With the swift push of a button, German Chancellor Angela Merkel initiated for the first time the production of hydrogen plasma in the new Wendelstein 7-X fusion facility located at the Max Planck Institute for Plasma Physics (IPP) last week.
“It’s the starting shot for an experiment, unrivaled worldwide, that can bring us one decisive step closer to a renewable energy source of the future,” Merkel said.
“We want to make the source of energy of the sun and the stars usable on Earth,” said Sybylle Günter, IPP’s scientific director. The long-term goal is to fuse the nuclei of deuterium and tritium, heavy forms of hydrogen, into helium and a neutron to produce thermal energy. Günter pointed out that with just 40 L of water, which is a source of deuterium, and 5 g of lithium, which can be easily converted to tritium, it’s possible to generate the same amount of power as from 40 tons of coal.
Researchers at the Wendelstein 7-X facility, built over the past decade at a cost of $413 million, won’t attempt to achieve nuclear fusion, which requires temperatures higher than 100 million K to occur. Their goal is to learn how to optimally contain hydrogen plasma at 80 million K in a magnetic cage so that the extremely hot plasma does not touch the plasma chamber’s walls.
Two strategies invented in the 1950s have long been competing for “best design” in containing superhot plasma in a magnetic cage. The tokamak design originated in Russia; its simple doughnut shape creates a magnetic field cage, but it can optimally contain the plasma only with the help of a pulsed current and is prone to disruptions in the plasma.
The stellarator design—found in the Wendelstein 7-X facility—originated in the U.S.; its complicated twisty-curvy doughnut shape creates a magnetic field that can contain plasma without added current or disruptions.
However, these twists are so challenging to engineer that stellarator performance has lagged behind that of tokamaks for more than half of a century, ever since the Russians and Americans compared notes in 1958 at the Atoms for Peace conference, explains David Gates, a physicist at the Princeton Plasma Physics Laboratory.
“The simple symmetry of the tokamak was an advantage. It was easier to build a good tokamak than to build a good stellarator ,” explains David Campbell, head of science and operations at ITER, a tokamak facility being built in France. ITER aims to be the first facility to output more energy from fusion than is inputted—several steps beyond Wendelstein 7-X’s goal of containing the plasma.
Improvements in the stellarator design, however, have been made by supercomputers, precision engineering, and theoretical advances, making it possible for the Wendelstein 7-X to compete with similar-size tokamaks—at least in principle, Campbell says.
“If Wendelstein 7-X works the way we think it’s going to,” Gates says, “it will now have performance similar to a tokamak,” but without the problematic disruptions found in tokamaks, or the requirement for added currents.
This leaves up for debate which design will eventually be used to build the world’s first fusion power reactor—a milestone often predicted to still be several decades away.