 Felly, rydyn ni, Susie. I'm a physicist. I'm an accelerator physicist and I work at the University of Oxford. I run a research group there in actually high intensity hadron particle accelerators and I actually spent half my time at Harwell campus as this previous speaker was talking about. I'm also a member of the ISIS neutron and muon source, not the other ISIS, just to be clear. So what I'm going to talk about today is the fascinating world, and I really think it's wonderful, of particle accelerators. So just to get a handle on who I have in the audience, has anyone heard of a particle accelerator before? Good, I'm in safe hands. That's great. Has anyone heard of a particle accelerator other than the Large Hadron Collider? Ooh, a lot of you. Great. Okay, we actually have two at Harwell, by the way. And if you were pushed, could you give a back of the envelope explanation of how a particle accelerator works? Anyone? Ooh, a couple of... Ah, actually, okay, a few brave souls. Great. Thank you. Okay, that gives me a really good background before we get going. So most people now, when I say particle accelerator, think of this one. This is the behemoth. This is the Large Hadron Collider. It is almost 27 kilometres in circumference, which is why the tunnel looks almost straight. It's about 100 metres underground over the border between France and Switzerland. It's inside these magnets here, these big blue long ones. It's one of the coldest places in the universe at 1.9 degrees above absolute zero. And it accelerates two beams of protons from inside the atom in opposite directions at 99.99999%, that's the exact number of the speed of light, and smashes them into each other. And it is what I like to call an impressive shiny huge piece of kit that's bigger than everyone else is. This, however, is only one particle accelerator in the world, and there are actually about 35,000 of them. And later in my talk, you'll see what some of the other ones are used for. Right, so why was that particular one built? Now, I don't have time to give you a crash course in particle physics. Are there any particle physicists in the room, by the way? No, right, I'm safe, it's fine. Okay. No, I used to be one, and then I switched field. So the reason the Large Hadron Collider was built was in order to really investigate the fundamental constituents of matter. And when it really comes down to it, inside the atom, there are only actually three different types of particles, which are the up and down quarks, they're the constituents of protons and neutrons inside the atom, and the electron. Everything else there plays very little role in our day-to-day lives, but over about the last century, we've discovered that all of these particles fit together in a neat theory that describes our universe to something like nine or ten decimal places. It is an incredible amount of discovery and work that's gone into it, and I cannot do it justice in about two minutes flat. But the latest piece that we've discovered using the Large Hadron Collider, and one of the reasons, but not the only reason that it was built, was to discover this guy up over the side here that's called the Higgs boson. And the way that we've learnt all of this stuff about the universe is by taking the particles mostly and smashing them into each other, and literally seeing what comes out. Now, if you take Einstein's equation equals mc squared, is energy, m is a mass, and c is 299,792,458 mps. So that squared, I'd have to get Siri to tell me what that is. But that's a very big number, right? So it takes an enormous amount of energy to create even a tiny, tiny amount of matter. So that's why over the years, our machines have gotten bigger and bigger and bigger and reached up to higher and higher energies in order to create particles of higher and higher masses. Now, that might seem slightly counterintuitive, but if we look down at the low energy scale, we get our sort of everyday objects, and in fact up here in sort of 10 MeV, which is like a sort of everyday energy scale, are the up and down quarks where our protons and neutrons are created from. And if we go up in energy scale, we slowly discover and over time discovered all these other types of quarks and leptons and all these other things that seem to play no role in our everyday lives. And if you go up and up and up and up, we understand how the different forces in the universe work from electromagnetism to the strong and weak nuclear force. And then finally right at the top, we get to this Higgs thing, which is the theory behind why all of the other particles in the standard model have a mass. So the amazing thing about this collection of particles, which admittedly looks arbitrary until you learn it in more detail, is that you can take the entire description of every known particle and interaction other than gravity in the universe and write it down on a mug. And this is called the standard model Lagrangian, the curly L at the start is for a Lagrangian. If any of you studied physics at university, you may have come across this. And there's lots of different components of that. Now if I write it out in full, I get what is the most egotistical physics t-shirt in the entire world. So if I write it out in full, this is, sorry it's fuzzy, but really you don't need to read it, I promise, all of the different terms in that equation describe an interaction between different types of particles and force carriers. And you may have seen in the news, when the LHC was in the news, diagrams that look a little bit like this, these are called Feynman diagrams after the famous physicist Richard Feynman. And so what we