Stalking the Elusive Ball Lightning

German researchers have found a reliable way to simulate ball lightning by producing clouds of plasma above a water surface. Ball lightning has intrigued scientists for centuries, in part because it lasts so much longer than the microsecond flashes of ordinary lightning.

A plasma cloud produced in an underwater discharge simulates ball lightning. Courtesy of Max Planck Institut für Plasmaphysik.

Physicists from Max Planck Institut für Plasmaphysik in Garching at Humboldt University in Berlin have built on former Russian experiments to create gaseous apparitions that are visible for nearly one-half second, that have diameters up to 20 cm and that come in different colors. They apply very high voltage to a beaker of saltwater containing two electrodes, one of which is protected by a clay tube. Flashover from the water sends the current into the tube, evaporating the water inside, which emerges as a luminous plasmoid of ionized molecules.

The phenomenon is still quite mysterious. Among the questions that remain to be answered are why the illumination lingers after the energy is cut off and why the glowing plasma appears to be cold. Perhaps these puzzles will be solved by several diploma theses getting under way that plan to analyze the entire process using spectroscopic means.

And the students involved may just have a ball doing their doctoral work.