Bulletin of the American Physical Society
59th Annual Meeting of the APS Division of Plasma Physics
Volume 62, Number 12
Monday–Friday, October 23–27, 2017; Milwaukee, Wisconsin
Session JO6: Waves and Space Plasmas |
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Chair: Yi-Min Huang, Princeton University Room: 202C |
Tuesday, October 24, 2017 2:00PM - 2:12PM |
JO6.00001: The Dynamic Local Field Correction of Yukawa Plasmas Yongjun Choi, Gautham Dharuman, Michael Murillo The mean-field approximation is the cornerstone of modern statistical mechanics; therefore, unknowns are ``beyond mean field'' (BMF). Being tantamount to solving the complete many-body problem, however, few accurate BMF models exist even for simplified systems. Knowing the exact representation for the dynamics of a model system provides an important constraint on model validation and an exact limit. The dynamic local field correction (DLFC) is a complex function of wave vector and frequency in which all BMF information is contained. All collisional (e.g., wave damping, transport, equation of state, etc.) information is contained in the DLFC, since it represents the exact solution of the many-body problem. From these two functions (real and imaginary parts) we can validate theoretical models and compute many physical properties (e.g., wave dispersions). In this research, the DLFC will be obtained through molecular dynamics simulations on the Yukawa plasmas. The study covers full range of coupling and screening regimes. [Preview Abstract] |
Tuesday, October 24, 2017 2:12PM - 2:24PM |
JO6.00002: Data-model comparisons of storm-time ion dynamics Amy Keesee, Earl Scime, Yu Huang, Raluca Ilie, Michael Liemohn Plasma sheet conditions play a significant role in inner magnetosphere dynamics, particularly during periods of strong convection, such as during geomagnetic storms. To be able to accurately model the geospace environment, particularly during storm intervals, we must improve our understanding of the mechanisms that influence plasma sheet characteristics, such as ion heating, as well as the processes that transfer plasma sheet particles to the inner magnetosphere. The global view provided by energetic neutral atom (ENA) imaging provides a way to conduct data-model comparisons with both spatial and temporal resolution. Thus, TWINS measurements can provide a useful method for determining which physical processes in a simulation yield accurate modeling of actual events. In turn, the simulations can be used to determine which processes cause the features observed in the measurements. Recent advances in the Hot Electron and Ion Drift Integrator (HEIDI) model enable the use of more realistic magnetic field geometries. HEIDI has been incorporated as one of the inner magnetosphere components within the Space Weather Modeling Framework (SWMF) for global modeling. We present data-model comparisons of ion temperatures during the high speed stream-driven storm on 2 May 2010. [Preview Abstract] |
Tuesday, October 24, 2017 2:24PM - 2:36PM |
JO6.00003: Modelling tangential discontinuities at the Magnetopause with the new Energy Conserving Moment Implicit Method Elisabetta Boella, Alfredo Micera, Diego Gonzalez-Herrero, Maria Elena Innocenti, Giovanni Lapenta Kinetic modeling of heliospheric plasmas is computationally very challenging due to the simultaneous presence of micro and macroscopic scales, which are often interconnected. As a consequence, simulations are expensive and hard to deploy within the existing Particle-In-Cell techniques, being them explicit, implicit or semi-implicit. Very recently we have developed a new semi-implicit algorithm, which is perfectly energy-conserving and as such, stable and accurate over a wide range of temporal and spatial resolutions. In this work, we are going to describe the main steps that led to this great breakthrough and report the implementation of the method in a new massively parallel code, called ECsim. The new approach is then employed to investigate tangential discontinuities (TD) at the magnetopause. Two and three-dimensional simulations of TDs are carried out over MHD time scales, retaining a kinetic description for both electrons and ions with a realistic charge to mass ratio. The formation of a high-energy tail Maxwellian is observed in the distribution function of the electrons on the Earth side. This leads to a crescent-shaped distribution in the plane perpendicular to the magnetic field, in agreement with recent observations of the Magnetospheric Multiscale (MMS) mission. [Preview Abstract] |
Tuesday, October 24, 2017 2:36PM - 2:48PM |
