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 UO5: Shocks, Magnetic Field Generation, and Astrophysics |
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Chair: Boris Breizman, University of Texas at Austin Room: Governor's Square 10 |
Thursday, November 14, 2013 2:00PM - 2:12PM |
UO5.00001: Shock Waves in Weakly Collisional Plasmas Scott Wilks, Peter Amendt, Claudio Bellei, Frederico Fiuza Shock waves in plasmas have been intensively investigated in the past, but a close examination of the literature reveals that the majority of the studies are in either one of two limits: the highly collisional limit or the collisionless limit. Interestingly, a large number of experiments are in an intermediate regime, where the shock is set up due to ion-ion collisions, but at the same time the plasma is sufficiently collisionless such that the presence of an electric field associated with the shock wave cannot be neglected. We present the results of detailed fluid and kinetic simulations that elucidate several key features of plasma shock waves in this relatively unexplored regime, and compare these results to analytic solutions. In particular, it is found that for low plasma densities and high Mach numbers, the kinetic simulations predict a significant population of reflected ions upstream of the shock, not captured in fluid simulations. LLNL-ABS-640279 This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and LDRD 11-ERD-075. [Preview Abstract] |
Thursday, November 14, 2013 2:12PM - 2:24PM |
UO5.00002: Generated Wave Behavior from Laser-Driven Magnetic Pistons Relevant to Magnetized Collisionless Shock Formation E.T. Everson, D.B. Schaeffer, A.S. Bondarenko, S. Vincena, B. Van Compernolle, S.E. Clark, C.G. Constantin, C. Niemann The dynamics of energetic plasma explosions through a tenuous, magnetized plasma is of relevance to many astrophysical, ionospheric, and magnetospheric phenomena, such as the formation of collisionless shocks. Recent experiments at the University of California at Los Angeles (UCLA) utilized the LArge Plasma Device (LAPD) and the Raptor laser system to drive super-Alfv\'{e}nic laser-plasma explosions through the uniform, magnetized background plasma of the LAPD. The $100$ J, $25$ ns FWHM Raptor laser ablated a graphite target directing the exploding debris-plasma quasi-perpendicularly to the background magnetic field ($300$ G). The debris-plasma interacted with the low-density ($2-5\times10^{12}$ cm$^{-3}$), He plasma of the LAPD for $60$ cm across the field lines and about $8$ m along the field lines. Magnetic flux probes were used to measure wave behavior both perpendicular and parallel to the background field. Across field behavior shows signs of collisionless coupling between the debris and ambient plasma, leading to a field compression on the order of the Alfv\'{e}nic Mach number ($\sim1.4$). The debris-explosion also produced strong parallel wave behavior resulting in large amplitude whistler ($\Delta B/B_{o}\sim4\%$) and Alfv\'{e}n ($\Delta B/B_{o}\sim10\%$) waves. [Preview Abstract] |
Thursday, November 14, 2013 2:24PM - 2:36PM |
UO5.00003: Spectroscopic Measurements of Collision-less Coupling Between Explosive Debris Plasmas and Ambient, Magnetized Background Plasmas Anton Bondarenko, Derek Schaeffer, Erik Everson, Stephen Vincena, Bart Van Compernolle, Carmen Constantin, Eric Clark, Christoph Niemann Emission spectroscopy is currently being utilized in order to assess collision-less momentum and energy coupling between explosive debris plasmas and ambient, magnetized background plasmas of astrophysical relevance. In recent campaigns on the Large Plasma Device (LAPD) ($n_{elec} = 10^{12} - 10^{13} $ cm$^{-3}$, $T_{elec}\approx5$ eV, $B_{0} = 200 - 400$ G) utilizing the new Raptor laser facility ($1053$ nm, $100$ J per pulse, $25$ ns FWHM), laser-ablated carbon debris plasmas were generated within ambient, magnetized helium background plasmas and prominent spectral lines of carbon and helium ions were studied in high spectral ($0.01$ nm) and temporal ($50$ ns) resolution. Time-resolved velocity components extracted from Doppler shift measurements of the C$^{+4}$ $227.1$ nm spectral line along two perpendicular axes reveal significant deceleration as the ions stream and gyrate within the helium background plasma, indicating collision-less momentum coupling. The He$^{+1}$ $320.3$ nm and $468.6$ nm spectral lines of the helium background plasma are observed to broaden and intensify in response to the carbon debris plasma, indicative of strong electric fields (Stark broadening) and energetic electrons. The experimental results are compared to 2D hybrid code simulations. [Preview Abstract] |
