The lasers fuelling hopes of unlimited, clean nuclear energy
A milestone has been reached in the 60-year struggle to harness the
nuclear reactions that power the Sun in an experiment that could lead to
a way of producing an unlimited source of clean and sustainable energy
in the form of nuclear fusion.
Scientists in California said on Wednesday night that they have for
the first time managed to release more energy from their nuclear fusion
experiment than they put into it, which marks a critical threshold in
eventually achieving the goal of a self-sustaining nuclear-fusion
A worker inspects a target chamber at the National Ignition
Facility in California
Nuclear fusion uses a fuel source derived from water and produces
none of the more dangerous and long-lasting isotopes, such as enriched
uranium and plutonium, that result from conventional nuclear power
plants, which rely on the fission or splitting of atoms rather than
Researchers involved in the Nuclear Ignition Facility (NIF) at the
Lawrence Livermore National Laboratory said that they have used 192
laser beams to compress a tiny fuel pellet less than half the diameter
of a human hair in such a way that it triggered the net release of
energy by nuclear fusion.
The fuel, composed of the two hydrogen isotopes tritium and deuterium
derived from water, was compressed together under enormous pressures and
temperatures for less than a billionth of a second, but this was enough
to see more energy coming out of the experiment than went into it. "We
are fusing deuterium and tritium, which are isotopes of water, in a way
that gets them to run together at high enough speed to overcome their
natural electrical repulsion to each other," said Omar Hurricane of the
"We are finally, by harnessing these reactions, getting more energy
out of these reactions than we are putting into the deuterium-tritium
fuel... We took a step back from what we tried before and in the process
took a leap forward," said Dr Hurricane, who led the NIF study published
in Nature .
There are currently two parallel approaches to nuclear fusion. One
uses laser energy to compress fuel pellets -- like the NIF experiment -
and aims to keep the fuel in place by a process known as inertial
The other approach is to build a complex magnetic "bottle" to hold
the hot, electrically charged plasma of the fuel in place. This magnetic
confinement is the strategy of the Joint European Torus (JET) experiment
in Culham, Oxfordshire, and the international ITER nuclear fusion plant
under construction at Cadarache in southern France. Both approaches aim
to gain more energy than is put into the system, and ultimately to a
critical stage called "ignition" when the reaction becomes
self-sustaining, which would mean that fusion could be exploited
practically in power plants as an unlimited source of clean energy.
The breakthrough at NIF was made possible by altering the laser
pulses focusing on the fuel pellet in such a way that it led to the even
compression of the capsule holding the deuterium and tritium, said
Debbie Callahan, one of the researchers involved.
"We had to compress the capsule by 35 times. This is like saying that
if you started with a basketball it would be like compressing it down to
the size of a pea, but keeping the perfect spherical shape, which is
very challenging," Dr Callahan said.
Professor Steve Cowley, director of the Culham Centre for Fusion
Energy, said that the two approaches to nuclear fusion are beginning to
make significant headway after decades of painstakingly slow 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," Prof Cowley said.
"The engineering milestone is when the whole plant produces more
energy than it consumes - ITER, the successor to JET, will be the first
experiment to do this. ITER is going slowly but progress is happening,"