Electron-Beam Generated Air Plasma: Beam Current and Electron Density Distributions

Summary form only given. Plasma generated by means of electron impact ionization of air with a 100-keV electron source involves porting the electron beam from vacuum to an air-plasma test cell filled with air at pressures between 1 mTorr and 760 Torr. Energetic electrons propagate through a thin foil transmission window that separates the vacuum in the electron source from air in the test cell. Current stopped in the transmission-window foil is used to quantify the beam flux incident on the foil and additional calibrations of current measurements within the test cell quantify electron-beam flux at various points in the test cell. Use of an air chemistry program allows the estimation of the rate of electron-ion pair production per cm³ from energy deposition measurements. From this rate the electron density is derived. General results for several pressures will be presented. Data related to using 337.1 nm emissions from the nitrogen second positive band N₂(C³Pi_u -B³Pi_g) suggests an alternative optical means of estimating electron density in air.