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 BO6: Compression and Burn I |
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Chair: Christopher Walsh, Imperial College London Room: OCC B115-116 |
Monday, November 5, 2018 9:30AM - 9:42AM |
BO6.00001: Signatures of systematic azimuthal asymmetry in nuclear diagnosis of ICF implosions on the NIF Hans Rinderknecht, Daniel T Casey, Richard Marshall Bionta, Robert Hatarik, Gary Grim, Otto L Landen, Pravesh K Patel In ICF experiments on the NIF, several nuclear diagnostics provide information about the state of the converged hotspot and fuel near peak convergence. Net velocity of the fusing plasma is diagnosed by Neutron Time-of-Flight (NTOF) diagnostics via Doppler shifts in the primary DT-neutron peak energy; asymmetry of the converged DT fuel areal density (ρRfuel) is diagnosed by Nuclear Activation Diagnostics (NADs) that record differences in neutron fluence with position due to scattering in the fuel. On recent implosions using high-density carbon (HDC) ablators, both high net hotspot velocities (> 50 km/sec) and large mode-1 ρR asymmetries (> 25%) have been inferred. In these experiments, the direction of hotspot flow coincides with the direction of minimum ρR, and across many experiments this direction clusters preferentially toward one half of azimuthal space in the NIF geometry (φ = 0˚—180˚). These results are consistent with a persistent, unintentional azimuthal drive asymmetry or offset on this series of implosions. Results from various campaigns will be compared and the effect on ICF ignition will be discussed. |
Monday, November 5, 2018 9:42AM - 9:54AM |
BO6.00002: Impact of fill tube perturbation on implosion experiments conducted with high density carbon ablators Arthur Pak, C. Weber, Laurent Divol, Laura Robin Benedetti, Laura Berzak Hopkins, Daniel Clark, Eduard L. Dewald, David Neal Fittinghoff, Otto L Landen, Sebastien Le Pape, Tammy Yee Wing Ma, Edward Marley, Sabrina R Nagel, Louisa Pickworth, Petr L Volegov, David K. Bradley, Debra Ann Callahan, Gary Grim, Omar A Hurricane, Pravesh K Patel, Marilyn Beth Schneider, Michael J Edwards At stagnation, all implosion experiments conducted with a high density carbon (HDC) ablator exhibit signatures of fill tube induced mix. This perturbation could potentially be a significant cause of performance degradation. This talk will discuss the impact that the fill tube perturbation has on state of the reacting plasma and on integrated performance. The changes in the observed fill tube perturbation size, temperature and radiative loss as well as the overall integrated performance between experiments where the initial fill tube diameter was varied will be examined. Additionally, the observed fill tube dynamics and implosion performance will be compared to detailed radiation hydrodynamic calculations that include a fill tube perturbation. Using radiation hydrodynamic simulations, the relative impact on performance from enhanced radiative losses, conduction losses, heat capacity, and shell rho r nonuniformity that arise from the fill tube perturbation will be discussed. |
Monday, November 5, 2018 9:54AM - 10:06AM |
BO6.00003: Simulating Experiments with Radiation Asymmetries and Fill Tubes on the National Ignition Facility Kristopher McGlinchey, Aidan Crilly, Jon Tong, Christopher Alexander Walsh, Brian Appelbe, Jeremy Chittenden Recent High Density Carbon (HDC) implosion experiments on the National Ignition Facility have reached over 1016 neutrons owing to increased control of the shape of the capsule. Perturbation sources such as the fill tube and residual 3D shape defects are thought to be the leading candidates for the current limitation in implosion performance. We present 3D simulations of HDC capsule implosions with multiple sources of perturbations using our in-house 3D radiation-hydrodynamics code Chimera. We assess the impact that the fill tube and radiation asymmetry has in simulations and then post-process the results with synthetic diagnostics to see how they affect observables such as the flange Neutron Activation Diagnostic (fNAD) sky-map and the neutron Time of Flight (nTOF) diagnostic spectrum, as well as the neutron yield, burn width and bang time. Doing so allows us to look at the diagnostic signatures of each perturbation and directly link them back to the dynamics in simulations to determine different mechanisms of burn truncation. Focusing on the fill tube perturbation and asymmetric drive conditions allows us to explore the hypothesis that they are the current sources of the asymmetry observed in the fNADs. |
Monday, November 5, 2018 10:06AM - 10:18AM |
BO6.00004: 3D HYDRA Capsule Studies on the Effect of Hohlraum Windows Ryan Nora, John E Field, Chris Young, Derek Mariscal, Tammy Yee Wing Ma, Brian K. Spears We present low-resolution three-dimensional radiation hydrodynamic simulation studies of capsule-only implosions using the code HYDRA [1]. These simulations are capable of resolving radiation drive asymmetries with spherical harmonic degrees of at least five and utilize Particle Monte Carlo neutronics. The simulations are heavily diagnosed with synthetic neutron and x-ray diagnostics, similar to the actual diagnostics used on the National Ignition Facility. These simulations are executed on the TRINITY supercomputer at Los Alamos under the Advanced Technology Computing Campaign.
