Previous observations have suggested a number of dusty plasma phenomena on the lunar surface, including dust charging, levitation and horizontal transport. These observations include Surveyor images of Horizon Glow (HG), astronaut sketches of dust "streamers" and in-situ measurements made by the Lunar Ejecta and Meteorite (LEAM) experiment. Recent laboratory experiments have approximately reproduced the near surface lunar plasma environment and shown that charging can lead to the levitation and transport of dust grains in a tenuous electron sheath. A critical ingredient to the observed phenomena is the presence of a photoelectron sheath, formed when solar ultraviolet radiation causes the lunar regolith to emit electrons. In order to understand the dynamics of dust particles on the surface of the Moon, the lunar photoelectron sheath has been modeled via a 1-dimensional particle-in-cell (PIC) code. Simulations have focused on the effects of a non-Maxwellian photoelectron velocity distribution and the presence of an incoming solar wind flux. Using the sheath profiles obtained by the PIC code, the charging and dynamics of micron-sized dust grains in the lunar photoelectron sheath are investigated. The presence of non-monotonic sheath potential profiles and their possible impact on the analysis of Lunar Prospector data will also be discussed.
Dust particles detected by sensors on spacecraft carry precious information about their parent bodies. For example, the composition of dust grains ejected from a moon's surface by meteoroid impacts can be analyzed by a dust mass spectrometer on a spacecraft orbiting the moon. Thus, the compositional in-situ analysis of a satellite's surface can be performed even without a lander. High resolution compositional data of dust measured in the vicinity of a dust-producing moon such as Ganymede provides key chemical constraints for understanding the satellite's history and geological evolution.
During recent years the Heidelberg dust group designed and built high resolution mass spectrometers of large and intermediate sensitive areas. An important constraint for the optimum design of the spectrometer's field optics is the properties of the plasma produced by the hypervelocity impacts. Furthermore, the reliable interpretation of a mass spectrum of an impact plasma requires a good knowledge of the various processes that produce the impact plasma. To this aim we performed experiments with a mass spectrometer designed to investigate the energy distributions of the ionized species. Furthermore, we reanalyzed the mass spectra of various materials such as silicates obtained from laboratory experiments using the Heidelberg dust accelerator as well as cosmic water ice dust impacts recorded by the Cassini dust detector CDA. After the initial acceleration the plasma energy was found to be surprisingly low, with a non-Maxwellian distribution. We also investigated which impact parameter actually controls the properties of the impact plasma. Our experiments suggest that this parameter is the energy density at the site of impact rather than the impact speed.
Dr. Konopka is from the Max-Planck-Institut fur Extraterrestrische Physik in Garching and is a candidate for the faculty position associated with the lunar science center. He conducts dusty plasma experiments both in the laboratory and in space. The space experiments are done in the International Space Station in microgravity. Floating dust particles form crystalline arrays that allow exploration of strong coupling and phenomena normally associated with condensed matter. Laboratory experiments with dust in plasma are conducted in high magnetic field (up to 4 T). Two dimensional crystalline arrays rotate rigidly or rotate differentially in concentric shells revealing the relative importance of the Lorentz force and drag forces from ions and neutrals.
Previously flown dust instruments in space were not designed to provide accurate measurement of the velocity of individually detected dust particles. This information, however, can be important to find the source of the cosmic dust and its interaction with the space environment before detection. A future instrument with high trajectory resolution capability could provide a way, for example to a) explore the interaction of interstellar dust particles with the heliosphere, b) enhance the performance of dust sample return missions, c) or enable planetary dust spectroscopy. The Dust Trajectory Sensor (DTS) is an instrument under development to measure the velocity vector of individual dust grains in space. The operation is based on measuring the pickup charge from the dust by an array of wire electrodes. The Coulomb Software is used for the modeling of DTS and simulating the measured signals from particles passing though the instrument. Experimental data (both low and high speed) have been analyzed, which suggests the DTS has a high resolution in speed and angle.
