Comparison of hollow cathode and penning discharges for metastable He production

The production of helium 2¹S singlet metastable atoms has been investigated using a hollow cathode discharge and a Penning discharge, under dc discharge conditions. The density of metastable atoms was measured by atomic absorption using the 2¹S-3¹P transition (501.57 nm). A range of plasma currents, varying from 16 to 180 mA, and a range of pressures, from 100 mTorr to 5 Torr, were investigated. This work is directed ultimately to the production of a supersonic metastable helium beam for plasma diagnostics, in particular the measurement of electric fields using laser induced fluorescence.