Bulletin of the American Physical Society
56th Annual Meeting of the APS Division of Plasma Physics
Volume 59, Number 15
Monday–Friday, October 27–31, 2014; New Orleans, Louisiana
Session TO4: Compression and Burn III |
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Chair: Bruce Remington, Lawrence Livermore National Laboratory Room: Salon E |
Thursday, October 30, 2014 9:30AM - 9:42AM |
TO4.00001: Time-Resolved Imaging of Cryogenic Target X-Ray Emission at Peak Compression on OMEGA F.J. Marshall, J.A. Delettrez, R. Epstein, V.N. Goncharov, D.T. Michel, T.C. Sangster, C. Stoeckl This talk will describe the measurements of cryogenic target region size and time history inferred from the combination of a high-speed x-ray framing camera and two time-integrating x-ray microscopes. The high-speed framing camera infers the time of peak stagnation from pinhole images taken at 30-ps time intervals with 30-ps frame times and with $\sim$ 15$\mu$m resolution. The two Kirkpatrick--Baez-type x-ray microscopes have spatial resolutions of $\sim$ 5$\mu$m and $\sim$ 7$\mu$m respectively, and are currently time integrating. The inferred x-ray core size and emission time interval will be compared to the measured neutron emission time and to simulations of the experiments. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Thursday, October 30, 2014 9:42AM - 9:54AM |
TO4.00002: Correlations of Multiple Ion-Temperature Measurements with Shot Parameters in DT Cryogenic Implosions on OMEGA V.Yu. Glebov, C.J. Forrest, T.C. Sangster, C. Stoeckl Several neutron time-of-flight (nTOF) detectors installed at different lines of sight (LOS) are used to measure neutron-averaged ion temperature in direct-drive DT implosions on the OMEGA laser. The measurement precision of the ion temperature in different LOS for ambient targets is less than 4{\%} rms. In DT cryogenic implosions, however, the ratio of the ion temperature measured in different LOS can vary by a factor of 2. Correlations of the ion-temperature difference with parameters such as target offset, beam power balance, and phase plates in DT cryogenic implosions on OMEGA will be presented. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Thursday, October 30, 2014 9:54AM - 10:06AM |
TO4.00003: Ultraviolet Thomson Scattering from Direct-Drive Coronal Plasmas in Multilayer Targets R.J. Henchen, V.N. Goncharov, D.T. Michel, R.K. Follett, J. Katz, D.H. Froula Ultraviolet ($\lambda_{4\omega} = $ 263 nm) Thomson scattering (TS) was used to probe ion-acoustic waves (IAW's) and electron plasma waves (EPW's) from direct-drive coronal plasmas. Fifty-nine drive beams ($\lambda_{3\omega} = $ 351 nm) illuminate a spherical target with a radius of $\sim 860 \mu$m. A series of experiments studied the effect of higher electron temperature near the 3$\omega $ quarter-critical surface ($\sim 2.5 \times 10^{21}$ cm$^{-3}$) on laser--plasma interactions resulting from a Si layer in the target. Electron temperatures and densities were measured from 150 to 400 $\mu$m from the initial target surface. Standard CH shells were compared to two-layered shells of CH and Si and three-layered shells of CH, Si, and CH. These multilayer targets have less hot-electron energy than standard CH shells as a result of higher electron temperature in the coronal plasmas. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Thursday, October 30, 2014 10:06AM - 10:18AM |
TO4.00004: Fast-Electron Temperature Measurements in Laser Irradiation at $10^{14}$ W/cm$^2$ A.A. Solodov, B. Yaakobi, J.F. Myatt, C. Stoeckl, D.H. Froula The temperature $T$ of the fast electrons in planar-target irradiation using 2-ns UV pulses at $10^{14}$ W/cm$^2$ was measured on the OMEGA EP laser using the bremsstrahlung radiation [hard x-ray (HXR)] and the K$_{\alpha }$ radiation from high-$Z$ signature layers. The HXR was measured by a nine-channel filter spectrometer [hard x-ray image plate (HXIP)]. Two types of experiments used the K$_{\alpha }$ radiation. The first used a thick Mo (or Ag) target and the ratio of K$_{\alpha }$ emitted toward the front and the back of the target, measured and simulated by a Monte Carlo (MC) code. The ratio decreases with increasing $T$ (since K$_{\alpha }$ is emitted deeper in the foil and therefore absorbed less on the way back out). The second type used a target composed of five consecutive-$Z$ layers (Nb, Mo, Rh, Pd, Ag) and K$_{\alpha}$ lines emitted from the back (highest-$Z)$, measured and simulated by the MC code. For higher temperatures, the K$_{\alpha }$ energy decreases more slowly with $Z$. All of these measurements agree with each other. However, a three-channel scintillation photomultiplier system systematically yields higher temperatures. This indicates a higher-energy radiation component that is not detected by the HXIP because of the sharp drop in image plate (IP) sensitivity. Extending the HXIP detection to higher energies (using K$_{\alpha }$ fluorescence, for which the IP sensitivity is high) is planned. