Bulletin of the American Physical Society
60th Annual Meeting of the APS Division of Plasma Physics
Volume 63, Number 11
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session CO6: Hohlraum and X-ray Cavity Physics |
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Chair: Pierre Michel, Lawrence Livermore National Laboratory Room: OCC B115-116 |
Monday, November 5, 2018 2:00PM - 2:12PM |
CO6.00001: Understanding hohlraum drive in low-fill hohlraums on NIF Debra Callahan, Omar A Hurricane, Kevin L Baker, Daniel T Casey, Laurent Divol, Tilo Doeppner, Denise E Hinkel, Matthias Hohenberger, Laura Berzak Hopkins, Andrea Kritcher, Sebastien LePape, Stephan A MacLaren, Laurent Pierre Masse, Pierre A Michel, Arthur Pak, Louisa Pickworth, Joseph E Ralph, Harry Francis Robey, Mordecai D Rosen, James Ross, David Jerome Strozzi, Cliff A Thomas, Sunghwan Austin Yi, Alex Zylstra Over the past few years, we have been focusing our attention on low-fill, larger case-to-capsule ratio hohlraums in NIF experiments. These low-fill hohlraums have, in general, been proven to have low laser-plasma instability (LPI) losses, which simplifies our analysis and understanding. For DT implosions that are nearly 1-d, neutron yield should scale as ~ v 7.7 S4.5, where v is the implosion velocity and S is the dimension of the capsule. Last year, we put our attention on understanding the factors that control symmetry in these hohlraums in order to achieve a nearly 1-d implosion. Ultimately, we will need to understand the trade-off between the capsule size, hohlraum size, and the achievable implosion velocity, given the laser energy/power available on NIF. In order to better understand the trade-off between size and achievable velocity, we are comparing hohlraum drive across the suite of designs. These designs use different wall materials, case-to-capsule ratios, initial LEH sizes, beam pointing, ablator materials, laser energies and powers. This talk will describe the scaling of hohlraum drive with these parameters and how this scaling can be used to better optimize our designs. |
Monday, November 5, 2018 2:12PM - 2:24PM |
CO6.00002: Exploring 3D radiation asymmetries in inertial confinement fusion hohlraums with a dynamic view factor model Christopher V. Young, Nathan B. Meezan, Daniel T. Casey, Debra A. Callahan, Nobuhiko Izumi, John D. Moody, Joseph E. Ralph Inertial confinement fusion (ICF) experiments at the National Ignition Facility (NIF) seek to drive a spherical deuterium-tritium target to high temperatures and pressures. Fusion performance is significantly affected by the symmetry of the radiation environment produced inside the cylindrical hohlraum enclosure driven by 192 laser beams. Presently, full 3D ICF radiation-hydrodynamic calculations with sufficient resolution are very computationally expensive, limiting their utility. We combine a view factor model [1] with dynamic data from 1D and 2D radiation-hydrodynamic simulations [2] to rapidly assess the impact of drive asymmetry arising from a variety of sources across a range of NIF experiments. Special attention is given to measured laser power imbalance and the ablated hohlraum wall plasma (“gold bubble”) that interferes with inner laser beam propagation and symmetry control in the latter half of ICF experiments.
