Lightning Box

Posted on May 24, 2011
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Lichtenberg Figures are branching, tree-like patterns that are sometimes formed on the surface or within the interior of insulating materials by high voltage electrical discharges. The first Lichtenberg Figures were two-dimensional patterns formed in dust on charged insulating plates by the German physicist who discovered them, Georg Christoph Lichtenberg (1742-1799). The principles involved in the formation of these early figures are also fundamental to the operation of modern copy machines and laser printers. Using modern materials and powerful particle accelerators, beautiful 3-D Lichtenberg Figures can now be created inside clear acrylic, creating lightning sculptures.

We use acrylic (Polymethyl Methacrylate or PMMA) to make our Lichtenberg Figures, since it has an ideal combination of optical, electrical, and mechanical properties. We also use a linear accelerator (LINAC) to create a beam of high-speed electrons. Electrons in the beam are accelerated to as much as 99.5% of the speed of light. These “relativistic” electrons have a very large amount of kinetic energy, measured in millions of electron Volts (MeV). Polished acrylic specimens are placed in the path of the beam. As speeding electrons hit the acrylic surface, they don’t stop immediately. Instead, they collide with acrylic molecules, rapidly slowing down, and eventually coming to rest deep within the acrylic.

As we continue to irradiate the specimens, huge numbers of electrons accumulate inside, forming an invisible cloud-like layer of excess negative charge. Since acrylic is an excellent electrical insulator, the excess electrons are trapped within the charge layer. The growing charge creates very strong electrical stresses inside the plastic, similar to the way that regions of excess charge grow within clouds in a thunderstorm. If the electrical stress becomes too large, it overcomes the insulating strength of the plastic, and branching ionized (electrically conductive) pathways rapidly form within the acrylic in an irreversible process called electrical breakdown. The excess charge violently escapes, creating a brilliant blue-white flash of miniature lightning and a loud bang. The high current main discharge may last for less than 100 billionths of a second, but secondary discharges may randomly occur for 30 seconds or more afterwards. Read more


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