In 1927, a tall man
from New Zealand, called Ernest
Rutherford, stood not far from this location
at the Royal Society. And as the new president
of that institution, he had this to say--
that he desires a copious supply of
atoms and electrons which have an individual
energy far transcending that of alpha and beta particles. Now the reason he
was saying this is because awhile
before, in his lab, they'd been doing the so-called
famous gold foil experiments, where they had taken
alpha particles from radioactive decay
and impinged them on a piece of gold foil. Now those of you who
know the story know that what they were expecting
was that these alpha particles would kind of go straight
through and some of them would be deflected a little bit. And what they actually
found was that just a few of these alpha particles
pinned straight back at them in the direction
they were firing them. And that was a real surprise. And now we know that
they had discovered the nucleus of the atom-- the
tiny nucleus at the center. But Rutherford
understood that in order to learn more, in order to
dig deeper into the atom, in order to understand our
universe at a deeper level, he was going to have
to find something with a bit more energy--
some projectiles which went a little bit faster. And so, effectively,
what he was asking for at that time was the
particle accelerator. And boy, did he get some. So 90 years on, this is what
we think of now when we talk about a particle accelerator. This is the Large
Hadron Collider, in case you're not familiar with it. It is a 27 kilometer long
ring underneath the border between Switzerland and France. And now we think
of these machines as a sort of huge
behemoths, really. They are incredible feats of
engineering, design, science, and even culture--
breaking down boundaries between different countries. But the question is,
are these things useful? I mean, when you think about
what we're looking at there and what Rutherford was
looking at with the atom-- atoms are tiny. And there are loads, and loads,
and load of them in anything useful. So in the universe,
for example, if I was to add up all the
stars in the universe, there would be 10 to the
29 in scientific notation. So that's 1 with
29 zeros after it. That's the same
number as the number of atoms just in the people
sitting in this room-- not even in the chairs and the ground. So there are as many atoms
in us-- in this room-- as there are stars in
the entire universe. Remember that the universe
is 13.8 billion years old and pretty massive. So atoms, being
very, very tiny, it doesn't immediately
make sense that they're going to be that useful. And especially the
particles inside them-- the subatomic particles--
it's not entirely obvious that they're going
to be useful either. And actually, if we go
back further in history, we find that the
initial people who worked with other
types of particles were also skeptical
about their use. One of the famous Friday
evening discourses here was given by J.J.
Thomson, the physicist, where he demonstrated
the particle which later became known as the electron. And he actually came back. And this isn't that well-known--
but the Royal Institution kindly dug through
their archives for me and they gave me this
document beautifully titled-- allthediscoursesever.xls. And there was a whole host
of lovely information. And one of them that they
found for me was this, from J.J. Thompson. And he says-- and I'll
have to read up here because my screen
is tiny-- "if there are any 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 skeptical if they'd been told they
would, in another 20 years, be listening to
another discourse on the commercial application
of these electrons. For electrons are so small that
it takes about 1,700 of them to give a mass [INAUDIBLE] out
of an atom of hydrogen and they move at such a rate"--
blah, blah, blah. "So such properties appear
rather transcendental and not promising from a
practical point of view." How wrong he was. And in fact, there was a toast
that famously went around the Cavendish Lab-- it's J.J.
Thomson's favorite quote-- "to the electron... May it never be of
any use to anybody." So I thought, with
particle accelerators, what I'd start with is to
show you how we can actually make some particles. So I have here a very
small particle accelerator rather like the one that
J.J. Thomson would have used. And to power it, over here, I
have a high voltage oscillator, which is actually an induction
coil, which Faraday-- himself presenting in here-- would
have been very proud of. So I'm going to switch
this on and it actually converts a DC from a battery
here to a very high voltage AC. And then over this
side-- fingers crossed my camera is working. If we dim the lights
a little-- perhaps I can move that on there. There we are. OK. So that's is actually
generating a beam of electrons. So to generate
electrons is quite easy. You, more or less, apply
voltage to a piece of metal and they start jumping out. So this is what's called
a cathode ray tube. And some of you will
be familiar with those because they were in
the back of televisions for many, many years, before
we had flat panel ones. So this has some of the basic
components of a particle accelerator. So it starts with
some particles. And then the next thing we have
to do is give it some energy. And in this, all I'm doing
is applying a high voltage across the terminals to rip
the electrons out of one side and attract them
to the other side. Now the other thing I can do
with this beam of particles is I can actually
move it around. And that's an incredibly
important part of a particle
accelerator-- being able to control the
beam of electrons. And to do that, we
actually use magnets. So I have, literally, just
a simple bar magnet here. And I can show you that the
beam bends when I bring it near. So this is just a
simple magnetic field. I hope you can
see that up there. I'll do that again. And this is a basic property
of charged particles in a magnetic field. They will bend around a corner. So if I hold the magnet the
opposite direction, then, as predicted, we should
get the opposite effect. So we'll turn it around
