As reported by EURfusion in Phys.org and other media today, the large and powerful tokamak in the U.K. called the Joint European Torus (JET), generated an output of 69 megajoules from a plasma which was stable and self-contained for 5.2 seconds, setting a record for tokamaks. The temperature to which the plasma was raised was very high, 150 million degrees K.
The experiment may have been further from “breakeven,” or an “ignited plasma,” than the JET’s previous experiment in 2021; this, presumably, because of the low density of the deuterium-tritium plasma. The ratio of the energy of the plasma from internal (fusion) heating, to the energy injected into the plasma by external heating—a ratio known as “Q”—was apparently below .50, while the JET had attained a “Q” of .67 in a 2021 experiment in which the output was 59 megajoules and the plasma was stable for 5 seconds. The JET, which has operated for 40 years, is now being shut down by U.K. budgeteers despite scientific petitions to keep it going.