ENGINEERING RESEARCH INSTITUTE UNIVERSITY OF MICHIGAN ANN ARBOR QUARTERLY TECHNICAL STATUS REPORT September 15, 1953 to May 31,1954 submitted by Otto Laporte Professor of Physics Project 2189 AIR RESEARCH AND DEVELOPMENT COMMAND, U oS AIR FORCE CONTRACT AF 18(600)-983, PROJECT R-357-40-6 June, 1954

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN QUARTERLY TECHNICAL STATUS REPORT INTRODUCTION Luminosity was first observed in the University of Michigan twoby seven-inch shock tube in April 1952 in connection with the study of moderately strong shock waves. At that time a brief but intensive preliminary investigation was made and the results reported by Professor Otto Laporte, principal investigator of this project, to the Fluid Dynamics Division of the American Physical Society at Salt Lake City in June 19520 2 Later these results were published in a Letter to Nature. Because of the interesting possibilities suggested by this phenomenon, it was decided to construct a smaller and stronger shock tube designed expressly for the production of very strong shock waveso For this purpose, two-thousand dollars s was made available by the University of Michigan in August 19520 However, because the project personnel were previously committed to other work, work on the small shock tube was not begun until the spring of 19535 The sections of the tube, together with the vacuum plumbing, were completed in September of that year with University funds. During this time, negotiations were under way for the present Air Force contract, and the project was finally set up on November 30o EQUIPMENT The photographs of the shock tube included at the end of this report show the pressure and vacuum plumbing, gauges, and the prism spectrograph pointed toward the window at the end of the tube. The high-pressure I The pressure ratio across the shock waves was 15-20 2 Nature, 171_, 95 (1953) 5 The old shock tube of two-lnch by seven-inch cross section was built primarily for aerodynramic studies and was not capable of withstanding the high pressures or reaching the high vacuum necessary for the production of very strong shock waves o

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN chamber, built to withstand 2000 psio, is at the righto The vacuum system includes an oil diffusion pump which can evacuate the low pressure chamber to less than one micron absolute pressure; since only a few millimeters of mercury pressure of rare gases are usually used, the purity of these gases is insured. RESULTS When the tube was first fired in January of this year, a two4 prism spectrograph was set up to observe the luminosity in the tube~ The resulting flash of light was far more brilliant than any seen previously in the old two-inch by seven-inch shock tubeo As the reproductions on pages 4 and 5 show, the spectra contained a wealth of metallic lines, of lines of the carrier gases (argon, or xenon), and a very prominent continuous background. As the shock strengths become greater, the emission lines are gradually submerged in the continuous backgroundo Most striking is the spectrogram taken with neon gas which exhibits the hydrogen lines H, H6S, H, as impurities. The hydrogen lines exhibit a considerable first-order stark effect by being broadened to a half-width of as much as 80A, while the neon lines remain comparatively sharp Except for the fact that all shock tube spectra are emission spectra, they are quite similar to the absorption spectra observed for stars of class A or Bo Indeed, this work has created considerable interest among astrophysicists here at the University and elsewhere. FUTURE PLANS Except for the successful construction of the shock tube and the obtaining of numerous but as yet primitive spectrograms, the work is still 4 Property of the University of Michigan light laboratory ----- 2 _ ------

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN in the preliminary stage. It is intended to investigate the following topics in more detail: (1) High temperature hydrdynamics The standard theory for shock flow has to be altered profoundly due to the fact that a large percentage of the gas atoms behind the shock will be ionized. In other words, the passage of the shock through the gas is accompanied by what might be compared to a chemical change, in view of the circumstance that the material behind the shock now consists of three different kinds of gases; a) neutral atoms b) ionized atoms c) free electrons. The investigation of this phenomenon will have to proceed on the one hand experimentally, that is to say, towards the observation of the flow variables, and on the other hand, theoretically, namely, toward the calculation of an equation of state and of Rankine-Hugoniot curves. For the observation of flow variables a revolving drum camera, now under construction, will be used to measure shock velocities Also electromagnetic measurements with the variablevolume cavity formed by the tube and the approaching shock are contemplated. The theoretical work, while in principle fairly clear cut, seems very involved and may necessitate the use of a high speed computero (2) The influence of high densities upon light emission Light emission at high gas and electron pressures makes itself felt in the broadening and red shift of the spectral lines briefly referred to above. A detailed exploration of this phenomenon should be of greatest value to astronomers and will give interesting new information on the interaction of elementary particles. In order to investigate the temporal relations between light emission and broadening, it is intended to employ timeresolved spectroscopy, which can be done by photographing the spectral lines by means of the previously mentioned drum camerao 5

Note: For the four pages of photographs refer to file copy.