I can't go into detail right know - but the thing is: in order to make a real antimatter engine one would need to make a loop of SCs wire r = 70 m, where r(wire) is approx. 20 cm. I need to generate about 10 T in the center of the field, that is 70 m from the nearest wire. How much mechanical stress is this going to put onto the loop? I suspect that it will be more than even carbon nanotubes can handle, but a number would be handy, still.