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 PO6: Compression and Burn III |
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Chair: Hans Rinderknecht, University of Rochester Room: OCC B115-116 |
Wednesday, November 7, 2018 2:00PM - 2:12PM |
PO6.00001: Synthetic Diagnostic Signatures of Burn Truncation within Simulations of ICF Implosions Aidan Crilly, Brian Appelbe, Kristopher McGlinchey, Christopher Alexander Walsh, Jon Tong, Griffin Farrow, Jeremy Chittenden The 3D radiation hydrodynamics code Chimera is used to run simulations aiming to investigate possible yield degradation mechanisms in ICF experiments. By modelling the observable signals measured in experiments, synthetic diagnostics can probe simulations in an analogous way to their experimental equivalents. This allows current and novel analysis techniques to be investigated with full knowledge of the capsule properties for comparison. Drive asymmetries and capsule defects cause current ICF experiments to exhibit yields below those expected from an idealised symmetric implosion. By considering these perturbations in isolation and in combination, the effect on nuclear observations can be simulated. These observations include neutron imaging and spectroscopy as well as fusion and Carbon γ ray time histories and imaging. For drive asymmetries, correlations between the burn width, time between bang time and stagnation and the mechanical work timescale are found. For capsule defects these correlations are broken. Signatures of burn truncation can also be observed in the residual fluid velocity of both the hotspot and the dense DT shell. Spectral measurements of the DT primary and backscattered neutrons can be used to infer both hotspot and shell fluid velocities around bang time. |
Wednesday, November 7, 2018 2:12PM - 2:24PM |
PO6.00002: Nuclear and x-ray burn widths in recent high-yield implosions on the National Ignition Facility Gerald Williams, Tammy Yee Wing Ma, Pravesh K Patel, Shahab Khan, Michael K Kruse, Hans Herrmann, Kevin Meaney, Hermann Geppert-Kleinrath, Yongho Kim, Daniel T Casey, Cliff A Thomas, Kevin L Baker, Brian K. Spears, Matthias Hohenberger, Christopher Weber, Ryan Nora, Sebastien Le Pape, Laura Berzak Hopkins, Laurent Divol, Arthur Pak, Eduard L. Dewald, Laura Robin Benedetti, Daniel Clark Cryogenic implosions on the National Ignition Facility (NIF) are primarily used to produce high neutron yields in the effort to achieve the goal of ignition. Two campaigns using high-density carbon ablator designs are leading this effort using low- and high-adiabat implosions that have achieved yields of more than 50 kJ, the highest to date on NIF. The time-history of the DT neutrons and x-rays emitted during the implosion with ~10-20 ps temporal resolution in the form of MeV photons (gammas) released from fusion events and 10s of keV x-ray photons from the hot dense core. These burn durations are typically longer than predicted by simulations and could be a signature of degradation mechanisms like preheat, fuel-ablator mix, or 3D effects. We also observe a second x-ray peak post-stagnation at lower photon energies, which we attribute to the outgoing shock propagating through the ablator. We discuss how this signature can provide insight into the conditions of the shell at late time. |
Wednesday, November 7, 2018 2:24PM - 2:36PM |
PO6.00003: Burn-Rate Measurements from the High-Performance Cryogenic Implosion Campaign on OMEGA J. P. Knauer, C. Stoekl, R. Betti, V. Gopalaswamy, K. S. Anderson, D. Cao, M. J. Bonino, E. M. Campbell, T. J.B. Collins, C. J. Forrest, V. Yu. Glebov, V. N. Goncharov, D. R. Harding, J. A. Marozas, F. J. Marshall, P. W. McKenty, P.B Radha, S. P. Regan, T. C. Sangster, R. C. Shah The neutron burn rate (dn/dt) is routinely measured for all cryogenic implosions. The high‑performance campaign implosions have neutron yields greater than 1014 and areal densities greater than 150 mg/cm2. The neutron burn-rate analysis presented uses a model that is convolved with a response function for the OMEGA neutron temporal diagnostic. Model parameters are determined with a maximum-likelihood fit to the recorded signal. These data are used to study the time evolution of OMEGA direct-drive implosions and how the “hot spot” is formed. |
Wednesday, November 7, 2018 2:36PM - 2:48PM |
