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 UO04: ICF: Compression and Burn IIIOn Demand
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Chair: Paul Bradley, Los Alamos Natl Lab Room: Rooms 304-305 |
Thursday, November 11, 2021 2:00PM - 2:12PM |
UO04.00001: Extrapolation of Experiments from OMEGA to the National Ignition Facility Beyond Hydroscaling Radha Bahukutumbi, Christian Stoeckl, Wolfgang R Theobald, Michael J Rosenberg, Riccardo Betti, Edward M Campbell, Stephen Craxton, Dana H Edgell, Valeri N Goncharov, Margaret Porcelli, Sean P Regan, Alexander Shvydky, Andrey Solodov Extrapolating experimental performance from OMEGA to the National Ignition Facility (NIF) is critical to make the case for future high-performance direct-drive NIF implosions. Typically, hydrodynamic scaling is invoked to design NIF experiments or predict NIF target performance. Several additional factors are important for increasing the accuracy of this extrapolation, including the physics of laser–plasma interactions and the effect of the different beam arrangement on OMEGA versus the NIF. Simulations that study this extrapolation beyond hydrodynamic scaling, using state-of-the-art models of laser drive (cross-beam energy transfer and nonlocal heat conduction) and beam geometry are presented. Currently, experiments involving radiography of ablatively driven shells and of shocks in solid spheres are used to quantify laser drive in hydrodynamically scaled experiments on OMEGA and the NIF. This talk will present simulations comparing designs and experimental results across the two facilities in the context of these two experiments. |
Thursday, November 11, 2021 2:12PM - 2:24PM |
UO04.00002: Energy-Coupling Experiments Using Solid Spheres in the Polar-Direct-Drive Configuration on OMEGA Christian Stoeckl, Wolfgang R Theobald, P. B Radha, T. Filkins, Sean P Regan Energy-coupling experiments in inertial confinement fusion experiments use the measurement of a trajectory in the implosion to infer the efficiency of the drive from the ablation of the outer layers of the target. Tracking the shock trajectory in solid spheres offers the advantage of quantifying energy coupling without the potentially confusing effects of hydro-instabilities that occur in thin-shell implosions. Solid plastic spheres of ~340 μm radius were irradiated with 40 OMEGA beams in the polar-direct-drive geometry with ~14 kJ of energy at an intensity of ~8 × 1014 W/cm2 to launch a spherically converging shock wave. A Fe foil target was driven by 11 beams, with ~4.5 kJ to backlight the shock onto an x-ray framing camera with 40-ps exposure time. The measured shock trajectories will be compared with 2-D radiation-hydrodynamic simulations. Similar experiments that were hydrodynamically scaled up have been performed at the National Ignition Facility to test the scaling arguments going from OMEGA to NIF energies. |
Thursday, November 11, 2021 2:24PM - 2:36PM |
UO04.00003: Laser-Direct-Drive Energy Coupling at 4×1014 W/cm2 to 1.2×1015 W/cm2 from Spherical Solid Plastic Implosions at the National Ignition Facility Wolfgang R Theobald, Michael J Rosenberg, P. B Radha, Sean P Regan, Christian Stoeckl, Riccardo Betti, Kenneth Anderson, John A Marozas, Valeri N Goncharov, Edward M Campbell, Claudia M Shuldberg, Rain W Luo, Wendi Sweet, David N Kaczala, Benjamin Bachmann, Tilo Doeppner, Matthias Hohenberger, Robbie H Scott, Arnaud Colaitis Laser-direct-drive energy-coupling experiments are being conducted at the National Ignition Facility (NIF) using a spherical, solid plastic target with a diameter of 2.1 mm. The targets are irradiated with 184 NIF laser beams in a polar-direct-drive (PDD) geometry. A series of shots was performed by varying the peak intensity in the range of 4×1014 W/cm2 to 1.2×1015 W/cm2 with a 7-ns-long shaped pulse. The trajectory of the spherically converging shock wave was recorded using ~100-ps gated, x-ray backlighting at 8.4 keV. In addition, the arrival time of the shock in the center of the sphere was measured from the x-ray flash created by the shock collapse with gated x-ray imagers. Solid spheres offer the advantage for quantifying energy coupling without the challenges from hydrodynamic instabilities of imploding shells. Good agreement is obtained of the measured shock trajectories with the trajectories from 2-D radiation-hydrodynamics simulations from the DRACO code using CBET and nonlocal heat-transport models. Similar experiments have been performed on OMEGA (configured for PDD) with an energy of 13 kJ to test the scaling arguments of PDD implosions from OMEGA to NIF energies. |