do, what most of my colleagues in particle physics do, is they take this equation, they figure out which particles interacting and how, what's coming in, what's coming out. They do 21 pages of calculations and they come out with a number that is the probability of that interaction happening. And depending on which particles go in, you choose a different term that corresponds to those and which particle comes out, you choose a different term that corresponds to those, turn in the handle and you get your result out the other end. I've just taught you quantum field theory in about two seconds. So I mean it's really hard to convey in a few minutes how amazing it is that we know this about the universe and the predictive power that it has and that is the reason why we really built the Large Hadron Collider. But I'm not anymore a particle physicist, I'm a particle accelerator physicist and so it's my job to understand how to build the machines that we use in this field. And so I want to briefly run down for those of you who couldn't give an explanation as to how they work, how these amazing machines actually operate. And I want to go back to about the late 1920s and 1930s when a new type of particle accelerator was invented called the cyclotron. These are still in operation today, but the original ones, this is the pattern from a guy called Ernest Lawrence. And this is two d's as we call them, electrical cavities, which would sit inside a whopping great magnet and I'll show you a picture on the next slide. And what we do is we start in the centre with some particles and they always have to be charged particles, so either electrons, protons, charged ions, charged atoms, things like that. And we give them a bit of a kick because there's a voltage between these two halves here. And each time the particles travel between those two halves, they get a little bit of a kick, a little bit of energy. Now because they're sitting in a whopping great magnetic field, the effect that that has on a charged particle is to actually bend it around a corner. So it bends around a corner and it comes back again crossing this gap, gaining a little bit more energy and as you can see, quite obviously in the diagram, as it continues to gain energy it spirals out from the machine. So the limit in the energy in this machine is mostly how big you can build your magnet and how much iron you're willing to afford. Now this really was the original type of high energy particle accelerator and this is a photograph of Ernest Lawrence and his student, Milton Stanley Livingstone, who I should say actually built the thing. And this machine got up to about one million electron volts. In physics I use this energy range of electron volts, which means the energy that an electron would gain if I put it through a potential of one volt. So MAV is million electron volts. And that's the scale of that one that they're standing next to there. So we still use a few cyclotrons, but most of the machines that people talk about, especially in the media, are a different type of machine which we call a synchrotron. And we have two of these types of machines at the Rutherford lab at Harwell. One is the ISIS neutron source that I'm associated with and there's also the diamond light source that some of you may have heard of. Now synchrotrons are fascinating machines. The original idea was actually from an Aussie, yes, called Marcus Olyphant. And the idea here instead of having particles that start in the centre and spiral outwards, instead you keep the particles confined to one radius, one torus, and as the particles gain energy you increase the field in the magnet, the magnetic field, in time with the energy gain in order to keep them going around the same path. That's the basic explanation. If you look at a real one, and this is a photograph of the ISIS synchrotron, there are ten sections that look almost identical to this, and you have these big yellow magnets, you can see at the top and bottom there, they're what we call dipole magnets, they bend the beam around. And then there's two other main components. There are quadrupole magnets, which I'll show you in a minute, and there's also what we call a radio frequency cavity. Now this is basically a big box like a microwave into which we pump electromagnetic waves, and they set up a standing wave inside there, and we have to time the voltage of that standing wave with the passage of the particles in order to get them to accelerate. Now it's not obvious to most people how this acceleration mechanism of using a wave to accelerate particles actually works. So I have a little demonstration here of an everyday example where I can use a wave to accelerate some particles. If I just pop it on. For those of you who can't see that low, I've just got a video up here, which hopefully will, if I wake my phone up, will work. Good, it's nice when technology works. All right, one of the people before who said they knew how accelerators worked, who were you? I need a volunteer. It's going to be fun, don't worry. All right, cool. What's your name? Patrick. This is just an ordinary fluorescent tube that you have in the ceiling, so you don't smash it. Over here I have a plasma ball which has a 30 kilohertz oscillating AC voltage supply. So there's a voltage and it's a couple of kilovolts that's going up and down and up and down and up and down in the centre of that thing 30,000 times a second. And because of that, out of the plasma ball, as well as looking pretty, I'll ignore that for now, comes an electromagnetic wave that's travelling through space. So Patrick, could you move towards the plasma ball and trying to get