You could build coreless transformers that worked at 60 Hz, with no losses. You could build electric motors without loss. You could fill the Tevatron tunnel a

You could build coreless transformers that worked at 60 Hz, with no losses. You could build electric motors without loss. You could fill the Tevatron tunnel at Fermilab with new magnets and use it as either an accelerator, or an energy storage facility, depending on the time of day and demand. I'd make a wedding ring out of it, and be able to feel magnetic fields. I'd make a SQUID with it, and experiment with the |A| field (electromagnetic vector potential).