The Framework Application for Core Edge Transport Simulation (FACETS) is a SciDAC proto-Fusion Simulation Program with the aim of performing tokamak core-to-wall transport simulations on massively parallel architectures. The FACETS team has developed a new parallel core transport solver designed to use a variety of transport models, including GLF23, MMM95, NCLASS, and the GYRO gyrokinetic code, and sources, including NUBEAM. The core transport code is coupled to the UEDGE code for two-dimensional transport in the open field region, with the
soon-to-be incorporated 1D WALLPSI model for plasma-wall interactions. Parallelism has been an integral part of FACETS since day one, with each component (core, edge, and wall) living
on disjoint sets of processors. Coupling between components, which involves the exchange of fields or fluxes at the interfaces, can be implicit. We will report on the status of the FACETS code development, and present initial studies of edge pedestal formation in the DIII-D tokamak.
We have previously developed a Lorentz force ion, fluid electron kinetic MHD hybrid model. This model has been extended to gyrokinetic electrons. Here we focus on the implementation of an isothermal fluid electron model in the GEM turbulence code. A second-order accurate implicit scheme that generalizes the previous implicit scheme for Lorentz force ions and drift kinetic electrons has been implemented. The generalized Ohm"s law is solved for the Harris sheet equilibrium configuration by Fourier decomposing the electric field along the equilibrium field and solving for each Fourier component in the direction perpendicular to the current sheet using direct matrix inversion. Test simulation results include Alfven waves, ion sound waves and the Whistler waves in a slab. And for the Harris sheet equilibrium with a guide field, linear instabilities such as resistive tearing mode is studied.
It is well known that a Hamiltonian system is integrable if it has sufficiently many integrals, and--by Noether's theorem--that each continuous symmetry gives rise to an integral. The resulting dynamics of integrable systems becomes uniform rotation on invariant tori.
What is the analogous structure for volume preserving systems? For the case of incompressible fluids, Bernoulli's theorem can be interpreted to say that an incompressible flow with a symmetry has an integral.This implies that a 3D fluid flow with a symmetry can be effectively reduced to a 2D flow that is Hamiltonian, and therefore integrable. For the case of maps, however, it seems that symmetries and invariants are independent. A 3D volume preserving map with a symmetry can be effectively reduced to an area preserving map. However, this map need not be integrable. To insure integrability requires an additional invariant. The result is similar to a notion of " broad integrability " for general flows defined by Bogoyavlenskij.
Solitary bipolar electric fields have been regularly observed in a wide variety of near-Earth space plasma environments probed by satellites, including the auroral current regions and in the vicinity of magnetic-reconnection sites. Such bipolar fields can indicate the presence of various nonlinear kinetic structures such as electron phase-space holes, ion phase-space holes, and ion solitons -- with electron holes being the most frequently invoked explanation for observed bipolar fields. Among established mechanisms for generating electron holes are the nonlinear saturation of instabilities such as the electron-electron two-stream instability and the electron-ion Buneman instability. Recently, an alternative mechanism involving a "notch" instability has been shown -- through the use of kinetic Vlasov simulations -- to be a potential mechanism for the generation of copious "weak" electron holes. Because the characteristics of electron holes depend on their source mechanism, they have the potential of providing diagnostic information regarding the region where they formed. However, it is first necessary to understand
how the properties of holes can evolve as they propagate away from their point of origin to the location where they are observed. To illustrate this idea, a different set of Vlasov simulations will be used to show how electron holes can be accelerated by ambipolar electric fields associated with weak quasineutral density perturbations
For the first time, a hot-filament discharge plasma with electron temperature near 200 K has been created continuously in the laboratory. The plasma is created in a double-walled vacuum chamber with the inner wall cooled by liquid nitrogen to 110 K. With 1.6 mTorr carbon monoxide at 140 K, the electron temperature is 19 meV (217 K) and the density is 4.7 x 108 cm-3. Electron temperatures are much higher with cooled Ar, He, H2, and N2. Electron cooling is greatest in CO because the heteronuclear CO molecule has a nonzero electric dipole moment which increases the cross section for electron energy exchange. The resulting plasma is unique in that electron-ion collisions are more frequent than electron-neutral collisions (even though the plasma is partially ionized) and recombination of ions and electrons is primarily into Rydberg levels. This plasma is also nearer to the strong coupling limit (lower Coulomb logarithm) than other continuous plasmas.
