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 GM10: Mini-Conference: Nonlinear Effects in Geospace Plasmas I |
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Chair: Evgeny Mishin, Air Force Research Laboratory Room: 102 |
Tuesday, November 17, 2015 9:30AM - 9:50AM |
GM10.00001: Weak Turbulence in Radiation Belts Gurudas Ganguli, Chris Crabtree, Leonid Rudakov Weak turbulence plays a significant role in space plasma dynamics. Induced nonlinear scattering dominates the evolution in the low-beta isothermal radiation belt plasmas and affects the propagation characteristics of waves. As whistler waves propagate away from the earth they are scattered in the magnetosphere such that their trajectories are turned earthward where they are reflected back towards the magnetosphere. Repeated scattering and reflection of the whistlers establishes a cavity in which the wave energy can be maintained for a long duration with, on average, a smaller wave-normal angle. Consequently, the cyclotron resonance time for the trapped energetic electrons increases, leading to an enhanced pitch-angle scattering rate. Enhanced pitch-angle scattering lowers the lifetime of the energetic electron population. Also, pitch-angle scattering of the trapped population in the cavity with a loss cone distribution amplifies the whistler waves, which in turn promotes a more rapid precipitation through a positive feedback mechanism. Typical storm-pumped radiation belt parameters and laboratory experiments will be used to elucidate this phenomenon [Preview Abstract] |
Tuesday, November 17, 2015 9:50AM - 10:10AM |
GM10.00002: Laboratory investigation of nonlinear whistler wave processes Bill Amatucci, Erik Tejero, Chris Crabtree, Lon Enloe, Dave Blackwell, Guru Ganguli Nonlinear interactions involving whistler wave turbulence result from processes such as wave-particle interactions in the radiation belts and instability generation in sharp magnetospheric boundary layers. Nonlinear scattering of large amplitude waves off thermal electrons substantially changes the wave vector direction and energy flux, while inducing a small frequency shift [\textit{Crabtree}, \textit{Phys. Plasmas }\textbf{19}, 032903 (2012)]. This nonlinear scattering of primarily electrostatic lower hybrid waves into electromagnetic whistler modes is being investigated in the NRL Space Chamber under conditions scaled to match the respective environments. Lower hybrid waves are generated directly by antennas or self-consistently from sheared cross-magnetic field flows with scale length less than an ion gyroradius via the Electron-Ion Hybrid Instability [\textit{Ganguli}, \textit{Phys. Fluids }\textbf{31}, 2753 (1988)), \textit{Amatucci}, \textit{Phys. Plasmas }\textbf{10}, 1963 (2003)]. Sufficiently large amplitude lower hybrid waves have been observed to convert into whistler modes by scattering from thermal electrons. The plasma response as a function of transmitted lower hybrid wave amplitude is monitored with magnetic loop antennas. Details of the observed wave spectra and mode characteristics will be presented. [Preview Abstract] |
Tuesday, November 17, 2015 10:10AM - 10:30AM |
GM10.00003: Whistler Turbulence Heating of Electrons and Ions: Three-Dimensional Particle-in-Cell Simulations S. Peter Gary, R. Scott Hughes, Joseph Wang Three-dimensional particle-in-cell simulations are used to study the decay of magnetosonic-whistler fluctuations in a collisionless, homogeneous, magnetized, electron-ion plasma model. The simulations are initialized with a distribution of narrowband long wavelength modes that is relatively isotropic and initial electron $\beta_e$ values of 0.25 and 1.0. The computations follow the temporal development of the fluctuations as they cascade to broadband, anisotropic turbulence at shorter wavelengths. Dissipation of the cascaded fluctuations at quasi-perpendicular propagation leads to electron heating preferentially parallel/antiparallel to the background magnetic field ${\bf B}_o$ and ion energy gain is preferentially in directions perpendicular to ${\bf B}_o$ The rate of perpendicular ion heating scales approximately as $\beta_e^{1/2}$ and as the initial energy density of the magnetic fluctuations. [Preview Abstract] |
Tuesday, November 17, 2015 10:30AM - 10:50AM |
GM10.00004: Mid-Latitude Plasma Density Irregularities and Electromagnetic Wave Scattering V. Sotnikov, T. Kim, E. Mishin, D. Rose, I. Paraschiv Ionospheric irregularities cause scintillations of electromagnetic signals that can severely affect navigation and transionospheric communication, in particular during space storms. At midlatitudes, such space weather events are caused mainly by subauroral electric field structures (SAID/SAPS) SAID/SAPS --related shear flows and plasma density troughs point to interchange and Kelvin-Helmholtz type instabilities as a possible source of plasma irregularities. A model of nonlinear development of these instabilities based on the two-fluid hydrodynamic description with inclusion of finite Larmor radius effects will be presented. The high-resolution simulations with continuous density and velocity profiles will be driven by the ambient conditions corresponding to the in situ Defense Meteorological Satellite Program (DMSP) satellite low-resolution data during UHF/GPS L-band subauroral scintillation events. These types of density irregularities play important roles in refraction and scattering of high frequency electromagnetic signals propagating in the Earth's ionosphere, inside the plasma sheath of reentry and hypersonic vehicles, and in many other applications. [Preview Abstract] |
