This Captured Lightning® sculpture was created by injecting a block
of polished acrylic with a beam of high speed electrons from a 5
million electron volt (MeV) particle accelerator. Electrons were first
injected from the left side. The specimen was then rotated 180 degrees,
and more electrons were injected into the right side. This created two
internal layers of electrical charge, each one located about 1/2" below
the surface. The internal charge layer on the right side was then
manually discharged, creating a miniature "lightning storm" within the
charge layer above. Additional electrical discharges then grew between
the right and left charge layers, forming a beautifully interconnected
3D discharge structure. The
entire discharge event occurred in less than 100 billionths of a second! The
sculpture above is illuminated from below by blue light emitting diodes
(LED's). Each sculpture contains a unique, incredibly detailed, fractal discharge
pattern. Unlike laser art, every sculpture is different. As they
branch, the discharge channels become increasingly finer and hair-like,
ultimately disappearing at the tips. The smallest discharges are
thought to extend to the molecular level. See our Captured Lightning Frequently Asked Questions (FAQ) for a quick overview of how these beautiful objects are created.
(Actual size: 3" x 3" x 2")
What are Lichtenberg figures?
The scientific name for our Captured Lightning® sculptures are "Lichtenberg figures".
Lichtenberg figures are branching, tree-like or fern-like patterns that
are created by high voltage discharges along the surface, or inside,
electrical insulators (dielectrics).
The first Lichtenberg figures were actually 2-dimensional "dust figures"
formed as dust settled on the surface of electrostatically charged
resin plates
in the laboratory of their discoverer, German physicist Georg Christoph Lichtenberg
(1742-1799). Professor Lichtenberg made this observation in the late
1700's, demonstrating the phenomenon to his physics students and peers. He reported his findings in
his memoir: Super nova methodo naturam ac motum fluidi electrici investigandi (Göttinger
Novi Commentarii, Göttingen, 1777). The physical principles involved
in forming these electrostatic figures eventually became the modern science of plasma physics.
Dr.
Lichtenberg used high-voltage electrostatic devices to electrically charge
the surfaces
of various insulating materials such as resin, glass, or ebonite (hard
rubber). He then sprinkled a mixture of finely powdered sulfur and
minium (red lead, or lead tetroxide) onto the surface. The powdered
sulfur (being
slightly negatively-charged through friction) was attracted to the
positively-charged regions while the red lead was preferentially
attracted to the negatively-charged regions. The powders made previously
hidden
regions of trapped surface charge clearly visible. Lichtenberg also
noted
that the shapes of the positively and negatively charged figures were
significantly different. Positive figures tended to be star-like with
long branches, while
negative figures tend to be shorter, rounded, and fan-like. By
carefully pressing a piece of paper onto the dusted surface, he was
able to transfer these images onto the paper, demonstrating what was
later to become the modern process of xerography and laser printing. Some drawings of positive and
negative figures that Lichtenberg created are shown below.
Positive Lichtenberg figure
Negative Lichtenberg figure
Notable 19th and 20th century Lichtenberg figure researchers included physicists Gaston Planté and Peter T. Riess (mid-1850's), French artist and scientist Etienne Leopold Trouvelot, Thomas Burton Kinraide (late 1800's), and professors Carl Edward Magnusson, Maximilien Toepler, P. O. Pedersen, and Arthur Von Hippel
(1920's-30's). Modern researchers often used photographic film to
directly
capture the faint light emitted by the positive or negative high voltage
discharges. An English industrialist and
electricity researcher, Lord William G. Armstrong of Cragside,
published two very beautiful books (now quite scarce!) about his high
voltage and Lichtenberg Figure research. Fortunately, a copy of the
first book, "Electric Movement in Air and Water, with Theoretical Inferences", was recently made available through the kind efforts of Jeff Behary at the Turn of the Century Electrotherapy Museum. In the mid-1920's, Von Hippel discovered that
Lichtenberg figures were actually created through complex interactions
between ionized gas (corona,
or small electrical sparks called streamers) and the
underlying dielectric surface. The discharges deposited matching patterns
of electrical charge onto the dielectric surface below, where they became temporarily stranded. Von Hippel also
discovered that increasing the applied
voltage, or reducing the surrounding gas pressure, caused the length of
the figures to increase.
The
relationship between the length of Lichtenberg figures versus voltage
was utilized to create various high voltage recording instruments, such
as klydonographs. Riess discovered that the diameter of a positive figure
was about 2.8 times the diameter of an equal voltage negative figure. These
properties were used to help measure the peak voltage and polarity of
lightning transients.
Klydonographs photographically recorded the size
and shape of Lichtenberg figures that were created by abnormal surges
on electrical power lines. These, and other similar instruments,
allowed lightning
researchers and power system designers in the 1930's and 1940's to
measure the peak voltage and
polarity of abnormal voltage transients when lightning
struck power lines, thus providing critical
information about the electrical characteristics of lightning strikes.
This information was essential so that power engineers could develop and
test the effectiveness of
various lightning protection approaches. Lightning protection is now a
key element in the design of all modern electrical
transmission and distribution systems. A schematic diagram of the
main parts of a klydonograph is shown on the leftmost drawing below, along with
examples of "klydonograms" from equal magnitude positive and negative
high voltage transients.
Schematic view of a klydonograph showing the position of the
photographic film and high voltage electrode. Light from the high
voltage discharges creates a photographic record of the event.
