Bulletin of the American Physical Society
58th Annual Meeting of the APS Division of Plasma Physics
Volume 61, Number 18
Monday–Friday, October 31–November 4 2016; San Jose, California
Session NO5: ICF: Integrated Experiments I |
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Chair: Radha Bahukutumbi, Laboratory for Laser Energetics Room: 230 B |
Wednesday, November 2, 2016 9:30AM - 9:42AM |
NO5.00001: Performance of Beryllium Targets with Full-scale Capsules in Low-fill 6.72-mm Hohlraums on the National Ignition Facility A. N. Simakov, S. A. Yi, J. L. Kline, G. A. Kyrala, E. N. Loomis, D. C. Wilson, T. S. Perry, S. H. Batha, E. L. Dewald, J. E. Ralph, D. J. Strozzi When used with full-size beryllium (Be) capsules [1], high-fill 5.75-mm hohlraums exhibit significant drive degradation via laser backscatter and ``missing energy''. Also, hard to simulate cross-beam energy transfer (CBET) must be used to control the implosion symmetry. Low-fill ($\le $0.6 mg/cm$^{\mathrm{3}})$ 6.72-mm hohlraums offer improved drive efficiency and the symmetry tunability without the CBET. In FY16, we carried out an exploratory campaign to evaluate performance of full-size Be capsules in such hohlraums. Specifically, we have performed a fill-density scan with a three-shock, 9.5-ns pulse and found that an appropriate laser beam repointing and outer-quad splitting results in approximately 5{\%} laser backscatter at fill densities $\le $0.3 mg/cm$^{\mathrm{3}}$, with the implosion becoming less oblate as the fill-density decreases. We also plan to perform an implosion with a lower-foot, 12.6-ns pulse, to observe a more prolate symmetry. [1] J. L. Kline et al., Phys. Plasmas 23, 056310 (2016). [Preview Abstract] |
Wednesday, November 2, 2016 9:42AM - 9:54AM |
NO5.00002: Developing a 1D ``like'' performance basecamp for beryllium capsule implosions John Kline, Austin Yi, Eric Loomis, Andrei Simakov, George Kyrala, Doub WIlson, Eddie Dewald, Joe Ralph, David Strozzi Experiments with Beryllium capsules in high density gas filled targets showed little difference in performance with respect to CH or HDC capsules. The hypothesis for the lack of performance difference is attributed to poor control of symmetry based on work by Clark et al. Going forward, the goal is to develop a target design that enables better comparisons between the performance of Be capsules and other ablators, as well as with simulations. To develop a platform in which Be capsules maximize performance with respect to 1D calculations, we have increased the case-to-capsule ratio and reduced the hohlraum drive. The stability properties of beryllium are expected to be accentuated at lower radiation temperature drives compared with other ablators. Experiments have been carried out with case-to-capasule ratio of 3.1 and 4.3. Results from these experiments are being used to develop an optimized case-to-capsule ratio to achieve controllable symmetric implosions with maximum 1D like performance. This presentation will focus on how results of the experiments are used to design the next series of optimized experiments.. [Preview Abstract] |
Wednesday, November 2, 2016 9:54AM - 10:06AM |
NO5.00003: First shock tuning and backscatter measurements for large case-to-capsule ratio beryllium targets. Eric Loomis, Austin Yi, John Kline, George Kyrala, Andrei Simakov, Doug Wilson, Joe Ralph, Eduard Dewald, David Strozzi, Peter Celliers, Marius Millot, Riccardo Tommasini The current under performance of target implosions on the National Ignition Facility (NIF) has necessitated scaling back from high convergence ratio to access regimes of reduced physics uncertainties. These regimes, we expect, are more predictable by existing radiation hydrodynamics codes giving us a better starting point for isolating key physics questions. One key question is the lack of predictable in-flight and hot spot shape due to a complex hohlraum radiation environment. To achieve more predictable, shape tunable implosions we have designed and fielded a large 4.2 case-to-capsule ratio (CCR) target at the NIF using 6.72 mm diameter Au hohlraums and 1.6 mm diameter Cu-doped Be capsules. Simulations show that at these dimensions during a 10 ns 3-shock laser pulse reaching 270 eV hohlraum temperatures, the interaction between hohlraum and capsule plasma, which at lower CCR lead to beam propagation impedance by artificial plasma stagnation, are reduced. In this talk we will present measurements of early time drive symmetry using two-axis line-imaging velocimetry (VISAR) and streaked radiography measuring velocity of the imploding shell and their comparisons to post-shot calculations using the code HYDRA (Lawrence Livermore National Laboratory). [Preview Abstract] |
