hi. Right behind me is a pretty unassuming forest. That forest is in
France but I'm in Switzerland .Oh. yep that's right I'm standing right on the
border between Switzerland and France at a place called Meyrin . That's not why
I'm actually standing on this particular spot. More importantly I'm standing on
the world's largest physics experiment. yep that's right I'm actually standing
at the site of CERN, and on this spot right below me 100 meters underground
are the pipes of the LHC the Large Hadron Collider pipes that fire protons
in that direction and protons in land direction at extremely fast speeds in
fact close to the speed of light and there are places at detectors such as
Atlas which is just over there and also CMS which is a number of kilometers in
that direction over there. Those particles are made to collide so in this
video I'm going to be discussing the physics behind the LHC so stay tuned
now before I continue although the specifics of the LHC may not necessarily
be part of your high school curriculum I plan to incorporate physics content that
most high school students should be familiar with now a secretin is simply a
circular path accelerator designed to speed up charged particles and generally
the larger they are the fuss at that they can speed up the particles so here
I have a circular path and I have a particle that goes around a circle
obviously it'll move at a particular velocity but I need something also to
accelerate it so I have this little section here where after the particle
has gone through that section it actually goes faster and then continues
to speed up and around and around and around so in essence there are two basic
needs that a synchrotron needs the first thing it needs is a force to continue to
keep it in a circle now that is the Lorentz force and the lowness force
becomes also your centripetal force so if I have my Lorentz force which is cute
V B that becomes our MV squared over R and a little rearranging you'll show
that are ends up being equal to MV squared over QV b which then becomes of
course MV over QB MV is its momentum so your models will just simplify it as P
over Q B the second thing it needs is a force to accelerate it and that is due
to an electric field that is being applied to a charge and that means our
electric field can be determined by a voltage difference over a certain
distance and in essence these two concepts the Lorentz force and the force
due to an electric field are the two key concepts involving a synchrotron now the
first synchrotron was came on to Lyon in 1949 and was relatively small
now some secret ons actually speed up electrons which can be used for
collisions but also electrons moving around a secret on
release a radiation called synchrotron radiation and so that can be used for
other experiments so a good example for that is the ANSTO synchrotron based in
Melbourne in Australia where it uses the synchrotron radiation that comes off
these particles in a whole range of applications such as agriculture
biomedicine environmental sustainability food and food technology just to name a
few now I plan to produce a video which will examine this training secret on
more closely so stay tuned now there are also synchrotrons that actually speed up
large ions such as the le IR or the low-energy iron ring which is also based
in soon now the LHC accelerates protons and it is one of a series synchrotrons
at CERN it just happens to be that the LHC is the world's largest synchrotron
and it's designed to speed up protons moving in opposing directions so that
they can be made to collide and here you can see a schematic of the Large Hadron
Collider we have the large 27 kilometer ring we have also shown here the super
proton synchrotron which is a smaller synchrotron and we have of course the
four main detectors that sit on the ring Atlas LHC be CMS and Alice and all of
this is a hundred meters underneath the border of Switzerland and France now you
can see he just like the LA IR that it's not truly circular there are curved
components that are circular in the geometry but there are also straight
sections so although I'm going to be using the LHC as our example of the
workings of a synchrotron the basic workings that I'll discuss are pretty
much the same in most secret ins that will that you can be disdain so we're
going to kind of turn ourselves to really four main aspects of the
synchrotron number one how do they speed up those particles number two how can we
make them turn we're going to briefly also discuss how we keep the particle
beams together or focus them and finally I'll also play why we call the
synchrotron and I will put the times in the description below if you want to
jump straight to the appropriate section now let's zoom the aim is to get the pro
to 99.999999 one presented spittle I'd that's only three meters per second
under the speed of light now these protons don't travel actually alone they
actually travel in bunches and there are about a hundred billion protons per
bunch so when the LHC is actually running there are two thousand eight
hundred and eight of these bunches traveling at that speed around eleven
thousand two hundred forty five times a second around the twenty seven kilometer
loop with about seven 1/2 meters between each bunch now the speed determines the
energy of the proton and accounting for relativity it's often quoted in terms of
energy terms or in electron volts so you can see in this animation that the speed
is attained gradually through a series of synchrotrons of increasing sizes so