From W.W. Lewis, "The Protection of Transmission Systems
Against Lightning", John Wiley & Sons, 1950
Lichtenberg figures are now known to occur during electrical breakdown processes
within most gases, insulating liquids, and solid dielectrics. Lichtenberg figures may be created very quickly (tens of nanoseconds) when dielectrics are heavily overstressed, or they can grow very slowly, through a progressive series of low-energy partial discharges, evolving into partially conductive surface patterns or 3D "electrical trees".
Electrical
trees often form on the surface of contaminated insulators. They can also form within
dielectrics due to internal defects or voids, or at points where an
insulator has been physically damaged. Since they eventually cause complete electrical failure of the insulator, preventing
their formation and growth is critical to the long-term reliability of
high voltage equipment.
3D Lichtenberg figures were first created inside transparent plastic by physicists Arno Brasch and Fritz Lange in the late 1940's. By using their newly-invented particle accelerator, they injected electrons inside plastic specimens, causing electrical breakdown and the formation of internal Lichtenberg figures. Electrons
are tiny, negatively charged particles that orbit the nucleus of the atoms that make up all condensed matter. At
their laboratory at AEG (Berlin, Germany), they used high voltage pulses from a 2.4 million volt Marx Generator
to drive a pulsed electron beam accelerator. An
article about their research and their accelerator (which they called a
"Capacitron") appeared in the March 10, 1947 issue of LIFE Magazine.
The Capacitron could deliver a 3 million volt pulse, and could generate a powerful beam of electrons with a peak current of
up to 100,000 amperes! The glowing region of ionized air created by the high-current
beam of electrons resembled a bluish-violet rocket engine flame. A complete set of previously unpublished 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.
Formal
scientific study of the behavior of charge storage and movement
within dielectrics was first conducted by the Brazilian physicist, Dr.
Bernhard Gross, in the early 1950's. Dr. Gross confirmed that internal Lichtenberg figures could be created within a variety of polymers and glasses by injecting them with high-energy electrons using a linear accelerator (LINAC).
The techniques that we use to make our sculptures build upon
the theoretical work and techniques originally developed by Gross,
Brasch, and Lange. These 3D Lichtenberg figures are sometimes
called electrical
trees, electron trees, or beam trees - we call oursCaptured Lightning® sculptures.
How do we make our Captured Lightning® sculptures?
Over many years, we have refined irradiation and fabrication
techniques to create a variety of beautiful 2D and 3D
sculptures.
We start with carefully cut and polished shapes made from a clear polymer, polymethyl methacrylate (or PMMA).
This material, commonly known as "acrylic", is sold under various trade names such as
Lucite, Plexiglas, or Perspex. PMMA has a unique combination of high optical clarity and superior electrical
and mechanical properties. And, it's actually clearer than glass! A number of other clear polymers, such as polycarbonate
(PC), polystyrene (PS) , polyethylene terephthalate (PET), and polyvinyl
chloride (PVC) can also be used to make Lichtenberg figures with varying degrees of success. However, most of
these other materials form darker gray or black discharge patterns instead of the sparkling,
mirror-like figures seen within PMMA.
We inject electrons into these specimens using a four-story high, 150 kW machine called a Dynamitron. The
heart of this device is the accelerator tube - a huge
evacuated
"vacuum tube". Electrons
are emitted by a glowing tungsten filament at the top of the tube. The
filament is also connected to the negative terminal of a multi-million volt power supply, while
the other end of the tube is connected to ground. The resulting high voltage electrical
field accelerates electrons from the filament to a very
high velocity as they "fall" though the large potential difference.
The energy of the
electrons exiting the accelerator is measured in millions of electron volts (or MeV). Most of our specimens were created using electrons with energies of 2 - 5 MeV. At these energies, the electrons are traveling at relativistic velocities - between 98.5% and 99.6% of the speed of light. When irradiated
by relativistic electrons, the electrons are driven deep inside the
acrylic before coming to a stop. The depth of penetration is
determined by the energy of the electron beam, the target material's
dielectric properties, and its atomic density.
The higher the energy of the electron beam, the deeper the electrons
can penetrate. Electrons with an energy of five MeV penetrate about 1/2 inch into PMMA.
As a specimen is irradiated, huge numbers of electrons accumulate inside, creating a strongly-charged cloud-like
layer called a space charge.
Since PMMA is an excellent electrical insulator, the injected electrons become trapped deep inside the specimens. By passing
specimens through the electron beam in two or more passes, or by rotating
specimens while they're being
irradiated, complex 3-dimensional regions of space charge can be created.
Under continued irradiation, the internal electrical field increases dramatically. Eventually, the immense electrical stress overcomes the
dielectric strength of the acrylic, causing some of the chemical
bonds that hold the acrylic molecules together to break, stripping away free electrons in a process
called ionization.
Newly-freed electrons are also accelerated by the
electric field, and these collide with, and ionize, even more acrylic molecules in a runaway process called avalanche breakdown.
Within
billionths of a second, a network of thin, electrically-conductive channels form within
the acrylic and, with a brilliant flash and a loud BANG, the
material abruptly undergoes dielectric breakdown.