PO6.00004: Investigation of the trends of time-resolved inferred electron temperatures of fusion experiments at the National Ignition Facility Shahab Khan, Pravesh K Patel, Leonard C Jarrott, Tammy Yee Wing Ma, John E Field, Ji Hoon Kang, Arthur Pak, Nobuhiko Izumi, Otto L Landen The electron temperature (Te) of the hot spot within the core of imploded inertial confinement fusion capsules is an effective indicator of implosion performance. Recently, an existing x-ray streak camera was upgraded at the National Ignition Facility to enable the inference of time-resolved Te of the hot core of controlled fusion imploded capsules. The upgrade involved a new dual slit and thick Titanium filters to isolate x-rays from specific energy regions. Herein, the trends of the inferred Te with measured performance parameters are investigated. In particular, inferred Te will be compared to measurements of neutron yield and ion temperatures as well as inferred levels of mix and hot spot bulk motion. |
Wednesday, November 7, 2018 2:48PM - 3:00PM |
PO6.00005: Experimental examination of ablator mix, electron temperature and shell opacity variations during the burn phase of inertially confined capsule implosions on the National Ignition Facility Benjamin Bachmann, Leonard C Jarrott, Tammy Ma, Michael K Kruse, Daniel Clark, Joseph E Ralph, Pravesh K Patel Hydro-instabilities in ICF implosions can cause ablator mix into the plasma hot spot and shell rho-r variations which impact confinement, volume, temperature, density and pressure of the stagnated DT fuel assembly and subsequent nuclear yield performance. Therefore, it is crucial to experimentally diagnose mix, ablator opacity and hot spot Te in ICF implosions in order to better understand the capsule stagnation and burn process. In the past, different types of hydrodynamic instabilities, originating from the capsule surface roughness, support tent and fill-tube have been identified as possible fusion performance degrading mechanisms. Using x-ray penumbral imaging we obtain differentially filtered (6-30keV), high-resolution (4-5um), hot spot images. By combining images obtained above and below the ablator opacity threshold as well as images filtered for high-Z dopant emission we can spatially separate such hydrodynamic mix features and assess Te variations during the burn phase. We will present our progress by examining penumbral images of a series of recent high-density carbon, CH and Be ablator ICF implosions carried out on the NIF. |
Wednesday, November 7, 2018 3:00PM - 3:12PM |
PO6.00006: Investigating the Differences Between Implosion Convergence Inferred From X-Ray Images and Secondary DT Neutrons At The NIF Brandon J Lahmann, Johan Frenje, Maria Gatu Johnson, Fredrick Seguin, Chikang Li, Richard David Petrasso, Edward P Hartouni, Charles B Yeamans, Hans Rinderknecht, Daniel B Sayre, Gary Grim, Kevin L Baker, Daniel T Casey, Eduard L. Dewald, Clement S Goyon, Leonard C Jarrott, S. Kahn, S. LePape, T. Ma, Louisa Pickworth, R. C. Shah, John L Kline, Theodore S Perry, Alex Zylstra, S. Austin Yi An important figure of merit for the performance of an ICF (Inertial Confinement Fusion) implosion is the capsule convergence: the ratio of the initial and final capsule radii. On the NIF, this is routinely inferred using imaging of the capsule’s self-emitted x-rays during peak compression. Additionally though, the yield ratio of secondary DT neutrons to primary DD neutrons can also be used to infer capsule convergence in deuterium-filled capsules. While these independent inferences track one another, x-ray imaging generally implies higher convergences (smaller final radii) than the secondary neutron based analysis. Understanding the nature of these differences could potentially offer interesting insights on the sensitivities of both methods to effects like high-Z mix, asymmetries, analysis assumptions, and plasma profiles. This work is supported in part by the U.S. Department of Energy and Lawrence Livermore National Laboratory. |
Wednesday, November 7, 2018 3:12PM - 3:24PM |
