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Lab. Results

Lab. Results. Differential Photoelectric Charging and Super-charging near the Lunar Terminator. + + + + + + + +. - - - - - - - -. UV Radiation. photons. e. e. Differential photoelectric charging near the boundary between lit and shadowed region.

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Lab. Results

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  1. Lab. Results

  2. Differential Photoelectric Charging and Super-charging near the Lunar Terminator + + + + + + + + - - - - - - - - UV Radiation photons e e • 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].

  3. Surface Potentials Near Static Lit-Dark Boundaries e 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.

  4. UV light Shadow Surface L 0 1 2 3 4 5 Surface Potentials Near Moving Lit-Dark Boundaries Surface L is ‘supercharged’ when the shadow approaches it (i.e. the progression of sunset).

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

  6. Dust Transport on A Surface in Plasma

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

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

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

  10. Observations with beam energy at 75eV

  11. Sheath profiles with different beam energy (JbJi) • E in the sheath increases significantly when Eb is sufficiently large and JbJi. • Secondary electron emission is believed to plays a role.

  12. Plasma Probes for Lunar Surface UV Light V1 and V2 are adjusted to make net current through two probes to be zero V1 Cylindrical probe Reference surface Zr Surface V2 Insulator standoffs The probe data becomes useful when the photoemission from the reference surface is sufficiently large.

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

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