? stnazkul #84059942, source:stock.adobe.com 2020
It is said that lightning never strikes the same place twice. But just one strike can be enough to cause substantial damage. Not only do lightning strikes kill up to 24 000 people every year, they’re also responsible for power outages, forest fires, and structural damage.
When lightning strikes important infrastructure and sensitive sites like airports and rocket launch pads, the result can be billions of euros in damage. To mitigate this risk, the EU-funded LLR project has set out to do what was once considered impossible: control lightning.
“Today’s lightning protection systems are still based on the lightning rod developed by Benjamin Franklin almost 300 years ago,” says Aurélien Houard, a researcher at Ecole Polytechnique in France and LLR (Laser Lighnting Rod) project coordinator. “Our project intends to update this concept using a very powerful laser.”
A powerful laser beam
At the heart of the project is a novel type of laser featuring a powerful beam. This beam will act as a preferential path for the lightning, diverting it away from potential victims. The unique laser will also guide lightning flashes to the ground to discharge the electric charge in the clouds.
To illustrate, when installed at an airport, the laser lightning rod would operate in conjunction with an early warning radar system. “Upon the development of thunderstorm conditions, the laser would be fired toward the cloud to deflect the lightning strike away from aircraft during take-off, landing, taxiing, and ground operations,” explains Houard. “In effect, this would create a safe corridor surrounded – and protected – by lasers.”
Ground-breaking technology
To achieve the necessary intensity and repetition rate, the project has employed a number of ground-breaking technologies. For example, it uses chirped pulse amplification (CPA), the current-state-of-the-art technique used by most of the world’s high-power lasers and the winner of the 2018 Nobel Prize in Physics. “CPA is a technique for amplifying an ultrashort laser pulse,” says Houard. “It works by stretching out the laser pulse temporally, amplifying it, and then re-compressing it.”
To deliver the short laser pulses at a high repetition rate of 1 000 shots per second, the project team had to scale up the laser’s average power. To do this, advanced amplification technology developed by Trumpf, a German industrial machine manufacturing company and member of the project consortium, was used.
According to Houard, the energy supplied by the technology’s many diodes is concentrated in a very thin disk of crystal cooled by water. “When the laser pulse goes though the crystal, the stored energy is transferred to the laser pulse through a quantum mechanism called ‘laser gain’,” he says. “The design of this thin disk amplifier allowed for an increase in the power of the ultrashort laser by an order of magnitude.”
The project also developed an innovative system for predicting lightning activity. “Using a combination of standard data from weather stations and artificial intelligence, the partners developed a new way of predicting lightning strikes within a forecast interval of 10 to 30 minutes and within a radius of 30 kilometres,” comments Houard. “This is the first time that a system based on simple meteorological data has been able to predict lightning strikes through real-time calculations.”
Demonstration planned for 2021
The LLR team is currently testing the laser in Paris, with the aim of validating the concept of safely guiding a lightning strike to the ground by projecting a long-range beam into the atmosphere.
A final demonstration of the LLR concept is set to take place on Mt. S?ntis in Switzerland, which is home to a Swisscom tower that is struck by lightning over 100 times every year. The demonstration is planned for 2021. Following a successful demonstration, the project team is confident that the system will be ready for full commercialisation within a few years.