Princeton Plasma Physics Laboratory’s advanced design of the world’s largest and most powerful stellarator demonstrates the ability to moderate heat loss from the plasma that fuels fusion reactions.

A key hurdle facing fusion devices called stellarators, those twisty facilities that seek to harness on Earth the fusion reactions that power the sun and stars, has been their limited ability to maintain the heat and performance of the plasma that fuels those reactions.

W7X Stellarator Design Graphic. Image Credit: . Click image for the largest view.

Now collaborative research by scientists at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) and the Max Planck Institute for Plasma Physics in Greifswald, Germany, have found that the Wendelstein 7-X (W7-X) facility in Greifswald, the largest and most advanced stellarator ever built, has demonstrated a key step in overcoming this problem.

The cutting-edge facility, built and housed at the Max Planck Institute for Plasma Physics with PPPL as the leading U.S. collaborator, is designed to improve the performance and stability of the plasma – the hot, charged state of matter composed of free electrons and atomic nuclei, or ions, that makes up 99 percent of the visible universe. Fusion reactions fuse ions to release massive amounts of energy – the process that scientists are seeking to create and control on Earth to produce safe, clean and virtually limitless power to generate electricity for all humankind.

Recent research on the W7-X aimed to determine whether design of the advanced facility could temper the leakage of heat and particles from the core of the plasma that has long slowed the advancement of stellarators.

PPPL physicist Novimir Pablant, lead author of a paper describing the results in Nuclear Fusion said, “That is one of the most important questions in the development of stellarator fusion devices.”

Pablant’s work validates an important aspect of the findings. The research, combined with the findings of an accepted paper by Max Planck physicist Sergey Bozhenkov and a paper under review by physicist Craig Beidler of the institute, demonstrates that the advanced design does in fact moderate the leakage.

Max Planck physicist Andreas Dinklage said, “Our results showed that we had a first glimpse of our targeted physics regimes much earlier than expected. I recall my excitement seeing Novi’s raw data in the control room right after the shot. I immediately realized it was one of the rare moments in a scientist’s life when the evidence you measure shows that you’re following the right path. But even now there’s still a long way to go.”

The leakage, called “transport,” is a common problem for stellarators and more widely used fusion devices called tokamaks that have traditionally better coped with the problem. Two conditions give rise to transport in these facilities, which confine the plasma in magnetic fields that the particles orbit.

These conditions are:

  • Turbulence. The unruly swirling and eddies of plasma can trigger transport;
  • Collisions and orbits. The particles that orbit magnetic field lines can often collide, knocking them out of their orbits and causing what physicists call “neoclassical transport.”

Designers of the W7-X stellarator sought to reduce neoclassical transport by carefully shaping the complex, three-dimensional magnetic coils that create the confining magnetic field. To test the effectiveness of the design, researchers investigated complementary aspects of it.

Pablant found that measurements of the behavior of plasma in previous W7-X experiments agreed well with the predictions of a code developed by Matt Landreman of the University of Maryland that parallels those the designers used to shape the twisting W7-X coils. Bozhenov took a detailed look at the experiments and Beidler traced control of the leakage to the advanced design of the stellarator.

“This research validates predictions for how well the optimized design of the W7-X reduces neoclassical transport,” Pablant said. By comparison, he added, “Un-optimized stellarators have done very poorly” in controlling the problem.

A further benefit of the optimized design is that it reveals where most of the transport in the W7-X stellarator now comes from. “This allows us to determine how much turbulent transport is going on in the core of the plasma,” Pablant said. “The research marks the first step in showing that high-performance stellarator designs such as W-7X are an attractive way to produce a clean and safe fusion reactor.”

This news is quite welcome for fusion enthusiasts. While both the stellarator and the tokamak designs have shown potential both have a very long way to go. Likened to holding water in your hands, these devices are much larger and the fuels are much smaller. They both look like immense engineering challenges with only a bit of macro practicality and essentially no micro elegance. Most all the small private efforts are making actual progress getting to net yield while these huge concepts are still trying to function steadily. But your humble writer isn’t giving up on them just yet. The mega billions of taxpayer wealth getting spent on these is more likely to drag things to a stop.

But moon shot outbound technological contributions seem to be missing, something that huge undertakings usually throw off in abundance. Its a “lots in little out” situation that drives skepticism. One wonders how long this can go on.


Name (required)

Email (required)


Speak your mind