Good idea but sadly not feasible

Relevant part (credit to [deleted] and u/chiagod):

Assuming D-T fusion, a single fusion event releases a 14.1MeV neutron and a 3.5MeV helium nucleus. Assuming you can absorb all this energy and you’ve got an efficient heat engine setup at around 50%, you’ll get about 1.5x10^-12 J per fusion, so for a 1GW output you’ll need 6.67x10^20 fusions per second. Say you have 1TWe (electric output) worth of fusion reactors worldwide (about half of current electricity generation), then you’re producing 1000 times as much helium, or 6.67x10^23 atoms per second. About a mole each second, or 4 grams. This works out to 126 tons of helium a year, or about 1000m^3 per year of liquid helium. The US strategic helium reserve had a peak volume of about a billion m^3 . World consumption of helium is measured in tens of millions of m^3 per year so you’d be short by several orders of magnitude in the best case.