Spectroscopic Investigations Of The Energy Flow In A Nonequilibrium Imploding Plasma

This book presents studies of complexity in the context of nonequilibrium phenomena using theory, modeling, simulations, and experiments, both in the laboratory and in nature.

During planetary atmospheric entries, thermochemical non-equilibrium processes in the shock layer limit the reliability of aerothermal environment prediction. To improve prediction accuracy, non-equilibrium kinetic models are being developed. These models are experimentally assessed through the comparison with well characterized non-equilibrium experiments. For this purpose, the present work is dedicated to the thermodynamic characterization of non-equilibrium in high enthalpy reactive flows. Conversely to common studies that employ short duration facilities to investigate shock layer kinetics, we will assess the possibility of producing significant departure from equilibrium using radio-frequency and microwave stationary plasma flows, including supersonic plasma flows where vibrational non-equilibrium is strongly expected. Suitable spectroscopic diagnostics have been applied allowing future comparisons to be made between the microscopic description of the experiments and theoretical non-equilibrium models.

Spectroscopic observations were made of the flow field behind a cylindrical hypersonic wave front resulting from an imploding electrical dischange into an initially low pressure quiescert gas. Sub-microsecond resolved spectra were obtained by use of a quartz prism monochromatorphotomultiplier detector system with photographic recording of an oscilloscope displayed output signal. Electrically produced plasma rings were established in detonabie as well as non-reactive gases. Strong indications were observed that exothermic reactions, as evidenced by H/sub 2/O emission, proceed in H/sub 2/ + 1/2 O/sub 2/ reactant mixtures within less than one microsecond under certain initial low pressure conditions. A reaction threshold at 1 mm Hg pressure was found for the particular reaction vessel used. Timeintegrated spectrometer photos support the conclusions reached with the transient spectra analysis equipment. (auth).