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 JO8: Fast Ignition and HED Kinetic Effects |
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Chair: Wolfgang Theobald, Laboratory for Laser Energetics Room: 212 CD |
Tuesday, November 1, 2016 2:00PM - 2:12PM |
JO8.00001: Probing kinetic and multi-ion-fluid effects in ICF implosions using DT and D}$^{\mathrm{\mathbf{3}}}$\textbf{He reaction histories on OMEGA H.W. Sio, J.A. Frenje, M. Gatu Johnson, C.K. Li, R.D. Petrasso, J. Katz, C. Stoeckl, T. Kwan, A. Le, C. Bellei To explore kinetic and multi-ion-fluid effects in D$^{\mathrm{3}}$He-gas-filled shock-driven implosions (with a trace amount of T$_{\mathrm{2}})$, D$^{\mathrm{3}}$He and DT reaction histories were measured using the upgraded Particle X-ray Temporal Diagnostic (PXTD) on OMEGA. The relative timing between the D$^{\mathrm{3}}$He and DT reaction histories was measured with 10-ps precision. The initial gas-fill density of the thin-glass targets was varied from 0.3 -- 2.2 mg/cc, spanning highly-kinetic to more hydrodynamic-like plasma conditions during shock burn. Multi-ion-fluid simulations of similar implosions show reaction histories that are quantitatively different than those from average-ion-fluid simulations, including differences in burn onset, burn width, and relative bang-time. The measured differences between the reaction histories will be contrasted to average-ion-fluid hydrodynamic simulations, as well as multi-ion-fluid and kinetic-ion simulations, using LSP. [Preview Abstract] |
Tuesday, November 1, 2016 2:12PM - 2:24PM |
JO8.00002: Changes in Concentrations of Plasma ION-Components In Hotspot Driven By Thermodynamic Forces and their Effects on Implosions D. Ho, G. Zimmerman, G. Kagan, P. Amendt, H. Rinderknecht, S. Haan, J. Perkins, J. Salmonson Changes in relative concentrations of plasma ion components driven by gradients of mass concentration, pressure, and temperature gradients, occur during shock flash and subsequent hotspot formation. This is a universal phenomenon in all laboratory implosions with two-ion component fuels, e.g., DT and D$^{\mathrm{3}}$He, occurring in the central region of the hotspot. Concentration differentials lead to noticeable yield reduction in Omega exploding pusher implosions, but not in NIF ``Symcaps'' where radiation-hydrodynamics simulations are in agreement with shot data. For all our ignition capsules designs that use a high-density carbon ablator and DT fuel adiabat $\alpha $ ranging from 1.5 to 4, substantial concentration differentials occur around shock flash but they are relaxed by the time of ignition resulting in no simulated yield degradation. We will provide explanations and present simulation results for this phenomenon. [Preview Abstract] |
Tuesday, November 1, 2016 2:24PM - 2:36PM |
JO8.00003: Measurements of Deuterium--Tritium Fuel Fractionation from Kinetic Effects in Ignition-Relevant Direct-Drive Cryogenic Implosions C. Forrest, V.Yu. Glebov, J.P. Knauer, P.B. Radha, S.P. Regan, T.C. Sangster, C. Stoeckl Measurements of DT and DD reaction yields have been studied using ignition-relevant, cryogenically cooled deuterium--tritium gas-filled cryogenic DT targets in inertial confinement fusion (ICF) implosions. In these experiments, carried out at the Omega Laser Facility,\footnote{T. R. Boehly\textit{ et al.}, Opt. Commun. \textbf{133}, 495 (1997).\par } high{\-}resolution time-of-flight spectroscopy was used to measure the primary neutron peak distribution required to infer the DT and DD reaction yields. From these measurements, it will be shown that the yield ratio has a $\chi $2/per degree of freedom of 0.67 as compared with the measured fraction of the target fuel composition. This observation indicates that kinetic effects leading to species separation are insignificant in ICF ignition-relevant DT implosions on OMEGA. This material is based upon work supported by the Department Of Energy National Nuclear Security Administration under Award Number DE{\-}NA0001944. [Preview Abstract] |
Tuesday, November 1, 2016 2:36PM - 2:48PM |
