I feel that with a modular design that includes remote handling capability you could test things out a lot faster on a full scale device.  As to internal heating issues, I don't think there is much problem extrapolating from Q0.7 at JET to Q1.2 at JT-60.<p>Large Plasma devices are "the sexy" but IMO it's just another engineering problem at this point.  And you don't design large scale power plants to sit at the outer edge of their capabilities 24x7.  So yes, the highest energy pulses are unable after a few seconds, but we have built steady state fusion reactors they just operate further from their limits.<p>PS: Finding T is a problem, but "just build it bigger" and suddenly D-D (or 75%D - 25%T etc) becomes reasonable.<p>Edit: I am suggesting building building something with 4x ITER's budget which should give you ~8x the plasma volume and a lower surface area to volume ratio etc.  We can also pump of the field strength etc.  But you are limited to how much heat the wall can take so the plasma conditions don't need to be as efficient.