Wednesday, November 2, 2016 10:06AM - 10:18AM |
NO5.00004: Control of symmetry in Be implosions using a large Case to Capsule ratio. George Kyrala, J. Kline, A. Yi, E. Loomis, A. Simakov, D. Wilson, J. Ralph, R. Rygg, D. Strozzi, G Ak \begin{enumerate} \item Tuning implosion symmetry in indirectly driven spherical capsules has been usually achieved by modifying the inner to outer beam powers inside a hohlraum. This has been done either by changing the wavelength difference between the beams in a gas filled hohlraum leading to cross beam energy transfer between the beams (CBET) , or by varying the inner to outer beam power ratio directly in low-density filled cylindrical hohlraums that permit much lower CBET. Symmetry had shown a large sensitivity to the power ratio of the inner to the outer beam power, partly due to the interaction of the inner beams with the ablated capsule material. To reduce the effect of the capsule ablation on the propagation of the inner laser beams, a larger ratio of the hohraum inner radius to the capsule outer radius has been investigated. This presentation will focus on the results of a series of experiments that monitored the symmetry of the imploding capsule shell as well as the later x-ray emission from the imploded core. We will compare to predictions and post shot calculations. \end{enumerate} [Preview Abstract] |
Wednesday, November 2, 2016 10:18AM - 10:30AM |
NO5.00005: Results from Direct-Drive Shock-Timing Experiments at the National Ignition Facility P.B. Radha, M.J. Rosenberg, M. Hohenberger, T.R. Boehly, E.M. Campbell, D.H. Froula, V.N. Goncharov, S.X. Hu, J.A. Marozas, J.F. Myatt, S.P. Regan, T.C. Sangster, S. Dixit The timing of multiple shocks is critical to set an inertial confinement capsule on a desired adiabat. Several factors including laser-energy deposition, heat conduction, and equation of state determine the adiabat of the compressing shell. Dual-axis cone-in-shell experiments, performed with plastic, (CH) shells and solid spheres, are used to diagnose the first shock velocity and the catch up of subsequent shocks at the National Ignition Facility. The shocks are launched with multiple pickets, expected to be used in ignition-relevant designs, at two different intensities. In separate experiments, continuous pulse shapes are also diagnosed. The measurements are compared to two-dimensional \textit{DRACO} simulations that include the effects of nonlocal heat transport,\footnote{D. Cao \textit{et al}., Phys. Plasmas \textbf{22}, 082308 (2015).} cross-beam energy transfer,\footnote{ J. A. Marozas \textit{et al}., Bull. Am. Phys. Soc. \textbf{56}, 241 (2011).}$^{\mathrm{\thinspace }}$and the first-principles equation of state of CH.\footnote{ S. X. Hu \textit{et al}., Phys. Rev. E \textbf{92}, 043104 (2015).\par } Designs that could potentially diagnose late-time energy coupling through shocks are also presented. This material is based upon work supported by the Department Of Energy National Nuclear Security Administration under Award Number DE{\-}NA0001944. [Preview Abstract] |
Wednesday, November 2, 2016 10:30AM - 10:42AM |
NO5.00006: Design of Platforms for Backlighting Spherical Implosions on OMEGA and the National Ignition Facility R.S. Craxton, M. Hohenberger, W.E. Kehoe, F.J. Marshall, D.T. Michel, P.B. Radha, M.J. Rosenberg A common problem when backlighting implosions on OMEGA and at the National Ignition Facility (NIF) is that the implosion uniformity can be compromised by the loss of those beams used to drive the backlighter. The 2-D hydrodynamics code \textit{SAGE},\footnote{ R. S. Craxton and R. L. McCrory, J. Appl. Phys. \textbf{56}, 108 (1984).} which includes 3-D laser ray tracing, has been used to design irradiation configurations in which beam pointings and energies are adjusted to restore optimal implosion uniformity. Experimental x-ray self-emission images have demonstrated the effectiveness of these configurations for an OMEGA platform in which six beams are removed to drive the backlighter and a polar-drive NIF platform in which two quads are removed. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Wednesday, November 2, 2016 10:42AM - 10:54AM |