JO8.00004: Kinetic study of run-away burn in ICF capsule using a quasi-1D model Chengkun Huang, K. Molvig, B. J. Albright, E. S. Dodd, N. M. Hoffman, E. L. Vold, G. Kagan The effect of reduced fusion reactivity resulting from the loss of fuel ions in the Gamow peak in the ignition, run-away burn and disassembly stages of an inertial confinement fusion D-T capsule is investigated with a quasi-1D hybrid model that includes kinetic ions, fluid electrons and Planckian radiation photons. The fuel ion loss through the Knudsen effect at the fuel-pusher interface is accounted for by a local-loss model developed in Molvig et al. [Phys. Rev. Lett. 109, 095001 (2012)]. The tail refilling and relaxation of the fuel ion distribution are evolved with a nonlinear Fokker-Planck solver. The Krokhin & Rozanov model is used for the finite alpha range beyond the fuel region, while alpha heating to the fuel ions and the fluid electrons is modeled kinetically. For an energetic pusher (~40kJ), the simulation shows that the reduced fusion reactivity can lead to substantially lower ion temperature during run-away burn, while the final yield decreases more modestly. Possible improvements to the present model, including the non-Planckian radiation emission and alpha-driven fuel disassembly, are discussed. [Preview Abstract] |
Tuesday, November 1, 2016 2:48PM - 3:00PM |
JO8.00005: Numerical solution of the quantum Lenard-Balescu equation for non-degenerate plasmas Frank Graziani, Christian Scullard, Andrew Belt, Susan Fennell, Marija Jankovic, Nathan Ng, Susana Serna For weakly-coupled plasmas, time-dependent non-equilibrium effects are usually studied by numerically solving the Landau equation in Fokker-Planck form. This system requires an input Coulomb logarithm, which adds a level of ambiguity to the calculation that can only be remedied by considering a more sophisticated collision operator. We have recently developed a spectral method for numerically solving the quantum Lenard-Balescu equation, which includes the effects of both quantum diffraction and dynamic screening, eliminating the divergences that require an input Coulomb logarithm. Our method allows a fast and accurate integration over the dielectric function for general non-equilibrium distributions. I will present calculations on various systems, including one- and two-component plasmas, and comparisons with the Landau equation. I will also discuss future prospects for the method. [Preview Abstract] |
Tuesday, November 1, 2016 3:00PM - 3:12PM |
JO8.00006: Analytic insights into nonlocal energy flux in laser fusion targets Wallace Manheimer, Denis Cotombant, Andrew Schmitt There have been several attempts to utilize a Krook model in a laser implosion simulation to study the effects of nonlocal transport of energetic electrons (1-4). Frequently these numerical studies give different and even contradictory results. As these studies use complex radiation hydrodynamics codes, with many processes simultaneously going on, there is little understanding of the various results. The results differ for two reasons, first, differences in the mathematical formulation; and second, differences in the numerical methods. This presents what hopefully will be a much-improved formulation, including a proper model for the Coulomb logarithm where it describes energetic particle collisions in the cool regions of the plasma. It presents analytic insights and simple calculations, which can be used as a check on the numerical results, and discusses various difficulties of implementation. \\1. G. Schurtz et al. Phys.Plasmas, 7, 4238, (2000), 2. W. Manheimer et al, Phys. Plasmas, 15, 083103, (2008), 3. A. Marrochino et al, Phys,. Plasmas, 20, 022702, (2013), 4. D. Cao et al, Phys. Plasmas, 22, 082308, (2015). Work supported by US DoE N [Preview Abstract] |
Tuesday, November 1, 2016 3:12PM - 3:24PM |
