Bulletin of the American Physical Society
55th Annual Meeting of the APS Division of Plasma Physics
Volume 58, Number 16
Monday–Friday, November 11–15, 2013; Denver, Colorado
Session JO6: Kinetic Effects and Computer Simulations |
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Chair: Claudio Belli, Lawrence Livermore National Laboratory Room: Governor's Square 11 |
Tuesday, November 12, 2013 2:00PM - 2:12PM |
JO6.00001: On the onset of kinetic effects in ICF implosions Peter Amendt, Claudio Bellei, Scott Wilks, Chikang Li, Hans Rinderknecht, Michael Rosenberg, Hong Sio, Richard Petrasso Central hot spot ignition requires the careful sequencing of several shocks that coalesce in the gaseous deuterium-tritium fuel to form a high Mach number shock. Near the instant of shock convergence at the origin (or ``shock flash''), the ion mean free path may be a significant fraction of the hot spot radius, leading to a potential violation of the fluid approximation that generally underlies mainline radiation-hydrodynamic simulation tools. Understanding this physical regime may have consequences on subsequent hot spot formation and ignition performance margins. Recent data obtained on the Omega laser facility point to a transition in direct-drive exploding pusher implosion behavior below a threshold pressure where the ion mean free path is on the order of the fuel radius at shock flash [1]. Adaptation of a Guderley-type shock solution in a converging geometry to include finite mean-free-path effects is undertaken to understand this kinetic regime. \\[4pt] [1] Courtesy of M. Rosenberg, Ph.D. candidate [Preview Abstract] |
Tuesday, November 12, 2013 2:12PM - 2:24PM |
JO6.00002: Multi-species effects in inertially confined plasmas Grigory Kagan, Xian-Zhu Tang Inertial confinement fusion (ICF) implosions are routinely modeled with single-fluid codes. Individual dynamics of the fuel constituents is not resolved; only the overall pressure, density and fluid velocity are evolved, though electron and ion temperatures are often distinguished. An obvious weakness of such an approach is impossibility to predict relative concentrations of multiple ion species that are to undergo fusion reactions. Multi-fluid plasma formalism, consistently capturing the physics behind and consequences of the relative motion of ion species, is presented. Implications for the ICF implosions are discussed. [Preview Abstract] |
Tuesday, November 12, 2013 2:24PM - 2:36PM |
JO6.00003: Validating kinetic models in a fluid code using data from high-Knudsen-number capsule implosions N. Hoffman, K. Molvig, E. Dodd, B. Albright, A. Simakov, G. Zimmerman, M. Rosenberg, H. Rinderknecht, H. Sio, A. Zylstra, N. Sinenian, M. Gatu Johnson, F. Seguin, J. Frenje, C.K. Li, R. Petrasso, V. Glebov, C. Stoeckl, W. Seka, C. Sangster We validate models of (a) ion diffusion and (b) fusion reactivity decrease from modified ion-distribution tails [Molvig et al., PRL 109, 095001 (2012)], implemented in a rad-hydro code, using data for five quantities (DD-n yield, D$^{3}$He-p yield, DD burn temperature, bang time, and absorbed energy) from recent thin-shell D$^{3}$He-filled capsules at OMEGA [Boehly et al., Opt. Commun. 133, 495 (1997)]. Four inputs (laser source fraction, electron thermal flux limiter, Knudsen number multiplier, and ion flux multiplier) are varied to find the best fit to the ten observables from two implosions (8-atm fill and 23-atm fill). The calibrated input values can explain the data from a set of other D$^{3}$He implosions with fill pressures from 1 atm to 17 atm (Knudsen numbers from 0.5 to $\sim$6). Using a new transport model for ion loss, we will develop a model of wide validity for OMEGA direct-drive implosions. [Preview Abstract] |
Tuesday, November 12, 2013 2:36PM - 2:48PM |