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Thursday, October 30, 2014 10:18AM - 10:30AM |
TO4.00005: Measurements of charged-particle stopping around the Bragg peak in OMEGA ICF plasmas J. Frenje, C.K. Li, F. Seguin, A. Zylstra, R. Petrasso, P. Grabowski, R. Mancini, S. Regan, J. Delettrez, V. Glebov, T. Sangster We report on measurements of charged-particle stopping around the Bragg peak in plasmas relevant to Inertial Confinement Fusion (ICF). The energy loss of DD-tritons, DD-protons, D3He-alphas and D3He-protons, which are ideal particles for validating approximations to the ion-electron collision operator, have been measured in D$^{3}$He gas-filled filled implosions. These experiments are relevant to alpha-particle transport and heating in hot-sport ignition experiments. As the DD and D3He fusion products span a large range of velocities, these measurements represent the first detailed experimental study of charged-particle stopping, ranging from linear low-velocity stopping, through the Bragg peak, to high-velocity stopping. The results are contrasted to commonly used theories, including the Brown--Preston--Singleton and Li--Petrasso formalisms. The data is also used to rule out theories that neglect quantum diffraction and dynamic screening. This work was supported in part by the US DOE, NLUF, LLE and GA. [Preview Abstract] |
Thursday, October 30, 2014 10:30AM - 10:42AM |
TO4.00006: Observation of variations in the T$+$T neutron spectrum with varying center-of-mass energy M. Gatu Johnson, J.A. Frenje, A. Zylstra, R.D. Petrasso, C. Forrest, V. Yu. Glebov, J.P. Knauer, F.J. Marshall, T. Michel, T.C. Sangster, W. Seka, W. Shmayda, C. Stoeckl, D. Sayre, J.A. Caggiano, D.T. Casey, R. Hatarik, D.P. McNabb, J.E. Pino, A. Bacher, H. Herrmann, Y. Kim, J-.L. Bourgade, O. Landoas, B. Rosse C. BRUNE, Ohio University -- The T$+$T fusion reaction, which produces two neutrons and an alpha particle in a 3-body final state, has been studied in a series of direct-drive, T2-gas-filled thin ($\sim$ 3 $\mu $m) glass-capsule implosions at OMEGA. The shapes of the reaction product spectra are dictated by the final-state interactions between n-$\alpha $ ($^{5}$He in the ground- and excited states) and n-n (di-neutron interaction). The theory behind final-state interactions is not well understood and detailed study of the reaction product spectra can teach us about the intricacies of the nuclear theory involved. In this presentation, measured neutron spectra are interpreted in terms of the sequential decay through $^{5}$He in the ground- and excited states. A clear energy dependence in relative reaction-channel strength at low center-of-mass energy (18-55 keV) is observed in the data. The role of the di-neutron interaction could be more clearly deduced through study of the alpha particle spectrum. In the presentation, we also identify steps required to successfully measure the T$+$T alpha spectrum in future experiments. This work was supported in part by the U.S. DOE, NLUF, LLNL and LLE. [Preview Abstract] |
Thursday, October 30, 2014 10:42AM - 10:54AM |
TO4.00007: Electric Fields Associated with Spherically Converging Shocks in Directly-Driven OMEGA Implosions C.K. Li, A. Zylstra, M.J. Rosenberg, H.G. Rinderknecht, J.A. Frenje, F.H. Seguin, R.D. Petrasso, S.X. Hu, R. Betti, T.C. Sangster, P.A. Amendt, C. Bellei, S.C. Wilks, N.M. Hoffman, A. Nikroo Time-gated, proton radiography provides direct measurements of radial electric fields and their temporal evolution in directly-driven capsule implosions. The experimental data indicate that such fields are associated with a spherically converging shock inside an imploding capsule. The implosions are simulated with the 2D hydrodynamic code DRACO. Several related mechanisms for generating such fields are discussed. The measurements provide physical insight into the structure, strength and dynamics of spherically converging shocks and have important implications in ICF implosion physics. This work was supported in part by the U.S. DOE, NLUF, LLNL and LLE. [Preview Abstract] |
