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 GO7: Space and Astrophysical Plasmas |
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Chair: Kristopher Klein, University of Michigan Room: 212 AB |
Tuesday, November 1, 2016 9:30AM - 9:42AM |
GO7.00001: 3D Laboratory Measurements of Forces, Flows, and Collimation in Arched Flux Tubes Magnus Haw, Paul Bellan Fully 3D, vector MHD force measurements from an arched, current carrying flux tube (flux rope) are presented. The experiment consists of two arched plasma-filled flux ropes each powered by a capacitor bank. The two loops are partially overlapped, as in a Venn diagram, and collide and reconnect during their evolution. B-field data is taken on the lower plasma arch using a 54 channel B-dot probe. 3D volumetric data is acquired by placing the probe at 2700 locations and taking 5 plasma shots at each location. The resulting data set gives high resolution (2cm, 10ns) volumetric B-field data with high reproducibility (deviation of ~3\% between shots). Taking the curl of the measured 3D B-field gives current densities (J) in good agreement with measured capacitor bank current. The JxB forces calculated from the data have a strong axial component at the base of the current channel and are shown to scale linearly with axial gradients in current density. Assuming force balance in the flux tube minor radius direction, we infer near-Alfvenic axial flows from the footpoint regions which are consistent with the measured axial forces. Flux tube collimation is observed in conjunction with these axial flows. These dynamic processes are relevant to the stability and dynamics of coronal loops. [Preview Abstract] |
Tuesday, November 1, 2016 9:42AM - 9:54AM |
GO7.00002: Three-Dimensional Hybrid-Kinetic Simulations of Alfvénic Turbulence in the Solar Wind Lev Arzamasskiy, Matthew Kunz, Ben Chandran, Eliot Quataert It is well established that the solar wind is turbulent, exhibiting a power spectrum extending over several decades in scale and with most of the energy at large scales is in form of Alfv\'{e}nic fluctuations. The solar wind is also weakly collisional, with a wide variety of non-Maxwellian features observed in the particle distribution functions. In this talk, we present the first hybrid-kinetic three-dimensional simulations of driven Alfv\'{e}nic turbulence in the solar wind. We confirm power-law indices obtained in previous analytical and numerical (e.g., gyrokinetic) studies, and carefully explore the location of and physics occurring at the ion Larmor scale. In the low-beta regime, we find evidence of stochastic heating, which arises when ions interact with strong fluctuations at wavelengths comparable to the ion Larmor scale. Finally, we discuss the interpretation of spacecraft measurements of the turbulence by testing the Taylor hypothesis with synthetic spacecraft measurements of our simulation data. [Preview Abstract] |
Tuesday, November 1, 2016 9:54AM - 10:06AM |
GO7.00003: ABSTRACT WITHDRAWN |
Tuesday, November 1, 2016 10:06AM - 10:18AM |
GO7.00004: Kappa distributions in the presence of a potential energy George Livadiotis Classical particle systems reside at thermal equilibrium with their velocity distribution function stabilized into a Maxwell distribution. On the contrary, collisionless and correlated particle systems, such as geophysical, space, and astrophysical plasmas, are characterized by a non-Maxwellian behavior, typically described by the so-called kappa distributions, or combinations thereof. Empirical kappa distributions have become increasingly widespread across plasma physics. A breakthrough in the field came with the connection of kappa distributions to non-extensive statistical mechanics. Understanding the statistical origin of kappa distributions was the cornerstone of further theoretical developments and applications, one of which is the generalization to the phase-space kappa distributions of a Hamiltonian with non-zero potentials. We present the theory behind the phase-space kappa distributions and discuss three important applications in collisionless plasmas: (i) origin of polytropic relation; (ii) gravitational field; (iii) barometric relation (i.e., pressure vs. altitude); and (iv) plasma magnetization. [Preview Abstract] |
Tuesday, November 1, 2016 10:18AM - 10:30AM |
