Researchers demonstrate first hot plasma edge in a fusion facility

July 5, 2017, Princeton Plasma Physics Laboratory
Physicist Dennis Boyle. Credit: Elle Starkman/PPPL Office of Communications

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 , 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 . 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

Fusion devices will operate near 100 million degrees Celsius, hotter than the 15 million-degree core of the sun. The edge of the plasma, just a few meters from the 100 million-degree core, will normally be a relatively cool few thousand degrees, like the ionized gas—or plasma—inside a fluorescent light bulb. "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 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 ."

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.

Upgrade next

Physicists performed the recent research prior to an upgrade of the LTX, which currently is in progress. The upgrade will add a neutral beam injector that will fuel the core of the plasma and supply more heating and plasma density to test whether lithium can still keep the temperature constant in conditions closer to an actual fusion reactor.

Achieving constant profiles has been a major goal of LTX. Reaching that goal "gives evidence for a new, potentially high-performance regime for fusion devices,"wrote the authors. The next step will be to see whether such a regime can be attained.

Explore further: US-China collaboration makes excellent start in optimizing lithium to control plasma

More information: Physical Review Letters (2017). DOI: 10.1103/PhysRevLett.119.015001

Related Stories

With lithium, more is definitely better

November 10, 2011

A team of scientists working at the U.S. Department of Energy's Princeton Plasma Physics Laboratory (PPPL) has found that increasing the amount of lithium coating in the wall of an experimental fusion reactor greatly improves ...

Postcards from the plasma edge

October 28, 2014

For magnetic fusion energy to fuel future power plants, scientists must find ways to control the interactions that take place between the volatile edge of the plasma and the walls that surround it in fusion facilities. Such ...

Recommended for you

How a particle may stand still in rotating spacetime

May 25, 2018

When a massive astrophysical object, such as a boson star or black hole, rotates, it can cause the surrounding spacetime to rotate along with it due to the effect of frame dragging. In a new paper, physicists have shown that ...

Long live the doubly charmed particle

May 25, 2018

Finding a new particle is always a nice surprise, but measuring its characteristics is another story and just as important. Less than a year after announcing the discovery of the particle going by the snappy name of Ξcc++ (Xicc++), ...

How can you tell if a quantum memory is really quantum?

May 23, 2018

Quantum memories are devices that can store quantum information for a later time, which are usually implemented by storing and re-emitting photons with certain quantum states. But often it's difficult to tell whether a memory ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

katesisco
1 / 5 (1) Jul 06, 2017
Could the result be that the cooler edge migrates in toward the center producing a hot core, a cooler halo ring and a hot edge?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.