Bulletin of the American Physical Society
54th Annual Meeting of the APS Division of Plasma Physics
Volume 57, Number 12
Monday–Friday, October 29–November 2 2012; Providence, Rhode Island
Session JM9: Mini-Conference: Nonlinear Effects in Geospace Plasmas II |
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Chair: Gurudas Ganguli, Naval Research Laboratory Room: 553AB |
Tuesday, October 30, 2012 2:00PM - 2:12PM |
JM9.00001: Wave-Particle Interactions in the Turbulent Plasmaspheric Boundary Layer Evgeny Mishin We present in situ satellite observations of plasmaspheric lower hybrid/fast magnetosonic turbulence and broadband hiss-like VLF emissions related with substorm subauroral ion drifts/polarization streams (SAID/SAPS) in the magnetosphere and topside ionosphere. SAID/SAPS appear in $\sim $10 min after the substorm onset consistent with the fast propagation of substorm injection fronts. The SAID channel follows the dispersionless cutoff of the energetic electron flux at the plasmapause. This indicates that the cold plasma maintains charge neutrality within the channel, thereby short-circuiting the injected plasmoid (injection front) over the plasmasphere. As with the well-documented plasmoid-magnetic barrier problem, plasma turbulence ensures the circuit resistivity and magnetic diffusion as well as significant electron heating and acceleration. The SAID/SAPS-related VLF emissions were used to simulate interactions with the outer zone electrons. These emissions appear to constitute a distinctive subset of substorm/storm-related VLF activity in the region co-located with freshly injected energetic ions equatorward of the plasma sheet boundary. Significant pitch-angle diffusion coefficients suggest that substorm SAID/SAPS-related VLF waves could be responsible for the alteration of the outer radiation belt boundary during (sub)storms. [Preview Abstract] |
Tuesday, October 30, 2012 2:12PM - 2:24PM |
JM9.00002: Laboratory investigation of nonlinear whistler wave processes B. Amatucci, E. Tejero, C. Cothran, G. Ganguli, C. Crabtree, M. Mithiawala, V. Sotnikov Nonlinear interactions involving whistler wave turbulence result from processes, including wave-particle interactions and instabilities in sharp boundary layers. Given sufficient whistler energy density, nonlinear scattering off thermal electrons substantially changes the wave vector direction and energy flux, while inducing a small frequency shift.\footnote{Crabtree \textit{et al}., \textit{Phys. Plasmas}, \textbf{19}, Art. No. 032903 (2012).} In the magnetosphere, boundary layers often have highly sheared plasma flows and lower hybrid turbulence. Such nonlinear processes are being investigated in the NRL Space Chamber in conditions scaled to match the respective environments. By creating boundary layers with controllable density gradient and transverse electric fields and scale length much smaller than an ion gyroradius, lower hybrid waves consistent with the Electron-Ion Hybrid Instability\footnote{Ganguli \textit{et al}., \textit{Phys. Fluids}, \textbf{31}, 2753 (1988).} have been observed. Sufficiently large amplitude lower hybrid waves have been observed to scatter into whistler modes by scattering from thermal electrons. The plasma response as a function of transmitted lower hybrid wave amplitude is monitored with magnetic antennas. Details of the observed wave spectra and mode characteristics will be presented. [Preview Abstract] |
Tuesday, October 30, 2012 2:24PM - 2:36PM |
JM9.00003: Laboratory Experiments of Electromagnetic Velocity Shear-driven Instabilities Erik Tejero, William Amatucci, Christopher Crabtree, Gurudas Ganguli, Christopher Cothran \textit{In situ} observations of sheared plasma flows collocated with electromagnetic wave activity have led to a laboratory effort to investigate the impact of electromagnetic, velocity shear-driven instabilities on the near-Earth space plasma dynamics. Results from laboratory experiments will be presented that demonstrate strongly localized DC electric fields perpendicular to the ambient magnetic field can behave as a radiation source for electromagnetic ion cyclotron waves, transporting energy away from the region of wave generation. The transition from electrostatic to electromagnetic ion cyclotron (EMIC) wave propagation has been investigated under scaled ionospheric conditions. The general wave characteristics and wave dispersion experimentally observed are in agreement with theory. In addition, the electromagnetic component of these waves increased by two orders of magnitude as the plasma $\beta $ was increased. The observed EMIC waves are predominantly azimuthally propagating m=1 cylindrical waves, which propagate in the direction of the \textbf{E}$\times $\textbf{B} drift. Experimental observations and comparison to theory will be presented. [Preview Abstract] |
Tuesday, October 30, 2012 2:36PM - 2:48PM |