JO6.00004: Formation and transport of entropy structures in the magnetotail simulated with a 3-D global hybrid code Yu Lin, Simon Wing, Jay R. Johnson, Xueyi Wang, Joe D. Perez, Lei Cheng Global structure and evolution of flux tube entropy $S$, integrated over closed field lines, associated with magnetic reconnection in the magnetotail are investigated using the AuburN Global hybrid codE in three dimensions (3-D), ANGIE3D. Flux tubes with decreased entropy, or “bubbles,” are found to be generated due to the sudden change of flux tube topology and thus volume in reconnection. By tracking the propagation of the entropy-depleted flux tubes, the roles of the entropy structure in plasma transport to the inner magnetosphere is examined with a self-consistent global hybrid simulation for the first time. The value of $S$ first decreases due to the shortening of flux tubes and then increases due to local ion heating associated with wave turbulence around the fast flows as the bubbles are injected earthward by interchange-ballooning instability, finally oscillating around an equilibrium radial distance where $S$ is nearly the same as the ambient value. The pressure remains anisotropic and not constant along the flux tubes during their propagation with a nonzero heat flux along the field line throughout the duration of the simulation. The correlation of these bubbles with earthward fast flows and specific entropy $s$ is also studied. [Preview Abstract] |
Tuesday, October 24, 2017 2:48PM - 3:00PM |
JO6.00005: Abstract Withdrawn
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Tuesday, October 24, 2017 3:00PM - 3:12PM |
JO6.00006: Three-dimensional, ten-moment multifluid simulation of the solar wind interaction with Mercury Chuanfei Dong, Ammar Hakim, Liang Wang, Amitava Bhattacharjee, Kai Germaschewski, Gina DiBraccio We investigate Mercury's magnetosphere by using Gkeyll ten-moment multifluid code that solves the continuity, momentum and pressure tensor equations of both protons and electrons, as well as the full Maxwell equations. Non-ideal effects like the Hall effect, inertia, and tensorial pressures are self-consistently embedded without the need to explicitly solve a generalized Ohm's law. Previously, we have benchmarked this approach in classical test problems like the Orszag-Tang vortex and GEM reconnection challenge problem. We first validate the model by using MESSENGER magnetic field data through data-model comparisons. Both day- and night-side magnetic reconnection are studied in detail. In addition, we include a mantle layer (with a resistivity profile) and a perfect conducting core inside the planet body to accurately represent Mercury's interior. The intrinsic dipole magnetic fields may be modified inside the planetary body due to the weak magnetic moment of Mercury. By including the planetary interior, we can capture the correct plasma boundary locations (e.g., bow shock and magnetopause), especially during a space weather event. [Preview Abstract] |
Tuesday, October 24, 2017 3:12PM - 3:24PM |
JO6.00007: Time-dependent study of anisotropy in Rayleigh-Taylor instability induced turbulent flows with a variety of density ratios Ye Zhou, William Cabot This study is part of our continued effort to understand the mixing, scaling, and anisotropy of flows induced by Rayleigh-Taylor instability (RTI). In particular, we utilize three large datasets with different Atwood numbers (density ratios) from well resolved numerical simulations at moderate Reynolds number with the goal of determining the degree of departure of this inhomogeneous flow from that of homogeneous, isotropic turbulence. A number of statistical measurements are considered in detail to delineate the role played by the acceleration or gravity. For example, the normalized dissipation rate is employed to inspect the forcing of the flow in the homogeneous and gravitational directions. The relationship between the outer-scale and the Taylor-microscale based Reynolds numbers is also clarified. These distinctive features of the high-Atwood number RTI flows are observed during the transition to turbulence. [Preview Abstract] |
Tuesday, October 24, 2017 3:24PM - 3:36PM |
JO6.00008: A new regime of whistler propagation in the laboratory Garima Joshi, G. Ravi Experimental observations of a new regime of whistler propagation in the laboratory are reported in this paper. The experiments are carried out in a large laboratory unbounded uniform plasma with density n$_{\mathrm{e}}$ \textasciitilde 10$^{\mathrm{10}}$ -- 10$^{\mathrm{12}}$ cm$^{\mathrm{-3}}$ and magnetic field B$_{\mathrm{0}}$ \textasciitilde 1 -- 20 G. Studies are performed in the electron magnetohydrodynamic regime which is governed by electron dynamics with $\rho_{\mathrm{Le\thinspace }}$\textless \textless L \textless \textless $\rho_{\mathrm{Li}}$, and $\tau _{\mathrm{ci\thinspace }}$\textgreater \textgreater $\tau $ \textgreater \textgreater $\tau_{\mathrm{ce}}$, where L and $\tau $ are spatial and temporal scale lengths of the perturbations, $\rho_{\mathrm{Le}}$ and $\rho_{\mathrm{Li}}$ the electron {\&} ion Larmour radii respectively and $\tau_{\mathrm{ci}}$ {\&} $\tau_{\mathrm{ce}}$ the temporal scales corresponding to the ion gyro frequency and electron gyro frequency respectively. The complete topology of the perturbed wave magnetic field is unraveled by mapping it on a two dimensional grid over repeated plasma shots. It is observed that the excited waves are elongated whistlers in the propagation direction, with the perpendicular extent limited to scale lengths of the order of natural scale length of plasma i.e. the skin depth (\textasciitilde c/$\omega_{\mathrm{pe}})$, rather than being more oblique as predicted by theory and observed in other experiments. The waves do not show any dispersive nature, contrary to the whistler characteristics, while still being able to maintain the whistler speed for the given plasma and pulsed current parameters. The above observed results are explained in terms of a new physical model. [Preview Abstract] |
