Date of Award

Spring 1-1-2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

First Advisor

Mihaly Horanyi

Second Advisor

Scott Robertson

Third Advisor

Tobin Munsat

Abstract

The Moon, lacking an atmosphere and a global magnetic field, is directly exposed to both solar ultraviolet radiation and a variety of ambient plasmas. On the lunar dayside, a photoelectron sheath develops and the surface typically charges positively since the photoemission current is at least an order-of-magnitude greater than any ambient current. This sheath dominates the near-surface plasma environment and controls the charging, levitation and transport of micron-sized dust grains. In this thesis, we first model the lunar near-surface plasma environment via a one-dimensional particle-in-cell code. The sheath potential, electric field and plasma densities are presented over a wide range of plasma parameters. Additionally, the charging and transport of micron- and sub-micron sized dust grains is modeled via a test-particle approach in an attempt to explain Apollo-era observations of lunar dust dynamics. Secondly, we present a comparison of the particle-in-cell results with theoretical, kinetic derivations of the lunar photoelectron sheath. We extend previous theories to include the presence of a κ-distribution for the solar wind electrons. Finally, we present a comparison of in-situ measurements of the lunar photoelectron sheet in the terrestrial plasma sheet by the Lunar Prospector Electron Reflectometer with particle-in-cell simulations to confirm the presence of non-monotonic sheath potentials above the Moon. Future work in all three sections, (simulation, theory and observation) is presented as a guide for continuing research.

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