Spectroscopic determination of energy conversion efficiency in laser sustained argon plasmas

An investigation of the properties of laser-sustained argon plasmas has been conducted at the University of Tennessee Space Institute over the last three years. A spectroscopic technique was developed to obtain spatially resolved temperature measurements in the hottest part of the plasmas (>10,000 K), and these temperature measurements were used, along with detailed knowledge of the path of the incident laser beam through the plasma, to obtain information about the power absorption and thermal radiation loss characteristics of the plasmas.

The results of experiments conducted in flowing argon at forced convective flow speeds between 0.4 m/s and 4.5 m/s, are reported in this thesis. At these speeds, the incident flow rate has a significant effect on the shape, size and position of the plasma which, in turn, affect the power absorption, thermal radiation loss and total energy conversion efficiency of the plasma. In addition to the incident flow rate, the focusing geometry, chamber pressure, and laser power were varied as parameters in the experiments. Thermal efficiency was found to range from 9% to 38%, depending on the various parameters.