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Dust has been recognized as one of the greatest hazards in continued lunar exploration. Thus, it is crucial to develop dust mitigation techniques that can minimize the damages done to both hardware and humans working on the Moon. Passive mitigation techniques, which modify the surface of a material prior to dust exposure, will aid in repelling dust or reducing adhesion for easier dust removal. Our experiments use various surfaces (black Kapton (polymide), quartz, and silicon) that have been treated to have low surface energies by a Ball Aerospace and Technologies Corporation proprietary surface treatment technique. We use the centrifugal force detachment method to measure the total adhesive force acting between lunar simulant grains and these surfaces, both untreated and treated, in vacuum. Both JSC-1 lunar simulant and a lunar highlands simulant (LHT), created by Zybek Advanced Products, are tested to examine the effect of different grain composition. Different size fractions of JSC-1 (< 25 µm, 25-32 µm, 38-45 µm) are used in order to evaluate the role of dust grain size on adhesion. Experiments with < 25 µm JSC-1 show that dust is removed from treated black Kapton with about 5% of the force required for untreated black Kapton, while treated quartz and silicon show greater than 50% reduction in force. Analysis of force differences with LHT grains and different grain size distributions is ongoing. We will also measure adhesion on surfaces that have previously been UV-irradiated, which are of interest because of the high levels of solar UV irradiation on lunar surface.

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The Lunar Dust EXperiment (LDEX) instrument is selected for the LADEE mission to map the lunar dust environment. The dust population is expected to be dominated by submicron-sized dust particles released from the Moon due to the continual bombardment by micrometeoroids, and due to plasma induced near-surface intense electric fields. LDEX is an impact ionization detector, capable of measuring the mass of dust grains with m ≥ 1.7´10e-16 kg (radius r ≥ 0.3 μm), in a ~50 km altitude periapsis orbit about the Moon. LDEX will also measure the collective current of the dust grains that are below the detection threshold for single dust impacts; hence it can search for the putative population of grains with r ~ 0.1 μm lofted over the terminator regions by plasma effects. LDEX has been developed at LASP and has a high degree of heritage based on similar instruments on the HEOS 2, Ulysses, Galileo, and Cassini missions. The LDEX engineering model has been successfully tested and calibrated at the Heidelberg dust accelerator facility.

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Charged particle beams are accelerated through interaction with electromagnetic waves confined to resonant cavities. Acceleration is usually most efficient for the fundamental cavity modes, such as the TM010 mode of a cylindrical pillbox. Higher-order modes tend to degrade beam quality. Since metallic/superconducting cavities confine all harmonics, special couplers must be designed to “clean up” the cavity fields. A recently proposed alternative is to use photonic crystal cavities to combat this higher-order mode problem. Photonic crystals are periodic arrays of electromagnetic scatterers (metallic or insulating) that can act as “frequency-selective reflectors.” This property can be exploited to confine the desired fundamental accelerating mode while allowing higher-order modes to escape. This talk will discuss the 2D/3D simulation of these structures. Topics will include: optimizations that increase disparities between fundamental and higher-order mode confinement, wakefields produced by relativistic beams traversing such cavities, and the subtle difficulties of accurately and efficiently simulating these structures.

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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.

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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.
A charging model is developed to investigate the coexistence of positively and negatively charged aerosols in the NLC environment. Natanson’s rate equations are used for the attachment of free electrons and ions and the model includes charging by photo-electron emission and photo-detachment. Although the MASS flight occurred during night time conditions, the solar flux was still significant to affect the charge state of the aerosols. The calculations are done assuming three types of particles with different photo-electron charging properties: 1) Icy NLC particles, 2) Hematite particles of meteoric origin as condensation nuclei, and 3) Hematite particles coated with ice. The charge model results are consistent with the MASS rocket data, displaying both positively and negatively charged aerosols for small radii and only negatively charged particles for large radii.

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There has been much evidence indicating dust levitation and transport on or near the lunar surface. Dust mobilization is likely to be caused by electrostatic forces acting on small lunar dust particles that are charged by UV radiation and solar wind plasma. Laboratory studies are needed for understanding physics of dust dynamics on the lunar surface. Differential photoelectric charging and so-called ‘supercharging’ near the lunar terminator region were created and studied in laboratory. Dust transport on surface in plasmas was investigated. A dust pile was observed to spread and form a diffusing dust ring on a negatively biased conducting surface in plasma. A dust patch was also found to spread on an electrically floating surface in plasma with an electron beam. Dust hopping was confirmed by noticing grains on protruding surfaces in both experiments. The 2-D electrostatic potential distributions were measured above the dusty surfaces and show electrostatic forces required for transport of the dust particles.

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We will discuss 2D and 3D Hall MHD magnetic reconnection physics. Two dimensional Hall MHD simulation results will be presented to demonstrate a steady state system can be obtained with open boundary conditions. It is shown that the asymptotic (i.e., time independent) state of the system is nearly independent of the initial current sheet width. This rate appears to be independent of the scale length on which the electron ‘frozen-in’ condition is broken (as long as it is < c/ωpi ) and the system size. Results will be presented for the cases of no guide field and a guide field. We will also present three dimensional Hall magnetic reconnection simulation results. The reconnection process is initiated with a magnetic field perturbation localized along the current channel in a reversed field plasma configuration. The perturbation induces a magnetic wave structure that propagates opposite to the current, and leads to the asymmetric thinning of the plasma layer, strong plasma flows in the direction of the current, and rapid magnetic reconnection. The propagating wave structure is a Hall phenomenon associated with magnetic field curvature. Again, we will show results for no guide field and with a guide field.

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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.

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We find that for exactly the same given macroscopic system described with the same visco-resistive MHD (without any Hall or extended MHD terms) method, magnetic reconnection can progress in two entirely different ways. The first is the well-known laminar Sweet-Parker process. But a second, completely different and chaotic reconnection process is possible. This regime presents properties of immediate observational and experimental relevance [1]: i) it is much faster, developing on scales of the order of the Alfvén time rather than the usual diffusive time of resistive processes, and ii) the areas of reconnection become distributed chaotically over a macroscopic area of the system. The onset of this fast chaotic reconnection process corresponds with the formation of closed circulation patterns where the jet going out of the reconnection region turns around and forces its way back in, carrying along copious amounts of magnetic flux and allowing fast macroscopic reconnection. [1] G. Lapenta, Self-Feeding Turbulent Magnetic Reconnection on Macroscopic Scales, Physical Review Letters, 100, 235001, 2008.

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