JO6.00004: ePLAS Studies of Viscous, Kinetic and Transport Effects in Laser ICF Target Dynamics R.J. Mason, R.J. Faehl, R.C. Kirkpatrick Noting that the artificial and/or grid viscosity used for most Laser ICF fluid modeling assumes a cell size much larger than the ion-ion mean free path, while the opposite can be true in many evolving target regions, we explore the effects of a generalized ion viscous treatment, as well as electron-ion charge separation fronts with reflected ions, on target dynamics. Transport effects from an added external B-field are also under consideration. We do this in a fluid context with support from kinetic calculations. We demonstrate results from an enhanced version of the ePLAS [1-3] simulation code that uses either fluid or Krook collisional PIC modeling for multiple ion species, particle, or fluid electrons with thermal flux limitation, interspecies collisional coupling, \textit{E {\&} B}-fields computed by the Implicit Moment Method [1] and a new hybrid method for efficient runs on the ion Courant time scale. \\[4pt] [1] R. J. Mason and C. Cranfill, IEEE Trans. Plasma Sci. \textbf{PS-14,} 45 (1986).\\[0pt] [2] R. J. Mason, Phys. Rev. Lett.\textbf{ 96}, 035001 (2006).\\[0pt] [3] T. Ma, M. H. Key, R. J. Mason, et al., Phys. Plasmas \textbf{16},112702 (2009). [Preview Abstract] |
Tuesday, November 12, 2013 2:48PM - 3:00PM |
JO6.00005: Fermi Acceleration and Fusion Reactivity in Low-$\rho R$ Inertial Fusion Hot Spots B.J. Albright, Kim Molvig, N.M. Hoffman, E.S. Dodd, A.N. Simakov For inertial confinement fusion hot spots at sufficiently low fuel $\rho R$, the ions that dominate the fusion reactivity may be effectively collisionless and the evolution of their distribution functions will be governed by nonlocal, kinetic physics. A simple model based on an analogy with Fermi acceleration of cosmic rays has been developed for the tail populations of these ions. It is found that a fraction of fast ions entering the pusher dominantly pitch-angle scatter in the shell and are isotropized upon reentering the fuel region. After a few encounters with the pusher, the fuel ion distribution functions adopt a common, exponential form scaling with the radial speed of the pusher and varying with the ``albedo'' of the shell to incident ions. Fusion reactivity and inferred hot spot temperature and density have features consistent with recent experimental data and may provide an alternative explanation for reported yield anomalies. [Preview Abstract] |
Tuesday, November 12, 2013 3:00PM - 3:12PM |
JO6.00006: Using combined D$^{3}$He-p and DT-n secondary yields to determine $\rho$R$_{\mathrm{fuel}}$ and mix in D2 implosions at OMEGA and the NIF H. Rinderknecht, M. Rosenberg, A. Zylstra, F. Seguin, J. Frenje, H. Sio, M. Gatu Johnson, N. Sinenian, C.K. Li, R. Petrasso, P. Amendt, S. Wilks, C. Bellei, R. Bionta, M. Moran, J. Caggiano, J. Knauer, R. Hatarik, S. Friedrich, E. Hartouni, S. Hatchett, J. Rygg, D.T. Casey, A. Mackinnon, M. Schneider O. LANDEN LLNL, T. MURPHY, G. KYRALA, M. SCHMITT, N. HOFFMAN LANL, V. YU. GLEBOV, C. SANGSTER, J. DELETTREZ, P. RADHA, S. REGAN, C. STOECKL LLE, J. KILKENNY, A.NIKROO, GA. -- Secondary yields of DT-neutrons and D$^{3}$He-protons from ICF implosions filled with pure deuterium fuel are used to experimentally determine fuel $\rho $R and electron temperature. Increased plasma stopping power tends to enhance the DT-n yield and reduce the D$^{3}$He-p yield. Simultaneous measurements of these secondary particles are used to constrain the modeling of the amount of fuel-shell mix in low-fuel-$\rho $R implosions on OMEGA and NIF. The range of application for this technique will be discussed and results from several experiments will be presented. This work was supported in part by the U.S. DOE, LLNL and LLE. [Preview Abstract] |
Tuesday, November 12, 2013 3:12PM - 3:24PM |
