Addition of tiny ingredient could help turn nuclear fusion into reality

Researchers have concluded that tiny pellets of a common metal used in spacecraft could stabilise plasma in a nuclear fusion reactor.

The number of important breakthroughs towards the goal of achieving stable nuclear fusion have ramped up in recent years. If successful, a working reactor could take the power of the sun and create a near-limitless, cheap and clean source of electricity.

Now, physicists from the US Department of Energy’s (DOE) Princeton Plasma Physics Laboratory and General Atomics have found that injecting the hard, silvery metal beryllium – commonly used in x-ray machines and spacecraft – could help stabilise the plasma that fuels fusion reactions.

Publishing their findings in Nuclear Materials and Energy, the researchers conducted some of the first experiments and computer simulations of their kind. These showed that the metal placed in the International Thermonuclear Experimental Reactor (ITER) based in France could trigger small eruptions called edge-localised modes (ELMs).

If triggered frequently enough, the tiny ELMs prevent giant eruptions that could halt fusion reactions and damage the ITER facility. In the experiments, the researchers injected granules of carbon, lithium and boron carbide – all of which share several properties with beryllium – into the DIII-D National Fusion Facility that General Atomics operates for the DOE in San Diego, California.

Because the internal structure of the three metals is similar to that of beryllium, the scientists deduced that all of these elements would affect ITER plasma in similar ways. They also used magnetic fields to make the DIII-D plasma resemble the plasma predicted to occur in ITER.

Explaining this discovery’s importance, lead author on the paper, Robert Lunsford, said: “The amount of energy being driven into the ITER first walls by spontaneously occurring ELMs is enough to cause severe damage to the walls.

“If nothing were done, you would have an unacceptably short component lifetime, possibly requiring the replacement of parts every couple of months.”

The injected granules would measure just 1.5mm in diameter – as wide as a toothpick – with the ability to penetrate the edge of the ITER plasma that could trigger ELMs. The researchers said the next step will be to calculate whether density changes caused by the impurity pellets in ITER would indeed trigger an ELM, and hope to test this with other reactors found across the world.