Reconstruction of the fast-ion deuterium distribution in a tritium-rich plasma in the JET DTE2 campaign

An important step on the way to future fusion power plants was the 2021 deuterium-tritium experimental campaign (DTE2) at the Joint European Torus (JET), in which crucial DT physics was investigated. In this study, we have reconstructed the fast-ion deuterium distribution function in JET discharge 99971 which broke the former fusion energy record. It is the first time that the fast-ion distribution has been reconstructed from experimental data in a DT discharge. The reconstruction shows that the fast-ion deuterium distribution is anisotropic, with a bias towards co-going ions (p > 0). The fast-ion deuterium distribution likely peaks in energy (E) at around E ∼ 60-70 keV and has a marginal high-energy tail (E ≳ 180 keV). Furthermore, an orbit analysis shows that the fast-ion distribution is composed of mostly co-passing orbits (50%), trapped orbits (21%) and counter-passing orbits (27%), as well as a small population of potato orbits (1.7%) and counter-stagnation orbits (0.3%). The orbit-type constituents of the neutron measurements are distributed in similar fractions.