Improved spectral analysis for the motional Stark effect diagnostic

Abstract

The magnetic pitch angle and the magnitude from reversed field pinch plasmas in the Madison symmetric torus (MST) have been routinely obtained from fully resolved motional Stark effect (MSE) spectrum analyses. Recently, the spectrum fit procedure has been improved by initializing and constraining the fit parameters based on the MSE model in the atomic data and analysis structure. A collisional-radiative model with level populations nlm-resolved up to n = 4 and a simple Born approximation for ion-impact cross sections is used for this analysis. Measurement uncertainty is quantified by making MSE measurements with multiple views of a single spatial location, ranging 5%-15% for typical MST operation conditions. A multi-view fit improves the goodness of fit of MSE spectral features and background.

Polarimetric spectra analysis for tokamak pitch angle measurements

“…This method was tried at low-field (a few tenths of Tesla) fusion devices where selecting particular polarization components with bandpass filters is limited by small Stark splitting and large broaden- ing due to the finite size of the aperture and velocity distribution in the beam [9]. However, some medium-field devices such as DIII-D attempted this direct spectrum method, compared the performance with that from its conventional counterpart, and demonstrated the feasibility [4].…”