GO7.00005: MMS observations of plasma wave and electron energization in the electron diffusion region of asymmetric reconnection with strong guide field Chijie Xiao, Siqi Zhao, Mijie Shi, Zuyin Pu, Xiaogang Wang Here we report an asymmetric reconnection event with strong guide field observed by Magnetospheric Multiscale Mission (MMS) on the dayside magnetopause. In this event there are multiple wave modes, such as electron Alfvenic mode, broadband waves between the lower-hybrid and electron cyclotron frequencies, exist in the vicinity of the electron diffusion region and the separatrix. And the electron velocity distribution functions show that bi-stream electrons with low energy (\textless 230eV) keep along the magnetic field, while fluxes of electrons with energy higher than 230eV increases dramatically around the X-line. The wave-particle interactions and electron energization processes are investigated and comparison with some 3D numerical simulation results. [Preview Abstract] |
Tuesday, November 1, 2016 10:30AM - 10:42AM |
GO7.00006: A Lower Hybrid Fluid Model and Asymptotic Solutions Xiaogang Wang Hall MHD is for ion dynamics with a zero mass electron fluid. EMHD is for electron dynamics with fixed (infinity mass) ions. Also, other approximations such as electron incompressibility and low frequency appraisal (by ignoring the displacement current) have limited the application of EMHD. We then introduce a “Lower Hybrid Fluid” model by keeping \begin{figure}[htbp] \centerline{\includegraphics[width=1.17in,height=0.23in]{150720161.eps}} \label{fig1} \end{figure} the higher order mass ratio terms in the two-fluid model to investigate the problems in a hybrid scale range between the electron skin depth and the ion inertial length. [Preview Abstract] |
Tuesday, November 1, 2016 10:42AM - 10:54AM |
GO7.00007: Conceptual Design of Tail-Research EXperiment (T-REX) on Space Plasma Environment Research Facility Qingmei Xiao, Xiaogang Wang, Peng E, Chao Shen, Zhibin Wang, Aohua Mao, Chijie Xiao, Weixing Ding, Hantao Ji, Yang Ren Space Environment Simulation Research Infrastructure (SESRI), a scientific project for a major national facility of fundamental researches, has recently been launched at Harbin Institute of Technology (HIT). The Space Plasma Environment Research Facility (SPERF) for simulation of space plasma environment is one of the components of SESRI. It is designed to investigate fundamental issues in space plasma environment, such as energetic particles transportation and the interaction with waves in magnetosphere, magnetic reconnection at magnetopause and magnetotail, etc. Tail-Research Experiment (T-REX) is part of the SPERF for laboratory studies of space physics relevant to tail reconnection and dipolarization process. T-REX is designed to carry out two kinds of experiments: the tail plasmamoid for magnetic reconnection and magnetohydrodynamic waves excited by high speed plasma jet. In this presentation, the scientific goals and experimental plans for T-REX together with the means applied to generate the plasma with desired parameters are reviewed. Two typical scenarios of T-REX with operations of plasma sources and various magnetic configurations to study specific physical processes in space plasmas will also be presented. [Preview Abstract] |
Tuesday, November 1, 2016 10:54AM - 11:06AM |
GO7.00008: Anomalous Faraday rotation in the ISM/ICM Mikhail V. Medvedev Faraday effect is a common and useful way to deduce cosmic magnetic fields in the interstellar and intracluster media (ISM and ICM). Faraday rotation is the result of magnetically-induced birefringence in a dielectric medium causing a linearly polarized wave to suffer a rotation of its polarization axis as it traverses such a medium. However, the standard $\lambda^2$-law of the rotation angle may not hold in strongly turbulent plasmas. Electromagnetic high-frequency and/or small-scale fluctuations may lead to effective collisionality with the pitch-angle diffusion coefficient being an effective ``quasi-collision" frequency. Recently, we showed that quasi-collisionality may radically alter radiative transport properties of plasmas, such as absorption, transmission and reflection and other effects, which can be very important in laboratory and astrophysical plasmas. Here we briefly discuss the quasi-collisional generalization of the classical Faraday effect, which is drastically modified and can even become negative. Furthermore, we explore the origin of the long-known anomaly of Faraday rotation in a famous Cygnus regions. We argue that the anomaly can be due to the anomalous Faraday rotation in a thin ``blanket" of turbulent plasma at the front of an interstellar bubble/shock. [Preview Abstract] |
Tuesday, November 1, 2016 11:06AM - 11:18AM |
