In Our Time - Plasma

Episode Date: October 13, 2016

Melvyn Bragg and guests discuss plasma, the fourth state of matter after solid, liquid and gas. As over ninety-nine percent of all observable matter in the Universe is plasma, planets like ours, with so little plasma and so much solid, liquid and gas, appear all the more remarkable. On the grand scale, plasma is what the Sun is made from and, when we look into the night sky, almost everything we can see with the naked eye is made of plasma. On the smallest scale, here on Earth, scientists make plasma to etch the microchips on which we rely for so much. Plasma is in the fluorescent light bulbs above our heads and, in laboratories around the world, it is the subject of tests to create, one day, an inexhaustible and clean source of energy from nuclear fusion.With Justin Wark Professor of Physics and Fellow of Trinity College at the University of OxfordKate Lancaster Research Fellow for Innovation and Impact at the York Plasma Institute at the University of Yorkand Bill Graham Professor of Physics at Queens University, BelfastProducer: Simon Tillotson.

Thank you for downloading this episode of In Our Time, for news about In Our Time, and for recommendations about our archive, please follow us on Twitter at BBC In Our Time. I hope you enjoyed the programmes. Hello, plasma thought of as the fourth state of matter after solid, liquid and gas. When we realise that over 99% of all observable matter in the universe is plasma, it makes planets like ours with so little plasma and so much solid, liquid and gas, exceptional and all the more remarkable. On the grander scale, plasma is what the sun is made from, and when we look into the night sky, almost everything we can see with the naked eyes made of plasma. On the smaller scale, here and our scientists make plasma to etch the microchips on which we rely for so much.

Plasma is in the fluorescent lights above our heads, and in laboratories around the world, it's a subject of tests that might create one day an inexhaustible and clean source of energy in nuclear fusion. With me, to discuss plasma are Justin Walk, Professor of physics and fellow of Trinity College at the University of Oxford. Kate Lancaster, research fellow for innovation and impact at the York Plasma Institute at the University of York and Bill Graham, Professor of Physics at Queen's University of Belfast.

Justin Walk, how does plasma differ from gas at the atomic level? Well, in your introduction, Melvin, you mentioned solids, liquids and gases, and we know that to transition through those three is one, a transition where you heat things up, ice becomes water, becomes water vapor when we put it in the kettle. And that works for most substances, for example, iron will melt and become a liquid at around 1,500 degrees centigrade and then also become a gas if you heat it up further to maybe 3,000. So how does a plasma differ from a gas? Well, we can think of a plasma as being the next stage, as you mentioned, the fourth state,

when we heat up the gas. So what is happening to the gas to go from the gas phase into this new thing that looks like a plasma? Well, to answer that, let's look at what a gas is. It's a set of atoms separated in space. So they're a little bit like billiard balls on a snooker table, that sort of separation to diameter ratio, moving around at high speed. But if we look at an individual atom, it looks a little bit like a solar system, a tiny solar system with a positive negative,

positive charge in the centre, which is heavy, and little negative charges we call electrons orbiting it. And those orbiting electrons are held to the positive charge in the middle by the force of electromagnetism, not the force of gravity that holds planets to the sun. But in an ordinary gas, if we look at one of those atoms, the number of electrons, the number of negatively charged particles orbiting the nucleus, is exactly equal to the number of positive charges in the heavy center. And so the overall thing is electrically neutral. If we heat the system up further, and there are other ways of creating plasmas as well that we might explore, the atoms move so quickly that when they bump into each other, they can start to knock off one or more of those orbiting light electrons.

Now you have a system where electrons on their own are free to move around in your volume, rather than being bound to the atoms, so you have free light negative charges moving around. And because some of the heavy atoms have lost an electron, their positive charge now outweighs the rest of the negative charge around them, and they become overall positively charged. So it's now as though we have two intermingled gases, one negatively charged and light, and one positively charged, which we call the ions, and heavy. How does this, plasma, why does this allow plasma to conduct electricity and why is that important? Well it allows it to conduct electricity precisely because we have freed the electrons. What is an electric current? It is a flow of charge. So imagine putting an ordinary

gas in a bottle and in this bottle there might be two metal plates that you put a voltage across, maybe with a high voltage battery. In an ordinary gas, the atoms, because the positive charges and the negative charges balance out and they're neutral, they don't react in a strong way to the electric field. But if I've already freed the electrons by heating the system up, they are now negatively charged. They're free to move in that electric field. An electric field causes a force on a charged particle.

