Thunderstorms as Nature's Particle Accelerators

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The global particle physics community poured a good $6 billion into building the Large Hadron Collider, one of the largest and highest energy accelerators ever built. But now it looks like Mother Nature has her own version of an accelerator, created by unique conditions that sometimes occur during thunderstorms, some 40 kilometers above the surface of the Earth.

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Back in 1925, a Nobel prize-winning physicist named Charles Thomson Rees Wilson speculated that discharges of lightning in the zone just above thunderstorms could give rise to naturally-occurring particle accelerators. But science hadn’t yet progressed to the point where it was possible to test that hypothesis.

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In April, Martin Fullekrug of the University of Bath, UK, presented new results at the Royal Astronomical Society National Astronomy Meeting in Glasgow that showed Wilson was right. Particularly intense discharges, combined with the cosmic rays that routinely bombard Earth’s atmosphere, give rise to the unique conditions required to create a giant particle accelerator in the sky. According to a university press release:

“The cosmic rays strip off electrons from the air molecules and these electrons are accelerated upwards by the electric field of the lightning discharge. The free electrons and the lightning electric field then make up a natural particle accelerator. “The accelerated electrons then develop into a narrow particle beam which can propagate from the lowest level of the atmosphere (the troposphere), through the middle atmosphere and into near-Earth space, where the energetic electrons are trapped in the Earth’s radiation belt and can eventually cause problems for orbiting satellites…. For the blink of an eye, the power of the electron beam can be as large as the power of a small nuclear power plant.

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Fullekrug and his colleagues used the radio waves emitted by the particle beam of one of those natural occurring accelerators to figure out how high up the phenomenon occurred, using computer simulations at Los Alamos National Lab’s supercomputing facility. Then a group of European scientists set up video cameras to monitor the area above thunderstorms. They observed lightning discharges strong enough to produce so-called “sprites”: telltale airglows that sometimes form above thunderstorms. A few of those sprites coincided with with the particle beams.

This is indirect evidence, of course. But over the next several years, no fewer than five different space missions are planned which will have the capability to measure those naturally occurring particle beams directly.

In the meantime, other scientists are using manmade accelerators on earth to create intriguing works of art. Below is the winning image in Princeton University’s “Art of Science” competition, called “Xenon Plasma Accelerator,” by Jerry Ross, a researcher at Princeton’s Plasma Physics Lab.  As Ross describes his image: “The Hall thruster is an electric propulsion technology that uses magnetic and electric fields to ionize and accelerate propellant. In this image the plasma accelerator is operating on xenon propellant.” Can Mother Nature produce an image as lovely as this? I guess we’ll have to see.

Photo credits: (top) Photo by Gregory Kramer. (middle) Photo courtesy of Oscar van der Velde, Universitat de Catalunya, Spain and Serge Soula, Laboratoire d’Aerologie, France. (bottom) Photo by Jerry Ross, Princeton’s Plasma Physics Lab.

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