Bulletin of the American Physical Society
57th Annual Meeting of the APS Division of Plasma Physics
Volume 60, Number 19
Monday–Friday, November 16–20, 2015; Savannah, Georgia
Session BO7: Shocks, Reconnection, Emission |
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Chair: Will Fox, Princeton Plasma Physics Laboratory Room: 203 |
Monday, November 16, 2015 9:30AM - 9:42AM |
BO7.00001: Laboratory High-velocity, Laser-Driven, Magnetized, Collision-less Flows Henri Pepin, D. Higginson, Ph. Korneev, J. Beard, S.N. Chen, M. Grech, L. Gremillet, E. d'Humi\`eres, S. Pikuz, B. Pollock, C. Ruyer, R. Riquier, J. Fuchs Understanding the mechanism leading to the acceleration of cosmic-ray particles up to extremely high-energies is an outstanding problem in astrophysics. This acceleration is thought to be linked to the collision-less shocks formed by the collision of energetic magnetized astrophysical outflows such as supernovae remnants and gamma-ray bursts. To gain insight on these particle accelerators, we have performed experiments on the Titan laser (60J/beam, 650fs). By irradiating opposing targets we launch two counter-streaming beams, embedded in an external 20T B-field. We observe a density increase in the middle of the streams and a proton acceleration at double the energy without external field. Particle-in-cell simulations show that the expansion of the beams causes a compression of the external B-field up to 500T, which is strong enough to reflect electrons from the strong field region. This creates a charge-separation and causes the development of strong E-fields which accelerates the ions at large energies, consistent with the experiment. [Preview Abstract] |
Monday, November 16, 2015 9:42AM - 9:54AM |
BO7.00002: The Design of Useful Mix Characterization Experiments for the LLNL Reshock Platform Tanim Islam The NIF Re-shock platform has been extensively engineered to minimize boundary effects and polluting shocks. It is capable of comprehensively and reproducibly exploring a large parameter space important in mix experiments: strength and timing of shocks and reshocks; the amplitude and wavelength of Richtmyer-Meshkov-unstable interfaces; the Atwood number of these mixing layers; and using a technique developed with experiments at the Omega laser, the simultaneous visualization of spike and bubble fronts. In this work, I explore multimodal and roughened surface designed, and combinations of light and heavy materials, that may illuminate our understanding of mix in plasmas. [Preview Abstract] |
Monday, November 16, 2015 9:54AM - 10:06AM |
BO7.00003: Quantum molecular dynamics simulations of argon along the multi-shock Hugoniot line Huayang Sun, Dongdong Kang, Jiayu Dai, Jiaolong Zeng, Jianmin Yuan The equation of states of argon along the multi-shock Hugoniot line from 0.02 eV, 0.5 g/cc to 3 eV 5.5 g/cc are calculated by the pair potential and the first principles calculations with and without van der Waals corrections. The calculations of 273 K isothermal line from 0.5 to 5.5 g/cc show that: (a). at 0.5 g/cc, the precision increase from Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional without vdW correction, PBE exchange-correlation functional with force-field corrections method by Grimme (DFT-D), van der Waals density functional method of version 2 (vdW-DF2), to pair potential [1]; (b). the pair potential and vdW-DF2 tend to overestimate the pressure at high densities. The pressures above 1 eV show that DFT-D gives consistent results with PBE, which are larger than those of the pair potential, while the pressures of vdW-DF2 increase a little quickly with temperature. The Hugoniot lines of DFT-D are consistent with the 1st shock results of the experiments [2], but have departures with the results after the 1st shock.\\[4pt] [1] K. Patkowski et al., Molecular Physics 103:15-16, 2031 (2005).\\[0pt] [2] Q. F. Chen et al., J. Chem. Phys. 140, 074202 (2014)\\[0pt] [3] Jiayu Dai et al. Phys. Rev. Lett. 109: 175701 (2012). [Preview Abstract] |
Monday, November 16, 2015 10:06AM - 10:18AM |
