A new landmark has been passed on the quest for fusion power with a new record for energy released. However, while the announcement marks a step towards the goal of powering the world from the same energy source as the stars, it is also a reminder of how far there is to go.

Models of fusion reactors suggest the optimum fuel will be a mixture of tritium – an isotope of hydrogen, made up of one proton and two neutrons – and deuterium. Yet, paradoxically, almost all fusion research has been done on ordinary hydrogen or deuterium.

Now, however, the first fusion experiments conducted using tritium since 1997 have produced a record amount of energy for a fusion reactor over a period of five seconds – 59 megajoules. The results were described at a press conference today.

It may seem illogical to do almost all our fusion research using lighter isotopes when tritium is expected to be an essential part of the ultimate fuel. However, "we can explore the physics in fusion plasmas very well by working with hydrogen or deuterium,” Dr Athina Kappatou of Max Planck Institute for Plasma Physics explained in a statement. Although Fukushima has more tritium than it would like, as a general rule tritium is expensive to produce, store, and handle, so most research facilities use the easier isotopes instead.

Indeed, the Joint European Torus (JET) near Oxford is the only fusion research facility currently set up to use tritium, and even it has spent decades working with other fuels.

All this is expected to change when International Thermonuclear Experimental Reactor (ITER) begins operations. Fusion advocates hope ITER will finally achieve the long-sought goal of producing much more energy than it takes to run, opening the door to commercial operations, although many are skeptical. Even though ITER’s output power is anticipated to reach 10 times its official input, that ignores requirements such as the energy required to build the plant. Once these are taken into account, it will still be a net energy sink.

JET is too small to produce even the temporary net energy that is ITER’s primary goal, but it can serve as a test site, giving the team that will operate ITER experience in working with tritium fuels for when operations begin.

“For the transition to…ITER it is important that we prepare for the conditions prevailing there,” Kappatou said. Consequently, JET’s carbon lining was replaced with beryllium and the more resistant tungsten to make it more closely resemble a smaller version of ITER.

Although these changes increased JET’s potential capacities, they also made plasma control harder. Nevertheless, Kappatou and colleagues were able to achieve a yield of 59 megajoules for a period of 5 seconds. This almost tripled the previous 22-megajoule world record for energy release set by JET 25 years ago when it last used tritium. It is also almost fifty times the output of the recent nuclear fusion experiment that released more energy than was applied for the first time.

“The record, and more importantly the things we’ve learned about fusion under these conditions and how it fully confirms our predictions, show that we are on the right path to a future world of fusion energy. If we can maintain fusion for five seconds, we can do it for five minutes and then five hours as we scale up our operations in future machines,” Professor Tony Donné of EUROfusion said in a statement seen by IFLScience.

The energy was released as neutrons. With an average power output of 11 megawatts, it would not have matched the largest model of offshore wind turbine, even if it could have been converted to electricity with 100 percent efficiency.

Fusion has been hailed as the ultimate clean energy for decades, and centuries from now that may indeed prove to be the case. However, with ITER not even scheduled to start working with deuterium/tritium fuel until 2035, and a further demonstration plant required before its lessons can be commercialized, it's unlikely to arrive fast enough to solve the climate crisis.