“A powerful shockwave
compresses the fuel so that
fusion begins. In effect it’s
a tiny hydrogen bomb”
(NIF), designed to enable inertial confinement- compressing the fuel enough to initiate
fusion. The idea is audacious in its simplicity: blast a
small pellet of deuterium/tritium fuel with intense
laser light from all directions. The outside of the
pellet instantly vaporises with such intensity that a
powerful shockwave travels inwards, compressing the
fuel to the extent that fusion begins. In effect it’s a
tiny hydrogen bomb.
Here’s how it works. A small triggering laser’s
infrared output is split 48 ways before each sub-
beam passes through an amplifying laser, boosting
the beam’s power by a factor of 10 billion. Each of
those beams is then split again, producing a final 192
beams. These pass through the vast main amplifiers,
adding another factor of a million to bring the overall
power up to a sizzling 6 megajoules. The flash is so
powerful that for a few trillionths of a second it is as
if the output of 5,000,000,000,000 traditional light
bulbs were concentrated into a tiny, but immensely
powerful, flare of coherent light.
These 192 beams are converted to ultraviolet,
better suited to its final task. In a reaction chamber
the beams converge on the tiny pellet, producing that
sudden, shocking compression. News reports over
the last few months have picked up on the milestone
at NIF that researchers have managed to get more
energy out of the fuel than they put into it. As is
the case at ITER, this is obviously essential if fusion
is ever to be used for power generation. But the
achievement is not as impressive as it sounds.
Although more energy came out of the fusion
reaction than was applied to the fuel, far more was
required to run the NIF machine. The process of
amplifying the lasers is very inefficient, so most of
the energy that is pumped
into the system is lost long
before the beam reaches
the fuel in its ‘hohlraum’.
This German word
meaning ‘cavity’ was first
applied to the casing of
hydrogen bombs but has
come to be used for the
fingernail-sized gold plated
container that holds the
fuel ready for the beam to
zap it.
There is a long haul
TECHNOLOGY – At NIF, 192 laser
beams converge from all directions
on a tiny deuterium/tritium target.
The sudden surge in energy as the
surface soars in temperature blasts
the target inwards, compressing and
heating until fusion takes place. It
was built to study both nuclear
fusion for power generation and for
weapons.ODDS OF WINNING RACE
5 to 1NIF
(NATIONAL IGNITION FACILITY)
DATE STARTED 1997
METHOD 192-beam laser inertial
confinement
SIZE 2x approx. 3,200m2 laser bays,
10m target chamber
LOCATION Livermore, California
completed 2009In NIF’s ignition chamber
laser light is focused
onto a tiny targetFUSION DESIGN #3
16
MEGAWATTS
is the world record
fusion power output,
recorded at JET in 1997.FUSION