Thursday, October 30, 2014 10:54AM - 11:06AM |
TO4.00008: Studies of $^{3}$He$+^{3}$He, T$+^{3}$He, and p$+$D nuclear reactions relevant to stellar or Big-Bang Nucleosynthesis using ICF plasmas at OMEGA Alex Zylstra, Maria Gatu Johnson, Johan Frenje, Chikang Li, Fredrick Seguin, Hong Sio, Michael Rosenberg, Hans Rinderknecht, Richard Petrasso, Hans Herrmann, Yong Ho Kim, Gerry Hale, Dennis McNabb, Dan Sayre, Jesse Pino, Carl Brune, Andy Bacher, Chad Forrest, Vladimir Glebov, Christian Stoeckl, Roger Janezic, Craig Sangster The $^{3}$He$+^{3}$He, T$+^{3}$He, and p$+$D reactions directly relevant to Stellar or Big-Bang Nucleosynthesis (BBN) have been studied at the OMEGA laser facility using high-temperature low-density `exploding pusher' implosions. The advantage of using these plasmas is that they better mimic astrophysical systems than cold-target accelerator experiments. Measured proton spectra from the $^{3}$He$^{3}$He reaction are used to constrain nuclear R-matrix modeling. The resulting T$+^{3}$He $\gamma $-ray data rule out an anomalously-high $^{6}$Li production during BBN as an explanation to the high observed values in primordial material. The proton spectrum from the T$+^{3}$He reaction is also being used to constrain the R-matrix model. Recent experiments have probed the p$+$D reaction for the first time in a plasma; this reaction is relevant to energy production in protostars, brown dwarfs and at higher CM energies to BBN. [Preview Abstract] |
Thursday, October 30, 2014 11:06AM - 11:18AM |
TO4.00009: Increased shell entropy as an explanation for observed decreased shell areal densities in OMEGA implosions Nelson Hoffman, Hans Herrmann, Yongho Kim A reduced ion-kinetic (RIK) model used in hydrodynamic simulations has had some success in explaining time- and space-averaged observables characterizing the fusion fuel in hot low-density ICF capsule implosions driven by 1-ns 60-beam laser pulses at OMEGA [Rosenberg \textit{et al}., Phys. Rev. Lett. \textbf{112}, 185001 (2014); Rinderknecht \textit{et al}., Phys. Plasmas \textbf{21}, 056311 (2014); Hoffman \textit{et al}., in preparation]. But observables characterizing the capsule shell, e.g., the areal density of $^{12}$C in a plastic shell, have proved harder to explain. Recently we have found that assuming the shell has higher entropy than expected in a 1D laser-driven RIK simulation allows an explanation of the observed values of $^{12}$C areal density, and its dependence on initial shell thickness in a set of DT-filled plastic capsules. If, for example, a 15-$\mu $m CH shell implodes on an adiabat two to three times higher than predicted in a typical unmodified RIK simulation, the calculated burn-averaged shell areal density decreases from $\sim$ 80 mg/cm$^{2}$ in the unmodified simulation to the observed value of $\sim$ 25 mg/cm$^{2}$. We discuss possible mechanisms that could lead to increased entropy in such implosions. [Preview Abstract] |
Thursday, October 30, 2014 11:18AM - 11:30AM |
TO4.00010: Predictions of secondary reactions, areal densities and hot-spot radii for Omega capsule implosions M.J. Schmitt, H.W. Herrmann, Y.H. Kim, N.S. Krasheninnikova, S.M. Sepke The radial density profile of an imploding capsule at the time of fusion burn is an important factor in determining the characteristics of the imploded shell and the conditions in the hot burning core. We have simulated a set of deuterium-filled Hoppe glass (SiO$_{\mathrm{2}})$ capsule implosions using Hydra and predicted the fraction of secondary protons ($^{\mathrm{3}}$He$+$D$\to $p[14.7MeV]$+^{\mathrm{4}}$He) and neutrons (T$+$D$\to $n[14.1MeV]$+^{\mathrm{4}}$He) that are generated. The importance of using the downshift of secondary reaction protons for diagnosing capsule areal density is well known. We show how the conversion efficiency changes with variations to the capsule gas fill. A strong correlation between the downshift of the secondary protons with respect to the areal density of the shell, i.e. the $\rho R$, at the time of peak burn is predicted. Predictions for primary and secondary yield variations for alternate gas fills including binary mixtures of H$_{\mathrm{2}}$, D$_{\mathrm{2}}$, $^{\mathrm{3}}$He and $^{\mathrm{4}}$He also will be shown. Synthetic self-emission diagnosis of the implosion trajectory will be compared to the radial temperature profile to assess the accuracy of hot spot measurement at the time of nuclear burn. The variation in the temporal burn profile, including the variation of three burn peak components will be discussed. [Preview Abstract] |