As breakdown occurs, previously trapped charges suddenly rush out
of the specimen, and thousands of electrically conductive branches feed
their current into the main channel of a miniature "lightning
bolt" that exits the acrylic. Although this "Tree of Fire" discharge may
look as though we're injecting high
voltage into the block, we are actually removing excess
charge that was previously trapped inside. Dielectric
breakdown occurs with incredible speed - the main electrical discharge
within a 4 inch square specimen lasts for less than 120
billionths of a second! Dielectric breakdown within a solid is thought
to be the most energetic (explosive) chemical reaction known, vastly exceeding
that of high explosives. The following image shows a 12 x 12 x 1 inch
specimen being discharged. A neutral density filter was used to reduce
the brilliance of the discharge so that the individual paths could be
captured by the camera. Note the bright high current discharge
jumping downward and along the top surface of the specimen to the grounded metal worktable below:
(Photo courtesy of Terry Blake)
As the
miniature
lightning bolts blast their way through the acrylic, they create millions of microscopic tubes and fractures,
leaving behind a permanent "lightning fossil". The peak current
within the electrical discharge can reach hundreds, or even thousands of
amperes depending upon the size of the specimen. The hot plasma within
the discharge causes the acrylic to melt and fracture along each path,
and higher
current "roots" may lightly char the surrounding acrylic to a caramel color. The exit point of the
discharge appears as a small crater on the surface. A specimen may "self discharge" while being irradiated due to a surface
imperfection or an internal defect. We can also manually trigger a discharge by creating a point of external mechanical stress
that weakens the dielectric. The defect concentrates
the electrical field, creating a small region where the dielectric breakdown process
can begin. Surprisingly, although we inject a huge amount of negative charge into our
specimens, the electrical breakdown originates from points which
are more electrically positive (versus the space charge layer), so our
Captured Lightning® sculptures are
actually "positive" Lichtenberg figures! Captured Lightning sculptures are completely
safe - they have been completely discharged and they have no trace
of radioactivity or X-rays.
Video of huge 15 x 20 x 2 inch figure being discharged: Following is a
video clip showing a huge 15" x 20" x 2" specimen being discharged during our November, 2010 production run.
This specimen was first charged on one side by a 5 MeV electron beam.
The electrically-charged specimen was then (very carefully!) flipped over to expose the other side and irradiated
once again. This created two internal charge planes, each located about
1/2" below the large surfaces. Prior to discharging,
the estimated potential of these internal charge
planes was about 2.6 million volts. Because of the two charge planes
and its large size, this specimen had considerably more
stored electrostatic energy (over 4,000 Joules) than most of our other
specimens. The discharge was quite loud and extremely
bright, and safety precautions were necessary to prevent the
possibility of being accidentally jolted by a potentially dangerous electrical shock.
Unfortunately, because the main discharge was so quick (under 500
billionths of a second!), the video fails to capture the full brilliance of the flash. Numerous
secondary discharges continued to flash after
the main discharge, continuing sporadically for over 30
minutes afterward. This video is courtesy of Bill Hathaway, GCL Laboratories.
A
similar specimen, cradled within its custom walnut light base and
illuminated by an array of white and blue LED's, is shown below.
(Click on above image for high-resolution image)
The rounded, crystalline flakes that make up the Lichtenberg Figure are actually chains of hollow tubes and tiny conchoidal
(shell-shaped) fractures. Conchoidal fractures are characteristic of the way glassy (amorphous) materials
fracture when stressed beyond their breaking point. The countless
fractures behave as tiny mirrors, so illuminating a
figure through an edge causes the entire Lichtenberg figure to glow brilliantly
with the reflected colors of the external light sources.
Lichtenberg figures are fractals
Lichtenberg figures exhibit branching patterns which look
similar at various scales of magnification. This self-similar property
suggests that Lichtenberg figures might be mathematically described through a branch of mathematics called Fractal Geometry.
Fractal objects do not have integral (2D or 3D) dimensions, but
instead have fractional dimensions. Regularly-branched 2D Lichtenberg figures typically have a fractal
dimension ranging between 1.5 (for thin, sparse discharges) to 1.9 for very dense discharges. The appearance of Lichtenberg figures depends upon
how much charge was injected into the acrylic and when the
specimens are discharged. Branched figures (technically called
"dendritic", arborescent, or tree-like). If a large amount of electrical charge is injected into the specimens, very dense
dendritic discharges are
created (see Figure 1 below).
These dense discharges are similar in appearance to fern fronds
("filiciform") or moss agate. Specimens exhibiting this form were
charged to just below the point of self-breakdown and immediately
discharged. If the level of
electrical charge is reduced, more classical, lightning-like or
tree-like discharges are created (Figure 2). If premature breakdown
occurs while we are
actively irradiating a specimen, a densely tangled mat of "chaotic"
discharges occurs (Figure 3). After the first discharge, electrons
continue to be injected from the beam, causing previously discharged
regions to recharge. This causes smaller secondary discharges to head in
random directions from existing discharge channels. This results in a
chaotic tangle of discharges that are reminiscent of
interconnected nerve cells and neural networks. Some specimens contain a fascinating and complex combination of both patterns.
Figure 3. Chaotic Discharges
(prematurely discharged
while being irradiated)
Self-similarity can easily be seen in the following sequence of zooms
from a 12" x 12" Lichtenberg Figure with typical dendritic discharges.
The branches become finer and
hairlike, ultimately disappearing.
Similar
fractal patterns are prevalent in nature. They're often seen in
aerial views of rivers and their tributaries, and organic structures
such as branching tree
limbs, your body's circulatory system, and lung tissue. The satellite
view below shows the fractal pattern of a river drainage system near
Grand Junction, Colorado, USA. The right image is a casting of the
bronchial tree of a human lung (courtesy Paul Cazeaux, PhD student at
Laboratoire Jacques-Louis Lions (LJLL), Paris, France).
