Bulletin of the American Physical Society
60th Annual Meeting of the APS Division of Plasma Physics
Volume 63, Number 11
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session BO8: Space and Astrophysical Plasma Processes |
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Chair: Jason TenBarge, Princeton University Room: OCC C120-122 |
Monday, November 5, 2018 9:30AM - 9:42AM |
BO8.00001: Structure of the diffusion region in magnetotail reconnection and its global consequences Li-Jen Chen, Shan Wang, Naoki Bessho, Michael Hesse, Yi-Hsin Liu, Masaaki Yamada, Thomas Moore, Barbara Giles, James L Burch, Roy Torbert The kinetic structure of the region where the plasmas are decoupled from the magnetic field (diffusion region) during reconnection in Earth's magnetotail will be reported based on recent measurements from NASA's Magnetospheric Multiscale (MMS) mission. The structure as exhibited in the plasma distribution functions and electromagnetic fields will be compared with predictions from kinetic simulations to address The derived picture of plasma energization will be discussed in light of the understanding obtained for symmetric reconnection from the Magnetic Reconnection eXperiment (MRX). Open questions will be posted for future investigations. |
Monday, November 5, 2018 9:42AM - 9:54AM |
BO8.00002: Energy conversion and flow in the asymmetric magnetic reconnection layer in laboratory and space plasmas Masaaki Yamada, Li-Jen Chen, Jongsoo Yoo, Shan Wang, Hantao Ji, William Randolph Fox, Jon Jara-Almonte, William Daughton, Ari Le The dynamics and physical mechanisms governing the transfer of magnetic energy to plasma particles are comparatively studied during asymmetric reconnection in both laboratory and space plasmas and within the context of two-fluid physics. Despite huge differences in the physical size of the reconnection layer, 30 cm in the MRX (Magnetic Reconnection Experiment) versus ~500 km at the magnetopause (MMS), remarkably similar characteristics are observed in both plasma dynamics and energy deposition profiles. Specifically, in a strongly asymmetric reconnection layers, in which the plasma density on one side of plasma inflow is significantly larger (>10) than the other, it is found that without guide field, the energy deposition to electrons primarily occurs through je⏊·E⏊ in the electron diffusion region. A modified saddle-back-shaped large potential well is observed within the reconnection plane due to the dynamics of the electron current in the layer, and ions are accelerated at the exhaust region resulting in strong ion heating. We find that nearly 60 % of the incoming magnetic energy is transferred to ions and electrons in almost equal portions while the remainder is transported out to the exhaust region. |
Monday, November 5, 2018 9:54AM - 10:06AM |
BO8.00003: Particle acceleration in compressible reconnection layer Xiaocan Li, Fan Guo, Hui Li Particle acceleration in space and astrophysical magnetic reconnection sites is an important unsolved problem. Earlier kinetic simulations have identified several acceleration mechanisms that are associated with particle guiding-center drift motions. Here, we show that, for sufficient large systems, the energization processes due to particle drift motions can be described as fluid compression and shear. By analyzing results from fully kinetic <div aju"=""> simulations, we show that the compression energization dominates the acceleration of high-energy particles in reconnection with a weak guide field, and the compression and shear effects are comparable when the guide field is 50% of the reconnecting component. Based on this result, we then study the large-scale reconnection acceleration by solving the Parker's transport equation in a background reconnection flow provided by MHD simulations. Due to the compression effect, particles are accelerated to high energies and develop power-law energy distributions. The power-law index and maximum energy depend on guide-field strength and diffusion model. This study clarifies the nature of particle acceleration in reconnection layer, and may be important to understand particle energization during solar flares. |
Monday, November 5, 2018 10:06AM - 10:18AM |
BO8.00004: Numerical study of driven 3D MagnetoHydroDynamics : dynamos and recurrences Rupak Mukherjee, Rajaraman Ganesh, Abhijit Sen Within the framework of MagnetoHydroDynamics, a strong interplay exists between flow and magnetic fields. This interplay is known to lead to several interesting phenomena such as mean-field and fluctuation (or small scale) dynamos, magnetic re-connection and recurrence phenomena, to name a few. Using a set of chaotic flow fields (eg, Arnold-Beltrami-Childress, Taylor-Green etc) driven at certain scales, we numerically integrate a self-consistent set of driven, 3D, weakly compressible MHD equations to study two fundamental processes, namely, the generation of mean magnetic field from the flow fields and the magnetic recurrence phenomena mediated by a dynamical exchange between magnetic and velocity fields via a reconnection process. After demonstrating the numerical convergence, we attempt possible explanation using Hamiltonian field models. |
