Fusion Failure Fixed
Scientists have worked out why the beams they use to heat hydrogen gas
to a plasma ten times hotter than the Sun sometimes destabilise their
fusion experiments before energy is generated.
The solution, published in Physical Review Letters (tinyurl.com/
hp6zn7d), used a new theory that treated plasma as a fluid rather than
individual atoms.
Nuclear fusion of hydrogen into helium is the process that powers
stars. It promises a large-scale energy source based on fuel extracted
from water, and doesn’t create the long-term waste that uranium-based
nuclear fission does.
The fusion experiments heat hydrogen gas until it becomes a plasma,
and then use strong magnetic fields to hold it in place until fusion
reactions occur. However, plasma this hot is extremely turbulent and can
behave in surprising ways that baffle scientists, at times becoming
unstable and dissipating before any fusion reactions can take place.“There was a strange wave mode which bounced the heating beams
out of the experiment,” said lead author Zhisong Qu, a PhD student at
The Australian National University.
Qu developed a simpler theory for plasma behaviour based on fluid
flow, and was able to explain an unstable wave mode that had been
observed in the United States’ largest fusion experiment, DIII-D.
Collaborator Dr Michael Fitzgerald, from the Culham Centre for
Fusion Energy in the UK, said the new explanation made much more
sense than previous “brute force” theories that tried to treat plasma as
individual atoms. “When we looked at the plasma as a fluid we got the
same answer, but everything made perfect sense,” Fitzgerald said. “We
could start using our intuition again in explaining what we saw, which is
very powerful.”
Leader of the research group, A/Prof Matthew Hole of ANU, said the
theory’s success with the DIII-D wave puzzle would “open the door to
understanding a whole lot more about fusion plasmas, and contribute to
the development of a long-term energy solution for the planet.”12 | APRIL 2016
Astronomershave discovered a spectacular tail of gas more than
300,000 light years across coming from a nearby galaxy. The plume
is made up of hydrogen gas and is ive times longer than the galaxy
itself.
Astronomers had observed that NGC 4569 contained less gas
than expected but could not see where it had gone. “We didn’t
have the smoking gun, the clear evidence of direct removal of gas
from the galaxy,” said Dr Luca Cortese of the University of Western
Australia node of the International Centre for Radio Astronomy
Research.
“Now, with these observations, we’ve seen a huge amount of gas
that creates a stream trailing behind the galaxy for the irst time.
What’s very nice is that if you measure the mass of the stream, it’s
the same amount of gas that is missing from the galaxy’s disc.”
NGC 4569 sits in the Virgo cluster, a group of galaxies 55
million light years from our own Milky Way. It is travelling through
the cluster at about 1200 km/s, and this movement is causing thegas to be stripped from the galaxy.
“We know that big clusters of galaxies trap a lot of hot gas,”
Cortese said. “So when a galaxy enters the cluster it feels the pres-
sure of all the gas, like when you feel the wind on your face, and
that pressure is able to strip matter away from the galaxy.”
The discovery, published inAstronomy & Astrophysics
(http://tinyurl.com/hn85hhm), was made when the international
research team used a super-sensitive camera on the Canada France
Hawaii Telescope to observe NGC 4569 for longer than ever
before.
Cortese said it could be the irst of many galaxies found to have
long tails of gas extending from them. “It’s pretty exciting because
this was just a pilot and we only targeted the brightest spiral galaxy
in the Virgo cluster,” he said.
“We were amazed by what we got... this is really promising
because it means it’s very likely we’ll ind similar features in many
other galaxy clusters.”The foreground galaxy is NGC 4569 of the Virgo cluster. The red filaments to the right of the galaxy show the hydrogen gas that
has been removed. The tail represents about 95% of the gas reservoir the galaxy needs to feed the formation of new stars.
Credit: CFHT/CoelumGalaxy Trailed by Stunning Plume of Gas