ELI5. Why do you need to use heavy hydrogen to start a fusion reaction?

Question

I am pretty sure the sun fuses just standard one proton hydrogen. So why do we need to use deuterium and tritium for our bombs?

In: Physics

Answer 1

Fusion doesn’t really work with just standard hydrogen on earth. The nuclear reaction for it almost always looks like:

>
H + H -> He-2 (with a half life of about 0) -> H + H

To get deuterium you need the He-2 to beta decay, which is governed by the weak force. This is extremely unlikely to occur and only happens in the sun because there is so much hydrogen present. On average a proton takes ~9 billion years to make it past this step.

We don’t have enough hydrogen on earth to rely on this process, so we need to skip this step and just start with the Deuterium.