Determination of Electron Density and its Temperature using Collisional Radiative (CR) Model for Argon Gas in High-Density Helicon Source*

To explore a deep space for a long-time period, a spacecraft must have a long-lifetime and highly efficient thruster. We have proposed an electrodeless plasma propulsion system using a high-density (~10¹³ cm^-3) helicon plasma [1]. To characterize this thruster, we need to measure plasma parameters, e.g., an electron density (n_e) and its temperature (T_e). A probe method, which is a general measurement, is useful, but it disturbs a plasma flow. To determine these parameters without any disturbance to a plasma, we have been developing a spectral measurement method using a Collisional Radiative (CR) model for the argon atoms [2,3]. This method needs many parameters, e.g., cross-section, diffusion coefficients, and various assumptions. In this study, improvement of some parameters and calculation results compared with probe experiments, will be presented. [1] S. Shinohara, H. Nishida, T. Tanikawa, T. Hada, I. Funaki, IEEE Trans. Plasma Sci., 42 (2014) 1245. [2] J. Vlček, J. Phys. D: Appl. Phys., 22 (1989) 623. [3] H. Akatsuka, Phys. Plasmas, 16 (2009) 043502.