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 JO5: HEDP Laboratory Astrophysics |
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Chair: Hye-Sook Park, Lawrence Livermore National Laboratory Room: Galerie 2 |
Tuesday, October 28, 2014 2:00PM - 2:12PM |
JO5.00001: Turbulent amplification of supernova magnetic fields in the laboratory Gianluca Gregori X-ray and radio observations of the supernova remnant Cassiopeia A reveal the presence of magnetic fields about 100 times stronger than those in the surrounding interstellar medium. Field coincident with the outer shock probably arises through a non-linear feedback process involving cosmic rays. The origin of the large magnetic field in the interior of the remnant is less clear but it is probably stretched and amplified by turbulent motions. Turbulence may be generated by hydrodynamic instability at the contact discontinuity between the supernova ejecta and the circumstellar gas. However, optical observations of Cassiopeia A indicate that the ejecta are interacting with a highly inhomogeneous, dense circumstellar cloud bank formed prior to the supernova explosion. We have conducted a series of laboratory experiments using high power laser facilities\footnote{G. Gregori \textit{et al.}, Nature 481, 480 (2012)}$^,$\footnote{J. Meinecke\textit{ et al.}, Nature Phys., accepted (2014)} in order to reproduce the essential features of the supernova shock interacting with strong density perturbations. Our results indicate the magnetic field is amplified when the shock interacts with a plastic grid. We show that our experimental results can explain the observed synchrotron emission in the interior of the remnant. These experiments provide an example of magnetic field amplification by turbulence in plasmas, a physical process thought to occur in many astrophysical phenomena. [Preview Abstract] |
Tuesday, October 28, 2014 2:12PM - 2:24PM |
JO5.00002: Numerical modeling of laser-driven experiments of colliding jets: Turbulent amplification of seed magnetic fields Petros Tzeferacos, Milad Fatenejad, Norbert Flocke, Carlo Graziani, Gianluca Gregori, Donald Lamb, Dongwook Lee, Jena Meinecke, Anthony Scopatz, Klaus Weide In this study we present high-resolution numerical simulations of laboratory experiments that study the turbulent amplification of magnetic fields generated by laser-driven colliding jets. The radiative magneto-hydrodynamic (MHD) simulations discussed here were performed with the FLASH code and have assisted in the analysis of the experimental results obtained from the Vulcan laser facility. In these experiments, a pair of thin Carbon foils is placed in an Argon-filled chamber and is illuminated to create counter-propagating jets. The jets carry magnetic fields generated by the Biermann battery mechanism and collide to form a highly turbulent region. The interaction is probed using a wealth of diagnostics, including induction coils that are capable of providing the field strength and directionality at a specific point in space. The latter have revealed a significant increase in the field's strength due to turbulent amplification. Our FLASH simulations have allowed us to reproduce the experimental findings and to disentangle the complex processes and dynamics involved in the colliding flows. [Preview Abstract] |
Tuesday, October 28, 2014 2:24PM - 2:36PM |
JO5.00003: The Biermann Catastrophe in Numerical MHD Carlo Graziani, Petros Tzeferacos, Dongwook Lee, Klaus Weide, Donald Lamb, Milad Fatenejad, Joshua Miller The Biermann Battery (BB) effect is widely invoked as a mechanism to generate cosmic magnetic fields from unmagnetized plasmas. The BB effect, which relies on large, non-aligned gradients of electron density and pressure, is expected to function most efficiently at shocks, where such gradients are largest. Simulations of cosmic magnetogenesis have accordingly relied on shocks to enhance the BB effect. What went unnoticed until recently is the fact that straightforward algorithmic implementations of the BB effect in MHD codes break down precisely at hydrodynamic discontinuities such as shocks -- where the BB effect is of greatest interest -- yielding results that fail to converge with resolution. We discuss this breakdown, show its origin, and present an alternative algorithm that gives finite and convergent results. We demonstrate convergence using an implementation of the algorithm within the FLASH code, and verify that the algorithm yields physically sensible results at shocks. We discuss novel -- and physically observable -- effects that attend the BB effect at shocks. [Preview Abstract] |
Tuesday, October 28, 2014 2:36PM - 2:48PM |