yourself in shot of the camera would be great. Point the fluorescent tube towards the plasma ball. Can you see what's happened? So actually if you move it away, notice that it's still on. Now a lot of people show this demonstration with the fluorescent tube touching the plasma ball and say it's something about plasma and completing a circuit or something or other. It's not, it's the electromagnetic wave that's coming out of that device which is travelling through the fluorescent tube, exciting the electrons inside, they're smashing to the side, emitting, okay, it's infrared first and then there's invisible and you know how fluorescent tube works. You're enjoying that, aren't you? No, it's great. Try something for me. Try switching it on by holding it near again and then hold it halfway down. Yeah, cool, huh? You can switch it on and off. Yeah, you can move your hand up and, yeah, that's it. Yeah, because you're stopping, you are then grounding any electrons that are sort of moving inside there effectively by doing that. Thank you, Patrick, give him a massive round of applause. Cheers. Okay, so that's one example of how a wave can be used to accelerate particles but I thought you were the kind of people who needed a bit of waking up on this afternoon so I've brought along some scale model protons and I thought what I'd get you to do is for you guys to be the wave and the scale model protons are going to accelerate across the wave so first we have to practice the wave, alright? 11-year-olds do this really well, I'm warning you, you've got competition so I'm going to start at this end, we're going to do an audience wave across to that side, I'm going to do a 3, 2, 1 and then we're going to go, alright? So 3, 2, 1, go! Very nice, very nice. Now, if anyone's in the back there, can you grab the scale model protons which I think it should be obvious what I'm referring to. Yes, the giant beach balls that I placed up the back earlier and if you can hand them to people on the end of this row that would be wonderful and try not to hit the projector, alright? I'm sure they're insured. So this is, unfortunately, because of radiation protection I couldn't bring a real particle accelerator for my talk today so that's why I decided to turn you into one instead. Okay, so I'm going to go 3, 2, 1, we're going to do that again and see if we can get them to accelerate to the other side. Ready? 3, 2, 1, go! I should have watched my stuff. Very nice, very nice, well done. Okay, so can we actually hang on to those because we're going to reuse those in a second for another part of the accelerator. Okay, so that's approximately how a particle accelerator works, yeah. No, so I mean you guys are a rubbish accelerator but we do that very, very precisely, right? So what happens in the synchrotron then is you have to time that wave very, very precisely with the timing of the increase in the magnetic field in order to get the particles all synchronised and that's why we call it a synchrotron. And here's an image, a little hard to see on this screen of a sort of cutaway of the large Hadron Collider radio frequency cavity which is one of the devices and this actually operates at a superconducting temperature at 400 megahertz, this one. And this is one of the devices into which we pump a large amount of RF energy send the particles through and as they go through, as you demonstrate it very nicely, they gain a little bit of energy as they go. This is actually a real one, it did bring something real. This is actually the smallest radio frequency accelerating cavity in the world. Don't steal it, thank you. This one is from a project called the compact linear collider which is one idea of the next generation of colliders to reach even more precise measurements in particle physics. And the inside of this thing is machined to a submicron precision but the thing I want to point out is that there's a hole at the end, right? This one's for electrons which are very small beams so it can be a very small hole and they travel through there. These are the ports into which the RF ports, these are the vacuum ports. And this thing would give an electron an energy gain of up to, this one's probably about 10 million electron volts. This is also a very, very high gradient cavity so it gives a lot of energy in a very small space. I'm going to leave it here but if you'd like to look at it afterwards, you're welcome to. So, yeah, the higher frequency, the smaller they get. That's why that one operates at 30 gigahertz. It was actually so small and the machining tolerances were so tight that they've actually decided to go for 12 gigahertz instead of a slightly larger one because it makes the engineering slightly easier which is how I managed to nab that one because I don't need it. Right. So, in something like a synchrotron you actually adjust the magnets in time with usually some kind of enormous tuned resonance circuit and you would inject at the low point of the magnetic field at the low point of the circuit which usually has a sinusoid because it's easier and then you'd accelerate and increase the field as you accelerate and then you'd extract at the top with the highest magnetic field and then reset the field and you would go again. But there's actually an extra element to an accelerator that most people don't get to in one of these talks which is why I thought for you guys let's get to it because it's fascinating because all of that thing that I've described works really, really well if you have one ideal particle directly on the orbit that you're looking for but if you have a particle with an energy that's slightly off that ideal energy