[1] J. J. MacFarlane, J. Quant. Spectr. Rad. Transfer 81, 287 (2003) [2] M. M. Marinak, et al., Phys. Plasmas 8, 2275 (2001) |
Monday, November 5, 2018 2:24PM - 2:36PM |
CO6.00003: Cross-Beam Energy Transfer (CBET) and Stimulated Brillouin Scattering (SBS) in NIF Hohlraums D. J. Strozzi, D. S. Bailey, R. L. Berger, P. Michel, T. Woods, O. Jones We explore the role of CBET and SBS in recent NIF experiments, which use relatively low hohlraum gas fill density ≤ 0.6 mg/cm3, and short laser pulses ≤ 10 ns. Even with no wavelength shift between “inner” (polar angle vs. hohlraum axis θ=21.2o–32.7o) and outer laser beams (θ=42.2o–52.4o), Lasnex simulations [1] with the self-consistent or “inline” CBET model [2] indicate transfer from inner to outer beams, induced by plasma flow. Especially for high-power shots, this CBET brings simulated implosion shape closer to measurements. These experiments also have moderate SBS from the outer beams, usually coming late in peak laser power. An inline SBS model has been implemented, and its effects will be presented. CBET may also be important in understanding the angular distribution of outer-beam SBS, which tends to be mostly from the highest θ beams (θ=52.4o). Namely, CBET from the θ=42.2o-47.7o beams to the θ=52.4o beams may be important. To assess this, including beam polarization, we use the “offline” CBET code Vampire [3]. 1. G Zimmerman and W Kruer, Comments PPCF 2, 85 (1975) 2. D Strozzi, D Bailey et al., PRL 118, 025002 (2017) 3. A Colaitis, T Chapman et al., PoP 25, 033114 (2018) |
Monday, November 5, 2018 2:36PM - 2:48PM |
CO6.00004: Data versus Simulations for Gated LEH Images on NIF ICF Campaigns Hui Chen, Oggie Jones, Denise E Hinkel, Benjamin Bachmann, Tilo Doeppner, Annie Kritcher, Leonard C Jarrott, Nathan E. Palmer, Louisa Pickworth, Joseph E Ralph, Marilyn Beth Schneider, Marc Vandenboomgaerde Laser entrance hole (LEH) size in a hohlraum has been shown to be important in interpreting the radiation drive [1] in indirect drive ICF experiments. However the time-dependent LEH size has not been routinely measured until the deployment of the G-LEH diagnostic [2] at the National Ignition Facility (NIF), which can provide 4-16 images from a single shot. We present a systematic study of measured data vs. simulations for the CH campaigns on NIF for gas fill densities of 0.3 to 0.6 mg/cc. We compare the measured LEH size vs. time to simulations using several different models for the atomic physics and electron heat transport. The comparison with the growth of the laser-heated gold plasma bubble, the change in brightness of inner beam spots due to time-varying cross beam energy transfer, and plasma instability growth near the hohlraum wall will also be discussed. [1]. S MacLaren, M. Schneider, K. Widmann, et al., PRL 112 105003 (2014) [2]. H. Chen, N. Palmer, P. Bell, et al., RSI, in press (2018) |
Monday, November 5, 2018 2:48PM - 3:00PM |
CO6.00005: 3D wall motion in hohlraum Stephane Laffite, Paul Edouard Masson Laborde, Scott Wilks, Chikang Li, Raphael Riquier, Gilles Kluth, Olivier Morice, Veronique Tassin Inside a hohlraum, the plasma blow-off of the wall heated by laser beams is a serious concern as this determines how the laser beams propagate through the hohlraum and where they subsequently deposit their energy in the hohlraum. In turn, this determines the X-ray drive that an ICF capsule sees, and therefore impacts the symmetry of the implosion. It is clear that there is here a need to benchmark wall motion in simulations with experimental measurements. Recently, a series of experiments have been carried out on the Omega laser facility to examine such an issue. In an open cylinder, the motion of the laser-driven plasma bubbles was observed with proton radiography. A nearly uniform irradiation of the 59° laser cone with 10 laser spots was compared to the classic irradiation with 5 laser spots for which more 3D effects are expected We present here 2D and 3D calculations of these experiments. The impact of the 3D is demonstrated: the 3D-calculated bubbles move faster than the 2D-calculated ones. Radial velocities are supersonic (Mach=3-5) and exceed 1000 km/s. However, the 3D calculations still underestimate the experimentally measured bubble motion. |