JO5.00004: Self-generated Magnetic Fields in Blast-wave Driven Rayleigh-Taylor Experiments Markus Flaig, Tomasz Plewa We study the generation of magnetic fields via the Biermann battery effect in blast-wave driven Rayleigh-Taylor experiments. Previous estimates have shown that in a typical experiment, one should expect fields in the MG range to be generated, with the potential to influence the Rayleigh-Taylor morphology. We perform two- and three-dimensional numerical simulations, where we solve the extended set of MHD equations known as the Braginskii equations. The simulation parameters reflect the physical conditions in past experiments performed on the OMEGA laser and potential future experiments on the NIF laser facility. When neglecting the friction force between electrons and ions in the simulations, magnetic fields of the order of a few 0.1 MG (with a plasma smaller than 1000) are generated, and are found to be dynamically significant. However, it turns out that once the friction force is included, the magnetic fields become much smaller (with a plasma beta greater than 100000) which have negligible influence on the dynamics of the system. Our results therefore indicate that, contrary to previous speculations, it is highly unlikely that self-generated magnetic fields can influence the morphology of a typical blast-wave driven Rayleigh-Taylor experiment. [Preview Abstract] |
Tuesday, October 28, 2014 2:48PM - 3:00PM |
JO5.00005: Shock formation in counter-streaming jets on the MAGPIE pulsed-power generator F. Suzuki-Vidal, S. Lebedev, L.A. Pickworth, G.F. Swadling, G. Burdiak, J. Skidmore, G.N. Hall, M. Bennett, S.N. Bland, J.P. Chittenden, P. de Grouchy, J. Hare, J. Music, L. Suttle, A. Ciardi, R. Rodriguez, J.M. Gil, G. Espinosa, E. Hansen, A. Frank Experiments looking at formation of shocks from the collision between two counter-streaming jets are under investigation. The experiments are in the context of high-energy density laboratory astrophysics looking at the formation of internal shocks in jets from young stars. The jets in the experiments are driven by the ablation of plasma from two opposite radial foil Z-pinches, subjected to a 1.4MA, 250ns current pulse from the MAGPIE pulsed-power generator. The dynamics of shock formation from the collision are determined by a combination of advected toroidal magnetic field carried with the jets, and other effects such as radiative cooling in the plasma. The dynamics of the collision are compared with numerical simulations using the code GORGON, whereas radiative cooling effects are investigated with the codes ABAKO/RAPCAL and the astrophysical code AstroBEAR. [Preview Abstract] |
Tuesday, October 28, 2014 3:00PM - 3:12PM |
JO5.00006: The dynamics of high energy density plasma jets magnetized by large dipole magnetic fields Pierre Gourdain, Tom Byvank, Dave Hammer, Bruce Kusse, Charlie Seyler, Simon Bland, Sergey Lebedev, George Swadling Astrophysical plasma jets expelled by proto-stars or galactic nuclei are often magnetized by the magnetic field that the star or galaxy generates. This field resembles the one of a dipole and, while strong near the celestial body, the field decays rapidly away from the source. Experimental observations of supersonic high energy density plasma jets generated in the laboratory by radial foils have shown that the field impacts strongly the dynamics of the jet. Such jets share some similarities with astrophysical jets in the magneto-hydrodynamics sense, e.g. large Reynolds, magnetic Reynolds and Peclet numbers. This work shows how a dipole field generated at the base of the supersonic jet affects the plasma dynamics. In regions where the plasma beta is low (near the base of the jet), the jet is conical. At higher altitudes, where the beta is high, the jet is strongly collimated. Numerical computations highlight the mechanisms responsible for such transitions. [Preview Abstract] |
Tuesday, October 28, 2014 3:12PM - 3:24PM |
JO5.00007: An experimental investigation of the collision of counter-streaming magnetized plasma flows with oppositely aligned embedded magnetic fields Lee Suttle, Sergey Lebedev, George Swadling, Francisco Suzuki-Vidal, Guy Burdiak, Matthew Bennett, Jack Hare, David Burgess, Adam Clemens, Nicholas Niasse, Jerry Chittenden, Roland Smith, Simon Bland, Siddharth Patankar, Nic Stuart We present first results from a new experimental platform designed to study the quasi-1D collision of counter-streaming plasma flows produced by the ablation from a pair of inverse wire array z pinches at the MAGPIE pulsed power facility. The flows are magnetized (B $\sim$ 2T, Re$_{\mathrm{M}}$ $\sim$ 100) and enter the interaction region with supersonic velocity (M$_{\mathrm{S}}$\textgreater 5, M$_{\mathrm{MS}}$\textgreater 3). The advected magnetic fields are perpendicular to the flow and aligned in anti-parallel directions, allowing studies of magnetic reconnection in a strongly driven regime. The setup allows parameters of the plasma to be measured in the reconnection region with a set of diagnostics which includes Thomson scattering, Faraday rotation, interferometry and detectors of energetic particles. The collisionality of the interaction and the relative role of the radiative cooling can be varied by choice of material of the colliding flows (e.g. Al or W). [Preview Abstract] |