JM9.00004: Novel Techniques for Exploring the Physics of the Radiation Belts Konstantinos Papadopoulos The plasma physics of the Radiation Belts (RB) is a premier scientific topic with important technological implications. A new mission the Radiation Belt Storm Probes (RBSP) will be launched in August, 2012, fully instrumented to explore the RB Physics with emphasis on particle interactions with low frequency plasma waves that control the rates of energetic particle precipitation, acceleration and transport. An important difficulty with passive observation, such as the RBSP, is the ``chicken {\&} egg'' problem. Namely particles drive waves while waves precipitate, accelerate and transport particles. It is a complex, non-linear interaction with multiple feedbacks. The two-satellite coverage provided by RBSP and similar missions does not allow for uniquely identifying cause and effect. A new technology recently developed using ionospheric heaters -- powerful HF transmitters or phased arrays - that allow controlled heating of the ionosphere provides us with means for injecting low frequency waves in the ULF/ELF/VLF range into the RB and using the satellites overflying the heater magnetic flux tubes to diagnose the wave particle interactions. The paper will provide a comprehensive planning of experiments that use the HAARP, Arecibo and SURA heaters in conjunction with RBSP and other satellite missions, such as the Air Force DSX and the Russian RESONANCE, to provide new inroads into the RB physics. [Preview Abstract] |
Tuesday, October 30, 2012 2:48PM - 3:00PM |
JM9.00005: 3D Simulations of Farley-Buneman Turbulence Demonstrates Anomalous Electron Heating Meers Oppenheim, Yakov Dimant Field aligned currents flow from the magnetosphere to the E-region ionosphere where they drive auroral electrojets. These currents often cause Farley-Buneman (FB) instabilities to develop and become turbulent. These irregularities substantially affect ionospheric conductivity, temperatures, and VHF and UHF radio wave propagation. Many of the observed characteristics of radar measurements of this region result from the nonlinear behavior of this unstable plasma. Supercomputers now allow Particle-In-Cell (PIC) codes, to run simulations with enormous meshes in either 2-D or 3-D. This talk will present recent 3-D PIC simulations showing anomalous electron heating due to FB turbulence, a phenomenon clearly observed by radars. The resulting temperatures can rise over an order of magnitude. These simulations also show the saturated amplitude of the waves; coupling between linearly growing modes and damped modes; the evolution of the system from shorter to longer wavelengths; and phase velocities close to the acoustic speed. These simulations reproduce many of the observational characteristics of type-1 radar echoes. As predicted by theory, the 3-D simulations show the development of modes with a small electric field component parallel to the geomagnetic field and this field causes the majority of the anomalous electron heating. [Preview Abstract] |
Tuesday, October 30, 2012 3:00PM - 3:12PM |
JM9.00006: Nonlinear Pressure Anisotropy Yielding Multiple Reconnection Regimes A. Le, J. Egedal, W. Daughton, H. Karimabadi Fully kinetic PIC simulations exhibit several regimes for the saturated state of a reconnecting current sheet. The electron dynamics vary with the characteristics of thermal electron orbits, which depend nonlinearly on the implemented mass ratio, strength of the guide magnetic field, and electron beta. The inflow electron pressure becomes anisotropic due to electron trapping effects with a strong dependence on density variations, and the highest anisotropy is predicted to develop in low beta plasmas [1]. For the weakest guide fields, effective pitch angle scattering causes the outflow electron pressure to become nearly isotropic. Above a certain threshold guide field, the electron orbits remain magnetized in the exhaust and the pressure anisotropy extends into the outflow. In simulations at the physical proton-to-electron mass ratio, the electron pressure anisotropy may then drive magnetized current layers [2] longer than 15 ion inertial lengths similar to layers inferred from spacecraft observations in the magnetosphere [3].\\[4pt] [1] Le et al., GRL 37, L03106 (2010).\\[0pt] [2] Ohia et al., PRL (2012).\\[0pt] [3] Phan et al, PRL 99, 255002 (2007) [Preview Abstract] |
Tuesday, October 30, 2012 3:12PM - 3:24PM |
JM9.00007: Formal Derivation of Model for Electron Anisotropy in Expanding Flux Ropes and Collisionless Magnetic Reconnection J. Egedal, A. Le, O. Ohia, F. Diaz, W. Daughton, V.S. Lukin Based on mainly heuristic arguments and an understanding of single electron motion within reconnection regions an approximate solution to the Vlasov equation was previously obtained [1]. This solution accounts for the anisotropy in the electron distribution that develops non-linearly due to trapping in magnetic wells and parallel electric fields, and it has been used as closure yielding general equation of state for the parallel and perpendicular electron pressures [2]. The model has been confirmed in kinetic simulations and through measurements by spacecraft in the Earth magnetotail [3]. It has also formed the basis for new fluid simulations that for the first time reproduces the detailed geometry of the reconnection region seen in kinetic simulations including elongated current sheets [4]. Here we report on a new rigorous derivation of the model using the drift kinetic equation, emphasizing its broad range of validity and application. \\[1ex] [1] J Egedal et al., J. Geophys. Res., 113, A12207 (2008).\\[0ex] [2] A Le et al., Phys. Rev. Lett., 102, 085001 (2009). \\[0ex] [3] J Egedal et al., J. Geophys. Res., 115, A03214 (2010). \\[0ex] [4] O Ohia et al., Phys. Rev. Lett (in press 2012). [Preview Abstract] |
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