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Ex fcl
x ray free electron
lasers, what's
what's that?
Yeah, something something like that,
it's just a little bit of a shorter
wavelength, and it doesn't definitely
fit the size of a pen.
Well, Preston Hallatt
is a physicist working at
the Deutche Electronic Synchrotron
in Hamburg, and he
knows the answers to that.
And he's going to introduce
us to his world of free electron
lasers and their applications
warm. Welcome to Toreson.
Yeah, thank you.
I have to admit, I'm quite nervous,
not only because of this thing, but also
because my computer broke and I got this
about one hour ago, and I don't know if
the presentation works on that as
well, but let's hope for the best.
Despite that, I'm very happy to see that
so many of you are interested in particle
accelerators.
And I have to say that this is not a one
directional relation.
I talked to many colleagues at DC and
also in the US and all of them
literally knew about this Congress,
and most of them even knew that it was
going to happen in Leipzig this year.
So I think I can say that at least
every particle accelerator physicist I
know likes the CCC as well
and is interested in this Congress.
OK, but.
Maybe enough small talk for now.
Let's get to some science.
So while you're watching this talk,
your neurons firing incessantly,
sending electrical impulses to
the neighboring neurons.
But how does this work?
I mean, what are the neurons made of?
Well, artists, you from Harvard
University. Let us have a look inside.
So inside each neuron, there's an
enormous variety of proteins, big
macromolecules, each consisting of
hundreds of thousands of atoms
of up to 40 percent of the volume
of each cell is occupied by these
proteins and by the DNA.
It serves as a blueprint.
The proteins are manufactured somewhere
inside the cell and then have to be
transported to the destination where they
are needed.
For example, membrane proteins have to be
transported to the outer shell of the
cell. Right.
And this is done by the so-called
vesicles like the Blue Fellow you see
over there. So the proteins stick on them
and then motor proteins like this.
Kinnison here pulls the
vesicle along these long molecular
strands, which sponsor of the cell
here, the green one.
I don't know if you've seen such an
animation before.
When I saw this movie for the first time
and when I realized about the enormous
complexity of the molecular basis of
life, this was literally
breathtaking to me.
But have you ever wondered, how do we
know about this? I mean, how do we know
about the structure of this kind of
protein?
And the answer is synchrotron
light source. So the vast majority
of these proteins have been resolved
in the latest third generation
synchrotron light sources.
And in this talk, I will show you what it
takes to build such a machine and how
to make a picture.
But then the next question is, how do we
know about the dynamics?
So how do we know how how these proteins
fold?
And to be honest, we have no
fucking clue.
So don't get fooled
by the name Harvard University.
This is just an artist you and we have no
idea how a protein folds.
No one has ever seen something like this
or witnessed a chemical reaction.
But by the end of this talk, I will have
shown you that just by now we have a
machine at hand, the X-ray free electron
laser, which might be able to resolve
these proteins within their natural
timescale of a couple of femtoseconds.
But OK, to start and bring everyone on
the same page, I have to recall the
electromagnetic spectrum.
We are surrounded by a variety of
electromagnetic waves which can be
categorized according to their wavelength
into different ways.
For example, radio waves with a couple of
meters or more in wavelengths.
Then we have the microwaves with some
centimeters and then the infrared
and the visible light with a couple of
hundred of nanometers and wavelength.
If we decrease the wavelength further, we
will get to the ultraviolet.
And then finally, at 0.01 nanometer
or one angstrom, we have x rays,
OK? And there exists the fundamental
limitation if you want to observe
something with electromagnetic radiation,
namely the diffraction limit.
So it says basically
that if you want to resolve two objects
with the distance D, then you have to use
a wavelength, which is in the order of
that distance or smaller.
So if you want to study an end or a
bacteria, you can use visible light
because visible light has a wavelength
smaller than the size of these objects.
But if we want to study viruses or
the proteins we just saw or even smaller
molecules, we have to use X-rays.
But actually our ways of making a picture
from something that small is quite
different from what you are used to with
your eyes or your camera.
So we do X-ray diffraction images,
and before I can show you how that works,
I have to tell you something about
coherence.
So we start with an ordinary light source
which emits light in different
wavelengths, which is here indicated by
the different colors and the origin of
these wavefront is spread out.
OK, so we have no fixed Face-To-Face
relation at one point in space
and this we call incoherent light.
That's the kind of light we are all
surrounded by.
You may know from high school physics
that if I place an aperture in here, then
the wavefront propagate as they would be
emitted by a point source in the whole
of this aperture.
And now we have a fixed face relation at
one point in space and we call this
spatially coherent light.
And the next step towards coherence is
then to put a filter in
which lets through only one particular
wavelength.
OK, so now this is coherent light,
and if we consider ourselves to be very
far away from the source, we can consider
these ways to be plain ways.
And then if I play something,
for example, a double slit in here, I
will get an interference pattern
downstream and on the screen I would be
able to detect the
diffraction pattern.
And the clue is now that
mathematically there exists the relation
between the diffraction pattern and the
physical arrangement of these objects.
So I am able, if I know the diffraction
pattern and I know the distance between
the screen and the object, I'm
able. Calculate from the diffraction
pattern, the physical arrangement
of these objects, and in our case,
we're doing X-ray diffraction,
so we we don't have double slits, but we
have electrons on which the photons get
scattered.
