GA part of team finding new method for sustaining fusion plasmas
November 26, 2013
A multinational team led by Chinese researchers in collaboration with European and U.S. partners – including San Diego's General Atomics and a Princeton University-based team -- has discovered a new way to sustain fusion plasma that could move the worldwide effort to develop fusion as a clean energy source closer than ever.
The record-setting results of the tests were conducted on the Experimental Advanced Superconducting Tokamak (EAST) in Hefei, China, that successfully demonstrated a novel technique for suppressing instabilities that can cut short the life of controlled fusion reactions.
"This is a very good example of multinational collaboration on EAST," said Jiangang Li, director of the Institute of Plasma Physics in the Chinese Academy of Sciences (ASIPP), which headed the team. "I very much appreciate the effort of our collaborators."
First reporting the results was a paper published online in the November issue of the journal Nature Physics. U.S co-authors included Princeton Plasma Physics Laboratory physicists Jon Menard and Rajesh Maingi, who headed the wall-conditioning effort, and General Atomics physicist Gary Jackson, a plasma-control expert who helped draft the paper.
"This was good physics," said Jackson of General Atomics. A long pulse at the high performance level is important, he explained, because that is what's needed to connect to a power plant to generate electricity – the ultimate goal of harnessing the power of the sun for an intrinsically safe and abundant fuel supply from fusion.
The findings could hold particular promise for developers of future fusion facilities such as ITER, the international experiment now under construction in France. Controlling instabilities that erupt at the edge of the plasma will be crucial to the success of the huge doughnut-shaped ITER tokamak, designed to demonstrate the feasibility of fusion power.
The EAST experiments set a record for the duration of what is called an H-mode, or high-confinement plasma, the type that will be employed in ITER and other future tokamaks. To achieve this duration, the EAST team beamed what are known as "lower hybrid wave current drive" microwaves into the plasma. The antenna-launched beams reshaped the magnetic field lines confining the plasma and suppressed instabilities at the edge of the gas near the interior walls of the tokamak. Controlling these fast-growing
instabilities, called "edge localized modes" (ELMs), produced a record life span of more than 30 seconds for the H-mode plasma.
These results suggested a potent new method for suppressing ELMs to create an extended, or long-pulse, plasma. Many methods already exist. Among them are the use of external magnetic coils to alter the field lines that enclose the plasma, and the injection of pellets of deuterium fuel into the plasma during experiments.
The teamcombined the new technique with a method that the U.S. Department of Energy's Princeton Plasma Physics Laboratory (PPPL) has developed for protecting the walls that surround the hot, charged plasma gas that fuels fusion reactions. Contributing to the EAST results was the PPPL-designed wall treatment, which coated the plasma-facing walls of the tokamak with the metal lithium and inserted lithium granules into experiments to keep the coating fresh. The silvery metal absorbed stray plasma particles and kept impurities from entering the core of the plasma and halting fusion reactions.
"When lithium has been used to coat the walls of fusion devices, higher plasma temperature, pressure, and confinement have been achieved," said PPPL physicists Menard and Maingi.
Combining microwave beams for ELMs suppression with the advanced lithium wall treatment could thus provide a fruitful new direction for fusion-energy development. This combination of techniques offers what the Nature Physics paper called, "an attractive regime for high-performance, long-pulse operations."
About DIII-D National Fusion Facility: San Diego-based General Atomics operates the nation's largest magnetic confinement research devise, a user facility with more than 500 scientific users from over 100 laboratories, universities and industries worldwide. GA has been the center of fusion research for more than 45 years. The facility is managed by GA for the U.S. Department of Energy's Office of Science.
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GA Energy and Advanced Concepts Group Communications