The Secret Life of the Sun Page #3

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is pushing inwards,

exerting vast pressure.

And this is where sunlight is born.

To understand how

that vast pressure creates sunlight,

I've come to the National Ignition

Facility, NIF, in California.

Sunlight exists because of a process

going on deep in the core of the sun

called fusion.

And what's happening there is that

the pressures and temperatures

right in the middle of the sun

are so enormous...

..that hydrogen atoms

can fuse together.

And when that happens,

a tiny, tiny bit of mass is converted

into a huge amount of energy.

And that little process

is the key to a star like our sun.

Without that single process,

the sun would be a cold, dead star

and the Earth would be

a cold, dead planet.

So the key to the behaviour

of the sun

and to life on Earth

is fusion.

I'm about to see

how the scientists at NIF

are trying to make a tiny sun

and recreate fusion.

All this is about getting ignition

that could change the world.

Here, in this dust-free environment,

Beth Dzenitis

creates hydrogen fuel capsules

smaller than a grain of rice

and destined

for a very violent fate.

This is called

the capsule fill-tube assembly.

It's a two-millimetre diameter

plastic capsule.

192 laser beams converge

on the capsule,

and that plastic material

blows away from the capsule

when it gets hot

and under high pressure.

And that causes a subsequent

reaction of the fuel there

to be compressed

so that the hydrogen atoms fuse.

To get those atoms to fuse,

they need to generate similar

pressures to those at the sun's core,

340 billion times

the pressure on Earth.

It's a tall order.

But there is a way.

The 192 individual laser beams

they use

are each more powerful

than any other laser on the planet.

And they all fire at a spherical

chamber at the heart of the complex.

This is the target chamber,

and when the lasers hit

the fuel capsule at its centre,

they bring the atoms together with

the same force as in the sun's core.

But to truly mimic our star,

the NIF team needs to pull off

an even greater trick.

Proceeding to system shot

countdown state.

Once ignited, the fusion reaction

must keep itself going.

Starting system shot sequence

on my mark.

Three, two, one, mark.

May I have your attention?

Preparations for shot operations

in laser bay two are under way.

Leave laser bay two now.

It's not without its dangers.

Before every shot,

the area is evacuated.

Steel and concrete doors a metre

thick enclose the target chamber.

A misfire from the most powerful

laser in the world

could cause a catastrophic explosion.

MOR ready for system shot

countdown clock.

And even the smallest

fusion reaction

unleashes a lethal blast of neutrons

and high-energy light.

..Three, two, one.

The only visible sign

is this flash from the world's

biggest laser as it fires.

But inside that fuel capsule,

they're hoping to create a tiny sun

and with it, man-made sunlight.

Another day, another shot.

The NIF team routinely achieve

short-lived fusion.

But today,

still no self-sustaining fusion.

Yet if we could achieve it on Earth,

we'd have the sun's energy on tap.

Recreating a small sun

in this target chamber

that's not too far away is always...

daunting, in a lot of respects.

We will get there eventually.

It's that elusive trick

of generating endless energy

that makes our sun so miraculous.

The result is the birth of sunlight

in the sun's core,

in particles of light energy

known as photons.

But their journey is far from over.

Imagine this pinball

is a newly created photon.

That light must now reach

the sun's surface.

And that is a really complex

and difficult journey,

because in-between

the core of the sun and the surface

there is a seething mass of stuff

that we call plasma.

Like my pinball

dodging the flippers and bumpers,

the photon now has to navigate

through that plasma.

But my pinball - or photon -

can't take a direct route out.

It's forever colliding

with particles of plasma

moving at thousands of miles

per hour.

And with hundreds of thousands

of miles of plasma to cross

between the sun's core

and its surface,

a journey that should take two and

a half seconds at the speed of light

takes much, much longer.

Even though it's travelling

at the speed of light,

as fast as anything can go,

it's still estimated that

it'll take 10,000 to a million years

just to get from the core of the sun

to its surface.

And then...freedom.

What we think of

as sunlight's journey,

the 90 million miles

from the sun to the Earth,

is only the last eight minutes

of an odyssey that could have taken

thousands and thousands of years.

It's...lovely, fantastic,

to think that this gentle light

that's touching me now

started off in a violent,

dramatic beginning

right in the centre of a star

and then spent 100,000 years

finding its way out of that star,

and finally spent

just eight minutes

travelling as fast as anything

in the universe can travel,

the speed of light,

to get to me here.

But this extraordinary journey

raises a question.

Fusion in the core never stops.

So why does the sun's activity

go up and down

with the 11-year solar cycle?

Back at RAL,

that's one of the questions

that interests solar scientists.

The key lies in how the fusion

reaction affects the sun's plasma,

that seething mass

between the core and the surface.

To explain

why this leads to solar cycles,

we've been joined at RAL

by solar physicist Lucie Green.

The heat generated

by this reaction inside the sun,

it heats up the gas

and, in fact, it superheats it,

so the gas is...

the particles of gas are torn apart

to form a plasma.

Just as the hot air in the room

around us is rising in packets,

so the gases in the outer layers

of the sun do the same thing.

This is called convection.

So gases get heated from below

and they rise up

to the surface of the sun.

But because this gas, the plasma,

is so hot,

it's also electrically charged.

So as it moves up and down

with the convection currents,

it creates powerful magnetic fields.

And that's not all.

The sun, like the Earth,

spins on its axis,

so plasma also flows sideways.

Which has a dramatic effect

on those magnetic fields.

You start to see the magnetic

field lines being wound up,

and eventually it becomes so strong

that the magnetic fields rise up

and penetrate the surface

of the sun,

and that's when we have

the build-up to solar maximum.

At times of solar maximum,

those magnetic loops break out

from the surface of the sun,

drawing the sun's plasma with them.

This one loop

is many times bigger than the Earth.

But the sun doesn't stay like that.

Eventually,

the magnetic fields disperse

and they rearrange themselves,

and we go back to solar minimum

again,

where you have the nice ordering

of the magnetic field.

It does this every 11 years,

and though the sun

may be 90 million miles away,

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