Monday, November 5, 2018 10:18AM - 10:30AM |
BO8.00005: Operation and Saturation of the Turbulent Dynamo in a Collisionless Magnetized Plasma Denis A St-Onge, Matthew W. Kunz Turbulent amplification of cosmic magnetic fields is constrained in collisionless plasmas by phase mixing of flow variation along the magnetic field and by conservation of the first adiabatic invariant. Using hybrid-kinetic simulations, we show that ion-Larmor-scale instabilities (firehose, mirror), triggered by the adiabatic production of magnetic-field-aligned pressure anisotropy as the magnetic field is stretched, efficiently pitch-angle scatter particles and obviate these constraints. As a result, many features of the turbulent dynamo in a collisionless magnetized plasma are similar to those found in its Pm » 1 MHD counterpart, including an exponential kinematic phase, during which a folded-field topology and Kazantsev spectrum are established, and saturation, in which the magnetic and kinetic energies come into approximate equipartition (albeit not scale by scale). However, there are key differences in the field statistics and dynamo efficiency due to the interplay between the forcing scale, the shrinking ion-Larmor scale, and the evolving scales on which the magnetic field bends and folds. Comparisons with MHD and Braginskii-MHD simulations of turbulent dynamo are made |
Monday, November 5, 2018 10:30AM - 10:42AM |
BO8.00006: Turbulence in magnetized pair plasmas Nuno F Loureiro, Stanislav Boldyrev Alfvénic-type turbulence in strongly magnetized, low-beta pair plasmas is investigated [N.F. Loureiro and S. Boldyrev, arXiv:1805.09224 (2018)]. A coupled |
Monday, November 5, 2018 10:42AM - 10:54AM |
BO8.00007: Fully kinetic simulations of 2D MRI-induced turbulence in an electron-ion plasma Giannandrea Inchingolo, Thomas E Grismayer, Nuno F Loureiro, Ricardo Fonseca, Luis O Silva The magnetorotational instability (MRI) is a crucial mechanism of angular momentum transport in a variety of astrophysical scenarios, as accretion disks near black holes. The MRI has been widely studied using MHD models and simulations, in order to understand the behavior of astrophysical fluids in a state of differential rotation. In radiatively inefficient accretion flow models for accretion onto compact objects, the accretion proceeds via a hot, low-density plasma with the proton temperature larger than the electron temperature. In order to maintain such a two-temperature flow, the typical collision rate must be much smaller than the accretion rate. This suggests that the standard MHD approach may be insufficient, and a kinetic description is required instead.Leveraging on our recent results obtained in 2D pair plasma configuration, we present our recent results on collisionless MRI in electron-ion plasma. Increasing the mass ratio of our simulations, we show the differences between electron-ion plasma and pair plasma in 2D turbulence induced consistently during the saturation regime of the MRI. In particular, we will explore the mechanism responsible for the temperature difference between the two species |
Monday, November 5, 2018 10:54AM - 11:06AM |
BO8.00008: Three-Dimensional Hybrid Kinetic Simulations of Solar Wind Turbulence Lev Arzamasskiy, Matthew W Kunz, Ben Chandran, Eliot Quataert The interplanetary medium hosts a solar wind, which contains a broadband turbulent spectrum of large-amplitude Alfven waves. We present results from hybrid-kinetic simulations of this turbulent and essentially collisionless system. We confirm power-law indices obtained in previous analytical and numerical (e.g., gyrokinetic) studies, and carefully explore the location of the spectral break and physics occurring at the ion-Larmor scale. In the low-beta regime, we find evidence of perpendicular ion heating, which we interpret as stochastic heating arising from interactions between ions and strong fluctuations at wavelengths comparable to the ion-Larmor scale. We explore the dependence of ion heating on plasma beta. Finally, we discuss kinetic features in the ion distribution function and present field-particle correlations. |
Monday, November 5, 2018 11:06AM - 11:18AM |
BO8.00009: Anisotropic phase-space cascades in 3D-3V hybrid-Vlasov-Maxwell simulations of plasma turbulence Silvio Sergio Cerri, Matthew W Kunz, Francesco Califano Elucidating the properties of turbulent fluctuations and how they are dissipated in weakly collisional plasmas is a fundamental step for understanding how turbulence feeds back on the macro-scale evolution of numerous space and astrophysical systems. In situ observations of the solar wind and the terrestrial magnetosheath have highlighted breaks in the turbulent spectra denoting a transition from the MHD inertial range to a kinetic range that arises at scales smaller than the proton gyroradius, as well as generation of structures in the particles distribution function. |
