The Electron Beam Fluorescence Probe in Experimental Gas Dynamics

The use in experimental gas dynamics of the electron beam fluorescence technique has been discussed. The several successes of this probing method have not been exhaustively reviewed; rather, emphasis has been placed on those aspects of an energetic electron beam's interactions with a gas that are not yet satisfactorily understood. The uncertainties which presently inhibit the development of the technique's full capabilities have been specified. It has been shown that many of the principal problems associated with the beam probe originate in the emission excited by secondary electrons. Also, in some cases, diffusion of the beam excited fluorescence as a result of resonance transitions can be a concern. The desirability of undertaking studies that will extend the technique's present operating range and accuracy has been emphasized. A simplified instrument (Rotational Temperature Apparatus) previously described by two of the present authors for measuring static temperatures in nitrogen flows has been optimized. It was found that for an error estimation based on the statistics of counting photons the optimum instrument comprised two narrow pass band interference filters each with a half width of about 8Å.