Helium Afterglow and the Decay of the Electron Energy

The electron energy decay in the afterglow of a pulsed dc discharge in helium has been studied over a pressure range from 0.03 mm to 5 mm Hg. The energy decay is found to be influenced by cooling due to electron-atom elastic recoil and heating due either to electron-metastable superelastic collisions at low pressures or to the ionizing collision between two metastable atoms at high pressures. The analysis allows for the deviation of the electron velocity distribution from Maxwellian resulting from these heating effects.