NO5.00007: Direct Measurements of Hot-Electron Preheat in Inertial Confinement Fusion A.R. Christopherson, R. Betti, J. Howard, A. Bose, C.J. Forrest, W. Theobald, E.M. Campbell, J.A. Delettrez, C. Stoeckl, D.H. Edgell, W. Seka, A.K. Davis, D.T. Michel, V.Yu. Glebov, M.S. Wei In laser-driven inertial confinement fusion, a spherical capsule of cryogenic DT with a low-$Z$ (CH, Be) ablator is accelerated inward on low entropy to achieve high hot-spot pressures at stagnation with minimal driver energy. Hot electrons generated from laser--plasma instabilities can compromise this performance by preheating the DT fuel, which results in early decompression of the imploding shell and lower hot-spot pressures. The hot-electron energy deposited into the DT for direct-drive implosions is routinely inferred by subtracting hard x-ray signals between a cryogenic implosion and its mass-equivalent, all-CH implosion. However, this technique does not measure the energy deposited into the unablated DT, which fundamentally determines the final degradation in hot-spot pressure. In this work, we report on experiments conducted with high-$Z$ payloads of varying thicknesses to determine the hot-electron energy deposited into a payload that is mass equivalent to the amount of unablated DT present in typical DT layered implosions on OMEGA. These are the first measurements to directly probe the effect of preheat on performance degradation. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Wednesday, November 2, 2016 10:54AM - 11:06AM |
NO5.00008: Density Profile of a Foil Accelerated by Laser Ablation J.P. Knauer, S.X. Hu, V.N. Goncharov, D. Haberberger An experiment to measure the density profile of a foil accelerated by laser ablation has been designed and is underway. High-density material is measured with x-ray radiography and low-density plasma is measured using 251-nm interferometry. Two-dimensional hydrodynamic simulation results from the code \textit{DRACO} will be compared to these data. The accelerated foil is an 80-$\mu $m-thick CH target with Ge and Si-doped layers. The incident laser is a 351-nm, 5-ns pulse with a total energy of 6.2 kJ. Si and Ti x rays are used for the radiography measurement. A 1-D image versus time data are recorded with an x-ray streak camera and 2-D image data at specific times are recorded with an x-ray framing camera using point-projection backlighting. Foil acceleration is measured with the 1-D data. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Wednesday, November 2, 2016 11:06AM - 11:18AM |
NO5.00009: Wavelength Detuning Cross-Beam Energy Transfer Mitigation for Polar Direct Drive and Symmetric Direct Drive J.A. Marozas, T.J.B. Collins, P.W. McKenty, P.B. Radha, M. Hohenberger, M.J. Rosenberg Cross-beam energy transfer (CBET) results from two-beam energy exchange via stimulated Brillouin scattering,\footnote{ C. J. Randall \textit{et al}., Phys. Fluids \textbf{24}, 1474 (1981).} which reduces absorbed light and implosion velocity, alters time-resolved scattered-light spectra, and redistributes absorbed and scattered light. These effects reduce target performance in polar direct drive (PDD) and symmetric direct drive (SDD) at the National Ignition Facility (NIF) and on the OMEGA Laser System. The CBET package (\textit{Adaawam}) incorporated into the 2-D hydrodynamics code \textit{DRACO} is an integral part of the 3-D ray-trace package (\textit{Mazinisin}). Detuning the initial laser wavelength $\left( {\mbox{d}\lambda_{0} } \right)$ reduces the CBET interaction volume, which can be combined with other mitigation domains (e.g., spatial and temporal). Recent PDD experiments on the NIF explored this option using a cone-swapping technique with $\mbox{d}\lambda_{0} =\pm 2.34\mbox{\thinspace {\AA}}$ UV, which are compared with \textit{DRACO} simulations. \textit{DRACO} simulations of wavelength detuning in SDD on OMEGA predict the expected mitigation using OMEGA's three main amplifier chains in both near-term $\mbox{d}\lambda_{0} =\left\{ {-3,0,+3} \right\}\mbox{-{\AA}}$ and long-term $\mbox{d}\lambda_{0} =\left\{ {-6,0,+6} \right\}\mbox{-{\AA}}$ UV configurations. The detuning simulations predict improved performance and changes in 2-D and 3-D morphology in both PDD and SDD. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Wednesday, November 2, 2016 11:18AM - 11:30AM |
