Electron Beam Fluorescence in Hypersonic Facilities

The Electron Beam Fluorescence (EBF) technique is well-suited to providing local measurements in low-density high-speed flows for atmospheric reentry studies. High fluorescence yields are obtained from the excitation of the molecules or atoms of a gas flow with high energy electrons, which makes this technique advantageous for studying very low density gases. The most common measurement is flow field visualization with a sweeping electron beam (or sheet of electrons) from which shock structures of the flow can be observed and in certain cases a density map of the flow field can be obtained. Spectroscopic analysis of fluorescence leads to species detection as well as rotational or vibrational temperature measurements. This is particularly useful for characterizing the shock layer chemistry at non–equilibrium which usually occurs with high speed flows or in studying boundary gas-surface interactions. Velocity measurements are also possible using the Doppler shift principle or with a time of flight method with a pulsed electron beam.