Investigation of T_e measurements discrepancies between ECE and Thomson diagnostics in high-performance plasmas in JET

¹ United Kingdom Atomic Energy Authority, Culham Centre for Fusion Energy, Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK
² CEA, IRFM F-13108 Saint Paul-lez-Durance, France
³ ENEA Department Fusion and Technology for Nuclear Safety, C R Frascati, 00044 Frascati, Italy
⁴ National Fusion Laboratory, CIEMAT, Madrid, Spain
⁵ Istituto per la Scienza e Tecnologia dei Plasmi, CNR, 20125 Milano, Italy
⁶ Max-Planck-Institut für Plasmaphysik, D-85748 Garching, Germany
⁷ Laboratory for Plasma Physics, LPP-ERM/KMS, Brussels, Belgium

^* e-mail: matteo.fontana@ukaea.uk
^** See the author list of ‘Overview of JET results for optimising ITER operation’ by J. Mailloux et al. to be published in Nuclear Fusion Special issue: Overview and Summary Papers from the 28th Fusion Energy Conference (Nice, France, 10-15 May 2021)

Published online: 23 February 2023

Abstract

For high-temperature JET and TFTR discharges, electron cyclotron emission (ECE) measurements of central electron temperature were systematically found to be up to 20% higher than those taken with Thomson scattering. In recent high-performance JET discharges, central T_e measurements, performed with LIDAR Thomson scattering and the X-mode ECE interferometer, have been studied in a large database, including deuterium (DD), and deuterium-tritium plasmas (DT). Discrepancies between T_e measurements have been observed outside of the experimental uncertainties. ECE measurements, at high T_e, have been found to be higher or lower than those of LIDAR, depending on the specific plasma scenario. In addition, discrepancies between the peaks of the second and third harmonic ranges of the ECE spectrum have been interpreted as evidence for the presence of non-Maxwellian features in the electron distribution function. These comparisons seem to suggest that such features can be found in most of the high-performance scenarios selected in this JET database.