Short-Duration Visible Afterglow in Helium

Abstract

A bright, reproducible afterglow which consists of helium atomic and molecular emissions has been observed in the flow products of an electrical discharge in a DeLaval nozzle clearly separated from the discharge. This afterglow has been observed at pressures from 0.4 to 20 mm Hg and with flows from 10 to 1000 cm³/sec NTP. At the low pressure the existence of the afterglow is extremely pressure sensitive to small changes in pressure. Metastable He‐atom concentration decreases after the discharge and then increases in the region of afterglow emission. The afterglow is very sensitive to impurities greater than a few parts in 10⁵ and emission intensity is reduced by the presence of an rf field, possibly because heating the electrons retards recombination.