or if you have a particle that's slightly displaced from that it doesn't work anymore. Your particle gets lost and in reality we have beams, right? We have millions or billions even hundreds of billions in some machines of particles all travelling through there at the same time and don't forget they're all charged and charged particles actually repel each other as well so there's a force that's trying to push them out of there. So we actually need focusing systems in these accelerators as well and in a synchrochon that's provided using what we call a quadrupole magnet because it has four poles opposing poles north, south, north and the fact that magnet has on a beam and if you did high school physics and you remember doing this at all you can convince yourself over time that this is true if you have a charged bunch of particles it actually squeezes it in one dimension and pulls it out in the other so it only focuses in one dimension at once and it's not possible to focus charged particles using a magnet like, using any magnet in both dimensions at once. So what we do instead is we have series of magnets focusing, defocusing, focusing, defocusing opposite fields laid out around the ring and what this gives us is a concept called strong focusing and you can even convince yourself of this with a series of lenses if you want that if you have focusing and then defocusing in order then you actually get a stronger focusing effect than you would if you had in the lens case one single focusing lens which is very very useful to us and so if you were to sit on the beam as it goes through these magnets what you would actually see is this kind of behaviour happening in the idealised case that it's actually, it's not a static thing at all it's sort of squishing and spreading around and people like me spend our days figuring out how to get that to happen with all the complexities of a real system without losing one in a million of those particles which is a very very challenging thing to do so what I thought I wanted to do next is actually get you guys to try and demonstrate this now I've never done this before but I think you're talented enough to get it to happen to split the audience into four and get you doing that opposite wave that those magnets are doing so up down up down and see if we can get the particles to focus in the centre because I thought it would be great fun and I'm going to record it by the way so let me just give me one second I'll just get that going okay so I'm going to split you from this gentleman here in that row behind that row is a different section and then I'll split you in the centre here so I'm going to call you so there's north and south so I'm going to call you north and I'm going to call you south so opposite quadrants and what we'll do is the north and the south will be opposite in their wave so north people go up and all the north people can you demonstrate on the earth well these people have their hands down and then we swap cool and that cool excellent this is good okay this is going to work so I'm going to start the particles in the centre if you can grab that to start with now you people in the centre don't cheat alright no cheating I really want to see if this works I mean you can take one good guess at the answer to that question and so what we'll do is we'll start with the north people up and the south people down and then I'll just say swap continuously okay alright on three so three two one swap swap swap swap it's actually working I'll stop you there I'll stop you there that was genuinely an accelerator physics experiment I've never tried it before thank you so much for working with me to do that thank you okay I'll check the footage later shall I but no really they did all stay in the centre and you may have noticed that when ones came flying out they were actually pushed back towards the centre so that actually worked sometimes I do these things with 1600 kids so thank you now in fact I can do that here I'm looking down the side of four metal rods on which I'm doing exactly the same thing and I'm doing it with electric fields instead of magnetic ones and they're varying at 50 hertz in this particular demonstration and I have some charged pollen particles which I'm putting into the centre of what's called a pole trap actually it's a different device which I work on a similar system to the one that you were just demonstrating there and if I pop the pollen particles in there you can't see the 50 hertz because the refresh rate on the camera wasn't high enough but you can see that they are actually confined in sort of midair as it were and it really does have the effect of trapping them and keeping them stable inside the trap or in an accelerator inside the magnetic focusing system great okay so one of the things I hear a lot though especially when people go and give a talk about the Large Hadron Collider on particle physics but these things have no practical applications right and I think you know the answer to that is no so back in 1897 JJ Thompson actually announced the first discovery of what I would call a fundamental particle which was the electron and he actually announced it at the Royal Institution in London and at that time he you know it was really a fundamental discovery they didn't know what it would be useful for 20 years later he was back with another talk saying industrial applications of electrons and I'm just going to read this out because it's a fascinating piece of history that I think is repeating itself over and over again so he says if there are among my audience any who 20 years ago listened to the announcement I made here of the