Lichtenberg figures were first modeled using a process called "Diffusion Limited Aggregation" (DLA). An enhanced model that combines an electric field with DLA is called the Dielectric Breakdown Model (DBM).
The DBM appears to fairly accurately describe the macroscopic branching
forms of electrical breakdown that occur within solid, liquid, and
gaseous insulators.
Solarization, fluorescence, birefringence, dead zone
When acrylic is irradiated by high-energy electrons, it glows brightly with a blue-white
color. Radiation chemistry studies suggest that this may be primarily luminescence (peaking at a wavelength of 435 nm), with some fainter x-ray fluorescence, and Cherenkov radiation.
However, the precise light-producing mechanisms are not completely
understood. You may also notice a discharge-free "dead zone" along all
of the outside edges. Because
acrylic is not a perfect insulator, some of the internal charge "leaks
away" along all the edges. Leakage is highest in the region
between the edge of the space charge region and the perimeter of each
specimen. In this region, the stored charge decreases to the point
where the electrical field is no longer high enough to break down the
acrylic, and the result is a discharge-free zone along the perimeter.
Newly-irradiated specimens often have an amber-colored layer. Called solarization, it is thought to be caused by defects that were created by energetic electron
collisions and high energy x-rays, and by temporarily trapped electrons within the molecular structure of
the acrylic. Solarization occurs in the region between any surface that was
irradiated by the electron beam and the discharge layer. During irradiation, electrons are initially traveling at
about 99% of the speed of light. As they penetrate the specimen, they collide with the acrylic molecules, rapidly coming to a stop within a fraction
of an inch. The electrons in the beam have a tremendous
amount of kinetic energy, and as they suddenly brake to a stop,
they release this energy in the form of heat and powerful X-radiation.
The trapped electrons and x-rays stimulate chemical and physical reactions that alter the physical and optical
properties of the acrylic. Some of these changes are temporary, while others appear to be longer-lived or permanent. Although
the specific causes of solarization are not completely understood, there
is evidence that irradiation creates unstable, longer-lived
"metastable" compounds that preferentially absorb light at the blue end of
the spectrum (250 - 400 nm). This causes portions of the acrylic to turn a green, brown, or amber color.Some electrons may remain trapped for months, or even years, creating color centers which also contribute to solarization.
Most
specimens initially turn a beautiful lime green color immediately after
irradiation. This fades to an amber color over a few minutes to a few
hours, and the residual solarized region may
take months, or even years, to eventually fade away.
Fading
can usually be accelerated by gently heating the block in the
presence of oxygen, or by leaving the specimen in sunlight for an
extended period of time. It has also been determined that atmospheric
oxygen plays a role in the fading process. As oxygen diffuses into the
acrylic from the outside surfaces and the discharge layer, it slowly bleaches the
solarized region, causing the solarized layer to gradually become thinner and thinner,
until it eventually disappears. Most older Lichtenberg figures are completely bleached.
Although older specimens no longer show any solarization, some specimens may show slight
residual "fogging" due to permanent radiation damage in the acrylic. Some
specimens exhibit little initial solarization, while a small number of specimens permanently retain
their amber color. We recently discovered that fully-charged specimens retain their green color and stored electrical charge
indefinitely when kept at dry ice temperatures. This suggests that the initial green color may be mainly due
to a high density of trapped charge. If these specimens are then discharged weeks
or months later, they quickly change to the longer-term amber color. Clearly,
a number of different processes appear to be associated with solarization.
Recently, it has also been discovered that the solarization layer is often fluorescent.
An amateur scientist from Australia, Daniel Rutter, discovered that monochromatic light from a green laser pointer changes color
when passed through the solarized layer of a Lichtenberg figure. More
recently, we have discovered that the light from a near-ultraviolet
source (such as a Blu-ray laser or even bright blue LED's) may also cause
the solarized region to glow with a brilliant yellow-green
fluorescence. This occurs on some specimens but not others, and as the
solarization fades over time, so does the fluorescence.
Most specimens also exhibit
slight changes in the refractive index in the regions near the discharge layer. This is
thought to be due to residual mechanical stresses near the discharge fractures. Residual
stresses near the Lichtenberg figures can easily be seen as
multicolored regions near the discharge plane when a sculpture is illuminated by polarized
light and then viewed through a second polarizing filter (crossed
polarizers). When physically stressed, acrylic exhibits a property called birefringence.
When viewed through cross polarizers, stress-induced
birefringence causes changes in color that are directly related to the
amount and distribution of otherwise hidden stresses. A charged specimen
clearly shows internal stresses created by the high electrical field -
these stresses are then relieved when the specimen is discharged.
Discharge current measurements... and a paradox During our 2007 and 2009 production runs, we measured and recorded discharge
current waveforms for a number of 4" x 4" x 3/4" specimens. We designed a special holding
fixture with copper foil plates that made physical contact
with the large surfaces of a charged acrylic specimen. A heavily insulated wire connected the pair
of foil plates to a pointed discharge tool, and this wire was also passed
through the center of a wideband Current Transformer (CT). When the
specimen was discharged, the main current pulse flowed through the wire
and was measured via the CT. The CT
transformed the discharge current pulse
that flowed through the wire into a voltage pulse that could then be
captured and stored within a high speed
Tektronix digital storage oscilloscope. One of the digitized waveforms
is shown below. We found that, for this 4" x 4" specimen, the discharge
lasted for less than 120 billionths of a second (120 ns), the
peak current reached almost 600 amperes, and the waveform contained
four discrete current peaks. Other specimens showed between three and seven
current peaks.
