'Ghostly' whistler waves created by lightning may help to protect experimental nuclear fusion reactors and make limitless energy a reality.

That's the claim made by a group of researchers who detected the ghostly presence of the waves inside their reactor, in what they say is a world first.

Whistlers are normally found whipping across the ionospheric layer of the Earth's atmosphere at heights of up to 620 miles (1,000km) above the planet.

Now, scientists say they have detected the mysterious electromagnetic waves inside their reactor.

They were surprised to find that whistlers appeared to help prevent runaway electrons, produced in the nuclear fusion process.

These particles, travelling at ever faster speeds, risk burning holes in the equipment if they accelerate too fast.

Experts hope to tame this by developing methods of controls based on their findings, which could lead to a breakthrough in fusion reaction.

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Ethereal waves known as whistlers created by lightning may help to protect experimental nuclear fusion reactors from damage. That's the claim made by a group of researchers who detected the ghostly presence of whistler waves inside their reactor (pictured)

Whistlers are normally found whipping across the ionospheric layer of the Earth's atmosphere at heights of up to 620 miles above the planet. Now, scientists say they have detected the mysterious electromagnetic waves inside their tokamak reactor (graphical representation)

The findings were made by a research team led by the US Department of Energy's (DOE) Oak Ridge National Laboratory (ORNL).

For decades, experts have been building the scientific basis for nuclear fusion as an energy source to generate limitless electricity.

Fusion happens when the nuclei of lighter atoms join under extraordinarily high temperatures to create a heavier nucleus, releasing energy.

The hot, fused atoms form a plasma that is confined by high magnetic fields in an experimental vessel called a tokamak - designed to withstand conditions hotter than the sun.

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.

Instabilities can occur in such an extreme environment, causing a dramatic quenching, or cool down, of the plasma and producing runaway electrons that could veer off and burn holes in the tokamak’s interior wall.

Using sophisticated technologies, the team made direct measurements of whistler waves produced when a laboratory plasma becomes unstable and generates runaway electrons.

By better understanding this process, they hope they can reverse engineer it, and create whistler generating antennas to prevent electrons from getting too fast.

WHAT ARE WHISTLER WAVES AND WHAT DO WE KNOW ABOUT THEM? Whistler waves are electromagnetic waves that originate during lightning strikes and are usually in the frequency range of 300 to 30,000 hertz. They are sometimes detected by a sensitive audio amplifiers as a gliding high-to-low-frequency sound. Whistlers waves last about half a second, and they may be repeated at regular intervals of several seconds, growing progressively longer and fainter with time. Whistler waves travel through the ionosphere, which begins at a height of about 30 miles (50km) above the Earth’s surface, and reaches as high as 620 miles (1,000km). These waves travel along ducts, or regions of enhanced ionisation, where they pass from one hemisphere to another along the Earth’s magnetic field. They are then reflected back at the corresponding geomagnetic latitude in the opposite hemisphere. The whistle effect occurs because the reflected high-frequency waves arrive at the amplifier before the lower-pitched signals. Repeated reflections, dispersion, and absorption of the waves are responsible for their subsequent fainter and longer whistling tones. Scientists have studied whistler wave propagation to determine electron density in the Earth's atmosphere at altitudes as high as 12,000 to 16,000 miles (19,000 to 26,000 km). They can also be used to calculate the daily, annual, and long-term variations of electron density in the upper atmosphere. Advertisement

Runaway electrons also occur in nature. They are energised when lightning strikes or solar substorms disrupt the plasma environment of the Earth’s ionosphere, which is the atmosphere’s ionised upper layer.

Scientists have theorised that whistler waves regulate space weather and may help mitigate the damaging effects of energetic electrons on satellites orbiting the Earth.

'We have known that runaway electrons drive whistler waves in the ionosphere during natural events, which led to theories that runaways would also drive similar electromagnetic waves in a tokamak plasma, said ORNL's Don Spong who led the study.

For decades, scientists have been building the scientific basis for nuclear fusion as an energy source to generate electricity. This artist's impression shows what fusion energy generation could look like inside a tokamak reactor

'Observing whistler waves helps us better understand their underlying physical mechanisms, which could open an avenue to develop new techniques to control runaway electrons and keep them from potentially damaging fusion reactors.

'As we learn more about the characteristics and excitation of whistler waves in tokamaks, we may be able to mimic similar behaviour to protect plasma-facing components.'

The team’s experiments took place at the DIII-D National Fusion Facility, a DOE user facility, which is operated by General Atomics in San Diego, California.

The full findings were published in the journal Physical Review Letters.