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 UO6: Kinetic Effects |
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Chair: Suxing Hu, University of Rochester Room: Galerie 3 |
Thursday, October 30, 2014 2:00PM - 2:12PM |
UO6.00001: Exploration of kinetic and multiple-ion-fluids effects in D$^{3}$He and T$^{3}$He gas-filled ICF implosions using multiple nuclear reaction histories Hong Sio, Hans Rinderknecht, Michael Rosenberg, Alex Zylstra, Fredrick S\'eguin, Maria Gatu Johnson, Chikang Li, Richard Petrasso, Nelson Hoffman, Krigory Kagan, Kim Molvig, Peter Amendt, Claudio Bellei, Scott Wilks, Christian Stoeckl, Vladimir Glebov, Riccardo Betti, Thomas Sangster, Joseph Katz To explore kinetic and multi-ion-fluid effects in D$^{3}$He and T$^{3}$He gas-filled shock-driven implosions, multiple nuclear reaction histories were measured using the upgraded Particle Temporal Diagnostic (PTD) on OMEGA. For D$^{3}$He gas-filled implosions, the relative timing of the DD and D$^{3}$He reaction histories were measured with 20 ps precision. For T$^{3}$He gas-filled implosions (with 1-2{\%} deuterium), the relative timing of the DT and D$^{3}$He reaction histories were measured with 10 ps precision. The observed differences between the reaction histories on these two OMEGA experiments are contrasted to 1-D single-ion hydro simulations for different gas-fill pressure and gas mixture. This work is supported in part by the U.S. DOE, LLNL, LLE, and NNSA SSGF. [Preview Abstract] |
Thursday, October 30, 2014 2:12PM - 2:24PM |
UO6.00002: Studies of multi-ion-fluid yield anomaly in shock-driven implosions H.G. Rinderknecht, M.J. Rosenberg, C.K. Li, A.B. Zylstra, H. Sio, M. Gatu Johnson, J.A. Frenje, F.H. S\'eguin, R.D. Petrasso, P.A. Amendt, C. Bellei, S.C. Wilks, G. Zimmerman, N.M. Hoffman, G. Kagan, K. Molvig, V.Yu. Glebov, C. Stoeckl, F.J. Marshall, W. Seka, J.A. Delettrez, T.C. Sangster, R. Betti, V.N. Goncharov, D.D. Meyerhofer A. NIKROO, GA -- Anomalously reduced yields relative to hydrodynamically calculated values have been observed for mixtures of D:$^{3}$He compared to pure D$_{2}$ gas-filled implosions in a series of shock-driven implosions at OMEGA. An extensive suite of measurements including temporal and spatial measurements of both the DD- and D$^{3}$He-fusion reactions were obtained to identify the origin and physics behind this anomalous yield reduction. Measured spectral linewidths of fusion products suggest that the D ions are not thermalized to $^{3}$He during the burn, contributing to the reduced yield. The hypothesis that ion-species separation due to diffusive processes contributes to the observed yield reduction is explored using hydrodynamic simulations incorporating ion diffusion. Recent observations by Rosenberg et al.\footnote{Rosenberg \textit{et al. Phys. Rev. Lett. }\textbf{112, }185001 (2014)} of a yield reduction with increased ion-ion mean free path do not explain the observed anomalous yield trend. Future work that will directly probe species separation with high-precision relative fusion reaction rate measurements between DD-neutrons and D$^{3}$He-protons using the DualPTD instrument is discussed. This work was supported in part by the U.S. DOE, NLUF, LLE, and LLNL. [Preview Abstract] |
Thursday, October 30, 2014 2:24PM - 2:36PM |
UO6.00003: Studies of ion kinetic effects in OMEGA shock-driven implosions using fusion burn imaging M.J. Rosenberg, F.H. Seguin, H.G. Rinderknecht, H. Sio, A.B. Zylstra, M. Gatu Johnson, J.A. Frenje, C.K. Li, R.D. Petrasso, P.A. Amendt, S.C. Wilks, G. Zimmerman, N.M. Hoffman, G. Kagan, K. Molvig, V. Yu. Glebov, C. Stoeckl, F.J. Marshall, W. Seka, J.A. Delettrez, T.C. Sangster, R. Betti, D.D. Meyerhofer, S. Atzeni, A. Nikroo Ion kinetic effects have been inferred in a series of shock-driven implosions at OMEGA from an increasing yield discrepancy between observations and hydrodynamic simulations as the ion-ion mean free path increases.\footnote{Rosenberg et al. Phys. Rev. Lett. 112, 185001 (2014)} To more precisely identify the nature and impact of ion kinetic effects, spatial burn profile measurements of DD and D3He reactions in these D3He-filled shock-driven implosions are presented and contrasted to both purely hydrodynamic models and models that include ion kinetic effects. It is shown that in implosions where the ion mean free path is equal to or greater than the size of the fuel region, purely hydrodynamic models fail to capture the observed burn profiles, while a model that includes ion diffusion is able to recover the observed burn profile shape. These results further elucidate the ion kinetic mechanisms that are present under long mean-free-path conditions after shock convergence in both shock-driven and ablatively-driven implosions. This work was supported in part by the U.S. DOE, NLUF, LLE, and LLNL. [Preview Abstract] |