This
suggests that propagating electrical trees may progress via a series of
advancing breakdown waves. Each current peak may reflect a surge of newly
conducting channels ("streamers" and "leaders") as they tap into new sources of stored charge. Newer channels
apparently blast their way into previously untapped reservoirs of
charge within the acrylic, pause briefly, then surge again, etc. The
average discharge velocity was between 8.5 x 105 and
1.3 x 106 meters/second (526 and 790 miles/second, or around 0.3% the speed of
light). However, pauses between successive current surges suggest that the peak discharge
velocity during propagating phases was significantly faster. Surprisingly,
the average velocity within the specimen was actually 10-100 times faster
than the velocity of positive lightning leaders in air. This is thought to be
due to the extremely high electrical field (estimated to be in the range of 10 - 20+
million volts/cm) at the tips of the propagating discharges within the
acrylic.
However,
these high streamer velocities create a paradox, since they are over 800 times the speed of
sound within PMMA. This is completely inconsistent with Griffith's theory of crack propagation within solids,
which predicts that the maximum speed that cracks can propagate within a solid
is limited to the speed of sound within the material, or about 1.6 x 103
meters/second for PMMA. The current waveform
clearly demonstrates that the breakdown process (the complete formation
of chains of cracks
and gas channels across the specimen) for our Lichtenberg
figures propagates at speeds that are almost 1000 times
FASTER than the maximum predicted by classical materials
theory! A series of electro-optical measurements were recently taken by
Dr. Timothy Koeth in his laboratory at the University of Maryland. Dr.
Koeth measured the time delay
between optical (light) emissions at the beginning and ends of
propagating discharges within 6" x 6" x 1" specimens. His measurements
confirmed similar streamer velocities that ranged between 7.4 x 105 and 1.55 x 106 m/s.
Some insights into this paradox come from a Russian
researcher, Yu N. Vershinin. Dr. Vershinin
explored electrostatic energy storage and release within solid
dielectrics. Specifically, he studied how energy is stored within
acrylic when charge is slowly injected (called "charge trapping") and
the effects of then rapidly releasing it ("charge detrapping") when the
dielectric undergoes electrical breakdown. Vershinin proposed
that, when a dielectric contains significant trapped space charge,
the electrostatic potential energy stored within the material is rapidly liberated, contributing to
explosive formation and growth of crack tips. As chemical bonds in the surrounding material are ruptured,
high pressure gases are liberated, expanding the channels behind the
propagating crack tips. Vershinin speculated (and experimentally
confirmed) that for very high internal electrical fields (E-fields), the potential
energy initially stored within the E-field was rapidly converted into
kinetic and thermal energy that drove crack
propagation at hypersonic velocities.
Vershinin found that this occurred only for propagating positive
discharges within highly divergent E-fields. American researcher Paul
Budenstein has developed a theory of dielectric breakdown in solids that
seems to explain many of the observations. Based upon the rate of
channel expansion, Budenstein concludes that dielectric breakdown is the
most rapid chemical reaction in nature.
Electronic
detonation is hundreds of times faster than the detonation waves that propagate through even the fastest chemical explosives!
Vershinin termed the explosive breakdown process
"electronic detonation" since it was similar to the way that chemical
reaction waves (shock waves) supersonically propagate through a high
explosive as it detonates. Because of the large amount of electrostatic energy stored within our
specimens, and the extremely short discharge intervals, the
instantaneous power liberated during a Captured Lightning discharge can
exceed a gigawatt (109 watts)! Not surprisingly, the discharge creates
a loud BANG(!), and the brilliant, blue-white
lightning-like spark channels wreak considerable havoc inside the acrylic as they blast
countless permanent fractures and tubes along the space charge
layers. Charge detrapping is now known to play a very important role in the degradation
and breakdown of solid dielectrics that are subjected to long-term high voltage
stresses, sudden voltage changes, or abrupt polarity reversals. In some
respects, sudden charge detrapping in a solid dielectric is similar
to a high-voltage capacitor discharge that occurs solely within the insulating material.
After we discharge a specimen, hundreds of smaller
secondary electrical discharges continue to occur throughout the
specimen as small pockets of residual stranded charge redistribute
themselves. Large figures sparkle and sizzle, making a sound similar to
frying bacon, and intermittent sparking has been seen over 30 minutes after the main discharge.
Harmless secondary discharges often sting our fingers when we handle
recently-discharged specimens. Click on the following image to see some high
resolution video captured during one of our production runs that shows
primary and secondary
discharges.
(Photo and video courtesy of Mike Walker and Theodore Gray) Click on the Above image to see a video clip
of many Lichtenberg figures being discharged
Natural Lichtenberg figures - fulgurites and lightning tattoos
Occasionally, nature creates "fossilized lightning", called fulgurites. These
are hollow, glass-lined tubes that are formed when the powerful
electrical
current from a lightning strike creates underground discharge channels within poorly-conducting sandy or sandy-clay soils. The intensely hot channels from the lightning arc fuse the surrounding sand
and soil particles to form glassy tubes. Some
fulgurites also exhibit fractal characteristics as they split into
smaller diameter root-like branches at further distances from the site
of the main strike.
