Laser 'lightning rod' diverts strikes high in the Alps

Host: Benjamin Thompson

Welcome back to the Nature Podcast. This week: how to guide lightning with lasers.

Host: Shamini Bundell

And the latest from the Nature Briefing. I’m Shamini Bundell.

Host: Benjamin Thompson

And I’m Benjamin Thompson.

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Interviewer: Benjamin Thompson

First up on the show this week, we’ll be hearing about a recent paper in the journal Nature Photonics that’s using lasers to guide lightning, which could represent a new way to protect vulnerable structures. Now, around the world, there are estimated to be dozens of lightning flashes happening every second of the day. The majority of these will be within clouds, but even so, huge numbers strike the Earth at any given time. And these giant electrical discharges can be incredibly destructive, starting forest fires, injuring or killing people, and damaging buildings and powerlines. Of course, many buildings employ a simple technology demonstrated by a certain Benjamin Franklin back in the mid-1700s to protect against strikes: the lightning rod.

Interviewee: Jean-Pierre Wolf

The work of Benjamin Franklin was very important, and we still use the same technology because it works very well.

Interviewer: Benjamin Thompson

This is Jean-Pierre Wolf from the University of Geneva in Switzerland.

Interviewee: Jean-Pierre Wolf

So, the idea is to use a metallic rod, and so basically what you do is you favour the lightning path, or you guide the lightning path to the tip of this rod.

Interviewer: Benjamin Thompson

So, how does a rod guide lightning’s path to a particular place? Well, it’s a bit complicated because exactly what causes lightning strikes isn’t completely understood. But, very generally, during a storm, a difference in charge builds up between the base of a cloud and the ground below. When sufficient charge has built up, a lightning precursor known as a leader travels down from the cloud, and upward precursors known as streamers reach up from the ground to meet it. When down and up connect, boom: a lightning strike. However, of the streamers reaching upward, only one connects, which makes knowing where the lighting will strike difficult to predict. What a metal lightning rod does is concentrate the charge on the ground in one spot. Lighting is then more likely to strike this spot and less likely to strike the area around it.

Interviewee: Jean-Pierre Wolf

And so, you protect a zone which is about the height of the lightning rod, so if you have a 10-metre-high lightning rod then you would protect roughly a radius of approximately 10 metres around it.

Interviewer: Benjamin Thompson

And this is great for individual buildings, say.

Interviewee: Jean-Pierre Wolf

But now, imagine you are in a situation where you want to protect an airport or you want to protect a launching pad for a rocket, or an electrical power plant also. You would like to protect a large area, say 1 kilometre, then you would need a metallic stick of 1 kilometre high, which is not easy to produce.

Interviewer: Benjamin Thompson

Scientists have long been trying to produce alternatives to the lightning rod to provide this sort of wide protection, and one idea that’s been extensively explored has been the use of intense lasers. In the lab, these have been used to heat up and ionise the air, creating channels of lower air density which are more conductive and so favourable for lightning to travel along. The laser is kind of creating a wire in the air for electricity to pass along – in theory, guiding it away from things like buildings, like a giant lightning rod. But while this has been shown in the controlled conditions of a laboratory, it hasn’t worked in the real world. That is until last summer, when Jean-Pierre and his colleagues took a laser up a mountain.

Interviewee: Jean-Pierre Wolf

We went on the top of Mount Säntis in Switzerland. It’s 2,500 metres altitude, and it has also a telecom remitter. And why we went there is because it’s one of the places in Europe and maybe even in the world which is the most often struck by lightning.

Interviewer: Benjamin Thompson

Understandably, because it gets hit so much, the telecom tower at the top of the mountain is used a lot for lightning research, making it the perfect place for the team to test the laser. But once they’d constructed it, they had to play the waiting game, firing a beam of intense green light over the tip of the communication tower during storms to see if the channel it created would affect the path of any lightning. In total, the team saw four events where lightning was guided by the laser and captured images of one using high-speed cameras. Now, it’s worth pointing out that this lightning was a bit different from the type you usually think of. These events were a were a type of upward-going lightning, with an emerging precursor that begins the strike starting at the tip of the communications tower, rather than starting in the clouds. This type of lightning is less common, but it can happen in high-altitude environments.