Thursday, November 11, 2021 2:36PM - 2:48PM |
UO04.00004: Mitigation and scaling of hot electron preheat in direct-drive ICF implosions on the NIF and OMEGA Michael J Rosenberg, Andrey Solodov, Alison R Christopherson, Riccardo S Betti, P. B Radha, Christian Stoeckl, Matthias Hohenberger, Benjamin Bachmann, Pierre A Michel, Gareth N Hall, Chad Forrest, Vladimir Y Glebov, Frederic J Marshall, Christine M Krauland, Timothy J Collins, Valeri N Goncharov, Sean P Regan Hot electron preheat and the resulting degradation of compression is a potential concern for direct-drive ICF ignition designs and must be studied at the appropriate scale and plasma conditions. Polar-direct-drive implosions at the National Ignition Facility (NIF) and OMEGA studied the scaling of preheat with capsule size and laser intensity and demonstrated partial mitigation of hot electron preheat. Hard x-ray emission from buried Ge-doped layers was measured on NIF to infer ~0.2% of laser energy deposited as hot-electron preheat in the inner ~80% of the unablated shell at an intensity of 1015 W/cm2, varying by +50% for +25% excursions in intensity. This is close to the tolerable level of preheat in direct-drive ignition designs. A thin buried Si layer reduces preheat by a factor of ~2 and effectively suppresses preheat at intensities of 8x1014 W/cm2. Hydrodynamically equivalent implosions on OMEGA at 3.4 times smaller scale and 40 times less laser energy show similar levels of preheat. This result supports the hydrodynamic scaling of ambient target implosions with respect to preheat. Extrapolation of preheat in ignition-scale cryogenic implosions will be discussed and shown to be near acceptable levels. |
Thursday, November 11, 2021 2:48PM - 3:00PM |
UO04.00005: Hot-Electron Preheat and Mitigation in Polar-Direct-Drive Experiments at the National Ignition Facility Andrey Solodov, Michael J Rosenberg, Manuel Stoeckl, Alison R Christopherson, Riccardo S Betti, Radha P Bahukutumbi, Christian Stoeckl, Reuben Epstein, Russell K Follett, Wolf Seka, Sean P Regan, John P Palastro, Dustin H Froula, Valeri N Goncharov, Matthias Hohenberger, Benjamin Bachmann, Pierre A Michel, Jason F Myatt Superthermal electrons generated by laser–plasma instabilities can degrade the performance of direct-drive inertial confinement fusion implosions by preheating the target. Polar-direct-drive experiments were performed at the National Ignition Facility (NIF) to assess the extent of hot-electron preheat, develop mitigation strategies, and extrapolate preheat levels to ignition designs. In these experiments, hot-electron temperature, fraction, divergence, and radial energy deposition profile in the unablated capsule were inferred by employing mass-equivalent plastic targets with Ge-doped layers and comparing the measured hard x-ray spectra to simulations. Silicon layers buried in the ablator were used to mitigate stimulated Raman scattering and reduce preheat. Experiments determine the parameter regime (e.g. intensity) that produces acceptably low preheat. Extrapolating these results to ignition-scale cryogenic DT implosions on the NIF shows that preheat level should be acceptable at on-target intensity close to 1015 W/cm2. |
Thursday, November 11, 2021 3:00PM - 3:12PM |