Thursday, October 30, 2014 11:30AM - 11:42AM |
TO4.00011: Inferring multiple ion temperatures and fluid velocities from neutron spectra Brian Appelbe, Jeremy Chittenden Thermal broadening of the DD and DT neutron spectra is a common method for measuring ion temperature. However, recent work has shown that bulk motion of the fuel in ICF capsule implosions can also have a broadening effect on the emitted spectra. This can lead to errors in ion temperature estimates. In this presentation we show that, in addition, the neutron spectra emitted by non-igniting ICF plasmas are not dominated by a single ion temperature or velocity but are the superposition of component spectra produced by regions of the plasma with a wide variation of densities, temperatures and fluid velocities. In order to identify the different component spectra, it is necessary to analyze the overall shape of the spectra and not just the width. We develop a Maximum Likelihood Estimator (MLE) algorithm for analyzing the emitted spectra which allows us to identify multiple temperatures and fluid velocities and the relative density of these components. The algorithm works by finding a best fit to the emitted spectra for a specified number of components. It allows us to estimate the range of temperatures and fluid velocities which make significant contributions to the neutron spectra and estimate the peak ion temperatures achieved in the experiment. The algorithm is tested using 3D simulations of imploding capsules. [Preview Abstract] |
Thursday, October 30, 2014 11:42AM - 11:54AM |
TO4.00012: On thermonuclear ignition criterion at the National Ignition Facility Baolian Cheng, Thomas Kwan, Yi-Ming Wang, Steven Batha A novel analytical model [1] for thermonuclear burn (TN) in inertial confinement fusion capsules is derived from fundamental physics principles and is found to be consistent with available experimental data. Based on the model, we obtained a general thermonuclear ignition criterion in terms of the areal density and temperature of the hot fuel. This newly derived TN ignition threshold and its alternative forms explicitly show the minimum requirements of the hot fuel pressure, mass, areal density, and burn fraction for achieving ignition. Comparison of our criterion with existing theories, simulations, and the National Ignition Facility (NIF) experimental data show that our ignition threshold is more stringent than those in existing literature and that our results are consistent and compare well with the NIF experimental data. Model applications to various inertial confinement fusion capsules and differences between our model and others are discussed. \\[4pt] [1] B. Cheng, T. J. T. Kwan, Y.M. Wang, and S. H. Batha, LA-UR-14-14110, 2014. [Preview Abstract] |
Thursday, October 30, 2014 11:54AM - 12:06PM |
TO4.00013: Applying the minimal energy scaling law to NIF data Yi-Ming Wang, Baolian Cheng, Thomas Kwan, Steven Batha The minimal energy implosion-scaling model [1] was recently developed to characterize the physical properties of the hot spot in terms of the peak implosion energy. In this model, the hot spot energy, volume, pressure, mass and areal density at the stagnation time are uniquely determined by the peak implosion velocity, the equation of state and the adiabat of the pusher and the DT fuel (cold and hot) at the peak implosion time. In this work, we apply this model to a number of published low-foot and high-foot experiments performed at the National Ignition Facility. Our model analysis is in a good agreement with the experimental data when a high adiabat is assumed for both low and high foot experiments. Implications of the results are discussed. 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. \\[4pt] [1] B. Cheng, T. Kwan, Y-M. Wang, and S. Batha, Scaling laws for NIF ignition from first principles, Phys. Rev. E 88 (2013) 041101. [Preview Abstract] |
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