Description
Burning plasma conditions studies are of fundamental importance for future fusion reactors: next-generation tokamaks will reach very high temperatures and sustain them for long durations [1]. This makes it essential to deepen our understanding of the underlying physics in such conditions. Among the aspects that still need to be fully clarified are the behavior and the modeling of electron transport, which is affected by different interactions and consequently influence the shape of the electron energy distribution function (EEDF) [2]. Deviations from a Maxwellian distribution can significantly affect electron temperature measurements [3], which strongly depend on the shape of the EEDF [4–6]. In tokamaks, measuring high core electron temperatures (above 6–7 keV) is particularly challenging, often leading to discrepancies between Thomson Scattering and Electron Cyclotron Emission diagnostics, the two most commonly used and reliable techniques. Several diagnostics have been proposed in the past either to evaluate the shape of the EEDF or, alternatively, to provide reliable electron temperature measurements, such as oblique ECE or vertical ECE. However, their implementation has proven to be non-trivial.
In the present contribution, data from the entire JET-DTE3 experimental campaign are analyzed, confirming the possibility of identifying the conditions under which the EEDF deviates from a Maxwellian distribution. This is achieved using methods developed and refined to date [7], which allow systematic effects to be excluded. The analysis also demonstrates that findings previously reported for DTE2 and for other experimental campaigns (not limited to JET [6]) remain valid for DTE3, where a significantly larger dataset is available in regimes in which discrepancies are most evident (i.e. high electron temperatures).
A detailed determination of all the causes that may lead to these modifications are beyond the scope of the present paper. Likewise, the possible forms or perturbations that the EEDF may assume are not addressed here, although reference is made to the modelling work that allows to address these problems [5]. This study is ongoing and is being carried out within the framework of ITPA Joint Experiment #17 initiative, with the aim of investigating these aspects through dedicated experiments and the development of a cross-machine database.
References
[1] D. J. Cambell et al. - ITER Research Plan - ITR24-0000, 2024
[2] B. Applebe et al. - Phys. Plasmas 2019
[3] F. P. Orsitto et al - 49th EPS, 2023.
[4] M. Fontana, et al. -Physics of Plasmas, 2023.
[5] G. Giruzzi, et al. - EDP Sciences, 2023.
[6] V. Krivenski. Fusion Engineering and Design, 2001.
[7] L. Senni et al. – JINST, 2025