It lights our homes,

家の中を照らし 食料を育て

grows our food,

機械を動かしている

powers our computers.

その生成には

We can get it lots of ways:

化石燃料 核分裂 太陽光が使われる

burning fossil fuels,

だが欠点もある

splitting atoms

化石燃料は有害

or sunlight striking photovoltaics.

核分裂は核廃棄物

But there's a downside to everything.

太陽光は曇りの日には使えない

Fossil fuels are extremely toxic,

だが太陽のエネルギーは無尽蔵だ

nuclear waste is... well, nuclear waste,

太陽を地上に作り

and there are not enough batteries to store sunlight for cloudy days yet.

瓶詰めできたら

And yet, the Sun seems to have virtually limitless, free energy.

太陽は核融合で光っている

Is there a way we could build a sun on Earth?

太陽の核融合は熱核反応だ

Can we bottle a star?

とてつもなく熱いと

The Sun shines beacuse of nuclear fusion.

原子から電子が離れ

In a nutshell - fusion is a thermonuclear process,

自由に動けるプラズマ状態ができる

meaning that the ingredients have to be incredibly hot, so hot,

核同士は正の電荷なので弾き合うが

that the atoms are stripped of their electrons,

この反発力に勝つには

making a plasma where nuclei and electrons

すごい速さが必要になる

bounce around freely.

ここでの速さとは熱さのことで

Since nuclei are all positively charged, they repell each other.

数百万度だ

In order to overcome this repulsion

星の核の中では

the particles have to be going very, very fast.

その星の重さによる圧力が

In this context, very fast means very hot:

核が融合するほどの熱を生み

millions of degrees.

核が融合すれば エネルギーが出る

Stars cheat to reach these temperatures.

このエネルギーが期待を生んだ

They are so massive, that the pressure in their cores

新世代の発電所は核融合炉であると

generates the heat to squeeze the nuclei together

地球にはそこまで強い力はないので

until they merge and fuse,

核融合を起こす装置を作るには

creating heavier nuclei and releasing energy in the process.

知恵が必要だ

It is this energy release

プラズマ状態を作るのには

that scientists hope to harness

２つの方法がある

in a new generation of power plant:

１つは 磁場を使って

the fusion reactor.

ドーナツ状の装置内で

On Earth, it's not feasible to use this brute-force method

プラズマを起こすもの

to create fusion.

フランスのITERなど このタイプでは

So if we want to build a reactor that generates energy from fusion,

絶対零度近くまで冷やした

we have to get clever.

超伝導電磁石を使う

To date, scientists have invented two ways of making plasmas

宇宙最大の温度差のできあがりだ

hot enough to fuse:

２つに 超強力なレーザーを使って

The first type of reactor uses a magnetic field

燃料の表面を温め

to squeeze a plasma in a donut-shaped chamber

高い熱と密度を作り出す方法がある

where the reactions take place.

アメリカの国立点火施設で

These magnetic confinement reactors, such as the ITER reactor in France,

世界最強のレーザーを使い実験中だ

use superconducting electromagnets cooled with liquid helium

このような様々な実験は

to within a few degrees of absolute zero.

まだただの実験だ

Meaning they host some of the biggest temperature gradients in the known Universe.

技術はまだ発展途上にある

The second type, called inertial confinement,

今は生み出されるエネルギーより

uses pulses from superpowered lasers

コストの方が高い状況だ

to heat the surface of a pellet of fuel,

技術の商用化は長い時間を要するが

imploding it,

核融合炉の場合

briefly making the fuel hot and dense enough to fuse.

有用なものは作れないかもしれない

In fact,

だがもし作れれば

one of the most powerful lasers in the world

グラス一杯の海水が

is used for fusion experiments

今の石油１バレル分になり

at the National Ignition Facility in the US.

公害も出ない

These experiments and others like them around the world

核融合炉の燃料は水素かヘリウムで

are today just experiments.