UO04.00006: Observation of Kinetic Structures in Simulations of NIF Cryo Implosions Benjamin Reichelt, Chikang Li, Maria Gatu Johnson, William T Taitano, Steven Anderson, Andrei N Simakov, Brett Keenan, Luis Chacon, Brian M Haines, Joshua P Sauppe, Hans Rinderknecht Over the past few decades, most simulations of Inertial Confinement Fusion (ICF) implosions have utilized fluid models due to computational constraints and limitations. However, advances in computational technology and algorithms have begun to enable the use of more complex models. In this work, we present a common modeling framework between the LANL Vlasov-Fokker Planck code iFP and LANL's rad-hydro code xRAGE, and compare results of the two codes. It is shown that during a typical cryo implosion, high Knudsen numbers are expected along the shock front, and kinetic modeling confirms that non-Maxwellian, bimodal features arise in the ion-distribution function. A discussion of the possible implications of this effect is presented, the most immediate of which is increased mix of ice into the hot spot. Additionally, preliminary results from recent experiments at OMEGA are discussed, which extend separated reactant experiments to a more shock driven regime in an attempt to quantify diffusive and kinetic effects. |
Thursday, November 11, 2021 3:12PM - 3:24PM |
UO04.00007: Progress on the magnetized ignition experimental platform for the National Ignition Facility John D Moody, Bradley B Pollock, Hong W Sio, David J Strozzi, Darwin Ho, Chris Walsh, Sergei Kucheyev, Bernard Kozioziemski, Evan Carroll, Johnathan Fry, Vincent Tang, Suhas Bhandarkar, Jim Sater, Grant Logan, Jeff Bude, Mark C Herrmann, Ken Skulina, Scott Winters, Edward P Hartouni, Jeremy P Chittenden, Sam O'Neill, Brian D Appelbe, Aidan Boxall, Aidan C Crilly, Jonathan R Davies, Jonathan L Peebles, Shinsuke Fujioka Magnetizing the DT fuel in an inertial confinement fusion (ICF) indirect drive (ID) target is expected to increase the ion temperature by > 0.5 keV and the neutron yield by > 50% relative to unmagnetized fuel due to reduced electron thermal conduction and alpha particle trapping. A magnetized ID project at NIF is underway and has started applying a ~ 25 T seed field to D2 gas-filled capsules in a Au:Ta high electrical resistivity hohlraum to quantify the B-field effects in these room temperature implosions and compare with modeling predictions. Ice-layered DT implosions will follow and require a new pulser design and a modified DT ice layer growth strategy. We will describe the status of the experiments and the project plan. |
Thursday, November 11, 2021 3:24PM - 3:36PM |
UO04.00008: First Magnetized Hohlraum-Driven Implosions on the NIF David J Strozzi, John D Moody, Bradley B Pollock, Hong W Sio, George B Zimmerman, Darwin Ho, Sergei O Kucheyev, Christopher A Walsh, Burl G Logan Magnetizing an ICF hotspot to reduce electron-thermal and fusion-alpha losses is an old idea to improve performance and reach ignition. A campaign is underway on NIF to study how an imposed axial magnetic field affects hohlraum-driven "symcap" (gas-filled) implosions. The goal is to demonstrate field compression in the implosion, and quantify its effect on the temperature and density of the hotspot, as measured by nuclear and x-ray output. Facility limitations require these shots to be room-temperature (not cryogenic) and use <~ 1 MJ of laser energy. Four shots have taken place as of June 2021. The two shots with no imposed field unfortunately had no capsule gas fill due to fielding issues, and thus no data on hotspot conditions. The other two shots had an imposed 26 T field at capsule center. They varied the hotspot self-emission shape from extremely prolate ("sausaged") to roughly round, by varying the ratio of powers on the NIF inner and outer beams. This standard method for tuning implosion shape on unmagnetized targets also works in magnetized ones. We hope to have an unmagnetized comparison shot before the APS meeting. I will review the results of these experiments, and radiation-magneto-hydrodynamic modeling of them with the LASNEX code. |
Thursday, November 11, 2021 3:36PM - 3:48PM |
UO04.00009: Secondary DT neutron spectra in magnetized indirect-drive implosions Hong W Sio, John D Moody, Bradley B Pollock, David J Strozzi, Darwin Ho, Edward P Hartouni, Christopher A Walsh, Burl G Logan, Sergei Kucheyev, Bernard Kozioziemski, Jim Sater, Johnathan Fry, Ken Skulina, Evan Carroll, Vincent Tang, Scott Winters, Jeremy P Chittenden, Aidan C Crilly, Brian D Appelbe Diagnosing plasma magnetization in inertial-confinement-fusion (ICF) implosions is important for understanding how magnetic fields affect implosion dynamics. Secondary deuterium-tritium (DT) reactions provide two diagnostic signatures to infer neutron-averaged magnetization. Magnetically confining fusion tritons from deuterium-deuterium (DD) reactions in the hot spot increases their path lengths and energy loss, leading to an increase in the secondary DT reaction yield. In addition, the distribution of magnetically-confined DD-triton is anisotropic, and this drives anisotropy in the secondary DT-neutron spectra along different lines of sight. Neutron spectra from magnetized and unmagnetized indirect-drive implosions at the National Ignition Facility (NIF) will be discussed. |