Thursday, October 30, 2014 2:36PM - 2:48PM |
UO6.00004: Kinetic Plasma and Turbulent Mix Studies using DT Plastic-shell Implosions with Shell-thickness and Pressure Variations Y. Kim, H.W. Herrmann, N.M. Hoffman, M.J. Schmitt, P.A. Bradley, G. Kagan, S. Gales, C.J. Horsfield, M. Rubery, A. Leatherland, M. Gatu Johnson, V. Glebov, W. Seka, F. Marshall, C. Stoeckl, J. Church Kinetic plasma and turbulent mix effects on inertial confinement fusion have been studied using a series of DT-filled plastic-shell implosions at the OMEGA laser facility. Plastic capsules of 4 different shell thicknesses (7.4, 15, 20, 29 micron) were shot at 2 different fill pressures in order to vary the ion mean free path compared to the size of fuel region (i.e., Knudsen number). We varied the empirical Knudsen number by a factor of 25. Measurements were obtained from the burn-averaged ion temperature and fuel areal density. Preliminary results indicate that as the empirical Knudsen number increases, fusion performances (e.g., neutron yield) increasingly deviate from hydrodynamic simulations unless turbulent mix and ion kinetic terms (e.g., enhanced ion diffusion, viscosity, thermal conduction, as well as Knudsen-layer fusion reactivity reduction) are considered. We are developing two separate simulations: one is a reduced-ion-kinetics model and the other is turbulent mix model. Two simulation results will be compared with the experimental observables. [Preview Abstract] |
Thursday, October 30, 2014 2:48PM - 3:00PM |
UO6.00005: Particle Simulations of Knudsen Layer Effects on DT Fusion* Bruce Cohen, Andris Dimits, George Zimmerman, Scott Wilks Kinetic effects have been shown to degrade fusion reactivities near an absorbing bounding surface in some circumstances, the so-called Knudsen layer (KL) effect. There is renewed interest in the KL effect [1] in the context of inertial fusion [2]. We report particle simulations (1D Cartesian in space, 3D in velocity) of the transport of deuterium and tritium (DT) plasma in a system with a partially absorbing boundary and including Coulomb collisions and the effects of non-Maxwellian velocity distribution functions on fusion reactivity. Ion-ion Coulomb collisions are implemented with a pairwise scheme that conserves number, momentum, and energy. The influences of the albedo and temperature of the boundary, ion slowing on electrons, ambi-polar electric fields, fusion alphas, and a Cu minority species are studied. Reductions in fusion reactivity are quantified. For DT at 9 keV, the Gamow peak in the fusion reactivity is at 29 keV; but the KL decrements in the ion tail from Maxwellian are observed to occur at higher energies so that the Maxwellian-averaged formula for the fusion reactivity using the space-time local temperatures and densities gives a good fit to the kinetic fusion rate. Kinetic effects are nevertheless important in determining end losses, velocity tail decrements and anisotropy, and ion axial plasma profiles for density, kinetic energy, fluxes, and flows. [1] D. B. Henderson, Phys. Rev. Lett. 33, 1142 (1974). [2] K. Molvig, et al., Phys. Rev. Lett. 109, 095001 (2012). *Work performed for the USDOE under contract DE-AC52-07NA27344 at Lawrence Livermore Nat. Lab. [Preview Abstract] |
Thursday, October 30, 2014 3:00PM - 3:12PM |
UO6.00006: Molecular Dynamics Investigations of the Ablator/Fuel Interface during Early Stages of Inertial Confinement Fusion Liam Stanton, Michael Murillo, James Glosli At the National Ignition Facility, high-powered laser beams are used to compress a small target to generate fusion reactions. A critical issue in achieving this is the understanding of mix at the ablator/fuel interface. Mixing occurs at various length scales, ranging from atomic inter-species diffusion to hydrodynamic instabilities. Because the interface is preheated by energy from the incoming shock, it is important to understand the dynamics before the shock arrives. The interface is in the warm dense matter phase with a deuterium/tritium fuel mixture on one side and a plastic mixture on the other. We would like to understand various aspects of the evolution, including the state of the interface when the main shock arrives, the role of electric field generation at the interface, and the character and time scales for diffusion. We present a molecular dynamics approach to model these processes, in which the ions are treated as classical point particles. Because we must reach extremely large length and time scales, we have also developed a simplified electronic structure model, which includes time- and space-dependent ionization levels, external heating and electron-ion energy exchange. Simulation results are presented and compared with other models and experiments. [Preview Abstract] |