Tuesday, October 24, 2017 3:36PM - 3:48PM |
JO6.00009: Observation of multiple chirping events in electron cyclotron emission of non-equilibrium mirror-confined plasma Mikhail Viktorov, Alexander Shalashov, Dmitry Mansfeld, Sergey Golubev Chirping frequency patterns have been observed in the electron cyclotron emission from a strongly non-equilibrium mirror-confined plasma created by powerful microwave radiation of gyrotron (37.5 GHz, 80 kW) under ECR conditions. The dynamic spectrum of emission is a set of highly chirped radiation bursts with both increasing and decreasing frequencies. Such patterns are typical for the formation of nonlinear phase-space structures in a proximity of the wave-particle resonances of a kinetically unstable plasma, also known as the ``holes and clumps'' mechanism or Berk-Breizman model [1]. Our data provide the first experimental evidence for the acting of this mechanism in the electron cyclotron frequency domain [2]. Following the Berk-Breizman model, the frequency drift within each wave packet is proportional to the instability growth rate and has a predetermined time dependence. Resulting from the analysis of the microwave emission spectrum, the value of the growth rate is consistent with previous studies of excitation of extraordinary waves at the stage of plasma decay, which confirms the applicability of the model. [1]~H.L. Berk, B.N. Breizman, N.V. Petviashvili, \textit{Phys. Lett. A} , V.234, P.213 (1997). [2]~M.E.~Viktorov, \textit{et al.}, \textit{EPL}, V.116, P.55001 (2016) [Preview Abstract] |
Tuesday, October 24, 2017 3:48PM - 4:00PM |
JO6.00010: Nonlinear frequency shift on an electron plasma wave : hysteresis, nonlocality and multidimensional effects in an inhomogeneous plasma Didier Benisti We provide a general derivation of the nonlinear frequency shift, $\delta \omega $, for a sinusoidal electron plasma wave (EPW) that varies slowly enough for neo-adiabatic theory to apply. We first consider the situation when the EPW monotonously grows and then monotonously decays in a homogeneous plasma. In this situation, we show a hysteresis in the wave frequency, which does not converge back to its linear value as the wave decays to small amplitudes. We then address the derivation of $\delta \omega $ for an EPW that keeps growing in a one-dimensional (1-D) inhomogeneous plasma. We show that, usually, the frequency shift does not only depend on the local EPW amplitude and wavenumber. It also depends on the whole history of the density variations, as experienced by the wave. In a multidimensional inhomogeneous plasma, the values assumed by $\delta \omega $ are usually different from those derived in 1-D because, due to the transverse electron motion, one must account for the hysteresis in $\delta \omega $ in addition to plasma inhomogeneity. Hence, unless the EPW keeps growing in a homogeneous 1-D plasma, one cannot derive $\delta \omega $ a priori as a function of the local wave amplitude and wavenumber. Due to the nonlocality in the action distribution function, $\delta \omega $ depends on the whole history of the variations of the EPW amplitude and plasma density. [Preview Abstract] |
Tuesday, October 24, 2017 4:00PM - 4:12PM |
JO6.00011: Cinematic Characterization of Convected Coherent Structures Within an Continuous Flow Z-Pinch Thomas Underwood, Jesse Rodriguez, Keith Loebner, Mark Cappelli In this study, two separate diagnostics are applied to a plasma jet produced from a coaxial accelerator with characteristic velocities exceeding $10^{5}$ m/s and timescales of $\sim 10$ $\mu$s. In the first of these, an ultra-high frame rate CMOS camera coupled to a Z-type laser Schlieren apparatus is used to obtain flow-field refractometry data for the continuous flow Z-pinch formed within the plasma deflagration jet. The 10 MHz frame rate for 256 consecutive frames provides high temporal resolution, enabling turbulent fluctuations and plasma instabilities to be visualized over the course of a single pulse. The unique advantage of this diagnostic is its ability to simultaneously resolve both structural and temporal evolution of instabilities and density gradients within the flow. To allow for a more meaningful statistical analysis of the resulting wave motion, a multiple B-dot probe array was constructed and calibrated to operate over a broadband frequency range up to 100 MHz. The resulting probe measurements are incorporated into a wavelet analysis to uncover the dispersion relation of recorded wave motion and furthermore uncover instability growth rates. Finally these results are compared with theoretical growth rate estimates to identify underlying physics. [Preview Abstract] |
Tuesday, October 24, 2017 4:12PM - 4:24PM |
