[willis936]

I think the largest issues here are:

1. as you acknowledged, the assumption that energy production would increase by tenfold

2. that all electrical energy produced would be made by fusion reactors

By the time we get to a state where a serious percentage of energy production was from fusion power we would likely be looking into more aggressively into other reactions and designs.

Even if we just said 30% of all energy used today was made from D+T fusion that would still be generating 10% of our current helium usage. That's a significant amount and a lot more than the 4 orders of magnitude that is oft cited online (https://www.reddit.com/r/askscience/comments/12r2s7/helium_i...). At a glance, it appears that the posts in this thread miscalculate how much fuel is necessary for a certain amount of energy. They glaze over that part of their calculations. I much prefer your dimensional analysis approach.

[willis936]

For any readers looking for the same warm fuzzy I have, you can paste this into wolframalpha and actually get a rate of helium production over time.

https://www.wolframalpha.com/input/?i=(.3++438000+TWh+%2F+year)+%2F+(17.59+MeV)+%2F+(avogadro%27s+number+1%2Fmol)++(4.002602+g%2Fmol)

  (.3 * 438000 TWh / year) / (17.59 MeV) / (avogadro's number 1/mol) * (4.002602 g/mol)