

Lichtenberg figures are now known to occur during the electrical breakdown of gases, insulating liquids, and solid dielectrics. Lichtenberg figures may be created within billionths of a second (nanoseconds) when dielectrics are subjected to very high electrical stress, or they may develop over y ears through a progressive series of small, low-energy, partial discharges. Countless partial discharges on the surface or the interior of solid dielectrics often create slowly-growing, partially-conductive 2D surface Lichtenberg figures or internal 3D "electrical trees". 2D electrical trees are often found along the surfaces of contaminated power line insulators. 3D trees can also form, hidden from view, inside dielectrics due to the presence of small impurities or voids, or at locations where an insulator has been physically damaged. Since these partially-conductive trees can eventually cause the complete electrical failure of the insulator, preventing their initial formation and growth is critical to the long-term reliability of all high-voltage equipment. The study of electrical trees and their prevention has been critical to the reliable design of the high-voltage power transmission systems that transfer electrical power to our homes and businesses.



3D Lichtenberg figures inside transparent plastic were first created by physicists Arno Brasch and Fritz Lange in the late 1940's. Using their newly-invented electron accelerator, they injected trillions of free electrons into plastic specimens, triggering electrical breakdown and creating carb on ized internal Lichtenberg figures. Electrons are tiny, negatively charged particles that orbit the positively-charged nucleus of the atoms that make up all condensed matter. Brasch and Lange used high voltage pulses from a multi-million volt Marx Generator to drive a pulsed electron beam accelerator. An article about their research and their accelerator (which they called a "Capacitron") originally appeared in the March 10, 1947 issue of LIFE Magazine. The Capacitron could deliver a three-million volt pulse, and could generate a powerful blast of free electrons with an incredible peak current of up to 100,000 amperes. The glowing region of heavily-ionized air created by the exiting high-current beam of electrons resembled a bluish-violet rocket engine flame. A complete set of B&W pictures, including Lichtenberg figures inside a clear block of plastic, has recently become available online, as has another article with color pictures from the April, 1951 issue of Popular Mechanics. In 1944, Brasch founded the Electronized Chemicals Corporation (ECC), a pioneering researcher of using electron beams to cross-link monomers and polymers to improve their electrical and physical properties. ECC was eventually purchased by the 3M Company in 1985.



The first formal scientific study of the injection and movement of electrical charges and charge trapping/detrapping within dielectrics was conducted by Brazilian physicist Dr. Bernhard Gross in the early 1950's. Dr. Gross confirmed that internal Lichtenberg figures could be created within a number of different polymers and glasses by injecting them with high-energy electrons from a particle accelerator. The techniques that we use to make our modern sculptures are built upon the theoretical work and experimental techniques originally developed by Brasch, Lange, and Gross. 3D acrylic Lichtenberg figures are sometimes called "electron trees" or "beam trees". We call our state-of-the-art creations Captured Lightning® sculptures.





How do we make our Acrylic Captured Lightning® sculptures?

Since 2004, we have developed and refined irradiation and fabrication techniques to create a wide variety of beautiful 2D and 3D sculptures. We begin by carefully cutting and polishing various shapes from a clear, glass-like polymer called polymethyl methacrylate (or PMMA). This material, commonly called acrylic, is sold under various trade names such as Lucite, Plexiglas, or Perspex (UK). Acrylic has a unique combination of high optical clarity and superior electrical and mechanical properties. Besides being an excellent electrical insulator, acrylic is actually clearer than glass! We have tried a number of other clear polymers, such as polycarbonate (PC), polystyrene (PS) , polyester/polyethylene terephthalate (PET), epoxy, and clear polyvinyl chloride (PVC). Lichtenberg figures can be made inside all of these polymers with varying degrees of success. However, the branches tend to be dark gray or even black instead of the sparkling white, mirror-like figures seen within acrylic. We have also experimented with making Lichtenberg figures in glass. However, since glass Lichtenberg figures often explosively shatter upon discharge or, unpredictably, days or even months later , we no longer make them.