a few times there. So that has a few of the
basic components of a particle accelerator. And I'll just come
back over here. But I think you might
not be surprised to hear that they get a little bit
more complicated than that. And we'll get onto
that in a little bit. I'm just going to
switch that off. A lot of people
think, when you start talking about
particle accelerators, that we should start
from the very start-- from generating
particles-- and then build up how we get to
the very high energies at the speed of light. But actually, when we
design accelerators, we start from the other end. We sort of start
with, what would you like a beam of particles
to actually do? So it might be, for
example, that you would like to sterilize medical products. And in that case,
what you'd need is actually a 10
megaelectron-volt beam of electrons, so quite a bit
higher in energy than this one. And in that case, a high
intensity beam of electrons is sent through all of
the medical products that go into your hospital. So syringes, bandages, and that
kind of thing are sent through on a conveyor belt,
irradiated with electrons, and that's actually able
to kill any of the germs-- every single germ or bit of
bacteria that might be on those products when they;re generated. So that translates from a
use back into the design of the accelerator. And that's a commercial system
that's sold on the market to do that. Or maybe instead, I
want a beam of something to, say, scan some cargo. In that case, you could start
with a fairly similar system with electrons, use those
electrons into a heavy metal target to generate x-rays,
and send the x-rays through your cargo, and by
doing so, map out the density and if there's any contraband
or whatever that's inside cargo. And these are used as well. And there's another
option, actually, at the moment of
potentially using neutrons to do the same kind of scanning. So that's another thing. Perhaps you might
want to treat cancer. Are you getting the
impression there's a couple of uses here of
particle accelerators? I hope so. You might want to treat cancer. And actually, radiotherapy--
LINACs, as we call them, linear accelerators--
are some of the most ubiquitous accelerators around. There's five or six of them
in most major hospitals. And this is actually just a
small electronic accelerator. Again, it smashes electrons
into a metal target, generates x-rays,
and that's what's used to treat
cancer in something like 40% of successful
treatment cases. So that's a huge application. Now I think it's fair to
say J.J. Thomson did not predict that. We've come quite a long way. And that's sort of electrons,
but we can also move on to other types of particles. We know how to generate
beams of protons and use those to
generate other things as well, with our
understanding of isotopes. So one other area
in medicine where we use protons in particular
is to generate radioisotopes. And one example of
where they might be used is in PET scans-- positron
emission tomography scans. And they're great
because they actually also use our understanding
of anti-matter. So in a positron
emission tomography scan, if you don't know, someone is
fed a small amount of what's called fluorodeoxyglucose. It's a sweet liquid. And into that is a tiny bit
of radioactive fluorine-18, which is being generated
by a particle accelerator, using a beam onto a
target to generate that radioactive isotope. When it's inside the
body, it emits positrons. It's a beta emitter. Now positrons,
being anti-matter, when they come in contact
with normal matter-- electrons-- they annihilate. So they literally
disappear and, instead, generate two photons--
two particles of light-- in exactly opposite directions. So we're able to then
catch those photons, going in opposite directions,
every time they happen and build up a picture of what's
happening inside the person's body. And because this
fluorodeoxyglucose actually concentrates in high
metabolic areas, that means you're more
likely to map out areas where there might be cancer,
heart disease, et cetera. So that's another potential use. So if you add them
all up, far from just being particle physics
machines, there are loads and loads
of those things. So there's over 35,000 particle
accelerators in the world. And I've just sort of
given a bit of a pie chart of how they're broken down. So something like 45% of them
are used for radiotherapy and then most of
the rest of them are used for industrial
use-- so whether that's treating things, scanning
things, treating radial tires, changing the properties
of gemstones, treating dirty drinking
water to clean it up. All kinds of different things. So you might get the idea
that, actually, these things are pretty useful machines. And for me, working on
them, I'd really quite like to see what else
we could do with them. But before we go
into that, we're going to have to understand
a little bit more about how they work. So in the cathode
ray tube before, I had just a single voltage
supply-- just a single voltage that the particles are moving
through and gaining energy as they did so. But that's quite limiting
because you can only gain as much energy as
that voltage gives you. But the other way you can do
it is you can take a voltage and try and re-use
it again and again. And that's what this
little demonstration here is supposed to show
you, in one second. So this is powered by a Van
de Graaff generator, which, I should say, Van de
Graaff accelerators were one of the original types
of particle accelerators. They use a rubber belt to build
up static electricity, which goes on the top of the dome. And then I've attached
that high voltage, which is about 30,000 volts on this
device, onto my plastic bowl here, onto four strips which
are crossed in the center. So those four strips in
the center get charged up and the other ones
around the outside-- I've kept those at ground. So what happens here-- and
it's a very, very simple model of an accelerator--
is I have a ping pong ball covered in
conducting paint. So it picks up the charge
on the charge strip and gets pushed away. And then it rolls around
a bit, dumps the charge on the grounded strip,
but keeps rolling. So every time it goes
