What do spectra tell us?

Abstract

The collisional-radiative(CR) model is introduced as an improvement to the corona model. Its formulation indicates that the population of every excited level is divided into two independent components, i.e., the ionizing and recombining plasma components. For the pulsed discharge with helium gas in a Pyrex tube which exhibits intense line radiations twice, the first and second peaks are found to correspond to the ionizing and recombining plasmas, respectively, from the different population distributions over the n3D levels. The spectrum taken in the stationary phase of the main discharge in the Large Helical Device (LHD) with helium gas suggests an ionizing plasma, and for the other two spectra taken in the plasma terminating phase, the first and the second spectra indicate the recombining plasmas of ionized and neutral helium, respectively. In all these analyses, the electron temperature and density are the variable parameters and are determined as a result of fitting of calculation to the experimental data. The spectrum observed in the helium glow discharge cannot be reproduced by CR model calculations even if the quasi-steady-state approximation for meta stable states of neutral helium is removed. The opacity effect may be the origin of this difficulty.