Thursday, November 14, 2013 2:36PM - 2:48PM |
UO5.00004: Multidimensional Hybrid Simulations of Super-Alfv\'enic Laser Ablation Experiments in the Large Plasma Device S.E. Clark, D. Winske, D.B. Schaeffer, E.T. Everson, A.S. Bondarenko, C.G. Constantin, C. Niemann Two dimensional hybrid simulations are performed to determine the best plasma and laboratory parameters for the next generation of laser ablation experiments in the Large Plasma Device (LAPD). After installation of a new plasma source in the LAPD, the ambient plasma density is expected to reach $n_i \sim 10^{13}$ cm$^{-3}$ with a diameter $> 20$ cm embedded within the main cathode discharge of $n_i \sim 10^{12}$ cm$^{-3}$, which has a diameter of $\sim 80$ cm. The electron temperature is expected to be $T_e > 5$ eV and the ion temperature will be $T_i \sim 1$ eV. The background magnetic field will be selected to have a strength between 275 G and 800 G. The debris plasma is assumed to be C$^{+4}$, which is ejected conically and relatively monoenergetically from the target at a super-Alfv\'enic speed $V_d > 100$ km/s into an ambient plasma of H$^{+1}$ or He$^{+1}$, where collisions with neutrals is neglected. Simulations with uniform background density will be compared to those with a non-uniform radial density profile and the effect of the density gradient on debris-ambient coupling will be examined. These simulation results will be used to help determine the parameter space in which to operate the next experiment. [Preview Abstract] |
Thursday, November 14, 2013 2:48PM - 3:00PM |
UO5.00005: Collisionless shock formation, spontaneous electromagnetic fluctuations, and streaming instabilities Antoine Bret, Anne Stockem, Frederico Fiuza, Charles Ruyer, Laurent Gremillet, Ramesh Narayan, Luis Silva Collisionless shocks are ubiquitous in astrophysics and in the lab. Recent numerical simulations and experiments have shown how they can arise from the encounter of two collisionless plasma shells. When the shells interpenetrate, the overlapping region turns unstable, triggering the shock formation. As a first step towards a microscopic understanding of the process, we analyze here in detail the initial instability phase. On the one hand, 2D relativistic Particle-In-Cell simulations are performed where two symmetric initially cold pair plasmas collide. On the other hand, the instabilities at work are analyzed, as well as the field at saturation and the seed field which gets amplified. For mildly relativistic motions and onward, Weibel modes govern the linear phase. We derive an expression for the duration of the linear phase in good agreement with the simulations. This saturation time constitutes indeed a lower-bound for the shock formation time. PHYSICS OF PLASMAS 20, 042102 (2013) [Preview Abstract] |
Thursday, November 14, 2013 3:00PM - 3:12PM |
UO5.00006: ABSTRACT WITHDRAWN |
Thursday, November 14, 2013 3:12PM - 3:24PM |
UO5.00007: Driving Weibel-mediated collisionless shocks with NIF Frederico Fiuza, Anatoly Spitkovsky, Dmitri Ryutov, Steven Ross, Channing Huntington, Warren Mori, Luis Silva, Hye-Sook Park, Bruce Remington Collisionless shocks are ubiquitous in astrophysical plasmas and are known to be responsible for particle acceleration; however, the microphysics underlying shock formation and particle acceleration is not yet fully understood. High-power lasers are bringing the study of collisionless shocks into the realm of laboratory experiments. In particular, the National Ignition Facility allows for the generation of collisionless plasma flows that are hundreds of ion skin-depths long and provides ideal conditions for the study of Weibel-mediated shocks. We have performed detailed 2D and 3D particle-in-cell simulations with OSIRIS to explore the laboratory conditions associated with counter-streaming high-velocity plasma flows for realistic profiles. We have modeled the proton radiography of the interaction for self-consistent fields and determined the experimental signatures of the generation of Weibel B-fields and collisionless shocks. We will discuss the importance of modeling realistic ion to electron mass ratios and of taking into account Biermann battery B-fields. Our work identifies the conditions for the formation of collisionless shocks in laboratory, both in unmagnetized and magnetized scenarios, showing the possibility of observing for the first time Weibel-mediated shocks in near future experiments. [Preview Abstract] |
Thursday, November 14, 2013 3:24PM - 3:36PM |