JO8.00007: Development of a PDXP platform on NIF Heather Whitley, Marilyn Schneider, Warren Garbett, Jesse Pino, Ronnie Shepherd, Colin Brown, John Castor, Howard Scott, C. Leland Ellison, Lorin Benedict, Hong Sio, Brandon Lahmann, Richard Petrasso, Frank Graziani Over the past several years, we have conducted theoretical investigations of electron-ion coupling and electronic transport in plasmas. In the regime of weakly coupled plasmas, we have identified models that we believe describe the physics well, but experimental measurements are still needed to validate the models. We are developing spectroscopic experiments to study electron-ion equilibration and electron heat transport using a polar direct drive exploding pusher (PDXP) platform at the National Ignition Facility (NIF). Initial measurements are focused on characterizing the laser-target coupling, symmetry of the PDXP implosion, and overall neutron and x-ray signals. We present images from the first set of shots and make comparisons with simulations from ARES and discuss next steps in the platform development. Prepared by LLNL under Contract DE-AC52-07NA27344. LLNL-ABS-697489 [Preview Abstract] |
Tuesday, November 1, 2016 3:24PM - 3:36PM |
JO8.00008: Measurements of Ion Stopping around the Bragg Peak in High-Energy-Density Plasmas (HEDP) J. Frenje, C.K. Li, F.H. Seguin, M. Gatu Johnson, R. Petrasso, T. Nagayama, R. Mancini, R. Hernandez, P. Grabowski, V. Yu Glebov Ion stopping around the Bragg peak and its dependence on plasma conditions was recently measured for the first time in HEDP [1]. The data support most stopping-power models for ion velocities (vi) larger than the average velocity of the thermal electrons (vth), but there are some differences at vi\textasciitilde vth, which could not be validated. The work described here makes significant advances over the first experimental effort by quantitatively assessing the characteristics of the ion stopping around the Bragg peak while at the same time more accurately characterizing the plasma conditions. This effort represents the most sensitive test of plasma-stopping-power models around the Bragg peak to date, which is an important first step in our efforts of getting a fundamental understanding of DT-alpha stopping in HEDP, a prerequisite for understanding ignition margins in various implosion designs. The work was performed under NLUF and supported by DOE, LLNL and LLE. [1] Frenje et al., PRL (2015). [Preview Abstract] |
Tuesday, November 1, 2016 3:36PM - 3:48PM |
JO8.00009: Extracting the Electron-Ion Temperature Relaxation Rate from Ion Stopping Experiments Paul E. Grabowski, Johan A. Frenje, Lorin X. Benedict Direct measurement of i-e equilibration rates at ICF-relevant conditions is a big challenge, as it is difficult to differentiate from other sinks and sources of energy, such as heat conduction and pdV work. Another method is to use information from ion stopping experiments. Such experiments [Frenje et al, PRL {\bf 115}, 205001 (2015)] at the OMEGA laser have made precision energy loss measurements of fusion products at these conditions. Combined with the multimonochromatic x-ray imager technique [Nagayama et al, J. Appl. Phys. {\bf 109}, 093303 (2011); Phys. Plasmas {\bf 19}, 082705 (2012); {\bf 21}, 050702 (2014)], which gives temporally and spatially resolved electron temperature and density, we have a robust stopping experiment. We propose to use such stopping measurements to assess the i-e temperature relaxation rate, since both processes involve energy exchange between electrons and ions. We require that the fusion products are 1) much faster than the thermal ions so that i-i collisions are negligible compared to i-e collisions and 2) slower than the thermal electrons so that the stopping obeys a linear friction law. Then the Coulomb logarithms associated with ion stopping and i-e temperature relaxation rate are identical and a measurement of the former provides the latter. [Preview Abstract] |
Tuesday, November 1, 2016 3:48PM - 4:00PM |
