Making a Star on Earth

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The controlled fusion of atoms - creating conditions like those in our Sun - has been touted as a potentially revolutionary energy source. However, there have been doubts about the planned use of powerful lasers for fusion energy because the "plasma" they create could interrupt the fusion. The Science article showed that plasma is far less a problem than expected. The report is based on the first experiments from the National Ignition Facility in the US that used all 192 of its laser beams.

Along the way, the experiments smashed the record for the highest energy from a laser - by a factor of 20.

The goal, as its name implies, is to harness the power of the largest laser ever built to start "ignition" - effectively a carefully controlled thermonuclear explosion.

It is markedly different from current nuclear power, which operates through splitting atoms - fission - rather than squashing them together as in fusion.

Proving that such a lab-based fusion reaction can release more energy than is required to start it - rising above the so-called breakeven point - could herald a new era in large-scale energy production.

In the approach Nif takes, called inertial confinement fusion, the target is a centimetre-scale cylinder of gold called a hohlraum. Giant laser experiment powers up It contains a tiny pellet of fuel made from an isotope of hydrogen called deuterium. Inside the hohlraum is a tiny pellet containing an extremely cold, solid mixture of hydrogen isotopes. Lasers strike the hohlraum's walls, which in turn radiate X-rays. X-rays strip material from the outer shell of the fuel pellet, heating it up to millions of degrees. If the compression of the fuel is high enough and uniform enough, nuclear fusion can result

A significant potential hurdle to the process that many have suggested over 30 years of the laser fusion debate regards the "plasma" that the lasers will create in the hohlraum.

The fear has been that the plasma, a roiling soup of charged particles, would interrupt the target's ability to absorb the lasers' energy and funnel it uniformly into the fuel, compressing it and causing ignition.

Siegfried Glenzer, the Nif plasma scientist, led a team to test that theory, smashing records along the way.

"We hit it with 669 kilojoules - 20 times more than any previous laser facility," Nif's Siegfried Glenzer told BBC News.

That isn't that much total energy; it's about enough to boil a one-litre kettle twice over.

However, the beams delivered their energy in pulses lasting a little more than 10 billionths of a second.

By way of comparison, if that power could be maintained, it would boil the contents of more than 50 Olympic-sized swimming pools in a second.

http://news.bbc.co.uk/1/hi/sci/tech/8485669.stm

http://sciencenow.sciencemag.org/