Investigation of High-Te Discrepancies Between ECE and TS Using Super-Resolved Thomson Scattering at DIII-D

Significant discrepancies have been observed in the JET tokamak [1] between electron temperature (Te) profiles measured by Electron Cyclotron Emission (ECE) and Thomson Scattering (TS). These discrepancies have also been observed in high Te DIII-D plasmas. At DIII-D, ECE provides high temporal resolution (~500 kHz), while TS is limited to ≤200 Hz, complicating time-resolved comparisons and analysis of fast events. A statistical survey of high-performance DIII-D discharges is conducted to investigate the occurrence and magnitude of discrepancies depending on plasma conditions and identify correlations with ohmic versus auxiliary heating methods like ECH and NBI. Observed patterns are evaluated against proposed explanations including optical depth effects, equilibrium mapping inaccuracies, and non-Maxwellian energy distributions. This project uses the Diag2Diag machine learning framework to generate super-resolved TS (SRTS) profiles at high time resolutions [2], enabling synchronized comparisons between the two Te diagnostics. Based on these statistical observations, preliminary models are proposed to characterize and predict when ECE-TS discrepancies emerge. Insights from this project serve to improve the accuracy of Te profiling in diverse plasma scenarios at DIII-D and future fusion devices.

[1] Fontana M. et al, Phys. Plasmas 30, 122503 (2023)

[2] Jalalvand A. et. al https://arxiv.org/abs/2405.05908, accepted to be published in Nat.Comm, (2025)