Suzie Sheehy

"In answer to some of the questions that we had a few years ago when the Large Hadron Collider started up... "Could it destroy the world?" ...The most convincing answer to me as to why it couldn't, is because we have particles in outer space from cosmic rays and things like that, at much much higher energies than we could ever dream of creating in the lab. And so far they haven't done anything catastrophic to us and we're perfectly fine. So in terms of just reaching a higher and higher energy... it doesn't really matter what we do in the lab. We should be safe on earth from these high energy particles."

"[I]f we start creating things like mini black holes, which we may or may not, they will pop out of existence so quickly that they wouldn't have time to suck any matter in... [T]he interesting message that I take from this is that these machines are built so infrequently... 25-30 years between these big accelerators. Every time it happens, I'm told by my... retired colleagues... It happens every time, this scare story that we're going to destroy the earth with it, because it's so long between them that people actually forget the media hype that happened the last time around."

"So I'm tasking you with the job. When you're older and one of these machines starts up, and people start going, "It's going to destroy the earth!" That you think uh-huh, I've heard this before. It's not really going to happen."

"[S]ometimes some of our craziest ideas, and I've been through some pretty crazy ideas of things that you could do with a particle accelerator here... [S]ometimes they turn out to be surprisingly good ones if you do them in the right way, and these machines are not just useful for particle physics. They're useful for all sorts of other things like cancer treatment, like killing bacteria in food, and other things I haven't discussed like carbon dating, and imaging down to the atomic scale, and all sorts of other things..."

"I'd just like to leave you with my advice in choosing your career... [F]ind something that makes you sit up and think, "This is really important" or "This is fascinating" or "This is what I'm passionate about" and it can be in any area... Something like space might get you, of climate change... you might really like astronomy, or you might be more passionate about world hunger, injustices in the world, the availability of water, energy, health, aging, anything like that. Think about it, and do something about it. That's all, really, you need to do, and make a career out of doing something about it. Because if you do something that you're passionate about, and you love... You're not even going to feel like you're going to work each day. ...You're just going to feel like you're getting up and you're doing what it is that you're passionate about..."

"[D]on't be afraid to challenge yourself. Don't shy off doing something just because you think that it's hard. It's when we're doing something hard that we really make a difference. So dig deep and don't be afraid to dream."

"I will leave you with some photographs of some of the places that my career in physics has taken me so far, and I hope to add many more to this list in the future."

"So that's 5 things you should never do with a particle accelerator. Thank you."

"So my name's Suzie. I'm a physicist... an accelerator physicist, and I work at the University of Oxford. I run a research group there in... high intensity s... I... spend half my time at Harwell campus... I'm also a member of the , not the other ISIS, just to be clear."

"What I'm going to talk about today is the fascinating world, and I really think it's wonderful, of particle accelerators."

"Has anyone heard of a particle accelerator other than the Large Hadron Collider? ...We actually have two at Harwell... If you were pushed, could you give a back of the envelope explanation of how a particle accelerator works?"

"Most people now, when I say particle accelerator, think of... the bohemoth. This is the . It is almost 27 km in circumference, which is why the tunnel looks almost straight. It's about 100 meters underground, over the border between France and Switzerland. ...Inside these magnets here, these big blue long ones it's one of the coldest places in the universe at 1.9°K above . ...[I]t accelerates two beams of s, 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... [I]t is what I like to call an impressive shiny huge piece of kit that's bigger than everyone else's!"

"This... is only one in the world... there are actually about 35,000 of them..."

"So why was that particular one built? ...I don't have time to give you a crash course in particle physics. Are there any particle physicist in the room..? No, I'm safe. It's fine, okay. No, I used to be one, and then I switched fields."

"The reason the Large Hadron Collider was built was... to... investigate the fundamental constituents of matter..."

"[I]nside the atom there are only... three different types of particles, which are the up and s, they're the constituents of s and s 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 9 or 10 decimal places. It is an incredible amount of discovery and work that's gone into it, and I cannot do it justice in... two minutes. 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... the Higgs boson."

