Electron-beam produced air plasma: I/Q detector and optical system used to measure electron density and momentum-transfer collision rate

Electron-beam generated air is discussed in the context of a 100-keV 5-mA electron-beam source and a 400-liter test cell filed with laboratory air from 1 mTorr to 638 Torr. A 10-GHz in-phase and quadrature detection system is described as well as the measurement of the real and complex parts of the wavenumber under free space and plasma conditions. The determination of electron density and momentum-transfer collision rate depends on the electron-density profile along the RF propagation path. Nitrogen optical emissions from an 8-chord measurement system are used to quantify the volumetric ionization rate across the RF propagation path. This data is Abel inverted to provide a Gaussian radial profile of the volumetric ionization rate as a function of gas pressure. An air-chemistry code is used in an iterative procedure to determine the electron density profile expressed as a Gaussian profile. This Gaussian profile is subsequently used to evaluate the electron density and the momentum-transfer collision rate. Estimates of electron temperature are discussed in the context of the measured values and published curves for the momentum-transfer collision rate versus electron energy. The feasibility of direct measurement of electron temperature with radiometry is also described.