BO7.00004: Investigations of Molecular Emission from Laser Ablation Plumes Interacting with Background Gases of Varying Density Jeremy Iratcabal, Aaron Covington, Manolo Sherrill Laser ablation of solid targets provides a versatile platform for investigating the interplay between molecular spectral emission and fluid dynamic properties of low-temperature plasmas. To this end, we have developed an experimental apparatus capable of measuring the plasma plume${'}$s spatial- and temporal-evolution in a controlled environment. Changes in molecular emission were recorded as a function of changing the Reynolds number of the background gas by varying gas pressure and species. In the experiments, time-gated molecular spectra were measured from plumes produced from low- to mid-Z targets with laser intensities ranging from 10$^{7}$ to 10$^{11}$ W/cm$^{2}$. The experimental results will be discussed within the framework of radiation hydrodynamic models being developed to describe these complex plasma phenomena. [Preview Abstract] |
Monday, November 16, 2015 10:18AM - 10:30AM |
BO7.00005: ABSTRACT WITHDRAWN |
Monday, November 16, 2015 10:30AM - 10:42AM |
BO7.00006: Effects of Synchrotron Cooling on Relativistic Magnetic Reconnection Jake Fish, Gregory Werner, Dmitri Uzdensky Magnetic reconnection studies have traditionally focused on plasmas for which radiative processes are dynamically unimportant. However, astrophysical phenomena can create conditions such that radiative cooling can become important over the timescale of reconnection. In particular, synchrotron radiation should play an important role in the strongly magnetized, highly relativistic pair plasmas found in the magnetospheres of gamma-ray pulsars. We study the effects of radiative cooling on reconnection using the particle-in-cell code Zeltron that includes, self-consistently, the synchrotron radiation reaction force. Basic plasma parameters, such as the average particle energy and density at magnetic X-points in the reconnection layer, are measured as functions of radiative cooling strength. We also examine the resulting global particle energy distribution and the emitted synchrotron radiation spectrum. These results allow us to assess reconnection as a possible mechanism powering the pulsed high-energy gamma-ray emission observed in pulsar magnetospheres. [Preview Abstract] |
Monday, November 16, 2015 10:42AM - 10:54AM |
BO7.00007: Electron and ion heating characteristics during magnetic reconnection in MAST Hiroshi Tanabe, Takuma Yamada, Takenori Watanabe, Keii Gi, Kazutake Kadowaki, Michiaki Inomoto, Ryota Imazawa, Mikhail Gryaznevich, Clive Michael, Neil Conway, Rory Scannell, Brendan Crowley, Ken McClements, Yasushi Ono Localized electron heating at X point and global ion heating in the downstream during merging/reconnection startup of ST in MAST have been studied in detail using 130 channel YAG- and 300 channel Ruby-Thomson scattering measurement and a new 32 chord ion Doppler tomography diagnostics. In addition to the previously achieved record heating of $\sim$1keV, 2D profile of electron temperature revealed highly localized heating structure at X point with the characteristic scale length of 0.02-0.05m $< c/\omega_{pi}$, while the ion temperature increases in the downstream of outflow jet with the width of $c/\omega_{pi}\sim0.1$m where reconnected field forms thick layer of closed flux surface. The effect of $T_i-T_e$ energy relaxation also affects both heating profiles in MAST, finally the formation of triple peak structure for both profiles was observed with the delay of $\tau^{E}_{ei}$. The toroidal guide field mostly contributes to the formation of a localized electron heating structure at the X point but not to bulk ion heating downstream. [Preview Abstract] |
Monday, November 16, 2015 10:54AM - 11:06AM |
BO7.00008: Asymmetric coupled interchange-ballooning dynamics during magnetic reconnection in the solar wind driven magnetosphere Ehab Hassan, W. Horton, D.R. Hatch, O. Agullo, M. Muraglia, S. Benkadda Fast reconnection in the magnetosphere and the geomagnetic tail involves electron scale dynamics that includes the electron inertial scale length on the inner scale and the ion gyroradius on the outer scale. New forms of the partial differential equations for the electric and magnetic field during the fast interchange dynamics. Typical data is that of the fast reconnection with dominant electron heating reported in the Nakamura et al. from CLUSTER data. New formulas extend to smaller scales the previous simulations of Horton et al. [2007] for this event by including more electron dynamics and heating. 3D-simulations and movies of the dynamics are presented. [Preview Abstract] |
Monday, November 16, 2015 11:06AM - 11:18AM |
