NUCLEAR fusion on a tabletop is now possible. Physicists have unveiled a reactor that uses a small laser to fuse atoms. While it won't solve the world's energy problems, it will make it possible to study fusion for a tiny fraction of the usual cost.
The fusion process is hard to start. Atomic nuclei repel each other, and it takes a lot of energy to force them to fuse. In the past, physicists have overcome this repulsion by using the energy of massive lasers costing hundreds of millions of dollars, or even more expensive options-uncontrolled nuclear fission or reactors using superhot gas confined within magnetic fields.
But researchers at the Lawrence Livermore National Laboratory in California have triggered fusion with a small laser costing less than $1 million. Each infrared laser pulse has less energy than a Christmas tree light emits in a second. But because the laser pulse lasts just 35 femtoseconds (35 x 10-15 seconds), its energy is highly concentrated.
Todd Ditmire and his colleagues injected deuterium gas into a vacuum, in which the atoms clustered together. Then they fired the laser at the deuterium clusters. When a laser pulse struck the clusters, the heat made them explode. Many of the deuterium nuclei hit others with enough speed to make them fuse, creating helium and neutrons.
"We looked to see if we were producing fusion neutrons-lo and behold, we were," said Ditmire. The fusion reaction also released energy, but only 10 millionths of the energy consumed by the laser. "This is not, in the present guise, a path to fusion energy production," admits Ditmire. "But it may potentially lead to a compact neutron source." A steady, cheap stream of neutrons could be slammed into materials to test their susceptibility to damage by energetic particles in space, for instance.
Martin Schmidt, a nuclear physicist at the Commission for Atomic Energy in Gif-sur-Yvette, France, agrees. But he thinks the best reason to celebrate is that fusion reactions can now be studied without expensive equipment. "You don't need $1.2 billion to produce fusion."
Author: Charles Seife
New Scientist issue 3rd April 1999
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