Philadelphia

A small burst of nuclear fusion has been induced for the first time using X-rays generated by a huge burst of electricity, according to US researchers.

Scientists from Sandia National Laboratory in New Mexico told the American Physical Society's meeting in Philadelphia on 5 April that the results were generated by the lab's Z-machine in late March. “This is the first observation of fusion from an electrical source,” says Sandia physicist Ray Leeper.

Fusion occurs when two small nuclei — usually of hydrogen or one of its isotopes, deuterium or tritium — fuse together to form a larger one. Physicists try to reproduce the phenomenon, which powers the stars, using one of two techniques: magnetic confinement, which holds a plasma in place magnetically and heats it; or inertial confinement, which uses X-rays to crush a small target so rapidly that fusion takes place.

The Z-machine attempts the latter, using energetic X-rays to crush a small sample of deuterium to form helium. The X-rays are generated by releasing a massive electrical power surge through a small cylinder of 360 tungsten filaments, which surrounds a 2-mm pellet filled with the deuterium. At the flip of a switch, scientists release a 40-terawatt pulse just 75 nanoseconds long through the filaments, vaporizing the wires instantly, and emitting X-rays that crush the pellet.

The Z-machine has been running since September 1996, but last month's experiment confirmed that emissions of neutrons — a by-product of the fusion reaction — had been detected.

The result could strengthen the case for a larger Z-machine — which Sandia has wanted to build for years, at a cost of several hundred million dollars. It may also help with research at the National Ignition Facility, an experiment under construction at the Lawrence Livermore National Laboratory in California, which will use the world's most powerful laser to achieve inertial confinement fusion.

The fusion energy generated in the experiment is estimated to be 4 millijoules — about a billionth of the electricity put in — so the technique has some way to go in terms of efficiency.

But Per Peterson, chair of the nuclear engineering department at the University of California, Berkeley, says it could one day be possible to scale up something like the Z-machine to create an affordable fusion power plant. “Pulsed power has the potential to be by far the cheapest approach” to fusion power, he says.