Monday, November 5, 2018 11:18AM - 11:30AM |
BO8.00010: Undamped sound waves in a high-beta collisionless plasma Matthew W Kunz, Jonathan Squire, Alex A. Schekochihin, Eliot J Quataert Many space and astrophysical plasmas are so hot and dilute that they cannot be rigorously described as fluids. These include the solar wind, low-luminosity black-hole accretion flows, and the intracluster medium of galaxy clusters. At the 2017 APS-DPP meeting, we presented hybrid-kinetic simulations of shear-Alfvén waves in high-beta, collisionless, magnetized plasmas, confirming the conjecture by Squire et al. (2016) that such waves "interrupt" at sufficiently large amplitudes by adiabatically driving a field-biased pressure anisotropy that both nullifies the restoring tension force and excites a sea of ion-Larmor-scale instabilities (viz., firehose) that pitch-angle scatter particles. This physics places a beta-dependent limit on the amplitude of shear-Alfvén waves, above which they do not propagate effectively. Here, we demonstrate that similar physics afflicts compressive fluctuations, except that it is the collisionless damping of such waves that is interrupted. Above a beta-dependent amplitude, compressive fluctuations excite ion-Larmor-scale mirror and firehose fluctuations, which trap and scatter particles, thereby impeding phase mixing of the distribution function and yielding MHD-like dynamics. Implications for magnetokinetic turbulence and transport will be discussed. |
Monday, November 5, 2018 11:30AM - 11:42AM |
BO8.00011: Numerical Prediction of Magnetorotational Instability in Magnetized Taylor-Couette Flow with Conducting Endcaps Himawan Wicaksono Winarto, Kyle J Caspary, Dahan Choi, Fatima Ebrahimi, Erik P Gilson, Jeremy Goodman, Hantao Ji Simulations of the Princeton Magnetorotational Instability (MRI) experiment with conducting axial boundaries using the SFEMaNS code have numerically established MRI unstable region in the operating parameter space of rotation speed and external axial magnetic field. Effects of MRI can be seen both through an increase of the radial magnetic field and through the formation of a radially-inward jet at the mid-plane. The generation of radial magnetic field is currently being investigated experimentally using Hall sensors on the inner and outer cylinder of the Taylor-Couette device in which the experiment is conducted. These measurements can be directly compared to the simulation results. |
Monday, November 5, 2018 11:42AM - 11:54AM |
BO8.00012: Laboratory Astrophysics - Cold Absorption Itay Gissis, Ehud Behar, Amnon Fisher The ability to create plasma sources similar in nature to astrophysical sources, but scaled to the laboratory, is extremely challenging. Specifically, photo-ionized plasmas that are common around black-hole accretion sources, nebulae and the cold interstellar medium, require powerful radiation sources that are not usually accessible in the laboratory. This leaves the photo-ionized plasma models and codes used by astrophysicists with severe uncertainties. In the following study, we use a high-energy current generator combined with a gas-puff z-pinch load, to create a controlled X-ray source. The source is used to photo-excite and photo-ionize cold gas of astrophysical abundant elements such as oxygen and nitrogen in vacuum. We developed a spectroscopic apparatus dedicated to measure absorption spectra from which we calibrate atomic and molecular electronic transitions, coefficients, wavelengths, oscillator-strengths and cross-sections of the cold absorber. These measurements can be used to mitigate the lack of accurate atomic data in these elements, which is specifically important to better analyze many astrophysical spectra. The experimental plasma source, the diagnostic system, and preliminary results of the X-ray source characterization will be presented. |
Monday, November 5, 2018 11:54AM - 12:06PM |
BO8.00013: Atomic Modeling of Photoionization Fronts in Nitrogen Gas William J Gray, Paul A Keiter, Heath Joseph LeFevre, Cody R Patterson, Joshua S Davis, Bartholomeus Van der Holst, Ken Powell, R. Paul Drake Photoionization fronts play a dominant role in many astrophysical situations, but remain difficult to achieve in a laboratory experiment. Recent papers have suggested that photoionization fronts can be generated in nitrogen gas held at ten atmospheres of pressure and is irradiated by a source with a radiation temperature of TR ∼ 100 eV. We present a suite of one-dimensional numerical simulations using the Helios multi- material radiation hydrodynamics code. We present the results of varying the atomic kinetics and radiative transfer on the formation of a photoionization front and the results of a suite of models that vary the nitrogen pressure and peak radiation temperature.
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