April 13, 2024

Ancient Japanese art inspires next-generation fusion reactor advancement

Inspired by Kintsugi, PPPL scientists have developed a method for managing plasma in fusion reactors by utilizing magnetic field imperfections, increasing stability and paving the way for more reliable and efficient fusion energy. Credit: SciTechDaily.com

Scientists take advantage of imperfections in magnetic fields to improve fusion

PPPL physicist Seong-Moo Yang led the research team, which spans multiple institutions in the U.S. and South Korea. Yang says this is the first time a research team has validated a systematic approach to adapting the imperfections of magnetic field to make the plasma suitable for use as a power source. These imperfections in the magnetic field are known as error fields.

“Our new method identifies optimal error field corrections, improving plasma stability,” said Yang. “This method has been proven to improve plasma stability under different plasma conditions, for example when the plasma was under high and low magnetic confinement conditions.”

Yang presents research at DOE’s National Research SLAM.

Difficult to fix errors

The error fields are typically caused by tiny defects in the magnetic coils of the device that contains the plasma, called a tokamak. Until now, error fields were only seen as a nuisance because even a very small error field could cause a disruption in the plasma that halted fusion reactions and could damage the walls of a fusion vessel. Consequently, fusion researchers have spent considerable time and effort painstakingly finding ways to correct error fields.

“It is very difficult to eliminate existing error fields, so instead of correcting these irregularities in the coil, we can apply additional magnetic fields around the melt pot in a process known as error field correction,” Yang said.

In the past, this approach would also have damaged the plasma core, making it unsuitable for generating fusion power. This time, the researchers managed to eliminate instabilities at the edge of the plasma and maintain the stability of the core. The research is an excellent example of how PPPL researchers are bridging the gap between current fusion technology and what will be needed to bring fusion energy to the power grid.

“This is actually a very effective way to break the symmetry of the system, so that humans can intentionally degrade the confinement. It’s like making a very small hole in a balloon so it doesn’t explode,” said SangKyeun Kim, research scientist on the PPPL team and co-author of the paper. Just as air would leak from a small hole in a balloon, a small amount of plasma would leak from the error field, which helps maintain its overall stability.

Managing the Plasma Core and Edge Simultaneously

One of the hardest parts of managing a fusion reaction is getting the plasma core and edge to behave at the same time. There are ideal zones for plasma temperature and density in both regions, and hitting these targets and eliminating instabilities is difficult.

This study demonstrates that tuning the error fields can simultaneously stabilize the plasma core and edge. By carefully controlling the magnetic fields produced by the tokamak coils, the researchers were able to suppress edge instabilities, also known as edge localized modes (ELMs), without causing disruptions or a substantial loss of confinement.

“We are trying to protect the device,” said Qiming Hu, a research physicist on the PPPL team who authored the paper.

Extending research beyond KSTAR

The research was carried out using the KSTAR tokamak in South Korea, which stands out for its ability to adjust the configuration of the magnetic error field with great flexibility. This ability is crucial for experimenting with different error field configurations to find the most effective ones for stabilizing the plasma.

The researchers say their approach has significant implications for the design of future tokamak fusion pilot plants, potentially making them more efficient and reliable. They are currently working on an artificial intelligence (AI) version of their control system to make it more efficient.

“These models are quite complex; they take a while to calculate. But when you want to do something in a real-time control system, you can only spend a few milliseconds to make a calculation,” Snipes said. “Using AI, you can basically teach the system what to expect and be able to use that artificial intelligence to predict in advance what it will take to control the plasma and how to implement it in real time.”

Although his new paper highlights work done using KSTAR’s internal magnetic coils, Hu suggests that future research with magnetic coils outside the fusion vessel would be valuable because the fusion community is moving away from the idea of ​​housing such coils inside the sealed vessel. vacuum due to the potential destruction of such components due to the extreme heat of the plasma.

Reference: “Adapting tokamak error fields to control instabilities and plasma transport” by SeongMoo Yang, Jong-Kyu Park, YoungMu Jeon, Nikolas C. Logan, Jaehyun Lee, Qiming Hu, JongHa Lee, SangKyeun Kim, Jaewoo Kim, Hyungho Lee, Yong -Su Na, Taik Soo Hahm, Gyungjin Choi, Joseph A. Snipes, Gunyoung Park and Won-Ha Ko, February 10, 2024, Nature Communications.
DOI: 10.1038/s41467-024-45454-1

Researchers from the Korea Institute of Fusion Energy (KFE),

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