Tuesday, November 17, 2015 10:50AM - 11:10AM |
GM10.00005: Break
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Tuesday, November 17, 2015 11:10AM - 11:30AM |
GM10.00006: Wave-Particle Interactions in the Turbulent Plasmaspheric Boundary Layer Evgeny Mishin A wealth of wave activity around the plasmasphere's boundary enhances during substorm injection events. A turbulent plasmaspheric boundary layer forms initially near the pre-substorm plasmapause due to interactions between the injected and plasmaspheric populations. The free energy for plasma instabilities driving lower hybrid/fast magnetosonic turbulence and broadband hiss-like VLF waves come from substorm-injected hot plasma particles impacting the cold plasmasphere. In particular, the hot electron diamagnetic drift and the highly anisotropic hot ion distribution drive the modified two-stream and ion-ring instabilities in the entry layer and the central part, respectively. The diamagnetic drift of hot ions dominates near the inner edge. Enhanced plasma turbulence leads to heating of the cold plasma and to acceleration of suprathermal electron tails, thereby enhancing the downward heat transport and concomitant heating of the ionospheric electrons. Broadband, hiss-like VLF waves have amplitudes sufficient to provide rapid precipitation of the radiation belt electrons thereby shaping the outer radiation belt boundary. In addition, the hot ions penetrating inside the plasmasphere satisfy the orbit chaotization condition and become demagnetized. These results can also be helpful for understanding impulsive penetration at the magnetopause. [Preview Abstract] |
Tuesday, November 17, 2015 11:30AM - 11:50AM |
GM10.00007: Experimental characterization of broadband electrostatic noise due to plasma compression Ami M. DuBois, Edward Thomas, Jr., William E. Amatucci, Gurudas Ganguli For a wide variety of laboratory and space plasma environments, theory states that plasmas are unstable to transverse shear flows over a very broad frequency range, where the shear scale length (L$_{\mathrm{E}})$ compared to the ion gyro-radius ($\rho_{\mathrm{i}})$ determines the character of the shear-driven instability that may prevail. During active periods in the Earth's magnetosphere, such sheared flows are intensified and broadband electrostatic noise (BEN) is often observed by satellites traversing natural boundary layers. An interpenetrating magnetized plasma configuration is used to create a transverse velocity shear profile similar to that found at natural space plasma boundary layers. The continuous variation and the associated transition of the instability regimes driven by the shear flow mechanism are demonstrated in a single laboratory experiment. For the first time, broadband wave emission, which is correlated to increasing/decreasing stress (i.e., $\rho_{\mathrm{i}}$/L$_{\mathrm{E}})$ on a plasma boundary layer, is found under controlled and repeatable conditions. This result provides evidence that the compression/relaxation of a plasma boundary layer leads to a BEN signature and holds out the promise for understanding the cause and effect of the in situ observation of BEN by satellites. [Preview Abstract] |
Tuesday, November 17, 2015 11:50AM - 12:10PM |
GM10.00008: Laboratory Study of Nonlinear Saturation of Velocity Shear-driven Instabilities Erik Tejero, C. Lon Enloe, Bill Amatucci, Chris Crabtree, Guru Ganguli Space observations, theory, and laboratory experiments have shown that small-scale, localized sheared plasma flows can drive a variety of electrostatic and electromagnetic turbulence over a large frequency range. The Space Physics Simulation Chamber at NRL has been used to study these instabilities from the ion cyclotron to the lower hybrid/whistler regime. Results from recent experiments investigating the nonlinear saturation of these non-local instabilities and the transition to turbulence will be presented. [Preview Abstract] |
Tuesday, November 17, 2015 12:10PM - 12:30PM |
GM10.00009: Laboratory study of spiky potential structures associated with multi-harmonic shear-driven EIC waves Robert Merlino, Guru Ganguli, Su-Hyun Kim A ubiquitous feature of electric fields observed in the Earth's auroral region is their spiky, repetitive nature, and appearance as either unipolar or bipolar pulses. They have been observed on a number of satellites including S3-3, Polar, Viking, and FAST. These spiky structures have been associated with regions of upward ion flows with transverse shear, and multi-harmonic electrostatic ion cyclotron (EIC) waves. The occurrence of these spiky structures has been attributed to various nonlinear processes, e.g., solitary waves. We will present results of a laboratory experiment performed in a double-ended Q machine, in which spiky potential waveforms were observed in association with coherent multi-harmonic EIC waves in a current-less plasma having a region of parallel ion flow with transverse shear. The spiky waveforms are shown to result from the linear superposition of phase-coherent EIC waves. [Preview Abstract] |
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