The energy-loss factor for slow electrons in hot gases is determined by a new method that employs a high-frequency (2.45 GHz) electric field to elevate the temperature of the electrons above the temperature of the gas and a Langmuir probe to determine the electron temperature. The electron energy-loss factor ${\delta }_{\kappa }$ in a given gas $\kappa$ is then determined by measuring the rate of change of the electron temperature with the high-frequency power used to illuminate the plasma. The determination of ${\delta }_{\kappa }$ by this method does not require knowledge of the collision cross sections for momentum transfer. The values of ${\delta }_{\kappa }$ obtained by this method are in agreement with theory for monatomic gases (e.g. argon). No previous theoretical or experimental results are available for diatomic gases (e.g., nitrogen) in this range of gas and electron temperatures ($T_g$ from 1700 to 6100°K, $T_e$ from 3260 to 7540°K). The values of ${\delta }_{\kappa }$ obtained for nitrogen at elevated gas temperatures are a "reasonable" extrapolation of the room-temperature data available in the literature. Thus it was found that ${\delta }_{N_2}$ ranges approximately from 3×${10}^{-4\mathrm{}}$ at a gas temperature of 1700°K to 7×${10}^{-4\mathrm{}}$ at 5000°K.

• Received 6 February 1967

DOI:https://doi.org/10.1103/PhysRev.158.215