It causes a force on the electrons, which makes them want to move one way, a force on the positive ions that wants to make them move the other. but the electrons being much lighter get a far greater acceleration. And that movement of charge, that movement of electrons, is electricity. Fine. I'm going to ask you a very stupid question. Could you give me a short answer saying? I know what ice looks like. I know what water looks like.

I know what vapour when you boil a kettle looks like, steam. What does plasma look like? Well, first of all, the steam, you know, when coming out of a kettle, is actually tiny droplets of the liquid. But it depends. It depends on the plasma because you can get light coming out of the plasma. So many people might have seen, for example, these plasma balls that you can buy of glass balls several inches in diameter.

And when the electrons pass through the plasma, if they can bump into some of the remaining ions and excite the bound electrons in those ions. And so therefore, you can get plasmas of different colours, by the positive ions that are left, having electrons being excited within them. So I think we're all familiar with neon lights and sodium lamps and the northern lights having colours.

And when you look at the northern lights, you're looking at a plasma. Thank you. Kate Lancaster, who first noticed the existence of plasma? So in the sort of late 1870s, there was a guy called William Crooks, and he built what's called a Crooks Tube, which is kind of similar to what Justin was talking about, which is a kind of glass bottle. At one end, there's a cathode, which is a negative electrode.

And at the other end, there's anode which is a positive electrode. Now, there are some free charges present at any given time in this very, very low level of gas that's inside the tube. And basically, what happens is when you put a current, when you put a voltage across this cathode and anode, the ions can move towards the... the negative electrode, and then the electrons move towards the positive. Now, when the electrons start to move, they start to crash into more ions, start to free more electrons up,

and you get a kind of cascade. And those electrons then rush towards the anode, and then the ions then rush towards the cathode, strike the cathode very hard, freeing up more electrons. And those electrons escape and rush towards the anode. And they shoot past because they've got lots of energy. They're moving about 20% of the speed of line. Now, what does this have to do with plasma? Well, basically, they were trying to study these... They mean crooks in this...

Yeah, Crooks was trying to discover what they called these cathode rays. They didn't know that they were electrons until JJ Thompson a bit later identified this matter that was zooming past the anode as electrons. But because it's an imperfect experiment, ironically, what happens is, you've got a bit of plasma present there because in an ideal world, you want that tube to be a vacuum. But actually, what there is is a very low level of gas.

And because you've got this low level of gas, you've created a plasma. Now, they didn't know exactly what that was. He kind of termed it radiant matter. So they didn't identify it as plasma and they weren't really interested in it. It wasn't until the early 20s when a guy called Irving Langmere,

who was actually working on these kind of lamps, like mercury vapor discharge lamps, which are sort of modified version of a crooks tube, but with a higher gas pressure inside. He saw this plasma and tried to understand what it was. He could see this sort of quasi-neutral matter, so balance of ions and electrons kind of glowing and moulding to the shape of the container.

And so it's the Greek definition of the word plasma, which means to mould, and that's where this term comes from. So it's in the early 20s where we first see plasma physics emerging as a kind of discipline. Why can plasmus emit light? So Justin just touched on that actually. So when you've got a gas

and it's turned into a plasma, you've got these free electrons and you've got these ions moving around. Now there are a number of ways in which light can be emitted in that situation. One way is that some of the free electrons can recombine with the ions that are needing some negative charge.

and in order to do that, they need to lose energy and they lose energy emitting a chunk of light, which we call a photon. So that's what's happening there. Another way is if you've got ions and electrons moving by the ion, they can be bent by the positive charge of the ion.

And that kind of causes the electron to lose some kinetic energy. It's moving energy. So where does that energy go? It's emitted as light. That's called Bremstra-Long radiation, which is a German term called breaking radiation. And then there's another way in which basically the atoms themselves,

electrons can sort of move to higher, more excited energy states and then decay back to less excited energy states. And that also emits light, but very specific wavelengths. So some of this produces kind of continuum of light, some of this produces very specific lines. Extraordinary furious activity down there, Bill. Bill Graham, how do you create prasmas in your laboratory? Well, in fact, I go back to the old days. I think Justin uses very sophisticated techniques. He's got these massive lasers, which he kind of pumps into different materials, and he was just telling me he can make, I think it's aluminium transparent by doing this.