This work focuses on sensitivity studies affecting capsule implosion stability due to diagnostic windows in the hohlraum, in support of the Windowless Hohlraum experimental campaign. The three-dimensional drive asymmetries are derived from VISRAD [2] view factor simulations, accounting for time-dependent laser beam power imbalance, capsule ablation, and hohlraum wall expansion. We will present the results of the sensitivity studies with various hohlraum-window models and compare them to experimental observations.
[1] M. M. Marinak, et al., Phys. Plasmas 8, 2275 (2001) [2] J. J. MacFarlane, J. Quant. Spectr. Rad. Transfer, 81, 287 (2003) |
Monday, November 5, 2018 10:18AM - 10:30AM |
BO6.00005: Evaluating the Residual Kinetic Energy in Direct-Drive Cryogenic Implosions on OMEGA Chad Forrest, Ken S Anderson, Vladimir Yu Glebov, Valeri N Goncharov, James P Knauer, Owen M Mannion, Radha Bahukutumbi, Sean P Regan, Rahul C Shah, Christian Stoeckl Efficient conversion of the shell kinetic energy to the hot-spot thermal energy is an essential requirement in inertial confinement fusion implosions. The spectral moments of the neutron energy distribution emitted from a fusing deuterium–tritium (DT) plasma is used to infer the yield, mean energy, and neutron averaged ion temperature of the implosion. Flows in the reacting plasma will have a different effect on the DD and DT neutron distribution, resulting in a disagreement between the inferred ion temperatures from the two separate reactions. Enhanced broadening of the peak distributions of the different reactants provides a measure of the residual kinetic energy in the fusion plasma.[1] Evaluation of residual kinetic energy from direct-drive cryogenic DT implosions on OMEGA is presented. [1] T. J. Murphy, Phys. Plasmas 21, 072701 (2014). |
Monday, November 5, 2018 10:30AM - 10:42AM |
BO6.00006: Impact of Three-Dimensional Hot-Spot Flow Asymmetry on Ion-Temperature Measurements in Inertial Confinement Fusion Experiments Ka Ming Woo, Riccardo Betti, Dov Shvarts, Owen Mannion, Dhrumir P Patel, Valeri N Goncharov, Kenneth Anderson, P.B Radha, James P Knauer, Arijit Bose, Varchas Gopalaswamy, Alison R Christopherson, E. M. Campell, J. Sanz, Hussein Aluie Three-dimensional implosion asymmetries lead to significant ion-temperature measurement variations in inertial confinement fusion experiments. We have developed an analytical method to generalize the physical properties of velocity variance in the Brysk ion temperature model. The hot-spot flow asymmetry on ion-temperature measurement variations are shown uniquely governed by a complete set of six hot-spot flow parameters in terms of variance and co-variance of the hot-spot flow velocity distribution. An approximated solution to the minimum inferred ion temperature is derived and is shown close to the thermal ion temperature for low-mode ℓ = 1, which exhibits the largest an-isotropic velocity variance in the single-mode spectrum. The isotropic velocity variance for low‑mode ℓ = 2 is shown causing minimum inferred ion temperatures well above the thermal ion temperature. |
Monday, November 5, 2018 10:42AM - 10:54AM |
BO6.00007: Diagnosing effects of laser-drive asymmetry on hot-spot flow dynamics and implosion performance on NIF David Schlossberg, Daniel T Casey, Mark J Eckart, Gary Grim, Edward P Hartouni, Robert Hatarik, Joseph David Kilkenny, Alastair Moore Asymmetries in laser indirect drive during inertial confinement fusion implosions dramatically reduce performance due to energy transfer into residual capsule motion and thus lost from hot spot heating. Dedicated experiments on the National Ignition Facility were recently performed which characterized these effects. This investigation kept capsule, fuel, and hohlraum features identical while varying the balance of laser energy entering each end of the hohlraum. Flow velocities >130 km/s in the imbalanced cases were observed using neutron time-of-flight techniques and corroborated by neutron activation detectors. Variance in these bulk flows contributes to apparent ion temperatures and exhibits a cosine dependence on the angle between observations and flow direction. Distinct regions of peak x-ray and neutron emission are seen within the capsule, with brightened limbs in the P1-driven direction. Time-resolved x-ray imaging reveals fill-tube dynamics and suggests internal flow-fields during the implosion. Results from this set of shots will be presented, and comparison with simulations discussed. |
