Story

As far as I know, the reason Tokamaks have consistently failed for over 50 years has nothing to do with them being too large and expensive. Dozens of them have been tried, many very extensively. In all cases, nobody has figured out how to solve the exceedingly difficult problem of maintaining stable confinement for more than milliseconds. Confinement takes more than just a simple toroidal magnetic field.

There are other problems, huge ones, but until some progress is made on this overriding one, we are just stumbling helplessly in the dark.

I assume that many if not all Tokamaks have used superconducting magnets. You don't run currents of millions of amperes through copper. Not for long (more than milliseconds). Even if you had enough copper to carry it and enough refrigeration to keep the copper from melting, losses would be collossal.