And so he's in the process of making a plasma. In my case, we go back to the use of two of electrodes. And we basically pass, apply high voltages, and we then accelerate electrons. And it turns out we're quite lucky on Earth because we've got a few cosmic res kicking around. We've got some radio activity. And so, in fact, most of the time, you've got some electrons in that volume already.

Now you apply a field, and those electrons start moving. and as those electrons start moving What do you mean by applying a field? Oh, an electric field, I'm sorry. So basically we put a positive potential at one end and a negative potential on the other side. You can imagine that enclosed in a vessel and we have some gas in there.

We just connected up to a battery is one way to do it. I was going to mention that a little bit more detail, a little bit more sophisticated in other ways, and I'll mention that a little bit later. So we apply this field and the electrons start to move in the electric field. As Kate just said, the electrons are repelled from the positive anode,

attract the words of positive anode, repelled by the cathode, and the ions start to move the other way. However, the electrons are much lighter than any of the ions that we'd have around. They're about 2,000 times lighter than anything else. So they're moving, they start to gain velocity, and they move very rapidly through this gas, making collisions with atoms. And when they strike those atoms then,

they can either excite them up to a high level and then they decay back, that's your light, or they can actually strip the electron off. Now that you've got two electrons moving, then they go through the same thing. You start to get an avalanche of electrons, 24, 668, and so you start to get this ionization wave moving through the vessel.

And eventually after a while... What's an ionization wave? Well, that's because you've got your, kind of driving these electrons and they're moving through the gas ionising as they go along. You're knocking the electrons off.

Exactly. And therefore amplifying the number of electrons, increasing the number of ions and electrons that you have in that gas. And then you can kind of start to control that because once you start to get enough, for example, positive ions around, that starts to shield out

the effect of this electric field. And so then you can kind of get to some kind of equilibrium where you're making, the volume has been kind of ionized and it's kind of in an equilibrium, and you have then a plasma with constant properties. I mentioned at the beginning that the Earth is fortunate, or we're all fortunate, that we're not hit by great showers of plasma. Why is that? We're not hit by that because we are actually being hit. by it, but we've got something out there

that helps protect us. We've got magnetic fields. Charge particles follow magnetic fields. But it doesn't hit us sitting in the studio. It's dissipated above the earth. So you have magnetic field? You want to come in, Justin? Well, yes. I mean, the thing that as Bill said that really protects us,

because we have this plasma streaming towards us all the time from the sun, the solar wind. And what protects us, as Bill said, is the magnetic field of the earth. Because the charge particles react to a electric fields and can get pushed by them. They also get pushed by magnetic fields in a very strange way, deflected in directions you wouldn't expect. But it's the magnetic field of the Earth that pushes most of that plasma round. This is known as, and where that pushing occurs is known as the

magnetosphere. Now, some of the particles do get round. Is this because the Earth itself is a sort of magnet? Yes. We are one large, big magnet. And in fact, when we're looking, for example, for planets out around other suns, but often or in our own solar system, we're very interested to know they have magnetic fields because one would need to have a magnetic field to protect a planet in order for life perhaps to develop.

But on the Earth, a lot of the plasma gets deflected around. Some of it gets trapped by the magnetic fields. And if you imagine the Earth is one big bar magnet, that plasma streams down to the top to the poles where the magnetic field lines come together. And that's why we see the northern lights

or those in the South Pole as well. That's that plasma interacting with the upper atmosphere. You all said in your notes that over 99% of the observable universe is plasma. Has it always been the case?

No. That's a fascinating story. So first of all, let's say that it's true that 99% of the observable universe is plasma, but the The reservable universe that we see ordinary matter is only about 5% of what there is. So I'll qualify that first of all. But note, there is something that physicists call the Dark Ages.

