Cross-pollinating physicists are using a novel technique to improve the design of facilities aimed at generating fusion energy

Newswise – physicists are like bees – they can pollinate each other, take ideas from one area and use them to develop breakthroughs in other areas. Scientists at the Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have moved a technique from one area of ​​plasma physics to another to enable the more efficient design of powerful magnets for donut-shaped fusion devices known as tokamaks . Such magnets limit and control plasma, the fourth physical state that makes up 99 percent of the visible universe and drives fusion reactions.

Designing these magnets is not straightforward, especially when they must be precisely shaped to create complex, three-dimensional magnetic fields to control plasma instabilities. Hence, it is appropriate that the new technology should come from scientists developing stellarators, crooked fusion devices that require such carefully constructed magnets. In other words, the PPPL scientists use stellarator computer code to envision the shape and strength of twisted tokamak magnets that can stabilize tokamak plasmas and survive the extreme conditions expected in a fusion reactor.

This knowledge could facilitate the construction of tokamak fusion devices that bring the power of the sun and stars to earth. “It’s been a voyage of discovery in the past,” said Nik Logan, a physicist at the DOE’s Lawrence Livermore National Laboratory who led the research during his time at PPPL. “You had to build something, test it, and use the data to learn how to design the next experiment. Now we can use these new computing tools to design these magnets more easily, using principles derived from years of scientific research. ”The results were published in a paper published in Nuclear Fusion.

Fusion, the force that drives the sun and stars, combines light elements in the form of plasma – the hot, charged state of matter made up of free electrons and atomic nuclei – and creates enormous amounts of energy. Scientists are trying to recreate the fusion on Earth in order to obtain an almost inexhaustible energy supply for generating electricity.

The results could aid in the construction of tokamaks by compensating for inaccuracies that occur when a machine is transferred from a theoretical design to a real object, or by applying precisely controlled 3D magnetic fields to suppress plasma instabilities. “The reality of building is that it’s not perfect,” Logan said. “It has small irregularities. The magnets we develop with this stellarator technology can both correct some of the irregularities that appear in the magnetic fields and control instabilities. ”This helps the magnetic field stabilize the plasma so that there are no potentially damaging heat and particle bursts .

Logan and colleagues also learned that these magnets can act on the plasma even at a relatively large distance of up to several meters from the walls of the tokamak. “That’s good news because the closer the magnets are to the plasma, the more difficult it is to design them for the harsh conditions around fusion reactors,” Logan said. “The more equipment we can place away from the tokamak, the better.”

The technique is based on FOCUS, a computer code that was mainly developed by PPPL physicist Caoxiang Zhu, a stellarator optimization scientist, to design complicated magnets for stellarator systems. “When I first started FOCUS as a postdoctoral fellow at PPPL, Nik Logan stopped at my poster presentation at an American Physical Society conference,” said Zhu. “We later had a conversation and discovered that there was a way to apply the FOCUS code to tokamak projects.”

The cooperation between different sub-areas is exciting. “I’m excited to see that my code can be extended to a wider range of experiments,” noted Zhu. “I think this is a nice connection between the tokamak and stellarator worlds.”

Although stellarators have long been the number two fusion device behind tokamaks, they are used more and more today as they tend to generate stable plasmas. Tokamaks are currently the first choice for a fusion reactor design, but their plasmas can develop instabilities that could damage the internal components of a reactor.

Currently, PPPL researchers are using this new technique to design and update magnets for several tokamaks around the world. The list includes COMPASS-U, a tokamak operated by the Czech Academy of Sciences; and the Korea Superconducting Tokamak Advanced Research (KSTAR) facility.

“It’s a very practical paper that has practical applications, and we actually have some takers,” said Logan. “I think the results will be helpful for the future of tokamak design.”

This research was supported by the DOE (Fusion Energy Sciences).

PPPL, located on Princeton University’s Forrestal campus in Plainsboro, NJ, is dedicated to discovering new insights into the physics of plasmas – ultra-hot, charged gases – and developing practical solutions for generating fusion energy. The laboratory is administered by the University for the US Department of Energy’s Office of Science, which is the United States’ single largest contributor to basic research in the physical sciences and works to address some of the most pressing challenges of our time. Further information can be found at https://energy.gov/science