Assessing the role of ITER ECE oblique view in resolving non-thermal emissions

TL;DR

This study evaluates the ITER oblique ECE diagnostic's ability to measure electron temperature accurately amidst non-thermal electron populations, showing it remains effective despite spectral broadening effects.

Contribution

The paper presents simulations demonstrating that the ITER oblique ECE view can reliably measure Te profiles even with non-Maxwellian electron distributions at reactor conditions.

Findings

Above a critical oblique angle, Doppler broadening masks non-thermal spectral signatures.

Higher EC harmonics in either polarization are unaffected by non-thermal emissions.

The ITER oblique ECE view maintains sensitivity to non-thermal electrons while providing accurate Te profiles.

Abstract

Systematic discrepancies between electron temperature (Te) measurements from radially viewing electron cyclotron emission (ECE) and Thomson scattering (TS) diagnostics have been observed in multiple tokamaks and are widely attributed to non-Maxwellian features in the electron velocity distribution function (EVDF). As the International Thermonuclear Experimental Reactor (ITER) is expected to operate at much higher core temperatures than present devices, accurate Te measurements from ECE become increasingly critical, particularly in the presence of non-Maxwellian EVDFs. This work presents ECE spectra simulations performed to assess the diagnostic capability of the ITER oblique view under ITER conditions where non-Maxwellian distributions are present. The results show that above a critical oblique angle, Doppler broadening becomes the dominant effect, masking fine-scale spectral signatures of non-thermal distortions across a wide range of conditions. Furthermore, at higher EC harmonics in either polarization, the spectra remain largely unaffected by non-thermal emissions, enabling reliable reconstruction of Te-profiles. These findings demonstrate that the ITER oblique ECE view retains sufficient sensitivity to non-thermal electrons while providing robust and accurate Te-profile measurements under reactor-relevant conditions. The results presented here also have direct implications for ITER ECE system operation and channel selection, particularly in the presence of non-Maxwellian electron populations.