenty, Stephen Craxton Recent directly-driven double shell implosion experiments fielded at the National Ignition Facility indicate anomalous heating of the ablator shell resulting in decreased laser ablation pressure with respect to rad-hydro simulations for I~250 TW/cm2 at the capsule surface. Self-emission images during the 6.5 ns laser pulse combined with backlit radiographs of the inner shell near 17ns constrain both the ablation drive and collision driven physics of the double shell target. Additional scattered light data indicate that 2% or less of the 1.1 MJ laser drive energy is not absorbed by the target. Simulations with full laser drive over predict the implosion convergence speed of both outer and inner shells. Artificially reducing the laser drive power (by ~25%) to force a match to the experimental outer shell implosion trajectory results in an inner shell implosion trajectory that is too slow. Only by removing 16% of the laser drive energy and injecting this energy as thermal energy into the outer half of the ablator shell can one simultaneously match the trajectories of both shells. Neither relaxed flux limiting, enhanced electron thermal conduction nor nonlocal heat conduction provide a suitable match to the data. Detailed results and implications of these comparisons will be given. |
Wednesday, November 10, 2021 9:42AM - 9:54AM |
NO04.00002: Imaging 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, David A Martinez, Daniel H Kalantar 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 are developing a platform to study the evolution and shape of the inner shell starting with surrogate materials and utilizing the Advanced Radiographic Capability (ARC) on the National Ignition Facility (NIF). We will discuss the current status and present initial results. |
Wednesday, November 10, 2021 9:54AM - 10:06AM |
NO04.00003: MCNP® calculations for inner-shell radiography of double-shell implosions on the NIF David D Meyerhofer, Paul A Keiter, Tom Byvank, David S Montgomery, Eric N Loomis The National Ignition Facility (NIF) Double Shell Team is planning radiography experiments using the Advanced Radiographic Capability (NIF-ARC) to measure the properties of the imploding inner Cr shell. These include the shape, the energy transfer from the outer to inner shell, the density profile, etc. The NIF-ARC produces a broad-band x-ray source with energies from ~10 keV to a few hundred keV. The Monte Carlo N-Particle® (MCNP®) code was used, in photon mode, to simulate the radiography, with a particular focus on understanding the transmission and scattering. The ultimate goal is to develop a technique to reconstruct the density profile of the compressed inner shell from the radiograph. |
Wednesday, November 10, 2021 10:06AM - 10:18AM |
NO04.00004: Comparing 2-Shock and 3-Shock drives for Pushered Single Shell Implosions David A Martinez, Eduard L Dewald, Steve A MacLaren, Darwin Ho, Jesse E Pino, Robert E Tipton, Christopher V Young, Hongwei Xu, Casey Kong, Shahab Khan, Cohl Vardon Houldin Hatala, Justin Buscho, Gregory Mellos, Steve Johnson, Daniel H Kalantar, Scott Vonhoff, Corie Horwoodd At the National Ignition Facility, we are exploring an alternative ignition capsule design called the pushered single shell (PSS) which utilizes a high Z pusher in between the ablator and gas fuel [1]. To mitigate ablative Rayleigh Taylor (RT) instabilities, this design uses a pusher layer that that gradually increases the high-Z concentration [2]. The high Z layer creates a dense pusher with a slower peak implosion velocity that reduces radiation losses and tamps the core, resulting in a longer burn than typical low-Z capsule implosions. However, the layer is prone to RT instabilities during deceleration which limits the advantages of the high Z pusher. The PSS campaign is investigating the balance between enhanced confinement and mix with a series of DT gas filled capsules comparing a more compressible 3-shock drive vs a more stable 2-shock laser drive. Experimental results and mix simulations are employed to determine the optimal drive that will be used for future experiments. |
Wednesday, November 10, 2021 10:18AM - 10:30AM |
