||Measurement of the helium 2S metastable atom density by observation of the change in the 2S–2P emission line shape due to radiation reabsorption
Shikama, T ,
Ogane, S ,
Iida, YHasuo, M
Journal of Physics D: Applied Physics
2015-12-15 , IOP Publishing
In helium discharge plasmas, the relative emission intensities of the fine-structure transitions belonging to the HeI 2S–2P transition can be affected by radiation reabsorption. Since the magnitude of the reabsorption depends on the density and temperature of the 2S metastable atoms, their density can be determined by measuring the 2S–2P emission line shape using a high wavelength-resolution spectrometer. In this study, the applicable conditions of the method in terms of the opacity and line broadening are revealed, and possible causes of errors in the measurement, i.e. spatial distributions of the density and temperature and the effects of external magnetic and electric fields, are investigated. The effect of reabsorption under an external magnetic field is experimentally confirmed using a glow discharge plasma installed in a superconducting magnet.