Monday, November 5, 2018 10:54AM - 11:06AM |
BO6.00008: Signatures of flows in ion-temperature, areal-density and x-ray imaging data obtained in asymmetrically driven OMEGA DT implosions Maria Gatu Johnson, Johan Frenje, Brandon J Lahmann, Fredrick Seguin, Richard David Petrasso, Brian Appelbe, Jeremy Chittenden, Christopher Alexander Walsh, Jacques Alain Delettrez, Igor Igumenshchev, James P Knauer, Vladimir Glebov, Chad Forrest, William Grimble, Roger Janezic, Frederic J Marshall, Tomline Michel, Christian Stoeckl, Brian Michael Haines, Alex Zylstra Ion temperatures (Tion) in Inertial Confinement Fusion (ICF) experiments are inferred from the broadening of primary neutron spectra. Directional motion (flow) of the fuel at burn, originating from asymmetries imposed by e.g. engineering features or drive non-uniformity, also impacts the broadening and may lead to artificially inflated “Tion” values. Flow due to low-mode asymmetries is expected to give rise to line-of-sight variations in measured Tion, as observed in OMEGA cryogenic DT implosions but not in similar experiments at the NIF. In this presentation, we report on OMEGA implosions intentionally driven asymmetrically to test the ability to predict and measure line-of-sight differences in apparent Tion due to low-mode asymmetry-seeded flows. Neutron peak shift, areal-density asymmetry and x-ray imaging measurements are also brought to bear. These measurements are contrasted to CHIMERA, xRAGE and ASTER simulations, providing insights into implosion dynamics and the interplay between different asymmetry sources, including laser drive non-uniformity, stalk and capsule offset. The results highlight the complexity of hot-spot dynamics, which is a problem that must be mastered to achieve ICF ignition. This work was supported in part by the U.S. DOE, NLUF and LLE. |
Monday, November 5, 2018 11:06AM - 11:18AM |
BO6.00009: Modeling of Target Offset in Warm Implosions on OMEGA Kenneth S. Anderson, Chad J. Forrest, Owen M. Mannion, D. Tomline Michel, Rahul C Shah, John A Marozas, P.B Radha, Frederic J Marshall, Timothy J Collins, James P Knauer, Maria Gatu-Johnson In inertial confinement fusion, small errors in capsule positioning within the target chamber have been identified through simulations as a significant source of implosion nonuniformity and yield degradation. However, neutron yields from both warm and cryogenic implosions on the OMEGA‑60 Laser System have exhibited little sensitivity to target offset. This talk will present 2-D simulations showing that cross-beam energy transfer plays a large role in mitigating laser drive asymmetry from target offset. A comparison of simulated and experimental observables is presented for warm target implosions. These observables include bulk hot-spot flow as measured by neutron time-of-flight diagnostics, variations in the observed ion temperature as a function of line of sight, and x-ray images both in-flight and at stagnation time. |
Monday, November 5, 2018 11:18AM - 11:30AM |