NO5.00010: Planar Laser--Plasma Interaction Experiments at Direct-Drive Ignition-Relevant Scale Lengths at the National Ignition Facility M.J. Rosenberg, A.A. Solodov, W. Seka, J.F. Myatt, S.P. Regan, M. Hohenberger, R. Epstein, D.H. Froula, P.B. Radha, P.A. Michel, J.D. Moody, L. Masse, C. Goyon, D.P. Turnbull, M.A. Barrios, J.W. Bates, A.J. Schmitt The first experiments at the National Ignition Facility to probe laser--plasma interactions and the hot electron production at scale lengths relevant to direct-drive ignition are reported. The irradiation on one side of planar CH foils generated a plasma at the quarter-critical surface with predicted density scale lengths of $L_{\mbox{n}} \sim 600\mbox{\thinspace }\mu \mbox{m,}$ measured electron temperatures of $T_{\mbox{e}} \sim 3.5$ to 4.0 keV, and overlapped laser intensities of $I\sim 6$ to $15\times 10^{14}{\mbox{\thinspace W}} \mathord{\left/ {\vphantom {{\mbox{\thinspace W}} {\mbox{cm}^{2}}}} \right. \kern-\nulldelimiterspace} {\mbox{cm}^{2}}.$ Optical emission from stimulated Raman scattering (SRS) and at $\omega $/2 are correlated with the time-dependent hard x-ray signal. The fraction of laser energy converted to hot electrons increased from $\sim 0.5\% $~to $\sim 2.3\% $ as the laser intensity increased from $\sim 6$ to $15\times 10^{14}{\mbox{\thinspace W}} \mathord{\left/ {\vphantom {{\mbox{\thinspace W}} {\mbox{cm}^{2}}}} \right. \kern-\nulldelimiterspace} {\mbox{cm}^{2}},$ while the hot electron temperature was nearly constant around 40 to 50 keV. Only a sharp red-shifted feature is observed around $\omega $/2, and both refracted and sidescattered SRS are detected, suggesting that multibeam SRS contributes to, and may even dominate, hot-electron production. These results imply a diminished presence of two-plasmon decay relative to SRS at these conditions, which has implications for hot-electron preheat mitigation strategies for direct-drive ignition. This work is supported by the DOE NNSA under Award Number DE-NA0001944. [Preview Abstract] |
Wednesday, November 2, 2016 11:30AM - 11:42AM |
NO5.00011: Three-Dimensional Analysis of the Effects of Low-Mode Asymmetries on OMEGA Cryogenic Implosions K.S. Anderson, P.W. McKenty, A. Shvydky, J.P. Knauer, T.J.B. Collins, M.M. Marinak Understanding the role of low-mode asymmetries is essential to characterizing inertial confinement fusion implosions. Asymmetries seeded by nonuniformities in laser drive, capsule manufacture, and target positioning lead to shell modulation as well as nonradial hydrodynamic flow in the hot spot at stagnation, which can adversely affect peak pressure and neutron yield. Full-sphere three-dimensional simulations are required to quantify the flow in the hot spot and its impact on hot-spot pressure and other observables. This paper will analyze results from \textit{HYDRA} simulations of OMEGA cryogenic implosions modeling various sources of low-mode asymmetries (e.g., target offset, laser power imbalance, ice layer roughness) and show comparisons with experimental observables. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Numbers DE-NA0001944 and performed under the auspices of the LLNL under Contract No. DE-AC52-07NA27344. [Preview Abstract] |
Wednesday, November 2, 2016 11:42AM - 11:54AM |
NO5.00012: Measurements of Sensitivity of Implosion-Phase Mixing to Low-Mode Symmetry at the National Ignition Facility S.A. MacLaren, D.B. Sayre, S.F. Khan, T. Ma, R.E. Tipton, J.E. Pino, J.D. Salmonson, J.E. Ralph, J.R. Rygg, D.T. Casey, G.A. Kyrala The 2-Shock platform at the National Ignition Facility (NIF) is a non-igniting indirect-drive target designed to produce a near 1D-like implosion for hydro-code validation.~ This is accomplished with a sub-scale (675 \textmu m radius) capsule in a nominal (2.875 mm radius) near-vacuum hohlraum, providing a case-to-capsule ratio 63{\%} larger that that of a standard ignition target.~ Additionally, the low aspect ratio (3.9) of the capsule shell combined with the temperature of the foot pulse essentially eliminates ablation front instability growth.~ The result is a platform that is well suited to the study of mixing at the gas-ablator interface without these complicating factors. A layer of CD plastic on the inner 3.2 \textmu m of the CH capsule shell filled with a mixture of hydrogen and tritium allows us to infer the mixture of ablator material into the gas through the ratio of DT to TT neutron production. In 2015, we used the 2-Shock platform to measure the sensitivity of ablator-gas mixing to inner surface roughness and implosion convergence ratio. ~This year we developed the capability to deliberately adjust the low-mode in-flight symmetry of the implosion in both the prolate and oblate directions. We present the initial results of mix measurements from deliberately low-mode asymmetric implosions aimed at determining the relationship between this type of asymmetry and mix. This work was performed under the auspices of the Lawrence Livermore National Security, LLC, (LLNS) under Contract No. DE-AC52-07NA27344 [Preview Abstract] |