over a charged strip, it gets a little bit of a kick. And so you saw, when I turned
it on, it started in the middle and slowly, it built up some
speed, built up momentum, and now it's limited by friction
as to how fast it could go. Otherwise, I'm sure it could
reach the speed of light. I'm sure. I'm sure it could. So this is a very basic model
of a particle accelerator, but there's a little
bit of a problem with how that one in
particular operates. I'm just going to
switch him off. So one of the flaws in that
demonstration actually-- and it is lovely,
but it's flawed-- is that I've just got
a single voltage there, which I'm really
using again and again. But in order to do
that, I actually have to change the
charge on the particle. And real particles don't
change charge, sadly. So we have to come
up with another way. And in the real
world, we actually use radio frequency
cavities, which I'll show you in a moment. But this was the idea
that Ernest Lawrence had when he invented a type
of particle accelerator called the cyclotron. So what he was doing was taking
a single, oscillating voltage and using it again and again. And the particle
would gain energy. And because it was in a
simple magnetic field, it would spiral
outwards as it did. So as you gain
energy, the particle's going to spiral outwards. And so these machines
were limited, in terms of energy--
physically, by their size. So this is a 1
electron volt, I think, proton machine that he built
with his graduate student, Milton Stanley
Livingston, who did a lot of the practical work. And cyclotrons really became the
cornerstone of nuclear physics research for a long time. And they're still
used today, especially in things like
radioisotope production and actually new forms of
cancer treatment as well. So that's the cyclotron. The other type of
accelerator I'd like to introduce you
to-- because there's two circular types which
are related to my work. That's one of them. The other type is
the synchrotron. And this now is
the type of machine that we use to reach
higher and higher energies. The cyclotron was limited
by the size of the magnet that you could use. So instead, we had to come
up with another idea of how we can reach higher
energies but without having to have these huge, huge magnets
that were just incredibly heavy. And then a guy called Marcus
Oliphant-- an Australia, actually-- invented the
machine called the synchrotron. Now this machine's
a bit different because it looks quite
different from the cyclotron. It just has a single
large ring of a series of different magnets
around the ring. So what we have to do
is we have to ramp up the strength of
those magnets in time with the acceleration
of the particles in order to actually keep
everything synchronized. And that's where it
gets its name from me. That's where the synchrotron
actually comes from. And there are three
main components of that-- there's
dipole magnets, which do the bending, quadrupole
magnets, which we'll come onto in a minute, and
then there's these RF cavities that I alluded to before. So I've just got a
little video here. Here we go. So this is what a
radio frequency cavity looks like on the
Large Hadron Collider. And that thing's
probably about this tall. This thing operates
at 400 megahertz, so the oscillations in that
are 400 times per second. And it's fed by a high voltage
radio frequency signal. So inside that cavity,
effectively, there's an electromagnetic wave
goes up, and down, and up, and down 400 million
times a second. And as the particles
go through that, they have to be timed
exactly in order that when the field is up
and in accelerating mode, it gets a kick forward. And when the field
is down, they're not seeing the field because we
can't always have the field up. So that's quite a large one. That's 400 megahertz, so
they're quite big cavities. I actually have here the
world's smallest radio frequency cavity, which I'm
lucky to have one. This was developed
for a new project at CERN called the
Compact Linear Collider. So that was 400
megahertz, that one. This one is 30 gigahertz--
so very, very high frequency. So the particles would
travel through the center of this device. And the RF is fed
in through some wave guides, which are on the top,
and these ones are really tiny. And inside there is where
the particles actually gain some energy as they go through. But it's not very easy to see
exactly what happens inside of there, so I've got a really
simple demonstration to show you, which is how a
sort of radio frequency electromagnetic feel can give
some energy to some particles. So if we can dim the
lights a little bit? I have a plasma ball
here, in the center. I know it's pretty, but
ignore the plasma bit. It's generated using a 30
kilohertz oscillation, which is emanating electromagnetic
waves outwards, which is what's forming the plasma. But also, those waves
continue outside the confines of the plasma ball,
which means that if I put some particles in the
way, those particles actually get accelerated. And you'll notice
that, actually, I'm not touching that. And actually, I can
ground it as well. So I can sort of
turn it on and off-- sort of creating a
little bit of a circuit. So it does work if I
touch it, but, actually, one of the main things
I want to show you is the sort of RF
waves coming out here, accelerating the particles. And that's why it actually
switches on and off, just in proximity. A new party trick for you. So yes. So that's how we give
particles energy now. But we need to go a little
bit further than that. And we need to understand how
particles are focused as well. So it would be easy to assume
that all you have to do is get the particles, give
them energy, bend them round in a corner, job done. No. We actually have to keep
them focused as well. And we have a problem with that
because the types of magnets we use-- and any
type of magnet-- can't focus a beam of particles
in both dimensions at once. So if I squeeze it horizontally,
it's pulled apart vertically. And I'll solve this dilemma
for you in a little while, but first, I just
want to show you-- this is a real, physical
quadrupole magnet over here. It weighs about 30 kilos, so