Interviewee: Jean-Pierre Wolf

So, when the laser is on, you see the lightning starting from the tower and following the channel pretty precisely. If the laser is off, it’s a completely different situation. It just starts at the tip of the tower but it branches. Some of the branches are going left, the other ones right, so it really looks like a tree. And when you put the laser, the tree disappears and you have a straight line.

Interviewer: Benjamin Thompson

The images of the recorded strike show that the lightning leader followed the laser upwards for around 50 metres. When it met the cloud, the resulting lightning strike was directed through the tower's existing lightning rod and travelled safely to the ground. So, why did the team succeed at laser-guiding lightning when other attempts have been unsuccessful? Jean-Pierre says it’s down to the special type of laser they used, which flashes on and off extremely quickly.

Interviewee: Jean-Pierre Wolf

It flashes 1,000 times a second, and all the other attempts, including ours, was flashing 10 times a second, so 100 times less. And the probability of having the conductive channel at the right moment if you have only 10 times in a second, you might miss it. So, this laser is unique in the world, but it was developed within the project.

Interviewer: Benjamin Thompson

Creating the channel in the sky requires a lot of energy. Using a pulsing beam allows the laser to reach that energy level for brief fragments of time and repeatedly, rather than having to run a continuous beam. But the setup needed to produce the laser light is huge, and much of it had to be carried up the mountain by helicopter. And while the team have demonstrated that this system has potential, Jean-Pierre says there’s a lot more work to do in order to optimise the laser. But this work does show that using lasers to guide lighting can be done. Nature’s Lizzie Gibney, who covers all things physics, has been writing about this story and she’s been talking to researchers around the world about what they make of it.

Interviewee: Lizzie Gibney

So, I think there’s been a lot of excitement because this is a really big project. It’s 25-odd people, it was 5 years long, it’s this massive laser on top of a mountain, and they’ve come out with this result that actually does show what they set out to show – that you can use a laser as a lightning rod. There were a few little caveats in that what people really hoped that this would do would actually trigger the lightning itself, and by that they mean force a cloud to discharge at will. And that would be even more useful because then you could use it to, say, discharge a storm before it got really dangerous or to completely guide it away from really sensitive bits of equipment. So, what they’ve done here is used the laser as, essentially, a much bigger lightning rod. You can protect a much bigger area. But it still doesn’t quite go as far as they’d like it to go ultimately, which is this idea of triggering. But it’s still a really big and impressive result.

Interviewer: Benjamin Thompson

There’s also the question of whether this type of system will work in other environments and with more common types of lightning – those that go from cloud to ground – and this is something that Jean-Pierre is keen to investigate. But for now, he and his team are appreciating their achievement that has been decades in the making.

Interviewee: Jean-Pierre Wolf

When I saw this first picture that is in the paper, I mean, I said like, ‘Wow’. We dreamed of this picture for 20 years. And then just after this first emotion I say, ‘Aye, relax, maybe it’s an artefact’. This is a typical scientist’s reflex.

Interviewer: Benjamin Thompson

That was Jean-Pierre Wolf from the University of Geneva in Switzerland. You also heard from Nature’s Lizzie Gibney. You can find links to Jean-Pierre’s article and to Lizzie’s news story over in the show notes.

Host: Shamini Bundell

Coming up: how Roman concrete has stood the test of time. Right now, though, it's time for the Research Highlights, read by Dan Fox.

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Dan Fox

The brachyuran crabs that thrive around a hydrothermal vent system off the coast of Taiwan present a puzzle: how do they survive in such a toxic environment? Well, perhaps through a bit of teamwork. The geothermally heated water of their home is heavily laden with hydrogen sulfide, which is extremely toxic to most living things. Now, researchers have discovered how the crabs not only survive but actually access the energy locked in the chemical bonds of the hydrogen sulfide. The crab converts sulfide into less toxic thiotaurine in its gills. Next, bacteria that live in the gill cells extract energy from the thiotaurine and detoxify it further. The authors propose that the energy the bacteria extracts is shared with the host crab. The researchers say the crab is a keystone species for the entire ecosystem of bacterial species living in and around it. You can read that research in full in Proceedings of the Royal Society B.