Lichtenberg figures, sometimes called "lightning flowers" or "skin feathering", sometimes form
beneath the skin of unfortunate humans who have been struck by lightning. The victim often has one
or more reddish radiating feathery patterns that branch outward from
the entry
and
exit points of the strike:
OUCH! A temporary lightning tattoo on a "lucky" survivor
From "Lichtenberg Figures Due to a Lightning Strike" by Yves Domart, MD, and Emmanuel Garet, MD,
New England Journal of Medicine, Volume 343:1536, November 23, 2000
Medical terms for this phenomenon include arborescent lightning burn, arborescent
(tree-like) erythema, keraunographic markings, or ferning
patterns. Although the exact causes are subject to
some debate, they appear to be the result
of physical damage to capillaries under the skin, perhaps caused
by the flow of electrical current, or by shock wave bruising from external
flashovers just above
the skin. These reddish marks fade away over a
period of hours or days. They are recognized by forensic pathologists as clear evidence
that a victim has been struck by lightning. The patient above survived
with no permanent injuries, and the lightning flowers completely faded
within two days. A small Lichtenberg figure
has also been observed at the entry point
where a high voltage spark penetrated the skin of an unfortunate (but
surviving) local electrical experimenter who was accidentally zapped by a
homemade 60,000 volt Marx Generator. No... it wasn't me!
A similar phenomenon is sometimes seen when lightning
hits a grassy field, as in this picture where lightning struck a
flagpole, leaving this beautiful 25 foot Lichtenberg figure on the
green of a golf course:
(From "Lightning and Lichtenberg Figures" by Cherington, Olson and Yarnell, Injury, Volume 34, Issue 5, May 2003)
Note the similarity between the figure above and the Lichtenberg figure below (illuminated by blue LED's):
High voltage discharges to the surface of water can also create Lichtenberg figures. Some very beautiful examples
of
both positive and negative Lichtenberg figures on water surfaces can be seen on Dr. Colin
Pounder's Lichtenberg figures web site.
Natural lightning sometimes creates transient "Lichtenberg figures" in the sky. Air is an excellent dielectric and, although the physical breakdown
mechanisms for air and PMMA are considerably different, the appearance of the
branching discharges is quite similar. So it should not be surprising that the branching forms of lightning also have fractal
characteristics. This similarity can clearly be observed during "anvil crawler" and horizontal "spider lightning".
Spider lightning follows a thin, positively charged cloud layer, and the
slowly propagating discharges can crawl across the sky for 30-40 miles
- literally spanning from horizon to horizon. On a much smaller scale, transient Lichtenberg figures
(sometimes mistakenly called St. Elmo's Fire) often appear on the outer
surface of cockpit windows of airplanes as they fly within
thunderstorms.
Similar
branching fractal patterns also occur when thunderstorms generate electrically conductive leaders that
propagate downward from a charged cloud to the ground below. When one
of these leaders connects with an unfortunate object on the ground, a high current pulse (called the return stroke) surges back upward through the completed path, resulting in a Cloud-to-Ground (CG) lightning
strike.
Exceptional examples of downward propagating positive leaders have been captured by South Dakota lightning
researcher, Tom Warner. Using high speed video imaging equipment, he
was able to capture the downward progression of leaders and the return
stroke from a positive lightning bolt. Positive lightning
is a significantly rarer, and considerably more dangerous, form of lightning than negative lightning. The
"slow motion" video (below) shows the air breaking down, forming
glowing conductive plasma paths (called leaders) that fan
downward from the huge reserve of positive charge within the cloud
above. The brightly glowing tips of the positive leaders smoothly propagate,
unlike negative leaders which propagate in a series of discrete jumps (called stepped leaders). The
first descending leader to finally connect with the Earth below
completes the circuit, resulting in a powerful Positive Cloud-to-Ground (+CG) lightning discharge.
The video clip
below was captured at 7200 frames/second (FPS), and the actual elapsed
time for the clip was only a little longer than three thousandths of a
second. The speed of the propagating leaders was between
3 x 104 and 6.5 x 105 meters/second. This clip even contains a single frame
which captures the beginning of the return stroke from the Earth going
back up one of the leader channels. Even at the majestic scale
of natural lightning, you can clearly see similarities between the
collection of branching leaders and Lichtenberg figures.
Positive lightning also has a very long lasting "tail" of
follow-through current which typically lasts for several hundred milliseconds after the initial strike
connects to ground. The combination of long propagation distance (often
many miles from the main storm), very high current (up to 300,000
amperes), and long follow-through current make positive lightning
exceptionally dangerous. It tends to set fire or kill anything, or
anyone, unfortunate enough to be in its path. More of Tom Warner's
fascinating videos can be seen on his YouTube page.
Lichtenberg figures can also be seen at some high energy pulsed
power facilities, especially where deionized water is used as a dielectric to briefly store
large amounts of electrical energy. The photo below is from Sandia National Laboratory's mighty Z
Machine, the world's most powerful electrical pulse generator. After
the completion of a high energy experiment, the water breaks down from the huge electrical stress,
becoming an electrical conductor that safely dissipates unwanted
residual energy from the system. The filamentary breakdown paths form Lichtenberg figures that dance across
the water's surface. If you look closely, you'll notice that many of the paths actually trace out high voltage
electrical field lines along the surface of the water. Although impressive, this display is only dissipating "left over" energy,
representing only a very small fraction (perhaps 5%) of the energy that was
actually used during the previous pulsed power experiment.