And to give you an example, this is
a microscopic image from a sample which
was hit by an X-ray laser pulse.
And this is the diffraction pattern you
record at the screen at your detector.
So it's a bit more difficult than the
previous example.
But the key is this is the reconstructed
image. So from this, you
are able to calculate this one, these
two, although this is not very intuitive
or mathematically equivalent.
Okay, we can calculate this from
the diffraction pattern without knowing
the original original sample
and this kind of X-ray diffraction images
have been carried out for many decades.
Just to give you one example, the
discovery of the DNA structure was only
possible because Rosalind Franklin
made these diffraction images of a DNA
crystal and just a side story.
Guess who got the Nobel Prize for this?
Of course, the two white men.
But this is another nasty story
I recommend you to look up afterwards.
The thing is about these X-ray tubes.
They are very limited in brightness and
this becomes a problem if you want to
study, which moves.
You all know if you want to make a
picture from something which moves, you
have to decrease the shutter speed.
So for running whores, for example, it's
sufficient to have a shutter speed of one
millisecond. But if you want to watch a
bullet smashing a melon, you have to use
like 1000 frames per second more.
And finally, if you want to go to
chemical reactions, the shutter speed is
orders beyond that.
And you may have seen how such a movie is
made. So you need big lamps in order to
get enough light hitting your object
in the very short amount of time where
the shutters open.
Right. So the figure of merit for
a normal lamp is the luminous and
luminous intensity which
is defined as the photons per time
for a solid angle.
So basically the amount of light
which are directed to your target.
But we want to make X-ray diffraction
images, so we need coherent light.
And our figure of merit looks a bit
different, as it is called the brilliance
of a light source. And what we want is
basically we want a lot of photons
per time.
We want them emitted in a small spot size
with a small, angular divergence and
basically only one wavelength.
OK, so this is the brilliance.
This is our key.
But before I want to show you what it
takes for the brilliance to get from here
to here, I want to sensitize you a bit
more about the scale of what we are
talking.
So this is an example of some objects
which I sorted according
to their length on a logarithmic scale.
So we start with a fingertip of some
centimeters over a human hair
down to molecules and atoms,
and we are able to produce plenty
of technology basically on the whole
scale so we can produce a microglia
with the diameter of some micrometer
and even nanotubes.
And although this is rather something
academic yet, but in principle we are
able to arrange metter on an atomic
scale.
The corresponding plot in time domain
could look something like this.
So we start with enabling of a couple of
hundred microseconds down over
the time. It takes a shockwave to
propagate by one atom in a crystal
finally to the chemical reactions or
the ball period.
And it takes a one gigahertz CPU about
one nanosecond to make one computational
step and optical networks, which
is even a bit faster.
But basically we are not really
able to produce technology and that
timescale.
I mean, we are able to produce
a laser pulse in the visible light, which
is as short as one femtosecond, which is
really amazing.
But keep in mind the diffraction limit.
So with this, we can watch macroscopic
objects like, for example, the microglia
and we can watch the microglia within one
to femtosecond and see how it changes.
But macroscopic objects don't change
with an femtoseconds.
Things which changed in femtoseconds are
proteins or molecules, and we are
literally blind at these objects within
their natural timescale.
And to give you a better feeling of the
scaling here, a fingertip is
to an atom is about
two times, two times ten to the
eight times bigger
than an atom.
OK, and that's about the scaling of
the walking distance from here to Tel
Aviv to a fingertip
and in time domain and eyeblink is
to a chemical reaction like one year is
to enabling.
And now keep in mind, when you go to a
hospital and you want to make an X-ray
image with a modern X-ray tube from
the finger, you have to stand still for,
let's say, a second.
Right.
And if you want to scale that to an atom
and to such a timescale,
you immediately see that X-ray tubes are
nowhere near what is needed
for resolving proteins on their
natural timescale.
And I want to relate the
the development of our brilliance with
something new. So, you know, so.
This is the computer speed, and you all
know Moore's Law and you have kind
of a feeling what it means as a figure of
merit increases in 12 orders of magnitude
and 60 kids ride
the extra brilliance increased by 18
orders of magnitude in five decades.
And this was not possible by small
innovations, but very
different steps.
So we have different generations of
synchrotron light sources.
And finally, the fourth generation
we call X-ray free electron lasers.
And in this talk, I will go through the
steps, what it takes to build these
machines.
But before I can tell you how
we can build such a particle accelerator,
I have to tell you why these particles
actually radiate.
And for doing that, I have
to tell you something about relativity.
Maybe you have been on his talk
yesterday.
I will try to summarize it on one side.
So we call
our machines particle accelerators.
Right. But I guess your intuitive
understanding of acceleration is an
increase of velocity, but that's not
really the case, but a
step by step. So maybe you are familiar
with Newton's law of kinematics telling
you that the kinetic energy is one over
two times the mass of a particle times
the velocity squared.
But as Einstein revealed, the speed of
light is a constant which can't be
exceeded by any particle with a finite
mass.
So it turned out that Newton's laws of
mechanics is only a borderline case for
very low velocities,
for Einstein's more general equation of
kinematics.
And in here you have this relativistic
factor. Gamma Gamma is one over the
script, over this square root, and
it basically relates to the energy of a
particle with the thrust mass.
And it's quite an important parameter
for us and it will pop up a couple of
times in this talk.
So let me give you an example.
