Burning plasma: are we close to cracking fusion?

By Annalise Stockley

Scientists in the U.S. have taken us one step closer to safe, sustainable fusion technology. In a paper published in the academic journal Nature at the end of January, they confirmed that they have achieved the ‘burning plasma’ phase of a fusion reaction for the first time in the facility’s history. If cracked, fusion has the potential to be a source of limitless clean energy – something that Earth is in dire need of.

But firstly, what is nuclear fusion, and how does it work? Current nuclear reactors are powered by a process called fission, where heavy elements are split into lighter ones. Despite generating large amounts of energy with limited greenhouse gas emissions, fission produces harmful radioactive by-products and has the potential to cause a nuclear meltdown.

Fusion, however, is a nuclear reaction that harnesses energy emitted when light elements are fused together. It is the process that powers every star in the universe, including our Sun. In theory, fusion technology could be a viable source of endless amounts of clean energy, producing little to no greenhouse gases or radioactive materials.

Current fusion reactions work by fusing heavy isotopes of hydrogen, mostly deuterium and tritium, together. Deuterium can be cheaply extracted from sea water and fused with tritium to provide energy. To put this into scale; the deuterium extracted from one litre of seawater produces energy equivalent to the combustion of 300 litres of oil, which can power a home for around three months in winter.

This promise of clean, limitless energy might sound too good to be true. Indeed, there are some big issues yet to overcome if we are to power the planet with fusion technology.

A viable source of endless amounts of clean energy

Fusion occurs naturally in the centre of stars, where the immense heat and pressure needed to overcome the innate repulsion between atomic nuclei come easily.

It is extremely difficult to replicate these conditions in a laboratory on Earth. To compensate for the lack of gravitational pressure, temperatures of around 100 million Kelvin are required for fusion to begin — that is approximately six times hotter than the Sun’s core!

To achieve these temperatures, scientists use high-energy laser beams to squeeze and heat an extremely dense hydrogen plasma — an electrically charged ionic gas. In the plasma, electron particles are stripped from their atoms, leaving atomic nuclei which can go on to fuse.

However, with these immense temperatures must also come a huge energy debt. Although scientists have been carrying out reliable fusion experiments for years, producing a state that is economically viable has proven to be more challenging — current experiments require far more energy to sustain than has yet been produced in a single reaction.

This issue has stumped researchers for decades, which is why the recent announcement by scientists at the National Ignition Facility (NIF) in California is so exciting. By using powerful lasers to heat the hydrogen fuel to 100 million Kelvin and compress it to 100 times the density of lead, NIF have — for the first time ever — created a ‘burning plasma’ state where more energy is emitted from the fuel than was required to initiate the reaction.

Burning plasma occurs when a fusion reaction is itself the primary source of heating in the plasma. This phase is seen as an important milestone on the road to ignition (the point where a fusion reaction can self-sustain) and scientists are confident that this breakthrough will lead researchers to develop new and improved technologies to sustain fusion reactions.

Until recent years fusion has been seen as somewhat of a pipe dream, but advancements like those at NIF mean that people are starting to think seriously about fusion tech as a viable fuel for the future. So, what next?

Until recent years fusion has been seen as somewhat of a pipe dream

Governments around the world are collaborating to build a new facility, by far the biggest of its kind, in southeast France — the International Thermonuclear Experimental Reactor (ITER). This project is set to cost almost £16bn and is being funded by the likes of the EU, the U.S., China, and Russia.

Unlike NIF, which uses lasers to heat and compress the hydrogen fuel, ITER will be a tokamak reactor. Tokamaks are thought to be the best hope for fusion power, and work by containing highly pressurised plasma within intense magnetic fields. In June 2021, a tokamak reactor in China sustained a plasma for 101 seconds at 120 million Kelvin, beating the previous record of 20 seconds significantly.

ITER is set to be fired up in 2025, and, when open, will massively expand the scope of current global fusion technology. If ITER is successful, it will eliminate most, if not all, doubts about the science and elicit investment to pursue fusion technology going forward.

There is no doubt that harnessing fusion technology will prove to be a massive feat of both engineering and physics. However, with some of the greatest minds in the world collaborating in the search for sustainable energy, this is certainly an exciting time to be watching the fusion industry grow.

Image: ITER Organisation