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Lasers advance quest for energy from sea water By Roger Highfield, Science Editor (Filed: 23/08/2001)

THE dream of harnessing the energy source that powers the sun to provide unlimited supplies of cheap energy comes a step closer to reality today.

A milestone is reported by a team from Britain and Japan in the effort to use lasers to harness fusion power, the Holy Grail of energy research.

Nuclear fusion offers the potential of vast quantities of cheap power from fuels such as sea water, without creating significant waste. However, despite more than half a century of research, there have been many false dawns.

Now a new way to use lasers to make atoms fuse together to release vast amounts of fusion energy is reported in the journal Nature by Dr Ryosuke Kodama and his colleagues at Osaka University, Japan, and a team from Britain.

"We have provided the first demonstration that this new scheme we call fast ignition can provide an efficient route to fusion energy," said Dr Peter Norreys of the CLRC Rutherford Appleton Laboratory, Oxfordshire, who conducted the work with colleagues at Oxford University, Imperial College and the University of York.

The work brings the prospect of commercial fusion power "significantly closer", he said, because it could reduce the amount of energy needed to achieve ignition of fusion fuel to as little as one tenth of the current level.

Because of their ability to deposit vast amounts of energy into a small area, lasers have been studied intensively in fusion research, notably by weapons scientists who want to understand what goes on inside hydrogen bombs, which are fusion explosions.

Laser fusion works like an internal combustion engine - the pellet used as a target is compressed to high density and then a spark is formed that ignites the fuel.

The combination of high temperature (10 million degrees centigrade) and high density where the laser energy is deposited (1/1000 the density of solid matter) means that the generated pressure on the outside of the pellet is enormous - equivalent to 10 million atmospheres.

The outer layers of the pellet explode causing the remaining shell to implode at high velocity and eventually compress to super-high density.

However, there are huge difficulties in depositing additional energy to form the spark that will trigger a fusion burn wave to ignite the compressed fuel.

The team found the answer by inserting a millimetre high gold cone inside the pellet that allowed a second ultra-intense, short-pulse laser to pass through the inside.

The cone produces a "channel" that remains empty long enough for the ignitor beam to travel through and deposit energy in the compressed matter.

The approach has been tested using nine laser beams to implode fuel pellets at the GEKKO XIII laser at Osaka University, when temperatures rapidly rose by 1.4 million degrees centigrade.

The team plans to go to larger short pulse laser energy levels for the next stage of its work.

-- Anonymous, August 22, 2001