  Providing stable and clean energy sources is a necessity for the increasing
demands of humanity. Energy produced by fusion reactions, in particular in
tokamaks, is a promising path towards that goal. However, there is little
experience with plasmas under conditions close to those expected in future
fusion reactors, because it requires the fusion of Deuterium (D) and Tritium
(T), while most of the experiments are currently performed in pure D. After
more than 20 years, the Joint European Torus (JET) has carried out new D-T
experiments with the aim of exploring the unique characteristics of burning D-T
plasmas, such as the presence of highly energetic ions. A new stable, high
confinement and impurity-free D-T regime, with strong reduction of energy
losses with respect to D, has been found. Multiscale physics mechanisms
critically determine the thermal confinement and the fusion power yield. These
crucial achievements importantly contribute to the establishment of fusion
energy generation as an alternative to fossil fuels.