JO6.00012: Reception of Microwave Signals through a Shear Flow with Lower Hybrid Turbulence Saba Mudaliar A variety of instabilities is known to be generated in plasma flows with velocity shear. We consider the case when an external magnetic field is present orthogonal to the flow direction. The scale length of the velocity shear is assumed to be considerably larger than the electron gyro radius but much smaller than the ion gyro radius. Thus, the ions are unmagnetized while the electrons are magnetized. These conditions induce lower hybrid instabilities (LHI) in the flow. Our interest is to understand the impact of such LHI on the reception microwave signals propagating through the flow. A statistical analysis is carried out by decomposing the received signal into two parts: coherent and diffuse. We find that the coherent part has the same spectrum as that of the incident signal, but undergoes dispersive attenuation. The diffuse part is obtained as a convolution (in wavenumber and frequency) of the source signal with the spectrum of electron density fluctuations. We find that the mean free path is an important quantity for understanding the impact of the turbulent flow on the coherent and diffuse parts of the received signals. Detailed analysis is presented to investigate the physics of various scattering processes involved in this problem. [Preview Abstract] |
Tuesday, October 24, 2017 4:24PM - 4:36PM |
JO6.00013: Spatial Studies of Ion Beams in an Expanding Plasma Evan Aguirre, Timothy Good, Earl Scime, Derek Thompson We report spatially resolved perpendicular and parallel ion velocity distribution function (IVDF) measurements in an expanding argon helicon plasma. The parallel IVDFs, obtained through laser induced fluorescence (LIF), show an ion beam with v ∼ 8 km/s flowing downstream that is confined to the center of the discharge. The ion beam is confined to within a few centimeters radially and is measurable for tens of centimeters axially before the LIF signal fades, likely a result of metastable quenching of the beam ions. The axial ion beam velocity slows in agreement with collisional processes. The perpendicular IVDFs show an ion population with a radially outward flow that increases with radial location. The DC electric field, electron temperature, and the plasma density in the double layer plume are all consistent with magnetic field aligned structures. The upstream and downstream electric field measurements show clear evidence of an ion hole that maps along the magnetic field at the edge of the plasma. Current theories and simulations of double layers, which are one-dimensional, completely miss these critically important two-dimensional features. [Preview Abstract] |
Tuesday, October 24, 2017 4:36PM - 4:48PM |
JO6.00014: Evidence of Mixed-mode oscillations and Farey arithmetic in double plasma system in presence of fireball Vramori Mitra, Bornali Sarma, Arun Sarma Plasma fireballs are luminous glowing region formed around a positively biased electrode. The present work reports the observation of mix mode oscillation (MMO) in the dynamics of plasma oscillations that are excited in the presence of fireball in a double plasma device. Source voltage and applied electrode voltage are considered as the controlling parameters for the experiment. Many sequences of distinct multi peaked periodic states reflects the presence of MMO with the variation of control parameter. The sequences of states with two patterns are characterized well by Farey arithmetic, which provides rational approximations of irrational numbers. These states can be characterized by a firing number, the ratio of the number of small amplitude oscillations to the total number of oscillations per period. The dynamical transition in plasma fireball is also demonstrated by spectral analysis, recurrence quantification analysis (RQA) and by statistical measures viz., skewness and kurtosis. The mix mode phenomenon observed in the experiment is consistent with a model that describes the dynamics of ionization instabilities. [Preview Abstract] |
Tuesday, October 24, 2017 4:48PM - 5:00PM |
JO6.00015: Development of a methodology for deriving Plasmaspheric Total Electron Content from In-Situ electron density measurements in highly eccentric equatorial orbits Aliyuthuman Sadhique, Andrew Buckley, Paul Gough The contribution of the Upper Plasmasphere (defined as the altitudes above semi-synchronous orbit height to the Plasmapause height) to the TEC has been and continues to be un-quantified. The PEACE instrument in the Chinese -- ESA Double Star TC1 satellite, the mission's orbit's high eccentricity, low perigee, high apogee and the resulting smaller incident angle while in the above altitude range provide the ideal geometric opportunity to build a methodology and to utilize its empirical in-situ electron density measurements to determine the Upper Plasmaspheric TEC component. Furthermore, the variation of the Inclination Angle of TC1 makes it a suitable equatorial mission confined to the Near-Equatorial region, ie 20$^{\mathrm{0}}$ - 25$^{\mathrm{0}}$ on either sides of the magnetic equator. As the most pronounced absolute TEC values and variations are within this region, it offers an excellent opportunity to build a Upper Plasmaspheric TEC database. This research generates such, first-ever database along its orbital path, using a methodology of approximation equating arcs of the orbits to straight-line TEC Bars, utilizing complex mathematics, also enabling the determination of the whole Plasmaspheric TEC from any eccentric orbital probe [Preview Abstract] |
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