NewScITech

A small sphere can make a big bang. Fraunhofer researchers are producing tiny high-precision hollow capsules of synthetic diamond. These midgets could play a central part in future energy production by means of nuclear fusion.

Scientists at the Lawrence Livermore National Laboratory (LLNL) in the USA are planning to commission a reactor for laser-assisted nuclear fusion, the National Ignition Facility, by the year 2011. Their vision is to tap a virtually inexhaustible, environmentally friendly source of energy modeled on the sun. In this method, a mighty laser flash impacts a hydrogen-filled hollow sphere and compresses the sphere to about one ten-thousandth of its original volume. This forces the atomic nuclei so close together that they fuse. On one condition: the spheres must be perfectly spherical.

“Diamond has outstanding properties that predestine it for this application,” states Dr. Christoph Wild of the Fraunhofer Institute for Applied Solid State Physics in Freiburg. “It is made of the lightweight element carbon, it is extremely hard and it exhibits the highest atomic density of all materials.” The Freiburg scientists are well known in professional circles for their artificial diamond discs. Until now, the diamond has been available mainly as discs of varying diameters and thicknesses. But how can diamond discs be transformed into hollow spheres ? This was the question addressed by the Freiburg team at the suggestion of Dr. Jürgen Biener and Dr. Alex Hamza of the LLNL, who also assisted the research work. The core of the solution consists of tiny silicon balls, which are coated with diamond in a plasma reactor patented by the IAF. Unlike the discs, the balls have to be kept constantly in motion in the reactor in order to obtain a homogeneous coating.

The IAF team also developed the subsequent high-precision grinding and polishing process for the diamond spheres. The result is well worth seeing: perfectly formed diamond spheres with a mirror finished surface. At this point, however, the silicon is still inside the spheres. To get it out, the researchers drill a tiny hole, measuring just a few microns across, using a laser. They then dissolve the silicon out of the sphere using a special ultrasound-assisted etching technique.

Dr. Christoph Wild, Dr. Eckhard Wörner and Dipl.-Ing. Dietmar Brink have been awarded one of the 2006 Joseph von Fraunhofer Prizes for this new development. The jury was very impressed by their scientific and technical achievements. And the fact that a renowned American research establishment turns to Germany for expertise speaks for itself.

Source: Fraunhofer Institute