JO8.00010: Two-Dimensional Simulations of Electron Shock Ignition at the Megajoule Scale W. Shang, R. Betti Shock ignition uses a late strong shock to ignite the hot spot of an inertial confinement fusion capsule. In the standard shock-ignition scheme, an ignitor shock is launched by the ablation pressure from a spike in laser intensity. Recent experiments on OMEGA\footnote{R. Nora\textit{ et al.}, Phys. Rev. Lett. \textbf{114}, 045001 (2015); W. Theobald\textit{ et al.}, Phys. Plasmas \textbf{22}, 056310 (2015).} have shown that focused beams with intensity up to $6\times 10^{15}{\mbox{W}} \mathord{\left/ {\vphantom {{\mbox{W}} {\mbox{cm}^{2}}}} \right. \kern-\nulldelimiterspace} {\mbox{cm}^{2}}$ can produce copious amounts of hot electrons. The hot electrons are produced by laser--plasma instabilities (LPI's) and can carry up to $\sim 15\% $ of the instantaneous laser power. Megajoule-scale targets will likely produce even more hot electrons because of the large plasma scale length. We show that it is possible to design ignition targets with low implosion velocities that can be shock ignited using LPI-generated hot electrons to obtain high energy gains. These designs are robust to low-mode asymmetries and they ignite even for highly distorted implosions. Electron shock ignition requires tens of kilojoules of hot electrons, which can only be produced on a large laser facility like the National Ignition Facility. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Tuesday, November 1, 2016 4:00PM - 4:12PM |
JO8.00011: Study of hot electron spatial energy deposition in spherical targets relevant to shock ignition Shu Zhang, M.S. Wei, C. Krauland, H. Reynolds, M. Hoppe, J. Peebles, F.N. Beg, W. Theobald, E. Borwick, J. Li, C. Ren, C. Stoeckl, W. Seka, R. Betti, M. Campbell Understanding hot electron generation and coupling is important for the high-intensity shock ignition (SI) inertial confinement fusion concept. Recent hard x-ray experimental data from a SI-relevant platform on OMEGA-60 suggest that \textless 100 keV hot electrons may augment shock pressure by depositing their energy in the solid density region behind the ablation front [1]. These results deduced from simulation are convincing support for electron assisted SI. To further investigate beneficial hot electron characteristics from both high intensity UV and IR lasers in this relevant regime, we performed a joint OMEGA-60/OMEGA EP experiment in the spherical geometry. 60 UV laser beams (18 kJ, 1.8 ns, up to 10$^{\mathrm{15}}$ W/cm$^{\mathrm{2}})$ irradiated a low-density Cu foam ball target with a CH ablator followed by a single IR short pulse laser (2.6 kJ, 100 ps, 10$^{\mathrm{17}}$ W/cm$^{\mathrm{2}})$ at various delays. The electron spatial energy deposition was diagnosed via imaging Cu K$\alpha $ emission with a spherical crystal imager; total K$\alpha $ photon yield and bremsstrahlung radiation were also measured to infer electron spectra. Experimental results are compared with radiation hydrodynamic modeling and will be presented at the meeting. [1] W. Theobald et al., Phys. Plasmas 22, 056310 (2015). [Preview Abstract] |
Tuesday, November 1, 2016 4:12PM - 4:24PM |
JO8.00012: Hot electron generation and energy coupling in planar experiments with shock ignition high intensity lasers M.S. Wei, C. Krauland, N. Alexander, S. Zhang, J. Peebles, F.N. Beg, W. Theobald, E. Borwick, C. Ren, R. Yan, D. Haberberger, R. Betti, E.M. Campbell Hot electrons produced in nonlinear laser plasma interactions are critical issues for shock ignition (SI) laser fusion. We conducted planar target experiments to characterize hot electron and energy coupling using the high energy OMEGA EP laser system at SI high intensities. Targets were multilayered foils consisting of an ablator (either plastic or lithium) and a Cu layer to facilitate hot electron detection via fluorescence and bremsstrahlung measurements. The target was first irradiated by multi-kJ, low-intensity UV beams to produce a SI-relevant mm-scale hot ($\sim $1 keV) preformed plasma. The main interaction pulse, either a kJ 1-ns UV pulse with intensity $\sim $1.6x10$^{\mathrm{16}}$ Wcm$^{\mathrm{-2}}$ or a kJ 0.1-ns IR pulse with intensity up to $\sim $2x10$^{\mathrm{17}}$ Wcm$^{\mathrm{-2}}$was injected at varied timing delays. The high intensity IR beam was found to strongly interact with underdense plasmas breaking into many filaments near the quarter critical density region followed by propagation of those filaments to critical density, producing hot electrons with T$_{\mathrm{hot}}\sim $70 keV in a well-contained beam. While the high intensity UV beam showed poor energy coupling. Details of the experiments and the complementary PIC modeling results will be presented. [Preview Abstract] |
