Amanda Anne Sickafoose

Experimental investigations on photoelectric and triboelectric charging of dust

Experiments are performed pertaining to the charging of single dust particles in space due to three effects: (1) photoemission, (2) the collection of electrons from a photoemissive surface, and (3) triboelectric charging. The particles tested are 90 -106 mm in diameter and include JSC-1 (lunar regolith simulant) and JSC-Mars-1 (Martian regolith simulant). Isolated conducting grains (Zn, Cu, and graphite) illuminated by ultraviolet light reach a positive equilibrium floating potential (a few volts) that depends upon the work function of the particle. Conducting grains dropped past a photoemitting surface attain a negative floating potential for which the sum of the emitted and collected currents is zero. Nonconducting grains (glass, SiC, and the regolith simulants) have a large initial triboelectric charging potential (up to 615 V) with a distribution approximately centered on zero. The nonconducting grains are weak photoemitters, and they attain a negative floating potential when dropped past a photoemitting surface. Our experimental results show that for silicate planetary regolith analogs, triboelectric charging may be the dominant charging process and will therefore play an important role in the subsequent behavior of dust grains released from planetary surfaces.

Contact charging of lunar and Martian dust simulants

micron dust grain is typically more than 10 5 elementary charges and varies linearly with dust size. The measured contact charge of a dust particle increases with repeated agitation of the surface. The average contact charge also varies linearly with the work function of the contacting surface. The contact charging with oxidized metal surfaces is found to be independent of the metal’s work function. The effective work functions of the planetary analogs are determined by extrapolation to be 5.8 eVand 5.6 eV for the lunar and Martian dust simulants, respectively. INDEX TERMS: 3914 Mineral Physics: Electrical properties; 3947 Mineral Physics: Surfaces and interfaces; 5470 Planetology: Solid Surface Planets: Surface materials and properties; 6225 Planetology: Solar System Objects: Mars; 6250 Planetology: Solar System Objects: Moon (1221); KEYWORDS: Dust, contact charging, lunar dust, Martian dust, work function

Measurements of electrical discharges in Martian regolith simulant

Due to the prevalence of Martian dust devils and dust storms, an understanding of the underlying physics of electrical discharges in Martian dust is critical to future Mars exploratory missions. Measurements on the charging of single dust grains show that particles of Martian regolith simulant can have large electric potentials due to triboelectric charging. As a result of this charging, agitated Martian regolith simulant in a low-pressure CO/sub 2/ atmosphere produces electrical discharges. Under extremely dark viewing conditions, electrical discharges are visually observed at pressures between 0.1 and 50 torr. Measurements of the frequency and intensity of these discharges as a function of pressure (from 0.1 to 5 torr) and stirring speed (corresponding to wind speeds from 0.1 to 2.6 m/s) show that discharges occur at pressures and wind speeds similar to those expected on the Martian surface.

Photoelectric Charging of Dust Particles

Publisher Summary This chapter discusses the experimental work on the photoelectric effect, focusing on the determination of the photoelectron energy distribution function through the use of a retarding potential and measurement of photoelectric yields. The chapter describes laboratory experiments that have been performed on the photoelectric charging of dust particles which are either isolated or adjacent to a surface that is also a photoemitter. It is found that zinc dust charges to a positive potential of a few volts when isolated in vacuum and that it charges to a negative potential of a few volts when passed by a photoemitting surface. The illumination is an arc lamp emitting wavelengths longer than 200 nm and the emitting surface is a zirconium foil.

Experimental Dust Levitation in a Plasma Sheath near a Surface

We report the results of experiments on the levitation of dust particles in an argon plasma sheath above a flat, conducting surface. Types of particles tested include hollow glass microballoons, polystyrene DVB (divinylbenzene) microbeads, and JSC‐1, a lunar regolith simulant. Plasma characteristics are determined using a Langmuir probe, while the sheath potential profiles are measured by an emissive probe. Dust particles levitating above the surface of the plate are illuminated by an Ar laser and observed by a video camera. Our experimental results suggest the following: (1) various types and sizes of particles can levitate in a plasma sheath above a surface; (2) particle levitation height and corresponding charge are comparable to the values calculated from orbital motion limited (OML) theory; (3) exposure to a UV source slightly alters the particle levitation height; (4) a mechanism to inject particles into the sheath is not necessary given a large enough surface bias; (5) complex particle dynamics occ...

Levitation and Transport of Charged Dust Over Surfaces in Space

Dust in planetary regoliths may become charged and levitated in plasma sheaths and photoelectron sheaths near the surface [1,2]. This provides an explanation for the observations of the lunar horizon glow [3]. Horizontal electric fields or inhomogeneities in the sheath may lead to net transport of dust on the surface. Electrostatic levitation of dust may also explain observations of regolith deposits in craters on the asteroid 433 Eros by the NEAR spacecraft [4]. We present the results of a simple model of dust transport in a photoelectron sheath across a surface with simple topographical forms. We find a net deposition of particles launched in random directions at photoelectron sheath boundaries such as might occur in the terminator region. Topographic boundaries such as blocks and craters provide an additional sink for particles moving horizontally across the surface in a sheath.