Thursday, November 11, 2021 3:48PM - 4:00PM |
UO04.00010: Magnetized ICF: role of e-thermal conductivity on imploding shock and high-yield capsule designs George Zimmerman, Darwin Ho, Alexander L Velikovich, Russell M Kulsrud, John D Moody, Judy Harte, Andrea L Kritcher Simulations with a 40-50 T seed B-field is observed to make the requirements for ignition less stringent.1 Imploding shocks propagating in uniform embedded B field have elliptical shapes.2 This is because after the imploding shock decouples from the shell, the fast magnetosonic shock speed along the perpendicular direction is faster than that along the parallel direction. However, in the strong shock limit, which is the case for high-adiabat implosions with high gas fill, shock speed is almost independent of B field without e-thermal conduction. The presence of e-thermal conduction slows the shock speed along the parallel direction and induces the ellipticity in the imploding shock. We will demonstrate this by numerical simulations and physical arguments. The ice-layered HDC shot N210207 had reached record neutron yield close to 6e16, in agreement with simulations. Magnetizing this implosion can boost the simulated yield by 2x to above 1e17. |
Thursday, November 11, 2021 4:00PM - 4:12PM |
UO04.00011: Effect of strong magnetization on heat flow and shape of inertial fusion implosions Arijit Bose, Jonathan L Peebles, Chris Walsh, Johan A Frenje, Neel Kabadi, Patrick J Adrian, Graeme Sutcliffe, Maria Gatu Johnson, Riccardo Betti, Jonathan R Davies, Vladimir Y Glebov, Suxing X Hu, Frederic J Marshall, Sean P Regan, Christian Stoeckl, Mike Campbell, Hong W Sio, John D Moody, Aidan C Crilly, Brian Appelbe, Jeremy P Chittenden, Stefano Atzeni, Chikang Li, Fredrick H Seguin, Richard Petrasso This talk reports on the observation on how a strong 500 kG applied B-field increases the mode-2 asymmetry in inertial confinement fusion implosions. We used directly-driven implosions with a drive anisotropy and an externally imposed B-field. The magnetized implosions exhibit a significantly increased mode-2 compared to reference experiments, with identical drive but with no applied field. The X-ray self emission images show a 2.5x higher P2 (Legendre polynomial) amplitude with a reduced compression in the direction transverse to the B-field. Strongly magnetized electrons (ωe τe >>1) restrict the transverse heat flow, causing the mode-2 anisotropy to increase with magnetization. |
Thursday, November 11, 2021 4:12PM - 4:24PM |
UO04.00012: Modelling burn physics in a magnetized ICF plasma Sam T O'Neill, Brian Appelbe, Jeremy P Chittenden The pre-magnetization of inertial confinement fusion capsules is a promising avenue for reaching hotspot ignition, as the magnetic field reduces electron thermal conduction losses during hotspot formation. However, in order to reach high yields efficient burn-up of the cold fuel layer is vital. Suppression of heat flows out of the hotspot due to magnetization can restrict the propagation of burn and has been observed to reduce yields in previous studies [1]. This work investigates the potential suppression of burn in a magnetized plasma utilizing the radiation-MHD code ‘Chimera’. This code includes extended-MHD effects, such as the Nernst term, and a Monte-Carlo model for magnetized alpha particle transport and heating. We observe 3 distinct regimes of magnetized burn in 1D as initial magnetization is increased: thermal conduction driven; alpha driven; and suppressed burn. Field transport due to extended-MHD is also observed to be important, enhancing magnetization near the burn front. In higher dimensions, burn front instabilities have the potential to degrade burn even more severely. Magneto-thermal type instabilities (previously observed in laser-heated plasmas [2]) are of particular interest in this problem. |