I wouldn't try picking it up. But this one is for a fairly
medium energy electron beam. But once we get up to the
very, very high energy-- say, proton beams-- we need
much, much stronger magnets. And that's why you get these
huge ones at the Large Hadron Collider. So all of that then
in the synchrotron has to be synchronized together. So we have to have the
accelerating cavities, we have to have the
bending magnets, and we have to have
the focusing system all acting on the beam
in perfect timing in order to accelerate the beam. And on most synchrotrons,
we use something like a sinusoidal cycle
of the magnetic field and we link everything to that. So this is just showing you
what that cycle would look like. We would inject the beam at
the low point of the cycle. As the particles
are accelerated, the field increases. And then we would extract
the beam at the top. Now that's a limitation
for the synchrotron because it means-- great as they
are and they can reach whatever energy you want, as long as you
have strong enough magnets-- they have a cycle limitation. They only cycle-- most of
them-- often once or a few times a second. The rapid cycling versions are
up to sort of 50 to 70 times per second. So that's a limitation
that will become important in a little while. Now backtracking a little
while-- at the start, I was showing you
lots of applications. We face many, many
challenges today, especially in the 21st century. And as a scientist,
like me, you don't have to go very far
to pick a challenge, you just have to sort of
watch the headline news. This morning I wrote
down-- what was there? There was climate change,
overpopulation, food and water shortages, incurable diseases,
aging populations, security and terror threats,
or our planet being destroyed by an asteroid--
not an astronaut, sorry. An asteroid. Don't get too depressed though. Yet I've chosen
to work on these. I've chosen to work on
particle accelerators when all those glorious
challenges are out there. And the reason is
because I believe and I want to use
what we've learned from this field
and these machines to help solve some of these
real challenges facing us today. Now the next generation of
accelerators for particle physics could take any form. So we're researching lots
of different options-- whether that's a very
long, straight line linear accelerator,
whether that's a circular accelerator,
or even a more exotic one, colliding different
types of particles-- say particles called muons,
which are like the heavier version of the electron. And they're brilliant
and that's really pushing our technology forward. But there are other areas
of accelerated science which are pushing us in a
slightly different direction. So in the accelerator
world, we talk about there being two frontiers. There's the energy frontier--
and, in particle physics, that's where we're
going with that. We're trying to get to
higher and higher energies in order to reach heavier
and heavier mass and more rare and exotic particles. But there's also something
called the intensity frontier. And that's the one
that I work on. And the intensity
frontier tends to lead us towards different applications. It could also lead us towards
a new particle physics applications. But one of the main
ones is actually to generate neutrons using a
high intensity beam of protons and then use those neutrons
to do other things. In the UK especially, people
are really good at that because we have a spallation
neutron source called ISIS, which is at the Rutherford
Appleton Lab in Oxfordshire. And that's been going
for more than 30 years. And it's generating
wonderful science from all kinds of
fields using neutrons to investigate matter, and
materials, and biology, and aircraft wings,
and oil part blockages, and how to save babies with
[INAUDIBLE], and all kinds of amazing science. So on the one hand,
we need to understand, to generate more
science that way, how we can generate more
neutrons using a particle accelerator. But there's actually
other challenges which are pushing our
field further, and further, and further. And one of those
is how we might be able to deal with the nuclear
waste problem or parts of the nuclear waste problem. And there's an idea out
there called accelerator driven subcritical reactors. Some of you may have
heard of this already. Now this idea is to take a very
high intensity proton beam, smash it into a target,
generate neutrons in the same way we do in the
ISIS accelerator, and then, using those neutrons to drive
existing nuclear waste-- especially minor actinides,
high level nuclear waste-- through their cycle
in order to reduce the lifetime of that they
would have to be stored for. So one particularly popular
idea is to mix in an element called thorium. And thorium is actually
a fertile element, not a fissile one-- unlike
parts of uranium. But thorium is about
twice as abundant in the earth as uranium is and
you don't have to refine it. So if you mix in
thorium and then you mix in these existing types
of nuclear waste from existing reactive fleets, you would
be able to bombard it with neutrons from
the accelerator, transmute the nuclear
waste, and get rid of it. If you did it in the right way
and within enough power coming in, you could generate energy
from that process as well. But this is an incredibly,
incredibly challenging application. So let me give you kind of
where we're at versus where we'd like to be. This is a plot,
which is often used in my part of the accelerator
field, which shows the beam power of different
accelerators, which I'll explain a little bit at the moment. But all you need to
know is the energies are on the x-axis and the beam
current-- so how many particles per second-- are on the y-axis. And we can see sort of different
generations of machines there. So you can see, for example,
some of the high energy particle physics machines are
very high on the energy axis, not so high up the
beam current axis. And so when we
multiply those two numbers to give a beam power,
it's maybe not that high. It's maybe 0.1 megawatts. On the other hand, the optimum
energy for generating neutrons is about 1 gigaelectron vote. And so you'll see on
sort of the left hand, but up at the top, a bunch
