SM43C-1541
Can kinetic plasma simulation and MHD talk to each other?
Kinetic simulations show faster tearing mode growth and higher amplitude saturation with electron temperature anisotropy. Implicit simulations in 3D show the lower-hybrid drift instability (LHDI) generates anisotropy and that spontaneous, small-scale tearing evolves into rapid, large-scale reconnection. These results for idealized problems on very small scales need to be tested on larger systems with more realistic boundary conditions, for which we need new methods. We extend implicit simulation to magnetohydrodynamic (MHD) scales by adding a simple but self-consistent collision model to Celeste. An input parameter switches Celeste from a kinetic simulation to Hall-MHD, and can be given different values in different regions so that MHD and kinetic regions interact, flux conservation conditions are rigorously satisfied, and the two plasma populations mix on ion time scales. In 2D, we simulate the LHDI with uniform collisionality, and it grows and saturates normally at low collision rates, but with reduced temperature anisotropy. We model a finite-width current sheet in the direction of current flow, as in the magnetotail, using adjacent collisional and collision-less regions. The resistance to current flow in the collisional region induces an out-of-plane return current flow in the collision-less region. To study embedding a kinetic region in a larger MHD domain, we introduce a collisional region along the magnetic field direction, which can cause localized reconnection unless done carefully. We characterize the transparency of the boundary between kinetic and MHD regions to the propagation of waves and plasma flow, and evaluate the adequacy of our simple collision model.
SM43C-1542
On the Anti-critical Temperature for Spacecraft Charging
In recent years, evidence has been found for the existence of a critical temperature for the onset of spacecraft charging to high voltages. Spacecraft charging to high voltages affects scientific instruments on board. However, less attention has been given to low-voltage charging which can also affect scientific experiments on board and is relevant to surface chemistry. There also can exist an anti-critical temperature for low-voltage spacecraft surface charging. Ambient electrons at very low temperatures tend to cause negative surface charging, albeit at low voltages and as the electron temperature increases, the charging ceases at a critical value depending on the surface material. We present the theory and numerical results of anti-critical temperatures for typical surface materials in Maxwellian space plasmas. The change in anti-critical temperature due to a low incident-energy enhancement of the electron backscatter yield, consistent with recent measurements, is discussed. Approximate expressions for the anti-critical temperature upper limits are given, based on Taylor expansions at low temperature of the charging onset equation. It is shown that that the existence of the anti-critical temperature slightly modifies the possible triple root configurations in the flux-voltage characteristic curve for a material. The surface charging effect of a Maxwellian plasma with flux components spanning the anti-critical and critical temperatures is considered. A comparison with an empirical low-voltage charging curve is given.
SM43C-1543
Numerical Analysis on Electric Field Antennas in Space Plasma Environment via Electromagnetic Particle-In-Cell Simulation
For the sophisticated use of electric field antennas for electric field measurements or some active experiments in future magnetospheric missions, we need the precise knowledge of the antenna behavior in space plasma environment. For example, antenna characteristics such as impedance and effective length are essential parameters for determining transfer functions used in the plasma wave data calibration. For the investigation of such antenna behaviors, inhomogeneous plasma environment resulting from plasma-antenna interactions should be taken into consideration in the analyses. However, the analysis of the antenna immersed in space plasma is generally complex because the plasma is a dispersive and anisotropic medium, and thus it is too difficult to include the effects of the inhomogeneous plasma distribution near the spacecraft in antenna analyses using analytic approaches. To conquer the difficulties, we investigated the characteristics of electric field antennas by making the most use of the electromagnetic Particle-In-Cell (EM-PIC) simulations. The PIC simulation enables us to include the kinetic effects of antenna-plasma interactions in the antenna analysis in a self-consistent manner. The present EM-PIC tool is capable of simulating both transmitting and receiving antenna behaviors. In the receiving antenna simulation, we set up external waves in a simulation region and receive them with the antenna placed in the simulation region. By using this method, we evaluated the effective length of antennas onboard scientific spacecrafts. We have also started the investigation of the behavior of antennas that transmit waves with large amplitude. Such high-power antenna behavior will be important for some experiments as the control of high- energy particle flux by wave emissions from the antenna in Earthfs radiation belts. We will report the present status of the EM-PIC simulation tool and the preliminary results obtained in the investigations described above.
SM43C-1544
Cross-Phase Investigation of a Field Line Resonance and a Discrete Continuous Oscillation in the Solar Wind
Discrete field line resonances (FLRs) are a common occurrence in the magnetosphere and are readily observed with the Super Dual Auroral Radar Network (SuperDARN). The source of the stable, monochromatic FLR frequencies is still an unresolved problem. Recent work has presented some evidence that discrete continuous oscillations in the solar wind directly drive magnetospheric FLRs but these studies have concentrated primarily on frequency and amplitude comparisons. Phase is an additional parameter which can be exploited. If discrete solar wind oscillations are the source driving FLRs then they should exhibit phase coherence with the FLR for the duration of the wave event. We present Fourier Transform and wavelet cross-phase measurements to determine the degree of phase coherence between an FLR observed with the SuperDARN Kodiak radar and oscillations in solar wind parameters.
SM43C-1545
Research Tools Available at the Community Coordinated Modeling Center
The Community Coordinated Modeling Center (CCMC), located at NASA Goddard Space Flight Center, provides access to state-of-the-art space weather models to the research community. The majority of the models residing at the CCMC are comprehensive computationally intensive physics-based models. The CCMC also provides free services and tools to assist the research community in analyzing the results from the space weather model simulations. We present an overview of the available services at the CCMC: the Runs-On-Request system, the online visualizations, the Kameleon access and interpolation library, and the CCMC Space Weather Widget. Finally, we discuss the future services and tools in development.
SM43C-1546
Development of a High Energy Ion and Electron Beam Calibration System for Space Plasma Analyzers
It has increasingly become important to have space plasma mass analyzers which can measure 3-dimensinal velocity distributions with wide energy range and fine time and space resolution for comprehensive understanding of space environment surrounding the Earth. A reliable calibration facility capable of simulating variety of space plasma flows is necessary to develop such analyzers. A new system is being developed for calibration of space plasma instruments that uses ion and electron beam of energy range of 5 keV to 150 keV in Plasma and Space Science Center, National Cheng Kung University. The system consists of ion and electron source, ExB mass spectrometer, beam expander, beam accelerator, drift tube and 3-axis turntable in the main chamber. Neutral gas such as N2, O, He, and H2 is introduced to ion source and ionized by an electron gun, then accelerated to an energy of 10 keV/charge and passed to mass spectrometer. The mass spectrometer has a 90 degree crossed electric and magnetic field to select desired mass species. Ion or electron beam is expanded by means of electric field oscillation, 2 set of meshed electrodes, and lends electric field, then accelerated to up to 150keV by potential drop in accelerator tube. Drift tube has two position adjustable slits and a 2-dimentional-beam profile monitor. In the main chamber 3-axis turntable is set. We will discuss the design and progress of the system