High-density metastable helium atoms produced by Penning-type discharges

A high density of metastable helium atoms has been created using a Penning-type discharge. Experimental data indicate that the metastable density increases with the increase in the helium gas pressures in the range from 0.1 mTorr to 0.5 Torr. The highest metastable density of 3.5 × 10¹⁶ m^-3 is observed at a steady-state gas pressure of 0.5 Torr. The relationships between the densities of the metastable helium atoms and the plasma discharge current are also obtained. Based on the results obtained using a spectral absorption technique and a theoretical collisional-radiative model, the data of the helium plasma spectroscopic emissions have been used in diagnosing plasma electron density and electron temperature. The results suggest the possibility of generating high-density metastable atoms with a high discharge current.