UO5.00008: Magnetic field production in an expanding plasma: Biermann or Weibel? Kevin Schoeffler, Nuno Loureiro, Luis Silva, Ricardo Fonseca Recent laboratory experiments focusing intense lasers ($\sim kJ$) at solid targets show the production of strong magnetic fields (of order a megaGauss). It is conjectured that these fields arise via the Biermann battery mechanism, due to non-aligned electron density and temperature gradients. We investigate the generation and amplification of such magnetic fields in a kinetic particle-in-cell model, and its dependence on system size, $L$. For moderate system sizes ($L$ $\ga$ $d_i$), we find that the strength of the magnetic fields scales as $1/L$, consistent with their origin being due to the Biermann effect. However, for large $L/d_i$, we discover that the Weibel instability (due to electron temperature anisotropy) supersedes the Biermann battery effect as the main mechanism behind the production of magnetic fields. The Weibel-produced fields, unlike the ones due to Biermann, saturate at a finite amplitude (plasma $\beta\sim 1$) for large $L/d_i$. These results have strong implications for the interpretation of laser-solid interaction experiments. They may also be important to the understanding of the origin of the observed magnetic fields in the universe. [Preview Abstract] |
Thursday, November 14, 2013 3:36PM - 3:48PM |
UO5.00009: Study of interaction of hot core plasma sources and micro-shock waves Leela Chelikani, Suman Bagchi, Prem Kiran Paturi Laser Induced Shockwaves (LISWs) have many applications from material processing to therapeutics. In almost all the processes and applications, understanding the conversion of laser energy to kinetic energy propagating as a shockwave (SW) is essential. We present the results on interaction of multiple plasma sources leading to SWs generated using Nd:YAG laser pulses (532 nm, 7 ns) (a) in atmospheric air and (b) from 1-D periodic structured surfaces (PSS) of 30 $\mu$m depth and 240 $\pm$ 20 $\mu$m diameter having 25 and 64 lpi (lines per inch). Using time resolved shadowgraphy the novel aspects of (1) the presence of two distinct sources of ionization along the laser propagation direction modifying the nature of SWs around the focal plane and (2) the interaction of these two sources leading to the transition of hot core plasma in air analogous to that of a cavitation bubble in fluids are presented. Analogous phenomena of modification SW nature were observed from 1-D PSS. The effect of surface modulation on the SW and Contact Front dynamics was compared from that of a flat surface (FS). The initial studies in two different media indicate the possibility to control the SWs, either accelerate or decelerate by varying the plasma dynamics. [Preview Abstract] |
Thursday, November 14, 2013 3:48PM - 4:00PM |
UO5.00010: Non-thermal Plasmas Around Massive Black Holes: Collective Modes, Ring Configurations and Magnetic Field Generation* B. Coppi The discovered gamma-ray bubbles emanating from the center of Our Galaxy are a new motivation to develop theories for large scale structures in the Universe in terms of plasmas for which electromagnetic interactions are no less important than the relevant (e.g. density wave theory of spirals) gravitational interactions. Moreover, considering the observed emission spectra, the particle distributions in phase space cannot be represented by isotropic Maxwellian in significant cases. The consequent theory of plasmas surrounding rotating massive black holes has led to identify new stationary plasma and field configurations (in particular Solitary Rings) and modes, emerging from conventional (currentless) disks, that depend on the existence of temperature anisotropies. These modes, which produce outward transport of angular momentum at a significant rate, involve large amplifications of a seed magnetic field. In the related (by the envisioned non-linear mode evolution) stationary configurations, without a seed magnetic field, the field energy densities are of the order of the particle thermal energy densities. Thus a clear sequence of processes for the generation of magnetic fields in the Universe is identified. *US DOE partly sponsored.\\[4pt] [1] B. Coppi, A\&A, 548, A84 (2012). [Preview Abstract] |
Thursday, November 14, 2013 4:00PM - 4:12PM |
