Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Laser fusion experiment extracts net energy from fuel

Milestone is passed on the long road to fusion energy.

Positioning the target for the National Ignition Facility's lasers. Credit: Eddie Dewald/LLNL

Using the world's most powerful assembly of lasers, a team of researchers say they have, for the first time, extracted more energy from controlled nuclear fusion than was absorbed by the fuel to trigger it — crossing an important symbolic threshold on the long path toward exploiting this virtually boundless source of energy.

Stephen Hawking questions the nature of black holes Bumblebees can fly at altitudes higher than peak of Mount Everest UK immigration debate alienating scientists and students

The latest feat, achieved at the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory in California, is still a way off from the much harder and long-sought goal of 'ignition', the break-even point beyond which a fusion reactor can generate more energy than is put in. Many other steps in the current experiments dissipate energy before it even reaches the nuclear fuel.

Nevertheless, the new result represents “a critical step on the path to ignition”, according to Mark Herrmann, head of a project investigating high-energy X-ray pulses at Sandia National Laboratory in Albuquerque, New Mexico, and who was not involved with the NIF work.

Whereas nuclear fission extracts energy released during the break-up of very heavy nuclei such as those of uranium, nuclear fusion — the process that powers stars and thermonuclear bombs — produces energy from the coalescence of light nuclei, such as those of hydrogen. During such a reaction, a tiny part of the masses of the separate hydrogen nuclei is converted into energy.

Controlling fusion has proved immensely difficult, partly because of the challenge of containing the plasma that fusion generates, which reaches temperatures of millions of degrees. Fusion projects in different parts of the world are exploring a variety of methods. Notably, the ITER experiment, under construction in southern France, will keep the plasma confined with magnetic fields inside a doughnut-shaped reactor.

Shaping pulses

A lot of energy must be pumped into the fuel to drive the nuclei close together to overcome their electrical repulsion. At NIF, this energy is provided by 192 high-powered lasers, which send their beams into a bean-sized gold container called a hohlraum. In the hohlraum, the fuel sits inside a plastic capsule.

The laser energy is absorbed by the hohlraum, which re-radiates it as X-rays, some of which are absorbed by the fuel capsule. The outer plastic shell then explodes, creating an implosion of the fuel inside, which raises the density high enough to trigger fusion. Most of the laser energy, however, stays absorbed by the hohlraum itself. That is why obtaining a net gain (more energy out than in) within the fuel itself is only a step on the way to ignition.

The NIF team’s success, which is described in a paper published online today in Nature1, has come in experiments conducted between last September and this January. It relies on shaping the laser pulses to deliver more power early in the pulse. This creates a relatively high initial temperature in the hohlraum that 'fluffs up' the plastic shell and makes it less prone to an instability during the explosion that disrupts the fusion process. “This fluffing up greatly slows down growth of the instability,” says team leader Omar Hurricane, a Livermore physicist.

As a result, the researchers have been able to achieve a 'fuel energy gain' — a ratio of energy released by the fuel to energy absorbed — of between 1.2 and 1.9. “This has never been done before in laboratory fusion research,” says Herrmann. He adds that much of the energy released was produced by self-heating of the fuel through the radiation released in the fusion reactions, an important requirement for sustaining the fusion process.

But fusion-energy generation still remains a distant goal, and Hurricane admits he cannot yet estimate a timescale for it. “Our total gain — fusion energy out divided by laser energy in — is only about 1%,” he says.


  1. 1

    Hurricane, O. A. et al. Nature (2014).

Download references


Additional information

Read the related News & Views article.

Related links

Related links

Related links in Nature Research

Laser fusion put on slow burn 2012-Dec-11

Ignition switch 2012-Nov-07

Laser fusion nears crucial milestone 2012-Mar-07

Fusion reactor aims to rival ITER 2010-Apr-30

Nuclear energy: The hybrid returns 2009-Jul-01

Laser facility flickers into life 2009-Jan-28

Related external links

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Ball, P. Laser fusion experiment extracts net energy from fuel. Nature (2014).

Download citation

Further reading


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing