Lab. Results

Differential Photoelectric Charging and Super-charging near the Lunar Terminator UV Radiation Differential photoelectric charging near the boundary between lit and shadowed region. It has been suggested that time dependent charging at the terminator region may lead to ‘super-charging’, and the lift-off of lunar fines [Criswell and De, 1977] photonse e

Surface Potentials Near Static Lit-Dark Boundaries When all surfaces float, surface L charges positively and charge on dark surfaces remain small and E // at lit/dark boundary can be as large as 800 V/m. e

Surface Potentials Near Moving Lit-Dark Boundaries Surface L Shadow UV light Surface L is ‘supercharged’ when the shadow approaches it (i.e. the progression of sunset).

Dust Transport and Levitation above the Lunar Surface The image of lunar horizon glow taken shortly after sunset [Criswell, 1973]

Dust Transport on A Surface in Plasma

Dust spreading process after plasma is turned on Dust Ring Bull’s Eye Pattern Initial Pile Uniform Spreading Observations Insulator Initial dust pile 6 mm Dust hopping

Potential contours above an insulating disc sitting on the graphite surface biased at -80V E E E Potential Dip

Dust Transport on Surface in Plasma with An Electron Beam Emissive probe Filament Dust pile Graphite plate Vacuum pump Filament & Mesh CCD camera

Observations with beam energy at 75eV

Sheath profiles with different beam energy ( J b  J i ) E in the sheath increases significantly when E b is sufficiently large and J b  J i. Secondary electron emission is believed to plays a role.

Plasma Probes for Lunar Surface Cylindrical probe Zr Surface Insulator standoffs UV Light Reference surface V2V2 V1V1 V 1 and V 2 are adjusted to make net current through two probes to be zero The probe data becomes useful when the photoemission from the reference surface is sufficiently large.

Both spherical and cylindrical probes show nearly identical Maxwellian electron distribution. Electron energy probability function (EEPF) and Druyvesteyn’s second derivative method Electron Energy Distribution