Dr. Žiga Štancar, a former colleague at the Jožef Stefan Institute’s Reactor physics department, contributed to the first direct experimental observation of thermonuclear fusion plasma self-heating by alpha ions in deuterium-tritium (DT) plasma, which is an important milestone on the pathway to demonstrative fusion reactors. The experiment, summarized in Physical Review Letters, was carried out at the largest magnetic confinement fusion device, the Joint European Torus (JET) tokamak. Led by dr. Vasily Kiptily of UKAEA, the researchers ran experiments with a DT and a comparable pure deuterium (D) plasma, externally heated with neutral beam injection, which resulted in high plasma temperature and fusion rate. Comparing the properties of the two plasmas immediately after the heating had been switched off revealed that the temperature of plasma electrons decreased in the D plasma, whereas it kept increasing for an additional 100 milliseconds in the DT plasma. This rise in electron temperature without external heating was ascribed to the collisional transfer of energy by the fusion-born fast alpha particles, which was corroborated by plasma simulations.