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×${10}^{17}$ ${\mathrm{cm}}^{-3\mathrm{}}$) and at an electron temperature of 10 °K is (40 ± 6) × ${10}^{-6\mathrm{}}$ ${\mathrm{cm}}^3$ ${\sec }^{-1\mathrm{}}$. It varies with the electron temperature as $T_e^{-\chi }$, where $\chi =1\mathrm{}\pm 0.2$, and shows no dependence on electron density over the range we have covered from 5×${10}^8$ to 2.5×${10}^{10}$ ${\mathrm{cm}}^{-3\mathrm{}}$.