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 TO8: HED Laboratory Astrophysics and Magnetized Plasmas |
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Chair: Fredrico Fiuza, Stanford University Room: 212 CD |
Thursday, November 3, 2016 9:30AM - 9:42AM |
TO8.00001: Exploring the universe through discovery science on NIF Bruce Remington New regimes of science are being experimentally studied at high energy density facilities around the world, spanning drive energies from microjoules to megajoules, and time scales from femtoseconds to microseconds. The ability to shock and ramp compress samples to very high pressures and densities allows new states of matter relevant to planetary and stellar interiors to be studied. Shock driven hydrodynamic instabilities evolving into turbulent flows relevant to the dynamics of exploding stars (such as supernovae), accreting compact objects (such as white dwarfs, neutron stars, and black holes), and planetary formation dynamics are being probed. The dynamics of magnetized plasmas relevant to astrophysics, both in collisional and collisionless systems, are starting to be studied. High temperature, high velocity interacting flows are being probed for evidence of astrophysical collisionless shock formation, the turbulent magnetic dynamo effect, magnetic reconnection, and particle acceleration. And new results from thermonuclear reactions in hot dense plasmas relevant to stellar and big bang nucleosynthesis are starting to emerge. A selection of examples providing a compelling vision for frontier science on NIF in the coming decade will be presented. [Preview Abstract] |
Thursday, November 3, 2016 9:42AM - 9:54AM |
TO8.00002: Accretion Shocks in the Laboratory: Using the OMEGA Laser to Study Star Formation R. P. Young, C. C. Kuranz, C. K. Li, P. Hartigan, D. Froula, G. Fiksel, J. S. Ross, P. Y. Chang, S. Klein, A. Zylstra, H. W. Sio, A. Liao, D. Barnak We present an on-going series of experiments using the OMEGA laser (Laboratory for Laser Energetics) to study star formation. Spectra of young stars show evidence of hotspots created when streams of accreting material impact at the surface of the star to create accretion shocks. These accretion shocks are poorly understood, as the surfaces of young stars cannot be spatially resolved. Our experiment series creates a scaled ``accretion shock" on the OMEGA laser by driving a plasma jet (the ``accretion stream") into a solid block (the ``stellar surface"), in the presence of a parallel magnetic field analogous to the star's local field. Thus far, visible image data from this experimental series either shows very thin accretion shocks forming or does not show them forming at all. We intend to present this data, provide possible explanations for why shocks may not have formed, and discuss potential improvements to the experimental design. This work is funded by the U.S. Department of Energy, through the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant number DE-NA0002956, and the National Laser User Facility Program, grant number DE-NA0002719, [Preview Abstract] |
Thursday, November 3, 2016 9:54AM - 10:06AM |
TO8.00003: Numerical and experimental study of magnetized accretion phenomena in young stars Benjamin Khiar, Andrea Ciardi, Guilhem Revet, Tommaso Vinci, Julien Fuchs, Salvatore Orlando Newly formed stars accrete mass from the circumstellar disc via magnetized accretion funnels that connect the inner disc regions to the star. The ensuing impact of this free-falling plasma onto the stellar surface generates a strong shock, whose emission is used as a proxy to determine the accretion rates. Observations show that the X-ray luminosity arising from the shock heated plasma at the base of accretion columns is largelybelow the value expected on the basis of optical/UV observations. As a result, current 2D numerical simulations matching X-ray accretion rates cannot reproduce optical accretion rates. To understand the impact of accretion flows on the stellar surface in the presence of a strong magnetic field we have developed laboratory experiments reproducing crucial aspects of the accretion dynamics in Young Stellar Objects. As a model of accretion columns, we use laser-produced super-Alfvenic magnetically confined jets [,4] to collide them on solid targets. Here we present results from these experiments and from multi-dimensional MHD simulations.\newline $[1] Curran et al. 2011, A{\&}A 526, A104\newline [2] Orlando et al. 2010, A{\&}A 510, A71\newline [3] Albertazzi B., et al., Science 346, 325 (2014)\newline [4] Ciardi A., et al. Phys. Rev. Lett. 110, 025002 (2013) [Preview Abstract] |
Thursday, November 3, 2016 10:06AM - 10:18AM |