Let's assume that we accelerate an
electron and the proton with five million
volts, OK, so five megawatts.
And then the kinetic energy of both
particles is five mega electron
balls and the rest mass
for an electron is about 500 KVI
kilo electron balls, while it is about 20
times more for proton.
And this means you can now plug the
numbers in that the gamma factor is about
10 four electrons while it is about one
four protons.
And if you calculate the speed now from
this, you will see that
electrons, while being accelerated with
five million volts, travel with ninety
nine point five percent of the speed of
light, while protons only travel 10
percent or so electrons and
protons, or in general, light and
heavy particles have a very different
relation between the energy and the
velocity.
And in our case, as in synchrotron light
sources, we are always interested in a
very high gamma.
So it's obvious that we are only using
electrons.
OK, so the next
step is why do they radiate?
This is an electron and here I plotted
the electric field lines and you may be
familiar with the relativistic effect
called length contraction or lorence
contraction.
A very neat example is a ruler which
travels close to the speed of light
and it gets compressed with respect to
an observer and rest.
And if you apply this length contraction
to the electric field lines, we will see
that where the speed of
the particle is increased, the electric
field lines are compressed into a very
narrow cone perpendicular to the speed of
the particle.
OK, and now consider
you want to change the velocity from here
to here so you accelerate the particle
and the electric field configuration has
to change from that set up to this one.
But this can not happen infinitely fast,
but only with the speed of light.
So you have a time varying electric field
and this is basically radiation
maybe come a bit more clear
on this slide.
I make this simulation, you can download
the simulator from the center.
This is, again, a point charge and I drag
it now with the mouse and
increase its velocity.
And you can see as I increase the
velocity, the field lines are compressed
into this very narrow cone
and the radiation pattern gets more
obvious. If I change the direction of
motion, for example, by running it on a
circle.
And if you think you sit here
and watch the electron, you will get hit
by narrow flashes of electromagnetic
radiation.
Right. And this is basically a
synchrotron light source.
But I would like to look a bit more
detail on the
radiation properties.
So here again, this is our electron.
And I calculated the radiation
pattern for this motion and I plotted
the angle of distribution here with this
surface plot.
So you see that most of the radiation
is directed in the forward direction.
Yeah, and the opening angle here
of this radiation cone scales with
one over Gamma and the overall power
which is emitted scales with gamma to
the four is directly proportional
to the energy. So if we have a very high
energy, basically
all the radiation is emitted into
a very narrow cone and forward direction.
And in our cases, Gamma is something like
10000, so it's really
small and a nice property of
this radiation is that it covers a
relatively wide range and frequency
domain and you can easily tune it by
changing the gamma or the energy of your
particle.
And this kind of radiation was first
observed in a particle accelerator called
synchrotron, and that's why we call this
synchrotron radiation.
So coming back to that picture,
synchrotron radiation is very suited
to study small things like proteins
or molecules.
Now, the question is, how can we put this
into technology? So how can we make use
of it? And, of course, you know, it's
particle accelerators.
So what are the principles of a light
source? Well, first of all, we have to
generate our electrons.
So we need a device which
serves as an electron source.
Then we need something to increase the
energy. And finally, we need a device to
make them radiate.
And with this radiation, we can then
perform our X-ray experiments.
It's as simple as that.
And it's not too ambitious
analogy to think of such a light source
as a radio station.
There also you have your input signal,
then you have a high power amplification,
and then you put this high power signal
through a device which is designed to
produce electromagnetic radiation,
of which only a tiny fraction hits your
receiver.
OK, so in the following, I want to go
through these different devices,
starting with the acceleration.
You may know that if I connect a
capacitor with a DC voltage source,
I will get an electric field between the
plates and if I place
a negatively charged electron in here,
it will get accelerated.
Right.
And we have these kind of accelerators,
we call them fundido of accelerators
and modern ones like this one is
up to 10 meters long and reach
can accelerate the particles by six
million volts, which is not
bad. But the problem is we can't really
put them in serious and we can't increase
the voltage either because we would
simply get a discharge between the two
plates. So the problem with this
technology is it doesn't scale.
So what we do is we replace
our capacitor with an empty metallic
resonator called cavity, and we connect
this cavity with a waveguide to an
AC voltage source.
And this water source is operated usually
in the radio frequency domain.
So some gigahertz, that's why we call
this RF.
And the nice thing about such a resonator
is that a relatively small r a field
will start to resonate
inside. So we will get a relatively
high oscillating electric field and
we can easily put these in serious.
And if we put the face or set up the
face relation between adjacent cells
correctly, we will get an alternating,
oscillating electric field.
And the real cool thing is now that we
can put holes in here without really
changing the geometry and now the
cells are coupled so we can remove
all the power sources except of one.
And if you put the beam pipe in here, an
electron there, and if we synchronize
everything correctly, you will see that
we get an acceleration in each cell
of the cavity.
Right. And of course, I mean, the devil's
in the details, but this is the basic
principle of an RF cavity.
And
there was no gel content that.
And basically, every particle accelerator
on earth is operated of these kind of
devices, just to give you
one example, this is a Tesla cavity
we have in our linear accelerator that
here we have these nine cells and
it's a superconducting technology.
So everything has to be assembled in the
clean room, which is very challenging.
And then we put eight of them into one of
these cryo vessels with a lot of support.
