Inference of impurity parameters in the C-2W experiment through an optimized reconstruction of local emission spectra

The C-2W experiment at TAE Technologies is an advanced fusion device that generates beam-driven field-reversed configuration (FRC) plasmas within a magnetic mirror [1]. A spectroscopic impurity diagnostic collects line-integrated emission from multiple radially spaced lines-of-sight at the center of the confinement vessel. These lines-of-sight are coupled to a high resolution spectrometer and fast camera acquisition system that is focused near an O4+ transition line at 278.1nm. To accurately determine plasma parameters from Doppler shift and broadening the local emission spectra must be reconstructed. Bayesian methods have been used to reconstruct local parameters from line-integrated measurements, but the application of these methods is encumbered by high computation time [2]. An alternative method is proposed which efficiently reconstructs the local emission spectrum through an iterative process consisting of inversion, least-squares fitting, postulation of local data, and optimization of the line-integrated data. Finally, local impurity plasma parameters are extracted, and the uncertainty of the method of determination is quantified. 

[1] H. Gota et al., Nucl. Fusion 61, 106039 (2021)

[2] M. Nations et al., Rev Sci Instrum 93, 113522 (2022)