If I mention the Dark Ages, probably most listeners will think immediately of that time between the 6th and the 14th century, when in a very simplistic view, we think that the intellectual lights of Europe went out. But if you say Dark Ages to a physicist or to a cosmologist, they think of a much longer period of time lasting not just a few centuries, but maybe millions of centuries. We clearly don't have time to go through the whole history of the universe before the end of the programme. Sorry about that, but another time, right. But just after the Big Bang, just a few minutes after, actually,

you had something that did look like plasma. We had hydrogen and helium were created in that process and electrons. But it was a plasma. None of the electrons were combined making a gas. As the universe, as the space itself expanded, the universe cooled. After 380,000 years, it was cool enough for those electrons to bind back on to the atoms, to the hydrogen and helium nuclei, and become a normal gas. And at that point, there was no plasma after 380,000 years.

The glow left over from the plasma also started to disappear from our vision, and the lights went out. It went out for something in the region of tens to hundreds of millions of years. how did it switch on again? How did it switch on? What ended the Dark Ages? It switched on because the universe cooled even more and the gas cooled even more till eventually clumps of gas, gravity took over such that if you had a little bit more gas in one place than another, more gas would come and join it, more gas would come and join it and so forth, and you'd get an effect where you'd get clumpiness in the universe, which eventually led to the first stars and galaxies. And that process took tens or hundreds of millions of years. It's what the cosmologists call re-ionization. But for that, several tens or hundreds of millions of years, there was no plasma, there was no light that we could see. It was without form and void, if you like.

We're back to Tyndall, aren't we? Kate Lancaster, let's now talk about, could you tell us about the ionosphere? What significance that has? Sure. So basically Justin and Bill were talking about the fact that we've got a lot of charged particles coming from the sun, and we're protected by the Earth's magnetosphere from those particles largely. But also there's other radiation coming from the sun, so UV radiation, soft x-rays, and they're harmful to us as well. But actually, there's a

unique section of our upper atmosphere called the ionosphere, which extends from about 60 kilometres up to about 1,000 kilometres. And the UV and the x-ray radiation interact with the atoms in that layer, and they ionise them, so release electrons, and they turn. turn them into plasma. And so essentially that the ionosphere is a sort of protecting layer for us, actually absorbing some of the energy from the radiation coming from the sun. I mean, obviously, UV does reach us on Earth because we burn, but it'd be a lot worse without the ionosphere. Also, the ionosphere was quite important in the past when, in the radio age, where some frequencies of radio waves actually bounce off the ionosphere and then back down, bounce off Earth. And so there's a kind of

wave guide effect between the Earth's surface and the, and the, bottom of the ionosphere as well. How far away is the a ionosphere? So it starts at about 60 kilometres and then ends at about 1,000 kilometres up. And there's that how is it different? Then there's the magnetic field. Is that above and beyond the airspace? Actually there's a bit where the ionosphere and the magnetosphere actually overlap. So there is two things sort of coddling the earth really? Quite, yeah, absolutely. And it's sort of protecting us from the harshness of space. Really? And do we know why they are? Why that's happened? Well, I mean, in a sense, why in what sense?

Why we've got those two fields up there? Is that because we're a magnet? Yeah, yeah. So essentially the Earth's magnetic field is the magnetosphere. And then, of course, we've got this ionosphere, which is actually the ionisation, the degree of ionisation in the ionosphere, really depends on what time of day it is, because it's the sun that's doing that, the seasons. And also solar activity. So when there are intense periods of solar activity, the ionosphere, the composition, the composition. if that changes.

Just the reading about this from the notes of all three, it became more and more exceptional that we sort of survived the first frazzle at all, right? Absolutely. Back to Bill Graham, can you just go into, for our listeners and for myself, actually, about the properties of plasma that make it possible for them to be used in laboratories such as yours,

for, let's say, microchips. Can you go through the process? Yes, I can, hopefully. So I think, I mentioned earlier on that we make the plasmas by having electrons present and putting energy into them. They are the real sort, the drivers, because of their mobility. They can move around quickly.

They can accept energy quickly. They can get up to, and they can start to disrupt the gases that you have there. And you get, so we've already talked about ionization, and we've already talked about excitation. And so ionization, you make ion electron pairs. In excitation, you start to get light production as they decay back down. Also, if you've got molecules present, you can start, they'll dissociate molecules. And so you can then start to drive a new kind of chemistry.

So one of the real important things in the microelectronics industry is that they're able to create this new chemistry. So you can take relatively inert gases and like oxygen, and you can then dissociate it, and you can make it react. Is this driven by technology? This is, well, initially, of course, it's all driven by fundamental science. But then, for the microchip, then it became very much a technological drive to develop that. So there's something called Moore's Laws, which says, you know, that this part, the feature sizes on microchips continue to get small.