NO04.00005: Modeling of Beryllium-Chromium Pushered Single Shells Jesse E Pino, Eduard L Dewald, Steve A MacLaren, David A Martinez, Darwin Ho, Vladimir Smalyuk, Robert E Tipton, Christopher V Young The Pushered Single Shell (PSS) design is an alternative ignition concept at the National Ignition Facility1. By leveraging recent advances in target fabrication, the inner region of a Be ablator is blended with mid- or high-Z material using a graded concentration profile that decreases gradually toward the outer region of the ablator. This Mid-Z material increases the confinement time at stagnation and lowers the temperature requirement for ignition, while the graded profile substantially reduces hydrodynamic instabilities that would arise from a discrete interface. This talk describes simulation results from a recent series of PSS experiments on graded Beryllium-Chromium capsules driven with 2-shock and 3-shock temperature profiles. We investigate sensitivity to drive, hydrodynamic instabilities, mix, as well as symmetry and fill tube perturbations. LLNL-ABS-824550 |
Wednesday, November 10, 2021 10:30AM - 10:42AM |
NO04.00006: High ρR Mo-doped Be heavy ablator for high yield: Experimental design and implosion physics Darwin Ho, Steve A MacLaren Beryllium ablators with inner layer doped with increasing Mo concentration towards the center can increase ρR and the burn fraction. The mass of this type of “heavy ablator” is >30% than conventional ablators with same radius. Implosion simulations of heavy ablators with acceptable RTI and high yield were reported.1 Based on this, implosion experiments with capsule radius of 1175 µm using 1.7 MJ of laser energy is designed. The ratio of the high-mode 2D simulated yield to the 1D simulated yield using the heavy ablator is lower than that of the HDC N210207 shot that gives record neutron yield close to 6e16 using 1.93 MJ of laser energy. However, the simulated 2D yield of the heavy ablator design is still higher than either the N210207 simulated or measured yield. The 2D/1D yield ratio for the heavy ablator is lower because high-ρR implosions in general have a steeper ignition cliff. The implosion moves away from the cliff if the laser energy is increased to 1.87 MJ, which boosts the 2D simulated yield to multi-MJ range. |
Wednesday, November 10, 2021 10:42AM - 10:54AM |
NO04.00007: Quantification and Assessment of Radiation-Trapping Efficiency in Inertial Confinement Fusion Implosion Experiments with High-Z–Lined Single-Shell Targets Reuben Epstein, Valeri N Goncharov, Suxing X Hu, Duc M Cao, Alexander Shvydky, Patrick m McKenty, Thomas C Sangster, Gilbert Collins, Daniel J Haberberger, John L Kline, Sean M Finnegan Achieving high-temperature “volume-burn” ignition conditions in inertial confinement fusion implosions requires a shell that contains the DT fuel and, at the same time, minimizes the escape of thermal energy from the fuel in the run-up to ignition conditions. Volume burn involves the entire fuel mass igniting at once, as opposed to ignition by a propagating burn wave, as in conventional cryogenic shell implosions. Single-shell “pushered” implosions utilize an opaque high-Z inner shell lining to “trap” the radiation that would otherwise escape and cool the fuel. We employ radiation-hydrodynamic simulations, utilizing enhanced radiation visualization tools to arrive at a meaningful measure of the effectiveness of radiation trapping. The radiation energy density of the fuel is a meaningful ignition parameter only if the fuel mass is optically thick. The radiative flux that escapes the fuel is a more important consideration than the radiation energy that may be trapped in the fuel. Opaque shell linings are strong absorbers, not mirrors, and they reduce fuel cooling only to the extent that they retard the escaping energy flux. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856. |
Wednesday, November 10, 2021 10:54AM - 11:06AM |
NO04.00008: A pathway towards burning plasmas through low-convergence-ratio direct drive ICF implosions Robert W Paddock, Robbie H Scott, Warren J Garbett, Brian M Haines, Alex B Zylstra, Timothy J Collins, Stephen Craxton, Peter A Norreys The 1D radiation hydrodynamics code Hyades was used to simulate direct-drive implosions in the low-convergence-ratio regime, which restricts hydrodynamic instability growth through limits on implosion velocity and in-flight aspect ratio and parametric instability growth through limits on incident intensity. The simulations demonstrated potential gains of 0.2 on LMJ-scale (0.8 MJ) systems and 0.8 on NIF-scale (1.7 MJ) systems, and a reactor-level gain of 50 for an 8.5 MJ implosion. Further simulations for the lower-energy systems demonstrated a major increase in yield with the deposition of electron energy into the hotspot through auxiliary heating. Results included yield amplification (compared to the case of no auxiliary heating) of up to 80 times (for a capsule requiring 100 kJ of laser compression), and break-even for 1.1 MJ of total energy input (including an estimated 370 kJ of short-pulse laser energy to produce electron beams for the auxiliary heating). |