existence of electrons they will I think admit that they would have been very skeptical if they'd been told they would in another 20 years be listening to another discourse on the commercial applications of those electrons for electrons are so small that it takes about 1700 of them to give a mass equal to that of an atom of hydrogen and they move so quickly that they get out of the field of operation in a fraction of a million of a second and their properties appear rather transcendental and not promising from a practical point of view but as a matter of fact electrons are now not only in trade circulars but also in the law courts so what had changed in that 20 years after the discovery of the electron people figured out that they are useful I think anyone who knows about electricity would not really debate that fact but nowadays we use electrons in accelerators for all kinds of practical applications and one of the main ones that takes up about 50% of those 35,000 accelerators I told you about is in cancer treatment with using radiotherapy so this is a mainstay of cancer treatment about half of all successfully treated cancer cases use radiotherapy to do it as part of the collection of treatment options and this then consists of a small linear particle accelerator which is sitting in this device here which smashes electrons at about 25 million electron volts onto a metal target and that generates x-rays and those x-rays are then shaped by a complex system of sort of interleaving fingers to the shape of the region inside the human body that the doctor would like to treat and the whole thing is mounted on what we call a gantry which then rotates 360 degrees around the patient and this is really the mainstay of cancer treatment that we have today and it's all based on a small sort of meter or two meter long particle accelerator that we have up there now at the moment people are looking forward from radiotherapy to say ok is radiotherapy the best way that we can treat cancer and with some kind of ionising radiation and people have discovered over the years actually starting back in 1945 that it might not be if I were to plot for you the depth in the human body in tissue or in water pretty much the same thing versus the dose delivered to so the radiation dose which in this case you want the dose delivered to the area to kill cancer cells and I do that for a photon beam so x-rays what you find is that just under the skin is where the peak dose is deposited and the dose drops off all the way through the body and goes all the way out the other side now this sounds very useful especially for something deep inside the body right and the reason that this thing is so complicated and rotates all the way around you is to add up fields of radiation from loads of different angles in order to create the ideal distribution exactly where you want it inside the body and it does really a pretty good job but if instead we use a charged particle it has a fundamentally different interaction with tissue with water inside the body so if I use protons instead one's about 20,000 times lower in energy than the Liatadron Collider so about 250 megarelectron volts they actually come in and they don't interact much when they have a high energy so they don't deposit much dose on the way in and then as they slow down they deposit more and more dose until they stop at the end of their range depositing most of the dose there this characteristic curve which we call the Bragg Peak and this Bragg Peak looks fundamentally different from the X-ray peak and this is a very exciting discovery in about 1945 because they realised that they could use that very specific depth which you can tune based on the starting energy of the beam to actually deliver more dose where they wanted it in the body and less dose in the healthy tissue that they were trying to spare and this is now also an established treatment method over 100,000 people have been treated with it around the world and I think later this year or early next year the first UK centres full body UK centres will open there's one in Manchester and one in London on the NHS and to generate these beams at the moment most places use the cyclotron for the one I talked about earlier and the patient by the way sees none of this jazz in the background and the people that may get excited by it they see what looks like a normal treatment room with a sort of port that comes out of the wall and rotates around them so this particular application is really driving forward development of this accelerated technology on the smaller scale trying to shrink it down and this is just an example of the dose distribution this is kind of a glamour example I'm not a medical doctor but I will say it's great for some cases it's not necessary for other cases but this is an example of a child who had a tumour removed from the base of the skull and then the rest of the spine needs irradiating in order to stop that cancer spreading down the spine with photons with X-rays that's the best you can do with a single field because it goes all the way through but with protons you can get a dose distribution that obviously spares the rest of the body which is obviously a better thing later in the child's life right one of the other main medical applications in particular is to generate radioisotopes such as those you would use in a scan like a PET scan ask me all about that later if you like so that's an increasing use of them in hospitals but I do want to explain before I finish because I've only got a few minutes left what the other 50% of the application so I'm just going to really quickly go through a few others