of facilities and machines which are more attuned to
this intensity frontier, which has slightly low energy,
but they're generating quite enormous beam currents. And actually, state of
the art, at the moment, is to get to about
1 megawatt or just over 1 megawatt, which has
being done at the SNS Spallation Source in the US and at PSI,
which is in Switzerland, that's done that before. Now where we need to be for
these future applications is at least 10
megawatts, if not 100. So we need to be 10 to
100 times more powerful than we are at the moment. Now I haven't mentioned
reliability yet. When you get higher in
power, it's much harder to make your machine
reliable, so you can leave it on all the
time, run it all the time. But actually, a
real application, like transmuting nuclear
waste, would also require us to be
switched on all the time. So we actually have to
be up to 1,000 times more reliable-- so less small
trips and small problems than we have at the moment. And we've never designed an
accelerator with that in mind. So just to backtrack a second--
how might we actually do that? Which parameters do
we have to play with? Well, to get to high power,
which is what we need, we have sort of three pieces
of the puzzle-- there's the energy-- but,
as I said, that's kind of fixed because if
we're generating neutrons, 1 GeV is about
right-- then there's the particles per
beam-- and that's a limitation which I'll
get to in a little while. And then there's the
repetition rate-- there's how many
times per second you can run the
machine-- because that limits your average
intensity over time. And I said before that the
two machines I was looking at are the cyclotron
and the synchrotron. The cyclotron is
limited in energy. It can't go up 1 GeV, so it
can't get to the optimum energy that we need for
this application. The synchrotron is limited
in its repetition rate. So in order to generate
a high average current, it has to try and operate
it many times a cycle or to really, really ramp
up how many particles there are in the machine at one time,
which is really problematic. But there is actually
another option. And this it's a type of machine
that I have specialized in. And this is called a
fixed field alternating gradient accelerator. Right now, this isn't going to
make a huge amount of sense, but the main points in
that are in the title-- it's a fixed field,
so that means we don't ramp the
magnetic field in time, and alternating gradient. And this alternating
gradient has something to do with the
focusing system, which I'll explain a little bit
more about in a second. So it uses the same
focusing as a synchrotron so we can reach high
energies, but also the fixed magnetic field of
the cyclotron, which means high energies, and
also no sort of limitation, and giant magnets,
and things like that. So the beam in this
machine, it does actually spiral outwards a little
bit, but only a small amount. And we've arranged
the magnetic field to increase with radius
in a very particular way, so that as the beam
spirals outward, it sees a higher
and higher field. So it sees a field
like a synchrotron, but we don't have to
ramp the thing in time. And in terms of
high intensity, this could be a huge advantage
to us in the future. And to understand a little
bit more about that, I actually want to talk
about how we trap particles and how we focus. I've kind of been alluding
to this magnet that squeezed one way and didn't the other. So I've got, over here, a very
sort of visual demonstration to show you how this works. So if I have my
particles in a beam and they're traveling
through a series of magnets, when they go through,
say, a focusing magnet, they're going to say a magnetic
field which controls it like this-- so if
it's too far that way, it'll push it back
to the center. And if it's too far this
way, it will push it back to the center. But unfortunately, when it
goes through the other type of magnet, it will be defocused. So no matter where
it is, it's always going to be pulled away from
the center and defocused. Now I think, to those of you
looking at this demonstration, there's an obvious solution
to how we solve that problem and how we make that
focusing stable. And that is--
well, in this case, we have to alternate the
gradient of that focusing. That's what I mean by
alternating gradient. And in this particular
case, we can do that by actually physically
spinning this device. It creates quite a wind. Here's the difficult bit. I have to try and trap
a particle with it. Let's have a go. Thank you very much. And again, we'll come back to
that in a little while as well. So if we get the alternating
gradient correct, and the right speed, and
the right everything, then we can trap our particles. And that's quite a fundamental
thing in accelerator physics. And it leads to this principle
that we call strong focusing. And this is why the synchrotron
was such a great invention and allowed us to reach
higher energies-- because by alternating the magnets
back and forth between focusing and defocusing, we were able
to focus in both planes. And not only that, but we can
focus in both planes stronger than any other way we
know of focusing particles because it's sort of
analogous, but not quite like lenses of light. But the slight
other problem though is that you can't
choose anywhere. Now this is, genuinely, a
plot from my PhD Thesis. I'm actually not kidding. So what I was showing to you
before, with this Paul trap-- I've set it to a
particular speed. I set it running--
this saddle shape. And I put the particle on. And it was trapped for a short
while before it flew off again. But that actually only
works at certain speeds. So this diagram here
is showing you-- on the x and the y-axis-- kind
of the focusing strengths, so the curvature, on one. And let's say we're looking at
the speed on the other axis. It doesn't matter. There's two parameters there. We're changing a couple of them. And only for certain sets of
those parameters is it stable. The green and the
red show that it has to be stable in
two different ways. So if I set this running
again-- and those of you, especially if you're
higher up, you might be able to observe