JO6.00007: Observations of nuclear-burn-region size in shock-driven implosions of capsules with different D3He fill pressures at OMEGA F.H. Seguin, M. Rosenberg, H. Rinderknecht, A. Zylstra, J. Frenje, C.K. Li, H. Sio, M. Gatu Johnson, R. Petrasso, R. Betti, J. Delettrez, V. Glebov, T.C. Sangster, C. Sorce, C. Stoeckl, A. Nickroo Fuel capsules with thin glass shells, filled with D3He gas at a wide range of pressures (1 atm to 25 atm), have been imploded at OMEGA in order to quantify how the accuracy of hydrodynamic modeling breaks down when fuel pressure is reduced to the point where the ion-mean-free-path lengths are no longer small compared to the plasma size. The spatial distribution of nuclear burn in these shock-driven implosions is being studied directly with penumbral imaging, utilizing the 14.7-MeV protons generated by the D-3He reaction, and the results will be used in conjunction with measurements of yield and fuel temperature to constrain modeling and improve our understanding of implosion behavior in this kinetic regime. This work was supported in part by the U.S. DOE and LLE. [Preview Abstract] |
Tuesday, November 12, 2013 3:24PM - 3:36PM |
JO6.00008: Studies of PDD Shock-Driven D2 and D3He Implosions at the NIF M. Rosenberg, A. Zylstra, F. Seguin, H. Rinderknecht, J. Frenje, H. Sio, M. Gatu Johnson, N. Sinenian, C.K. Li, R. Petrasso, S. Le Pape, A. Mackinnon, M. Hohenberger, J. McNaney, P. Amendt, R. Bionta, C. Bellei, D. Casey, S. Glenzer, O. Landen, T. Ma, J. Moody, M. Moran, J. Pino, S. Wilks P. MCKENTY, J. DELETTREZ, V. GLEBOV, R. BETTI, J. KNAUER, D. MEYERHOFER, T. SANGSTER LLE, J. KILKENNY, A. NIKROO GA -- Measurements of yield, ion temperature, areal density and bang time in shock-driven polar-direct-drive implosions with D2- and D3He-filled glass capsules at the NIF are presented. These measurements probe the dynamics of shock convergence, a critical process in hot-spot ignition experiments, and the results are compared to 1-D LILAC and 2-D DRACO hydrodynamics simulations. Ion temperature data generally agree with simulations, but measured yields are a factor of $\sim$ 5-10 ($\sim$ 2-4) lower than predicted by LILAC (DRACO). Both models over-predict the fuel areal density, which suggests that these simulations overestimate the fuel density after shock convergence. Kinetic effects may also partly explain this yield discrepancy. This work was supported in part by the U.S. DOE, LLNL and LLE. [Preview Abstract] |
Tuesday, November 12, 2013 3:36PM - 3:48PM |
JO6.00009: Ab-Initio Calculation of the Flux-Limiter Determining Thermal Diffusion in High Energy Density Plasmas C.P. Ridgers, A.L. Rossall, R.J. Kingham, G.J. Pert, J.J. Bissell, M.M. Marinak Full-scale simulations of high energy density plasmas (HEDP) use approximate models models for some important plasma processes. Indeed, the inaccuracy of such models could play a role in the discrepancy between simulated and measured drive temperatures in gas filled hohlraums on the National Ignition Facility (NIF). A specific example of such a model is the application of a flux limiter to thermal transport, limiting the flux to some fraction $f $of the free-streaming limit which is then tuned ``post hoc'' to fit data from a particular experiment. The recent modification of $f$ in NIF simulations from the more usual 0.05 to 0.15 to obtain such a fit demonstrates the limited predictive capability of a flux-limited heat flow model [1]. The value of the flux limiter is also important in direct drive inertial fusion experiments and in shock ignition and so ``first-principles'' calculations of the flux limiter are potentially important in many HEDP scenarios. We will show how an existing fluid code can be modified to include an ab-initio calculation of the flux limiter by replacing the energy equation with a direct solve of the kinetic Vlasov-Fokker-Planck (VFP) equation. Sample simulations of laser-solid interactions with the resulting hybrid VFP-fluid code will be presented, demonstrating for the first time that a VFP simulation framework can be used for realistic simulation of HEDP experiments.\\[4pt] [1] M.D. Rosen, HEDP, 180 (2011) [Preview Abstract] |
