Researchers at the Lawrence Livermore National Laboratory in California have demonstrated nuclear fusion on a table top. Todd Ditmire and colleagues fired a small high-power laser at a gas of deuterium clusters and detected an output of about 100000 neutrons for every joule of laser energy input (Nature 398 489). The neutrons were produced in fusion reactions in which two deuterium nuclei fuse to form a helium-3 nucleus and a neutron. The main application of the technology is likely to be in the development of a table-top neutron source that could be used to study materials.
The clusters were produced by expanding a deuterium gas jet into a vacuum. A laser beam focussed near the top of the plume heats the clusters, causing them to explode. This creates a small plasma of high energy (keV) deuterium ions which collide with each other and undergo a fusion reaction.
The experiment converted laser energy into fusion energy at an efficiency comparable with that displayed by much larger lasers. One advantage of the table-top technique is that the laser can fire 10 shots per second for short periods of time, compared with about one shot per hour from traditional fusion lasers.
