The World's Largest Tokamak Just Crushed the Record for Nuclear Fusion Energy


Caroline Delbert - Yesterday 
Popular Mechanics
© EUROfusion


England's Joint European Torus (JET) tokamak has produced 59 megajoules of energy for five seconds, breaking the previous nuclear fusion record from 1997.
JET is a training ground for the much larger, more ambitious ITER reactor.
The 59-megajoule record has a power ratio of Q=.33, with an industry goal of Q=1.

The Joint European Torus (JET) experiment housed in England has set a new record for the power generated by a burst of unfathomably hot plasma. The circular tokamak reactor, which looks like a donut, reached 59 megajoules of energy—a new high for a family of reactors that require an enormous amount of energy to get up to operational speed.

JET is part of the Culham Centre for Fusion Energy just outside Oxford, England. The Centre is the national laboratory for nuclear fusion research in the United Kingdom, previously known as "UKAEA Culham" after the U.K. Atomic Energy Authority. It's awkward that the Joint "European" Torus is no longer a part of Europe, but that's partly because the project dates back 40 years to the early 1980s.

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For about ten years, the original JET tokamak operated with the same goal that fusion projects have today: to generate enough energy to be productive against the fusion reactor's enormous energy cost for operation. For decades, the reactor iterated, meaning it was adjusted and refined over time to continue trying to reach its goals. Then, in 2009, it shut down completely for more of an overhaul. Today's JET is almost unrecognizable when you compare it to what the 1980s researchers built.

JET is a tokamak, which is basically a donut- or spherical-shaped tunnel where hydrogen isotopes are contained by a powerful magnetic field and then superheated until they're far hotter than the sun. It's at these high temperatures that the atoms' nuclei smash together, literally nuclear fusion. The reaction generates enormous energy relative to the amount of fuel required.

Over time, JET has learned lessons from the International Thermonuclear Experimental Reactor (ITER), a project that started later, but had massive funding and truly global participation. Results from ITER experiments helped JET to further tailor its goals, proving especially helpful while revamping JET between 2009 and 2011. Now, the two are working together to design experiments at JET that will help researchers at ITER make better decisions.

One way JET has led the way globally is by using fuel made of deuterium and tritium, names for two isotopes of hydrogen. Protium is the most common form of hydrogen, consisting of just one proton. Stable deuterium has a proton as well as a neutron (its name meaning two, like "deuce"), while radioactive tritium has one proton and two neutrons. The fuel sources are far better than protium, but the extra neutrons are sprayed around and can cause problems. To counter this, JET now has a special tungsten and beryllium shielding that will also be part of ITER.

All this background leads us to the exciting new record. In December, JET created an astonishing 59 megajoules of energy and sustained that for five full seconds—the longest possible amount of time before the reactor overheats. With nuclear fusion, the goal is to reach an advantageous power ratio of Q=1, where Q is the amount of energy generated divided by the amount of energy the reactor requires to operate. That means each facility's Q value is made from different parts: 59 megajoules might mean a Q of 20 at some tiny fusion reactor.

At JET, 59 megajoules is.33Q, which is still a step in the right direction, scientists say. They insist that at the massive ITER, which will be the largest fusion reactor in the world by far, the same processes that led to the record at JET will mean ITER is reaching productive fusion, or a Q greater than 1. Time will tell, because ITER isn't set to power up its first plasma run for years to come.