So if you take your smartphone, it's probably been in a, the chip in your smartphone has probably been in a plasma, about 100. times. And what they're doing in there is they're actually, so the initial microchip is a series of layers of materials. So they've got conducting materials, semi-conducting materials and insulators. And from those thin layers, they build circuits, microcircuits. And those circuits

have now got dimensions of about 10 nanometers. And that is smaller than the size of a bacteria. and they build structures of that size on it, and they do it using plasmas. So the key element is that you have these layers, and then you can create those layers because the ions can be accelerated from the plasma onto a surface, a substrate.

And it'll actually, when it impacts on that surface, it can kick some of that material out of that surface. It's got that process is called sputtering and then those atoms move across the plasma and they deposit on the surface and you can deposit them one atomic layer at a time. So because this process is, and you can control this by controlling the plasma.

So I mentioned that we put an electric field across the plasma nor that electric field can be pulsed and it can also be, they can be wave trains of pulses that are different each time and they kind of then

you can really tune the plasma to do what you want to do so you can do this sputtering moving particles from one place to another and then you can also have the ions bombard the surface in particular

regions and in those regions and you can start to drill holes through these layers and you can drill them at very, very high accuracy down to nanometer sizes. So you're depositing layers. You then put another layer on top,

a third layer on top of that, and then what you want to do is you need to make a connection between that top layer and that bottom layer. So then you can actually use a plasma to etch a hole through one layer to the next layer. And of course, these can be a few nanometers apart, so then you can start to build up a

circuit. For people like me, that's a form of magic. It's almost like rearranging the fundamentals in the universe, isn't it? It's like changing the way the whole thing works. Can I just turn now to Justin, you gave us that brilliant brief history.

At the beginning it was, it was great. What role might plasma have, as you've been said in the nose, in solving the energy problem and getting limitless almost. Well, limitless full stop. You can't four stop limitless, can't get on with it? In energy.

Right. Well, this relates back to what I was saying after a few tens or hundreds of millions of years when the lights switched on again and they switched on because of stars the gas coming together under gravity and under gravity that holds stars together. At the centre we have nuclear fusion occurring which is when the centres of these atoms of hydrogen, the protons and so forth,

come to get a push together and fuse. And that releases energy. I think if light atoms like hydrogen, if their nuclei come together, they release energy. I think people may be familiar that if you split up heavy atoms, like uranium, for example, that releases energy. But that does so and creates a significant amount of radioactivity. So what we'd like to do is use the same reaction in the sun. It clearly works because we're here because of it.

We also know it works on Earth in the sense that it's been produced on Earth in a hydrogen bomb. But if we could control plasma, because we need to get something extremely hot, hot as the centre of the sun, if we could control a plasma for long enough that we had in the lab miniature suns, we could solve the energy crisis because the fuel for that process, heavy hydrogen we would use. is in seawater and there's other ways of getting something from lithium, which is in every mobile phone, it would be almost a limitless source of energy. But it's extremely difficult to do. Can I turn to Kate and Kate Langay?

Well, you're in the lab trying to recreate the sun in your lab without blowing us all up. How do you do that? Well, so there's a number of ways of doing it. So one way is to kind of make a magnetic bottle. Because essentially what you've got here is material at a high. 150 million degrees Kelvin, right? So you're not going to want to touch it, but you want to keep it together

so that the particles actually interact. So one way is to put this material in a magnetic bottle with shaped magnetic fields. So we know that charge particles respond to magnetic fields. And essentially, you can shape these fields to make sure that the plasma essentially levitates in this donut-shaped device,

which we call a tokamak. So basically within that, you've got this levitator, well, you start off with a gas and you pass the current through it, turns it into plasma. And then you need it to get hotter further. So you can do two things. You can fire radio or RF into it and it transfers some energy. You can also fire neutral particles in it which collide with the particles in the plasma. And all of those things combined raise the temperature to this 150 million degrees.