this quite closely. I have to feel exactly when
it's in the right spot. There we go. So if you were to observe
that closely-- whoa. I'll try again--
you would actually notice that there's a
couple of different types of oscillations. There's sort of one round this
way, a sort of radial one, and then there's
also a vertical one. And both of those have
to be correct in order for it to stay put. So let me just put that
back on there again. Oh, I think that's
the sweet spot. There we go. I'm not the best at doing that. We have other people
who are better at it. Otherwise, if it's not
rotating at the right speed or if it's not in the
sweet spot particularly, it goes flying off. So for example, if I do it
much, much slower-- a little bit too slow. Come on-- and if
I pop it on then, I think, based on
just intuition, you can probably tell that
that's not going to work. But I'll give it
a fair try anyway. So more or less, it just builds
up and comes straight off. And I'll do the same thing at
an incredibly dizzying speed. Full power? Yeah. Yeah? All right. Full power. Woo. It gives off quite a wind. All right. I'll pop that back on there. And again, complete rubbish. Completely unstable. And that's because, as
this diagram shows you, you can only be stable
in particular dimensions. And the fascinating thing
is that the mathematics that describes this saddle shape and
the mathematics that describes are focusing in a
particle accelerator are pretty much identical. And this thing has a name. It's called a Paul trap. And I'll come back to
that in a little while. So we have to set
up our accelerator with a focusing system
in a very specific way so that it sits in one
of these stable regions. We usually use the
region which is on the sort of bottom
left corner of that plot because it's fairly easy
to reach with normal magnet strengths and things like that. But you can see that it's
a relatively small area, so we can't just put
magnets anywhere. We actually have to choose
them and design them very, very carefully. But I showed you before,
with this device here, that when we do that,
we set off oscillations. Now in physics, in any system
which has an oscillation, there's one problem which
we're always going to run into, which is the problem
of resonances. Now when I say the word
resonance, I'm sure most of you know what I'm talking about. If you have a system
that's oscillating, and you occasionally
kick it, and you kick it in the same way every time,
it builds up and builds up exponentially, and you get a
resonance, and, in this case, your beam goes flying into
the wall of your particle accelerator, which
isn't such a good thing. So this diagram is showing
you, on the x-axis, say, the oscillation rate of,
say, one of these oscillations. So maybe that's the
one around this way. And the vertical axis is
showing you the oscillation rate in the other direction. So they interact as well. And so one of the reasons why
I can never get this thing to stay more than
about 30 seconds is because the turntable
isn't precisely flat because there's imperfections
in the building up. Not that it's imperfect--
it's beautiful. It's beautifully made, but
it's not submicron level, just saying. So we will always have little
imperfections which build up. So when we're designing
an accelerator, we have a really
tapped choice to make, which is, what value do I
choose for those oscillations to keep my beam in the machine? And that's why I've
shown you this diagram because it's pretty
tough to spot. Your guess is, literally, as
good as mine, in that case. But we do-- we choose a
specific point in that diagram. We might choose a few. We have some flexibility, so
we might operate the machine in slightly different ways. And usually, we try
and place that spot as far away from any
and especially the crossing over points, where
different orders of resonances actually cross over. And they can be driven
by magnet misalignments, they can be driven by magnetic
fields having a slightly wrong shape-- all kinds of things. So that sounds kind
of like a disaster, but we do, in fact, as I said,
operate 35,000 accelerators quite successfully. Thank you very much. But we have always
designed accelerators to stay away from
these resonances until a couple of years
ago when we came up with a new type of accelerator,
which was one of these fixed field alternating gradient
machines that I talked about before. But we actually
simplified it right down. The machine I showed
you before had quite a complicated
magnetic field shape. And someone said, well,
what happens if we just simplify the field and
just use these-- just use these so-called quadrupole
magnets, which have a nice, linear field shape? And everyone said, well,
you'll get resonances. Yeah. OK. So what we found was that we
have resonances all the way through the acceleration cycle. But we let it do that
intentionally because one of the things you need to
know about resonances is they need time to build up. So this type of
machine-- and it's same was EMMA, the Electron Model
for Many Applacations-- was, literally, the first of
its kind in the world where we intentionally crossed through
resonances in the acceleration cycle-- major resonances,
which everyone else said, that's never going to work. But the theory was, if
we went quickly enough, we'd be able to cross through
them because there wouldn't be enough time for those
resonances to build up and destroy the beam. And that's what we demonstrated
and published back in 2012. And the plot on the bottom
left of the screen there, the lower half of that plot
just shows a red and black line coming down. That's our measurement of
what we call the tune-- that is, the oscillation
rates-- in this accelerator as they're going to
the acceleration cycle. So you can see that it sort
of decreases over time. And that was our demonstration
that we were, indeed, crossing through resonances. And we did, indeed, manage
to accelerate particles, get them out the
other end, and show that, actually, if you go fast
enough, this system works. Now unfortunately,
that machine can't be applied to very high
intensity very easily. And there's an
extra complication. When we have charged
