Where is the hottest place in the universe?
As far as we know, it's in England: right here.
Just south of Oxford, in a place that feels
like the modern day equivalent
of where they cracked the enigma code, there
are some seriously bright people
who have built the hottest place in the universe.
Effectively, it's a star in a box at a
whopping 200 million degrees C.
now that number is far too hot to really
mean anything to me at all.
But I will tell you this:
the centre of the sun is 15 million degrees C,
which is also...  pretty much
completely meaningless to me.
Did you know that it only takes light 8 minutes
to get from the Sun to the Earth,
but it takes it thousands of years to get
from the centre of the sun to the edge of the sun.
I won't go into why that is now, but the brilliant
Randall Munroe once did a calculation to show
that a lizard gives out heat faster than a
lizard-sized piece of the centre of the sun.
"I wish we could hear the sun,"
said nobody ever.
It would be awful.
If sound could travel through the vacuum of space
in the same that it travels through the
air that we breathe,
it would take 15 years to get from the sun to us,
and when it did, it would sound like a chainsaw
right next to our ears, all the time, day and night.
So why have these big names near
Oxford built a star making machine?
It's because this is the world
centre of fusion research.
They invited me to visit a few weeks ago.
It's surprising how many people don't
know that fusion power is actually working.
Now we're just working on making it cheaper.
In a moment, I'm going to show you an unbelievably
cool video of the inside of a working fusion reactor,
but first... let's talk about fusion.
Some of you will know this already,
so in very brief summary,
fusion is sort of like squeezing
together two grapefruits
in order to try to make a very hot melon.
It's very difficult to do, which is a
very, very small part of the reason
why this is not working now.
For hundreds of years, people have
Been trying to change lead into gold.
That's called alchemy.
But it's crazy difficult to change chemical
elements into other elements,
because you have to go into
every single atom
and change the number of protons
that every single one of them has.
We're not even nearly technologically
advanced enough yet, to be doing alchemy.
We can switch between chemical elements
in a very few special cases,
but even then we're not
really fully in control of it.
The key idea to understand about switching
between chemical elements is that
the most stable element in the
entire of the periodic table is iron.
This means that, theoretically, elements that are
smaller than iron can be squeezed together
in order to release energy: that's called fusion.
And it also means that elements larger
than iron can be pulled apart
to release energy as well:
that's called nuclear fission.
I already made another episode about that called
Nuclear Disasters & Radioactive Batteries,
watch that after this one if you haven't already!
In stars, hydrogens fuse together to make
heliums, releasing an f-tonne of energy.
Just south of Oxford, we've managed to build
a box, called JET, which does the same thing;
squeezing hydrogens together to make helium...
and it's been really difficult.
It's all well and good having a load of hydrogen,
but you need something literally the size of the sun
before the central particles will be
crushed into one another
under the weight of the hundreds of thousands
of km of other particles on top of them.
The breakthrough for us humans,
not having much room for a star
came when we realised that if we heated
these particles up enough
then they might smash into one
another at such incredible speeds
that they might just fuse anyway.
And so we made a machine that can reach
200 million degrees, and it worked.
It might look like a lot of it is very
empty, but actually it's crazy hot in there.
And you see those white flecks on the screen?
That's where neutrons being thrown
off by the reaction
have damaged the otherwise
incredibly durable camera.
Those high-speed neutrons are really
dangerous to living things,
which is why we have to surround the
whole of our fusion reactor
with incredibly, incredibly
thick concrete walls.
It's also why we use gaming tech to control robots
inside the reactor to do the maintenance work.
Engineers stand outside the concrete
shields with VR headsets on,
and then they use robots that copy the
movement of their arms
to do the maintenance work.
As these neutrons fly out of the reactor,
going straight through the inner walls
as if they're not even there
(don't worry though; they don't make it
through the outer concrete shields),
they heat up a lithium metal blanket that's
wrapped around the edge of the reactor.
And that heats up water,  which is
used to drive turbines.
Seriously, if you have a better way
of turning heat into electricity
than just using steam to drive turbines,
I want to work with you.
So back at the 200 million degrees
inside the box...
at these ridiculous temperatures,
we need to use super strong magnetic
fields to suspend the hydrogen in mid air,
away from the walls...
otherwise the heat of it would vaporise the walls.
You might be thinking, how hydrogen,
which is barely magnetic at all,
can be suspended by magnetic fields?
The trick is that when it gets to these
crazy hot temperature
all of the charge bits separate apart
from one another
it becomes something called a "plasma"
and that means it can conduct electricity.
We can then induce a huge voltage in the donut,
which will cause it to have its own magnetic field,
and so then it can be suspended by
our magnetic field.
What this means is that not only is
the donut at millions of degrees,
but it also has hundreds of thousands
of amps of electricity racing around it too.
Sounds suspiciously like something dangerous...
But it really isn't.
The big difference between traditional
nuclear fission and nuclear fusion,
is that nuclear fission occurs in a chain reaction.
Most of a nuclear fission power plant is designed to
slow down and keep the reaction under control.
Which means that if things go wrong,
then they can go very wrong.
With fusion, it's the opposite,
almost everything in the design is there
just to try to keep the reaction going:
that's why it flickers; because it's just so
difficult to sustain.
If anything goes wrong in a fusion
reactor it just stops, immediately.
Now, in case you want to build
your own nuclear fusion reactor,
here are some key things to know:
Firstly, there's only a minuscule amount of
hydrogen ever actually in the reactor.
1g of hydrogen releases the same
amount of energy as 14 tonnes of coal.
Secondly, it's not just normal hydrogen
that we're using;
it's heavy hydrogen, with extra neutrons.
This is normal hydrogen, and these 2
are heavy hydrogen, deuterium and tritium.
We can get deuterium from the sea
(there's a silly amount in there),
and we can get tritium, from the
lithium blankets that surround the reactors.
Conveniently, as the neutrons bombard that lithium
some of the lithium turns into tritium....
suspiciously convenient.
As for what to build you reactor out of, I know that
it can be tempting to build it out of graphite,
what with its amazing heat resistant properties.
I know how tempting it is, but don't succumb;
it absorbs the fuel!
Instead, it's much better to 3D print it
with tungsten.
Thanks for watching, spread the knowledge,
deliciously subscribe for more,
and remember that you can follow me on
Instagram and Snapchat @MatthewShribman...
If you have a science question about this episode,
or anything at all, send it my way
and I'll try to get it answered for you!
