On the application of He I collisional-radiative model to the He-H2 mixture plasmas in MAP-II divertor simulator

Atomic helium (He I) optical emission spectroscopy was carried out in a MAP-II divertor simulator to investigate the applicability of He I collisional-radiative (CR) model for the measurement of electron temperature (T-e) and density (n(e)) in He-H-2 mixture plasmas. The result was compared with Langmuir probe measurements. The excited population distribution of the He-H-2 mixture plasma was not reproduced by the He I CR model, although it was reproduced well for pure He and He-Ar mixture plasma. Specifically, the deviation of the population ratio of singlet to triplet states became more evident as the concentration of H-2 increased. This fact implies that the measurement of T-e for He-H-2 plasma using the He I CR model could lead to a significant error under a certain condition, such that T-e < 10 eV as in the case of divertor plasmas. (C) 2013 Elsevier B. V. All rights reserved.