What is behind me is the powerhouse of the Universe.
It is just a conventional star.
It is our Sun.
And this power station has been running for billions of years,
reliably delivering energy to us and to the rest of the Universe
just by light emission.
So, that's a very nice thing, and it obviously runs,
and the mechanism through which it runs is fusion,
and I'm going to explain to you something about that.
But I will also ask the question:
can we bring this mechanism on Earth directly?
And the answer is no, by no means.
The Sun is too big, the Sun is too hot, the Sun is too dense,
everything speaks against that;
but... and the story about the but:
we have to build machines, clever machines;
we, humans have to build machines
in order to mimic this process, in order to bring it on Earth.
So, for that, we have to understand a few little things of physics.
Don't be afraid.
You have to carefully distinguish between fission and fusion.
Fission is splitting heavy nuclei; fusion is fusing light nuclei.
And they both belong to the same process:
it's a conversion of mass into energy,
and that's Einstein's famous formula E=mc²,
and that's the common mechanism.
And this energy is released just by speed, by kinetic energy, by heat in other words.
So it generates heat.
And that's what we would like to make use of.
And for that, we have to use a trick.
Instead of using conventional hydrogen, we use versions of hydrogen.
And these two so-called isotopes are called deuterium and tritium.
Deuterium is just heavy hydrogen, tritium is super heavy hydrogen.
They both are actually hydrogen isotopes,
they behave like hydrogen, just the mass is different.
And you can much more easily fuse them than conventional hydrogen,
than the hydrogen we know from the everyday world.
And when we fuse them, they collide,
and in the collision, they generate a helium nucleus, an alpha particle,
and a neutron, and lots of energy.
And that's the process we would like to make use of; we, fusion scientists.
And in order to get a feeling what is this fuel about:
fusing one gram of deuterium-tritium
releases the same energy as burning 10 million grams of coal.
And so, that's a fantastic fuel.
And so, you can say: is it available on Earth, or is it just a dream?
And the answer is yes, it is basically available.
So, deuterium is found just in seawater, in a low concentration,
but we do not need much.
Tritium is available on Earth
by making use of a mechanism
that generates tritium from lithium.
And so, if you now put everything together,
you can say that a half-filled bath tub of water and an accumulator -
here, there's a lithium-ion accumulator in this mobile phone -
would release enough energy
to supply an average European for 25 years with electric energy.
That's of course, a big, big promise.
How to make it happen?
And this big promise has driven mankind for 50 years already
to explore how it can work.
And this diagram here shows the early days of fusion research.
It's from the 1950s, so that's from Los Alamos [Lab]
and they built a device, a machine.
And there is this ring in the background -
at the center of the photo, there's a ring with a purple glow -
and this ring, together with what's surrounded by
was called the Perhapsatron -
and that's because the scientists didn't know if it would work at all.
It worked somehow, but not sufficiently,
because the very basic problem of fusion is fusion is very easy to do.
The fundamental nuclear process is known, and it's easy to do.
The exercise is to make a lot of fusion processes at the same time.
Again, so we need a lot of fusion
in order to generate substantial amounts of energy.
And so, it became obvious
that one has to work on different things in order to build the right machine.
The Perhapsatron not being the right machine was discarded.
Many, many others followed, other generations followed,
and I would like to give you an update on the current status.
So, the magnetic field is very important:
you have to make use of the magnetic field
in order to confine this super hot gas which we call plasma.
And you might have seen a plasma already in reality
if you have seen the Northern Lights or an Aurora Borealis.
That's a photo through the window of an airplane
of the Aurora Borealis over the Northern Pole.
The structure of the Aurora Borealis -
this stripe-like structure is given by the magnetic field of the Earth.
So this is naturally occurring.
And the plasma is actually the ingredient that's the boiling soup
that makes fusion happen so many times as it should be
in order to really gain energy.
That's in the kind of standard machine.
We are building a fusion science:
it is called tokamak - tokamak not tomahawk;
that's a big difference!
The tokamak consists of superconducting coils
in which a very strong current is running.
It is also based on a strong current running in the actual plasma,
and the plasma is ring-shaped.
So this purple ring there,
or this magenta ring shown there,
is the actual plasma that is attached to the magnetic field.