And then we plug it in these yellow
things here and put it down in
the tunnel. Then we cool it down with
liquid helium to two Kelvin.
And in these cavities, we can reach
something like 30 million volts within
one meter.
So this is 50 times more
what you can get in a Vandergriff
accelerator. And I mean, think of this 30
million walls between these two hands.
To me, this is really an impressive
technology.
Seriously.
OK, so the next step is
the electron source.
This is a movie made from the photo
injector test sent home in Sweden.
But the electron source, we have a DC
look basically the same.
So you see it's a very complicated device
and there are whole laboratories only
building these electron sources.
But this movie shows basic principles.
On the inside, you have a copper cavity,
which with its connection to the
waveguide and from the inside
you have a photo Cassard sitting here
and this photo Cassard is impinged by a
UV laser pulse and why the UV laser
hit this photo that there are
electrons emitted due to the photo
effect.
So each of these red
things are about one billion or 10
billion electrons and we call this an
electron bunch.
And then again we have two cells of RF
cavity and everything is synchronized in
a way that accelerates the electrons
immediately as they are generated.
OK, finally, we need
a device to make them radiate, and I
already told you, we just have to
bend them around the circle, right.
And we can do this most easily.
And dipole magnets, you may know from
high school physics or whatever the left
hand rule, if we have an electron with
speed, we and the magnetic
field perpendicular to it will get the
Lawrence force in the third direction.
So the whole thing is
bent around a circle.
So now we have to have everything
together to build our storage ring
electron source.
We need an RF cavity and then a big type
magnet so the particle will move
on a circle and continuously emit
synchrotron radiation.
But it's not that easy because we have
energy conservation and while the
particle emits power, it will lose
kinetic energy. So it will finally spiral
in and get lost.
So we have to replace that and
in insert straight sections
where we can place an RF cavity to
compensate for the power loss in the
dipole magnets.
And then we have to put some focusing
elements in here.
We use quadripolar magnets
to stabilize the system.
And this particle accelerator is
called a synchrotron.
And originally, these kind of devices
were built for high energy physics
applications like, for example,
LHC, the Large Hadron Collider
and CERN is nothing more.
But this, of course, but the basic
principle is the synchrotron.
And this could be your Atlas detector.
Okay. And then the, uh, in
the early 50s, when they started to build
these kind of accelerators, the
synchrotron radiation was found to be
nothing more but a nuisance, which made
everything more complicated.
But in the 60s, uh,
X-ray diffraction became a thing and
scientists started to realize about
the capabilities of this radiation.
So they placed some X-ray optics
in here which guided the synchrotron
radiation to the experiments.
And these kind of devices are considered
as the first generation synchrotron light
sources.
And as an example, this is the Tantalus
one accelerator in the late 60s.
Here is the accelerator.
So this is the RF cavity and there are
some dipole magnets.
You see, it's a fairly small device.
And very soon scientists started to want
to have more power in their radiation.
So in a bending magnet, each electron
radiates. So the intensity or the
brilliance scales with the number of
electrons, right?
Double the electrons, double the power.
And starting from that, if you want to
increase the power, the first obvious
step is to put more dipole magnets in.
So this is an insurgent
device called Wikler, and it's basically
nothing else but a series of dipo magnets
with alternating polarity.
So the electrons will move on a slalom
trajectory. And in each curve you
will get synchrotron radiation as from
a single dipole magnet.
And by doing that, you will increase the
brilliance by a factor of the number of
magnets.
Right. So nothing more but that
then the next generation or
the next step towards
brighter synchrotron light source, as
was the invention of Ananda later.
And Undulated is very similar device
that a wikler.
The only difference is that now
the bending radius is so small that the,
um, that the education can
basically always point in the direction
of the experiment.
And the mathematical details of this
radiation is a bit are a bit
complicated. But the idea is that now
you have interference of the light
emitted in each of these curves.
And by doing this, you compress the
overall power here from a Regla into
very narrow spikes and frequency domain.
And this is great because remember, we
want to make X-ray diffraction images,
so we need coherent light.
So we need only one wavelength anyway.
So we put a filter in somewhere.
And if you place a filter at that
frequency, you will gain a huge
amount of brilliance.
Right. And these kind of devices
are considered as third generation
synchrotrons. So facilities
which are dedicatedly built to produce as
much synchrotron radiation as possible
with many beamlines and many experiments.
And as you can see here, there are plenty
of them operated in the industrialized
countries around the world right now.
And as an example, I want to show you
the three accelerator.
We have a DC in Hamburg.
But let me
drink something.
OK, so
this is a D.C. campus, and here this ring
is Petcare three, it has
a circumference of about two point three
kilometers. So it's a fairly large
device, including this 300
meter long experimental hall, of which
a schematic sketch you can see here.
And each of these lines is an X-ray
beam line with dedicated experiments
from the inside. It looks like this.
So you can't really see the accelerator
because everything has to be shielded
with these concrete walls because of the
radiation.
But the accelerators here on the inner
ring, this is a picture from the inside.
And here you have the beamlines with
the experimental chambers at the end.
OK.
As I said, this is a picture from the
inside. So these are the quadripolar
magnets. And we have some steering
magnets and the yellow devices here.
These are the undulates which produce
the radiation.
And beamline at these facilities is
very expensive.
So most of the beamlines have to be
optimized.
For example, at this one here
we have a robot arm which takes the
crystal samples out of the viewer
here and then mounted on the sample
holder.