so all of us have a smartphone nowadays inside your smartphone, inside your laptop there are the processor chips on those chips nowadays the electronics are so small that actually the ions in the substrate need to be deposited individually into individual locations you can't do that with chemistry you have to do it with what is effectively a miniature particle accelerator so this is one huge application area even in things like the security of our lives on a day to day basis you don't realise they're there, they're hanging around in the background but they're being used to do things like scanning cargo using either x-rays or neutrons to discover contraband inside it this is a challenging application because you can't accidentally irradiate someone under international law but it's very very hard to get a beam to travel all the way through a cargo container so we have to weigh up the intensity and beam energy required to actually do a good measurement versus what would happen if someone was stowed away inside there because we're not allowed to accidentally irradiate them which is beyond everyday level a lot of other accelerators are used in industry to do things like sterilisation most of the medical products that are used in our hospitals have to be sterilised in some way and it's far easier to run a beam of either gamma rays or electrons through it then it would be to open it all up and chemically wash it and then safely put it back in together so that kills any unwanted pathogens that might be present in some places food is actually irradiated as well it's actually quite rare in the European Union and in the UK in the supermarket I couldn't find one thing by law it has to say treated with ionising radiation so if you ever see it there you go but you can do things like extend the shelf life of bananas kill someone on fish and chicken and kill any pathogens that exist in things like herbs and spices which is a very common reason to use that in the US if you see that symbol that means it's being treated by ionising radiation it doesn't mean it's organic and just one final one I'm not afraid of all the multiferous applications of accelerators but one that I'm thinking about for the future is something called an accelerator driven system and I'm particularly driven by this because it's a potential way that we can actually get rid of our stockpile of nuclear waste around the world and reduce its storage lifetime and we do have a problem at the moment we don't know what to do with our existing stockpile of nuclear waste from say the US weapons programme so very quickly the idea is you have a nuclear reactor a fission reactor but instead of being critical it's what we call subcritical so by itself it doesn't do anything and in the core you can have multiple things but you could have uranium you could have something called thorium which is much more abundant in the earth's crust doesn't need refinement etc and into that you mix all the high level nuclear waste that you have from the plutonium from the bombs or the high level waste from other fission reactors that we also don't know what to do with and still by itself it wouldn't do anything so you build a whopping great accelerator ok not that whopping not LHC size but still pretty big with a very very high energy high current proton beam sorry very high current one GEV so actually to me it's not that high energy you whack it into a heavy metal target inside the reactor and that undergoes a process called dispilation and spits out neutrons in all different directions and it's those neutrons that then drive the nuclear reaction to send all of those isotopes down through their decay chains to reduce the lifetime of that high level waste from hundreds of thousands of years down to a few hundred now you can actually extract energy from that process it is a reactor feed it back into the accelerator if you want you can send power to the grid if you have the reliability to do that if you don't want you just use it as a transmitter to get rid of your waste and that means that over what you do is reduce the particle toxicity of these decay products from something like 300,000 years which is what we're currently having to deal with how to tell future generations how to stay away from that down to something less than a thousand years they say between about three and five hundred years that it would have to be stored for which in my view is much less of a future generation problem and you would need in the UK you would need if we had more reactors per ten reactors so it's about that ratio so in the US they would need probably five or six of these to get rid of their entire stockpile in about ten years and they are slowly but there are movements to to build them China will get their first because they don't have the regulatory issues that we have in the west and just to finish with you can even use accelerators to improve the taste of chocolate based on the crystalline structure by studying it using a synchrotron light source or you can tell whether or not your very very expensive bottles of wine are real or fake by comparing the composition of the glass after smashing some ions into it and that tells you exactly what's in the glass and you can compare a real known one to a sample one and there's still a massive court case going on for a $500,000 bottle of wine that turned out to be fake using this analysis and I will stop there but if anyone ever asks you why a particle accelerator might be useful I'll put that back on at the end and you can memorise it for future use right and I'll stop there and take some questions thank you very much for your attention