Now there's another way of doing it, which is where you take a tiny little pellet of the Deuterium and Tritium, these two types of hydrogen that we're going to use. Take 200 of the most powerful lasers in the world and crush the hell out of this tiny little pellet until it's extremely dense. At the same time as the, basically when the lasers interact with this pellet, they launch a shockwave which travels in

and when the shockwave carries a lot of energy and when that shockwave stops in the centre of the fuel, that's what raises the temperature of that fuel to the 150 million degrees Kelvin. So there are two ways of confining. one, using magnetic fields, one, just the inertia of the own of the pellet. And they're very different because the ultimate aim for the magnetic bottle is you would want to do that and keep confined indefinitely, whereas the laser form is an inherently pulsed.

So it's kind of like a diesel engine where you compress the fuel until itself ignites and you do it over and over again, essentially. Bill and Bill Graham, many people will be very excited by the idea of having limitless, clean energy. and it's something that all three you talk about is a possibility. How far are we down the track in your laboratory at all? In my laboratory,

we're much, much cooler than that. In fact, we work with cold plasmas. I just needed that spanner in the works to help me along him. Thanks for that. Can we just stick to the mini suns in your laboratories when we get the hang of that first? I think that probably

in terms of getting to break even, I would see that the large laser facilities probably have a better chance of doing that than the controlled fusion inside in the magnetic bottle. But you're not giving any data. I'm going to take you up on cold plasma. I think it's very important

that we do keep developing this because it really is such a very important potential source of energy. But what about, you mentioned coal plasmas, and I must have that day. What are you talking about that? Okay, so in fact, what we try to do is to make plasmas

that are essentially at room temperature. And to do that, then, we play tricks with, as I'm starting to mention earlier on, with how we actually make the plasma. So we make it in short bursts. So we have very sophisticated pulse systems that

pulse of plasma and when we make the plasma what we're interested in is we make it in a flowing gas and this flowing gas contains um atoms those atoms get ionized but they also contain molecules and those molecules then as i mentioned can be air so we actually make the the the discharges in air and you've got hydrogen you've got oxygen and if you live in ireland it's quite easy to get water in there. And we also have nitrogen. And so what happens is then we can start to make very reactive species, things that have a very interesting effect. For example, we can make hydrogen peroxide, which of course doesn't seem to be that important because you can make that in other ways, but we can also make other things like peroxy nitrites and so forth. And these can have

influence our cells behave. They can destroy bacteria. And so we're trying to work on making these environments where we can use them for antimicrobial work and also to explore their effects on different cells. Justin, you wanted to come in. Yes, you were asking how close might we be to getting some energy. To give some idea of how far away we are, if we discuss the laser method, the compression of this little pellet that Kate alluded to, The facility in the world that's geared up to do that is in the United States in California called the National Ignition Facility.

And at the moment, they only get 1% of the energy out in the fusion reaction of the light that they put in. And they have to put even more electricity in to get the light. So it doesn't sound too good because clearly if you're getting less energy out than you're putting in, you're going to have a huge electricity bill and not solve the energy crisis. But having said that over the six or seven years, since that facility has been in existence, there's great progress has been made, and we're starting to understand

why we're only getting 1%. So the question is, my view is that if the investment was there, one would be able to get the fusion reaction to go. I don't think there's any doubt about that in the sense that, if you had large enough technology, as I say, we've created fusion reactions on Earth, but they happen to be uncontrolled

in the sense of an H-bomb. So you know technologically it's possible. There is a big question is whether you could do it rapidly enough to really produce electricity. But it's technology rather than the laws of physics that are stopping this working. So more funding in this case?

Well, more funding and more thinking. So throwing money at a problem won't solve it on its own, but it's always useful. No, I wasn't making a plea for more funding. I was just trying to clarify it in my own. I was saying, Kate, how difficult is it to control plasma? Justin referred to it, you working with it. How difficult are they to control?

Is it to control? Well, so it kind of depends what you want to do with the plasma. So, for example, say I was talking about the magnetic bottle where we're controlling the plasma with these magnetic fields. The problem that we have with the plasmas at the moment is they become quite unstable. And so we can only control and hold these plasmas for a few seconds. And we need to be able to hold them for much longer than that.

How much longer? Well, indefinitely, it would be the ideal. Not much longer. But there's a next step being device being built at the moment. It's in the south of France because physicists like sunny holidays. And it's called ETA. And the aim for that device is to be able to control the plasma for maybe 400 seconds and get net energy output.

