A powerful laser that diverts the rays towards the sky to avoid its effect | Technique

Since June 1752, nearly 271 years ago, the main protection of buildings and their occupants from powerful lightning discharges has been based on Benjamin Franklin’s invention: the lightning rod. Also a Boston-born politician and thinker, he demonstrated that clouds are charged with electricity by flying a kite with a metal frame and a tethered switch that attracts a discharge. Since then, metal rods on buildings that catch lightning and bring it to the ground to neutralize it have saved thousands of lives and vital facilities. Nature photonics Monday publishes the first major breakthrough in nearly three centuries and has successfully mastered this force of nature. A total of 28 international researchers presented the results of a powerful laser capable of deflecting rays into the sky.

The device is capable of firing a thousand very short laser pulses every second to generate an ionizing channel, called a laser filament, which directs the beam into the atmosphere by creating a preferred discharge path away from vulnerable locations. “By firing a thousand laser pulses per second into the clouds, we can safely unload the beam and make the world a little safer,” says Clemens Herkommer, engineer at TRUMPF Scientific Lasers, one of the LLR project partners.Laser lightning rod or Laser Lightning Rod) and co-author of the paper.

The device, about the size of a large family car, was tested on the Säntis mountain in northeastern Switzerland, along with a 123-meter-high communications antenna. Markus Rubinstein, a physicist at the Lausanne University of Applied Sciences, also worked on the site. The scenario was ideal to demonstrate that a laser lightning rod is capable of trapping and redirecting the discharge skyward, avoiding its impact on utilities.

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“What we’ve done is measure these electromagnetic fields to understand how the physical mechanisms work and validate the model we’re developing,” explains scientist Farhad Rashidi, also a co-author on the paper. “Thanks to the lasers,” adds Aurélien Houard, project coordinator, “we can project energy over long distances in order to create a path for the beam and turn it into a kind of guidance. The air discharge with the help of laser pulses is very powerful.”

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

The researchers of the latest experiment consider the achievements now being made due to the fact that “the laser repetition rate was greater.” during the fuse [la generación del canal ionizado], a small part of the free electrons generated is captured by the neutral oxygen molecules. At the laser’s high repetition rates, these charged oxygen molecules accumulate, preserving the laser’s path memory. “Today’s laser detonators are among the most powerful of their kind,” asserts Herkommer.

Test results show that during more than six hours of operation (378 minutes) during electrical storms detected three kilometers from Santis Peak, the laser was deflected in the path of four upward lightning discharges. This was confirmed by observations of electromagnetic waves and X-ray bursts, and one of the impacts was recorded directly by two high-speed cameras at 1.4 and 5 kilometers from the tower, respectively. Videos showed that the beam followed the laser path for more than 50 metres.

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

Restart the laser lightning rod work.
Restart the laser lightning rod work.Martin Stolberg

According to satellite data, the total rate of lightning strikes and lightning strikes around the world is between 40 and 120 per second. In addition to mastering it with devices such as a laser installed in Switzerland, it is important to anticipate it. In this sense, researchers from the Federal Polytechnic School of Lausanne (EPFL) have developed an artificial intelligence system, complementary to LLR, for their prediction.

The model allows predicting between 10 and 30 minutes of lightning impact in an area of ​​30 kilometers with a margin of error of 20%. This system provides a key advantage over existing systems which, according to Amir Hossein Mostagabi, one of the developers responsible and also involved in the laser research, are “extremely slow and complex and require expensive external data obtained by radar or satellites.”

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 artificially initiate lightning discharges. Launched at the right time, the success rate of this method can reach 90%. But they are expensive and dangerous because of the impact of the missile fall and generate waste. In 1999, the use of lasers was proposed, but only now have been achieved encouraging results with many advantages.

According to the LLR study, “The filament process can be controlled to start up to 1 km away from the laser source.” “Therefore,” the authors stress, “it is conceivable that the channels generated could serve, in addition to directing lightning, even to trigger discharges in appropriate climatic conditions.”

Every day, about 8.6 million lightning strikes occur around the world, each traveling at over 320,000 kilometers per hour, generating a large amount of electricity. “Improving lightning protection is very important now because of the more severe weather events of climate change,” says John Locke, a professor at the University of South Australia (UniSA) who was not connected to the experiment in Switzerland.

In this sense, the scientist Abdullah Kahraman, a climate change researcher at the University of Newcastle, published in Environmental Research Letters Research paper on how global warming is changing the distribution of thunderstorms in Europe: “More frequent lightning strikes over mountains and in the north of the continent could lead to more wildfires in higher-level forests. We would see relatively less risk from lightning in more densely populated downtown areas.” “.

An Australian plasma physicist has investigated the role of oxygen molecules, which is key in the work of the LLR, in determining the behavior of lightning. According to the study published in applied physicsAnd Lightning occurs when electrons strike oxygen molecules with enough force to form high-energy oxygen molecules. “We need to understand how lightning strikes so we can find ways to better protect buildings, planes, skyscrapers, and people,” says Lockie.

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