Thursday, November 11, 2021 4:24PM - 4:36PM |
UO04.00013: A Model for Magnetic Flux Generation in ICF Hot-Spots Chris Walsh, Daniel S Clark, Jonathan R Davies, James D Sadler Self-generated magnetic fields are expected to be generated in excess of 10,000T in ICF hot-spots [1]. A model for magnetic flux generation is presented, showing that more flux is expected around large amplitude and high mode perturbations. The model compares favorably with Gorgon extended-MHD simulations, allowing for greater understanding of which target designs will be susceptible to MHD effects. For example, the model can be used to ascertain when most magnetic flux is expected to be generated. If generation is weighted more towards early times, then more high-mode magnetic field loops will be generated; even if the high-mode perturbations are ablatively stabilized at later times, the high mode magnetic field will still be present. |
Thursday, November 11, 2021 4:36PM - 4:48PM |
UO04.00014: Design of Inverted Corona neutron sources for NIF Nathan Meezan, Matthias Hohenberger, Andy J Mackinnon, Jacob A Pearcy, William Riedel, Mark A Cappelli, Siegfried Glenzer We describe the design of gas-filled Inverted Corona neutron sources for the National Ignition Facility (NIF). In an Inverted Corona target, the inside of a spherical shell is illuminated by lasers. The ablating plasma from the inner liner launches a converging shock wave into a fusion fuel gas, generating neutrons in a similar manner to an exploding pusher. Targets were initially designed in 2D using the ICF code Hydra. Later 1D simulations with the hybrid Particle In Cell (PIC) code Chicago predicted non-Maxwellian ion distributions and species interpenetration in the plasma . Chicago simulations matched data trends in Omega experiments that Hydra could not reproduce. Recently, the targets have been simulated in 1D using the ICF code Ares. With its plasma diffusion model, Ares can reproduce some of the species mixing observed in Chicago. We are currently developing a 2D Ares model for making practical design choices for future NIF experiments, such as finding the optimum layer thickness, window thickness, and gas-fill density. The experimental design must also consider the debris wind, which can restrict the stand-off distance of objects under test. |
Thursday, November 11, 2021 4:48PM - 5:00PM |
UO04.00015: ARES Simulations of Inverted Corona Experiments at the OMEGA Laser Facility Jacob A Pearcy, Nathan Meezan, Matthias Hohenberger, William Riedel, Neel Kabadi, Patrick J Adrian, Justin H Kunimune, Tim M Johnson Inverted corona experiments, wherein lasers are focused onto the inside walls of a capsule lined with deuterated plastic (CD), are a promising candidate for use as neutron sources in laser experiments. While such targets are expected to achieve significant yields at NIF energy scales, the effects of specific target design elements (such as liner thickness) on yield are not yet well-understood and -characterized. 2-D hydrodynamic simulations of inverted corona experiments indicate that the ion-ion mean free path is very long, necessitating more robust computational methods. However, more physically complete PIC simulations are computationally expensive; this raises the question of whether a hydrodynamic code with molecular diffusion and mix models could serve as a useful middle ground. ARES is a massively parallel, multi-dimensional, multi-physics code developed and maintained by Lawrence Livermore National Laboratory (LLNL). In this study, we used ARES’ well-established and benchmarked molecular diffusion and dynamic mixing packages to investigate the effect of diffusion and mix on neutron yield, and to compare simulated results with an experiment performed at OMEGA exploring the effect of CD liner thickness on neutron yield in DD and 3He filled inverted corona targets. We found that while ARES overpredicts the neutron yields by roughly a factor of 10, its predictions of yield scaling with liner thickness closely match those experimentally observed. |
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