How much helium will be produced as a by-product of world fusion energy generation?

I was just wondering. Suppose technology to make net energy gain from fusion is discovered. How much helium will be produced? Enough to be useful? So much that it's a pollutant?

I could probably take a guess myself, but I want to see what other people suggest. Possible approaches to an answer:

1) Zero. The fusion reaction that will be successful is not one that produces helium as a product.

2) Estimate world electrical energy use. Calculate the energy produced by one fusion reaction and the amount of helium produced. Solve.

3) Somewhat less than that, because fusion won't meet all the world's energy demand, because of some limitation of resources, if only limitation of money to construct the facilities.

4) A bit more than that, because fusion will be used for more than just electrical production, for example for large ship propulsion.

5) A lot more than that, because with a nearly free source of energy, mankind will come up with many more uses for energy, and multiply its energy use many times.