Tuesday, November 12, 2013 3:48PM - 4:00PM |
JO6.00010: Adapting a Collision Package in Particle-in-Cell Simulations on a GPU J. Li, C. Ren, M.C. Huang, W.B. Mori A collision package is developed for a PIC (particle-in-cell) code on parallel graphics processing unit (GPU) with CUDA.\footnote{X. Kong\textit{ et al.}, J. Comput. Phys. \textbf{230}, 1676 (2011).} The collision package is based on the cumulative collision theory.\footnote{K. Nanbu, Phys. Rev. E \textbf{55}, 4642 (1997).} It uses the sorting cell (or cluster) in the GPU PIC code as the collision cell. The benchmarks show that this collision package has a performance of 0.07- to 0.09-ns particle/step---only a 5{\%} increase to the performance of 2-ns particle/step without collisions. Test problems of beam-plasma scattering and electron plasma wave damping show that the collision frequencies calculated from the simulation results are consistent with theory. This material is based upon work supported by the Department of Energy National Nuclear Security Administration DE-NA0001944, the Office of Science under DE-FC02-04ER54789, NSF under Grant No. PHY-0903797, and NSCF under Grant No. 11129503. [Preview Abstract] |
Tuesday, November 12, 2013 4:00PM - 4:12PM |
JO6.00011: Anisotropic Thermal Diffusion Thomas Gardiner Anisotropic thermal diffusion in magnetized plasmas is an important physical phenomena for a diverse set of physical conditions ranging from astrophysical plasmas to MFE and ICF. Yet numerically simulating this phenomenon accurately poses significant challenges when the computational mesh is misaligned with respect to the magnetic field. Particularly when the temperature gradients are unresolved, one frequently finds entropy violating solutions with heat flowing from cold to hot zones for $\chi_{_\parallel} / \chi_{_\perp} \ge 10^2$ which is substantially smaller than the range of interest which can reach $10^{10}$ or higher. In this talk we present a new implicit algorithm for solving the anisotropic thermal diffusion equations and demonstrate its characteristics on what has become a fairly standard set of test problems in the literature. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND2013-5687A [Preview Abstract] |
Tuesday, November 12, 2013 4:12PM - 4:24PM |
JO6.00012: Behavior of the coupling parameter under isochoric heating in a high Z plasma Jean Clerouin, Philippe Arnault, Gregory Robert, Joel Kress, Lee Collins We have performed orbital-free molecular dynamics simulations on tungsten along the $\rho$=40 g/cm$^3$ isochore corresponding to twice the normal density with temperatures ranging from 10 eV to 5 keV [1]. The structure of the plasma is interpreted with an effective one component plasma model defining an ion-ion coupling constant and an effective ionization. We show that along an isochore the effective ionic coupling parameter is almost constant over a wide range of temperatures (in our case $\Gamma\simeq 20$) due to the competition between rising temperatures and increased ionization. This $\Gamma$-plateau effect depends on the chosen density and is well delineated at normal density but almost disappears at five times the normal density. Taking advantage of the Thomas-Fermi scaling laws, we have produced a simple and universal formulation which allows to predict the existence, the coupling, and the the range of temperatures of the plateau. Our predictions are found in reasonable agreement with recent isochoric heating experiments and can be used to obtain well defined and predictable experimental conditions.\\[4pt] [1] J. Cl\'erouin, G. Robert, P. Arnault, J. D. Kress, and L. A. Collins, Phys. Rev. E 87, 061101 (2013). [Preview Abstract] |
Tuesday, November 12, 2013 4:24PM - 4:36PM |
