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Spectroscopic Analysis of Electron-beam-induced Fluorescence in Hypersonic Helium Flow

出版	National Aeronautics and Space Administration, 1970
URL	http://books.google.com.hk/books?id=t8Oybw_QgW4C&hl=&source=gbs_api
EBook	FULL_PUBLIC_DOMAIN

註釋The ability to visualize low-density hypersonic helium flow has been substantially improved through the use of a high-energy (26-keV) electron beam in the Langley 22-inch helium tunnel at a Mach number of about 20. It has been found that the electron beam efficiently excites the test gas to produce visible fluorescence throughout the flow field with a brightness which is dependent upon the local gas density. The present investigation involved the spectroscopic analysis of the electron-beaminduced fluorescence. It was conducted in order to better understand the excitation and emission mechanisms involved and to use this knowledge to improve the visualization technique further. Spectrograms of the fluorescence, both in the free-stream and modelflow fields, have been made; and the major radiating species have been identified as atomic helium, molecular helium, and the molecular nitrogen ion. The molecular nitrogen ion was found to be the emitter whose fluorescence enhanced the shock structure. Based on the results of this work, areas for further work have been identified.