Stable Secondary Ionization in a Test Geometry for Electron Beam Precipitators

Stable secondary ionization which produces an ion current density as much as a factor of four higher than that produced by primary ionization alone has been observed in a test electron beam precipitator geometry. Full utilization of secondary ionization in precipitator design considerations critically depends upon the stability of the secondary ionization processes which are ordinarily the immediate precursor phenomena to breakdown. Measurements are reviewed in which the ion current saturation is followed by the onset of secondary ionization as the electric field is increased. Secondary ionization currents are large and override saturation effects at high electron beam currents or large electrode spacings. Recent measurements of primary and secondary ionization, ion current saturation, and secondary ionization stability are presented. High electron beam currents are used to produce large ion current densities, and the resistance of the ionized gas is determined. The effects of the electron beam on the stability of secondary ionization and on the onset electric field for secondary ionization are discussed.