All you need to know about Laser Fusion

There's a big new kid on the nuclear energy block.

Last week British firm AWE (formerly the Atomic Weapons Establishment), based in Aldermaston, the Rutherford Appleton Laboratory in Harwell, UK, and the Lawrence Livermore National Laboratory in California said they would team up to develop laser fusion as a clean energy source.

Laser fusion is an alternative to magnetically induced nuclear fusion, which is used in the Joint European Torus (JET) now operating in Culham, UK, and the test reactor ITER, under construction in Cadarache, France.

Historically, laser fusion has been used focused mostly for weapons testing, while power generation research has concentrated on magnetic fusion. Is that about to change?

What is laser fusion?
At high temperatures and pressures, the nuclei of the heavy hydrogen isotopes deuterium and tritium form a plasma and can be fused to form helium, releasing energy and a neutron.

Firing a synchronised barrage of laser pulses can vaporise the surface of a pellet filled with these isotopes, forcing the pellet to implode and so producing fusion conditions inside the pellet for a few billionths of a second.

The physics resembles the detonation of a thermonuclear (or hydrogen) bomb – although on a much smaller scale – and so the US has used laser fusion to simulate these explosions.

What advantages does it have over magnetic fusion?
Magnetic fusion reactors zap heavy hydrogen gas with a powerful electrical pulse to produce a plasma. A strong magnetic field is then required to confine the plasma before fusion can take place.

That's hard, because plasmas can quickly leak or become unstable. By contrast, laser fusion produces much higher temperature and pressures, so fusion occurs faster, and the plasma must be confined for only billionths of a second.

Fusion of either kind is attractive as a power source because the fuel is more abundant than uranium, and the process does not produce the highly radioactive isotopes generated by splitting uranium atoms.

What stage is the tech at, and who is working on it?
Laser fusion has been studied since the 1960s, with most US funding coming from the nuclear weapons programme.

Today's biggest fusion laser is the National Ignition Facility (NIF) at Livermore. By the end of next year, Livermore hopes to reach "ignition" by producing more energy from fusion than is needed to generate the laser pulse.

Smaller lasers are used in fusion programmes at Rutherford Appleton, the University of Rochester in New York and Osaka University, Japan; France is building a NIF-sized system called Megajoule Laser. ITER, meanwhile, is a decade from igniting magnetic fusion.

When will laser fusion come to the power grid?
Livermore's Mike Dunne says that if all goes well, a plant delivering about 440 megawatts of electricity could be up and running in a decade; full-scale versions that follow would deliver about 1000 megawatts.

But don't hold your breath. "So far this is at the border of science fiction," says Hans Kristensen, director of the nuclear information project of the Federation of American Scientists. "The technological hurdles are not nearly explored yet."

Is there anything I need to worry about?
Laser fusion reactors will not have a large volume of hot material that might melt down if power failed, as occurred at the Fukushima Daiichi plant in Japan earlier this year. But fusion neutrons are hazardous and will make other materials in the reactor radioactive.

The tritium in the fuel is also radioactive: it emits beta particles so is dangerous if inhaled and has a half-life of 12.5 years.