Bulletin of the American Physical Society
56th Annual Meeting of the APS Division of Plasma Physics
Volume 59, Number 15
Monday–Friday, October 27–31, 2014; New Orleans, Louisiana
Session NO5: Space Plasma |
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Chair: Jason TenBarge, University of Maryland Room: Galerie 2 |
Wednesday, October 29, 2014 9:30AM - 9:42AM |
NO5.00001: Properties of Plasma Turbulence in Two and Three Dimensions Tak Chu Li, Gregory Howes, Jason TenBarge Two important time scales in a turbulent system are the time of nonlinear energy cascade, which occurs dominantly in the plane perpendicular to a strong background magnetic field B$_{0}$, and the crossing time of Alfven waves propagating parallel to B$_{0}$. Two-dimensional (2D) turbulence studies assume the former to be much shorter than the latter and hence neglect the latter. Without the direction along B$_{0}$, 2D studies can only account for a weak in-plane component of Alfven waves, which does not fully describe the dynamics involving the propagation of Alfven waves dominantly along B$_{0}$. Using gyrokinetic simulations, we explore the properties of plasma turbulence with equivalent systems in two and three dimensions. Preliminary results show very different behavior in the two cases. The 3D system is much more dynamic than the 2D system, implying that processes in 3D are occurring at a different time scale than those in 2D. Key properties of the two systems are being investigated. [Preview Abstract] |
Wednesday, October 29, 2014 9:42AM - 9:54AM |
NO5.00002: ABSTRACT WITHDRAWN |
Wednesday, October 29, 2014 9:54AM - 10:06AM |
NO5.00003: Current sheets and heating in fluid and kinetic simulations of MHD turbulence Kirit Makwana, Fausto Cattaneo, Hui Li, William Daughton, Vladimir Zhdankin Magnetohydrodynamic (MHD) turbulence is often invoked as a way to convert magnetic and kinetic energy in large scale plasma motions to thermal energy of plasma particles, thus leading to energy dissipation. However, collisional diffusion is very weak in plasmas. It is believed that kinetic diffusion processes might play an important role in the dissipation mechanism. To understand such processes, we analyze MHD turbulence using both fluid and particle-in-cell kinetic codes. We simulate an ensemble of strongly interacting shear-Alfven waves and compare their turbulent spectra. The kinetic code produces a slightly steeper energy spectrum. The global energy dynamics for both the codes are very similar, despite their vastly different physics at the small scales. We focus on the formation of thin current sheets and the dissipation within them by comparing the current sheet morphology between the two codes. It is found that the current sheet thickness is related to the particle inertial length. Heating is correlated with the current sheets and is preferentially in the parallel direction. This provides a way for directly simulating physical dissipation in plasmas. [Preview Abstract] |
Wednesday, October 29, 2014 10:06AM - 10:18AM |
NO5.00004: Energy Dissipation in Magnetohydrodynamic Turbulence: Coherent Structures or Nanoflares? Vladimir Zhdankin, Stanislav Boldyrev, Jean Carlos Perez, Steven Tobias Energy dissipation in magnetohydrodynamic (MHD) turbulence is known to be highly intermittent, occurring mainly in current sheets. However, the question remains whether the overall energy dissipation is dominated by small (dissipation-scale) structures or by large (inertial-range) structures. To systematically investigate this question, we develop and apply a procedure to identify and characterize dissipative structures in numerical simulations of reduced MHD. We find that the probability distribution of energy dissipation rates exhibits a power law tail with index very close to the critical value of -2.0, indicating that structures of all intensities contribute equally to the overall energy dissipation. We then measure the characteristic spatial scales of structures using two methods: one based on the linear scales across the structure and the other based on the Minkowski functionals, which rigorously characterize the morphology of any shape. We find that energy dissipation is dominated by coherent structures with lengths and widths uniformly distributed across the inertial range, while thicknesses lie deep within the dissipative regime. As the Reynolds number is increased, structures become thinner and more numerous, while the energy dissipation continues to occur mainly in large-scale coherent structures. The current sheets therefore exhibit features of both coherent structures and nanoflares. [Preview Abstract] |