TO8.00004: Design of laboratory experiments to study photoionization fronts R.P. Drake, G. Hazak, P.A. Keiter, J.S. Davis, C.R. Patterson, A. Frank, E. Blackman, M. Busquet This paper analyzes the requirements of a photoionization-front experiment that could be driven in the laboratory, using thermal sources to produce the necessary flux of ionizing photons. It reports several associated conclusions. Such experiments will need to employ the largest available facilities, capable of delivering many kJ to MJ of energy to an x-ray source. They will use this source to irradiate a volume of neutral gas, likely of N, on a scale of a few mm to a few cm, increasing with source energy. For a gas pressure of several to ten atmospheres at room temperature, and a source temperature near 100 eV, one will be able to drive a photoionization front through a system of tens to hundreds of photon mean free paths. The front should make the familiar transition from the so-called R-Type to D-Type as the radiation flux diminishes with distance. The N is likely to reach the He-like state. Preheating from the energetic photons appears unlikely to become large enough to alter the essential dynamics of the front beyond some layer near the surface. For well-chosen experimental conditions, competing energy transport mechanisms are small. [Preview Abstract] |
Thursday, November 3, 2016 10:18AM - 10:30AM |
TO8.00005: Neon photoionized plasma experiment at Z D. C. Mayes, R. C. Mancini, J. E. Bailey, G. P. Loisel, G. A. Rochau We discuss an experimental effort to study the atomic kinetics in neon photoionized plasmas via K-shell line absorption spectroscopy. The experiment employs the intense x-ray flux emitted at the collapse of a Z-pinch to heat and backlight a photoionized plasma contained within a cm-scale gas cell placed at various distances from the Z-pinch and filled with neon gas pressures in the range from 3.5 to 30 torr. The experimental platform affords an order of magnitude range in the ionization parameter characterizing the photoionized plasma from about 3 to 80 erg*cm/s. An x-ray crystal spectrometer capable of collecting both time-integrated and time-gated spectra is used to collect absorption spectra. A suite of IDL programs has been developed to process the experimental data to produce transmission spectra. The spectra show line absorption by several ionization stages of neon, including Be-, Li-, He-, and H-like ions. Analysis of these spectra yields ion areal-densities and charge state distributions, which can be compared with results from atomic kinetics codes. In addition, the electron temperature is extracted from level population ratios of nearby energy levels in Li- and Be-like ions, which can be used to test heating models of photoionized plasmas. [Preview Abstract] |
Thursday, November 3, 2016 10:30AM - 10:42AM |
TO8.00006: Experimental design to understand the interaction of stellar radiation with molecular clouds Robert VanDervort, Josh Davis, Matt Trantham, Sallee Klein, Yechiel Frank, Erez Raicher, Moshe Fraenkel, Dov Shvarts, Paul Keiter, R Paul Drake Enhanced star formation triggered by local O and B type stars is an astrophysical problem of interest. O and B type stars are massive, hot stars that emit an enormous amount of radiation. This radiation acts to either compress or blow apart clumps of gas in the interstellar media. For example, in the optically thick limit, when the x-ray radiation in the gas clump has a short mean free path length the x-ray radiation is absorbed near the clump edge and compresses the clump. In the optically thin limit, when the mean free path is long, the radiation is absorbed throughout acting to heat the clump. This heating explodes the gas clump. Careful selection of parameters, such as foam density or source temperature, allow the experimental platform to access different hydrodynamic regimes. The stellar radiation source is mimicked by a laser irradiated thin gold foil. This will provide a source of thermal x-rays (around \textasciitilde 100 eV). The gas clump is mimicked by a low-density foam around 0.12 g/cc. Simulations were done using radiation hydrodynamics codes to tune the experimental parameters. The experiment will be carried out at the Omega laser facility on OMEGA 60. Funding acknowledgements: This work is~funded~by the~U.S. DOE, through the~NNSA-DS and SC-OFES Joint Program in HEDPLP, grant No.~DE-NA0001840, and the NLUF Program, grant No.~DE-NA0000850, and~through LLE, University of Rochester~by the NNSA/OICF under Agreement No. DE-FC52-08NA28302. [Preview Abstract] |
Thursday, November 3, 2016 10:42AM - 10:54AM |
TO8.00007: Influence of heavy elements on the properties of H-He dense plasma mixtures in giant planet envelopes Francois Soubiran, Burkhard Militzer Hydrogen and helium are by far the dominant species in gaseous giant planet interiors. It is also certain that heavier elements must be present, up to a few percents in number. The influence of these heavy elements on the properties of H-He mixtures is however unknown and so is their distribution throughout the envelope, although they must influence the density profile in the envelope and can inhibit a large-scale convection. In order to investigate the properties of H-He dense plasma mixtures enriched in heavy elements, we performed molecular dynamics coupled to density functional theory of several mixtures on a wide range of temperature and pressure. We studied the influence of different elements on the equation of state, the chemistry and the transport properties of giant planet H-He envelopes. We also studied their effect on predicted structure for giant planets. [Preview Abstract] |
Thursday, November 3, 2016 10:54AM - 11:06AM |
