Breakthrough In Controlling Heat Bursts Could
Help Stabilise Fusion Reactors
19 Mar (NucNet): Researchers
from General Atomics and the US Department of Energy’s
Princeton Plasma Physics Laboratory (PPPL) have made what
they called “a major breakthrough” in understanding
how potentially damaging heat bursts inside a fusion
reactor can be controlled.
The breakthrough could help nuclear fusion researchers to
stabilise their reactors, increasing the length of time
that fusion can occur.
PPPL said the findings represent a key step in predicting
how to control heat bursts in future fusion facilities
such as the International Thermonuclear Experimental
Reactor (Iter), an international experiment under
construction in southern France to demonstrate the
feasibility of fusion energy.
Scientists performed the experiments on the DIII-D
National Fusion Facility, operated by General Atomics in
The findings build upon previous work pioneered on DIII-D
showing that these intense heat bursts – called “ELMs”
for short – could be suppressed with tiny magnetic
fields. These tiny fields cause the edge of the plasma to
smoothly release heat, thereby avoiding the damaging heat
But until now, scientists did not understand how these
fields worked. “Many mysteries surrounded how the
plasma distorts to suppress these heat bursts,” said
Carlos Paz-Soldan, a General Atomics scientist and lead
author of the first of the two papers that report the
findings in the journal ‘Physical Review Letters’.
Mr Paz-Soldan and a team of researchers found that tiny
magnetic fields applied to the device can create two
distinct kinds of response, rather than just one response
as previously thought. The new response produces a ripple
in the magnetic field near the plasma edge, allowing more
heat to leak out at just the right rate to avert the
intense heat bursts. Researchers applied the magnetic
fields by running electrical current through coils around
the plasma. Pickup coils then detected the plasma
response, much as the microphone on a guitar picks up
A second result, from a team led by PPPL scientist Raffi
Nazikia, identified the changes in the plasma that lead
to the suppression of the large edge heat bursts or ELMs.
The team found clear evidence that the plasma was
deforming in just the way needed to allow the heat to
slowly leak out. The measured magnetic distortions of the
plasma edge indicated that the magnetic field was gently
tearing in a narrow layer, a key prediction for how heat
bursts can be prevented.
“The configuration changes suddenly when the plasma is
tapped in a certain way and it is this response that
suppresses the ELMs,” Mr Nazikian said.
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