(Click for a higher resolution 840 x 554 pixel image)
Are there any practical uses for Lichtenberg figures? Analysis
of the form and origination points of Lichtenberg figures is a powerful
tool
for diagnosing, and subsequently preventing, high voltage breakdown of
solid dielectrics. By examining these figures, experts can diagnose and
prevent future electrical faults within a variety of devices, such as
high voltage transformers,
capacitors, and insulators used by electrical utilities. Historically,
Lichtenberg figures were a powerful tool for measuring the polarity and
magnitude of transient overvoltages on power lines during direct and
indirect
lightning strikes. These early measurements were critical for the
development of
reliable electrical power transmission and distribution systems.
Lichtenberg figures are still used as a forensic clue for identifying
the cause of
injury or death of human and animal lightning victims. Recent studies
of Lichtenberg figures and charge detrapping in polymers are revealing
important details on the mechanisms that are involved in the
degradation and electrical breakdown of solid insulating materials.
There may be future medical applications as well. In 2009, a team of researchers at Texas A&M University proposed using
3D Lichtenberg figures created within various polymeric materials as
"templates" for growing blood vessels (vascular tissue).
There are significant similarities between branching Lichtenberg
figures and animal circulatory systems - a fact not lost on many
medical researchers. The hope is that, by creating branching 3D
Lichtenberg figures inside a biodegradable polymer, such as polylactic
acid (PLA), scientists can then use these as "molds" to support the development and growth of vascular tissue. Vascularization
is essential for growing functional replacement tissues and organs. It's possible that the 18th century technology
of Lichtenberg figures may ultimately play a critical role in organ growth and replacement
therapy during the 21st century!
Captured Lightning Sculptures - fossilized lightning bolts
Captured
Lightning® is indeed an accurate description for our sculptures. Holding a Captured Lightning sculpture is about the closest
you can
come to holding a fossilized lightning bolt. As with snowflakes, every Lichtenberg Figure is unique - a one-of-a
kind treasure, sculpted in exquisite detail by the same forces contained within natural lightning.
Two
dimensional photos cannot begin to capture the beauty and exquisite detail of our 3D
sculptures. Following are a pair of 3-D images that can be rotated 360
degrees so that you can more fully
appreciate the detail within some of our doubly-irradiated sculptures. Once the images have been completely
downloaded, you can drag your mouse over the image to rotate each for a full 360
degree view. [Note: because of the large image size, a high speed Internet connection is recommended].
3D Rotatable Image
3D Rotatable Image
"Heavy Weather"
(Courtesy of Theodore Gray)
"Windblown Lightning"
(Courtesy of Theodore Gray)
Very
few
people have actually seen
or held one of these rare objects. Far fewer have had the
opportunity to own sculptures as beautiful and spectacular as these.
Stoneridge Engineering is proud to be the world's most experienced
provider of these rare
treasures.
Can I make my own Lichtenberg Figures?
Unfortunately,
a multimillion-volt electron accelerator is required to make 3D
Captured
Lightning sculptures inside acrylic. However, 2D Lichtenberg figures can
be made on the surfaces of some materials, such as carbonized
Lichtenberg figures on wood, or as dust figures on the surfaces of some
plastics. For
carbonized figures, a high voltage (HV) power source, such as an
ignition
coil or
neon sign transformer, is required. The experiment should be done
outside since it generates a significant amount of smoke and some small
flames. Two nails are
pounded into the wood with a gap of 4 - 10 inches. The
wood surface is lightly sprayed with saltwater to make it
semiconducting, and the high voltage source carefully connected across
the two nails. When high voltage is applied, carbonized
paths begin to form near the nails. Accompanied by lots of smoke and
even small flames,
they begin branching as they grow towards each other. The branches head
in various directions, but generally towards the opposite nail. They
eventually form carbonized Lichtenberg Figures with "roots" at each
nail. This technique must be done VERY
carefully, since dangerous high voltages and water are being used
together. A
method to adjust the voltage (a variable autotransformer or Variac)
helps to control the discharge process and will improve the shape of the
resulting figure. The following video
clip shows this technique using a 9,000 volt 30 mA neon sign
transformer as the HV source:
How can I get a Captured Lightning sculpture of my very own?
We
offer a wide selection of Captured Lightning sculptures that range in size from
affordable 2 x 2 inch specimens through museum quality two inch thick blocks as large as 15 inches by 20 inches. Please visit Gallery 1 or Gallery 2
to select a sculpture at the right price for you. We also offer
a wide variety of lighted bases with white, blue, and multi-color
color changing options. Many of these are available with UK, Australian,
or EC power options. Our light bases illuminate the
delicate patterns within, causing the discharge channels to glow so that the finest
hair-like details become visible. We also offer a variety of factory 2nd sculptures priced at a very attractive 50% discount. And, be sure to visit our Eye Candy page to see some of the best work done by us and some of our very talented friends.
Everyone is a genius at least once a year.
The real geniuses simply have their bright ideas closer together.
– G.C. Lichtenberg
Thunder is good; thunder is impressive. But it is the
lightning that does the work. - Mark Twain
References and Further Reading: 1. Gross, Bernard, "Irradiation Effects in Plexiglas", Journal of Polymer Science, Volume 27, 1958, Issue 115, Pages 135 - 143 2.
Hashishes. Yuzo, "Two Hundred Years of Lichtenberg Figures", Journal of
Electrostatics, Volume 6, Issue 1 , February 1979, Pages 1-13
3. Chadwick, K. H., "The Effect of Light Exposure on the Optical
Density of Irradiated Clear Polymethylmethacrylate", 1972 Phys. Med.
Biol. 17, Pages 88-93 4.