"[T]he way that we've learned all of this stuff about the universe is by taking the particles... smashing them into each other, and literally seeing what comes out."

"[I]f you take Einstein's equation E=mc2, E is energy, m is the mass and c is 299,792,458 meters per second, so that squared, I'd have to get to tell me what that is, but that's a very big number. 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... everyday objects, and in fact up here at sort of 10 MeV, which is like a sort of everyday energy scale, are the up and s where our s and s are created from. And if we go up in energy scale, we slowly... over time discovered all these other types of s and s, 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 ."

"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."

"[T]his is called the Standard Model Lagrangian, that curly \mathcal{L} at the start is for Lagrangian... 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 teacher in the entire world. So if I wrote it out in full... 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..."

"[Y]ou may have seen... when the LHC was in the news, diagrams that look a little bit like this. These are called s after the famous physicist, Richard Feynman... [W]hat... most of my colleagues in particle physics do, is they take this [full Standard Model] equation, they figure out which particle's interacting and how: what's coming in, what coming out. They do twenty-one pages of calculations, and they come out with a number that is the probability of that interaction happening... [D]epending 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 the handle and you get your result out the other end. I just taught you quantum field theory in about 2 seconds."

"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... [T]hat 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 briefly want to run down... how these amazing machines actally operate."

"I want to go back to about the late 1920s and 1930s when a new type of was invented, called the . These are still in operation today, but the original ones... This is a patent from... and this is 2 Ds as we call them... electrical cavities which would sit inside a whopping great ... [W]e start in the center with some particles, and they always have to be charged particles. So either electrons, s... s, charged atoms. Things like that, and we give them a bit of a kick, because there is a voltage between these two [Ds] halves, and each time the particle moves 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 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 it continues to gain energy it spirals out... 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 Livingston, who I should say, actually built the thing... [T]his machine got up to about 1 million s."

"In physics I use this energy range of s which means the energy an electron would gain if I put it through a potential of 1 . So MeV is million electronvolts. And that's the scale of that... [cyclotron] they're standing next to..."

"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 , 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 ..."

"[S]ynchrotrons are fascinating machines. The original idea was actually from an Aussie... called Marcus Oliphant and the idea here... instead of them having particles that start in the center and spiral outwards... you keep the particles confined to one , one , and as the particles gain energy you increase the field in the magnets, the magnetic field, in time with the energy gained, in order to keep them going around in the same path."

"If you look at a real one... the ISIS synchrotron. There are 10 sections that look almost identical... and you have these big yellow magnets... They're... s. They bend the beam around, and then there's two other main components. There are ... and... a radiofrequency cavity. Now this is basically a big box like your microwave, into which we pump electromagnetic waves, and this sets up a inside there, and you 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... of an everyday example where I can use a wave to accelerate some particles. This is just an ordinary fluorescent tube that you have in the ceiling... Over here I have a plasma ball which has a 30 kHz oscillating AC voltage supply. So there's a voltage, it's a couple of kilovolts that's going up and down, up and down, up and down in the center of that thing, 30,000 times a second. And because of that, out of the plasma ball... comes an electromagnetic wave that's traveling... through space. So move towards the plasma ball and point the fluorescent tube toward the plasma ball. [It lights up] ...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 that it's something about completing a circuit... It's not. It's the electromagnetic wave that's coming out... which is traveling through the fluorescent tube, exciting the electrons inside. ...you know how a fluorescent tube works."

"Try something for me. ...Hold [the tube] halfway down. [Half of the lamp goes out] ...You're grounding any of the electrons which are... moving inside there..."

"So that's one example of how a wave can be used to accelerate particles, but... I brought along some scale model protons [large beach balls] 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 [beach balls moved by audience hand wave]... Eleven-year-olds do this really well, I'm warning you. You've got competition."

"I mean you guys are a rubbish accelerator, but we do that very very precisely. ...So what happens in a synchrotron... is that you have to time that wave very very precisely with the increase in the magnetic field in order to get the particles all synchronized, and that's why we call it a synchrotron."

