by Staff Writers
Plainsboro NJ (SPX) Jul 07, 2017
Two major issues confronting magnetic-confinement fusion energy are enabling the walls of devices that house fusion reactions to survive bombardment by energetic particles, and improving confinement of the plasma required for the reactions. At the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL), researchers have found that coating tokamak walls with lithium-- a light, silvery metal-- can lead to progress on both fronts.
Recent experiments on the Lithium Tokamak Experiment (LTX), the first facility to fully surround plasma with liquid lithium, showed that lithium coatings can produce temperatures that stay constant all the way from the hot central core of the plasma to the normally cool outer edge.
The findings confirmed predictions that high edge temperatures and constant or nearly constant temperature profiles would result from the ability of lithium to keep stray plasma particles from kicking - or recycling - cold gas from the walls of a tokamak back into the edge of the plasma.
Near 100 million degrees Celsius
"This is the first time that anybody has shown experimentally that the edge of the plasma can remain hot due to reduced recycling," said physicist Dennis Boyle, lead author of a paper published online July 5 in the journal Physical Review Letters. Support for this work comes from the DOE Office of Science.
A hotter edge can improve plasma performance in numerous ways. Preventing recycled gas from cooling the edge reduces the amount of external heating that must be applied to keep the plasma hot enough for fusion to occur, making a reactor more efficient.
"If the edge is hot, it expands the volume of plasma available for fusion," Boyle said, "and the lack of a temperature gradient prevents instabilities that reduce plasma confinement."
Researchers performed this set of experiments with solid lithium, Boyle explained, but a coating of liquid lithium could produce similar results. Physicists have long used both forms of lithium to coat the walls of LTX. Since flowing liquid lithium could absorb hot particles but wouldn't wear down or crack when struck by them, it also would reduce damage to tokamak walls - another critical challenge for fusion.
Achieving constant temperature profiles has been a major goal of LTX. Reaching that goal "gives evidence for a new, potentially high-performance plasma regime for fusion devices,"wrote the authors. The next step will be to see whether such a regime can be attained.
Gothenburg, Sweden (SPX) Jun 23, 2017
Fusion power has the potential to provide clean and safe energy that is free from carbon dioxide emissions. However, imitating the solar energy process is a difficult task to achieve. Two young plasma physicists at Chalmers University of Technology have now taken us one step closer to a functional fusion reactor. Their model could lead to better methods for decelerating the runaway electrons, wh ... read more
Princeton Plasma Physics Laboratory
Powering The World in the 21st Century at Energy-Daily.com
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