Thursday, October 30, 2014 3:12PM - 3:24PM |
UO6.00007: Self-Diffusion in Dense Plasmas Julie Stern, Michael Murillo Large angle scattering has been shown to be important in ICF plasmas [Turrell et al. PRL 112, 245002 (2014)]. We use molecular dynamics to obtain effective Coulomb logarithms across coupling regimes through a careful study of self-diffusion in screened ionic systems. Through a theoretical analysis of the MD data, we assess the applicability of the Coulomb logarithm in different regimes, finding three distinct regimes of transport. Although theoretical models of Ornstein-Uhlenbeck typically model Brownian motion processes, they cannot fully capture collective dynamics in all regimes of plasma coupling. Modified memory based theoretical OU models are introduced. In order to make the models more accurate, the role of stochastic charge fluctuations relative to the mean ionization state \textless Z\textgreater is investigated. The Yukawa pair potential is combined with a Stewart-Pyatt continuum-lowered Saha method. Transport coefficients using average charges \textless Z\textgreater are compared with charge state distributions \textbraceleft Z$_{i}$\textbraceright . We model the time-evolving charge state fluctuations using a discrete stochastic evolution algorithm. Mixtures are investigated and compared to single-species. *murillo@lanl.gov [Preview Abstract] |
Thursday, October 30, 2014 3:24PM - 3:36PM |
UO6.00008: Modeling viscosity and diffusion of plasma mixtures across coupling regimes Philippe Arnault Viscosity and diffusion of plasma for pure elements and multicomponent mixtures are modeled from the high-temperature low-density weakly coupled regime to the low-temperature high-density strongly coupled regime [1]. Thanks to an atom in jellium modeling, the effect of electron screening on the ion-ion interaction is incorporated through a self-consistent definition of the ionization. This defines an effective One Component Plasma, or an effective Binary Ionic Mixture, that is representative of the strength of the interaction [2, 3]. For the viscosity and the interdiffusion of mixtures, approximate kinetic expressions are supplemented by mixing laws applied to the excess viscosity and self-diffusion of pure elements. The comparisons with classical and quantum molecular dynamics results reveal deviations in the range 20-40\% on average with almost no predictions further than a factor of 2 over many decades of variation. Applications in the inertial confinement fusion context could help in predicting the growth of hydrodynamic instabilities.\\[4pt] [1] Arnault, HEDP 9 (2013) 711\\[0pt] [2] Cl\'erouin et al, PRE 87 (2013) 61101\\[0pt] [3] Arnault et al, PRE 88 (2013) 63106 [Preview Abstract] |
Thursday, October 30, 2014 3:36PM - 3:48PM |
UO6.00009: Effects of large-angle collisions on inertial confinement fusion plasmas A.E. Turrell, M. Sherlock, S.J. Rose Large-angle Coulomb collisions cause energetic fusion produced ions to up-scatter thermal fuel ions to many times their initial energy in a single collision, creating fast ``knock-on'' ions. These collisions are not included in models of plasmas based on fluids or the Vlasov-Fokker-Planck equation but they affect the exchange of energy in fusion plasmas, and the evolution of ion distribution functions. It is well known that the relative importance of large-angle Coulomb collisions to small-angle collisions is $\mathcal{O}$($1/\ln\Lambda$). Their effects are expected to be important in the $2 < \ln\Lambda < 5$ regime, which includes high intensity laser-plasma interactions at solid density, ICF, and stellar cores. In this regime, large-angle collisions are infrequent but have noticeable effects because they transfer large amounts of energy per collision. Knock-on ions generated by this process have experimentally detectable signatures, including in neutron spectra. We present a method which uses plasma Monte Carlo techniques to include the effects of large-angle Coulomb collisions in fusion plasmas and which self-consistently evolves distribution functions according to the creation of knock-on ions of any generation. The method is applied to ``burn'' in the hot fuel in inertial confinement fusion capsules. [Preview Abstract] |
Thursday, October 30, 2014 3:48PM - 4:00PM |