We inject electrons into acrylic specimens using a 5 million volt, 150 kW commercial particle accelerator called a Dynamitron. The heart of this device is the accelerator tube - a huge three-story high "vacuum tube" that operates at voltages between one and five million volts. At the top of the tube, electrons are emitted by a small, white-hot tungsten filament. The filament is connected to the negative terminal of an adjustable multi-million volt power supply. The bottom of the tube is connected to ground and the positive terminal of the high voltage supply. This configuration creates a very strong electrical field that accelerates electrons emitted from the filament. As they "fall" though the large potential difference, and they acquire a very high velocity. The bottom of the vacuum tube has very thin (only 2.3 thousandths of an inch thick!) titanium window that separates the high vacuum on the inside from atmospheric air on the outside. The high-velocity electrons pass right through the titanium window, almost as though it wasn't there! Trillions of free electrons emerge through the outside surfac e of the window , travel 24 inches through air then crash into our acrylic specimens on the moving carts below. Although the average lifetime of free electrons in air is only 11 billionths of a second, that's more than enough time for them to work their magic on our acrylic specimens.



The energy of the accelerated electrons is measured in millions of electron volts (or MeV). Most of our sculptures were created using electrons that had energies between 2 and 5 MeV. At these energies, electrons are traveling at relativistic velocities - between 98.5% and 99.6% of the speed of light. During irradiation, these energetic electrons burrow deep inside the acrylic before finally coming to rest. The penetration depth is a function of the energy of the electrons in the beam, the target material's dielectric properties, and its atomic density. The charging process is called "deep dielectric charging". The higher the energy of the electrons in the beam, the deeper they penetrate. For example, electrons with an energy of five MeV will penetrate about one-half inch into acrylic, but a 1/16-inch thick piece of much denser lead will completely block them.



When a thick piece of acrylic is irradiated, huge numbers of electrons accumulate inside the specimen, creating a strongly-charged cloud-like layer called a space charge. Because acrylic is an excellent electrical insulator, injected electrons become temporarily trapped inside the acrylic. By passing thick specimens through the electron beam in two or more passes, changing specimen orientation between passes, or rotating them while they're being irradiated, complex 3-dimensional space charge regions can be created inside the acrylic. As electrons accumulate during irradiation, the electrical stress (called the electric field or "E-field") inside the acrylic dramatically increases, reaching several million volts per centimeter. We normally charge our specimens to just below the point where they'll break down. We then force the charged specimens to release ("discharge") the electrons at the desired location by poking them with a heavily-insulated, pointed metal tool. This creates a small fracture that greatly concentrate s the E-field at that point. The intense electrical field at the tip of the fracture overcomes the dielectric strength of the acrylic, initiating complete electrical breakdown of the specimen. During breakdown, some of the chemical bonds that held acrylic molecules together suddenly break, stripping away free electrons in a process called ionization. The newly-freed electrons become accelerated by the extreme electric field, and as they collide with other molecules, they rapidly create an ever-increasing number of new electrons in an exponentially-growing runaway process called avalanche breakdown.

Within billionths of a second, a tree-like network of white-hot plasma channels form within the acrylic and, w ith a bright flash and a loud BANG, the material undergoes complete dielectric breakdown. The previously-trapped electrical charges rush out in a river-like torrent. Thousands of smaller tributaries dump their share of stored charge into larger channels that eventually merge into a single, brilliant discharge path that exits the acrylic. Although images and videos appear to suggest that we're injecting high voltage into each piece, we are actually removing the excess charges that were previously trapped inside each piece. Dielectric breakdown occurs with incredible speed - the main electrical discharge within a 4-inch square specimen lasts less than 120 billionths of a second (120 nanoseconds)! Some physicists think that dielectric breakdown within a charge-injected solid may be the most energetic (explosive) known chemical reaction.