So it is quite difficult, but there are physics problems you need to overcome in order to do these things. And again, with lasers, it's about their, you know, there are its own equivalent kind of instability. and things that they kind of mess it up, which means we're not quite there yet. So it's not an easy task. Can we continue with you, Bill, and when you're producing plasmas in liquids,

can you tell us about that? Well, of course, what happens when you do that? Well, essentially, that's a bit of a misanomer because what we do initially is we have to vaporize the water. So in fact, it's the same procedure that we use for making it in gases, except we generally have to use more power, our voltages, and we actually heat, locally heat the water and it becomes a vapor.

And then in that vapor, we can create an electric field, and we start to get ionization taking place. There is, we pulse it, the vapor layer then starts to grow. And so basically this is a thermal plasma, and the viper layer grows, and it has little fingers. And so it moves from one electrode to the other. And as it goes, it kind of is creating light emission, and also we get some UV from it. And so this is, again, a way in which you can start to do chemistry inside a liquid as well as in it. What are the medical applications of this?

Sorry, what are the medical applications? Well, in fact, currently, again, because we can get these reactive species there, these devices can be used, for example, I think the most important example at the moment is if you've torn a ligament or something and you need to remove some collagen, the surgeon wants to sculpt that, then rather than having to use a knife, you can actually go in and use this kind of localized plasm, create it within the liquid close to an electrode and that's only that little plasma then is in contact with the material

and it kind of uses a chemical etching process to remove the material rather than cutting. So we're superseding surgery there. Yeah, and so this is starting to find applications in other areas and cosmetic surgery and so forth. Justin, Justin Walker, how are experiments on Earth in the astrolabs? They call, are they changing our understanding of what's happening inside?

the sun? Oh, that's a very interesting question. What we would ideally like to do in these sorts of experiments is recreate in a controlled way bits of the sun in the lab for a short period of time. The famous physicist Eddington said, who can pierce the layers of the sun and go within? Well, of course, we can't, but we can bring the sun to us. So experiments have been taking place for a number of years now where physicists will... How do you mean bring this on to us? It's a great phrase, but how do you do it? I mean, take a small piece of material and heat it up to the same sort of conditions. So if you only go halfway to the centre of the sun, the temperature is about two or three million degrees.

So it's hot, but actually halfway in, the density is no different from the density of ordinary water or ordinary solid. It gets very dense at the centre, but halfway in it's the same density is normal matter. So that means that if we take normal matter at its density, a thin layer of it and heat it rapidly, it doesn't have time to expand very much, to 3 million degrees or 2 million degrees, we have something that looks like the sun. It will only last for a billionth of a second, or less than a billionth of a second, because it's going to want to expand rapidly. But what scientists have been doing is looking at how light is transported through that thin layer, because a lot of the way that the sun works, radiation has to escape.

We see the outside of the sun, but a lot has been going on within it from the centre going out of these photons struggling to get out. And when physicists who study the sun and want to know how it works, one of the most important properties is how do those photons get out. So experiments in the lab, just recently, in fact, published in Nature magazine, have shown that the models that physicists have for how that light gets out, how much of it, how transparent that slab of sun is,

is very different from what all of the theoreticians were telling us. And that's aroused an awful lot of curiosity because the difference pushes things more in agreement to how we'd like them to be for the sun. So, yes, making little slithers of the sun in the lab is really starting to change.

And radically changing the understanding of the... The particular physicist who did that is a chap called Jim Bailey from Sandia Labs in the US. He won the... this year's big prize in plasma physics and will be awarded it next month for that work. And Kate, thank us. So we're coming towards the end now. But could you give us,

could you give the listeners some idea of the practical, of any practical down-to-earth applications for plasmas? Sure. So obviously we've heard about the microchips and we've also heard about some medical applications. There are the medical applications of low-temperature plasma, for example. there's research going on whereby the quite reactive nature of the plasma itself and the UV radiation as well that's produced from that can actually cause DNA damage in cancer cells, prostate cancer cells, for example. So it's being looked at as a treatment for prostate cancer, for example, which is a good thing. Going to the sort of laser-produced plasmas, you can actually drive huge mega-amp currents, which then results. in energetic particles being produced like protons,