Chadwick, K. H., and Leenhouts, H. P., "Fading of
radiation-induced optical density in polymethylmethacrylate on oxygen
diffusion", Phys. Med. Biol. 15 No 4 (October, 1970), Pages 743-744
5. L. Niemeyer, L. Pietronero*, and H. J. Wiesmann, "Fractal Dimension
of Dielectric Breakdown", Phys. Rev. Lett. 52, Pages 1033–1036 (1984) 6.
Gardner, Donald G., et. al., "Radiation-induced changes in the index of
refraction, density, and dielectric constant of poly(methyl
methacrylate)", Journal of Applied Polymer Science, Volume 11, Issue 7,
July 1967, Pages 1065-1078 7.
Akishin, A.A.; Tseplyaev, L.I., "Edge effect in radiation-charge
dielectric materials", Physics and Chemistry of Materials Treatment, v
31, n 1, Jan.-Feb. 1997, p 30-1. A similar paper is also contained
within the book "Effects of Space Conditions on Materials", Akishin, A.
I., Nova Science Publishers, 2001, ISBN 1590330285
8. Fothergill, J.C.; Dissado, L.A.; Sweeney, P.J.J., "A
discharge-avalanche theory for the propagation of electrical trees. A
physical basis for their voltage dependence", Dielectrics and
Electrical Insulation, IEEE Transactions on, Volume 1, Issue 3 , June
1994, Pages 474 - 486
9. R. A. Galloway, T. F. Lisanti and M. R. Cleland, "A new 5 MeV –300
kW Dynamitron for radiation processing", Radiation Physics and
Chemistry, Volume 71, Issues 1-2, September-October 2004, Pages 551-553
10. Sessler, G.M.. "Charge distribution and transport in polymers",
IEEE Transactions on Dielectrics and Electrical Insulation, Volume 4 ,
Issue 5 , Oct. 1997
Pages 614 - 628 11. Karczmarczuk, Jerzy, "Dendrites in Nature and in Computer", Foton 84/SPECIAL ISSUE, Spring 2006 12.
C.
M. Foust, General Electric Review: Instruments for Lightning
Measurements (Includes Klydonograph and Lichtenberg Figures), Volume
34, #4, April, 1931, Pages 235-246
13. Watson, Alan and Dow, Julian, "Emission Processes Accompanying
Megavolt Electron Irradiation of Dielectrics", Journal of Applied
Physics, December 1968, Volume 39, Issue 13, pages 5935-5940
14. Fujimori, S., "Fractal properties of breakdowns", Properties and
Applications of Dielectric Materials, 1988. Proceedings, Second
International Conference on Properties and Applications of, 12-16
Sept. 1988, Volume 2, Pages 519 - 522
15. Domart, Yves, M. D., Garet, Emmanuel, M.D., "Lichtenberg Figures
Due to a Lightning Strike", New England Journal of Medicine, Volume
343:1536, November 23, 2000, Number 21, Images in Clinical Medicine
16. H. Hiraoka, "Radiation Chemistry of Poly(methacrylates)", Radiation Chemistry, March 1977, pages 121-130
17. Brown, R. G., "Time and Temperature Dependence of Irradiation
Effects in Solid Dielectrics", Journal of Applied Physics,
September 1967, Volume 38, Issue 10, pages 3904-3907
18. Yu. S. Deev, M. S. Kruglyi, V. K. Lyapidevskii and V. I. Serenkov,
"Mechanism underlying the formation of dendritic or tree-like channels
in a dielectric irradiated with charged particles", Atomic
Energy, Volume 29, Number 4, October, 1970, pages 1037-1040
19. Ebert, Ute and
Arrayas, Manuel, "Pattern Formation in Electric Discharges", p. 270 -
282 in: Coherent Structures in Complex Systems, eds.: D. Reguera et
al., Lecture Notes in Physics 567 (Springer, Berlin 2001)
20. Yu.N.
Vershinin, S.V. Barakhvostov, "Electron Processes in the Pulse
Breakdown of Solid Dielectrics", 3rd International Conference on
“Technical and Physical Problems in Power Engineering”, (TPE-2006), May
29-31, 2006 - Gazi University, Ankara, Turkey (covers detonation theory of high field breakdown in solid dielectrics) 21.
Vershinin, Yu. N., "Parameters of Electronic Detonation in Solid
Dielectrics", Technical Physics, Vol. 47, No. 12, 2002, pages 1524–1528.
Translated from Zhurnal TekhnicheskoÏ Fiziki, Vol. 72, No. 12,
2002, pp. 39–43, ISSN: 10637842
22. Budenstein, P.P., "Dielectric Breakdown in Solids", Technical Report
RG-75-25, US Army Missile Command, December 20, 1974, DTIC accession
#ADA012177
23. C. M. Cooke, E. R. Williams and K. A. Wright, "Space Charge
Stimulated Growth of Electrical Trees", Proc. Intl Conf on Properties
and Applications of Dielectric Materials, Xian, China, 1985, Pages 1-6 24. N, I, Kuskova, "Spark Discharges in Condensed Media", Technical Physics, Volume 46, Number 2, 2001, pages 182-185
25. Theodore Gray, "Theo Gray's Mad Science: Experiments You Can Do At Home - But Probably Shouldn't", Black Dog & Leventhal Publishers, 2009, ISBN 978-1579127916
26. Jen-Huang Huang, Jeongyun Kim, et al, "Rapid Fabrication of
Bio-inspired 3D Microfluidic Vascular Networks", Journal of Advanced
Materials, Volume 21,Issue 35, pages 1-5, DOI: 10.1002/adma.200900584
