* Daunting scientific and engineering challenges remain
* Research done at Lawrence Livermore National Laboratory
* Experts see decades before fusion is viable energy source
By Will Dunham
WASHINGTON, Feb 12 U.S. scientists announced on
Wednesday an important milestone in the costly, decades-old
quest to develop fusion energy, which, if harnessed
successfully, promises a nearly inexhaustible energy source for
For the first time, experiments have produced more energy
from fusion reactions than the amount of energy put into the
fusion fuel, scientists at the federally funded Lawrence
Livermore National Laboratory in California said.
The researchers, led by physicist Omar Hurricane, described
the achievement as important but said much more work is needed
before fusion can become a viable energy source. They noted that
did not produce self-heating nuclear fusion, known as ignition,
that would be needed for any fusion power plant.
Researchers have faced daunting scientific and engineering
challenges in trying to develop nuclear fusion - the process
that powers stars including our sun - for use by humankind.
"Really for the first time anywhere, we've gotten more
energy out of this fuel than was put into the fuel. And that's
quite unique. And that's kind of a major turning point, in a lot
of our minds," Hurricane told reporters.
"I think a lot of people are jazzed."
Unlike fossil fuels or the fission process in nuclear power
plants, fusion offers the prospect of abundant energy without
pollution, radioactive waste or greenhouse gases.
Unlike the current nuclear fission energy that is derived
from splitting atoms, fusion energy is produced by fusing atoms
Experts believe it still will be many years or decades
before fusion can become a practical energy source.
"I wish I could put a date on it," said Hurricane. "But it
really is (just) research. And, you know, although we're doing
pretty good, we'd be lying to you if we told you a date."
Of the uncertain path ahead in fusion research, Hurricane
compared it to "climbing half way up a mountain, but the top of
the mountain is hidden in clouds. You can't see it. You don't
have a map".
The research was conducted at the laboratory's National
Ignition Facility (NIF), which was completed in 2009.
ZAP A TINY TARGET
The scientists used 192 laser beams to zap a tiny target
containing a capsule less than a tenth of an inch (about 2 mm)
in diameter filled with fusion fuel, consisting of a plasma of
deuterium and tritium, which are two isotopes, or forms, of
The fuel was coated on the inside of the capsule in a frozen
layer less than the width of a human hair.
At very high temperatures, the nucleus of the deuterium and
the nucleus of the tritium fuse, a neutron and something known
as an "alpha particle" emerge, and energy is released.
The experiments, published in the journal Nature, created
conditions up to three times the density of the sun.
In two experiments described by the researchers that took
place in September and November of last year, more energy came
out of the fusion fuel than was deposited into it, but it was
still less than the total amount deposited into the target.
The deuterium-tritium implosions were more stable than
previously achieved. The researchers did so by doubling the
laser power earlier in the laser pulse than in earlier tries.
The fusion-energy yield was increased by about tenfold from
past experiments, in a series that started last May. One of the
experiments produced more than half of the so-called Lawson
criteria needed to reach ignition - but only about one-100th of
the energy needed for ignition.
Lawrence Livermore National Laboratory, located about 45
miles (70 km) east of San Francisco, is overseen by the National
Nuclear Security Administration, an agency of the U.S.
Department of Energy.
Eager to exploit the potential this type of energy offers to
reduce dependence on oil and other fossil fuels, the United
States and other nations have invested many millions of dollars
into fusion research, often with uneven results.
There are two main approaches. This team focuses on what's
known as inertial confinement fusion energy - using lasers to
compress fuel pellets, which triggers fusion reactions.
Other labs like the Culham Centre for Fusion Energy, which
is the British national laboratory for fusion research, and the
Princeton Plasma Physics Laboratory in New Jersey focus on
magnetic confinement fusion energy - putting plasma in a
magnetic container and heating it up until nuclei fuse.
Steve Cowley, director of the Culham Centre, called new
findings "truly excellent" but said different measures of
success make it hard to compare with his type of research.
"We have waited 60 years to get close to controlled fusion,
and we are now close in both magnetic and inertial confinement
research. We must keep at it," Cowley said in a statement.
Mark Herrmann, a fusion researcher at Sandia National
Laboratories in New Mexico which is also overseen by the U.S.
National Nuclear Security Administration, called the new
findings important, but sees a "very long road to assessing the
viability of fusion as a long-term energy source".
"I believe a compact carbon-free energy source is very
important for humankind in the long term," he said by email.
"Fusion is one bet. If it pays off, the return will be big."
(Reporting by Will Dunham; Editing by Sophie Hares)