3.3. Measurement of Density by Analysis of Electron Beam Excited Radiation

Abstract

This chapter elaborates the measurement of density by analysis of electron beam excited radiation. The electron beam fluorescence technique has been widely used for the measurement of specie concentrations and temperatures in low density gas flows. It is found that with suitable interpretation, it is possible to deduce directly from the intensity and spectral distribution of the fluorescence of the state of the gas at the point of measurement. Among the properties that can be measured are species number density, rotational temperature, vibrational temperature, and translational temperature. It is also possible to measure flow velocity and provide flow visualization. Analysis of electron beam fluorescence begins by considering radiation of a particular frequency, which is tantamount to considering a particular pair of energy levels as excited and final states. The fluorescence excited by a beam of electrons in a gas has two properties that include the spectral composition of the emission and the intensity of prominent lines. The spectrum gives an indication of the gas species that are present although not invariably because of possible dissociative excitations.