Monday, November 5, 2018 3:00PM - 3:12PM |
CO6.00006: Effects of plasma interpenetration on hohlraum stagnation Chikang Li, Scott Wilks, Paul-Edouard Masson-Laborde, Stephane Laffite, Peter Andrew Amendt, Riccardo Betti, Archie Bott, Edward Michael Campbell, Johan Frenje, Richard David Petrasso, Thomas C Sangster, Fredrick Seguin, Veronique Tassin Understanding plasma stagnation in laser-driven hohlraums is important for optimizing inertial confinement fusion experiments. It has been realized that single-species-averaged hydrodynamic codes are incapable of modelling this phenomenon, as they overlook the ion kinetic process and multi-fluid effects, leading to discrepancies between simulations and experimental results. A number of mechanisms that play important roles in these non-hydrodynamic processes but are missing in hydrodynamic simulations have been identified, including ion interpenetration and diffusion. To explore these important phenomena, observations made with various diagnostic techniques at Omega such as proton radiography and x-ray imaging are compared with modified three-dimensional hydrodynamic simulations, providing insight into the effects of plasma interpenetration on hohlraum stagnation and a more complete physical picture of hohlraum dynamics. The work described herein was performed in part at the LLE National Laser User’s Facility (NLUF), and was supported in part by US DOE, LLNL and LLE. |
Monday, November 5, 2018 3:12PM - 3:24PM |
CO6.00007: Hybrid C Campaign: Optimizing Implosions With CH Ablators at the National Ignition Facility Denise E Hinkel, Tilo Doeppner, Laurent Pierre Masse, Joseph E Ralph, Louisa Pickworth, Benjamin Bachmann, Laurent Divol, Andrea Kritcher, Marius Millot, Pierre Michel, Peter M Celliers, Jaebum Park, Hui Chen, Felicie Albert, Matthias Hohenberger, Debra Ann Callahan, Omar A Hurricane Recent work on ICF implosions using CH ablators at the National Ignition Facility (NIF) includes key optimizations relevant to not just CH implosions, but also to implosions with other ablators, such as HDC and Be. Utilizing low levels of wavelength separation between the inner and outer beams, i.e., cross-beam energy transfer at low values of Δλ ~ 1 Å, the Hybrid C campaign has demonstrated a change in P2 symmetry from oblate to prolate of over 20 µm, corresponding to an increase in inner beam intensity by a factor of 1.3. Energy coupling remains high (> 97%), with low levels of backscatter, SBS fluence, and hot electrons. The capsule is further optimized in two ways. First, capsule dopant levels (Si) will increase, to further shield against M-band at high power (see talk by T. Döppner, LLNL). Also, to reduce oxygen uptake (S. Ali, PoP, May, 2018) the capsule is flash coated with aluminum. Results from the Hybrid C campaign will be presented along with future plans to explore generic optimization strategies. A design for a scale-up in capsule size by a factor of 1.1 will also be discussed. |
Monday, November 5, 2018 3:24PM - 3:36PM |
CO6.00008: Hohlraum models applied to suite of HDC capsule experiments Ogden S Jones, David J Strozzi, Douglas T Woods, Laurence J Suter, Mordy D Rosen, William A Farmer, Kevin L Baker, Daniel T Casey, Nobuhiko Izumi, Sebastien Le Pape For several years we have been working toward hohlraum models that are more predictive and require fewer ad hoc adjustments to match experimental observables [1]. We generally find that the results are most sensitive to the model choices for non-LTE atomic physics, electron thermal transport, cross beam energy transport, and the self-consistent treatment of any backscattered light. In this work, we apply a model with very restricted electron thermal transport (flux-limited transport in wall material with FL = 0.02) to a broad set of experiments using HDC ablator capsules. These experiments include shock timing experiments, symmetry capsules, and DT layered implosions. The primary observables we compare to are the capsule bang time, capsule yield, radiation drive and spectrum (from Dante), and the drive symmetry (as inferred from the inflight shell shape and the final self-emission x-ray shape). For a limited number of experiments, we also compare the plasma temperature and the relative brightness of the inner beam spots (via thin wall hohlraums). [1] O.S. Jones, et al., Phys. Plasmas 24, 056312 (2017). |
