A Julia synthetic diagnostic for charge exchange recombination spectroscopy on the Helically Symmetric eXperiment

Synthetic diagnostics are tools that facilitate rigorous validation of high-fidelity simulations. By thoroughly modeling individual diagnostic processes, synthetic diagnostics reduce the amount of assumptions that are needed to relate simulation data to experimental measurements. This work introduces a new synthetic diagnostic system that has been developed for the charge exchange recombination spectroscopy (chERs) system on the Helically Symmetric eXperiment (HSX). Written in Julia, this synthetic diagnostic models the collection optics and constituent components of the spectrometer. PyFIDASIM [1,2] is used to compute the impurity emission intensity. An integrating sphere is used to measure light loss through the spectrometer. Additionally, a convolution scheme is used to model broadening of the spectral lines. A workflow for implementing and validating the synthetic diagnostic is created and applied. We present results from verification and validation studies using synthetic data generated by PyFIDASIM, experimental data taken via the integrating sphere, Neon calibration lamps, and data from measurement of carbon impurity lines.

[1] Geiger, Benedikt, et al. "Progress in modelling fast-ion D-alpha spectra and neutral particle analyzer fluxes using FIDASIM." Plasma Physics and Controlled Fusion 62.10 (2020): 105008.

[2] Stagner, L., B. Geiger, and W. W. Heidbrink. "FIDASIM: A neutral beam and fast-ion diagnostic modeling suite." Zenodo. https://doi. org/10.5281/zenodo 1341369 (2020).