that eventually it reaches a total of seven thousand billion electron volts or
seven tera electron volts now that's like having about an equivalent of 170
Big Macs so how does the synchrotron do that now the source of the protons is
simply a bottle of hydrogen they are basically fired through a
cavity that rips the electrons off and now you have protons then they pass
through a series of radiofrequency cavities that speed them up as well as
force them into bunches but how does that work so here's my charged particle
and I want to speed it up and I'm going to speed it up through a series of
terminals now of course it becomes an anode if it's positively charged and a
cathode if it's negatively charged but it doesn't have to remain positive or
negatively charged so here is a cross-section here's my proton red being
positive and it is accelerating towards a cathode no I've got it I've got it
here labeled blue but as it passes through the cathode what's going to
happen is that another particular cathode will come into play now it's
already there I'm just doing this to show you how it works
and of course it's attracted towards this particular cathode and now because
the previous terminal has now become an anode positively charged it's going to
repel away from that so what your end up
getting is an electric field going in that direction in this particular moment
in time now as my particle travels through that then it's going to
experience a third terminal in this case the previous terminals become an anode
and the next terminals become a cathode so again at that time it's producing an
electric field in that direction as it passes through and then again as the
particle goes through it repeats the process and every time my positively
charged particle is experiencing an electric field that pushes it on further
so it's going to continue to accelerate bit by bit so as you can see though that
this would become really inefficient and since the rate at which the voltage
changes has to be kept in sync with the speed of the charges every time as it
goes around the frequencies will start to get higher and higher and higher and
eventually the frequency are going into the microwave range and that's becomes
an important point so really instead of using cathodes and anodes switching the
acceleration is actually done by a resonant frequency tabel or RF chamber
now in the LHC there are modules containing full of four resonating
chambers such as the one here so considering the LHC has a circumference
of 27 kilometers only about 16 meters or so actually diverted to the accelerating
the proton so as the particle passes through these chambers they rapidly
experience changing electric fields microwave 3 frequencies and this causes
the proton bunches to get sped up in other words they get a speed boost so in
essence the charges are writing an electromagnetic wave in the RF chamber a
bit like a surfer in the sea who's sitting in front of the wave decrease
their speed so now let's examine how the charges are made to turn using the
Lorentz force now although there is only one small section of the LHC devoted to
speeding up the charges the vast majority is made up of magnets designed
to bend and focus the mean the main unit for the bending medic magnet is often
referred to as the dipole and it is a 15 meter long
pipe that basically contains the two pipes that carry the proton beams over
the nine and a half thousand magnets in the LHC ring twelve hundred and thirty
two of these are the dipole magnets and there are four there are three hundred
eight at every turn so here you can see a 15 meter section of pipe being lowered
on a truck in fact the limit of the pipe is
actually due to the road limits that these trucks can actually carry you can
see over here on the right hand side the pipe being lowered down a tunnel which
is the service tunnel for the LHC because it's 100 meters underground so
you get a sense of how big that tunnel is and me hugging this tube shows you
approximately its diameter so here's a cross-section of the dipole tube you can
see that our actual pipes that carry the beam which is in these spaces right here
that most of it is actually support structures for the beam itself we have
these jokes which are going to provide both these strengths that this these
pipes need and I'll explain why that is the case in a moment it'll provide also
the magnetic fields that wouldn't be needed to deflect the beam and of course
we also have lots of space to allow the flow of liquid helium which is going to
cool this down to under two Kelvin and again I'll explain that in a second
moving that away you can see here a cross-section of my pipe we have here
the yokes that hold this all together these straps here are going to be our
electromagnets that provide the magnetic field and then inside this tube you'll
also have this tube right here you'll see that the inner pipe has holes in it
so let's check in from CERN as to why this is the case why is it perforated
you notice that very good so you're talking about this yes this cream from
top because it has as well it has a certain preparation on the side you can
touch it with a finger oh yeah so it's old or not not by coincidence everything
has a purpose so the top ones for so called dark Clarence so as I just
mentioned every moving charged particle generates current alright so if you
don't have these the charge cards can induce any counts like eddy currents so