Monday, November 5, 2018 3:36PM - 3:48PM |
CO6.00009: Advanced Hohlraum Designs on the NIF for High Coupling Efficiency Peter Andrew Amendt, Darwin Ho, William Kruer, John D Lindl, Nathan Meezan The coupling of 3ω laser light to the capsule in hohlraum designs for the NIF is typically <10%, resulting in an absorbed energy Ecap of 200 kJ or less in cylindrical hohlraums driven at 2 MJ. Ignition thresholds or performance margins scale linearly with Ecap, so that a significant improvement in these metrics may require considering non-standard hohlraum shapes, e.g., rugbys [1] or a “frustraum”. The frustraum is formed by joining a pair of frusta (or truncated right-circular cones) above the capsule. The low surface area of the frustraum allows for a tradeoff in increased volume above the capsule to facilitate inner beam propagation and accommodate a far larger capsule than the nominal ~1 mm radius size. Integrated hohlraum simulations suggest Ecap~ 500 kJ at only 1.8 MJ laser energy and 460 TW peak power for HDC capsules of radius 1.5 mm may be achievable under conditions of adequate drive symmetry and low backscatter risk. The greatest modeling uncertainty in these candidate hohlraum geometries is the relative balance of specular and diffuse reflection of the outer cones from the oblique hohlraum wall and its high impact on drive symmetry. [1] P. Amendt et al., PoP 21, 112703 (2014) |
Monday, November 5, 2018 3:48PM - 4:00PM |
CO6.00010: Initial Experimental Results of indirectly-driven ICF implosions in the I-Raum James Steven Ross, Harry Francis Robey, Hui Chen, Nobuhiko Izumi, Steve Johnson, Tammy Yee Wing Ma, Nathan Meezan, Marius Adrien Millot, John D Moody, Alastair Moore, Arthur Pak, Brandon Nathan Woodworth A new advanced hohlraum concept, the I-Raum [1], has been experimentally tested on the NIF. Initial results show enhanced inner beam propagation compared to a typical cylindrical hohlraum. This enhanced propagation is achieved by recessing the location where the outer beam cones hit the hohlraum wall. This target modification delays when the Au wall material, driven by the outer beam cones, obstructs the inner beam and reduces propagation. X-ray images of the Au wall motion and measurements of the shape of the imploded capsule show improvements over the standard cylinder geometry. Detailed hohlraum simulations are presented in a companion talk by Robey et al. [1] H. F. Robey et al., “The I-Raum: A new shaped hohlraum for improved inner beam propagation in indirectly-driven ICF implosions on the National Ignition Facility”, Phys Plasmas 25, 012711 (2018). |
Monday, November 5, 2018 4:00PM - 4:12PM |
CO6.00011: Validated simulations of indirectly-driven ICF implosions in the I-Raum H. F. Robey, J. S. Ross, L. Berzak Hopkins, D. A. Callahan, T. Ma, B. J. Macgowan, N. B. Meezan, M. Millot, J. L. Milovich, A. Nikroo, A. Pak, C. R. Weber A new shaped hohlraum design has recently been experimentally tested on NIF, and the results are presented in a companion talk by Ross et al. This new hohlraum, called the I-Raum [1], was specifically designed to improve late-time inner-beam propagation to the hohlraum equator by adding a localized pocket of increased wall radius at the location where the outer beam cones hit the hohlraum wall. This simple modification displaces the growing bubble of Au wall material to larger radius at all times throughout the implosion, thereby improving inner beam propagation and the resulting implosion symmetry. Integrated hohlraum simulations using HYDRA are benchmarked to the recent experimental results, providing a validated methodology for more accurate prediction of future implosions using this new hohlraum. [1] H. F. Robey et al., “The I-Raum: A new shaped hohlraum for improved inner beam propagation in indirectly-driven ICF implosions on the National Ignition Facility”, Phys Plasmas 25, 012711 (2018). |
