Optical diagnostics of helium recombining plasmas with collisional radiative model

Optical diagnostics for plasmas has many advantages that allow for the determination and understanding of plasma parameters. A method employing the line intensity ratio (LIR), combined with the collisional-radiative (CR) model considering the radiation trapping effect (RTE), was developed to analyze the recombining helium plasmas. The recombining plasma component and the ionizing plasma components in the He CR-model were evaluated, and the RTEs for from the ground state to n1P states were analyzed. The electron temperature and density of the helium recombining plasmas were determined using seven LIRs with the He CR-model, considering the RTEs of 11S–31P, 11S–41P, and 11S–51P. When the He gas pressure was above 100 mTorr, the electron temperature was less than 0.8 eV and the electron density was more than 1012 cm−3. The determined plasma parameters were compared with those obtained by the continuum method and in reasonable agreement with those by the continuum method.