And the accuracy is very impressive.
I mean, we have X-ray
sample crystals as small as 100
nanometer, and then they are rotated
around the axis inside a photon
beam, which is as small as 100 nanometer
as well.
But why do we need crystals at all?
The reason for this is that the
cross-section between our x rays
and metal is very low.
So statistically, we need one million
atoms in a row to get one single
refracted photon.
And you can imagine we need much more
than one single photon to get an
image on our detector, which we can
calculate something from.
Right. So what we do is we have to
increase the amount of photons.
But this is limited by
some constraints of our particle
accelerators. So we have to increase the
amount of atoms in our sample and we
do this by growing growing
crystals. So this is a protein
and we have to find proteins which
we can form unit cells out of and
then grow a crystal from.
So we need many of these and then we can
put the crystal in our light and our
X-ray beam and get some diffraction
spots, and while turning the crystal
around its axis, we'll get a 3D
diffraction pattern.
And from this, we can then calculate the
Fredi electron density map of our sample.
And if we know the electron density map,
we know the structure.
Here you can see the cumulative number
of structures which are available in the
protein database, and
you can see that within the last 20
years, there's been an astonishing
increase, most importantly made possible
by X-ray diffraction images
in these modern third generation
synchrotron light sources.
And right now, we are not only able to
make pictures of small proteins
like the myoglobin, but even very big
ones like the ribosome.
But this is not really by far not
trivial. So, for example, the ribosome,
the first X-ray diffraction pattern of
ribosome was made in 1980,
but it took scientists 20 years
to calculate the structure from this.
And although this number here
seems very high today, less than two
percent of the human protein is known.
So 89, 98
percent of the proteins of our
body are unknown.
And the reason for this, the bottleneck
is the crystal growth.
So it's very hard to get most
of the proteins to form big crystals.
Some of them might even not.
It's just not possible to crystallize
them at all, for example, membrane
proteins.
But for others, it's very difficult to
grow large crystals.
So what we ideally want is to make
be able to make a picture from a
very small crystal or even a single
molecule.
But in order to do that, we have to
increase the amount of photons by
something like 100 million.
And this is really not easy.
But let's consider for now that we would
be able to make a storage ring bright
enough so 100 million times brighter
than it is.
And to make an
diffraction image of a single lysosome,
what would happen?
Well, this this is
a simulation published a couple of years
ago. And what you see is the Coulomb
explosion of lysozyme.
So as the X-ray beam hits the hits
the sample, it immediately blows
away all the electrons in the molecule.
And what is left are the positively
charged nuclei which repel
each other.
So the whole molecule blows apart.
And the problem is now that because a
fundamental particle beam dynamics, it's
not possible to make an X-ray storage
ring smaller or shorter than
about a picosecond.
So even if we would be able to make a
storage ring pulsed bright enough to
watch a single molecule, we would just be
able to see a blurry picture of an
explosion.
And this is where free electron laser
came into play, because in a linear
accelerator, it is fundamentally possible
to produce an X-ray pulse as short as
some femtosecond.
But as I told you, we have to put
100 million times more photons
in that short putts.
So this is not easy.
And what we do is, well, first of all,
let me rescale this picture.
We replace
we replace the underlaid
by a very long Angelito and
by doing.
And now comes to mind, because
if we set up everything correctly, we
will get on top of this radiation pattern
from a long, unrelated, we will get
narrow spikes of coherent radiation.
And this is what makes a free electron
laser so important.
So mathematically, the radiation
scales now with a number of electrons
squared and the number of electrons in
our bunches is something like 100 million
or a billion. So this is really a huge
number. But let's have a look
inside what's happening in the undulate.
So this is an electron bunch and all the
red circles are supposed to be electrons
and the whole bunch moves in the
undulate, OK?
And they exist. The resonance condition
between the undulate period and the
period of the emitted light.
So here you have the underlaid period,
the the emitted light,
the relativistic gamma factor in this
Cavalia, which corroborate some
information about the magnetic field.
But it's not important for now.
So I'm only looking at the wavelength
of the emitted light, which satisfies
this condition.
OK.
Now, let's have a look.
So this is the electromagnetic wave
which is emitted by that electron
and the whole bunch is moving up and down
in that picture.
So some of the electrons move in the
direction of the electric field.
Sorry, this is the electric field line,
which I plotted here.
So some of the electrons move in the
direction of the electric field while
some of them move in the opposite
direction. OK, so some of
them will gain transverse momentum
while others will lose it.
And if we hit this resonance condition,
both the direction of the motion of the
electrons and the electromagnetic
waves flip side at the same
time. So this process repeats
itself.
And while all of this is happening, we
are in a magnetic chicane, meaning that
there exists a dispersion and dispersion
means that the bending
radius depends on the energy.
So if you have a larger energy and the
bending radius is bigger, if you have a
smaller energy, the bending radius of
smaller.
So some of these particles have
larger transverse momentum, so larger
transverse energy, so to say, and they
will move, they will fall
back and others will overtake
the bunch. So we have a self ordering
effect which repeats itself
now coming back to the big picture.
So from at the beginning, we start
with an incoherent radiation.
So all the electrons, while they are
moving out of where they are bent around
the circle, radiate,
but there is no fixed face relation
between them. OK, so this is incoherent
radiation and the intensity of that such
kind of radiation scales with the number
of emitters in this kind, in this
example number of electrons.
