Fast-Ignition Laser-Fusion

Fast ignition has been
demonstrated using the
Gekko XII laser at
Osaka University in
Japan
(image credit: ILE)














Laser physicists in Europe have proposed plans to build a £500m facility
to investigate a new approach to laser-driven nuclear fusion (nuclear
fusion is the process that powers the sun). The proposal from a panel of
scientists from 7 European Union countries relies on what is termed as
"fast ignition" laser fusion process.

In 'fast ignition' process the laser would be used to compress and heat a
small capsule of deuterium and tritium until the nuclei are hot enough to
undergo nuclear fusion and produce helium and neutrons. In a reactor the
energy of the neutrons would be used to generate electricity without the
emission of greenhouse gases or the generation of long-lived nuclear waste.

The most advanced approach to fusion involves using magnetic fields to
confine the deuterium–tritium plasma. This is the route to be taken by
ITER in our first posting today. An alternative "inertial confinement"
technique, which uses lasers or ion beams rather than magnets to confine
the plasma is described in our last posting.

'Fast ignition' was first proposed by Max Tabak of the Lawrence
Livermore National Laboratory in USA, relies on different lasers for
these two stages. The process requires less laser energy than the
conventional approach and so is considerably cheaper. Fast ignition was
first demonstrated at the Gekko XII laser at Osaka University in Japan
in 2001, working with a team of UK scientists. Currently they are
upgrading their laser system in order to approach "breakeven point" at
which the energy output is equal to the energy needed to sustain the
reaction. They then plan to further enhance their system so that it
reaches ignition at which point the fusion reactions generate enough
energy to sustain themselves without the need for further heating.
Finally, they plan to build a demonstration fast-ignition facility.
Physicists in the US are also studying fast ignition.

The European proposal is called HiPER. The aim of its design is to achieve
high energy gains, providing the critical intermediate step between
ignition and a demonstration reactor. It would consist of a long-pulse
laser with an energy of 200 kJ to compress the fuel and a short-pulse
laser with an energy of 70 kJ to heat it.