Electron-Ion Recombination in Cryogenic Helium Plasmas

The electron-ion recombination coefficient measured in a cryogenic helium afterglow at a constant gas temperature of 4.2 ^∘{}K at pressures between 0.075 and 1.25 Torr (neutral densities ranging from 1.7 to 28.7×{}10¹⁷ cm^-3) and at an electron temperature of 10 ^∘{}K is (40 ±{} 6) ×{} 10^-6 cm³ sec^-1. It varies with the electron temperature as Tₑ^-χ, where χ=1±0.2, and shows no dependence on electron density over the range we have covered from 5×{}10⁸ to 2.5×{}10¹⁰ cm^-3.