And now as the bands move through
the undulate are the self altering effect
leads to a micro bunching on exactly
that length scale of that radiation.
So for the wavelength satisfying
this condition, we will get a coherent
radiation and coherent radiation scales
with the number of electrons quit.
But it's not easy to get from
incoherent to coherent radiation,
especially if you want to
want to have x rays here.
Sorry.
So what we need is a small beam.
This is just to give you an idea of
the order, so don't take these well to
serious that can be affected two or three
between them. But we need a small beam,
something like 10 micrometer and
Transperth size.
We have to have it as short as 10
micrometer and we have to
get it on the energy, something like 10
billion electron loads.
And we need a very long until later some
hundred meters.
And within that undelete undue
later. We have to align the electrons
to better than 10 micrometer in order
to have an overlap between the electrons
and their and their light.
So this is really challenging.
This is a sketch of such a free electron
laser. So usually we have different
acceleration stages and in between we
have magnetic chicanes.
We call them bunched compressors, and in
them we are able to produce the very
short bunches and we have a long until
later. And finally we dump the electrons
in our light, gets to our experiments.
As you can see here, they are just now,
five of them in operation
and at least
five of them operating in the heart X
X-ray regime. And just another example I
would like to show you the European SFL,
which is the largest free electron laser
we have on earth.
This is a map from Hamburg.
You can see with its overall a length
of about three kilometers.
It reaches out the D.C.
campus and
reaches the adjacent federal state of
the college town where the experiments,
the experimental hall is built,
where you can't see much from above
because everything is just beneath
the Earth.
They would like to show you that movie
which was made.
Hmm.
Which was made by the accelerator,
was still under construction.
So right now, it would not be possible to
to walk down there.
It would just die.
But that was possible.
And I think,
yeah, it was really impressive to
be down there and see all this high tech
next to you and it just never stops.
But anyway, you can see this is
now the main accelerator.
It goes on for another kilometer.
You see where we are.
And this goes on for two minutes.
I think it's a bit boring, but you can
watch this movie if you want at home,
I think at double the speed anyway.
But I want to give you some numbers.
So in average, we we
take about nine point five megawatts
from the grid.
This is about the energy consumption of
a small city.
And from that, due to the utilization
of the superconducting RF technology, we
are able to put 10 percent into our beam.
So we have an average beam power of
900 kilowatts, which is really
impressive for linear accelerator.
From this, we get 0.01
percent into our X-ray beam,
but finally, only less than one percent
hitting or
getting the diffraction spots.
So you could argue that the overall
efficiency of this machine is terrible.
And I would agree.
And also, 900 watts of X-ray
beam power seems not very impressive.
But what makes this machine worth a
billion euro is its ability
to compress that power into very narrow
space.
So what is interesting is the peak
power in average.
We have a repetition rate of 27
kilohertz or 27000
X-ray pulses per second are produced
with a wavelength of about four point
five angstrom pulse energy
of one molecule and a pulse duration down
to three femtosecond.
I mean, this is the time it
takes light to travel one micrometer.
This is really short
and we can focus
this X-ray beam down to a very
narrow spot. And in this spot, in the
focal point, we have a power tent city
of about 10 to 17 watts per square
centimeter.
I guess you don't know what 2010
to the 17 watts per square centimeter is.
But let me give you an example.
Is this about the power density, as
is you if you would take the total
sunlight hitting the earth on
one square centimeter.
So this is really intense and
you have to be careful because if you
accidentally hit something.
Another thing I would like to
show you is that it's really
not easy to build or to operate such a
machine, like just for the European
SFL, we have nine million control
system variables.
This is the picture I made from the
control room at DC.
And you see that there are a lot of
screens and you have access to all of
them. So it's really not easy to design
a control system which can be operated by
many people and give
you access to all of these.
And I made an animation or screen
recording because once I had a
measurement shift at Flesche, which is
another electronic free electron laser,
we have it easy.
And I had to take out toroidal signal,
which was not on the top layer of the
control system.
It took me quite some time to find it.
So this is the this is
the top panel of the control system.
And as you can see, as you press some
of these buttons there, will open up a
panel with a lot of buttons.
And if you press one of these buttons,
another panel opens and
please.
OK.
And please note the saphenous over here
and here.
But finally.
So really, we need a lot of experts
working together because no one is able
to keep all of that in mind.
Another interesting number I find
is the data production rate, so
now I'm not talking about the machine,
I'm just talking about the x ray
detector. OK, and then there
we have about one megapixel with the
resolution of sixteen bit.
And we want to record this 27000
times per second.
And this means we have 60 gigabytes per
second.
Just to give you a number, the
LHC, after filtering has about 600
megabits per second.
So you can imagine that we also need very
sophisticated, uh, trigger
levels in order to deal with this amount
of data, because no one is able to record
or manage 60 gigabytes per second.
And as an example, this is the
amount of stored data in the first
weeks of operation of the European SFL.
So you see, we are hundreds of terabytes.
And keep in mind, within that period, the
machine was working with less than 10
percent of its full capacity.
So we are talking about petabytes here.
So this is also not that easy
to control.
But finally, I would like to close this
talk with a unique application, which
you can only do at these free electron
lasers. And it's about molecular movies.
So, for example, this
Iren complex in etc..