That's the basic principle of a tokamak,
and nowadays,
we are brave enough in fusion research to build big machines,
because they must be big in order to have a lot of fusion reactions.
The biggest tokamak in the world, now under construction,
is the tokamak ITER in the South of France.
And it's a world tokamak in a sense.
It's not only a big tokamak, the biggest tokamak in the world,
but it's also a world project,
because in the ITER project, half of mankind is involved:
China, the USA, Russia, the EU, India, Japan, and South Korea.
They're all joining forces in order to build
this really big superconducting tokamak in the South of France.
And this machine is going to start operating in 2025.
This is a big, big project.
There's another concept which is called a stellarator.
Stellarator means bringing the [power of] a star on Earth.
And here, in blue again, the magnets are shown
that generate a magnetic field.
And in yellow,
that's the shape of the plasma given by the magnetic field geometry.
Stellarators need optimization.
What does optimization mean?
Optimization means setting up a number of criteria:
good plasma stability, improved heat insulation,
equilibrium, confinement, things like that.
And you cast everything, all these requirements,
in a set of computer codes -
very massive computer codes with a lot of plasma theory in it -
and then you have to do
all these horribly complicated calculations using supercomputers.
And the supercomputer
that has calculated the Wendelstein 7-X - that's our stellarator -
was the Cray X-MP.
This device has more computer power than the Cray X-MP -
this goes back to the mid 80s, and supercomputers look different now -
but nevertheless,
the computing power was sufficient to determine the shape of the coils.
These calculations were repeated and confirmed many times,
and so we are pretty confident
that we have found the right magnetic field.
The Wendelstein 7-X stellarator consists now of the following elements:
the plasma - so that's the shape of the plasma,
it looks a little bit like a twisted tire of a bicycle -
the magnetic field coils, these calculated magnetic field coils;
another set of coils to change the magnetic field a little bit;
a massive steel structure that carries these coils -
each coil weighs six tonnes and has a diameter of three meters -
and of course, also many pipes and connectors
to connect the magnet system together;
and also an outer vessel -
it's a massive steel vessel
because the coils have to be operated in vacuum
since, for superconductivity,
you have to cool down the coils to minus 270 degrees centigrade.
That's then the outer shape of the machine.
It looks a little bit like a spaceship,
So the "Science" magazine wrote
it looks like Han Solo’s Millennium Falcon,
and they also wrote this machine was designed in hell.
It's all not true;
it's just a kind of engineering exercise, and that's the machine in reality.
And you also have the comparison to a person.
It is a complicated machine.
Four hundred technicians, engineers, and scientists
have worked 20 years to build the machine in Greifswald, Northern Germany.
Twenty years, one million assembly hours.
And the machine is running.
We were pushing the button,
and the physicists in the center did the job for us.
In the inset, you also see the plasma.
The plasma is glowing nicely bluish and reddish.
These are different stages of the plasma development.
The machine runs perfectly fine.
That's very satisfying after 20 years of construction,
and we are putting a lot of hope on the performance of this machine.
And here's the performance:
0.01 grams of hydrogen were injected into the vessel,
heated up with 4 million watts of microwave power
to 100 million degrees centigrade for the electrons
and 20 million degrees centigrade for the hydrogen.
That wasn't that bad for the first step of the machine.
We have to increase the particle density by a factor of 5,
which sounds easy,
but it needs more heating power.
We are currently upgrading the machine to increase the heating power
to ten million watts, to ten megawatts, for ten-second pulses,
and later on, also for longer ones.
I would like to conclude.
I would like to make a case here for fusion.
Fusion is clean;
it has no CO₂ emission - keyword 'climate change';
no long term waste - different from fission;
it is abundant - enough fusion fuel for millions of years;
and it's accessible to everybody -
so nobody owns the fusion fuel, which is very important, of course;
it's safe - there are no catastrophic failures possible;
and it's economic -
the machines are expensive, but the fuel cost is essentially zero.
Two key machines in the world are:
Wendelstein 7-X -
here the mission is to help create a hydrogen plasma for 30 minutes,
and this has never been done before, the standard is a few seconds up to now;
and the ITER mission is to create a fusion plasma
which generates ten times more energy than needed to create plasma.
I think that will be a major breakthrough,
and then, we have a new primary energy source,
and I should say
this is the only new primary energy source mankind is working on.
Thank you for your attention.
(Applause)