PO6.00007: Analysis of the backscatter edges on nToF data from NIF Robert Hatarik, Mark J. Eckart, Gary Grim, Edward P. Hartouni, Alastair Moore, David J. Schlossberg An important metric on a shot at the National Ignition Facility (NIF) is the uniformity of the compression of the capsule. In order to obtain information on the areal density (rhoR) distribution multiple diagnostics are being used: neutron activation diagnostics obtain an intensity profile at many different locations, while neutron Time-of-Flight (nToF) is used to obtain a down scattered ratio on four lines-of-sight. While the downscattered ratio measures the rhoR of the shell for small angle scattering towards the detector, the backscatter edges for (n,d) and (n,t) elastic scattering provide insight to the rhoR at the opposite side of the detector and could therefore be used to improve the angular coverage of the nToF detectors. The analysis of those backscatter edges from nToF data on the NIF will be discussed. |
Wednesday, November 7, 2018 3:24PM - 3:36PM |
PO6.00008: Jets and diffusion in ICF capsule implosions Nelson M Hoffman, Alex Zylstra, Paul A Bradley, Hans Herrmann, Yongho Kim, Erik L Vold The diffusion of deuterium ions, transported out of the plastic shell and into the fuel region, is of major importance in recent separated-reactant capsule experiments, using shells with very thin layers (0.15-μm thick) of deuterated plastic, either adjacent to gaseous tritium fuel, or recessed into the shell at various depths [Zylstra et al., Phys. Rev. E 97, 061201(R) (2018)]. But some features of the DT yield behavior in these experiments are not explainable in 1D simulations on the basis of diffusion alone, and seem to indicate that a hydrodynamic phenomenon, such as a jet induced by the target mount, also plays a role. Initial 2D simulations of such jets show that they can increase DT yield while decreasing the TT yield, compared to simulations without a jet. There is also evidence that deuterium diffusion may be occurring in the jet. |
Wednesday, November 7, 2018 3:36PM - 3:48PM |
PO6.00009: Internal Capsule Defects Quenching Thermonuclear Ignition in Inertial Confinement Fusion Hiroshi Azechi, Masaru Takagi, Masa Murakami, Shinsuke Fujioka Hydrodynamic instabilities such as the Rayleigh-Taylor (RT) instability may amplify perturbations on the capsule, and finally mix the cold main fuel and the capsule material into the hot spark, thereby quenching thermonuclear ignition in inertial confinement fusion targets. Surface roughness is generally considered as a primary source of the hydrodynamic instabilities, but internal capsule defects can also seed perturbations on the surface, being amplified by the instabilities. It is found by analyzing mode spectra of these defects that the perturbation amplitudes are well above the canonical surface roughness specification. Our mixing calculation for high gain targets suggests that the internal capsule defects in the present level are large enough to quench the thermonuclear ignition. It appears that in order to achieve ignition and burn one should adopt a technique such as density matched emulsion method that is free from the internal defects. |
Wednesday, November 7, 2018 3:48PM - 4:00PM |
PO6.00010: Preheat Effect on MARBLE Foams Yongho Kim, Thomas J Murphy, Carlos Di Stefano, Brian Michael Haines, Thomas H Day, Tana Cardenas, Brian James Albright, Richard E Olson, Joseph M Smidt, Melissa Douglas, Derek W Schmidt Recent experimental results from the MARBLE campaign at NIF shows that the initial size of macro-pore foam has no significant effect on the behavior of mix. The results suggest that the initial size of macro-pore foam may be disrupted by preheat from the hohlraum x-ray. The foam may expand due to the preheat, which results in decrease in the macro-pore size. Quantifying the amount of preheat will reduce uncertainty in MARBLE macro-pore simulations. Two types of preheat platforms were developed at Omega laser facility to provide data to guide NIF preheat simulation: the first study is to measure the aluminum expansion rates from a direct-drive laser condition, the second study is to measure the plastic expansion rates from an indirect-drive hohlraum x-ray. The amount of preheat will be quantified using radiographic x-ray images and a radiation-hydrodynamic code. |
Wednesday, November 7, 2018 4:00PM - 4:12PM |