Tuesday, November 1, 2016 4:24PM - 4:36PM |
JO8.00013: New Developments in Auxiliary Heating Peter Norreys The role of heating arising from the propagation of orthogonal petawatt-laser driven relativistic electron beams in dense plasma will be discussed. The energy cascade mechanism begins first with the rapid growth at 45 degrees to the two beams of electrostatic waves near the electron plasma frequency. These waves reach high amplitudes and break, which then results in the generation of a strongly driven turbulent Langmuir spectrum. Parametric decay of these waves, particularly via the modulational instability, then gives rise to a coupled turbulent ion acoustic spectrum. The resulting waves also give rise to ion heating through collisions via equilibration of both electrons and ions. In this talk, I will present the most recent analytic modelling, and particle-in-cell / Vlasov-Poisson simulation results from my team within Oxford Physics and the Central Laser Facility that explores the optimum parameter space for this process, focusing in particular on the requirements for auxiliary heating of the central hot spot in inertial confinement fusion target experiments. I will also describe new methods for hole-boring through the coronal plasma surrounding the fuel using strongly relativistic laser beams that demonstrates the strong suppression of the hosing instability under these conditions. Proof-of-concept experiments are under design for the Orion and OMEGA EP facilities. [Preview Abstract] |
Tuesday, November 1, 2016 4:36PM - 4:48PM |
JO8.00014: Diffusion of external magnetic fields into the cone-in-shell target in the fast ignition Atsushi Sunahara, Tomoyui Johzaki, Hideo Nagatomo, Shouhei Sakata, Kazuki Matsuo, Seungho Lee, Shinsuke Fujioka, Hiroyuki Shiraga, Hiroshi Azechi We simulated the diffusion of externally applied magnetic fields into cone-in-shell target in the fast ignition. In this ignition scheme, the externally magnetic fields up to kilo-Tesla is used to guide fast electrons to the high-dense imploded core, and understanding diffusion of the magnetic field is one of the key issues for increasing the coupling efficiency from the heating laser to the imploded core plasma. In order to study the profile of the magnetic field, we have developed 2D cylindrical Maxwell equation solver with Ohm’s law, and carried out simulations of diffusion of externally applied magnetic fields into a cone-in-shell target. Also, we estimated the conductivity of the cone and shell target based on the assumption of Saha-ionization equilibrium. We present our results of temporal evolution of the magnetic field and its diffusion into the cone and shell target. We also show that the target is heated by the eddy current. Because of the temperature dependence of the conductivity, the magnetic fields diffuse into the material with varying conductivity. Consequently, the magnetic fields into the cone-in-shell target depend on the temporal profile of the magnetic fields as well as the electrical and thermal properties of the material. [Preview Abstract] |
Tuesday, November 1, 2016 4:48PM - 5:00PM |
JO8.00015: Particle-in-Cell Simulations of Nonlinear Laser–Plasma Interactions and Hot-Electron Generations in the Shock-Ignition Regime R. Yan, E. Borwick, R. Betti, J. Li, W. Theobald, C. Ren, C. Krauland, M. S. Wei, S. Zhang, F. N. Beg We performed particle-in-cell (PIC) simulations with parameters relevant to laser–plasma interaction (LPI) experiments on OMEGA EP using high laser intensities ($10^{16}$ to $10^{17} W/cm^2$). Rich physics were observed in this new LPI regime, including laser filamentation and plasma cavitation, plasma waves beyond the Landau cutoff, and significant pump depletion. We will also compare hot-electron generation from the simulations with the experimental measurements. This material is based upon work supported by the Department of Energy under Grant No. DE-SC0012316; by NSF under Grant No. PHY-1314734; and by Laboratory for Laser Energetics. The research used resources of the National Energy Research Scientific Computing Center. [Preview Abstract] |
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