HR: 1340h
AN: SM43C-1542    [Abstracts]
TI: On the Anti-critical Temperature for Spacecraft Charging
AU: * Lai, S T
EM: Shu.Lai@Hanscom.af.mil
AF: Air Force Research Laboratory, Mail Stop: RVBXT 29 Randolph Road, Hanscom AFB, MA 01731, United States
AU: Tautz, M
AF: Retired, Formerly AER, Inc., Lexington, MA 02173, United States
AB: 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.
DE: 7800 SPACE PLASMA PHYSICS
DE: 7815 Electrostatic structures
DE: 7853 Spacecraft/atmosphere interactions
DE: 7855 Spacecraft sheaths, wakes, charging
DE: 7899 General or miscellaneous
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Fall Meeting