BO6.00010: Integrated Analysis of Nuclear Measurements from the Target-Offset Campaign on OMEGA Owen M Mannion, Kenneth S Anderson, Chad J Forrest, Vladimir Yu Glebov, James P Knauer, Zaarah L Mohamed, Sean P Regan, Thomas C Sangster, Rahul C Shah, Christian Stoeckl, Maria Gatu Johnson A series of room-temperature and cryogenic experiments with intentional target offsets have been performed on OMEGA to maximize the nuclear signatures of asymmetric compression of the hot spot. Introducing an intentional target offset seeds low-mode asymmetries that generate flows within the hot spot and asymmetries in the shell areal density. Flows within the hot spot manifest as shifts and non-thermal broadening in the neutron energy spectrum emitted by the hot spot, while areal-density nonuniformities lead to variations in the scattered neutron energy spectrum. Measurements of the inferred hot‑spot motion, ion temperature, and shell areal density along multiple lines of sight are presented and compared with 2-D radiation–hydrodynamic simulations including the effect of target offset as well as cross-beam energy transfer. |
Monday, November 5, 2018 11:30AM - 11:42AM |
BO6.00011: Experimental investigation of the source of mode one asymmetries in indirect-drive ICF implosions Tammy Ma, Derek Mariscal, Pravesh K Patel, Sebastien Le Pape, Laura Berzak Hopkins, Arthur Pak, Laura Robin Benedetti, Benjamin Bachmann, Paul T Springer, Christopher V Young, Ryan Nora, Jayson Dean Lucius Peterson, Omar A Hurricane, Debra Ann Callahan While recent indirect-drive ICF implosions on the NIF have demonstrated record performance such as a yield amplification of 3 and hot spot pressures of ~360 Gbar1, 3D asymmetry of the hot spot and assembled cold fuel shell continues to be a key performance degradation mechanism. In particular, measurements of the bulk hot-spot velocity from neutron time-of-flight measurements and spatial variations in the shell areal density from neutron activation diagnostics indicate a systematic mode-1 asymmetry. Diagnostic windows are cut out of the high-Z gold or depleted uranium hohlraum in order to provide a diagnostic line-of-sight for hot spot self-emission x-rays and to allow imaging of the capsule fuel pre-shot. One hypothesis for the low-mode asymmetry is that these windows are reducing the x-ray drive in the window directions. We will report on a series of experiments systematically varying the size of the hohlraum windows and the effect on implosion shape, hot-spot velocity, rhoR variations, and overall performance. 1S. Le Pape, et al., Phys. Rev. Lett. 120, 245003 (2018) |
Monday, November 5, 2018 11:42AM - 11:54AM |
BO6.00012: Diagnosing fuel areal-density asymmetries in cryogenic deuterium-tritium implosions at OMEGA using knock-on deuteron spectra Raspberry Simpson, Johan Frenje, Brandon J Lahmann, Hong Sio, Neel Kabadi, Graeme Sutcliffe, Patrick J Adrian, Arijit Bose, Cody E Parker, Maria Gatu Johnson, Fredrick Seguin, Chikang Li, Richard David Petrasso, Joe Katz, Sean P Regan, Chad Forrest, James P Knauer, Chuck Sorce, Vladimir Glebov Determining fuel areal-density (ρR) asymmetries is vital to assessing the performance of inertial confinement fusion implosions. The Charged Particle Spectrometers (CPS’s) on OMEGA have been used to infer fuel ρR asymmetries in cryogenic deuterium-tritium implosions by measuring the spectrum of knock-on deuterons emitted in different directions. These knock-on deuterons are produced by elastic scattering between primary DT neutrons and deuterium fuel. The CPS’s, which are located along different lines-of-sight, provide a complimentary measurement to the neutron-based ρR measurements. In this work, we discuss the knock-on deuteron data obtained in the 1-D cryogenic DT Campaign at OMEGA. Preliminary data analysis reveals that measured ρR vary significantly along different measurement lines-of-sight, which may suggest ρR asymmetries and systematic 3-D effects. This work was supported in part by the US DOE, LLE, NSF, and DOE NNSA. |
Monday, November 5, 2018 11:54AM - 12:06PM |
