Energy balance and temperature in a CO2-laser-produced plasma

An underdense CO2-laser-produced plasma is experimentally investigated to determine the electron temperature explained in terms of an energy balance. Soft x-ray measurements show a 300 eV thermal and a 2000 eV suprathermal temperature. Ulbricht integrating sphere measurements along with interferometric data for the electron density indicate sufficient laser energy absorption to attain Te of the order of 600 eV. A novel method of analysis of streak records of the radial expansion is implemented where the conditions of a Chapman–Jouguet detonation wave are applied to allow an independent determination of the thermal plasma temperature and absorbed energy. The observed thermal Te is found to be consistent with linear inverse bremsstrahlung absorption using the measured degree of absorption provided by the Ulbricht sphere. The suprathermal temperature can be ascribed to be the result of the parametric processes in the plasma which are known to occur.