Tuesday, October 28, 2014 3:24PM - 3:36PM |
JO5.00008: Accretion Shocks on Young Stars: A Laboratory-Astrophysics Investigation R.P. Young We intend to present results of a laboratory-astrophysics investigation of accretion shocks at the surface of young stars. We have scaled a stellar accretion shock to an OMEGA experiment by creating a plasma jet (representing the accreting material) and colliding it with a solid block (representing the surface of the young star). Magnetic fields are thought to play crucial role in this phenomenon, and therefore we conducted our experiments with imposed magnetic fields of 0 T, 3 T and 7 T. 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-NA0001840, and the National Laser User Facility Program, grant number DE-NA0000850, and through the Laboratory for Laser Energetics, University of Rochester by the NNSA/OICF under Cooperative Agreement No. DE-FC52-08NA28302. [Preview Abstract] |
Tuesday, October 28, 2014 3:36PM - 3:48PM |
JO5.00009: Creating astrophysically relevant jets from locally heated targets irradiated by a high-intensity laser Holger Schmitz, Alex Robinson The formation mechanism of jets in the vicinity of young stellar objects has been the subject of investigations for many years. It is thought that jets are formed by the stellar wind interacting with an inhomogeneous plasma. A density gradient from the equator to the poles causes the wind to encounter the inward facing reverse shock at an oblique angle. The wind is focused into a conical flow towards the poles where it emerges as a narrow jet. This mechanism is inaccessible to direct observations due to the small scales on which it operates. Using high intensity lasers to produce comparable jets offers a way to investigate the mechanisms in the laboratory. Previous investigations of jets in the laboratory have directly generated the conical flow, skipping the first part of the formation mechanism. We present simulations of a novel method of generating jets in the laboratory by using magnetic fields generated by resistivity gradients to control the fast electron flow. The return current selectively heats a small region inside the target which drives a blast wave into the low density region behind the target. A conical high density shell focuses the outflow into a narrow jet. We find jets with aspect ratios of over 15 and Mach numbers between 2.5 and 4.3. [Preview Abstract] |
Tuesday, October 28, 2014 3:48PM - 4:00PM |
JO5.00010: Formation of Radiatively cooled, Supersonically Rotating, Plasma Disks in Z-pinch experiments M. Bennett, S.V. Lebedev, L. Suttle, G. Burdiak, F. Suzuki-Vidal, J. Hare, G.F. Swadling, S. Patankar, G.N. Hall, M. Bocchi, J.P. Chittenden, R.A. Smith, A. Frank, E. Blackman, R.P. Drake, A. Ciardi We present data from z-pinch experiments aiming to simulate aspects of accretion disk physics in the laboratory. Using off axis ablation flows from a wire array z-pinch we demonstrate the formation of a hollow disk structure that rotates supersonically with velocity of $\sim$ 60km/s and M$\sim $2 for $\sim$ 150 ns. We use interferometry to measure the electron density as \textgreater 10$^{19}$ cm$^{-3}$ and analyze Thomson Scattered spectra to make estimates for the ion and electron temperatures; we find T$_{\mathrm{i}} \sim $60 eV and ZT$_{\mathrm{e}}$ $\sim $150 to 200 eV. Using these parameters we calculate the Reynolds number for the plasma on the order 10$^{5}$ putting the experiment within the correct viscous regime for turbulent flow and scaling to accretion disks. [Preview Abstract] |
Tuesday, October 28, 2014 4:00PM - 4:12PM |
