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Laser fusion nears energy gain

Laser fusion nears energy gain

Laser based fusion is nearing the point at which it delivers more energy than it consumes, according to one of the lead researchers working on the technology, although the target date will most likely slip from the September 2012 timeframe predicted at the start of the year. If the technology proves successful, laser fusion is likely to open up a large new market for semiconductor suppliers thanks to massive reductions in laser cost driven by the market for depilation products.

Mike Dunne, programme director for laser fusion energy at the Lawrence Livermore National Laboratory, said the task has meant building a laser that is '100 times larger than any other laser system in the world to provide the full scale physics performance demonstration needed for a gigawatt scale power plant.

"We completed the National Ignition Facility about three years ago. We think that, over the next few months – the original prediction was September, although it looks a little difficult to achieve that now – we will get to the point where we can get raw energy out. If we are successful, from there we think we can get to the 1000MW level needed for a power plant over the next 8 to 12 years," Dunne claimed.

The key to successful laser induced fusion is a combination of fine control over laser colour, pulse sequence and raw power. Dunne said initial 10nJ pulses are boosted to an energy of hundreds of megajoules through a series of amplifiers that almost fill at ten storey building. "It is timed to a few trillionths of a second and focused down to hit a tiny pellet," he said.

The laser heats the sample to such an extent that it emits soft X-rays that then crush the deuterium and tritium in the pellet together, fusing their nuclei into helium ions. "The energy coming out is still less than the energy going in. We started in September 2009 and a factor of 100,000 away of where we needed to be. We are now at the point where we need to figure out how to get up by a further factor of a hundred," Dunne said.
Even if successul, the architecture of the laser will have to change to accommodate power plants of a reasonable size.

"The NIF uses fluorescent lighting technology for the laser battery. It's 1990s technology," said Dunne. Moving to semiconductor lasers would slash the size of the batteries more than tenfold and increase the pulse rate from one every couple of hours – mainly to let the components cool down – to 20 per second. "This solution has been known for years, but it's been an issue of cost. The situation today is a reflection of how semiconductor technology has progressed.

"Until five years ago, you would be spending $10bn on the semiconductor diodes alone. It was completely prohibitive. But three industries have driven the cost of LEDs down," said Dunne. While flat panel displays and led lighting have contributed, but the biggest industry for laser diodes is the hair removal industry. "It has helped drive the cost of the laser diodes down by a factor of ten," Dunne noted. "They are still expensive, but it means now it is just about affordable to deploy semiconductor lasers in fusion power plants."

Author
Chris Edwards

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