Nitrile solution, if you hit it with the
UV laser or UV light in general,
then it will perform a chemical reaction
and will lead to an acid agent
and the building of such a solvent
molecule. OK, this is chemistry.
We know this for many decades.
But the problem is that basically all of
our knowledge of chemistry is
equilibriums science.
So we know the reactants and we know
the reaction products, but we don't
know what's happening in between.
And usually there is not only one
reaction, PAF, but there are many of
different probabilities.
And you can imagine if we don't know
anything in between, it's very hard
for us to design a drug or a catalyst
or something like this.
This is basically nothing more than
an applied science
alchemy. I mean, we just try and error.
So it would we would really benefit from
knowing what's happening in between and
with the FCL.
We can do this.
This is a picture of the experimental
hall and Shoenfeld here we have these
five beamlines and now we are watching
one of them.
So here
come our X-ray beams.
This is a photon diagnostic section where
you can analyze the properties of our
X-ray beams and here finally we have the
target.
This is a liquid jet
target.
And it's not easy to to design
because we want a single molecule
to get hit by our X-ray beam.
We don't want to have to and we don't
want to have zero.
And all of this has to happen in a
vacuum.
And it's really not trivial to build
these kind of experimental chambers.
OK, now how can we get to
a molecular movie from this?
So first of all, we have to be able to
trigger our reaction and we can do
this with a movie Laser Pulse.
So we hit our our molecules with the
laser and the reaction starts and then
we can make a snapshot with our X-ray
laser.
And by setting up the delay time between
the movie and the X-ray laser, we can
make a snapshot from different stages
of this reaction.
And that's basically everything.
But also the readout of this
detector is very sophisticated.
So between there are different layers
because between each pulse, there's only
200 nanoseconds and then the defector
has to be ready for the next picture.
So it's really not trivial to build
these. And this is basically the most
powerful X-ray detector we have on Earth.
But finally, we get our
images. And from each image, we
can calculate, um,
the structure of our molecule.
And by putting them all together, we
are able to make a molecular movie
from a chemical reaction.
You see what it takes to make something
like this. And you guys, I guess you
you understand that it's a long way
to get to something like this.
Right.
But in principle, I think
I have shown you not only how we are
able to resolve the structures of these
proteins, but also as
how free electron lasers may
enable us in a couple
of years, maybe decades, to watch
these kind of movies, but not as artists
used, but as real experimental
data.
So thank you very much.
And if there are any questions.
Person to person, thank
you very much for this highly educational
talk, if anything goes
wrong with your postdoc in
Berkeley, I recommend you go to
science communication.
OK, we already have a question from
the Internet. I have heard
yeah, there's actually one question from
Galkin.
How well do the experiments replicate?
I've seen the talk yesterday as well,
and I think, uh.
You mean in general, the x ray
experiments are from the European SFL.
It's on the Internet, right?
OK.
I, I
would say they replicate
quite well, there are experiments
made at different X-ray sources
and from time to time they try to
cross-check at other X-ray sources or
try to make the experiment
a bit different.
And I think this is kind of replicating
it right.
But I'm not a photon photon expert,
so I don't I'm not an I built
the machine. I don't really care
about the images.
So I'm sorry,
OK, microphone one,
please.
OK.
Yeah, really amazing talk.
I have to admit that what's
the current status of the X Files?
Because he showed now at the end, just as
this procedure, how you would do a movie.
How far are we actually to do that
for a simple example?
Something like a year, maybe,
I mean, it really depends for I didn't
told you how difficult it is to make
how many pictures you have to to combine
to make such a movie.
So you have to combine
several hundred of thousands of X-ray
images or diffraction
images to make such a movie.
So you need a lot of a lot of boom
time. And especially right now, I think
it's more difficult to prepare the
samples and and
and to get the full capacity because of
some issues of the accelerator, I
would guess something like one year
to get to something in general.
The machine is ready and operational
and it operates and could start doing
that. Yeah.
OK, thanks.
It's just not that all subsystems are
working, you know, like some of the some
of the experimental chambers are not
ready or some properties
can't be hit right now.
Yeah.
OK, microphone number four, please.
OK.
How do you stop the molecules degrading
by when they're
hit by the free electron laser?
Sorry again please.
So yourself before that, if you
don't have a crystal of molecules of the
degrades instantly.
And how do we stop it with the free
electron laser?
You mean how do we stop the molecule
from exploding.
Yes. Aren't we.
Don't. Oh OK.
It just it gets obliterated in each
shot, so that's why we have
to make 100000 pictures,
because after each week
maybe let me show you
this, maybe so.
So each shot, this is our
molecule and gets hit by this laser in
each shot gets destroyed.
And it's more difficult because the
orientation of this sample is
random in each shot.
So we need very sophisticated software to
calculate the 3D diffraction image
from this to
finally resolve the structure.
This is much more difficult than if you
have a crystal because they're, you know,
your orientation and you can rotate it in
a defined way.
But finally, each shot is
is you know, we need to get the data
from one shot.
OK, microphone number one, please.
So this is more of a technicality.
How is the
power on the electron beam dump and
what are you using for the electron beam
dump to get the
amount of damage along
with it to an acceptable level that
you don't destroy everything with that?
Yeah, that's basically the limitation of
this 900 kilowatts is the specification.
What we get finished should be heard
on.
To operate these machines,
we use big blocks of,
uh, what is it, graphene, I think,
and kind of rotating magnitude
to such that the beam doesn't
hit the same spot every time.
