Inference of Impurity Ion Temperature Using High-Resolution Spectroscopy in the Compact Toroidal Hybrid

Accurate ion temperature (T_i) measurements are essential for understanding transport and energy balance in magnetically confined plasmas. In the Compact Toroidal Hybrid (CTH), we infer T_i from the Doppler broadening of spectral lines emission of impurity ions: C III (229 nm) and C V (227 nm). The C III profiles were narrower than C V, implying a lower T_i for the lower charge state: 4 eV (C III) versus 28 eV (C V). These values are consistent with the expected charge-state fractional-abundance peaks for the corresponding CTH electron temperature and density.

To mitigate complications in inferring T_i due to magnetic fields, we developed a Zeeman-resolved line-shape fitting tool. The model constructs the Zeeman multiplet, applies the instrumental response, and includes thermal Doppler broadening; nonlinear least-squares fitting to CTH spectra then yields T_i​. Python scripts and SQL queries retrieve level data and transition parameters from the NIST atomic spectral database, from which Gaussian Zeeman components are assembled and summed to generate synthetic spectra for fitting. The discharge-resolved evolution of T_i will be quantified, revealing phase-dependent trends in impurity ion heating.