BO7.00009: Orientation of x-lines in asymmetric magnetic reconnection Yi-Hsin Liu, Michael Hesse, Masha Kuznetsova At Earth's magnetopause, reconnection proceeds asymmetrically between magnetosheath plasmas, namely solar wind plasmas compressed by Earth's bow shock, and magnetospheric plasmas. In an asymmetric configuration, it is unclear if there is a simple principle to determine the orientation of the x-line. Using fully kinetic simulations, we study this issue and a spatially localized perturbation is employed to induce a single x-line, that has sufficient freedom to choose its orientation in three-dimensional systems. The effect of ion to electron mass ratio is investigated, and the x-line appears to bisect the magnetic shear angle across the current sheet in the large mass ratio limit. The deviation from the bisection angle in the lower mass ratio limit can be explained by the physics of tearing instability.\footnote{Yi-Hsin Liu et al. (2015), arXiv:1504.03300 } The local physics control of the x-line orientation studied in this slab geometry could potentially interplay with global geometrical effects to determine the location of collisionless magnetic reconnection at Earth's magnetopause. [Preview Abstract] |
Monday, November 16, 2015 11:18AM - 11:30AM |
BO7.00010: How ions gain energy in driven magnetic reconnection? C.Z. Cheng, Shizuo Inoue, Yasushi Ono, Ritoku Horiuchi We report physical understanding of how ions move across the reconnection current layer and the separatrix regions into the downstream and how they are accelerated/heated by the inductive and electrostatic electric fields during driven anti-parallel magnetic reconnection in collisionless plasmas. Because the ion gyroradii are comparable to or larger than the electrostatic electric field spatial localization width and the magnetic field scale length in these regions, the ion dynamics decouples from the electron dynamics. Based on the full ion orbit dynamics under the influence of the inductive and electrostatic electric fields, which have both perpendicular and parallel electric field components, we explain how the ion velocity distribution changes and how ions flow through the reconnection current layer and across the separatrix into the downstream. We find that ions gain energy mainly from the inductive electric field and less from the electrostatic electric field. [Preview Abstract] |
Monday, November 16, 2015 11:30AM - 11:42AM |
BO7.00011: Magnetic Reconnection-Powered Relativistic Particle Acceleration, High-Energy Gamma-Ray Emission, and Pair Production in Coronae of Accreting Black Holes Dmitri Uzdensky Magnetic reconnection is a fundamental plasma process believed to play an important role in energetics of magnetically-dominated coronae of various astrophysical objects including accreting black holes. Building up on recent advances in kinetic simulations of relativistic collisionless reconnection, we investigate nonthermal particle acceleration and its key observational consequences for these systems. We argue that reconnection can efficiently accelerate coronal electrons (as well as ions) up to hundreds of MeV or even GeV energies. In brightest systems, radiation back-reaction due to inverse-Compton (and/or synchrotron) emission becomes important at these energies and limits any further electron acceleration, thereby turning reconnection layers into powerful and efficient radiators of $\gamma$-rays. We then evaluate the rate of absorption of the resulting $\gamma$-ray photons by the ambient soft (X-ray) photon fields and show that it can be a significant source of pair production, with important implications for the composition of black-hole coronae and jets. Finally, we assess the prospects of laboratory studies of magnetic reconnection in the physical regimes relevant to black-hole accretion flows using modern and future laser-plasma facilities. [Preview Abstract] |
Monday, November 16, 2015 11:42AM - 11:54AM |
BO7.00012: Magnetized Weibel filaments as a source of circularly polarized light Ujjwal Sinha, Joana Martins, Jorge Vieira, Ricardo Fonseca, Luis Silva We investigate radiation spectra of plasma particles trapped in Weibel filaments generated from multidimensional particle in cell simulations with OSIRIS in magnetized and unmagnetized plasmas. We show that an important parameter determining polarization of emitted radiation is the magnetization of ambient media. Polarization of radiation emitted during counter-propagating plasma flows with different~magnetizations is explored by extracting trajectories of particles sampled from PIC simulations and computing their radiation spectrum. Particle trajectories in magnetized plasmas undergo EXB drift at Weibel boundaries leading to a preferential drift direction, whereas, in unmagnetized case the particles have no net drift. As a result, significant fraction of radiated energy from magnetized filament is circularly polarized (CP). Energy attributed to different polarizations is calculated by measuring degree of polarizations. With increasing magnetization, the fraction of radiated energy attributed to CP increases. The direction of circular polarization also changes with direction of applied magnetic field. The study is of significance for understanding radiation from Gamma Ray Bursts. [Preview Abstract] |
