SH43B-01 INVITED 13:40h
Some Aspects of Dust-Plasma Interactions in the Solar System
Dust and Plasma co-exist in numerous environments in both space and the laboratory. Here we discuss some aspects of dust-plasma interactions in several solar system environments including comet tails, planetary magnetospheres and the terrestrial mesosphere. While dust grains interact with naturally occurring plasmas in the solar system, they can also be a source of plasma as they impact the ambient medium as well as spacecraft, thereby providing another way for their detection. Here we will also address this phenomenon.
SH43B-02 INVITED 14:00h
Laboratory Experiments on Charging of Individual Dust Grains
Dust particles in astrophysical and space environments are charged by a variety of mechanisms generally involving collisions with electron and ions, and from photoelectric emissions by interaction with incident UV radiation. The sign and the magnitude of the particle charge are determined by the net balance at equilibrium between the charging processes by UV radiation and collisions with charged particles. Knowledge of the charging processes, particle charge and equilibrium potential is important for understanding of a number of physical processes. The charge of a dust grain is a basic parameter that influences the physics of dusty plasmas, and physical and dynamical processes in the planetary, interplanetary and interstellar environments. A fundamental quantity in the charging of dust grains by the photoemission process is the photoelectric yield of the dust grains. Most of the currently available experimental data on photoemissions are based on bulk materials with very little on individual dust grains. It is, however, recognized that the photoelectric yields of micron size grains are different from those based on bulk materials. After a brief review of the currently available measurements, we will present the results of some recent experiments on charging of dust grains carried out on levitated micron size grains in an electrodynamic balance in simulated space environments. The charging/discharging experiments were conducted by exposing dust grains of radii in the 0.1 to 5 mm range, to low energy electron beams and UV radiation at 120 to 160 nm wavelengths. In particular, we will present experimentally determined photoelectric efficiencies and yields of individual micron size dust grains of Silica, Olivine, lunar simulants prepared by NASA-JSC, and the lunar sample dust grains retuned by the Luna 24 mission. Comparisons with the available measurements on bulk materials will be made.
SH43B-03 INVITED 14:20h
Radar Observations of Meteor Created Plasma Interactions in the Atmosphere
High Power Large Aperture (HPLA) radars have been used to monitor meteor head echoes for more than decade now. The method developed at the EISCAT Incoherent Scatter Facility in Northern Europe will be reviewed. This includes a general discussion of what parameters can be derived from the information sampled from head and trail echo observations. Various kinds of measurement strategies, such as multi-frequency, multi-static, pulse codes, geographic effects, perpendicular to magnetic field observations and observations along the Earth orbit are described. These will be related to what kind of information could be delivered to dust plasma interaction community.
SH43B-04 INVITED 14:40h
Coronal Mass Ejections, Ion Drag and Rotational Bursting of the Dust
The effects of plasma-dust interactions resulting from the high density of protons in Coronal Mass Ejections (CMEs) are surveyed. In particular, two effects are discussed: one is the rotational bursting of F coronal dust and the other is the increased ion-drag on the orbiting dust. Rotational bursting of the dust can occur from radiation pressure on the irregularly shaped dust particles and from protons in CMEs. Numerical simulations were used to study the rotational bursting of circumsolar dust in both circular and eccentric orbits. Model calculations were used to assess the increased ion-drag due to protons from CMEs. Thus the efficiency and implications of both mechanisms are assessed. Increased ion-drag from protons in CMEs was shown to be capable of forming density waves of F-coronal dust that can give rise to transient and certainly not permanent dust rings around the Sun.
SH43B-05 15:00h
Solar-Wind Drag on Fluffy Dust Particles
The impact of solar-wind particles on dust grains exerts not only a repulsive force but also a drag force on the grains, called the plasma Poynting-Robertson effect. The drag force decreases the orbital angular momentum of the grains and limits their lifetime in a manner similar to the photon Poynting-Robertson effect. We study the solar-wind drag and the lifetime of fluffy silicate and carbon dust aggregates. We calculate the momentum transfer cross section of the fluffy dust aggregate for the impinging solar wind taking into account the penetration of incident solar wind ions. We find that 1) the cross section of very small aggregates is approximately proportional to the volume of the grains and independent of their shape, while 2) the cross section of large aggregates approaches the geometrical cross section. The lifetime of the aggregates against both plasma and photon drag forces is shorter than that of spherical particles of the same mass. We show that the plasma Poynting-Robertson effect for aggregates is comparable to and in some cases more effective than the (photon) Poynting-Robertson effect. The importance of the plasma drag compared to the photon drag increases as the size of constituent particles of the aggregate decreases, irrespective of the passage of solar-wind ions through the dust grains. This contradicts the general understanding that the lifetime of dust particles is limited by the photon Poynting-Robertson effect.
SH43B-06 15:13h
Generation of Ions and Energetic Neutral Atoms from Near Solar Dust
Dust interactions with the solar wind are assumed to generate pick-up ions and some authors even suggest dust interactions to generate energetic neutral atoms and to account for some recent findings of the element abundances of the anomalous cosmic rays. Most models, however, are limited by our lack of understanding the dust plasma interactions. The near solar dust cloud allows for directly studying a cosmic dust-plasma cloud and therein processes that also appear in other cosmic environments. The number density of dust particles that are either produced by comets and asteroids in the solar system or are entering the solar system from interstellar space increases towards the sun where small particles are strongly affected in their orbits by the solar magnetic field. Dust sublimation becomes particularly important and surface processes release dust compounds in the ambient interplanetary medium. We discuss these different processes and their variation with the solar wind conditions. Based on current knowledge of the interplanetary dust cloud we quantify the production of pick up ions and energetic neutral atoms that is connected to the dust. We finally discuss how dust-plasma interactions could be studied with future dedicated experiments from spacecraft in the inner solar system.
SH43B-07 15:26h
Are Inner Source Pickup Ions further Accelerated in Interplanetary Space?
Inner source pickup ions originate most likely from the interaction of the solar wind with dust particles in interplanetary space. They are thought to be generated either through saturation of dust with solar wind, subsequent desorption, and pickup, or through penetration of small dust grains by solar wind, neutralization, and subsequent re-ionization. In both cases a velocity distribution emerges, which is genuinely suprathermal, but peaks below the solar wind speed. Based on the realization that interstellar pickup ions are preferentially injected for further acceleration it has been suggested that also inner source ions may contribute visibly to the energetic particle populations in interplanetary space. It has been shown that inner source ions do not contribute significantly to the CIR population that is accelerated mostly outside 1 AU and observed in Earth's orbit. Since inner source ions are generated close to the sun one might expect that they could contribute to energetic particles accelerated at traveling shocks. We will present results from the search of such ions in traveling shocks that have been identified to accelerate substantial amounts of He+. The results will be discussed in the light of models for inner source pickup ion distributions and for injection of ions into acceleration.