Detailed knowledge of the lunar plasma environment is of critical importance to the design of human habitats and instruments for future lunar missions. While theories for the lunar plasma environment have been developed for decades, large scale numerical simulations of the lunar plasma have only recently become feasible. These simulations can help to answer fundamental questions about the charge density distribution on the lunar surface as a function of local time, the plasma density distribution above the surface and its change with time, merging of the photo-electron layer with the solar wind and the distribution of local electric fields. The goal of this project, which is part of the Colorado Center for Lunar Dust and Atmospheric Studies, is to model the lunar plasma environment from first principles using the widely used plasma simulation code VORPAL. In this presentation we will summarize ongoing kinetic simulations of the lunar plasma environment. After initial comparisons of 1D simulations with theory, we will investigate the effect of topologies on the sheath properties in 2D and 3D.
Electron holes have been associated with the current sheet of magnetic reconnection by space observations and experiments. The development of these electron holes is poorly known. Using particle-in-cell simulations and kinetic theory, we investigate the formation of electron holes. We found that Buneman instability occur first and form slow-moving electron holes. After the saturation of Buneman instability, Buneman, electron-electron two stream and lower hybrid instabilities compete with each other. Both electron two-stream and lower hybrid instabilities can dominate. The increasing phase speeds of these two instabilities can transfer the momentum from high velocity electrons to low velocity electrons and form accelerating- fast-moving electron holes. In particular, if Buneman and lower hybrid instability dominate, both slow-moving and fast-moving electron holes can co-exist at the same location. The coherent relation between phase speed keep these electron holes stable. The phase speed of lower hybrid instability play an important role in determining which instability will win: Buneman or two-stream instability.
In August of 2007 two sounding rockets were launched from the Andoya Rocket Range, Norway carrying the MASS instrument (Mesospheric Aerosol Sampling Spectrometer). The instrument detects charged aerosols in four different mass ranges on four pairs of biased collector plates, one set for positive particles and one set for negative particles. The first sounding rocket was launched into a Polar Mesospheric Summer echo (PMSE) and into a Noctilucent Cloud (NLC) on 3 August. The solar zenith angle was 93 degrees and NLC were seen in the previous hour at 83 km by the ALOMAR RMR lidar. NLC were also detected at the same altitude by rocket-borne photometer measurements. The data from the MASS instrument shows a negatively charged population with radii >3 nm in the 83-89 km altitude range, which is collocated with PMSE detected by the ALWIN radar. Smaller particles, 1-2 nm in radius with both positive and negative polarity were detected between 86-88 km. Positively charged particles <1 nm in radius were detected at the same altitude.
The well-known guiding center (GC) model for charged particle motion in a strong magnetic field separates the particle's motion into a fast gyration around a magnetic field line, superimposed on the gyration-averaged motion of its guidiing center. Expanded in small gyroradius, the first order equations of motion can be derived directly from the particle motion. At higher order, the equations have only been derived using a noncanonical Hamiltonian or Lagrangian formulation. The result is valid to all orders in a uniform straight magnetic field. In three dimensions, however, the twisting of the magnetic field due to torsion imposes an separate geometrical xistence condition that is completely independent of the Lagrangian formalism. In 3D magnetically confined plasmas, this condition is not usually satisfied, since finite torsion is directly related to the presence of parallel plasma current. It can be satisfied in exactly 2D configurations, such as toroidal axisymmetry. The breakdown of the GC expansion appears to be related to the appearance of chaos in Hamiltonian systems.