Abstract
A simple model for predicting the small signal gain as a function of flow direction will be presented. The small signal gain was measured on the Weapons Laboratory Rotocoil 0 2 /I * gain medium. The characteristics observed in the experiment show a decrease in the small signal gain as a function of distance from the nozzle exit plane. Further results indicated that the small signal gain decreased with time and that the gain increased when the cold trap was turned on. All of these effects suggest a temperature dependence of the small signal gain. The approach presented in this paper is to develop a simple model which includes a simplified kinetics model and the gas dynamics for the flowing medium. An analytic solution to the model equations is also derived. These models account for the reduction in small signal gain in the flow direction due to heat release into the cavity when compared to the Rotocoil small signal gain data. The results show that the rise in gas temperature in the flowing 0 2 /I * medium is primarily due to water deactivation of the I * and the O 2 (1Δ) plus I * pooling leading to water deactivation of 1 Σ. Such temperature rise in the flowing medium causes the small signal gain to decay substantially in the flow direction due to the square root of the temperature dependence in the stimulated emission cross section, the shift in the equilibrium constant with temperature and the decrease in density which is inversely proportional to the temperature.
Published Version
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