BBC_Knowledge_2014-06_Asia_100p

MAY 2013 / FOCUS / 41

the laser approach needs to be continually driven,

limiting its efficiency.

Culham’s Steve Cowley is doubtful that NIF will

ever result in a fusion generator, pointing out that

while current plans are to increase the site’s power by

a factor of three or four, it would need something like

a 200-fold improvement to be commercial. And that’s

not the only problem, as the explosion could become

too powerful to confine. “Scaling it up, the explosion

gets too big. A 2GW explosion is the equivalent of

half a kiloton of TNT,” he says.

Feeling the pinch

It is likely that, were it not for the military application

of NIF’s ability to experiment with small scale fusion

bombs at a time when nuclear testing is banned,

this vast experiment would not even be in the

running in the power generating race. Lasers don’t

provide the only possibility for using confinement,

though. The Z-machine at the Sandia National

Laboratory, operated for the US Government by

Lockheed Martin at Albuquerque in New Mexico,

takes a different approach to achieving that dramatic

compression, employing a ‘Z-pinch’.

The pinch effect was first discovered in a dramatic

accident in the early years of the 20th Century. A

lightning strike hit the chimney of Hartley

Vale Kerosene Refinery in New South Wales,

indeed to get from the current laser confinement

experiments to a working reactor. Firstly, each shot of

fuel is extremely expensive, costing around £600,000;

a production machine would need costs driven down

to less than 5p per shot. And the reaction chamber

has to be set up with incredible precision, positioning

the hohlraum in the beam paths, powering up and

firing the system, then disposing of the hohlraum

and starting all over again. The possibility of doing

this several times a second to keep a power station at

work seems far-fetched. And where a tokamak, once

running, heats itself and doesn’t need external power,

A metallic case called

a hohlraum holds

a fuel target at NIF

A 2mm-diameter target

of fuel that will be

hammered at NIF by

powerful lasers triggering

a fusion reaction

These preamplifiers at

the National Ignition

Facility are used to

increase the power of

the laser beams

500

TERAWATTS

is the peak power of

the NIF laser.