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Dan Fox

If spring fills you with dread as hay fever encroaches, it's the makeup of bacteria in your nose that might be to blame. Researchers have found that people who have hay fever have a less diverse mix of nasal bacteria than people without the condition. The team found that one species of bacterium, Streptococcus salivarius, was especially plentiful in the noses of participants with hay fever, making up over 12% of their nasal bacteria, which is over 17 times more than the share in participants without hay fever. The researchers think that in the presence of allergens like tree pollen, the bacterium might be particularly prone to sticking to the cells that line nasal passages, triggering the immune system and causing symptoms like sneezing and a runny nose. These findings could offer hope to sufferers as disrupting the interaction between the bacteria and cells of the nose might bring relief from a season of sneezes. Don't turn your nose up at that research. Read it in full in Nature Microbiology.

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Host: Shamini Bundell

Finally on the show, it’s time for the Briefing Chat, where we discuss a couple of stories covered in the Nature Briefing. And, this week, Ben, I’ve got a story entitled ‘hot mixing’.

Host: Benjamin Thompson

Hot mixing. Okay then, Shamini. Is this the latest in your side hustle as a world-famous DJ?

Host: Shamini Bundell

It's chemistry. It's some very exciting chemistry I've got for you today. So, this is a news article in Ars Technica based on some new research published in Science Advances. The beginning of the paper title is in fact, ‘hot mixing’, and it's about the techniques that the Romans used to make concrete, which were apparently very, very complicated and, given the amount of sort of Roman concrete buildings around us, actually really successful.

Host: Benjamin Thompson

I mean, I can say that I am quite familiar with Roman concrete, Shamini. I, of course, was born in a town called Colchester, which used to be the Roman capital of Britain, and you can't help but fall over Roman concrete structures. In fact, I literally have, one of them is outside a pub that used to drink at as a young man. So, yeah, very robust and have been standing for thousands of years, I guess.

Host: Shamini Bundell

Yes, it lasts. And apparently, they had lots of different sort of specific recipes almost for different kinds of concrete to use for different kinds of things, and it seems that they've worked out. But there was one particular mystery. Well, I suppose people didn't know it was a mystery. But in quite a lot of Roman concrete, you get what's called lime clasts. So, this is basically little white mineral chunks that are sort of mixed up with concrete. And modern concrete often tends to be very sort of smooth and even, and when looking at these lime clasts, people thought, well, this is probably because it hasn't been mixed very well or they just sort of didn't quite have the quality control on this. But now, some researchers have looked into, well, actually, maybe these little white chunks actually serve a purpose.

Host: Benjamin Thompson

So, researchers have realised then that it wasn't the Romans sort of doing half a job then and not mixing their concrete properly. This stuff actually does something useful.

Host: Shamini Bundell

Yes, so this particular environmental engineer at MIT, who is one of the authors on the paper, is quoted in this article as saying that it always bothered them because if the Romans put so much effort into making an outstanding construction material, why would they put so little effort into ensuring the production of a well-mixed final product?

Host: Benjamin Thompson

And pray tell, Shamini, what are these lumpy clasts doing then in the concrete?

Host: Shamini Bundell

So, one of the reasons that these clasts are here is to do with how this concrete is made, and this paper actually found a slightly different production method than people previously knew. So, this is where the hot mixing comes in. They found that it looks like the ancient Romans made this concrete with quicklime. It's basically calcium oxide rather than slaked lime, which is calcium hydroxide. So, they use this slightly more reactive compound basically, and the hot part is the sort of high temperatures they were producing this at. And these high temperatures, the hot mixing, forms these clasts that end up in the concrete. And it turns out these clasts are actually super useful because when the concrete ends up cracking, water comes in, and water can actually react with the substance that these clasts are made of and sort of fill the cracks and strengthen the composite material that the concrete is made of. So, this paper, the researchers have basically recreated this, made some new concrete, formed some cracks and then showed that, within a few weeks, the cracks in the concrete that was made with this hot mixed quicklime had actually sort of healed up, which it doesn't do without that method.