GO7.00009: Explosive reconnection and particle acceleration in relativistic plasmas Maxim Lyutikov, Sergey Komissarov, Oliver Porth, Lorenzo Sironi We develop a model of particle acceleration in explosive reconnection events in relativistic magnetically-dominated plasmas. We identify two stages of particle acceleration: (i) fast explosive prompt X-point collapse and (ii) ensuing island merger. The fastest acceleration occurs during the initial catastrophic X-point collapse, with the reconnection electric field of the order of the magnetic field. During the X-point collapse particles are accelerated by charge-starved electric fields, which can reach (and even exceed) values of the local magnetic field. The explosive stage of reconnection produces non-thermal power-law tails with slopes that depend on the average magnetization sigma. The model has all the ingredients needed for Crab flares: natural formation of highly magnetized regions, explosive dynamics on light travel time, development of high electric fields on macroscopic scales and acceleration of particles to energies well exceeding the average magnetic energy per particle. [Preview Abstract] |
Tuesday, November 1, 2016 11:18AM - 11:30AM |
GO7.00010: A PIC Simulation Study of Electron Viscosity and Thermal Conduction in Collisionless Plasmas Mario Riquelme, Eliot Quataert, Daniel Verscharen We use particle-in-cell (PIC) simulations to study the interplay between electron- and ion-scale velocity-space instabilities and their effect on electron pressure anisotropy, viscous heating, and thermal conduction. The adiabatic invariance of the magnetic moment in low-collisionality plasmas gives rise to pressure anisotropy, with $p_{\perp,j}-p_{\parallel,j} > 0$ ($<0$) if the magnetic field magnitude $|\vec{B}|$ grows (decreases), where $p_{\perp,j}$ and $p_{\parallel,j}$ denote the pressure of species $j$ [electron or ion] perpendicular and parallel to $\vec{B}$. If the resulting anisotropy is large enough, it can trigger small-scale plasma instabilities. By imposing a shear in the plasma we either amplify or decrease the magnetic field $|\vec{B}|$. When $|\vec{B}|$ is amplified, we explored the nonlinear regime of the mirror, ion-cyclotron, and electron whistler instabilities. When $|\vec{B}|$ is decreased, we studied the nonlinear regime of the ion- and electron-firehose instabilities. We discuss the implications of our results for electron heating and thermal conduction in low-collisionality accretion flows onto black holes, like Sgr A*. We also discuss the possible implications for the thermal conductivity of plasma in the outer parts of massive, hot, galaxy clusters. [Preview Abstract] |
Tuesday, November 1, 2016 11:30AM - 11:42AM |
GO7.00011: Kinetic Magnetorotational Turbulence and Dynamo Matthew Kunz, James Stone, Eliot Quataert Low-luminosity black-hole accretion flows, such as that at the Galactic center, are collisionless. A kinetic approach is thus necessary to understand the transport of heat and angular momentum, the acceleration of particles, and the growth and structure of the magnetic field in these systems. We present results from the first 6D kinetic numerical simulation of magnetorotational turbulence and dynamo, using the local shearing-box model. Special attention will be paid to the enhanced transport of angular momentum by field-aligned pressure anisotropies, as well as to the ion-Larmor-scale kinetic instabilities (firehose, mirror, ion-cyclotron) which regulate those anisotropies. Energy spectra and phase-space evolution will be discussed. Time permitting, dedicated nonlinear studies of firehose and mirror instabilities in a shearing plasma will also be presented as a complement to the study of the magnetorotational instability. The profits, perils, and price of using a kinetic approach will be briefly mentioned. [Preview Abstract] |
Tuesday, November 1, 2016 11:42AM - 11:54AM |
GO7.00012: Analysis of the effects of atomic mass, jet velocity, and radiative cooling on the dimensionless parameters of counter-propagating, weakly collisional plasma flows Gilbert Collins, Julio Valenzuela, Farhat Beg We have studied the collision of counter-propagating plasma flows using opposing conical wire arrays driven by the 200kA, 150ns rise-time 'GenASIS' driver. These plasma flows produced weakly collisional, well-defined bow-shock structures*. Varying initial parameters such as the opening angle of the array and the atomic mass of the wires allowed us to modify quantities such as the density contrast between jets, intra-jet mean free path ($\lambda_{\mathrm{mfp}}$, scales with v, atomic mass A, and ionization state Z$_{\mathrm{i}}^{\mathrm{-4}})$, Reynolds number (Re, scales with AZ), and the Peclet number (Pe, scales with Z). We calculate these dimensionless quantities using schlieren imagery, interferometry, and emission data, and determine whether they meet the scaling criteria necessary for the comparison to and subsequent study of astrophysical plasmas. *J.C. Valenzuela-Ahumada \textit{et al.}, \textit{High Energy Density Physics}, (2015). [Preview Abstract] |
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