Tech Briefs Magazine - May 2024 - PIT-3

Catching Lightning
With Phantom Cameras
High-speed imaging systems support cutting-edge research
to study terrestrial gamma-ray flashes and other upper
atmospheric phenomena.
G
amma-ray emissions - a form of high-energy electromagnetic
radiation - are typically observed either
as radioactive nuclei or high-energy bursts traveling
through space. In 1992, however, a new kind
of gamma-ray source was discovered on Earth.
Found in high-altitude storm clouds, terrestrial gamma-ray
flashes (TGF) occur unpredictably, have energies up to 20
million electron volts and last less than a thousandth of a
second. Exactly how TGFs generate and propagate remains
under investigation, due to their elusive, short-lived nature.
Today, researchers are looking to advance their understanding
of how TGFs work.
Astroparticle Physicist Dr. Rasha Abbasi, an Assistant Professor
in the Department of Physics at Loyola University Chicago,
works with the Telescope Array project. Located west of
Delta, Utah, the project is an international collaboration between
universities to observe high-energy cosmic rays. Abbasi
and her team study how TGFs originate from the Earth's atmosphere
and propagate. In particular, the team hopes to
answer key questions, such as:
* Which part of the lightning flash do TGFs originate from?
* When do TGFs occur during the lifespan of a lightning flash?
* What is the overall behavior of TGFs - from generation to
termination?
As part of their work, the researchers pair their electromagnetic
radiation data with observations of the lightning's
optical emissions. In order to slow down the lightning, they
use a high-speed imaging system to record the lightning
flashes at very high frame rates while other instruments
track other metrics.
Photonics & Imaging Technology, May 2024
Casting a Large Net
Capturing TGF data requires a large, continuously running
experiment. The southwestern Utah desert provides enough
land and open sky for successful upper atmosphere research,
and this is where the Telescope Array project positions its
ground array.
The array consists of 500 scintillator detectors covering over
300 square miles. Each detector is housed within a metal container
roughly the size of a ping-pong table. Within the container
are several layers of acrylic material infused with molecules
that interact with charged particles. When high-energy
particles interact with the acrylic material, these molecules are
excited and emit ultraviolet (UV) light. Optical fibers gather
the UV light and direct it to a photomultiplier tube that converts
the light into an electrical signal. This signal is received,
stored and analyzed by a central computer. While the detectors
were originally designed to analyze high-energy particles from
space, the equipment can detect and analyze gamma-ray flashes
originating from Earth's atmosphere.
In addition to the detectors, this experiment relies on atmospheric
instruments including a lightning mapping array (LMA),
a fast electric field change antenna (FA) and a broadband very
high frequency (VHF) interferometer (INTF) which were installed
by New Mexico Institute of Mining and Technology collaborators
Paul Krehbiel, William Rison, Daniel Rodeheffer and
Mark Stanley. The instruments allow the researchers to study the
complete anatomy of lightning and provide valuable information,
including the lightning's direction, speed, height, relation
to the cloud base and radio emissions. The team's goal is to observe
how a lighting flash's optical and radio wave emissions relate
to the TGF it generates.
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(Image: Adobe Stock/Stephen Coburn)
Tech Briefs Magazine - May 2024

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