HR: 15:25h
AN: AE43A-08 INVITED    [Abstracts]
TI: Paschen Curves for Solar System Atmospheres
AU: * Sentman, D
EM: dsentman@gi.alaska.edu
AF: University of Alaska, Geophysical Institute, Fairbanks, AK 99775, United States
AB: An understanding of the nature of electrical discharges in planetary atmospheres is required to understand recent observations of lightning on Jupiter and Saturn, as well as to study electrical breakdown processes in planetary atmospheres in general. The atmospheric composition of bodies in the solar system falls into four major classes: 1. Nitrogen/Oxygen (Earth); 2. Carbon Dioxide (Venus/Mars); 3. Hydrogen/Helium (Jupiter/Saturn/Uranus/Neptune); 4. Nitrogen/Methane (Titan/Triton). Conventional electrical breakdown varies significantly among these composition classes on account of the differing electron impact ionization cross sections and electronegative properties of the respective constituent species. The avalanche stage of electrical breakdown in a homogeneous gas is the simplest, linear stage of breakdown. Its characteristics may be computed from solutions to the electron Boltzmann equation, yielding Townsend's first ionization coefficient α. Breakdown between two closely spaced material surfaces also involves numerous electrode effects such as photoionization, and secondary ionization arising from electron impact and ion bombardment of the electrodes. These secondary effects are empirically described by Townsend's second ionization coefficient γ, whose value depends on the composition of the electrodes. For a given gas and electrode composition, the first and second coefficients may be combined into Paschen's curve, which gives the minimum voltage required for breakdown to occur between two plane parallel electrodes separated by a distance d in a gas at pressure p, expressed as a function of pd. Knowledge of Paschen breakdown could be useful in environments such as on the surface of Mars, or in free floating balloon platforms at Venus or Titan, where differential electrostatic charging between different system elements may occur, potentially resulting in electrical discharges. In this talk Paschen curves are presented for the various composition classes of solar system atmospheres.
DE: 0343 Planetary atmospheres (5210, 5405, 5704)
DE: 3304 Atmospheric electricity
DE: 6200 PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS
SC: Atmospheric and Space Electricity [AE]
MN: 2007 Fall Meeting