Wednesday, November 2, 2016 11:54AM - 12:06PM |
NO5.00013: 2-Shock layered tuning campaign Laurent Masse, T. Dittrich, S. Khan, G. Kyrala, T. Ma, S. MacLaren, J. Ralph, J. Salmonson, R. Tipton The 2-Shock platform has been developed to maintain shell sphericity throughout the compression phase of an indirect-drive target implosion and produce a stagnating hot spot in a quasi 1D-like manner. A sub-scale, \textasciitilde 1700 \textunderscore m outer diameter, and thick, \textasciitilde 200 \textunderscore m, uniformly Silicon doped, gas-filled plastic capsule is driven inside a nominal size 5750 \textunderscore m diameter ignition hohlraum. The hohlraum fill is near vacuum to reduce back-scatter and improve laser/drive coupling. A two-shock pulse of about 1 MJ of laser energy drives the capsule. The thick capsule prevents ablation front feed-through to the imploded core. This platform has demonstrated its efficiency to tune a predictable and reproducible 1-D implosion with a nearly round shape [1]. It has been shown that the high foot performance was dominated by the local defect growth due to the ablation front instability and by the hohlraum radiation asymmetries. The idea here is to take advantage of this 2-Shock platform to design a 1D-like layered implosion and eliminates the deleterious effects of radiation asymmetries and ablation front instability growth. We present the design work and our first experimental results of this near one-dimensional 2-Shock layered design. This work was performed under the auspices of the Lawrence Livermore National Security, LLC, (LLNS) under Contract No. DE-AC52-07NA27344 [1] S. Khan et al, Phys. Plasmas \textbf{23}, 042708 (2016) [Preview Abstract] |
Wednesday, November 2, 2016 12:06PM - 12:18PM |
NO5.00014: Simulations of 2-shock Convergence Scan Shots Paul Bradley, R.E. Olson, J.L. Kline, S.A. MacLaren, T. Ma, J.D. Salmonson, G.A. Kyrala, J. Pino, E. Dewald, S. Khan, D. Sayre, J. Ralph, D. Turnbull The 2-shock campaign is a joint Los Alamos/Livermore project to investigate the role of shock timing, asymmetry, and shock convergence on the performance of ignition relevant capsules. This campaign uses a simple two step pulse that makes it easier to correlate the effect of changing the laser pulse on the performance of the capsule. The \textasciitilde 680 micron outer radius capsule has a CH$+$1 at{\%} Si ablator approximately 175 microns thick surrounding a DD or HT gas region with fill densities between 0.0085 and 0.00094 g/cc. The capsules are indirectly driven inside a gold hohlraum that is 9.2 mm long by 5.75 mm in diameter. Some capsules had about 3 microns of CD on the inner surface. The CD inner surface capsules utilized HT fuel so that the DT yield arises from mixing of CD shell material into the tritium of the gas region. Our simulated results compare well to the experimental yield, ion temperature, burn width, x-ray size, convergence ratio, and radius versus time data. Work performed by Los Alamos National Laboratory under contract DE-AC52-06NA25396 for the National Nuclear Security Administration of the U.S. Department of Energy. [Preview Abstract] |
Wednesday, November 2, 2016 12:18PM - 12:30PM |
NO5.00015: The Bigfoot Drive; Experimental Results Kevin Baker, Cliff Thomas, Shahab khan, Daniel Casey, Brian Spears, Ryan Nora, Davis Munro, David Eder, Jose Milovich, Dick Berger, David Strozzi, Clement Goyon, David Turnbull, Tammy Ma, Nobuhiko Izumi, Robin Benedetti, Marius Millot, Peter Celliers, Charles Yeamans, Robert Hatarik, Nino Landen, Omar Hurricane, Debbie Callahan The Bigfoot platform was developed on the National Ignition Facility to investigate low convergence, high adiabat, high rhoR hotspot implosions. This platform was designed to be less susceptible to wall motion, LPI and CBET and to be more robust against capsule hydrodynamic instabilities. To date experimental studies have been carried out at two hohlraum scales, a 5.75 and 5.4 mm diameter hohlraum. We will present experimental results from these tuning campaigns including the shape vs. cone fraction, surrogacy comparisons of self-emission from the capsules vs. radiography of the imploding capsule and doped vs. undoped capsules. Prepared by LLNL under Contract DE-AC52-07NA27344. [Preview Abstract] |
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