we have this performance here they are extremely non-repeatable so there's like
a random pattern of like so now let's have a closer look of a Lorentz force so
here we have our pipes and our pipes will carry protons they are going to be
represented by these red arrows you'll see that they're in opposite directions
cuz at certain points in the LHC those two beams are made to collide we want a
force that ensures that the force is going to be in the same direction and
we're going to want a force that is in that the direction so how are we going
to do that well we're going to do that by applying an electromagnetic effect
and here is our coils you can see we're going to get currents that are flowing
in one direction clockwise up here and anti-clockwise here these two coils of
wall therefore produce magnetic fields in opposing directions and when combined
the magnetic field is going to look something like this now you can see that
my magnetic field will be such that it's going downward in this direction and
upward in this direction and that means using your appropriate hand rule that
the force the Lorentz force will be in the same direction now the force that's
required is actually quite large and in order to produce the force to make this
turn because remember the Lorentz force is ultimately equal to Q V
B and we know that V is a very large then the magnetic field we need to cause
this to turn is approximately 8 Tesla now that's so large that conventional
wires are unable to produce magnetic fields that allow us to have a Tesla in
fact the maximum magnetic field for conventional electromagnets with
conventional wires even the best materials that you can have is
approximately only one Tesla so the only way we can achieve these magnetic fields
is by the use of superconductors and with superconductors we're able to
achieve a current of in the range of 11,500 amps and that will allow us to
get the magnetic fields we need of about 8 Tesla to get the superconductors
working you need to lower their temperatures this particular material is
a material that is nobilion 3sm it's a particular material designed at CERN
now it's critical temperature is in the range of about 2 Kelvin or minus 271
degrees below zero that's colder than space folks and so in order to do that
they bathe this in liquid helium and liquid helium is at the same temperature
at this particular temperature so that's why this is kept particular cool so it
certainly is not just interested in magnets and electromagnets and charged
particles but also in cryogenics in order to cool these tubes to the
particular temperature in order to get the magnetic field required to actually
cause the Lorentz force to work but we have one other little problem and if you
notice here we have two sections of wires that are close together that are
carrying currents in the same direction and because they're in the same
direction you know that in terms of amperes law that the force per unit
length is going to be proportional to the individual currents divided by the
distance separated by them and so therefore you're going to get in
this case a very strong attractive force between the two which you have to
certainly try to stop from occurring so going back to our diagram you can see
these yoke see we've got our electromagnets here which provide us the
magnetic fields but when you have these huge stainless steel yokes that are
designed to stop these two pipes from approaching each other and of course
we've got also these pipes here because those pipes are needed to increase the
magnetic flux passing through my course or what you would refer to as flux
linkage so that's a brief overview of the forces at work in order to return
our proton beam so apart from the dipoles that are also a series of
magnets the called quadruples and there are 392 of them in this in the LHC whose
job is to focus the beam now protons are positively charged so they would
normally repel away from each other as they move around you don't want that to
occur so you have quadruples will squeeze them so a series of four
electromagnets heads quadruples are applied to squeeze the beams together
both in terms of the X direction and the y direction finally why do we call it
the synchrotron well our force a Lorentz force is equal to QV B and therefore
because this is going to be a centripetal force you're going to get a
value for the radius equaling 2 MV over QB now that means that if my velocity is
increasing momentum is increasing but we want to keep the radius constant so the
magnetic field has to increase as well at the same rate at which the momentum
is going to increase and therefore it has to be kept in sync with the momentum
to keep that radius constant and that's what synchrotron means it literally
means keeping in time and of course as well as our resident chambers also have
need to alternate at a rate that is consistent with the
speed of our proton bunches so that's why it's called a synchrotron so I hope
that's helped you understand the basics of the physics behind the LHC and
clearly it's only the basics there's a lot more physics there but at least
you'll have an introduction to the LHC and also how the physics concepts you
learn in high school a little bit beyond apply to the workings of the LHC in
future videos I'm going to be discussing the workings of the particle detectors
other aspects that occur at CERN and hopefully you'll like share and
subscribe my channel so that you can keep up to date with my videos i'm paul
from highschool physics he explained bye for now