JO5.00011: Laboratory astrophysics experiments relating to ionising and weakly radiative shocks Joseph Cross, John Foster, Peter Graham, Clotilde Busschaert, Nicolas Charpentier, Colin Danson, Hugo Doyle, R. Paul Drake, Emeric Falize, Jim Fyrth, Edward Gumbrell, Michel Koenig, Carolyn Kuranz, Berenice Loupias, Claire Michaut, Sid Patankar, Jonathan Skidmore, Christopher Spindloe, Ellie Tubman, Nigel Woolsey, Roman Yurchak, Gianluca Gregori The aim of the POLAR project$^{1}$ is to simulate, in the laboratory, the accretion shock region of a magnetic cataclysmic variable binary star system. Scaling laws have shown that laser experiments can be related to astrophysical phenomena by matching relevant dimensionless parameters$^{2,3}$. As well as forming a reverse shock, relevant to the POLAR project, the experimental system is also likely formed of a weakly radiating shock and an ionisation front. Results from our experiment at the Orion Laser are presented here, alongside comparisons to simulation and the astrophysical case (of relevance to triggered star formation$^{4,5}$.) References~: 1. Busschaert et al., NJP,~15, 3, 035020 (2013), 2. Falize et al., ApJ. 730, 96 (2011), 3. Ryutov et al., ApJ. 518, 821 (1999), 4. Dale et al., MNRAS 377, 535 (2007), 5. Tremblin et al., A{\&}A 564, A106 (2014) [Preview Abstract] |
Tuesday, October 28, 2014 4:12PM - 4:24PM |
JO5.00012: Scaled Laboratory Experimental Design of Radiation-Driven Cloud Implosions Paul Keiter, James Stone, Matt Trantham, Guy Malamud, Sallee Klein When hot, massive stars form they ionize and heat the surrounding interstellar medium (ISM), forming an expanding region of hot, high-radiation-pressure, ionized hydrogen gas called an H II region. The H II region itself can then induce further star formation. The two main mechanisms of star formation involving H II regions are collect and collapse [Elmegreen 1977] and radiation-driven implosions [Axford, 1964, Lefloch and Lazareff 1994]. Two persistent questions for this mechanism are when in the compression process and where in the cloud does star formation occur? Our understanding of stellar formation is based on computer simulations and models. To improve our understanding of these models, data are required. We present the design of a scaled experiment to study the interaction of an ionization front with a high-density sphere, which acts as a surrogate for the molecular cloud. Irradiating a high-Z foil with laser beams generates the ionization front. The ionization front will propagate in a low-density medium before interacting with the sphere. [Preview Abstract] |
Tuesday, October 28, 2014 4:24PM - 4:36PM |
JO5.00013: Experimental investigation of Eagle nebula pillars using a multiple hohlraum array David Martinez, Jave Kane, Bruno Villette, Mark Pound, Alexis Casner, Robert Heeter, Roberto Mancini The ``pillars of creation'' are stunningly beautiful and physically puzzling molecular cloud structure in the Eagle nebula. Formation of these pillars has been subject of debate since their observation. Although extensive observation and modeling have attempted to answer the creation of the observed pillars, experiments have not adequately tested the theoretical models surrounding the photoevaporation of the molecular clouds. Recent Omega EP experiments at the LLE developed a 30ns x-ray drive using a multiple hohlraum array (``Gatling gun'' approach) to drive the photoevaporation process and test pillar formation. This proof of principle experiment imaged the initial stages of a pillar using Ti area backlighter through a driven 50mg/cc R/F foam with an embedded solid density CH ball. This presentation will give an overview of the experimental design and results from the experiment. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-656872 [Preview Abstract] |
Tuesday, October 28, 2014 4:36PM - 4:48PM |
JO5.00014: X-ray line formation in radiation dominated astrophysical plasmas G. Loisel, J.E. Bailey, S.B. Hansen, T. Nagayama, G.A. Rochau, D. Liedahl, R. Mancini, M. Koepke A remarkable opportunity to observe matter in a regime where the effects of General Relativity are significant has arisen through measurements of strongly red-shifted iron x-ray lines emitted from black hole accretion disks. A major uncertainty in the spectral formation models is the efficiency of Resonant Auger Destruction (RAD), in which fluorescent Ka photons are resonantly absorbed by neighbor ions. The absorbing ion preferentially decays by Auger ionization, thus reducing the emerging Ka intensity. If Ka lines from L-shell ions are not observed in iron spectral emission, why are such lines observed from silicon plasma surrounding other accretion powered objects? To help answer this question, we are investigating photoionized silicon plasmas produced using intense x-rays from the Z facility. For the first time in a terrestrial lab, we measured simultaneous absorption and emission spectra from these plasmas at high resolution. The charge state distribution, electron temperature, and electron density are determined through space-resolved absorption spectra. The emission spectra have been recorded at different column densities thus testing different radiative transport regime. These should allow us to answer quantitatively the original RAD hypothesis. [Preview Abstract] |
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