Electron Temperature Dependence of the Recombination Coefficient in Pure Helium

The phenomenon of "afterglow quenching" is employed to determine the electron temperature dependence of the electron-ion recombination coefficient in plasmas produced in purified helium (estimated impurity 1:${10}^9$). The total visible light intensity was studied as a function of electron temperature. By means of 1.5% bandwidth filters, the light intensity of two helium spectral lines (5876 A and 3888 A) were also investigated. It is found that the recombination coefficient for highly purified helium varies as the minus three-halves power of the electron temperature from 300° to ∼1500°K at electron densities of ∼${10}^{11}$/cc, and gas pressures from 12.6 to 30.3 mm Hg. At 300°K (temperature determined from collision frequency measurements), the recombination coefficient in purified helium is found to be (8.9±0.5)×${10}^{-9\mathrm{}}$ ${\mathrm{cm}}^3$/ion sec. It is found that both the recombination coefficient and its electron temperature dependence were strongly influenced by the addition of controlled amounts (2×${10}^{-4\mathrm{}}$ to 1300×${10}^{-4\mathrm{}}$%) of neon impurities.