and we're looking into how those protons are produced, what the spectrum of those protons looks like and whether we will be able to use those, for example, for proton therapy for cancer as well. So there are definitely medical applications for these things, but we're quite far away from that, I will say. Bill Graham, towards the Enna, it seems to me that two things have happened in the development of this,

just from what I've read. One is the Great Royal Society idea, and going back to the Greeks, curiosity, curiosity, men have curiously and women of curiosity, saying, I wonder what happens if, and doing it because they are curious, and not thinking it'll end up in a hospital, whatever it is. So that's driving. The other thing is accreted knowledge, the development of technology, the understanding you're on a track to something. Do you think these two things are still in any sort of balance in the world you inhabit? Well, I'm absolutely certainly, are. And I think the reason for that is

there is a real appreciation of the necessity to have this kind of this work done, have the basic research develop the new processes. And we're constantly being asked questions by people. I think the main thing that's happening now and that will sustain it is that the interest in plasmas has now become multidisciplinary. And so I've already mentioned there's a lot of kind of materials people, there's a lot of medics and so forth, interested now in the application of plasmus.

Just a good future for it. Well, thank you all very much. Thank you, Justin Wall, Kate Lancaster and Bill Graham. Next week, we'll be discussing the 12th century of Renaissance in Western Europe, new cities, monasteries, universities, and so on. Thank you very much for listening. And the In Our Time podcast gets some extra time now with a few minutes of bonus material from Melvin and his guests.

Well, I think what I miss out on is actually giving a reasonable explanation of the fact that plasmas are not only kind of physical phenomena, but also they've got real kind of potential in chemistry and biology, and I think I didn't kind of manage to get that across. But the fact that the plasma only is ionized, it emits light, but the fact that it can drive new chemistries is very, very important. Because, you know, what we can do is we can disrupt molecules and break them into constituents that you can't normally do and then have them

recombine and they form then more interesting and new molecules in many different environments. And I think the thing about, especially about low-temperature plasmas as well, is that you know, you've got your big disciplines, you've got physics, you've got chemistry and you've got biology and certainly with low-temperature plasma, it's enabling the really interesting science that's in the cracks between those disciplines. It's a truly multidisciplinary endeavor. And so science has to change to accommodate that, in fact, because we all speak different languages.

A biologist speaks different languages to a physicist, to a chemistry. So it really requires a different level of understanding to work in those areas as well. I think one thing that is interesting that's difficult to get across is how plasmas are so difficult to control. And the reason for that, One of the reasons for that is you're asking about why do they carry or why are they able to carry a current. And we said it's because they have these light free electrons that can move and that is an electrical current.

But as soon as you create an electrical current, you create a magnetic field. And plasmus being charged particles react also to that magnetic field. So they're constantly creating their own currents and creating their own fields and one's feeding back on the other. You can see this in the sun, for example, with the twist. sting of the magnetic field in the sun results in this huge bursts of energy being released suddenly projecting lots of matter towards the earth, what they're called coronal mass ejections. And so we didn't get a chance to talk about the fact that often there is this thing called solar weather, just as we might have been listening to the weather forecast for this morning for

what's going to happen. And then we know, well, it's probably going to be rain. But there's a physicist also have a weather forecast for the sun and its impact. on the Earth because every now and again you'll get a huge, not just the solar wind but a huge blob of matter coming towards the Earth and this, certainly if you're up in the space station you would want to

protect yourself from that sort of environment so they'll go to a special shielded area if that goes on but it can affect us here on Earth. I mean that can knock out power transmission lines across the Earth when those big ejections take place. The most famous event

in 1989 where in Quebec The whole Quebec went out for about nine hours and six million people were out of electricity owing to the sun. And so it also mucks up GPS and we all know that we rely on GPS. So it's very important for us as physicists to have a solar weather forecast. Every now and again it goes wrong. There's a case a few months ago when a certain set of forecasts predicted a massive solar storm and you should go out because you'll see the northern lights that day and it turned out in fact that what had happened is that a gardener on his,

sit on lawnmower, ridden past the magnetometer a bit too close. So it's like an anti-Michael fish moment, if you like, for solar weather. But it's useful for people to realise that scientists are predicting these sorts of things that will affect radio communications, satellites, GPS all the time, and taking evasive measures. I think the producer wants to make us an offer, we can't reviews. Tea, coffee or any other liquid form. Tea, please.

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