Researchers at the Experimental Advanced Superconducting Tokamak (EAST) in Hefei, China, were testing out how best to store ultra-hot plasma inside a reactor and they found that lithium did an extremely good job of keeping it cool and stable.

EAST hit the headlines in February 2016 when China said they had sustained the longest reaction in a tokamak reactor – 102 seconds. Various other nuclear fusion breakthroughs were reported last year, too.

Tokamaks are shaped like a donut and use large currents to twist a magnetic field and trap a plasma. Stellerators, another type of experimental reactor, achieve this by having the actual reactor itself twist in shape.

But now China and the US are advancing on their previous achievement. Seven US researchers flew to EAST in December 16, where they worked with Chinese researchers to deploy lithium inside the tokamak.

It was deployed inside in three ways. The first was as a “powder injector”, the second in a “granule injector”, and the third as a liquid.

In a statement, the Princeton Plasma Physics Laboratory (PPPL) – one of the collaborators on the project – said all three areas showed “excellent progress”. In powder form, for example, the lithium was able to eliminate instabilities in the plasma called edge localized modes (ELMs), which occur at the edge of the reactor. Similar results were achieved with the granule injector.

Injecting lithium as a liquid, meanwhile, reduced the amount of deuterium that made its way to the edge of the plasma. Nuclear fusion involves fusing deuterium into helium to produce energy. This method prevented the deuterium at the edge recycling back into the core, which can halt fusion reactions as heat is lost.

This is just one of several nuclear fusion experiments that are taking place around the world. We’ve seen breakthroughs in Germany and South Korea too, while Europe is busy building the International Thermonuclear Experimental Reactor (ITER) in France.

Most of the reactors have involved using a helium plasma. Only one, Germany’s Wendelstein 7-X reactor, has achieved hydrogen fusion, which provides more energy.

But it’s been a long road for all involved to get to this stage. That we can only sustain a plasma for seconds means there’s still a way to go before we have working nuclear fusion reactors. When we get there, though, we could have a waste-free power source that provides a huge amount of energy.