we usually think about fission or splitting the atom.

But there is another type,

one that turned out to be much more elusive.

I give the command!

Fusion!

It may seem like magic.

One kilogram of fusion fuel would generate

as much power as 10 million kilograms of coal.

Fusion has been called the holy grail of energy.

Theoretically,

now the particle should race around and around

until they hit some other particles and fuse.

Fusion is clean, it's green, it's safe.

But it's really hard to do.

If the conditions aren't perfect, everything stops.

This complexity is what earned fusion energy

an almost mythical status.

Governments have been chasing it

and claiming it for over half a century.

The big joke in fusion is

that it’s 30 years away

and always will be.

Yes, it’s a bit of a depressing joke if you ask me.

The next generation of fusion.

But there is renewed enthusiasm.

There are billionaires and investors, people like

Jeff Bezos and Bill Gates and Peter Thiel.

Dozens of companies are going after the silver bullet energy solution.

Atoms are constantly moving.

The hotter they get, the faster they move.

They also have a natural tendency to repel each other.

But with enough heat and density it's possible to merge atoms together.

This is fusion. And it creates enormous amounts of energy.

It’s also a potentially inexhaustible source of clean power

because it uses the most abundant element in the universe -

hydrogen.

There are some people who think it's science fiction and it'll never happen.

But it’s not science fiction.

The reason we know fusion works

is because it works in the stars.

In the sun, hydrogen is joining together to make helium,

and this releases huge amounts of energy.

Since scientists first figured out what was causing the sun to shine,

they’ve been dreaming

of harnessing this energy as a clean energy source on Earth.

The sun is huge so there’s a huge gravitational pressure

pushing down all the matter into the center

to really high densities and high temperatures.

The Earth is about, well, smaller than a sunspot on the face of the star

so we can’t do anything with that much gravity.

If we want to replicate these fusion reactions here on Earth,

we need temperatures of about 150 million degrees,

which is about 10 times hotter than the center of the sun.

One of the ways scientists are trying to achieve fusion is with machines called tokamaks.

A tokamak is shaped like a doughnut or a cored apple, filled with a gas

and surrounded by magnetic coils.

Electricity runs through the centre heating the gas.

When the particles are energized to the point that their electrons break free,

the gas turns into a plasma.

It can now be contained within the machine by a magnetic field,

which stops the molten plasma from burning through the walls.

Once the plasma reaches over 100 million degrees Celsius,

the ions inside it start to collide and fuse.

Among various fusion devices like stellarators,

colliding beam fusion reactors

or magnetized target reactors -

tokamaks are some of the oldest and most understood.

General thinking with these machines was the bigger the better.

A compact tokamak capable of reaching fusion conditions was thought to be impossible.

Until about a decade ago when Mikhail Gryaznevich did the maths.

Taking on the challenge, he co-founded Tokamak Energy.

Here in an ordinary business park near Oxford,

the company is trying to build their fusion machine

at a fraction of the time and money that it takes governments.

Last year this tokamak created a plasma as hot as the sun.

But the team needs higher temperatures so they’re adding a new heating system

and even more power.

That should get them to fusion temperatures of more than 100 million degrees Celsius.

A number of other facilities have triggered the fusion reaction in the past.

For a split second it's generated enough power to run thousands of homes.

So if we know how to do it, what’s holding fusion power back?

Well, so far all the machines have used more power to run

than they have generated from the reaction.

To make fusion a viable energy source the devices need to become much more efficient.

One tokamak which promises to get us there is called ITER

but it’s taken nearly 30 years to get it from concept to construction.

ITER, because of its size it became a worldwide collaboration

and this has made it very political and very bureaucratic.

And because it's taken so long, the prices have gone up.

The estimate has gone from $6 billion, to $25 billion.

That may sound like a lot but to put it in perspective

the Beijing Olympics cost $40 billion

and the 2020 Tokyo Games are expected to cost $25 billion.

Just for comparison, one country can afford to run a big sporting event,

but they don't want to fund a project that could solve the world's energy problems.

I think it's crazy but that’s the way it is.

But maybe fusion can be achieved for even less.

Tokamak Energy’s machine is much cheaper

and the team believes they can make a significant breakthrough for less than $1 billion.

But it’s not all about the cost or the scale

but who can be the first to actually produce more energy than is being used in the process.

When it happens, that's the Wright brothers moment where the plane finally takes off.

And that’s why working for a startup is so exciting.

Because you feel that you can make more progress.

We’re firing 2000 volt shots now so we’d prefer if you’re away from the passby.

After days of testing the rebuilt tokamak, the team is now trying to generate the plasma.

It’s not gonna be instant.

And it may not happen but...

OK fully charged.

Arming.

Ready to fire.

Firing in three, two, one.

Fire!

This image inside the tokamak shows white traces which are the magnetic field.

The darker area highlighted is the plasma.

This test puts the company on track to achieve the 100 million degrees milestone in 2020.

Then they’re planning to demonstrate a fusion reaction on their device around 2025.

But they’re not the only private company in the race.

The fact that there are more and more startups coming into this space is really, really hopeful.

Because the fusion program has been drip-fed for decades,

and then people wonder why we haven't yet achieved fusion.

You don't achieve fusion by just keeping it barely alive.

You have to put the money into it.

And I'm hoping that through the startups we can actually get enough investment into fusion

to get it over the line.

I know that you know, bottling the stars if you’d like, is going to be hard but

with determination and ingenuity humans have achieved incredible things

and there’s no reason why we shouldn’t achieve fusion.