How US scientists moved one step closer to dream of fusion power

US scientists have achieved energy gain in a fusion reaction for the first time, the country’s energy secretary Jennifer Granholm has confirmed, heralding the breakthrough as evidence that the technology could eventually provide an abundant, zero carbon alternative to fossil fuels.

“This is a landmark achievement,” Granholm said at a press conference in Washington on Tuesday, confirming the breakthrough first reported by the Financial Times.

“We have taken the first tentative steps towards a clean energy source that could revolutionise the world,” said Jill Hruby, administrator of the National Nuclear Security Administration.

But how much closer does this breakthrough take the energy sector to the dream of fusion power?

What is fusion?

Fusion is the reaction that powers the sun. It involves heating two hydrogen isotopes — normally deuterium and tritium — to such extreme temperatures that the atomic nuclei fuse, releasing helium and vast amounts of energy in the form of neutrons.

Unlike nuclear fission, the process produces no long-lived radioactive waste. It also emits no carbon, and scientists estimate a small cup of the fuel could power a house for more than 800 years.

Fusion’s supporters describe it as the “holy grail” of clean energy: a technology that could theoretically provide near limitless, zero carbon power.

But although Soviet scientists developed the first fusion machine in the 1950s using a process called magnetic confinement, until now no group had been able to produce more energy from a fusion reaction than it consumed — a scientific milestone known in the field as scientific energy gain or target gain.

What have the US scientists achieved?

Scientists at the US government’s National Ignition Facility at the Lawrence Livermore National Laboratory in California have achieved that goal of energy gain in the reaction for the first time.

The $3.5bn NIF, which opened in 2009, was primarily designed to test nuclear weapons by simulating explosions but has also been used to advance fusion energy research.

Magnetic confinement, which remains the most widely studied approach to fusion, uses huge magnets to hold the deuterium-tritium fuel in place while it is heated to temperatures hotter than the sun.

The NIF uses a different process, called inertial confinement, in which it fires 192 lasers at a tiny capsule of the fuel. The lasers heat the fuel to more than 3mn degrees Celsius, which blows off the surface of the target capsule, causing what the NIF describes as a “rocket-like” implosion. That compresses and further heats the fuel until the hydrogen atoms in the deuterium and tritium fuse, releasing helium and energy.

In the experiment on December 5, the reaction produced about 3.15 megajoules of energy, which was about 150 per cent of the 2.05MJ of energy in the lasers, the laboratory said on Tuesday. The gain was even greater than the preliminary results reported by the FT.

Does this mean they have cracked fusion power?

No. Achieving energy gain has been seen for decades as a crucial step in proving that commercial fusion power stations are possible. However, there are still several hurdles to overcome.

First, energy gain in this context only compares the energy out to the energy in the lasers, not to the total amount of energy pulled off the grid to power the system. In fact, each shot requires 330MJ of electrical energy, delivered in a 400-microsecond burst.

The system that powers the lasers at the NIF is old and not designed for maximum energy efficiency. However, scientists still estimate that commercial fusion will require fusion reactions that generate between 30 and 100 times the energy going in.

The NIF also makes a maximum of one shot a day, whereas an internal confinement power plant would probably need to complete several shots a second.

“The experiment demonstrates unambiguously that the physics of laser fusion works,” said Robbie Scott, a plasma physicist who has contributed research to the NIF. “Next steps include the demonstration of even higher fusion energy gain and the further development of more efficient methods to drive the implosion.”

How does it compare with other recent breakthroughs?

The achievement at the NIF follows big announcements in the past 18 months by other publicly funded fusion laboratories with slightly different research objectives.

Last year in China, a magnetic confinement machine, known as a tokamak, called East — the Experimental Advanced Superconducting Tokamak — managed to sustain a fusion reaction at 120mnC for a record 101 seconds. Temperatures of more than 100mnC, generally required for magnetic confinement fusion, had been attained before but never sustained for such a long time.

In May, researchers at the world’s largest, most powerful tokamak in Oxford, the Joint European Torus (JET), produced a record 59MJ from a sustained reaction lasting five seconds. That was enough energy to boil about 60 kettles and more than doubled the previous energy output record of 22MJ, achieved by JET in 1997.

Neither reaction demonstrated an energy gain as the NIF did, but neither facility had prioritised achieving gain, experts said.

What happens next?

The sector hopes the breakthrough will galvanise interest and investment and so accelerate progress.

Historically, most fusion science has been done by publicly funded laboratories such as the NIF and JET, but in recent years investment has also flooded into private companies promising to deliver fusion power in the 2030s.

Melanie Windridge, a plasma physicist who runs the consultancy Fusion Energy Insights, pointed out that the NIF, which cost $3.5bn to build, was 13 years old and based on laser-technology developed in the 1980s.

“If you can do that with ageing technology it just shows what could be possible with the newest equipment,” she said. “If they get private backing and they are able to move at these aggressive timescales, then they can use cutting edge technology . . . and that is tremendously exciting.”