Why is it so hard to make a nuclear fusion reactor efficient?

Question

In other words, why is it so hard to get the Q value above 1 (ration between energy output and input)

In: 179

Answer 1

The likelihood that hydrogen will fuse is very low, even at the insane temperatures inside of the sun. The sun gets around this by being huge, giving it a lot of opportunities to have that rare fusion event occur. Trying to do that in puny earth reactors requires we make fusion more likely, which means even more insane conditions than exist in the sun.

Also, the sun gets hot enough to destroy pretty much anything near it. But puny earth reactor walls needs to be close to reaction, so we need to worry a lot more about containment than the sun does.