Wednesday, November 10, 2021 11:06AM - 11:18AM |
NO04.00009: Effect of Mode-1 Perturbations on OMEGA Areal-Density Measurements James P Knauer, C. J Forrest, Z. I Mohamad, R. Betti, V. Gopalaswamy, S. P Regan, W. Theobold, M. Gatu-Johnson, J. A Frenje, A. J Crilly, B. D Appelbe Implosion areal density (ρR) is an important measurement to assess the performance of cryogenic implosions. The presence of a mode-1 (l = 1) perturbation compromises this measurement. The statistical model[1] used to design the high-performance cryogenic implosions on OMEGA have shown that the ion-temperature distribution is a good indication of the presence of a mode-1 asymmetry. Energy shifts in the neutron peak energies are used to measure the velocity of the fusing plasma,[2] also an indicator of a mode‑1 asymmetry. Data that utilize these two mode-1 signatures will be compared to the implosion ρR measurements using two backscatter signatures, neutron time of flight (nToF) and a downscatter signature (magnetic recoil spectrometer). An outstanding question is whether or not the high ρR values from early cryogenic implosions[3] have been affected by mode-1 asymmetries. The earlier experiments did not have the mode-1 asymmetry measurements of the recent implosions. 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] .O. M. Mannion et al., Nucl. Instrum. Methods Phys. Res. A 964, 163774 (2020). [3] S. P. Regan et al., Phys. Rev. Lett. 117, 025001 (2016). |
Wednesday, November 10, 2021 11:18AM - 11:30AM Not Participating |
NO04.00010: Impacts of Hot-Spot Flows from Drive Asymmetry on Implosion Performance at the National Ignition Facility (NIF) David J Schlossberg, Daniel T Casey, Edward P Hartouni, Otto L Landen, Brian J MacGowan, Alastair S Moore, Ryan C Nora, Christopher V Young Asymmetries in laser indirect drive during inertial confinement fusion dramatically reduce performance, due to implosion energy being transferred into residual plasma motion instead of hot spot compression and heating. A dedicated set of NIF experiments characterized these effects, using a simplified platform and single-variable changes to isolate physics and diagnostic signatures of low-mode asymmetries. Results provided clear measurements of performance degradation from a Legendre l = 1 asymmetry. [1] These results are now used to interpret more complex, ignition-relevant DT-ice layer implosions. Experimental signatures are directly applicable, and strong flows within the hot-spot with corresponding large variances, often correlate with large apparent-Tion asymmetries. Apparent ΔTion measured at different locations around the plasma can be used to estimate hot spot residual kinetic energy (RKE). 2D simulations of simplified and complex platforms show qualitative agreement but both overpredict measured apparent ΔTion. Observation of time-resolved flows within the hot spot during an implosion are directly compared to flow-fields from 2D HYDRA simulations. Higher-order flows are quantified and shown to directly contribute to RKE and performance degradation. |
Wednesday, November 10, 2021 11:30AM - 11:42AM |
NO04.00011: A polar direct drive liquid deuterium-tritium wetted foam target concept for inertial confinement fusion Rick E Olson, Mark J Schmitt, Brian M Haines, Gregory E Kemp, Charles B Yeamans, Brent E Blue, Derek Schmidt, Alex Haid, Michael Farrell, Paul A Bradley, Harry F Robey, Ramon J Leeper We propose a new approach to Inertial Confinement Fusion (ICF) that could potentially lead to ignition and propagating thermonuclear burn at the National Ignition Facility (NIF). The proposal is based upon a combination of two concepts -- Polar Direct Drive (PDD)1 and liquid deuterium-tritium wetted foam (WF) capsules2. With this new concept, 2D radiation hydrodynamic simulations indicate that ICF ignition and propagating thermonuclear burn are possible well within the laser power and energy capabilities available today on the NIF. |
Wednesday, November 10, 2021 11:42AM - 11:54AM |
