Skip to main content
Nuclear fusion

Nuclear fusion

National Ignition Facility heralds ‘significant step’ towards fusion break-even target

18 Aug 2021 Michael Banks
National Ignition Facility
Burning question: scientists at the $3.5bn National Ignition Facility are nearer to achieving ignition – the point at which fusion reactions generate at least as much energy delivered by the laser system (Courtesy: NIF)

Scientists at the $3.5bn National Ignition Facility at the Lawrence Livermore National Laboratory in California say they have come a step closer to their ultimate goal of realizing “ignition”, at which fusion reactions generate at least as much energy as its lasers put in. In an experiment conducted on 8 August they say they achieved a yield of more than 1.3 megajoules (MJ) – about 70% of the energy that the laser pulse delivered to the sample.

NIF trains 192 pulsed laser beams on to the inner surface of a centimetre-long hollow metal cylinder known as a hohlraum. Inside is a fuel capsule, which is a roughly 2 mm-diameter hollow sphere containing a thin deuterium-tritium layer.

This result is a historic step forward for inertial confinement fusion research.

Kim Budill, Lawrence Livermore director

Each pulse lasts just a few nanoseconds and the lasers can deliver about 1.9 MJ of energy. This powerful blast causes the capsule to implode rapidly, creating immense temperatures and pressures inside a central hot spot, where fusion reactions occur.

Since NIF was turned on over a decade ago, its long-term goal has been to show it can, achieve ignition. This involves self-sustaining reactions, in which the alpha particles that are also emitted during fusion emit heat to initiate further fusion.

But after experiments between 2009 and 2012 fell well short of reaching ignition, NIF’s focus switched to supporting the US National Nuclear Security Administration’s work on the physics of nuclear weapons and maintaining America’s nuclear deterrent without further underground testing.

While ignition is part of that overall programme, scientists at NIF decided to change their ignition strategy, which included alterations to the shape of the laser pulses to create much more stable implosions as well as improvements to the precision of the laser and diagnostic equipment.

What has been achieved has completely altered the fusion landscape

Steven Rose, Imperial College

The work began to pay off and in 2014, these “high-foot” pulses each yielded up to 17 kJ of fusion energy (and later 26 kJ) compared to just 10 kJ in earlier experiments. In 2017, NIF researchers then obtained 54 kJ of fusion energy per laser pulse – as measured by the number of neutrons and alpha particles produced – and by last year were creating regular shots that produced around 100 kJ of fusion energy.

More bang for your buck

The shot on 8 August, which was announced yesterday, produced 1.3 MJ, generating more than 10 quadrillion watts of fusion power for 100 trillionths of a second. Although still short of break-even, the figure far exceeded previous markers.

“This result is a historic step forward for inertial confinement fusion research, opening a fundamentally new regime for exploration and the advancement of our critical national security missions,” says LLNL director Kim Budil.

Thomas Mason, director of the Los Alamos National Laboratory, says that the work is the culmination of decades of scientific and technological work stretching across nearly 50 years. “This [result] enables experiments that will check theory and simulation in the high energy density regime more rigorously than ever possible before and will enable fundamental achievements in applied science and engineering,” adds Mason.

Fusion experts outside NIF are also enthusiastic about the latest results. Plasma physicist Steven Rose, who is co-director of the Centre for Inertial Fusion Studies at Imperial College London, says the NIF team has done an “extraordinary” job, dubbing the latest breakthrough is the “most significant advance” in inertial fusion since it began in 1972.

“What has been achieved has completely altered the fusion landscape and we can now look forward to using ignited plasmas for both scientific discovery and energy production,” adds Rose.

NIF officials say the lab now plans to repeat the experiments to get a better understanding of what parameters were responsible for such a leap in energy production, cautioning, however, that it will take “several months” to do that work.

Related events

Copyright © 2024 by IOP Publishing Ltd and individual contributors