UO5.00011: Interaction of co-propagating jets in the presence of an external magnetic field Michael MacDonald, Hugo Doyle, Erik Brambrink, Robert Crowston, R. Paul Drake, Carolyn Kuranz, Don Lamb, Michel Koenig, Pawel Kozlowski, Jean-Raphael Marques, Jena Meinecke, Alexander Pelka, Alessandra Ravasio, Brian Reville, Petros Tzeferacos, Nigel Woosley, Gianluca Gregori We observed the interaction of two co-propagating jets in 1 mbar of argon gas in the presence of an external magnetic field at the LULI laser facility. The jets were created by irradiating a 100 $\mu$m aluminum foil with two 1.5 ns laser pulses separated by 5 mm, each containing 500 J of 527 nm light. Optical interferometry and schlieren imaging were used to observe the flow of the interacting jets. Additionally, an induction coil was fielded to measure the magnetic field 3 cm from the initiation of the flows. Measurements were made with and without a 0.5 T external magnetic field. Preliminary results and analysis will be presented. The research leading to these results has received funding from the European Research Council under the European Community's Seventh Framework Programme (FP7/2007-2013) / ERC grant agreement no. 256973. and by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant number DE-NA0001840. [Preview Abstract] |
Thursday, November 14, 2013 4:12PM - 4:24PM |
UO5.00012: Measurement and Simulation of the Electric Current in a kpc-Scale Jet P.P. Kronberg, R.V.E. Lovelace, S.A. Coplgate, Giovanni Lapenta We present radio emission, polarization, and Faraday rotation maps of the radio jet of the galaxy 3C303. From these data we derive the magnetoplasma and electrodynamic parameters of this 50 kpc long jet. For one component of this jet we obtain for the first time a direct determination of a galactic-scale electric current (3 $\times$ 1018 A), and its direction-positive away from the active galactic nucleus. Our analysis strongly supports a model where the jet energy flow is mainly electromagnetic.\\[4pt] P.P. Kronberg, R.V.E. Lovelace, G. Lapenta, S.A. Colgate, Measurement of the Electric Current in a Kpc-Scale Jet, Astrophysical Journal Letters, 741, L15, doi:10.1088/2041-8205/741/1/L15, 2011. [Preview Abstract] |
Thursday, November 14, 2013 4:24PM - 4:36PM |
UO5.00013: Relativistic Shear Flows and Applications to Astrophysical Jets Edison Liang, Wen Fu, Parisa Roustazadeh, Ian Smith, Markus Boettcher We present Particle-in-Cell (PIC) simulations of relativistic shear boundary layers. Strong magnetic fields are generated by the shear flow and efficient nonthermal particle acceleration to high Lorentz factors are observed. We compare results for pure electron-positron, pure electron-ion and hybrid electron-ion-positron shear flows. Applications to relativistic astrophysical jets such as those observed in blazars and gamma-ray bursts will be discussed. [Preview Abstract] |
Thursday, November 14, 2013 4:36PM - 4:48PM |
UO5.00014: Gatling gun approach to long duration x-ray drives for laboratory astrophysics studies David Martinez, J.O. Kane, R.F. Heeter, A. Casner, B. Villette, R.C. Mancini, B.A. Remington Laboratory astrophysics studies investigating the pillar structures in the Eagle Nebula, or photoionization studies require a steady light source of sufficient duration to recreate relevant physics. To address these experimental requirements we successfully developed a 30ns, 90eV x-ray radiation drive using a foam-filled multi-barrel (``Gatling Gun'') hohlraum driven with three 10ns pulse UV beams on the Omega EP laser system located at LLE. The multi-barrel hohlraum consisted of three adjacent Cu cavities, heated in succession to generate long duration x-ray source. The Gatling gun approach mitigated the issues of LEH closure from a single hohlraum heated for extended durations. Characterization of the Gatling gun hohlraum, using uDMX and VISAR diagnostics, will be presented. [Preview Abstract] |
Thursday, November 14, 2013 4:48PM - 5:00PM |
UO5.00015: High-resolution absorption spectroscopy of photoionized silicon plasma, a step toward measuring the efficiency of Resonant Auger Destruction Guillaume Loisel, James Bailey, Stephanie Hansen, Taisuke Nagayama, Gregory Rochau, Duane Liedhal, Roberto Mancini 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 K$\alpha$ photons are resonantly absorbed by neighbor ions. The absorbing ion preferentially decays by Auger ionization, thus reducing the emerging K$\alpha$ intensity. If K$\alpha$ 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. The incident spectral irradiance is determined with time-resolved absolute power measurements, multiple monochromatic gated images, and a 3-D view factor model. The charge state distribution, electron temperature, and electron density are determined using space-resolved backlit absorption spectroscopy. The measurements constrain photoionized plasma models and set the stage for future emission spectroscopy directly investigating the RAD process. [Preview Abstract] |
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