Host: Benjamin Thompson

So, self-healing concrete then, which I guess helps explain why these structures have lasted so very, very long.

Host: Shamini Bundell

Yeah, and it potentially is something that we might want to copy because concrete is a huge CO2 emitter. And one thing we can really do is make concrete that will last longer and make structures that will last longer. So, it might be worth following the Roman recipe in this instance.

Host: Benjamin Thompson

Alright, cool. So, it looks like we can add self-healing concrete to the list of what the Romans did for us then.

Host: Shamini Bundell

Thank you very much, ancient Romans. So, what have you got for us this week, Ben?

Host: Benjamin Thompson

Well, Shamini, I've got a vaccine story that I read about in the New York Times, but it's a vaccine story with a difference. And it's about the first vaccine for honeybees, which has just been given conditional approval by the US Department of Agriculture. And apparently, it's the first vaccine has been approved for any insect in the US, the story says.

Host: Shamini Bundell

Right, oh, okay. So, I never really thought of giving insects vaccines before but we definitely have talked on the podcast before about how important honeybees are and how they are susceptible to various diseases.

Host: Benjamin Thompson

Yeah, absolutely right, Shamini, and, in this case, this vaccine is protecting against a disease called American foulbrood, okay, and it's a disease that is actually found all around the world. And it's a bacterial disease, right, and honeybee larvae ingest the spores of this species of bacterium, and, well, the disease basically causes them to turn into mush. It's very unpleasant, and the hives apparently smell really, really bad when there's an infection. And these spores are easily kind of spread throughout a hive and can be spread between hives as well on infected equipment that beekeepers are carrying and what have you. And it’s absolutely devastating, and ways to treat it are fairly limited. Antibiotics apparently can be used in some situations. But more often than not, the way to control it is literally just to set fire to the hives and any equipment, just burn it all because these spores are super hardy and will survive for years and years and years.

Host: Shamini Bundell

So, yeah, wow, something to be avoided by beekeepers. So, I can understand why a vaccine would be useful, but I am currently imagining them having to get their little bees like lined up so they can get a little injection in their arm. How do you give a vaccine to bees?

Host: Benjamin Thompson

That's a great question, Shamini. I will say bees don't have arms, so that's not necessarily a productive avenue. In this case, the vaccine is incorporated into royal jelly, right, and that's a food that's given to queen bees, okay. And the vaccine is then deposited into the queen bee’s ovaries and gets passed on to larvae, giving them immunity. And it's kind of an interesting one because in this article I read that for the longest time, scientists assumed that insects couldn't acquire immunity because they don't have antibodies, so their immune system is obviously very different to ours. But ultimately, researchers showed that insects could acquire immunity and pass it on, and the researchers involved in this vaccine identified a protein that prompts an immune response, and that knowledge eventually led to where we are now and a vaccine that's been conditionally approved. And it is going to be available to commercial beekeepers, and more data is being collected and certain things have to be shown before it gets full approval. But as you said at the start there, Shamini, honeybees are incredibly important for the world, right. They're super important pollinators, and they are threatened by diseases, by climate change, by all sorts of things. So, anything that could give them a leg up or, I mean, I guess, a wing up, that’s got to be good news.

Host: Shamini Bundell

I'm sure, yeah, for beekeepers that's going to be really valuable and maybe even open the door to sort of future insect vaccines as well. So, thanks for that, Ben. Listeners, if you want to get more details on either of these stories that we've talked about today, or you want know where you can sign up to the Nature Briefing and get more stories like these ones in your email inbox, then you can check out the show notes, and we'll put some links up for you.

Host: Benjamin Thompson

And that's all for the show this week. As always, you can keep in touch with us on Twitter – we're @NaturePodcast. Or you can send an email to podcast@nature.com.

Host: Shamini Bundell

And if you're interested in maybe some video content as well as audio, on our YouTube channel this week, I have just published a film on a paper about a new kind of 3D printing. It involves different materials, a rotating nozzle and some very interesting and useful helix shapes being printed. So, we'll put a link to that video in the show notes as well. I'm Shamini Bundell.

Host: Benjamin Thompson

And I’m Benjamin Thompson. See you next time.