Evaluation of the Electron Temperature of the Ablation Cloud for the Small-Size Hydrogen Pellet Using Paschen Series in Heliotron J

Abstract

We simultaneously measured the electron temperature (T_e) and electron density (n_e) using a low-dispersion near-infrared spectrometer in a small-size pellet ablation cloud in Heliotron J, a medium-sized helical-axis heliotron device. We applied the intensity ratio of the Paschen-α, β, γ and to determine T_e based on the collisional-radiative model, which was fairly consistent with the partial local thermodynamic equilibrium (LTE) in the upper principal quantum numbers of 4, 5, and 6. For a typical pellet injection discharge, T_e and n_e were determined to be 0.9 eV and 4 × 10²¹ m^－3, respectively. Our derived generalized empirical calibration curve demonstrates a weak influence of T_e on n_e evaluation, particularly in the range of 0.4 - 2.0 eV. Subsequently, we determined the region where the LTE is achieved for the Paschen series.