A powerful laser manages to divert rays towards the sky to avoid its impact | Technology

Since June 1752, almost 271 years ago, the main protection of buildings and their inhabitants against powerful lightning discharges rests on an invention of Benjamin Franklin: the lightning rod. Also a politician and intellectual born in Boston, he demonstrated that the clouds are charged with electricity by flying a kite with a metal frame and with a tied key that attracted a discharge. Metal bars on buildings that catch lightning and conduct it to the ground to neutralize it have since saved thousands of lives and critical facilities. Nature Photonics publishes this Monday the first significant advance in almost three centuries and successfully to master this force of nature. A total of 28 international researchers have presented the results of a powerful laser capable of deflecting rays into the sky.

The device is capable of firing a thousand ultra-short laser pulses every second to generate an ionized channel, called a laser filament, which guides the beam into the atmosphere by creating a preferred path for the discharge away from vulnerable locations. “By shooting a thousand laser pulses per second into the clouds, we can discharge the beam safely and make the world a little bit safer,” says Clemens Herkommer, an engineer at TRUMPF Scientific Lasers, an LLR project partner (Laser Lightning Rod or Laser Lightning Rod) and co-author of the research.

The device, the size of a large family car, has been tested on the Säntis mountain in north-eastern Switzerland, alongside a 123-meter-tall telecommunications antenna. “It is a tower that has the advantage of being struck by lightning a hundred times a year and allows us to know how much charge is transferred from the cloud to the ground.” comments Marcos Rubinstein, a physicist at the Lausanne University of Applied Sciences and also a signatory to the paper. The scenario was ideal to demonstrate that the laser lightning rod is capable of trapping and redirecting the discharge towards the sky, avoiding its impact on the facilities.

“What we have done is measure these electromagnetic fields to understand how the physical mechanisms work and validate the model we are developing,” explains scientist Farhad Rachidi, also a co-author of the research. “Thanks to the laser”, adds Aurélien Houard, project coordinator, “we can project the energy over long distances in order to create a path for the beam and turn it into a kind of guide, emptying the air with the help of laser impulses very powerful”.

The idea of ​​using intense laser pulses to guide the beams had previously been explored under laboratory conditions in New Mexico in 2004 and Singapore in 2011. However, no evidence was found of the ability of this technique to redirect laser beams. .

The researchers of the last experiment consider that the achievements that are now presented are due to the fact that “the repetition rate of the laser has been greater.” “During filamentation (the generation of the ionized channel) a small fraction of the free electrons created is captured by neutral oxygen molecules. At high repetition rates of the laser, these charged oxygen molecules accumulate, maintaining a memory of the laser path. “Today, the laser arrester is one of the most powerful of its kind,” confirms Clemens Herkommer,

The test results show that, during more than six hours of operation (378 minutes) during electrical storms detected three kilometers from the top of Säntis, the laser diverted the course of four lightning discharges upwards, as corroborated with the tracking of electromagnetic waves and X-ray bursts. One of the impacts was directly recorded by two high-speed cameras located 1.4 and 5 km from the tower, respectively, and showed that the beam followed the path of the laser for more than 50 meters.

The authors conclude that, although “more campaigns and theoretical work are needed”, their findings expand the current understanding of laser physics in the atmosphere and may help in the development of new lightning protection strategies for people and critical infrastructure, such as power plants. electricity, airports and launch pads.

According to satellite data, the total rate of lightning and lightning strikes around the world is between 40 and 120 per second. In addition to mastering them, with devices like the Swiss-proven laser, it’s important to anticipate them. In this sense, researchers from the Federal Polytechnic School of Lausanne (EPFL) have developed an artificial intelligence system, complementary to the LLR, to predict them.

The model allows to anticipate between 10 and 30 minutes the impact of lightning in an area of ​​30 kilometers and with a margin of error of 20%. This system provides a fundamental advantage over the current ones which, according to Amirhossein Mostajabi, one of those responsible for the development and also a participant in laser research, “are slow, very complex and require expensive external data acquired by radar or satellite” .

The oldest method of dealing with these phenomena, after Franklin’s invention, was a rocket attached to a long, grounded conductor wire that was tested in 1965 to start lightning discharges artificially. Launched at the right time, the success rate of this method could be as high as 90%. But it is expensive, dangerous due to the effect of the fall of the rocket and generates waste. In 1999, the use of lasers was proposed, but only now have encouraging results been achieved with several advantages.

According to the LLR study, “the filamentation process can be controlled to start up to a kilometer away from the laser source.” “Therefore”, the authors maintain, “it is conceivable that the generated channels could serve, in addition to guiding the lightning, even to trigger discharges in appropriate climatic conditions”.

Every day, around 8.6 million lightning strikes occur around the world, each of which travels at more than 320,000 kilometers per hour, generating a large amount of electricity. “Improving lightning protection is very important now because of the more extreme weather events of climate change,” says John Lowke, a research professor at the University of South Australia (UniSA) and unrelated to the experiment in Switzerland.

In this sense, Abdullah Kahraman, climate change researcher at the University of Newcastle and Scientist, has published in Environmental Research Letters a paper on how global warming changes the distribution of thunderstorms in Europe: “More frequent lightning strikes over mountains and in the north of the continent could trigger more forest fires in higher-level forests. We’re going to see relatively less lightning risk in more populated downtown areas.”

The Australian plasma physicist has investigated the role of oxygen molecules, key in the LLR’s work, in determining the behavior of lightning. According to the study published in Applied Physics, Lightning occurs when electrons hit oxygen molecules with enough power to create high-energy oxygen molecules. “We need to understand how lightning strikes so we can find ways to better protect buildings, planes, skyscrapers, and people,” Lowke says.

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