NO04.00012: Control of Shell Convergence and Deceleration Rayleigh–Taylor Growth in Dynamic Shell Ignition Designs Valeri N Goncharov, Yousef Lawrence, William T Trickey, Igor Igumenshchev, Ka Ming Woo, Nathaniel Shaffer, Timothy J Collins, Edward M Campbell The dynamic shell ignition target designs use a homogeneous-density fuel sphere (liquid of solid) inside a wetted-foam shell[1] to create a fuel shell dynamically by appropriately shaping the laser pulse. Compared to the nominal layered targets, the new designs offer greater flexibility in controlling density of the central, lower-density part of the target by changing the strength of the initial shocks launched into the fuel ball. This, in turn, affects the shell convergence ratio (CR) and Rayleigh–Taylor (RT) growth amplification during deceleration. This talk will review design options to control CR and RT growth in dynamic shell designs. [1] V. N. Goncharov et al., Phys. Rev. Lett. 125, 065001 (2020). |
Wednesday, November 10, 2021 11:54AM - 12:06PM |
NO04.00013: Deceleration-Phase Hydrodynamic Instability Growth in Dynamic Shell Inertial Confinement Fusion Designs Yousef Lawrence, Valeri N Goncharov, Ka Ming Woo, Igor V Igumenschev, William T Trickey A new dynamic shell concept1 has been recently proposed for inertial confinement fusion implosions that allows for control of the mass density in the central, lower-density region of the dynamically formed target. The central density affects the shell convergence ratio (CR), and consequently, perturbation amplification during the final stages of an implosion. Besides the CR, the Rayleigh–Taylor instability is another critical aspect of deceleration-phase instabilities. It develops on the inner surface of the shell during the deceleration phase where the growth rate is suppressed because of mass ablation driven by thermal conduction in the form of “fire polishing” and the “rocket effect.” With dynamic shell formation, shell convergence at the start of the deceleration phase and the mass ablation rate from the inner part of the shell can both be changed by varying the density of the central region via appropriate laser pulse shaping. Using DEC2D, a 2-D hydrodynamics code, we optimize robustness of a dynamic shell design against perturbation amplification during shell deceleration. |
Wednesday, November 10, 2021 12:06PM - 12:18PM |
NO04.00014: Stability of Dynamic Shell Targets Under 2D Low-Mode Perturbations William T Trickey, Mike Campbell, Timothy J Collins, Igor V Igumenschev, Nathaniel Shaffer, Valeri N Goncharov A novel inertial confinement fusion target design using liquid deuterium–tritium inside wetted-foam shells was recently proposed by V. N. Goncharov et al.[1] In these targets, a high-density outer shell is formed dynamically via the implosion, recoil, and subsequent deceleration of the capsule. Ignition is then triggered using standard implosion techniques. A high-density shell formed under such a dynamic process will be susceptible to fluid instabilities (both short and long wavelength), which can degrade implosion performance. We present a study that investigated low-mode nonuniformities in the shell using the 2-D radiation-hydrodynamics code DRACO. These simulations are used to evaluate the performance of different target designs and beam configurations. [1] V. N. Goncharov et al., Phys. Rev. Lett. 125, 065001 (2020). |
Wednesday, November 10, 2021 12:18PM - 12:30PM |
NO04.00015: Dynamic Shell Stability to Low-Mode Perturbations Igor Igumenshchev, Valeri N Goncharov, Edward M Campbell, Timothy J Collins, Michael J Rosenberg, Nathaniel Shaffer, Wolfgang R Theobald, William T Trickey, Rahul C Shah, Alex Shvydky, Arnaud Colaitis, Stefano Atzeni, Lorenso Savino A novel design concept in direct drive inertial confinement fusion utilizes a shell, which is developed from a spherical pellet of liquid DT and then imploded to produce conventional central hot-spot ignition [see Goncharov et al., Phys. Rev. Lett. 125, 065001 (2020)]. The stability of such a dynamic shell to short- and long-wavelength perturbations is of a great interest and importance since these perturbations can result in degradation of implosion performance. We investigate the evolution long-wavelength asymmetries (with spherical modes L < 50) in dynamic shell designs using the 3-D hydrodynamic code ASTER. Simulations help to identify the dependency of implosion performance on assumed mode perturbations. Results of these simulations will guide designs of proof-of-principal experiments on dynamic shell formation on OMEGA and NIF. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856 and ARPA-E BETHE Grant No. DE-FOA-0002212. |
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