What is nuclear fusion?

US government scientists announced a nuclear fusion energy breakthrough Tuesday that could be critical for tackling climate change.
Nuclear fusion is what happens in the Sun and other stars and involves joining two atomic nuclei to make one larger one.
Fusion power offers the prospect of an almost inexhaustible source of energy for future generations.

Scientists in the United States have made a breakthrough in nuclear fusion - achieving a 'net energy gain' in a step towards a cleaner energy future.

In a fusion experiment using lasers, the scientists at Lawrence Livermore National Laboratory in California managed to produce more energy from the reaction than it consumed - a net gain of 1.5 megajoules in less time than it takes light to travel one inch.

The breakthrough was announced in a livestreamed press conference Tuesday from the US Department of Energy, led by US Secretary of Energy Jennifer Granholm.

“This is such a great example of perseverance… it’s a scientific milestone, but it’s also an engineering marvel beyond belief,” said White House Office of Science and Technology Policy Director Dr. Arati Prabhakar in a statement.

"Monday 5 December was an important day for science," added Under Secretary for Nuclear Security and National Nuclear Security Administration (NNSA) Administrator Jill Hruby.

She explained that 192 lasers converged on a target no bigger than a peppercorn and heated it to more than 3 million degrees C, "briefly simulating the conditions of a star and achieving ignition".

It was hailed as a historic achievement for both national security and a clean energy future.

“This marks the dawn of the fusion age,” said Michl Binderbauer, CEO of TAE Technologies. “It’s a crucial step that validates a theory and bolsters our growing field of work in fusion energy. As we reach an inflection point for research and gain vital support, we are primed to invent a reality powered by commercial fusion energy.”

Public and private research would be needed to scale the technology and President Biden has a vision to get to a nuclear fusion plant in a decade, added Granholm.

What is nuclear fusion exactly?

Our current nuclear power stations use nuclear fission – essentially splitting an atom’s nucleus.

Nuclear fusion is what happens in the Sun and other stars and involves joining two atomic nuclei to make one larger one. Both reactions release large amounts of energy, but with nuclear fusion there is very high energy yield and very low nuclear waste production.

Fusion occurs when two light atoms bond together, or fuse, to make a heavier one. The total mass of the new atom is less than that of the two that formed it; the "missing" mass is given off as energy, as described by Albert Einstein's famous E=mc2 equation.

Nuclear fusion is the holy grail of clean energy.

There are several "recipes" for cooking up nuclear fusion, which rely on different atomic combinations.

The most promising combination for power on Earth today is the fusion of a deuterium atom with a tritium one. The process, which requires temperatures of approximately 72 million degrees Fahrenheit (39 million degrees Celsius), produces 17.6 million electron volts of energy.

Deuterium is a promising ingredient because it is an isotope of hydrogen. In turn, hydrogen is a key part of water. A gallon of seawater (3.8 liters) could produce as much energy as 300 gallons (1,136 liters) of petrol.

Challenges for nuclear fusion researchers

When nuclear fusion power offers the prospect of an almost inexhaustible source of energy for future generations, it has also presented many so-far-insurmountable scientific and engineering challenges.

In the Sun, massive gravitational forces create the right conditions for nuclear fusion in the star’s core, but on Earth they are much harder to achieve.

Fusion fuel – different isotopes of hydrogen – must be heated to extreme temperatures of the order of 50 million degrees Celsius, and must be kept stable under intense pressure, and dense enough and confined for long enough to allow the nuclei to fuse.

More milestones in nuclear fusion

This week's 'net energy gain' achievement is one of a few recent breakthroughs for fusion energy.

This past January, using the world's largest laser, scientists coaxed fusion fuel for the first time to heat itself beyond the heat they zapped into it, achieving a phenomenon called a burning plasma that marked a stride toward self-sustaining nuclear fusion energy.

And this February, researchers from England said they achieved 59 megajoules of sustained fusion energy at a facility in Culham, near Oxford. This amount more than doubled the previous mark.

The nuclear fusion reactions at the European joint project JET achieved 59 megajoules of energy over a five-second period. Expressed as a unit of power, that comes to just over 11 megawatts averaged over five seconds. The previous record achieved in 1997 of 22 megajoules was the equivalent of 4.4 megawatts averaged over five seconds.

Ian Chapman, the head of the UK Atomic Energy Authority, described it as a landmark event that moved researchers closer to conquering one of the biggest challenges in science.

Scientists have cautioned that years of work are still needed, and the level of energy achieved so far is modest. The 59 megajoules of energy produced in that experiment, for instance, was only enough to boil about 60 kettles of water.

"We're building the knowledge and developing the new technology required to deliver a low carbon, sustainable source of baseload energy that helps protect the planet for future generations," Chapman said earlier this year. "Our world needs fusion energy".