This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Physicist Todd Johnson has been working at Fermilab for 30 years, but he also dabbles in art. In the 1990s, he focused on holographic photography. These days -- inspired by a pal who builds Tesla coils in his spare time -- he's all about capturing lightning-like fractal patterns in plastic cubes with the help of a linear accelerator. He doesn't do this at Fermilab, but at a commercial polymer cross-linking facility in Ohio some 400 miles away. Per Symmetry Breaking:
Johnson arrives at the facility with stencils laser-cut from steel or handmade from sheet lead; clear acrylic hunks of varying sizes; and a lot of ideas. He sends his pieces of acrylic through the accelerator’s electron beam, which is designed to break chemical bonds in plastics. Because acrylic is an insulating material, the beam scatters through the material, losing momentum as it goes. Only areas of the acrylic not covered by a stencil are exposed to the beam, allowing Johnson to create shapes.Eventually the beam coalesces into a pool of electrons that desperately want to escape but can’t—an invisible puddle of potential energy. Releasing that energy is a simple but arresting process. To do it, Johnson uses a hand-made tool reminiscent of a crude, oversized syringe. It works like a click pen—press on one end and the tip comes out the other with enough force to puncture the acrylic. The instant the tool punctures the surface, there’s a burst of white light as the pool of excited electrons escapes from the material, leaving trails of vaporized acrylic in its place.
On their way out of the acrylic, the electrons follow the same natural laws that govern all systems that flow—electricity snaking its way from a storm cloud to Earth, rivers branching into ever smaller creeks and streams, or the spidery web of veins that distributes blood throughout your body.
Johnson even created a piece where the pattern looked like a capillary system as a gift for the wife of a pulmonologist. That's appropriate, since these fernlike patterns often form on the skin of people struck by lighting, caused by the capillaries under the skin rupturing from the shock wave generated by the electrical discharge. When lightning strikes sand, it can create fulgurites, as the sand is fused into glass by the intense heat.
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The colloquial name for these sorts of branching patterns is “lightning flowers,” but they are also called “Lichtenberg figures” in honor of 18th century physicist Georg Christoph Lichtenberg.
Born in 1742 to a pastor in Darmstadt, Germany, Lichtenberg showed a natural curiosity and penchant for math and science at an early age. Eventually he became a professor of physics there, a job he held for the rest of his life. A spinal deformation left him hunchbacked, a causing difficulties with his breathing in his later years. But he enjoyed an excellent reputation as a satirist as well as a scientist, and was wildly popular with women, enjoying several romantic dalliances before marrying one Margarethe Kellner, who bore him six children.
This was an era when scientists were fascinated by electricity (“electric fluid”), conducting experiments on charged objects and how sparks jumped between them, using Leyden jars and electricity tubes, among other equipment. Benjamin Franklin famously conducted his experiment with an elevated “lightning rod” or wire to “draw down the electric fire” from a storm cloud, while standing in the protection of an enclosure similar to a soldier’s sentry box.
Lichtenberg was among the first to bring Franklin’s lightning rods to Germany, installing several around his home in Göttingen. He also built a large (six feet in diameter) electrostatic generator, or electrophorus, to study the electric fire–including figuring out how to record the branching patterns left in the wake of electrical discharges.
First he used the electrophorus to blast an insulating material, such as resin, glass or hard rubber, with a very high voltage. Then he sprinkled the surface with a mix of powdered sulfur, red lead and lead tetroxide and watched the pretty branching patterns form, before pressing a piece of paper onto the surface to transfer those images to the paper.
The sulfur, you see, becomes negatively charged during handling, while the red lead becomes positively charged. So the sulfur sticks to those areas of the plate that are positively charged -- opposites attract! -- and the lead sticks to the negatively charged areas. (This is also the proof of principle for modern xerography.)
Lichtenberg noted two types of patterns: one for a positive charge, which had longer, more elaborate branching, and the other for a negative charge, which more closely resembled a shell. (Occasionally there would be a mixed figure, with the negatively charged area producing a red nucleus, surrounded by yellow rays resulting from the positively charged areas.) His conclusions were published in his 1777 memoir, Super Nova Methodo Naturam ac Motum Fluidi Electrici Investigandi.
Those experiments set the stage for modern plasma physics research. In the 1920s, Arthur von Hippel and others recorded light from high voltage electrical discharges onto photographic film. Von Hippel discovered he could change the length of the branching pattern simply by increasing the applied voltage or reducing the surrounding air pressure.
In the 1940s, Arno Brasch and Fritz Lange were working with one of the first particle accelerators (they called it a “Capacitron”) at AEG in Germany, capable of producing high-voltage electron beams that left bluish flame-like tails of ionized air in their wake.
Brasch and Lang were the first to inject free electrons into cubes of plastic, and the resulting electrical breakdown captured the branching pattern of Lichtenberg figures perfectly in three dimensions. Today, the Dynamitron at Kent State’s Neo Beam facility does similar work, and one can buy such “frozen lightning” sculptures as artwork.
A physicist first and foremost, Johnson doesn't seem to be all that interested in selling the fruits of his labors. He only spends a couple of days twice a year working on his Lichtenberg figures, although he spends months planning the next project and putting together the materials, like his laser-cut stencils. And it doesn't always work out the way he planned. "It's frustrating, but it's part of the excitement," he told Symmetry Breaking. "The minute you shut the machine off at the end of the day, you think of things you want to do next time."
UPDATE 7/24/2013: Good news for anyone interested in checking out more of Johnson's accelerator art, and possibly buying some. While it's not his primary motivation for making the pieces, he does sell his work over at Deviant Art, as well as through a group of friends he works on the pieces with.
References:
Cox, J.H. and Legg, J.W. "The Klydonograph and Its Application to Surge Investigation," Transactions of the American Institute of Electrical Engineers, January 1925.
Gross, Bernhard. (1958) "Irradiation effects in Plexiglas," Journal of Polymer Science 27(115): ,135-143.
Hashishes, Yuzo. (1979) “Two Hundred Years of Lichtenberg Figures,” Journal of Electrostatics, 6(1), 1-13.
Lichtenberg, Georg Christoph. De Nova Methodo Naturam Ac Motum Fluidi Electrici Investigandi (Concerning the New Method Of Investigating the Nature and Movement of Electric Fluid). Göttinger Novi Commentarii, Göttingen, 1777.
Merrill, F.H. and von Hippel, A. (1939) "The Atomphysical Interpretation of Lichtenberg Figures and Their Application to the Study of Gas Discharge Phenomena," Journal of Applied Physics 10(12): 873-887.
Reiss, Peter T. (1846) "Ueber elektrische Figuren und Bilde," Annalen der Physik und Chemie 145(9): 1-44.