Wednesday, October 29, 2014 10:18AM - 10:30AM |
NO5.00005: Predictions for in situ Observations of Turbulent Power Spectra within the Alfven Critical Point Kristopher Klein, Benjamin Chandran In preparation for the launch of Solar Probe Plus, which will make unprecedented \emph{in situ} measurements of the solar wind in the inner heliosphere, we present a series of predictions for these observed turbulent spectra. A number of mechanisms unique to the near-Sun solar wind will make the task of interpreting measurements quite difficult, including an imbalanced flux of turbulent Alfv\'enic fluctuations with possibly distinct spectral power laws, the possible violation of the Taylor hypothesis, and the rapidly varying motion both radial and transverse to the spacecraft. We incorporate these mechanisms into analytic predictions for the observed power spectra, as well as into previously validated techniques for creating synthetic time series from a spectrum of linear eigenmodes. These predictions for the observed spectra may be used to distinguish between competing turbulence theories which may impact solar wind acceleration and the heating of the Sun's corona. [Preview Abstract] |
Wednesday, October 29, 2014 10:30AM - 10:42AM |
NO5.00006: Properties of Magnetic Plasma Turbulence at Small Scales Stanislav Boldyrev, Qian Xia, Vladimir Zhdankin, Jean Carlos Perez Solar wind observations show that the Alfvenic energy cascade continues to and beyond the scales where the one-fluid magnetohydrodynamic description breaks down. We analyze the properties of small-scale Alfvenic turbulence in the presence of a strong background magnetic field, to understand the physics governing the transition from large-scale hydromagnetic to small-scale kinetic turbulence. The physical interpretation of subproton plasma turbulence is proposed. [Preview Abstract] |
Wednesday, October 29, 2014 10:42AM - 10:54AM |
NO5.00007: Self-Similar Kinetic Theory in the Solar Wind: Data and Simulations Konstantinos Horaites, Stanislav Boldyrev, Sergei Krasheninnikov, Chadi Salem, Stuart Bale, Marc Pulupa If the temperature Knudsen number $\gamma(x)=L_{mfp}|dlnT/dx|$ in a plasma is constant thoughout the system, the collisional kinetic equation for electrons admits self-similar solutions. These solutions have the novel property that the 'shape' of the eVDF does not vary in space. Such a theory should be applicable in the solar wind, where the density and temperature are observed to vary as power laws with heliocentric distance r such that $\gamma(r)\sim$constant. We present results of numerical simulations, where we find the steady-state eVDF for various $\gamma$. We then compare the predictions of the theory with satellite observations from the Helios and Wind missions. Overall, the theory exhibits remarkable consistency with a variety of electron measurements, and provides an intuitive context for understanding the steady-state solar wind eVDFs. [Preview Abstract] |
Wednesday, October 29, 2014 10:54AM - 11:06AM |
NO5.00008: Electron Magnetohydrodynamic Turbulence: Universal Features Bhimsen Shivamoggi The energy cascade of electron magnetohydrodynamic (EMHD) turbulence is considered (Shivamoggi [1]). Several basic features of the EMHD turbulent system are found to be universal which seem to transcend the existence of the characteristic length scale $d_e$ (which is the electron skin depth) in the EMHD problem--- \begin{itemize} \item {\it equipartition} spectrum, \item Reynolds-number scaling of the dissipative microscales, \item scaling of the probability distribution function (PDF) of the electron-flow velocity (or magnetic field) gradient (even with intermittency corrections), \item {\it dissipative anomaly}, \item {\it critical exponent} scaling. \end{itemize} [1] B. K. Shivamoggi: arXiv:1105.3741, (2014). [Preview Abstract] |
Wednesday, October 29, 2014 11:06AM - 11:18AM |