"[A]... Large Hadron Collider radiofrequency cavity... is one of the devices, and... operates at... superconducting temperature at 400 MHz... [T]his 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 demonstrated very nicely, they gain a little bit of energy..."

"This is actually a real one. ...This is ...the smallest radiofrequency accelerating cavity in the world... This one is from a project called the 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 sub-micron precision... [T]here's a hole at the end. ...This one's for electrons, which are a very small beam, so it can be very small hole, and they travel through there. ...These are the RF ports. These are the vacuum ports. ...[T]his thing would give an electron an energy gain of ...probably 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. ...The higher the frequency the smaller they get. ...That one operates at 30 GHz. It was actually so small and the machining tolerances were so tight that they've actually decided to go for 12 GHz instead... because it makes the engineering slightly easier."

"I'd just been asked by four particle physics professors... my PhD interview was conducted over an unstable internet connection... "what do you find fascinating about particle physics?" ...I told them of my wonder at the way physics seemed to be able to describe everything: from the smallest s to the atoms that make up our bodies, up to the largest scales of the Universe, and how all of this was connected. Particle physics, I said, was the foundation of it all."

"Five years earlier... [a]s my eyes adjusted to the darkness, the true wonder of this designated "dark sky site" revealed itself. ...The stars and planets weren't up there and I wasn't down here: it was all part of one enormous physical system called the Universe. I was a part of it too. ...I'd never really felt my place in it until that moment."

"Suddenly, nothing else mattered. I wanted to know... about gravity and particles and and relativity. About stars and atoms and light and energy. Above all, I wanted to know how it was all connected and how I was connected to it. ...[I]t mattered to me as a human ...if I managed it even a little bit, I'd not have wasted this little blip of time as a conscious being. I decided to become a physicist."

"[A]s I studied more physics the question... at the core... was: "What is matter, and how does it interact to create everything around us—including ourselves?""

"I suppose I was trying to figure out the meaning of my own existence. ...I went about it in a more indirect way: I set about trying to understand the entire Universe."

"Our view of the smallest constituents in nature has changed rapidly in the last 120 years... Some way into the twentieth century this work became known as "high-energy physics,"... Today the study of all the many particles and how they formed, behave and transform is simply called particle physics."

"The Standard Model of particle physics classifies all known particles in nature and the forces through which they interact. ...[O]ur current version came about in the 1970s. This theory is an absolute triumph: it is mathematically elegant and unbelievably precise, yet it fits on the side of a mug."

"The Standard Model tells us that all the matter that makes up our everyday existence is composed of just three particles. ...[T]wo types of s called "up" and "down" which forms our s and s. These... with the electrons make up atoms, held together by forces: electromagnetism and the strong and weak nuclear forces."

"The reason we can say today that we know all this stuff, that we think our theoretical models represent reality, is not because we have pretty mathematics but because we have done experiments."

"[E]xperiments take us to that frightening frontier of vulnerability: the real world."

"While a theoretical physicist's ideas must take into account the results of experiments, an experimental physicist has a more nuanced job. She is not simply testing out the ideas of theoretical physicists; she is asking her own questions and designing and physically building equipment she can use to test those ideas. ...[H]er practical knowledge ranges from to chemistry, from to ."

"Over the last century the experiments... have gone from single-room setups led by one person to the largest machines on Earth. The era of "Big Science," which began in the 1950s... now... involve collaborations of over a hundred countries and tens of thousands of scientists. ...[N]o individual country can achieve these feats alone."

"Accelerator physicists constantly discover new ways of creating beams to help learn... about particle physics. ...[T]he nearest hospital almost certainly houses a particle accelerator. ...We build particle accelerators to study viruses, chocolate and ancient scrolls."

"In this book, I will take you through twelve key experiments that marked... a discovery... we now see as essential to our understanding of the world... [T]hese experiments embody the spirit of enquiry that stems from human curiosity. ...[T]hey have changed our lives in almost every aspect, from computing to medicine, from energy to communications and from art to archaeology."

"Physics will always be, at its core, about understanding our place in the Universe..."