Estimation of Ion Density of Helium Plasma using Collisional-Radiative Models in Linear Plasma Device NUMBER

In the linear plasma experimental device NUMBER, the densities of ions and atoms in helium plasma were estimated using passive spectroscopic measurements. The collisional-radiative models were employed to derive the densities of atoms and ions from the measured line intensities of each species. The estimated densities of helium species showed that (1) the atom density is one order of magnitude smaller than that estimated from gas pressure before discharge, (2) the density of singly charged ions is one order of magnitude smaller than that of atoms, (3) the doubly charged ions have a density 4 orders of magnitude smaller than the singly charged ions.