If we want to rely on nuclear fusion to power the world’s homes, the first step is making reactors that can run as hot and as long as possible. 

Now, an experimental reactor called KSTAR in Daejeon, Korea, has set a new world record. 

The massive doughnut-shaped device, which has been dubbed ‘Korea’s artificial sun’ ran at 100 million°C (180 million°F) for 48 seconds. 

To put that into perspective, that’s seven times hotter than the sun’s core! 

The record-breaking test takes us one step closer to the ultimate goal of limitless clean energy.  

How nuclear fusion works: This graphic shows the inside of a nuclear fusion reactor and explains the process by which power is produced. At its heart is the tokamak, a device that uses a powerful magnetic field to confine the hydrogen isotopes into a spherical shape, similar to a cored apple, as they are heated by microwaves into a plasma to produce fusion

Engineers in South Korea have pushed the boundaries of nuclear fusion by setting a new record for maintaining plasma. Plasma is one of the four states of matter – the others being liquid, gas and solid – with examples being lightning and the sun

Nuclear fusion reactors around the world are in a race to operate at higher temperatures and for longer, to extract as much energy from the fusion process as possible. 

They work by colliding heavy hydrogen atoms to form helium, releasing vast amounts of energy – mimicking the process that occurs naturally in the centre of stars like our sun. 

KSTAR already set a record back in 2021 of 100 million degrees for 30 seconds, but it has now beat this record.

Rival China’s ‘artificial sun’ nuclear fusion reactor ran for over 17 minutes but at a lower temperature – 126 million°F (70 million°C).

Korean experts managed the feat between December 2023 to February 2024 by using tungsten instead of carbon in its diverters.

These diverters extract impurities from the fusion reaction while withstanding incredibly high heat, largely thanks to tungsten having the highest melting point of all metals. 

‘Thorough hardware testing and campaign preparation enabled us to achieve results surpassing those of previous KSTAR records in a short period,’ said Dr Si-Woo Yoon, director of the KSTAR Research Center. 

Like other fusion reactors, KSTAR is a ‘tokamak’, a type of doughnut-shaped chamber that creates energy via the fusion of atoms. 

Hydrogen gas inside the tokamak vessel is heated to become ‘plasma’ – a soup of positively charged particles (ions) and negatively charged particles (electrons). 

Plasma is often referred to as the fourth state of matter after solid, liquid and gas, and comprises over 99 per cent of the visible universe, including most of our sun. 

In the tokamak, the plasma is trapped and pressurised by magnetic fields until the energised plasma particles start to collide.

As the particles fuse into helium, they release enormous amounts of energy, mimicking the process that occurs naturally in the centre of stars.

The Korean ‘artificial sun’, the Korea Superconducting Tokamak Advanced Research device (KSTAR), at the Korea Institute of Fusion Energy (KFE) in Daejeon

It successfully sustained the plasma with ion temperatures of 100 million degrees Celsius for 48 seconds during the last KSTAR plasma campaign run from December 2023 to February 2024

Inside a tokamak, the energy produced through the fusion of atoms is absorbed as heat in the walls of the vessel Pictured, the KSTAR Vacuum vessel

READ MORE: British nuclear reactor sets a new record 

After more than 40 years, Britain’s nuclear reactor is still setting records 

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While using nuclear fusion to power homes and businesses may still be some way off, KSTAR proves that the burning of star-like fuel can be achieved and contained using current technology. 

‘To achieve the ultimate goal of KSTAR operation, we plan to sequentially enhance the performance of heating and current drive devices and also secure the core technologies required for long-pulse high performance plasma operations,’ Dr Si-Woo Yoon added. 

Like many other reactors around the world, KSTAR was built as a research facility to demonstrate the promising potential of nuclear fusion to produce power. 

Others include China’s experimental advanced superconducting tokamak (EAST) in Hefei and Japan’s reactor, called JT-60SA, recently switched on in Naka north of Tokyo,

Meanwhile, the $22.5 billion (£15.9 billion) International Thermonuclear Experimental Reactor (ITER) in France will be the world’s largest once construction is complete next year.

Other smaller reactors are being built and tested – including the ST40 in Oxfordshire, which is more squashed-up and compact compared with other ‘doughnut-shaped’ reactors. 

And the Joint European Torus (JET), also located in Oxfordshire, released a total of 69 megajoules of energy over five seconds before being recently decommissioned. 

The holy grail of clean energy: Pictured is how a reactor works, based on one developed by Tokamak Energy, based in Milton, Oxfordshire

They could all be precursors to fusion power plants that supply power directly to the grid and electricity to people’s homes. 

These power plants could reduce greenhouse gas emissions from the power-generation sector, by diverting away from the use of fossil fuels like coal and gas. 

Fusion differs from fission (the technique currently used in nuclear power plants), because the former fuses two atomic nuclei instead of splitting one (fission). 

Unlike fission, fusion carries no risk of catastrophic nuclear accidents – like that seen in Fukushima in Japan in 2011 – and produces far less radioactive waste than current power plants, its exponents say.

HOW A FUSION REACTOR WORKS

Fusion is the process by which a gas is heated up and separated into its constituent ions and electrons. 

It involves light elements, such as hydrogen, smashing together to form heavier elements, such as helium. 

For fusion to occur, hydrogen atoms are placed under high heat and pressure until they fuse together.

The tokamak (artist’s impression) is the most developed magnetic confinement system and is the basis for the design of many modern fusion reactors. The purple at the center of the diagram shows the plasma inside 

When deuterium and tritium nuclei – which can be found in hydrogen – fuse, they form a helium nucleus, a neutron and a lot of energy.

This is done by heating the fuel to temperatures in excess of 150 million°C and forming a hot plasma, a gaseous soup of subatomic particles.

Strong magnetic fields are used to keep the plasma away from the reactor’s walls, so that it doesn’t cool down and lose its energy potential.

These fields are produced by superconducting coils surrounding the vessel and by an electrical current driven through the plasma.

For energy production, plasma has to be confined for a sufficiently long period for fusion to occur.

When ions get hot enough, they can overcome their mutual repulsion and collide, fusing together. 

When this happens, they release around one million times more energy than a chemical reaction and three to four times more than a conventional nuclear fission reactor.