Monday, November 16, 2015 11:54AM - 12:06PM |
BO7.00013: Plasma waves around separatrix in collisionless magnetic reconnection with weak guide field Yangao Chen, Keizo Fujimoto, Chijie Xiao, Hantao Ji Electrostatic and electromagnetic waves excited by electron beam around the separatrix region are analyzed in detail during the collisionless magnetic reconnection with a weak guide field by using 2D particle-in-cell simulation with the adaptive mesh refinement. Broadband electrostatic waves are excited both in the inflow and outflow regions around the separatrices due to the electron bump-on-tail, two-stream, and Buneman instabilities. In contrast, the quasi-monochromatic electromagnetic waves are excited only in the inflow side of the separatrices due to a beam-driven Whistler instability. The localization of the Whistler waves is attributed to the non-uniformity of the out-of-plane magnetic field By. The Whistler instability is suppressed in the outflow side where By is too small for the oblique propagation. The electrostatic waves with distinct speeds can explain the in situ spacecraft observations. From the causality point of view, the waves are generated as the consequence of the electron bulk acceleration to thermalize the particles through wave-particle interactions. These simulation results provide guidance to analyze high-resolution wave observations during reconnection in the ongoing and upcoming satellite missions, as well as in dedicated laboratory experiments. [Preview Abstract] |
Monday, November 16, 2015 12:06PM - 12:18PM |
BO7.00014: Waves in 3D Magnetic Nulls: some preliminary results in the PPT device and in situ Measurements in the Magnetosphere Chijie Xiao, Xiaoyi Yang, Yangao Chen, Yihang Chen, Xiaogang Wang Plasma waves and the particle dynamics in the magnetic null are very important to understand the three-dimensional (3D) magnetic reconnection process. A small plasma device, which named PPT device (abbreviated form of PKU Plasma Test device), has setup recently to study the waves and particle dynamics around a magnetic null. Here we will report the first preliminary results, such as the waves along the spines and the fan surfaces, as well as the particle dynamics around it. Furthermore, some wave modes around 3D nulls detected by Cluster mission in the magnetosphere will also be reported to compare. These preliminary results will give more clues to understanding of the magnetic nulls and 3D magnetic reconnection. [Preview Abstract] |
Monday, November 16, 2015 12:18PM - 12:30PM |
BO7.00015: Conceptual Design of the Harbin Reconnection eXperiment (HRX) Aohua Mao, Peng E, Xiaogang Wang, Hantao Ji, Yang Ren A new terrella device, called the Space Environment Simulation and Research Infrastructure or SESRI, is under construction at Harbin Institute of Technology, in which the Harbin Reconnection eXperiment (HRX) system is one of the most important components. The goal of HRX reconnection experiment design is to provide a unique platform for studying reconnections relevant to those in magnetopause and magnetotail. Most of the currently existing terrella experiments have been focusing on global phenomena, e.g. bow shock, in either linear or toroidal geometry, which are typically very different in magnetosphere plasmas. The new HRX regimes explores both local and global reconnection dynamics by driving reconnection with a unique set of coils in a dipole magnetic field configuration which will be able to investigate a range of important reconnection issues in magnetosphere geometry. The design of the HRX device approximately follows the Vlasov similarity laws between the laboratory plasma of the device and the magnetosphere plasma to match local reconnection dynamics. Motivation, design criteria for the HRX experiments, and the preliminary experiment proposal will be discussed. [Preview Abstract] |
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