On the Anti-critical Temperature for Spacecraft Charging

Details On the Anti-critical Temperature for Spacecraft Charging On the Anti-critical Temperature for Spacecraft Charging

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsm43c1542l&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SM43C-1542

Physics

Plasma Physics

7800 Space Plasma Physics, 7815 Electrostatic Structures, 7853 Spacecraft/Atmosphere Interactions, 7855 Spacecraft Sheaths, Wakes, Charging, 7899 General Or Miscellaneous

Scientific paper

In recent years, evidence has been found for the existence of a critical temperature for the onset of spacecraft charging to high voltages. Spacecraft charging to high voltages affects scientific instruments on board. However, less attention has been given to low-voltage charging which can also affect scientific experiments on board and is relevant to surface chemistry. There also can exist an anti-critical temperature for low-voltage spacecraft surface charging. Ambient electrons at very low temperatures tend to cause negative surface charging, albeit at low voltages and as the electron temperature increases, the charging ceases at a critical value depending on the surface material. We present the theory and numerical results of anti-critical temperatures for typical surface materials in Maxwellian space plasmas. The change in anti-critical temperature due to a low incident-energy enhancement of the electron backscatter yield, consistent with recent measurements, is discussed. Approximate expressions for the anti-critical temperature upper limits are given, based on Taylor expansions at low temperature of the charging onset equation. It is shown that that the existence of the anti-critical temperature slightly modifies the possible triple root configurations in the flux-voltage characteristic curve for a material. The surface charging effect of a Maxwellian plasma with flux components spanning the anti-critical and critical temperatures is considered. A comparison with an empirical low-voltage charging curve is given.

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