TO8.00008: Particle acceleration in laser-driven magnetic reconnection Samuel Totorica, Tom Abel, Frederico Fiuza Particle acceleration induced by magnetic reconnection is a promising candidate for producing the nonthermal emissions associated with explosive astrophysical phenomena. We have used two- and three-dimensional particle-in-cell simulations to explore the possibility of studying particle acceleration from reconnection in laser-driven plasma experiments. For current experimental conditions, we show that nonthermal electrons can be accelerated to energies up to two orders of magnitude larger than the initial thermal energy. The nonthermal electrons gain energy primarily by the reconnection electric field near the X-points, and particle injection into the reconnection layer and escape from the finite system establishes a distribution of energies resembling a power-law spectrum. Energetic electrons can also become trapped inside the plasmoids that form in the current layer and gain additional energy from the electric field arising from the motion of the plasmoid. Based on our findings, we provide an analytical estimate of the maximum electron energy and threshold condition for suprathermal electron acceleration in terms of experimentally tunable parameters [1]. Finally, we investigate future experiments with a more energetic laser drive and larger system size. We discuss the influence of plasmoids on the particle acceleration, and the use of proton radiography to probe plasmoids. [1] S. Totorica, T. Abel, and F. Fiuza, PRL 116, 095003, (2016). [Preview Abstract] |
Thursday, November 3, 2016 11:06AM - 11:18AM |
TO8.00009: Flux-limitation of the Nernst effect in magnetized ICF Christopher Ridgers, Rion Barrois, Joshua Wengraf, John Bissell, Jonathan Brodrick, Robert Kingham, Martin Read Magnetized ICF is a promising scheme which combines the advantages of magnetic and inertial confinement fusion. In the relevant high-energy density plasmas magnetic field evolution is often controlled by the Nernst effect where the magnetic field advects with the electron heat flow. It is well known that non-local thermal transport necessitates a flux-limiter on the heat flow. This suggests that a flux-limiter should also be applied to the Nernst effect. We have shown that this is the case using Vlasov-Fokker-Planck simulations and that the flux-limter is not the same as that required for the heat flow itself, for example when a NIF-relevant flux-limiter of 0.15 is required to limit the heat flow a Nernst flux limiter of 0.08 is required. [Preview Abstract] |
Thursday, November 3, 2016 11:18AM - 11:30AM |
TO8.00010: Kinetic solution for the generation of magnetic fields via the Biermann Battery Kevin Schoeffler, Nuno Loureiro, Luis Silva Recent experiments with intense lasers are probing the dynamics of self-generated large scale magnetic fields with unprecedented detail. In these scenarios the Biermann battery effect is critical to understand the field dynamics. Similar dynamics play an essential role in astrophysical magnetic field generation. In our previous work, particle-in-cell simulations were used to investigate the formation of magnetic fields in plasmas with perpendicular electron density and temperature gradients, showing the development of both the Biermann battery, and the smaller scale Weibel instability (due to an electron temperature anisotropy). Now, a general kinetic theoretical model for the generation of the Biermann battery is presented, which shows agreement with both fluid models and our simulations, and predicts, for an arbitrary temperature and density distribution, the generation of the temperature anisotropies exhibited in the simulations. The anisotropy grows as $(t v_{the}/L_T)^2$, where $v_{the}$ is the thermal velocity of the electrons, and $L_T$ is the length scale of a linearly varying temperature gradient. Furthermore, we see signs of the Weibel instability in collisionless regimes where these anisotropies should occur in present experimental configurations. [Preview Abstract] |
Thursday, November 3, 2016 11:30AM - 11:42AM |
TO8.00011: Study of astrophysical collisionless shocks at NIF Hye-Sook Park, D. P. Higginson, C. M. Huntington, B. B. Pollock, B. A. Remington, H. Rinderknecht, J. S. Ross, D. D. Ryutov, G. F. Swadling, S. C. Wilks, Y. Sakawa, A. Spitkovsky, R. Petrasso, C. K. Li, A. B. Zylstra, D. Lamb, P. Tzeferacos, G. Gregori, J. Meinecke, M. Manuel, D. Froula, F. Fiuza High Mach number astrophysical plasmas can create collisionless shocks via plasma instabilities and turbulence that are responsible for magnetic field generations and cosmic ray acceleration. Recently, many laboratory experiments were successful to observe the Weibel instabilities and self-generated magnetic fields using high-power lasers that generated interpenetrating plasma flows [1,2]. In order to create a fully formed shock, a series of NIF experiments have begun. The characteristics of flow interaction have been diagnosed by the neutrons and protons generated via beam-beam deuteron interactions, the x-ray emission from the hot plasmas and proton probe generated by imploding DHe3 capsules. This paper will present the latest results from the NIF collisionless shock experiments. [1] C. M. Huntington, et al., Nature Physics, 11, 173 (2015); [2] W. Fox, et al., Phys. Rev. Lett., 111, 225002 (12013). [Preview Abstract] |