And but it's basically just a big,
big block, very long.
Like, how long is it?
Maybe eight meters, like this big.
And then we have several of them, which
can be changed and then
they have to put
away for some decades
to cool down.
I took my.
Microphone four, please.
First, thank you again for this really
amazing talk.
This is a very grizzly question,
but is it a it is
anticipated that the growth
in the ability of these will continue
to go beyond what free
electron lasers have achieved.
And is there a glimpse into what
the fifth generation of synchrotrons
would be?
I asked a couple of guys
in the scope of this talk and depending
on where they are, they
answer different things.
So some of them answer no.
It will be different techniques.
So free electron lasers have the unique
ability to make very short pulses and
this may be become even better.
So less than one femtosecond.
But there are other tools like electron
diffraction or also
electron microscopy, which are maybe
suited better for different samples.
But I actually I don't know what's
really gonna be the next step in
synchrotron radiation sources.
Thank you.
OK, let's be fair to the Internet,
is there any question?
Yeah, we have some more questions,
but is it all right?
Bucking Sheep is asking, how long does it
take to run an experiment, as
in riding the specter of the experiment,
sending the beam, collecting all the
images and producing, producing
a picture, a beam
time is
something like so unflashy
or other free electron laser.
The typical beam time slot is
eight hours. And so the machine runs
24/7. But some experiments
take eight, some 16, some two days.
But that's the order.
So let's say 10 hours.
And setting up the experiment
is actually the bottleneck.
So this can take up to one week.
So I don't unfortunately,
I don't have a picture from the
experiment. Experimental Hollett Flash.
But we have different timelines and
there are ten people working there to
build up the experiment for one week.
And then they have like eight hours of
X-ray beam and then they work half
a year on on reading
the data and then combining
these images.
So the prime time they are making
the images is the smallest part.
OK, microphone one, please.
Yes, thank you for the great talk as
well.
My question is, I'm sure you are aware
of these protein
folding software projects which
try to make these images by calculation.
How well do these work and
how much do you benefit from these
approaches? I mean, that's the point.
We don't know how well they work, right?
I mean, we have these simulations.
We can find them on YouTube and
they are nice. But
I what? You know.
Thank you.
All right. Another microphone.
One, please.
Yeah. And this was an amazing talk.
Can I talk a little bit more about how to
focus on the X-ray pulse?
Yes, but I don't know if I can answer
your question.
I should talk more.
I think for questions.
If you were have discussions, I think
that means to do that probably outside.
So Internet question.
And restricted Eve would like to know
if you could tell some more details about
how the X-ray camera manages to hold
so many data in such a
short period of time.
OK, to the Internet question.
No, I can't really.
I, uh, I wanted to ask
the guy who designed the detector
or who was responsible for
designing the detector, but he was on
holiday already in the last week before
Christmas. So I couldn't really
get an answer to this question.
I don't know it exactly.
I just know that there are several layers
and it's not,
uh, know, I would talk bullshit, I think,
but I guess
very soon they wanted to write a
big, uh, comprehensive,
um.
Some comprehensive stuff about the x ray
detector on on their home page of the
European X Files, so I would recommend
you to look it up there.
But to come to your question,
we do this with basically diamonds
or some some diamond like crystals.
This is an x ray mirror we have
and we have this
crazing incident angle.
So that's how we focus
these these beams.
And it's very
I don't know, it was in the news.
The flatness of this mirror is really
amazing. But I don't I don't have the
numbers right now.
But look it up. It's crazy.
And going microphone one, yeah,
this is, of course, an amazing piece of
hardware, but as you mentioned,
you showed us the controlled software.
It's also an amazing piece of
software and amount of software.
Can you give us some numbers on a
number of programs, lines of code,
manyas, whatever, because
you spent a billion in software.
But software is also
probably. Yes, yes, yes, yes,
for sure.
That would be an interesting no, no, I
don't have the number of lines involved
in this code.
I know that the amount of compute, uh,
of a CPU power
we need is not that much.
So it's more the most difficult
thing is to get all these channels
appear on our controlled system.
So the graphical, uh, the graphical
interfaces is more challenging
than, uh, than
work with the data.
But I really don't know how many.
Oh, no, I can't really tell you this, but
if you write me at the end
of the slide, I have my email address.
I could ask some some guy
said easy.
OK, microphone two, please.
I also have a question about the control
software. Do you have a query
language to find the controls you need
instead of having to step through all
those windows?
Oh, yes, of course.
Of course. But usually when you
when you have no clue of what you are
looking, it's sometimes easier if
you have a GUI where you can get at least
sorted.
But of course you can.
You can have access read and write also
by by by just writing
lines in your.
Internet questions.
No more questions.
OK, microphone one, please.
Yeah, my question is, is there
any policy in place
for, like, publishing stuff
like only open access or something like
that
at some risk to come
into your facility applying for time?
Do I have some policy to fulfill that?
Only I yeah, you have to publish.
I mean, you have to publish and then.
Is it open access?
That's the question. Yeah, that's a good
point. I think it doesn't have to be.
OK, so you have to make sure that
your results are published and.
But since it's not.
A good point.
I know that a private company can
also come and ask for prime time, but
they have to pay a lot of money
to get that. But if you are a scientific
researcher or university or whatever,
you get it for free.
Thanks.