水素は海水から採れる

Scientists are still developing the technology.

水素はどれでもいいのではなく

And although they can achieve fusion,

ここでは同位体の

right now, it costs more energy to do the experiment

重水素と三重水素が必要だ

than they produce in fusion.

重水素は海に大量にあるが

The technology has a long way to go

三重水素は厄介だ

before it's commercially viable.

放射性で 世界に20kgしか存在しない

And maybe it never will be.

核弾頭に使われ とてつもなく高価だ

It might just be impossible to make a viable fusion reactor on Earth.

だから重水素と融合させるお相手は

But, if it gets there it will be so efficient,

同位体のヘリウム３が適役だろう

that a single glass of sea water

これもまたすごくレアだが

could be used to produce as much energy as burning a barrel of oil,

月に答えがあるかもしれない

with no waste to speak of.

何億年をかけ 太陽風は

This is because fusion reactors would use hydrogen or helium as fuel,

月にヘリウム３を蓄積させた

and sea water is loaded with hydrogen.

掘り出すだけなら簡単だ

But not just any hydrogen will do:

うまくいけば

specific isotopes with extra neutrons, called deuterium and tritium,

数千年分の燃料が手に入るだろう

are needed to make the right reactions.

月を開拓するので

Deuterium is stable and can be found in abundance in sea water,

先の長い話だが

though, tritium is a bit trickier.

しかし ミニ太陽を作るのは

It's radioactive and there may only be twenty kilograms

危険に思える

of it in the world, mostly in nuclear warheads

だが他の発電所よりは安全だ

which makes it incredibly expensive.

原子力とは違い

So, we may need another fusion body for deuterium instead of tritium.

メルトダウンは起きない

Helium-3, an isotope of helium, might be a great substitute.

事故の時は

Unfortunately,

プラズマが冷えて反応は止まる

it's also incedibly rare on Earth.

爆弾ではないのだ

But here the Moon might have the answer.

三重水素の放出には危険性がある

Over billions of years,

放射性を持つ水が生まれ

the solar wind may have built up huge deposits

海に漏れ出す危険があるが

of helium-3 on the moon.

使っても数グラムの三重水素では

Instead of making helium-3, we can mine it.

すぐに薄まるだろう

If we can sift the lunar dust for helium,

ほぼ無尽蔵のエネルギーが

we'd have enough fuel to power the entire world

環境に優しい形で

for thousands of years.

水から取り出せる

One more argument for establishing a moon base,

問題はコストだ

if you weren't convinced already.

核融合が利益になるかは全く不明で

Okay, maybe you think building a mini sun

作れても 高価すぎるかもしれない

still sounds kind of dangerous.

これは見返りの保証がない

But they'd actually be much safer than most other types of power plant.

高額なギャンブルだ

A fusion reactor is not like a nuclear plant

他のクリーンエネルギーなら

which can melt down catastrophically.

お金は無駄にならない

If the confinement failed,

もうやめるべきか？

then the plasma would expand and cool and the reaction would stop.

いや 無尽蔵のエネルギーのためなら

Put simply, it's not a bomb.

やる価値はあるかも

The release of radioactive fuel like tritium

Subtitles by the Amara.org community

could pose a threat to the environment.

Tritium could bond with oxygen, making radioactive water

which could be dangerous as it seeps into the environment.

Fortunately, there's no more than a few grams of tritium

in use at a given time,

so a leak would be quickly diluted.

So we've just told you

that there's nearly unlimited energy to be had,

at no expense to the environment

in something as simple as water.

So, what's the catch?

Cost.

We simply don't know if fusion power will ever be commercially viable.

Even if they work, they might be too expensive to ever build.

The main drawback is that it's unproven technology.

It's a ten billion dollar gamble.

And that money might be better spent on other clean energy

that's already proven itself.

Maybe we should cut our losses.

Or maybe,

when the payoff is unlimited, clean energy for everyone,

it might be worth a risk?