Cosimo wants to know why we cannot just build a small star. A fusion reactor on Earth must do two things no star bothers with: heat its fuel even hotter than the sun's core, and hold that fuel without letting it touch anything.
You saw why stars fuse: a star's own gravity squeezes and holds its core. An Earth reactor has no star's gravity. This lesson shows what the reactor must do instead.
A star's gravity does two jobs at once: it squeezes the fuel hot, and it holds the fuel in place.
An Earth reactor has no star's gravity, so it must do both jobs another way.
First, heat: without the squeeze, the fuel must be heated even hotter than the sun's core before its nuclei fuse.
Tokamak reactors run their fuel above 100 million kelvin.
Second, holding: the reactor must keep the fuel confined without it touching any container wall.
A tokamak does this with a doughnut-shaped magnetic field: the fuel ring sits inside the field and touches nothing.
Holding that confinement steady long enough to harvest more energy than was spent remains an engineering frontier.
Fenella asks why engineers run tokamak fuel above 100 million kelvin when the sun's core fuses at a lower temperature. What does the sun have that the tokamak lacks?
The sun's own gravity squeezes and holds its core.
A tokamak has no such squeeze, so its fuel must be even hotter before its nuclei fuse.
The extra heat replaces the missing squeeze.
The sun squeezes; the tokamak cannot. So the tokamak must run its fuel hotter than the sun's core.
A news story says a tokamak held its fuel steadily for several minutes, but the run still used more energy than it harvested. Has fusion power arrived?
A fusion power station must harvest more energy than was spent heating and holding the fuel.
This run spent more energy than it harvested.
Not yet. Holding the confinement steady long enough to harvest more energy than was spent is still an engineering frontier.
Why must a fusion reactor on Earth heat its fuel even hotter than the sun's core?
What keeps a tokamak's fusion fuel from touching the container walls?
Fenella says: 'A fusion reactor on Earth must keep its fuel confined without the fuel touching any container wall.' Is Fenella correct?
A star fuses hydrogen steadily; an Earth reactor struggles to. What does the star have that the reactor lacks?
Inside a running tokamak, where does the fusion fuel sit?
Which statement about fusion power on Earth is correct today?