JO6.00013: Time-Dependent Density Functional Theory for Extreme Environments Andrew Baczewski, Rudolph Magyar, Luke Shulenburger In recent years, DFT-MD has been shown to be a powerful tool for calculating the equation of state and constitutive properties of warm dense matter (WDM). These studies are validated through a number of experiments, including recently developed X-Ray Thomson Scattering (XRTS) techniques. Here, electronic temperatures and densities of WDM are accessible through x-ray scattering data, which is related to the system's dynamic structure factor (DSF)--a quantity that is accessible through DFT-MD calculations. Previous studies predict the DSF within the Born-Oppenheimer approximation, with the electronic state computed using Mermin DFT. A capability for including more general coupled electron-ion dynamics is desirable, to study both the effect on XRTS observables and the broader problem of electron-ion energy transfer in extreme WDM conditions. Progress towards such a capability will be presented, in the form of an Ehrenfest MD framework using TDDFT. Computational challenges and open theoretical questions will be discussed. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Tuesday, November 12, 2013 4:36PM - 4:48PM |
JO6.00014: Kinetic Theory Molecular Dynamics Frank Graziani, Joseph Bauer, Michael Murillo Computational methods for simulating dense plasmas are limited by their inability to treat the dynamical quantum evolution of the electronic component. Based on the fact that electrons are typically weakly coupled but mildly quantum mechanical and the ions may be strongly coupled, we develop a method that combines a Wigner kinetic treatment of the electrons with classical molecular dynamics for the ions. We refer to this hybrid method as ``kinetic theory molecular dynamics,'' or KTMD. Using the N-body Klimontovich equation for the electron-proton plasma, three variations of KTMD are obtained. The first approach yields a closed set of equations consisting of a mean field quantum kinetic equation for the electron one-particle distribution function coupled to a classical Liouville equation for the protons. The latter equation includes both proton-proton Coulombic interactions and an effective electron-proton interaction. This approach is then extended to incorporate strong electron-proton correlations through the Singwi-Tosi-Land-Sjolander (STLS) ansatz. A third variation of KTMD is proposed by again extending the mean field approach to include dynamically evolving particle correlations. [Preview Abstract] |
Tuesday, November 12, 2013 4:48PM - 5:00PM |
JO6.00015: Wave packet spreading and localization in electron-nuclear scattering Andreas Markmann*, P.E. Grabowski*, I.V. Morozov, I.A. Valuev, C.A. Fichtl, V.S. Batista, F.R. Graziani, M.S. Murillo The wave packet molecular dynamics (WPMD) method solves the time-dependent Schr\"{o}dinger equation via a variational approximation. Application to high-temperature dense plasmas has yielded diverging electron width (spreading) with diminished electron-nuclear interaction. This was previously ascribed to a shortcoming of WPMD and has been counteracted by heuristic additions to the model. We employ various methods to determine if spreading continues to be predicted. Single electron scattering on a periodic array of statically screened protons is used as a model problem for comparison via the numerically exact split operator Fourier transform method, the Wigner trajectory method, and the time-dependent variational principle (TDVP). Within the TDVP, we use as ans\"{a}tze the standard form of WPMD, a single Gaussian wave packet (WP), as well as the split WP method, a linear combination of Gaussian WPs. Spreading is predicted by all methods, so is not the cause of unphysical diminishing interactions in WPMD. Instead, the Gaussian WP's inability to reproduce breakup of the density into fragments localized near ions is responsible for the deviation between methods. Hence, extensions of WPMD must include a mechanism for breakup. *Authors contributed equally [Preview Abstract] |
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