Thursday, November 3, 2016 11:42AM - 11:54AM |
TO8.00012: Parallel collisionless shocks forming in simulations of the LAPD experiment Martin S. Weidl, Frank Jenko, Chris Niemann, Dan Winske Research on parallel collisionless shocks, most prominently occurring in the Earth's bow shock region, has so far been limited to satellite measurements and simulations. However, the formation of collisionless shocks depends on a wide range of parameters and scales, which can be accessed more easily in a laboratory experiment. Using a kJ-class laser, an ongoing experimental campaign at the Large Plasma Device (LAPD) at UCLA is expected to produce the first laboratory measurements of the formation of a parallel collisionless shock. We present hybrid kinetic/MHD simulations that show how beam instabilities in the background plasma can be driven by ablating carbon ions from a target, causing non-linear density oscillations which develop into a propagating shock front. The free-streaming carbon ions can excite both the resonant right-hand instability and the non-resonant firehose mode. We analyze their respective roles and discuss optimizing their growth rates to speed up the process of shock formation. [Preview Abstract] |
Thursday, November 3, 2016 11:54AM - 12:06PM |
TO8.00013: Collisionless Interaction of a Magnetized Ambient Plasma and a Field-Parallel Laser Produced Plasma P. V. Heuer, A. S. Bondarenko, D. B. Schaeffer, C. G. Constantin, S. Vincena, S. Tripathi, W. Gekelman, M. Weidl, D. Winske, C. Niemann We present measurements of the collisionless coupling between an exploding laser-produced plasma (LPP) and a large, magnetized ambient plasma. The LPP was created by focusing the Raptor laser (400 J, 40 ns) on a planar plastic target embedded in the ambient Large Plasma Device (LAPD) plasma at the University of California, Los Angeles. The resulting ablated material moved parallel to the background magnetic field, interacting with the ambient plasma along the full 17m length of the LAPD. The amplitude and polarization of waves driven by the interaction were measured by an array of 3-axis magnetic flux probes. Emissive doppler spectroscopy and a high temporal resolution monochrometer were used to observe the velocity and charge state distributions of both ambient and debris ions. Measurements are compared to hybrid simulations of quasi-parallel shocks. [Preview Abstract] |
Thursday, November 3, 2016 12:06PM - 12:18PM |
TO8.00014: Kink deformation of Weibel-mediated current filaments and onset of shock formation Charles Ruyer, E. Paulo Alves, Frederico Fiuza The Weibel instability is believed to mediate the interaction of high Mach number collisionless shocks in weakly magnetized astrophysical environments. Although the generation of current filaments and strong magnetic fields by this instability has now been demonstrated experimentally, it is still not clear what is the long-term evolution of these filaments and how they lead to shock formation. We have studied the stability of Weibel-mediated current filaments using 2D/3D Particle-In-Cell simulations and analytical theory. We show that these are prone to kink-like instabilities that we characterize in both the linear and non-linear stage for a single filament, leading to an efficient ion slowing down and isotropization. We then demonstrate that our results are relevant to the self-consistent counter-streaming plasma interaction. Our 3D simulations show that the kink deformation dominates the late-stage of the interaction, when the current filaments break and most of the flow dissipation occurs, leading to the onset of magnetic turbulence and shock formation. We will discuss the important implications of these results for the shock structure and its ability to accelerate particles. [Preview Abstract] |
Thursday, November 3, 2016 12:18PM - 12:30PM |
TO8.00015: Shock Formation in Electron-Ion Plasmas: Mechanism and Timing Antoine Bret, Anne Stockem Novo, Fonseca Ricardo, Silva Luis We analyze the formation of a collisionless shock in electron-ion plasmas in theory and simulations. In initially un-magnetized relativistic plasmas, such shocks are triggered by the Weibel instability. While in pair plasmas the shock starts forming right after the instability saturates [1,2], it is not so in electron-ion plasmas because the Weibel filaments at saturation are too small. An additional merging phase is therefore necessary for them to efficiently stop the flow. We derive a theoretical model for the shock formation time, taking into account filament merging in the nonlinear phase of the Weibel instability. This process is much slower than in electron-positron pair shocks, and so the shock formation is longer by a factor proportional to $\sqrt{m_i/m_e}\ln (m_i/m_e)$ [3]. \\ \\ (1) Bret et al, Physics of Plasmas 20, 042102 (2013). \\ (2) Bret et al, Physics of Plasmas 21, 072301 (2014). \\ (3) Stockem Novo et al, The Astrophysical Journal Letters, 803:L29 (2015). [Preview Abstract] |
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