World’s most powerful stellarator begins experiment for better fusion energy

The world’s largest and most powerful stellarator, known as Wendelstein 7-X, is going to resume experimental operation from today at the Max Planck Institute for Plasma Physics (IPP) in Greifswald.

The stellarator had made headlines in February 2023 when it lasted eight minutes and delivered a power output of 1.3 gigajoules.

After the experiment, Wendelstein 7-X had been shut down as per plans and it has undergone maintenance. Several new modules have also been added to the stellarator, according to a press release by IPP.

The new experiment phase OP2.2 will begin today. Some of the improvements made to Wendelstein 7-X include the addition of updated control and data acquisition systems, and more plasma diagnostic mechanisms.

The team of researchers focused on improving the availability and reliability of the systems in place, and a systematic failure mode analysis was also carried out for the same purpose.

Stellarators and nuclear fusion

The stellarator concept was invented by Lyman Spitzer at Princeton University in 1951.

In the quest for achieving safe, clean, and renewable power, stellarators have emerged as one of the technologies which scientists think could lead to fusion energy at a commercial scale.

A stellarator is a machine that uses magnetic fields to confine plasma in the shape of a donut, called a torus. These magnetic fields allow scientists to control the plasma particles and create the right conditions for fusion, according to the US Department of Energy.

Some of the key benefits which stellarators offer over tokamaks are that they require less injected power to sustain the plasma, have greater design flexibility, and allow for simplification of some aspects of plasma control.

The Wendelstein 7-X is the world’s largest fusion device of the stellarator type. It’s goal is to find out whether stellarators can be used for producing energy at a commercial scale.

The main assembly of Wendelstein 7-X was concluded in 2014, the first plasma was produced on December 10, 2015.

On February 15, 2023, the researchers were able to achieve an energy turnover of 1.3 gigajoules using Wendelstein 7-X. This was 17 times higher than the best value achieved before the conversion (75 megajoules).

The energy turnover of 1.3 gigajoule was achieved with an average heating power of 2.7 megawatts, whereby the discharge lasted 480 seconds. This was also a new record for Wendelstein 7-X and one of the best values worldwide.

Upgradation in Wendelstein 7-X for new experiment phase

The two most significant enhancements in the device are the addition of a heating element (gyrotron) which can generate significantly more than 1 megawatt of power into the plasma via microwaves.

The next is the addition of a new steady-state pellet injector.

“It is used to ensure the supply of hydrogen particles into the plasma – an important step on the way to a nuclear fusion power plant. The pellet injector produces long rods of frozen hydrogen, from which small pellets are regularly cut off at intervals of fractions of a second in order to shoot them into the plasma at high pressure, as in a blowpipe,” the press release says.

The aim of the experiment is to gradually increase the performance parameters for the generated plasmas.

“We are gradually approaching higher heating powers,” says IPP Director Prof Thomas Klinger. “On the one hand, the aim is to carefully test the heat load limits on the carbon walls of W7-X. On the other hand, we want to understand turbulence-controlled transport processes in the plasma and the exhaust of heat and particles.”

The W7-X team is not aiming for new records for the plasma duration, but aims to increase the energy throughput.

“The aim is to achieve long pulses at high plasma temperatures. And that’s what we’re working on right now,” Klinger added.

The experiment phase OP2.2 will run from September to December 2024, this will be followed by OP2.3 which will run from February to May 2025. This will be followed by a scheduled break for maintenance and experiments will resume under OP2.4 in August-December 2026, followed by OP2.5 in February-May 2027.