These efforts are complemented by the world’s largest stellarator — Wendelstein 7-X (W7-X) at Max Planck Institute for Plasma Physics (IPP) in Germany — an alternative to the tokamak as the reactor layout. It is a twisted racetrack-shaped configuration, which is inherently stable and able to operate the plasma in a steady state for greater lengths of time than the tokamak, but it is technically harder to design.

Although W7-X will not produce energy, its designers hope to prove that stellarators are also suitable for application in power plants and to demonstrate their capability to operate continuously. Such continuous mode will be essential for commercial operation of a fusion reactor.

Sibylle Günter, Scientific Director of IPP, highlighted the most recent results from the first high-performance plasma operation of W7-X, which has recently achieved the highest stellarator fusion triple product: the density, confinement time and plasma temperature used by researchers to measure the performance of a fusion plasma.

“This is an excellent value for a device of this size, and it makes us optimistic for our further work. In the future, we expect to run the machine for a longer time,” she said.

The fusion triple product has seen an increase of a factor of 100,000 in the last fifty years of fusion experimentation; another factor of five is needed to arrive at the level of performance required for a power plant. Some of the improvements in this product were the result of experimental fusion reactors becoming larger. Plasma takes longer to diffuse from the centre to the walls in a bigger reactor, and this extends the confinement time.

Günter added: “Size matters in terms of heat insulation. Based on our experience, I believe that ITER will perform even better than planned today.”