NO5.00009: Parallel and Perpendicular Diffusion of Cosmic Rays in Turbulent Plasmas: Analytical Theory and Simulation Mohammad Hussein, Andreas Shalchi A fundamental problem in Space Science and Astrophysics is the interaction between energetic particles and a turbulent plasma. We have developed a test-particle code to simulate the interaction of charged particles with turbulent magnetic fields. Diffusion coefficients along and across the mean magnetic field are calculated and compared to different analytical theories. Different turbulence models where considered such as models with reduced dimensionality and full three-dimensional models. We have also included wave propagation effects. We explored the transport regimes in which the Bohm limit and the quasilinear limit are valid. We also shown that for perpendicular diffusion the so-called unified non-linear transport theory agrees very well with the numerical simulations. [Preview Abstract] |
Wednesday, October 29, 2014 11:18AM - 11:30AM |
NO5.00010: The Use of Orbital Tethers to Remediate Geomagnetic Radiation Belts Mathias Hudoba de Badyn, Richard Marchand, Richard Sydora The Van Allen radiation belts pose a hazard to spacecraft and astronauts, and similar radiation belts around other planets pose a hazard to interplanetary probes. We discuss a method of remediating these radiation belts proposed by Hoyt, Minor and Cash where a long, charged tether is placed in orbit inside a radiation belt. The electric field of the tether adiabatically scatters the belt particles into a pitch angle loss cone due to absorption of the particles in the atmosphere. We present a test particle calculation which computes the scattered pitch angle of belt particles as a function of initial pitch angle and gyrophase for different particle energies. We then use the moments of the resulting histogram of scattered angle versus initial pitch angle to compute the number density of the belt as a function of time using a Fokker-Planck diffusion model. Finally, we use the characteristic timescales of scattering for particles of different energies to discuss the feasibility of using such a system of tethers as a long and short-term remediation solution. [Preview Abstract] |
Wednesday, October 29, 2014 11:30AM - 11:42AM |
NO5.00011: Investigation of Storm-Time Magnetotail and Ion Injection Using 3-D Global Hybrid Simulation Yu Lin, Xueyi Wang, San Lu, Joe Perez, Quanming Lu Dynamics of the near-Earth magnetotail associated with substorms during a period of extended southward IMF is studied using a 3-D global hybrid simulation model that includes both the dayside and night side magnetosphere. Dayside reconnection leads to the penetration of the dawn-dusk electric field and thus a thinning of the plasma sheet, followed by the magnetotail reconnection with 3-D flux ropes. Hall electric fields in the thin current layer cause a systematic dawnward ion drift motion and thus a dawn-dusk asymmetry of the plasma sheet with a higher (lower) density on the dawn (dusk) side. Correspondingly, more reconnection and more earthward ion injections occur on the dusk side than the dawn side. Such finding is consistent with recent satellite observations. Ion particle distributions reveal multiple populations/beams. Oscillation of the dipolarization front is developed at the fast flow braking. Kinetic compressional wave turbulence is present around the dipolarization front. A shear-flow instability is found on the dusk side flank of the ring current plasma, whereas a kinetic ballooning instability appears on the dawn side. Shear Alfv\'en waves and compressional wave are generated, and they evolve into kinetic Alfv\'en waves (KAWs) in the dipole-like field region. [Preview Abstract] |
Wednesday, October 29, 2014 11:42AM - 11:54AM |
NO5.00012: Equatorial Electrojet Instabilities - New Fluid Model Approach Ehab Hassan, Wendell Horton, Andrei Smolyakov, David Hatch A fluid model combines both Farley-Buneman (Type-I) and Gradient-Drift (Type-II) plasma instabilities in the equatorial electrojet. The ion viscosity and electron inertia are considered in the ion and electron equations of motion, respectively. These two terms play an important role in stabilizing the growing modes in the linear regime and in driving Farley-Buneman instability into the saturation state. The simulation is stable in the saturated state and the results show good agreements with a number of rocket measurements and radar observations, where we find (1) a saturation of the plasma density around 7\% relative to the ionosphere background, (2) the horizontal secondary electric field stabilizes at 8.7 (mV/m), (3) the phase velocity of the perturbed density wave has a value close to the ion-acoustic speed inside the electrojet, (5) an up-down asymmetry in the vertical particle fluxes of plasma density, (5) an east-west asymmetry in the plasma drifts in the zonal direction, and (6) a generation of the small-scale; of the order of 3 meter scale length and less, irregularities embedded in the large-scale structures in the vertical direction. The break-up of the large-scale structures into small-scale structures explains the disappearance of Type-II echoes in the presence of Ty [Preview Abstract] |
