Shooting clouds with lasers triggers electrical discharge

 作者:巫马葭     |      日期:2019-03-02 08:14:03
By Flora Graham (Image: CNRS Photothèque/Claude Delhaye) In a step towards gaining the God-like ability to call down lightning bolts on a whim, researchers used an ultra-high-power laser to trigger electrical activity in storm clouds over New Mexico, US. They fired ultra-fast pulses of a powerful five terawatt laser into the clouds. These beams created channels of ionised molecules known as “filaments” that conduct electricity through clouds like lightning rods before it strikes earth. The filaments created were too short-lived to provoke an actual lightning strike. But an increase in the electrical activity inside the clouds was recorded. The French and German researchers that shot the laser skyward say using faster pulses should achieve thunderbolts on demand. Scientists have proposed using lasers to trigger lightening since the 1970s, but have not had ones powerful enough to properly test the idea. Rockets trailing long wires have successfully triggered lightning in the past. But that approach is more complex than using a laser that could rapidly hit targets all over the sky. Powerful lasers able to generate terawatts of energy have recently become common in physics labs. But until now they have been too bulky to play with outdoors. The researchers used a new mobile laser called Teramobile, developed by a collaboration of French and German engineers. It packs the typical equipment of a five terawatt laser into a standard six metre shipping container. In 2001 the average electrical power consumption of the world was just 1.7 terawatts. “This is the first laser that has terawatt power and is also mobile,” says André Mysyrowicz, a researcher at the École Nationale Supérieure de Techniques Avancées, Paris, France, who took part in the latest outdoor tests. “This was a breakthrough because it allowed us to bring this laser on top of a mountain.” The experiment was conducted during stormy weather on the top of South Baldy Peak in New Mexico. The team hoped to trigger actual lightning strikes by increasing the rate of the laser pulses and using more sophisticated sequences of pulses. As the laser beam travels through the air towards a cloud it becomes increasingly intense thanks to a process called “self-focusing”, explains Mysyrowicz. “The air acts like a succession of lenses, focusing the laser,” he says. The air ionises molecules to create the filaments of plasma, up to several hundred metres long, that can lead to a lightning strike. Mysyrowicz points out that harnessing lightning could have many practical applications – both for studying the elusive phenomenon and for draining electrically volatile storms before they can wreak unpredictable havoc. “Lightning control, if you want to protect particular sites, would be very useful. You could avoid lightning on very expensive or fragile sites,” explains Mysyrowicz. For example, in 1987 a US$78 million Atlas Centaur rocket carrying a $83 million military communications satellite had to be destroyed after it went off course after launch. Investigators said the malfunction may have been caused by lighting. Jean-Claude Diels, professor at the University of New Mexico agrees the technique has the potential to call down lightning strikes. But he says the ionisation caused by the laser pulses must last more than a thousand times longer than the nanosecond it does now. Diels adds that he thinks it possible that the plasma filaments created so far may not have converted into electrical discharge inside the targeted clouds. “There is some electromagnetic radiation generated by the filaments themselves, which may have contributed to the detected signal.” Journal reference: Optics Express (DOI: doi: