Temperature Dependence of Dissociative Recombination and Molecular-Ion Formation in He, Ne, and Ar Plasmas

Recombination-dominated decaying plasmas in He, Ne, and Ar gases are produced in a discharge tube energized with a capacitor bank capable of delivering 3×${10}^3$ J at 20 kV. The electron temperature, atom temperature, and electron number density as a function of time are measured by using a triple probe, a thin-film thermometer, and the triple probe and microwave apparatus, respectively. The atomic- and molecular-ion number densities are monitored by using a mass spectrometer. The electron-temperature dependence of the dissociative recombination coefficient ${\alpha }_2$, and the atom-temperature dependence of the molecularion formation coefficient $\gamma$ are calculated. The results indicate the following: (1) the electron-temperature dependence and absolute value of ${\alpha }_2$ are both affected by the atom temperature of the plasma; a simplified physical model is proposed to explain this variation of dependence; the previous controversial experimental results published in the literature on this subject can be understood with the use of this physical model; and (2) the atom-temperature dependence of $\gamma$ agrees with theoretical expectations.