An excellent post, but I will be surprised if we are ever able to make tokamak fusion economic. As far as I can tell it's a technological dead end. I think Polywell is far more promising as a technology. Polywell might well be able to able to achieve break-even with around a 2 meter diameter machine. Simulations have shown break-even with boron-proton fusion (which ONLY gives charged particles, much more efficient and with way less need for shielding, and with no radioactive waste, perfect for spacraft) with a 6 meter machine.