PO6.00011: High-Yield Implosions via Radiation Trapping and High rhoR Darwin D. Morris Ho, Stephan MacLaren, Y. Morris A Wang A thin layer of mid- or high-Z material (Mo or W) at the inner surface of the ablator can be used to reduce the implosion velocity and hotspot temperature thresholds for ignition. This is because this thin layer can reduce Bremsstrahlung radiation lost from the hotspot as well as improve the confinement by increasing the rhoR. The problem with the thin layer is that it forms an unstable interface and this is the paramount concern for this type of implosion configuration. However, recent advances in target fabrication enable the blending of the inner region of Be ablators with mid- or high-Z material with a graded concentration that decreases gradually toward the outer region of the ablator. This substantially reduces Rayleigh-Taylor growth during the acceleration phase and gives high yield based on 2D simulations. Two types of capsule configurations, with DT gas only and with a DT ice layer, will be presented. The yield of DT-gas only capsules can be considerably higher than gas-only capsules using conventional low-Z ablator configurations. |
Wednesday, November 7, 2018 4:12PM - 4:24PM |
PO6.00012: 2-D OMEGA Capsule Implosions Paul A Bradley, Brian Michael Haines We have an upgraded laser energy deposition package in our AMR-Eulerian radiation-hydrodynamic code called RAGE. As part of our validation effort, we ran 2-D simulations for a series of OMEGA direct drive implosion capsules that have shell thickness ranging from 7.2 to 29.3 microns and different gas fills. These simulations include the effect of surface roughness, laser spot non-uniformity, the mounting stalk, and the glue spot. We examined the sensitivity of our simulated results to equation of state choices, ion diffusion, and mix model. Our simulated results compare well to the experimental yield, ion temperature, burn width, and x-ray size data. |
Wednesday, November 7, 2018 4:24PM - 4:36PM |
PO6.00013: Observations of multi-ion and kinetic effects in OMEGA shock driven implosions relevant to ignition experiments at the NIF Neel Kabadi, Hong Sio, Raspberry Simpson, Cody E Parker, Brandon J Lahmann, Graeme Sutcliffe, Patrick J Adrian, Arijit Bose, Maria Gatu Johnson, Johan Frenje, Chikang Li, Fredrick Seguin, Richard David Petrasso, Vladimir Glebov, Chad Forrest, Christian Stoeckl, Nelson M Hoffman, Olivier Larroche, Stefano Atzeni, Jonas Eriksson Inertial confinement fusion implosions are almost exclusively modeled as hydrodynamic in nature, with the electrons treated as a fluid and the ions treated as a single average-ion fluid. However, in the shock-convergence phase of virtually all inertial fusion implosions the mean-free path for ion-ion collisions becomes sufficiently long that both the shock front itself and the resulting central plasma are inadequately described by hydrodynamic modeling. A series of OMEGA experiments relevant to the shock convergence phase of ignition implosions shows little to no species separation in a DT plasma, but they do implicate other kinetic effects, like reactivity reduction, decreased shock energy coupling, and thermal decoupling of the D and T ions, which may play a role in ignition implosions. This work was supported by DOE, NLUF, LLNL, and LLE. |
Wednesday, November 7, 2018 4:36PM - 4:48PM |
PO6.00014: Time evolution of ion and electron temperatures in shock-driven implosions at OMEGA Hong Sio, Johan Frenje, Stefano Atzeni, A. Le, Thomas J Kwan, Neel Kabadi, Grigory A Kagan, William T. Taitano, Brett D Keenan, Andrei N. Simakov, Luis Chacon, Christian Stoeckl, Maria Gatu Johnson, Chikang Li, Richard David Petrasso Time evolutions of ion and electron temperatures in shock-driven implosions are separately assessed using simultaneously measured nuclear-reaction and X-ray-emission histories. In these DT3He-gas-filled implosions, the Particle X-ray Temporal Diagnostic (PXTD) on OMEGA is fielded to measure the DT and D3He reaction histories, as well as several X-ray-emission histories in different energy bands. A spatially-averaged Ti(t) is inferred from the reaction histories using the different temperature sensitivities of the DT and D3He reactions. A spatially-averaged Te(t) is inferred from the ratios of the X-ray histories at different energy bands. These measured Ti(t) and Te(t) have been used to explore ion-electron equilibration rates in different plasma conditions. Finally, the implementation and use of PXTD, which represents a significant advance at OMEGA, has laid the foundation for the implementation of a Te(t) diagnostic in support of the main cryogenic DT programs on OMEGA. This work is supported in part by the U.S. DOE, LLNL, LLE, and NNSA SSGF. |
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