Nik Logan, physicist, next to computer-generated images fusion plasma. Credit: Elle Starkman / PPPL Office of Communications
Cross-pollinating is a characteristic of physicists. They can take ideas from one area and use them to create breakthroughs in another. The Princeton Plasma Physics Laboratory (PPPL), U.S. Department of Energy (DOE), has transferred a technique to allow the design of more powerful magnets for doughnut-shaped fusion plants known as tokamaks. These magnets contain and control plasma, which is the fourth state in matter and makes up 99 percent the visible universe. It also fuels fusion reactions.
It is difficult to design these magnets, especially when they have to be perfectly shaped to create complex three-dimensional magnetic fields that control plasma instabilities. It is fitting that this new technique comes from scientists who have designed stellarators, a cruller-shaped fusion device that requires such meticulously constructed magnets. PPPL scientists use a stellarator computer code for imagining the strength and shape of twisted tokamak magnetics that can stabilize tokamak Plasmas and withstand the extreme conditions in a fusion reactor.
This knowledge could be used to build tokamak facilities to bring the power and light of the sun and stars to Earth. Nik Logan, a physicist from the DOE's Lawrence Livermore National Laboratory, said that the past was a journey to discovery. He also led the research at PPPL. "You had to build something and then test it. Then you could use the data to design the next experiment. These new computational tools allow us to design these magnets much more quickly, using the principles of years-long scientific research. These results were published in Nuclear Fusion.
The power behind the sun and stars is fusion. Fusion is a combination of light elements in the form plasma. This hot, charged state, composed of free electrons, and an atomic nucleit, generates huge amounts of energy. Scientists are trying to recreate fusion on Earth to provide an inexhaustible supply power to produce electricity.
These findings could be used to aid in the construction of tokamaks. They can compensate for imprecision when a machine's design is converted to a physical object. Or they can apply precisely controlled 3D magnetic field to suppress plasma instability. Logan stated that "Building anything is not perfect." It has minor irregularities. We are creating magnets using the stellarator technique to correct some irregularities in the magnetic field and reduce instabilities. This helps to stabilize the magnetic field so that there are no potentially harmful bursts or particles of heat.
Logan and his colleagues discovered that the magnets can act on plasma even when they are placed at a distance of several meters from the walls of the tokamak. Logan stated, "That's great news because the closer magnets are to plasma, the more difficult is it to design them to withstand the harsh conditions near the fusion reactors." The more equipment we can put away from the tokamak the better.
This technique uses FOCUS, a computer program created mainly by Caoxiang Zhu (PPPL physicist), to create complex magnets for starlightator facilities. Zhu stated that Nik Logan visited my poster presentation at the American Physical Society conference when I first built FOCUS as a postdoctoral fellow. "We had a long conversation afterwards and realized there was an opportunity for the FOCUS code in tokamak projects.
It is thrilling to see the collaboration between different subfields. Zhu stated, "I'm glad to see my code can be expanded to a wider range of experiments," "I believe this is a beautiful link between the tokamak worlds and the stellarator worlds.
Although tokamaks were the second-ranked fusion facility, stellarators are becoming more popular because they can create stable plasmas. Tokamaks are the most popular fusion reactor design. However, their plasmas can cause instabilities that can damage internal components of a reactor.
Currently, PPPL researchers use this technique to update and design magnets for several different tokamaks in the world. This list includes COMPASS U, a Czech Academy of Sciences tokamak; and the Korea Superconducting Tokamak Advanced Research(KSTAR) facility.
Logan stated, "It's very practical paper with practical applications. And sure enough, we have some takers." "I believe the results will be useful for the future tokamak design."
Continue reading Scientists create a forecasting method that could aid in the pursuit of fusion energy
Further information: N.C. Logan and al., Physics basis to design 3D coils inside tokamaks. Nuclear Fusion (2021). N.C. Logan and al., Physics basis to design 3D coils for tokamaks. (2021). DOI: 10.1088/1741-4326/abff05
