What it means to build a sun on the ground
Why is fusion so hard?
Join two hydrogen nuclei and energy comes out. Yet that has been hard for seventy years. The quickest way to see what is hard about it is to try.
One minute first
The inside of the Sun is 15 million degrees, so why must it be over 100 million on Earth? Watch for a minute, then go down to the boards. The narration is in Korean.
Video “Fusion in one minute” (in Korean) · made by Park Hyo-soon · Watch on YouTube
Board 1 · Follow it in six steps
It starts with seawater and ends where electricity comes out. Swipe the pictures sideways.
Board 2 · Pack them into a tank and turn up the heat
Here nuclei are packed into one tank and heated. At low temperature they keep colliding but almost never fuse. Drag the temperature slider up.
Deuterium
Tritium
Helium — stays inside
Neutron — flies out
Temperature 15 million °C
Density — how tightly packed 26 nuclei
Board 3 · Run the Sun and KSTAR side by side
On the left, the inside of the Sun: crowded and slow. On the right, the inside of KSTAR: almost empty and fast. Both fuse. Drag the right-hand slider down to the same temperature as the Sun.
Inside the Sun
15 million °C · crowded
Inside KSTAR
100 million °C · almost empty
Temperature of the right-hand tank 100 million °C
The slider works only on the right-hand tank. The Sun is not ours to adjust.
Same temperature, yet only the right-hand side stops. The difference is how tightly packed they are. Earth has no weight like the Sun's to squeeze them together, so temperature has to make up for it. The Sun on the left is drawn fusing far more often than it really does. In reality a single nucleus waits billions of years to meet a partner, and drawn truthfully the screen would show nothing happening.
The story behind this board
It reads far more easily after you have tried it.
The first electricity from fusion is expected in the 2030s, and power stations selling it from the 2050s onward. It is not today's answer but tomorrow's, being built now.