Monday, November 5, 2018 4:12PM - 4:24PM |
CO6.00012: Design of a foam-lined hohlraum for ICF implosions on NIF Nathan B. Meezan, Alastair Moore, Laurent Divol, John D Moody, Warren Wen-Man Hsing, Brian Thomas, John Morton, James Fairley, Warren J. Garbett We describe a foam-lined hohlraum design for driving ignition implosions on the NIF, designed using the radiation hydrodynamics code HYDRA. In a typical hohlraum with a low density (ρ < 0.6 mg/cm3) helium fill, the plasma "bubble" formed where the outer laser beams strike the wall moves into the path of the inner beams and absorbs them. In this design, inner beam propagation is improved by lining the hohlraum wall with tantalum oxide (Ta2O5) foam of density 20 mg/cm3, initially below the critical density for 3ω light. The laser compresses the foam to a critical surface that moves radially outward until colliding with the incoming x-ray-ablated wall. The ablated plasma from the foam is lower density than plasma ablated from a solid gold wall, and inner beam absorption is reduced. The optimum foam thickness depends on the hohlraum radius, since the NIF beam angles and laser spot sizes are fixed: larger hohlraums with thicker foams improve laser propagation for a longer time. A 6.72 mm diameter hohlraum with a 400 μm thick liner provides increased waist-hot drive compared to a solid gold hohlraum, enabling symmetric implosions with a larger capsule. |
Monday, November 5, 2018 4:24PM - 4:36PM |
CO6.00013: Optimizing foam-liner performance to improve laser beam propagation in hohlraums Alastair Moore, Nathan Meezan, Laurent Divol, Ted Roswitha Baumann, Suhas Bhandarkar, Cliff A Thomas, Jarrod Williams, Warren Wen-Man Hsing, A. Nikroo, John D Moody Hohlraum wall expansion in low gas-fill hohlraums can reduce or prevent propagation of other laser beams into the hohlraum. To avoid such filling ignition hohlraums have typically been filled with a high density gas or irradiated with a short (< 10 ns) laser pulse. Foam-liners are predicted to mitigate wall motion in a low gas-fill hohlraum with little LPI, and so would enable the hohlraum to symmetrically drive a larger capsule over a longer duration providing a pathway to higher yield. |
Monday, November 5, 2018 4:36PM - 4:48PM |
CO6.00014: Re-evaluation of the Pulsed Power Indirect Drive Approach to Inertial Confinement Fusion R. E. Olson, R. R. Peterson, S. H. Batha, A. B. Zylstra, P. A. Bradley, R. J. Leeper Recently, the results of ICF experiments at the NIF have fostered discussions concerning a possible next generation ICF facility that could enable much higher levels of thermonuclear burn in the laboratory. Key questions include the type of driver that should be proposed and the power and energy parameters that would be required. In the 1990’s, LANL and SNL collaborated on a series of pulsed power experiments that demonstrated X ray driven hohlraums1,2. The X ray driven hohlraum experiments were motivated by an ICF concept that would use a 2-step radiation temperature to implode a high gain indirect-drive ICF capsule3,4. At that time, scaling studies indicated that the required driver size would be unfeasible with the existing pulsed power technology. However, with a new generation of efficient, reduced cost pulsed power technology, it is now feasible to envision a petawatt-class pulsed power facility5. Thus, it is timely to re-consider the pulsed power indirect drive approach to ICF. 1R. E. Olson et al., Phys. Plasmas 4, 1818 (1997). 2T. W. L. Sanford et al., Phys. Rev. Lett. 83, 5511 (1999). 3R. E. Olson et al., Bull. Am. Phys. Soc. 43, 1882 (1998) 4R. E. Olson et al., Fusion Technology 35, 260 (1999). 5W. A. Stygar et al., Phys. Rev. STAB 18, 110401 (2015). |
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