Conceptual design of Thomson scattering system with high wavelength resolution in magnetically confined plasmas for electron phase-space measurements

TL;DR

This paper presents a conceptual design for a high-resolution Thomson scattering spectrometer capable of detailed electron velocity distribution measurements in magnetically confined plasmas, demonstrating promising photon statistics and data analysis methods.

Contribution

The paper introduces a novel high-resolution, spatially-resolved spectrometer design with 2560 wavelength channels for plasma diagnostics, including simulation validation and Bayesian inference analysis.

Findings

Photon count per channel exceeds unity, enabling single-shot measurements.

Signal-to-noise ratio surpasses 5 at full spectral resolution in simulations.

Deviations from Maxwellian distributions can be detected with the proposed system.

Abstract

We discuss the conceptual design of a spatially-resolved spectroscopy system of Thomson scattering with high wavelength resolution capable of measuring the shape of electron velocity distribution functions in magnetically confined plasmas. We design a spatially-resolved spectrometer with 2560 wavelength channels. The estimated number of scattered photons in a single spectrometer channel is much larger than unity under the experimental setup and plasma parameters of the Compact Helical Device (CHD), indicating sufficient photon statistics for single-shot measurements. Simulations of the scattered spectra show that the signal-to-noise ratio exceeds 5 even under the most unfavorable conditions expected in CHD at full spectral resolution, and further improves with post-processing pixel binning. Bayesian inference applied to the simulated spectra demonstrates that the inferred plasma parameters agree with the input values within the estimated uncertainties. Comparisons between spectra generated from non-Maxwellian electron velocity distribution functions and their Maxwellian fits indicate that deviations from Maxwellian distributions can be identified using the proposed system.