Potential Barriers and Asymmetric Sheaths due to Differential Charging of Nonconducting Spacecraft.
Final rept. 1 Jul 76-30 Sep 77,
PARKER (LEE W) INC CONCORD MASS
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The differential charging of a nonconducting spacecraft is modeled numerically by following charged-particle trajectories in a self-consistent space-charge-less sheath. In the presence of a plasma flow, but independent of any photoelectric or secondary emission, a potential difference between the front and wake surfaces of the spacecraft is generated, resulting in an asymmetric sheath and in the creation of a potential barrier for electrons. The potential difference can amount to volts in the ionosphere, and kilovolts in the solar wind, that is, large compared with the potentials typically generated by photoemission alone. As in the more familiar case of photoelectric charging, the asymmetric sheath and potential barrier produced by the plasma flow can lead to erroneous interpretations of experiments measuring space electric fields and low-energy particle spectra. In an example of photoelectric emission, a sunlit area on an otherwise dark surface becomes positively charged by the emission, and is found to acquire a potential more than twice the emitted energy relative to the dark surface. This effect is associated with the physics of the terminator bounding the sunlit and dark areas. Author
- Electricity and Magnetism
- Plasma Physics and Magnetohydrodynamics
- Unmanned Spacecraft