The December 2022 issue of IEEE Spectrum is here!

Close bar

Fusion Stellarator Wendelstein 7-x Fires Up for Real

Will stellarators outperform tokamaks one day?

2 min read
Fusion Stellarator Wendelstein 7-x Fires Up for Real

Today the German Chancellor Angela Merkel, at a ceremony at the Max Planck Institute for Plasma physics in Greifswald in Germany, pressed a button that caused a two-megawatt pulse of microwave radiation to heat hydrogen gas to 80 million degrees for a quarter of a second.

No, she was not setting off some new kind of hydrogen bomb. She was inaguriating the fusion reactor Wendelstein 7-X, the world’s largest stellarator, by generating its first hydrogen plasma. 

Completed in April 2014 the toroidal reactor with its complicated magnetic field is viewed by many as a serious competitor to tokamak-style fusion reactors, such as ITER.  One of the advantages of a stellarator  is that nuclear fusion reactions can take place continuously, while a tokamak operates in a pulsed mode, making it much less efficient as an energy source.

However, whether plasma would survive  in an untested toroidal field created by a set of coils of unprecedented complexity was an open question. The coils were  the result of a decade of an enormous computational effort, only made possible by the power of modern supercomputers. On 10 December 2015 researchers at Greifswald loaded the nuclear reactor, also known as W-X with a helium plasma, and to their relief, the plasma behaved exactly as expected. “This was really the beginning, and the machine works nicely. The confinement time was very large, we knew we were on the right path,” says Hans-Stephan Bosch, who directs the division responsible for the operation of the stellarator.

imgHydrogen plasma navigates the tortuous turns of the stellarator.Photo: IPP

Hydrogen, of course, is the real stuff. “The behavior of hydrogen as a plasma is somewhat different, and with hydrogen we will  be in the real regime of operation,” says Bosch. Experiments with hydrogen plasma will continue until March when protective carbon tiles and a divertor for the elimination of impurities will be mounted inside the reactor vessel. The microwave plasma heating power will then be increased to 20 megawatts, allowing plasmas to last as long as 30 minutes.

In a first stage, the stellarator will only confine hydrogen, without any fusion reactions, says Bosch. “In a later phase of W-X, starting in 2019, we will use deuterium and we will get fusion reactions, but not enough to get more energy out than we are putting in,” he says. There are no plans to add tritium to the hydrogen plasma, which would be required to achieve break even, he adds.

Scientists expect that the fusion experiments with deuterium  would amply demonstrate that a stellarator would be suitable for power production. But whether the concept of a stellarator will overtake ITER remains questionable.  There are currently no plans for a stellarator that would demonstrate net fusion energy production, says Bosch. 

The Conversation (0)
This photograph shows a car with the words “We Drive Solar” on the door, connected to a charging station. A windmill can be seen in the background.

The Dutch city of Utrecht is embracing vehicle-to-grid technology, an example of which is shown here—an EV connected to a bidirectional charger. The historic Rijn en Zon windmill provides a fitting background for this scene.

We Drive Solar

Hundreds of charging stations for electric vehicles dot Utrecht’s urban landscape in the Netherlands like little electric mushrooms. Unlike those you may have grown accustomed to seeing, many of these stations don’t just charge electric cars—they can also send power from vehicle batteries to the local utility grid for use by homes and businesses.

Debates over the feasibility and value of such vehicle-to-grid technology go back decades. Those arguments are not yet settled. But big automakers like Volkswagen, Nissan, and Hyundai have moved to produce the kinds of cars that can use such bidirectional chargers—alongside similar vehicle-to-home technology, whereby your car can power your house, say, during a blackout, as promoted by Ford with its new F-150 Lightning. Given the rapid uptake of electric vehicles, many people are thinking hard about how to make the best use of all that rolling battery power.

Keep Reading ↓Show less