Wednesday, October 29, 2014 11:54AM - 12:06PM |
NO5.00013: Rossby-Khantadze Electromagnetic Planetary Waves Driven by Sheared Zonal Winds in the E-Layer Ionosphere S. Futatani, W. Horton, L.Z. Kahlon, T. Kaladze Nonlinear simulations are carried out for planetary scale [$>$ 1000km] electromagnetic Rossby and Khantadze planetary waves in the presence of a sheared zonal flow in the weakly ionized ionospheric E-layer. A variety of sheared flow profiles are studied. We shown that the nonlinear dynamics with the sheared zonal flows provides an energy source into the vortex structures. The energy transfer through the Reynolds stress tensor produces growth of the stable vortices under a variety of conditions. The energy accumulation breaks the vortex structure into multiple species according to the non-uniformity of profile of the external zonal shear flows. S. Futatani, W. Horton, T. D. Kaladze, Phys. Plasmas 20, 102903 (2013). T. D. Kaladze, L. Z. Kahlon, W. Horton. O Pokhotelov, and O. Onishenchenko, Shear flow driven Rossby-Khantadze electromagnetic planetary vortices in the ionospheric E-Layer, EPL, 106, A05302 (2014). doi: 10.1209/0295-5075/106/29001 [Preview Abstract] |
Wednesday, October 29, 2014 12:06PM - 12:18PM |
NO5.00014: Iron opacity experiments for the solar interior T. Nagayama, J.E. Bailey, G. Loisel, G.A. Rochau, S.B. Hansen, C. Blancard, Ph. Cosse, G. Faussurier, F. Gilleron, J.-C. Pain, A.K. Pradhan, C. Orban, M. Pinsonneault, S.N. Nahar, C.A. Iglesias, B. Wilson, J. Colgan, C. Fontes, D. Kilcrease, M. Sherrill, J.J. MacFarlane, I. Golovkin, R.C. Mancini Iron opacity experiments near solar interior conditions are performed at SNL Z-machine to better constrain solar models. The SNL opacity science platform satisfies the many challenging requirements for opacity measurements and successfully determines iron opacities at multiple conditions. We found that the agreement between the modeled opacity and the measured opacity deteriorates as Te and ne are raised to approach solar interior conditions. While the inaccuracy of the modeled opacity partially resolves the solar abundance problem, the announcement of such discrepancies has a high impact on the astrophysics, atomic physics, and high energy density physics, and thus more scrutiny on the potential experimental flaws is critical. We report the synthetic investigation for potential sources of systematic uncertainties in the experiments. [Preview Abstract] |
Wednesday, October 29, 2014 12:18PM - 12:30PM |
NO5.00015: Analysis of Electron Evolution in Air using Updated Cross Section Data (LA-UR-14-25207) Elise Pusateri, Heidi Morris, Wei Ji For the purpose of modeling the time evolution of electron temperature in an Electromagnetic Pulse, a swarm model has been developed. This code uses an adaptive time step and solves a system of coupled differential equations for the electric field, electron temperature, electron number density, and drift velocity. Our comparisons with microwave and DC breakdown measurements have revealed that, for high values of E/p, the swarm model underestimates the equilibrium temperature that is achieved in experiments. Our initial work used energy and momentum transfer collision frequencies that were reported in Higgins, Longmire, and O'Dell (1973). We have updated the electron-air cross sections using those reported in the LXcat database as a part of the Plasma Data Exchange Project. New momentum and energy transfer collision frequencies, defined over a broader energy range, have been calculated using a two-term Boltzmann Equation solver, BOLSIG$+$. We report on the use of these updated collision frequencies in the swarm code and show the improvement in our calculation by comparing the results with experimental data. [Preview Abstract] |
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