Continuous wave laser gas heating by sustained plasmas in flowing argon

This paper reports the results of an in-depth study of laser-sustained plasmas in flowing argon for application to laser propulsion. The experiments were performed in a pressurized absorption chamber using a 10 kW CO₂ laser. Global absorption measurements have been carried out under a range of laser powers, pressures, and flow rates, indicating a total absorption approaching 80%. Thermocouples have been used to map gas temperatures in the downstream mixing zone. These mappings were used to estimate thermal conversion efficiencies. Thermal efficiency was found to be 6-25%, depending on the pressure, flow rate, and laser power. These thermal efficiencies correspond to radiative losses of 64 and 30%, respectively. Two-dimensional spectroscopic relative-intensity temperature mappings of the plasma core agree spatially with the results of a numerical model. The spectroscopic data indicate peak plasma temperatures of 18,000 K, with the global absorption of laser energy calculated to be 56.2%.