Fusion: have we achieved the ‘holy grail’ of physics?

Researchers in the US are claiming to have successfully generated a nuclear fusion reaction, in the process generating more energy output than was put in. But what does this mean?

Nuclear fusion has long been seen as a safe and sustainable energy source of the future.

Every second, deep inside the Sun, around 9 billion billion billion fusion reactions occur, resulting in the life-giving energy that bathes us.

An image of the sun
Fusion occurs inside the Sun billions of times every second. Credit: NASA/SDO

Due to the intense pressures and temperatures involved, fusion has proven incredibly difficult to replicate in any way that is meaningful for energy production here on Earth.

For the first time, however, scientists at the U.S. Department of Energy’s Lawrence Livermore National Laboratory (LLNL) in California, US, have achieved an incredible breakthrough: net energy gain from a controlled fusion reaction.

What does this mean?

When light atoms fuse to make heavier elements, energy is released because the atoms don’t require as much energy when they are together, as when they are apart.

The scientists fused deuterium and tritium (the two heavy isotopes of hydrogen favoured for achieving fusion power). “The two positively charged nuclei have to be pushed together against their electrical repulsion,” says Professor Andrew Stuchbery, Head of the Department of Nuclear Physics and Accelerator Applications at the Australian National University.

Main isotopes of hydrogen
Main isotopes of Hydrogen. Protium, Deuterium (D) and Tritium (T) are the three naturally occurring isotopes of the chemical element hydrogen. They differ in number of protons and their atomic weight. Credit: PeterHermesFurian/Getty Images

“In this case, this is achieved by heating the isotopes in a plasma to temperatures where the nuclei are going so fast that they can overcome the repulsion and bang together.”

The turning point for fusion to be considered a viable source of future power generation is when the amount of energy released in the reaction surpasses that required to force the atoms together in the first place.

In this case, a laser delivered 1.8 MJ of energy to fuse the atoms, which then released 2.5 MJ.

It has taken more than 50 years to get to this point, and if confirmed by the National Ignition Facility (NIF) at LLNF, it marks a real watershed moment for physics, engineering and potentially humanity alike.

Read more: Fusion energy: a time of transition and potential

Although undoubtedly a breakthrough for nuclear physics, it isn’t quite the time to unplug from other energy sources yet.

“The calculation of energy gain only considers the energy that hit the target, and not the (very large) energy consumption that goes into supporting the infrastructure,” cautions Dr Patrick Burr, a Senior lecturer in Nuclear Engineering at The University of New South Wales.

Fusion target bay inside national ignition facility
NIF beamlines entering the lower hemisphere of the NIF Target Chamber, as seen from the ground floor of the Target Bay. Credit: Damien Jemison/Lawrence Livermore National Laboratory2

The infrastructure Burr is referring to includes the fact that a whopping 500 MJ of energy was required by the lasers just so they could deliver that 1.8 MJ pulse to the target, and it is these sorts of areas that we can expect to see advances in the coming years.

Burr identifies three main areas to improve: turning the one short pulse eventually into one continuous pulse; compensating for losses in the input infrastructure; and engineering stronger materials “capable of withstanding the harsh fusion environment for prolonged periods of time”.

“Fortunately,” notes Burr, “there are now many national laboratories, companies and universities (including in Australia) advancing fusion energy, with a remarkable rate of progress.”

A fusion future?

Despite the pace of technological advancement, it is unrealistic to base our hope for a climate change cure on fusion.

Inside the nif target bay
View from bottom of the NIF Target Chamber bottom showing target positioner being inserted. Pulses from NIF’s high-powered lasers race toward the Target Bay at the speed of light, arriving at the centre of the chamber within a few trillionths of a second of each other, aligned to the accuracy of the diameter of a human hair. Credit: Damien Jemison/Lawrence Livermore National Laboratory

“Nuclear fusion – the energy that powers the sun – has been a holy grail of physics for decades,” says Professor Ken Baldwin from the Research School of Physics at the Australian National University, who is currently attending the Australian Institute of Physics Congress in Adelaide, Australia – where this announcement has caused quite a stir.

“It’s unlikely that fusion power – which generates no greenhouse gases and minimal nuclear waste – will save us from climate change,” says Baldwin. “The energy apparently released from the Livermore experiments is only enough to boil a kettle.

“All the heavy lifting for the energy transition will be done by renewable energy and nuclear fission (existing nuclear power) – with nuclear fusion at commercial scale unlikely to be available until later this century, well after the 2050 deadline needed to keep global warming below two degrees.  But beyond that fusion might provide limitless energy for centuries to come.”

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