particles and they're all in the same place, we have,
in physics, the Coulomb force-- literally, the repulsion
of different charges against each other. It might not have occurred to
people to think, well, hang on, there's all these particles,
they're really dense, they're going through this
tube-- aren't they repelling against each other? Yes. They are. And you know what? It's a real pain. If it accelerators
were like this we had one particle-- one, like
this-- life would be a dream. Unfortunately,
the more particles we try and cram in
there, especially in high intensity machines,
the worse our problems get. Because instead of them having
one oscillation period-- instead of having one
tune-- all the particles are interacting with each other. They're also, mind you,
interacting with the beam pipe, with the magnets. There's a lot of electromagnetic
fields going around there. And so when we have
that diagram where I said before we
choose a point-- it ain't a point anymore. Instead, our beam
becomes this spread of different particles
where every particle has, more or less, a different tune. And this is really
what limits us when it comes to designing
higher and higher intensity machines. The more particles
we cram in there, the bigger this spread gets,
the more resonances we run into, the more beam loss we
create, and the more risk we have of, literally, melting
the beam pipe of accelerator, which we can't afford to do. So there's a couple
of different ways that we could potentially
think about solving that. And one way is to design
the type of machine that I work on, which is
this fixed field alternating gradient accelerator. But another one is something
a little bit wackier, which is to take a
synchrotron and add a special insertion of magnets,
which kind of does away with the existence, in
the physical questions, of resonances, which
sounds rather confusing. It is. It's a very theoretical concept. It's called an integral
optics accelerator. And that's being driven by
Fermilab in the United States. So there are a couple of ideas. There are also, of course,
other ways you could do this. You could use a giant
linear accelerator, although I work on circular ones
because I think, in the future, the linear ones will be
too large and costly. And I think we
ought to be looking at a generation of
smaller, circular machines. So that's when we have to come
back to this device over here because understanding
how those accelerators work is really hard. If I try and run a
simulation of billions-- literally tens of
billions-- of particles in one of these machines
interacting with each other, interacting with the beam pipe,
interacting with the magnets, generating secondary particles,
doing all kinds of-- this takes weeks and weeks, on
huge clusters of computers, in order to run a
single simulation to see what my beam is doing. If I try and study it
in a real accelerator, it takes weeks and
weeks of beam time. And I showed you before that
these machines are in use all the time. So the ISIS neutron source,
for example, when that's on, it runs 24/7. There's very little time for
someone to do a beam study. And there's,
particularly, no time for anyone to
intentionally lose any beam because we can't because it
would generate radiation. So a few years ago,
I was wondering, how can we study very intense
accelerators in the future without building the
accelerator first? Because it's a pretty big job. And that's when I
came across this idea for the first time
of the Paul trap. And I came across some
papers from a group from Hiroshima
university in Japan, who I now collaborate with. And they are using these
devices to actually study beams of particle accelerators
and intense beams, in particular. So this is, I promise,
the only slide I have in here with some
serious equations in it. This describes the
Hamiltonian of beam motion. This is on the lower side. And on the left,
that's the Hamiltonian for beam motion
in an accelerator. Now a Hamiltonian
sort of describes the overall motion in a system--
the physicist will be familiar. If you're not, all I
want you to recognize in that equation is how similar
it is to the other one. So the other equation
is the Hamiltonian for what we call a Paul trap. And if you sort of compare
all the different pieces of that equation,
you'll see that they're very, very similar in form. And what these colleagues
at Hiroshima University had realized is that
they could actually use a Paul trap-- a small
one rather than a large one, like this-- to actually
study the physics of the beams of accelerators. So just to point out a few
terms in that equation-- on the left, the
pxpy, that's momentum, and then there's a focusing
term, which is the k term, and then x squared
minus y, squared, which is the sort of the
hyperbolic shape here. And then, on the far right
hand side, there's this phi sc. And on the left,
there's a phi as well. This phi is what we call
a space charged term. That describes this defocusing,
weird, annoying effect from all the high
intensity interactions between the different particles. So this device I discovered
was able to not just simulate the beams in just
about any accelerator-- because we,
literally, can dial it in-- but it was also able to
simulate the intense dynamics of those beams. And that was very,
very exciting to me. So the first thing
I did was I had to learn what the
system is like. I'm an accelerator physicist. I don't I don't use
these things usually. So this is an electric
quadrupole trap. So the top right there shows
an image of the quadrupole mode excitation of one of
these traps, where we apply an electric
RF field at 1 megahertz and we change that in time--
kind of like we were changing this or like we change this
in time, as we spin it. And that changing
quadrupole field does exactly the same thing that
our focusing in the accelerator does. But this is fixed
in space, so it's like a tabletop experiment. So in the accelerator, our
beam is traveling through. It's going through
magnets like this, it's going through RF cavities. And it's experiencing these
focusing and defocusing forces. In this trap, we take
argon ions, which we ionize with a little
