Nuclear-fusion
The JET experiment uses a ‘tokamak’ (pictured) that confines plasma using a magnetic field in the shape of a torus. Image credit: JET

A milestone has been reached in the 60-year struggle to harness the nuclear reactions that power the Sun in an experiment that could lead to a way of producing an unlimited source of clean and sustainable energy in the form of nuclear fusion.

Omar Hurricane, a researcher at Lawrence Livermore National Laboratory, says that for the first time, they’ve produced significant amounts of fusion by zapping a target with their laser, which marks a critical threshold in eventually achieving the goal of a self-sustaining nuclear-fusion reaction.

“We’ve gotten more energy out of the fusion fuel than we put into the fusion fuel,” he says.

Strictly speaking, while more energy came from fusion than went into the hydrogen fuel, only about 1 percent of the laser’s energy ever reached the fuel. Useful levels of fusion are still a long way off.

“They didn’t get more fusion power out than they put in with the laser,” says Steve Cowley, the head of a huge fusion experiment in the U.K. called the Joint European Torus, or JET.

Nuclear fusion uses a fuel source derived from water and produces none of the more dangerous and long-lasting isotopes, such as enriched uranium and plutonium, that result from conventional nuclear power plants, which rely on the fission or splitting of atoms rather than their fusion.

The laser is known as the , or NIF. Constructed at a cost of more than $3 billion, it consists of 192 beams that take up the length of three football fields.

For a brief moment, the beams can focus 500 trillion watts of power — more power than is being used in that same time across the entire United States — onto a target about the width of a No. 2 pencil.

The fuel, composed of the two hydrogen isotopes tritium and deuterium derived from water, was compressed together under enormous pressures and temperatures for less than a billionth of a second, but this was enough to see more energy coming out of the experiment than went into it.

“We are fusing deuterium and tritium, which are isotopes of water, in a way that gets them to run together at high enough speed to overcome their natural electrical repulsion to each other,” said Omar Hurricane of the Livermore laboratory.

“We are finally, by harnessing these reactions, getting more energy out of these reactions than we are putting into the deuterium-tritium fuel… We took a step back from what we tried before and in the process took a leap forward,” said Dr Hurricane, who led the NIF study published in the journal Nature.

The goal is fusion: a process where hydrogen atoms are squeezed together to make helium atoms. When that happens, a lot of energy comes out. It could mean the answer to the world’s energy problems, but fusion is really, really hard to do. Hurricane says that each time they try, it feels like they’re taking a test.

There are currently two parallel approaches to nuclear fusion. One uses laser energy to compress fuel pellets — like the NIF experiment — and aims to keep the fuel in place by a process known as inertial confinement.

The other approach is to build a complex magnetic “bottle” to hold the hot, electrically charged plasma of the fuel in place. This magnetic confinement is the strategy of the Joint European Torus (JET) experiment in Culham, Oxfordshire, and the international ITER nuclear fusion plant under construction at Cadarache in southern France.

The breakthrough at NIF was made possible by altering the laser pulses focusing on the fuel pellet in such a way that it led to the even compression of the capsule holding the deuterium and tritium, said Debbie Callahan, one of the researchers involved.

“We had to compress the capsule by 35 times. This is like saying that if you started with a basketball it would be like compressing it down to the size of a pea, but keeping the perfect spherical shape, which is very challenging,” Dr Callahan said.

“We have waited 60 years to get close to controlled fusion, and we are now close in both magnetic and inertial-confinement research. We must keep at it,” Professor Cowley said.