BO6.00013: Imploding Cryogenic Shell Nonuniformity Measurements on OMEGA by Self-Radiography Reuben Epstein, Christian Stoeckl, Radha Bahukutumbi, Timothy J Collins, Patrick McKenty, Duc M Cao, Rahul C Shah, Dylan T Cliche, Roberto Claudio Mancini Radiographs of pure DT cryogenic imploding shells will help to validate progress toward ignition-scalable performance of inertial confinement fusion implosions. Imploding cryogenic D2 and DT shells can be radiographed with the core spectral emission, progressively from hν ≈ 1 keV to ≈2 keV, from the deceleration phase through peak compression. Utilizing the distinct spectral dependences of hydrogen continuum emissivity and opacity, shell optical‑thickness variations can be distinguished from core structure. This technique does not require shell additives, as used in previous applications of implosion self-radiography. Demonstrations with simulated data show that this technique is remarkably well suited to cryogenic implosions. Specifically, emission and absorption are well localized to the core and shell, respectively. Also, shell self-backlighting can be used near peak compression, unlike externally backlit radiography, where self-emission is a background signal that overwhelms the backlighter near peak compression. |
Monday, November 5, 2018 12:06PM - 12:18PM |
BO6.00014: Scaling of Ignition and Burn in Inhomogeneous Inertial Confinement Fusion Hotspots Jon Tong, Jeremy Chittenden, Kristopher McGlinchey, Brian Appelbe, Christopher Alexander Walsh, Aidan Crilly The performance of inertial confinement fusion (ICF) capsules is heavily dependent on the formation and shape of the hotspot, and the way these are influenced by the presence of different perturbations. Conversely, the evolution of the perturbations themselves changes due to the hotspot heat flow via electron thermal conduction, radiation transport and alpha transport. Understanding this interaction between perturbations and the hotspot is crucial to understanding the evolution of ignition and burn. We examine the scaling in performance with increased capsule size and laser energy, presenting simulations using the in-house 3D radiation hydrodynamics code Chimera, upgraded with a Monte-Carlo Particle-in-Cell (PIC) alpha transport. We consider the impact of various perturbations such as radiation asymmetries and multi-mode Rayleigh-Taylor spikes on the energy scaling of both High-Foot and High-Density-Carbon (HDC)-style capsules, based on current National Ignition Facility (NIF) capsule experiments. Larger scales produce enhanced burn and therefore increased heat flow, and we explore how the effect of the resultant feedback loop between this heat flow and the perturbations varies with scale. We also study the scale requirements for 1MJ yields under these perturbation scenarios. |
Monday, November 5, 2018 12:18PM - 12:30PM |
BO6.00015: Effects of asymmetry and hot spot shape on ignition Baolian Cheng, Thomas J. T. Kwan, Sunghwan Austin Yi, Otto L. Landen, Yi-Ming Wang, Charlie J. Cerjan, Steven Howard Batha, Fred J Wysocki Asymmetric implosion of inertial confinement fusion capsules is known, both experimentally and computationally, to reduce thermonuclear (TN) performance. This work shows that low-mode asymmetries degrade performance as a result of decrease in the hydrodynamic disassembly time of the hot spot core, which scales with the minimum dimension of the hot spot. The asymmetric shape of a hot spot results in decreased temperatures and areal densities and allows more alpha particles to escape, relative to an ideal spherical implosion, thus reducing alpha-energy deposition in the hot spot. Here, we extend previous ignition theory to include the hot-spot shape and quantify the effects of asymmetry on both the ignition criterion and capsule performance. The ignition criterion becomes more stringent with increasing deformation of the hot spot. The new results are validated by comparison with NIF experimental data. The shape effects on TN performance become more noticeable as both self-heating and yield increase. The degradation of TN burn can be as high as 45% for shots with yield lower than 2x1015and less than 30% for shots with yield above. This work was performed under the auspices of the U.S. Department of Energy by the Los Alamos National Laboratory under Contract No. W-7405-ENG-36. |
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