The Sun is Cheating

One criticism of fusion as an energy source that I particularly enjoy is this: “We already have a perfectly good fusion reactor. It’s called the Sun. We can get energy from it using solar panels. It’s not necessary to spend billions of dollars reproducing the Sun on Earth" 

It’s quite accurate. The Sun is rather a good fusion reactor, and it is free. Solar panels aren’t great, but they keep getting better, and if we can find a way to make them cheaply and from non-toxic elements it would be very nice indeed. Still, it’s rather a boring criticism – the fact that something already exists in nature shouldn’t prevent us from trying to recreate it. There are definitely situations in which it’d be nice to have our own miniature Sun on Earth.

But why is the Sun so good? Well, it cheats. As I discussed here, for fusion we need hot ions, densely packed and held in place for long enough for them to merge.  The Sun, you may have heard, is rather big. The force of gravity in this case is strong enough to keep the hot elements within from escaping. Fusion in the sun is quite a complicate chain of processes, with heavier elements being incrementally built up from hydrogen. 

We can’t get enough hydrogen in one place on Earth for gravity to be effective. Instead, we try and hold the elements in place with strong magnetic fields, or by quickly crushing them before they have chance to escape. It makes the whole process quite a bit more tricky!

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