gun of electrons, and then we do the same
thing, but we actually do it in time
instead of in space as the beam travels through. And so that means that
we can't necessarily look at all the
acceleration based effects, but we can look at all these
beautiful oscillations, resonances, and high
intensity effects as well. And so I started working with
these guys a couple of years ago. And the first thing
we looked at was to actually recreate
the EMMA experiment that I showed you before
and the resonance crossing that happens in that. So that brings me now to what
I'm working on at the moment as well as designing new
types of accelerators. I'm also building one of
these Paul trap devices. And one of the things I
find really incredible is how, in physics, the
mathematics and the description of these systems actually
translates between lots of different physical systems. So the beam in the accelerator,
the beam inside one of these Paul
traps, and the beam or the particle on this Paul
trap as well actually all have the same
equations of motion. And we can relate them to one
another and use it to study. So this is a picture
of my Paul trap. It's called IBEX-- intense
beam experiment-- which we're building at the moment. And this is a
picture of the design and then the manufacture. And I'm proud to say that this
is really an up-to-the-minute discourse because this is
a photograph I, literally, took yesterday. I went up to [INAUDIBLE]
Laboratory up north and I took this photograph
of this chamber, which actually just blew me away. It's so beautiful. It's cleaned for
ultra high vacuum. And inside that, is mounted
this Paul trap mechanism. And into that, very
soon, we'll also have a load of
electrical connections, and put the lid
on, pump it down, and then we'll be able to
start running experiments to explore the intensity
frontiers of accelerators with that. So I want to come back,
just for a moment, to sort of speculate
because I've shown you, all the way through, the design
of particle accelerators-- how they work, how
they're accelerated, how we bend the
beam, how we focus, and how we supply voltage. And there's a load
of technology that's come a long, long way in decades
and up to the present day. And alongside that, of course--
alongside the development of technology and
driving the development of that technology--
is the field of particle physics, which
a couple of you in the room are familiar with. But let me go through very
quickly some of the discoveries that we've made. So I talked before about the
discovery of the electron-- J.J. Thomson, in this theater. Well, the particle which later
became known as the electron because, apparently, his
nemesis named it, not him. And then we we're looking at
the discovery and understanding of the photon. And then other types of
slightly stranger particles. So there's muons. Now I mentioned before, muons
are like heavier versions of the electron. There's also an even
heavier version of the muon, called the tao, which
is further down there, in sort of medium
blue, which was only discovered in the late '70s. So there's three generations of
matter that we've discovered. We don't quite understand
why there's three. And as well as those particles--
the electron, muon, and tao-- there's all the ones that make
up the rest of our matter. So there's ones that make
up the protons and neutrons and those are the quarks. So on the left hand
side there, there's is down, strange,
up, charm, bottom, and, eventually, top, as they
were discovered in series. And those are the
six different types of quarks which go in-- and
only the up and down versions of those quarks go into
making our normal matter. Again, there's
three generations. We don't know why. And then, of course, there's
all the other force carrying particles-- things
like the photon, which does all the electromagnetic
forces that we've been playing with, the gluon, which is
holding the proton and neutron together with those quarks,
the W boson and Z boson do other sort of
weak contractions, and then, of course, recently
discovered as well, the Higgs boson, which is the
fundamental mechanism of how things get mass. That's a very quick rundown
of the standard model of particle physics. And then, of course, there's
other things in there which exist-- there's
neutrinos as well. They're really
mysterious particles. And those are the
ones, for example, that we could generate with the
next generation of intense beam accelerators. And so we have these different
strands of particle physics going into the future. But what I'd like
to ask you is, well, going back to the
start of my lecture, and looking at J.J. Thomson, and
his inability to predict what we were going to use
the electron for, and, admittedly, his complete
inability to predict-- I think we're at an
interesting place in history at the moment
because of our slight inability, ourselves, to predict
how we're going to use all of this
knowledge in the future. So I've shown you a few
applications of protons. There's lots of other
applications of ion beams and things. Maybe there's applications
of muons in the future. But I want to sort of leave you
with the thought that having learnt to understand and control
these beams of particles, it opens up the question of,
exactly what could we do with these beams of particles
and these accelerators in the future? So in the future, if someone's
going to give a toast in my presence, I'd like it
to be something like this-- I'd like it to be, "to the
particle accelerator... May it be of use to everybody." Thank you very much. I also am aware of people
from the high energy physics community investing in plasma
whitefield technologies-- not only for high
energy, actually, but also further applications. I just wondered if you
had any comments on that? Do you think it's a runner? Should we be worrying
more about that? Or is it interesting?
This woman is, without a shadow of a doubt, the most sexy woman I have ever heard.
I am crushing so hard right now.
/yes, yes, the blue one. I get it. I mean: she is so intensely smart and she knows how to convey her message. What an intensely satisfying and uplifting story she tells.
Suzie Sheehy, sweet mother mercy.