UO6.00010: Numerical modeling of radiation physics in kinetic plasmas [I] Yasuhiko Sentoku, Ioana Paraschiv, Ryan Royle, Rishi Pandit, Roberto Mancini High energy density plasmas created by ultraintense short laser light emit intense x-rays via atomic processes. There is no simulation code available to study the critical details of X-ray emission/absorption and the plasma formation with femtosecond temporal resolution. Since the plasmas are created in less than 1 ps, thermalization or equilibrium cannot be assumed so that we must treat the plasma kinetically. We have developed a novel simulation tool based on the collisional particle-in-cell (PIC) code, PICLS, in which we now solve the X-ray transport and photoionization self-consistently with the plasma dynamics. This talk introduces the idea of the numerical model of the radiation trasport and also introduces several applications such as Bremsstrahlung, K-$\alpha$ emission, and XFEL-matter interaction, of which details are presented in the following talks. [Preview Abstract] |
Thursday, October 30, 2014 4:00PM - 4:12PM |
UO6.00011: Numerical modeling of radiation physics in kinetic plasmas [II] Ioana Paraschiv, Yasuhiko Sentoku, Roberto Mancini X-ray radiation is an important feature of ultra-intense laser interactions with high Z materials. In order to take into account the radiation effects in the high energy density plasmas created by such interactions, we have modified the collisional particle-in-cell code PICLS to self-consistently model the x-ray radiation transport (RT). Solving the equation of radiation transport requires the creation of a non-LTE database of emissivities and opacities as functions of photon frequency for given densities, bulk electron temperatures, hot electron temperatures, and hot electron fractions. The database was generated using results computed by a non-equilibrium, collisional-radiative atomic kinetics code. Using the two-dimensional RT-PICLS code we have studied the X-ray transport in an ultrafast heated target and the dependence of the emitted K-$\alpha $ radiation on the fast electron dynamics in the solid target. The details of these results obtained from the implementation of the radiation transport model into the PICLS calculations will be reported in this presentation. [Preview Abstract] |
Thursday, October 30, 2014 4:12PM - 4:24PM |
UO6.00012: Numerical modeling of radiation physics in kinetic plasmas [III] - $\gamma$-ray transport via Bremsstrahlung in ultra-fast heated high Z matter Rishi Pandit, Yasuhiko Sentoku Radiation transport code coupled with fully relativistic collisional Particle-in-Cell (PIC) code, PICLS, has been developed to study the transport of X-ray photons produced in laser-solid interaction. We have implemented the radiation cross-section of relativistic Bremsstrahlung to simulate $\gamma$-ray transport in ultrafast heated high Z matter by an intense short pulse laser. We discuss the laser energy dependence of the emission energy and the intensity dependence of the angular distribution of $\gamma$-rays. By solving the transport of hard X-rays we find that high energy photons emitted by relativistic electrons are co-moving with the electrons and they are intensified continuously. As a result the $\gamma$-rays have the signature of the fast electrons' temporal and spatial distribution. We also calculate the number of pairs by solving the Bethe-Heitler cross-section in the radiation transport simulation. Comparing the details of $\gamma$-rays via Bremsstrahlung and pair creations with varying laser intensities in simulations, we will discuss the laser parameters and the target conditions (material) to produce the higher yield. [Preview Abstract] |
Thursday, October 30, 2014 4:24PM - 4:36PM |
UO6.00013: Numerical modeling of radiation physics in kinetic plasmas [IV] -- Isochoric heating by intense X-ray laser-produced photoelectrons Ryan Royle, Yasuhiko Sentoku An intense, hard X-ray laser such as an XFEL is an attractive light source since it can directly heat solid matter isochorically to a temperature of millions of degrees on a time scale of a few tens of femtoseconds, which is much shorter than the plasma expansion time scale. The X-ray laser interaction with carbon, aluminum, silicon, and copper is studied with a particle-in-cell code that solves the photoionization and X-ray transport self-consistently. Photoionization is the dominant absorption mechanism and non-thermal photoelectrons are produced with energy near the X-ray photon energy. The photoelectrons' stopping range is a few microns and they are quickly thermalized in tens of femtoseconds. As a result, a hot plasma column is formed behind the laser pulse with a temperature of more than 100,000 kelvin ($>$10\,eV) and energy density greater than $10^{11}$\,J/m$^3$. The heating depth and temperature depend on the material and are also controllable by changing the photon energy of the incident laser light. [Preview Abstract] |
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